Magnetic_Resonance_Imaging RSS : Gourt

Improvement of spectral density-based activation detection of event-related fMRI data.

Related Articles Improvement of spectral density-based activation detection of event-related fMRI data. Magn Reson Imaging. 2009 Sep;27(7):879-94 Authors: Ngan SC, Hu X, Tan LH, Khong PL For event-related data obtained from an experimental paradigm with a periodic design, spectral density at the fundamental frequency of the paradigm has been used as a template-free activation detection measure. In this article, we build and expand upon this detection measure to create an improved, integrated measure. Such an integrated measure linearly combines information contained in the spectral densities at the fundamental frequency as well as the harmonics of the paradigm and in a spatial correlation function characterizing the degree of co-activation among neighboring voxels. Several figures of merit are described and used to find appropriate values for the coefficients in the linear combination. Using receiver-operating characteristic analysis on simulated functional magnetic resonance imaging (fMRI) data sets, we quantify and validate the improved performance of the integrated measure over the spectral density measure based on the fundamental frequency as well as over some other popular template-free data analysis methods. We then demonstrate the application of the new method on an experimental fMRI data set. Finally, several extensions to this work are suggested. PMID: 19535208 [PubMed - indexed for MEDLINE]

On MRI turbulence quantification.

Related Articles On MRI turbulence quantification. Magn Reson Imaging. 2009 Sep;27(7):913-22 Authors: Dyverfeldt P, Gårdhagen R, Sigfridsson A, Karlsson M, Ebbers T Turbulent flow, characterized by velocity fluctuations, accompanies many forms of cardiovascular disease and may contribute to their progression and hemodynamic consequences. Several studies have investigated the effects of turbulence on the magnetic resonance imaging (MRI) signal. Quantitative MRI turbulence measurements have recently been shown to have great potential for application both in human cardiovascular flow and in engineering flow. In this article, potential pitfalls and sources of error in MRI turbulence measurements are theoretically and numerically investigated. Data acquisition strategies suitable for turbulence quantification are outlined. The results show that the sensitivity of MRI turbulence measurements to intravoxel mean velocity variations is negligible, but that noise may degrade the estimates if the turbulence encoding parameter is set improperly. Different approaches for utilizing a given amount of scan time were shown to influence the dynamic range and the uncertainty in the turbulence estimates due to noise. The findings reported in this work may be valuable for both in vitro and in vivo studies employing MRI methods for turbulence quantification. PMID: 19525079 [PubMed - indexed for MEDLINE]

Relaxo-volumetric multispectral quantitative magnetic resonance imaging of the brain over the human lifespan: global and regional aging patterns.

Related Articles Relaxo-volumetric multispectral quantitative magnetic resonance imaging of the brain over the human lifespan: global and regional aging patterns. Magn Reson Imaging. 2009 Sep;27(7):895-906 Authors: Saito N, Sakai O, Ozonoff A, Jara H The objective of this study was to determine the T1, T2 and secular-T2 relaxo-volumetric brain aging patterns using multispectral quantitative magnetic resonance imaging, both globally and regionally, and covering an age range approaching the full human lifespan. Fifty-one subjects (28 males, 23 females; age range: 0.5-87 years) were studied consisting of 18 healthy volunteers and 33 patients. Patients were selected after carefully reviewing their radiology reports to have either normal-by-MRI findings (25 patient subjects) or small focal pathology less than 6 mm in size (eight patient subjects). All subjects were MR imaged at 1.5 T with the mixed turbo spin echo pulse sequence. The soft tissues inside the cranial vault, termed intracranial matter (ICM), were segmented using a dual-clustering segmentation algorithm. ICM segments were further divided into six subsegments: bilateral anterior cerebral, posterior cerebral and cerebellar subsegments. T1, T2 and secular-T2 relaxation time histograms of all segments were generated and modeled with Gaussian functions. For each segment, the volumes of white matter, gray matter and cerebrospinal fluid were calculated from the T1 histograms. The age-related tendencies of three quantitative MRI parameters (T1, T2 and secular-T2) and the fractional tissue volumes showed four distinct periods of life, specifically a maturation period (0-2 years), a development period (2-20 years), an adulthood period (20-60 years) and a senescence period (60 years and older). For all ages, the anterior cerebral subsegment exhibited consistently longer gray matter T1s and shorter white matter T1s than the posterior cerebral and cerebellar subsegments. Volumetric age-related changes of the cerebellar subsegment were more gradual than in the cerebral subsegments. This study shows that relaxometric and volumetric age-related changes are synchronized and define the same four periods of brain evolution both globally and regionally. PMID: 19520539 [PubMed - indexed for MEDLINE]

Fast low-angle positive contrast steady-state free precession imaging of USPIO-labeled macrophages: theory and in vitro experiment.

Related Articles Fast low-angle positive contrast steady-state free precession imaging of USPIO-labeled macrophages: theory and in vitro experiment. Magn Reson Imaging. 2009 Sep;27(7):961-9 Authors: Mascheri N, Dharmakumar R, Zhang Z, Paunesku T, Woloschak G, Li D The feasibility of imaging macrophages labeled with ultrasmall superparamagnetic iron-oxide nanoparticles (USPIO) with fast low-angle positive contrast steady-state free precession (FLAPS) was investigated through theory and in vitro experiment. Human macrophage cells were labeled with USPIO and imaged at 1.5 T. The metric "visibility," which combines magnitude and spatial extent of positive contrast, was used to evaluate the images. Negative contrast steady-state free precession (SSFP) and gradient-echo (GRE) imaging were also evaluated. Positive contrast was observed for relatively high concentrations of labeled cells for flip angles less than alpha=25 degrees . Theoretical and experimental results indicate that positive visibility (VIS(POS)) was maximized at alpha=10 degrees and 15 degrees. Low flip angle SSFP also provided negative contrast comparable to standard SSFP and GRE imaging. Results suggest that USPIO-labeled macrophages are capable of producing the conditions necessary for positive contrast with FLAPS at clinical field strength (1.5 T) and resolution (0.8x0.8x3 mm(3)). PMID: 19520536 [PubMed - indexed for MEDLINE]

A fully automated algorithm under modified FCM framework for improved brain MR image segmentation.

Related Articles A fully automated algorithm under modified FCM framework for improved brain MR image segmentation. Magn Reson Imaging. 2009 Sep;27(7):994-1004 Authors: Sikka K, Sinha N, Singh PK, Mishra AK Automated brain magnetic resonance image (MRI) segmentation is a complex problem especially if accompanied by quality depreciating factors such as intensity inhomogeneity and noise. This article presents a new algorithm for automated segmentation of both normal and diseased brain MRI. An entropy driven homomorphic filtering technique has been employed in this work to remove the bias field. The initial cluster centers are estimated using a proposed algorithm called histogram-based local peak merger using adaptive window. Subsequently, a modified fuzzy c-mean (MFCM) technique using the neighborhood pixel considerations is applied. Finally, a new technique called neighborhood-based membership ambiguity correction (NMAC) has been used for smoothing the boundaries between different tissue classes as well as to remove small pixel level noise, which appear as misclassified pixels even after the MFCM approach. NMAC leads to much sharper boundaries between tissues and, hence, has been found to be highly effective in prominently estimating the tissue and tumor areas in a brain MR scan. The algorithm has been validated against MFCM and FMRIB software library using MRI scans from BrainWeb. Superior results to those achieved with MFCM technique have been observed along with the collateral advantages of fully automatic segmentation, faster computation and faster convergence of the objective function. PMID: 19395212 [PubMed - indexed for MEDLINE]

Image correction during large and rapid B(0) variations in an open MRI system with permanent magnets using navigator echoes and phase compensation.

Related Articles Image correction during large and rapid B(0) variations in an open MRI system with permanent magnets using navigator echoes and phase compensation. Magn Reson Imaging. 2009 Sep;27(7):988-93 Authors: Li J, Wang Y, Jiang Y, Xie H, Li G An open permanent magnet system with vertical B(0) field and without self-shielding can be quite susceptible to perturbations from external magnetic sources. B(0) variation in such a system located close to a subway station was measured to be greater than 0.7 microT by both MRI and a fluxgate magnetometer. This B(0) variation caused image artifacts. A navigator echo approach that monitored and compensated the view-to-view variation in magnetic resonance signal phase was developed to correct for image artifacts. Human brain imaging experiments using a multislice gradient-echo sequence demonstrated that the ghosting and blurring artifacts associated with B(0) variations were effectively removed using the navigator method. PMID: 19369023 [PubMed - indexed for MEDLINE]

Magnetic resonance imaging tracking of alginate beads used for drug delivery of growth factors at sites of cardiac damage.

Related Articles Magnetic resonance imaging tracking of alginate beads used for drug delivery of growth factors at sites of cardiac damage. Magn Reson Imaging. 2009 Sep;27(7):970-5 Authors: Gruwel ML, Yang Y, de Gervai P, Sun J, Kupriyanov VV Alginate-based beads labeled with contrast agent and loaded with vascular growth hormones were used for site-specific chronic delivery of hormones at the site of myocardial damage in a porcine model. Position of the beads within the pericardium could be monitored by MRI for optimal hormone delivery due to the presence of contrast agent. The beads facilitate the slow release of cytochrome c, myoglobin and methemoglobin used as protein models of growth factors. This application allows for site-specific delivery of hormones while the incorporated contrast agent in the beads provides a tool for MRI tracking in chronic studies. PMID: 19369022 [PubMed - indexed for MEDLINE]

A nonlinear BOLD model accounting for refractory effect by applying the longitudinal relaxation in NMR to the linear BOLD model.

Related Articles A nonlinear BOLD model accounting for refractory effect by applying the longitudinal relaxation in NMR to the linear BOLD model. Magn Reson Imaging. 2009 Sep;27(7):907-12 Authors: Jung KJ A mathematical model to regress the nonlinear blood oxygen level-dependent (BOLD) fMRI signal has been developed by incorporating the refractory effect into the linear BOLD model of the biphasic gamma variate function. The refractory effect was modeled as a relaxation of two separate BOLD capacities corresponding to the biphasic components of the BOLD signal in analogy with longitudinal relaxation of magnetization in NMR. When tested with the published fMRI data of finger tapping, the nonlinear BOLD model with the refractory effect reproduced the nonlinear BOLD effects such as reduced poststimulus undershoot and saddle pattern in a prolonged stimulation as well as the reduced BOLD signal for repetitive stimulation. PMID: 19369021 [PubMed - indexed for MEDLINE]

Acute pancreatic graft fistula and peripancreatic fluid collection: demonstration by secretin-stimulated MRI.

Related Articles Acute pancreatic graft fistula and peripancreatic fluid collection: demonstration by secretin-stimulated MRI. Magn Reson Imaging. 2009 Sep;27(7):1005-8 Authors: Alkaade S, Fattahi R, Balci NC, Akduman EI, Garvin PJ, Modanlou KA, Burton FR Peripancreatic fluid collections are among the common post pancreas transplant complications, which are mainly due to leakage from the anastomosis site to bowel and graft pancreatitis. Differentiation between these two entities is important because they are treated differently. In this case, secretin stimulated magnetic resonance cholangiopancreatography revealed gradual intraperitoneal fluid collection and accumulation of fluid in small bowel excluded leakage from the anastomosis of the pancreas to bowel and changed the management from surgery to medical treatment. PMID: 19369020 [PubMed - indexed for MEDLINE]

MRI findings in nonalcoholic steatohepatitis: correlation with histopathology and clinical staging.

Related Articles MRI findings in nonalcoholic steatohepatitis: correlation with histopathology and clinical staging. Magn Reson Imaging. 2009 Sep;27(7):976-87 Authors: Elias J, Altun E, Zacks S, Armao DM, Woosley JT, Semelka RC PURPOSE: To evaluate magnetic resonance imaging (MRI) findings of nonalcoholic steatohepatitis (NASH) and to determine the correlation of MRI findings with histopathology and Mayo End-Stage Liver Disease (MELD) score. MATERIALS AND METHODS: Thirty patients (18 males, 12 females; mean age: 57+/-8.9 years; age range: 35-71 years) with histopathologically proven NASH who underwent MRI examinations between January 2001 and October 2005 were included in the study. Two radiologists retrospectively reviewed all magnetic resonance (MR) examinations in consensus to evaluate the presence and extent of predetermined findings of NASH including liver steatosis, early patchy liver enhancement indicating inflammation and liver fibrosis. The findings detected on MRI were correlated and compared to histopathological findings and MELD score by using nonparametric Spearman correlation coefficient and Kruskal-Wallis analysis of variance. RESULTS: Liver steatosis was observed in 10 of 30 patients; early patchy liver enhancement, in 8 of 30 patients and liver fibrosis in 19 of 30 patients on MR images. Liver fibrosis was reticular in all these patients. There were statistically significant moderate correlations between MRI findings of liver steatosis and histopathologic grades of steatosis (r=0.43; P<.05), and between MRI findings of fibrosis and histopathologic stages of fibrosis (r=0.61; P<.001). Early patchy enhancement did not demonstrate statistically significant correlation with inflammation (P=.28). There was no statistically significant overall correlation between MRI findings of NASH and MELD score. CONCLUSION: MRI findings of liver steatosis and fibrosis in NASH showed moderate correlations with histopathologic grades of steatosis and stages of fibrosis, but MRI findings of NASH did not demonstrate any significant correlations with MELD score. PMID: 19356874 [PubMed - indexed for MEDLINE]

Improved SNR in linear reordered 2D bSSFP imaging using variable flip angles.

Related Articles Improved SNR in linear reordered 2D bSSFP imaging using variable flip angles. Magn Reson Imaging. 2009 Sep;27(7):933-41 Authors: Paul D, Zaitsev M This article presents a variable flip-angle approach for balanced steady-state free precession (bSSFP) imaging, which allows increases in signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) while keeping specific absorption rate (SAR) constant or reduces SAR for given CNR and SNR. The gain in SNR is achieved by utilizing the higher signal in the transient phase. Flip-angle variation during the echo train is realized using a trigonometric function with M steps (ramp length). Variation is combined with a linear k-space reordering such that outer parts of k-space are sampled using a lower flip angle alpha(min), while the central part of k-space is acquired with a higher flip angle alpha(max). No additional preparation or dummy cycles are applied prior to data acquisition. Several variation schemes with different starting flip angles alpha(min) and ramp length M are considered. For example, using alpha(min)=1 degrees and M=96, alpha(max) can be set to 47 degrees without exceeding SAR limits at 3 T and gaining up to 50% in SNR, while, conventionally, alpha=34 degrees is the maximal possible flip angle. Resolution seems unaffected in volunteer imaging. In all cases, no transient artifacts due to flip-angle variation were observed. This article demonstrates the use of flip-angle variations in bSSFP to increase SNR and CNR while keeping SAR constant, which is especially important at higher field strengths. Flip-angle variation can also be combined with other methods such as parallel imaging techniques for further SAR reduction. PMID: 19286338 [PubMed - indexed for MEDLINE]

Noninvasive monitoring of brain temperature during mild hypothermia.

Related Articles Noninvasive monitoring of brain temperature during mild hypothermia. Magn Reson Imaging. 2009 Sep;27(7):923-32 Authors: Weis J, Covaciu L, Rubertsson S, Allers M, Lunderquist A, Ahlström H The main purpose of this study was to verify the feasibility of brain temperature mapping with high-spatial- and reduced-spectral-resolution magnetic resonance spectroscopic imaging (MRSI). A secondary goal was to determine the temperature coefficient of water chemical shift in the brain with and without internal spectral reference. The accuracy of the proposed MRSI method was verified using a water and vegetable oil phantom. Selective decrease of the brain temperature of pigs was induced by intranasal cooling. Temperature reductions between 2 degrees C and 4 degrees C were achieved within 20 min. The relative changes in temperature during the cooling process were monitored using MRSI. The reference temperature was measured with MR-compatible fiber-optic probes. Single-voxel (1)H MRS was used for measurement of absolute brain temperature at baseline and at the end of cooling. The temperature coefficient of the water chemical shift of brain tissue measured by MRSI without internal reference was -0.0192+/-0.0019 ppm/degrees C. The temperature coefficients of the water chemical shift relative to N-acetylaspartate, choline-containing compounds and creatine were -0.0096+/-0.0009, -0.0083+/-0.0007 and -0.0091+/-0.0011 ppm/degrees C, respectively. The results of this study indicate that MRSI with high spatial and reduced spectral resolutions is a reliable tool for monitoring long-term temperature changes in the brain. PMID: 19282122 [PubMed - indexed for MEDLINE]

Assessment of the internal craniocervical ligaments with a new magnetic resonance imaging sequence: three-dimensional turbo spin echo with variable flip-angle distribution (SPACE).

Related Articles Assessment of the internal craniocervical ligaments with a new magnetic resonance imaging sequence: three-dimensional turbo spin echo with variable flip-angle distribution (SPACE). Magn Reson Imaging. 2009 Sep;27(7):954-60 Authors: Baumert B, Wörtler K, Steffinger D, Schmidt GP, Reiser MF, Baur-Melnyk A PURPOSE: Lesions close to the internal craniocervical ligaments are a common problem in patients with whiplash injuries. The aim of this study was to evaluate the morphology and visibility of these ligamentous structures with a new isotropic three-dimensional (3D) turbo-spin-echo (TSE) technique. MATERIALS AND METHODS: MR (MR) images of the cervical spine of 52 healthy subjects (27 women and 25 men; mean age=29 years; age range=18-40 years) were taken with a T2-weighted 3D TSE sequence with variable flip-angle distribution [SPACE (Sampling Perfection with Application optimized Contrasts using different flip-angle Evolution)] at 1.5 T (Magnetom Avanto, Siemens Erlangen, Germany). Two experienced musculoskeletal radiologists read the images independently on a 3D imaging and postprocessing workstation. The visibility and morphology of the alar ligaments were evaluated on a five-point scale, and inter-reader correlation was assessed with kappa statistics. RESULTS: Both alar ligaments were detected in all subjects. Twenty-eight (53.8%) of the alar ligaments could not be seen within one slice of the standard coronal imaging plane but could adequately be visualized in an oblique reconstruction adapted to the orientation of the ligaments on the axial slices. Inter-reader correlation for visibility on MR imaging (MRI) of the internal craniocervical ligaments was high (left+right side, kappa=0.95). Most (94%) alar ligaments presented symmetrically. In the axial plane, 60% were oriented neutral and 40% had a backward orientation. In the coronal plane, 67% were oriented caudocranially and 33% were oriented horizontally. The shape of the ligaments was parallel in half and was V-shaped in the other half. The alar ligaments had homogeneous low-signal intensity in 56% and heterogeneous low-signal intensity in 44%. The apical ligament of the dens was seen (excellent-good-moderate) in 61% (reader 1) and 52% (reader 2). The tectorial membranes and the transverse ligament of the atlas were shown (excellent-good) in all subjects. CONCLUSIONS: MRI with acquisition of an isotropic SPACE technique allows high-resolution imaging of the craniocervical ligaments in all orientations. Reconstruction of the image data in the variable orientation of the alar ligaments allowed for excellent depiction within one slice such that partial volume artifacts that hamper image analysis can be eliminated. PMID: 19282121 [PubMed - indexed for MEDLINE]

Improved matrix inversion in image plane parallel MRI.

Related Articles Improved matrix inversion in image plane parallel MRI. Magn Reson Imaging. 2009 Sep;27(7):942-53 Authors: Wu B, Millane RP, Watts R, Bones PJ A new 3D parallel magnetic resonance imaging (MRI) method named Generalized Unaliasing Incorporating Support constraint and sensitivity Encoding (GUISE) is presented. GUISE allows direct image recovery from arbitrary Cartesian k-space trajectories. However, periodic k-space sampling patterns are considered for reconstruction efficiency. Image recovery methods such as 2D SENSE (SENSitivity Encoding) and 2D CAIPIRINHA (Controlled Aliasing In Parallel Imaging Results IN Higher Acceleration) are special instances of GUISE where specific restrictions are placed on the k-space sampling patterns used. It is shown that the sampling pattern has large impacts on the image reconstruction error due to noise. An efficient sampling pattern design method that incorporates prior knowledge of object support and coil sensitivity profile is proposed. It requires no experimental trials and could be used in clinical imaging. Comparison of the proposed sampling pattern design method with 2D SENSE and 2D CAIPIRINHA are made based on both simulation and experiment results. It is seen that this new adaptive sampling pattern design method results in a lower noise level in reconstructions due to better exploitation of the coil sensitivity variation and object support constraint. In addition, elimination of the non-object region from reconstruction potentially allows an acceleration factor higher than the number of receiver coils used. PMID: 19269768 [PubMed - indexed for MEDLINE]

Heilum-3 MR q-space imaging with radial acquisition and iterative highly constrained back-projection

An undersampled diffusion-weighted stack-of-stars acquisition is combined with iterative highly constrained back-projection to perform hyperpolarized helium-3 MR q-space imaging with combined regional correction of radiofrequency- and T1-related signal loss in a single breath-held scan. The technique is tested in computer simulations and phantom experiments and demonstrated in a healthy human volunteer with whole-lung coverage in a 13-sec breath-hold. Measures of lung microstructure at three different lung volumes are evaluated using inhaled gas volumes of 500 mL, 1000 mL, and 1500 mL to demonstrate feasibility. Phantom results demonstrate that the proposed technique is in agreement with theoretical values, as well as with a fully sampled two-dimensional Cartesian acquisition. Results from the volunteer study demonstrate that the root mean squared diffusion distance increased significantly from the 500-mL volume to the 1000-mL volume. This technique represents the first demonstration of a spatially resolved hyperpolarized helium-3 q-space imaging technique and shows promise for microstructural evaluation of lung disease in three dimensions. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

Real-time MR thermometry for monitoring HIFU ablations of the liver

A high-resolution and high-speed pulse sequence is presented for monitoring high-intensity focused ultrasound ablations in the liver in the presence of motion. The sequence utilizes polynomial-order phase saturation bands to perform outer volume suppression, followed by spatial-spectral excitation and three readout segmented echo-planar imaging interleaves. Images are processed with referenceless thermometry to create temperature-rise images every frame. The sequence and reconstruction were implemented in RTHawk and used to image stationary and moving sonications in a polyacrylamide gel phantom (62.4 acoustic W, 50 sec, 550 kHz). Temperature-rise images were compared between moving and stationary experiments. Heating spots and corresponding temperature-rise plots matched very well. The stationary sonication had a temperature standard deviation of 0.15° C compared to values of 0.28° C and 0.43° C measured for two manually moved sonications at different velocities. Moving the phantom (while not heating) with respect to the transducer did not cause false temperature rises, despite susceptibility changes. The system was tested on nonheated livers of five normal volunteers. The mean temperature rise was - 0.05° C, with a standard deviation of 1.48° C. This standard deviation is acceptable for monitoring high-intensity focused ultrasound ablations, suggesting real-time imaging of moving high-intensity focused ultrasound sonications can be clinically possible. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

Arterial transit time effects in pulsed arterial spin labeling CBF mapping: Insight from a PET and MR study in normal human subjects

Arterial transit time (ATT), a key parameter required to calculate absolute cerebral blood flow in arterial spin labeling (ASL), is subject to much uncertainty. In this study, ASL ATTs were estimated on a per-voxel basis using data measured by both ASL and positron emission tomography in the same subjects. The mean ATT increased by 260 ± 20 (standard error of the mean) ms when the imaging slab shifted downwards by 54 mm, and increased from 630 ± 30 to 1220 ± 30 ms for the first slice, with an increase of 610 ± 20 ms over a four-slice slab when the gap between the imaging and labeling slab increased from 20 to 74 mm. When the per-slice ATTs were employed in ASL cerebral blood flow quantification and the in-slice ATT variations ignored, regional cerebral blood flow could be significantly different from the positron emission tomography measures. ATT also decreased with focal activation by the same amount for both visual and motor tasks ([sim]80 ms). These results provide a quantitative relationship between ATT and the ASL imaging geometry and yield an assessment of the assumptions commonly used in ASL imaging. These findings should be considered in the interpretation of, and comparisons between, different ASL-based cerebral blood flow studies. The results also provide spatially specific ATT data that may aid in optimizing the ASL imaging parameters. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

In vivo generalized diffusion tensor imaging (GDTI) using higher-order tensors (HOT)

Generalized diffusion tensor imaging (GDTI) using higher-order tensor (HOT) statistics generalizes the technique of diffusion tensor imaging by including the effect of nongaussian diffusion on the signal of MRI. In GDTI-HOT, the effect of nongaussian diffusion is characterized by higher-order tensor statistics (i.e., the cumulant tensors or the moment tensors), such as the covariance matrix (the second-order cumulant tensor), the skewness tensor (the third-order cumulant tensor), and the kurtosis tensor (the fourth-order cumulant tensor). Previously, Monte Carlo simulations have been applied to verify the validity of this technique in reconstructing complicated fiber structures. However, no in vivo implementation of GDTI-HOT has been reported. The primary goal of this study is to establish GDTI-HOT as a feasible in vivo technique for imaging nongaussian diffusion. We show that probability distribution function of the molecular diffusion process can be measured in vivo with GDTI-HOT and be visualized with three-dimensional glyphs. By comparing GDTI-HOT to fiber structures that are revealed by the highest resolution diffusion-weighted imaging (DWI) possible in vivo, we show that the GDTI-HOT can accurately predict multiple fiber orientations within one white matter voxel. Furthermore, through bootstrap analysis we demonstrate that in vivo measurement of HOT elements is reproducible, with a small statistical variation that is similar to that of diffusion tensor imaging. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

Multivariate statistical mapping of spectroscopic imaging data

For magnetic resonance spectroscopic imaging studies of the brain, it is important to measure the distribution of metabolites in a regionally unbiased way; that is, without restrictions to a priori defined regions of interest. Since magnetic resonance spectroscopic imaging provides measures of multiple metabolites simultaneously at each voxel, there is furthermore great interest in utilizing the multidimensional nature of magnetic resonance spectroscopic imaging for gains in statistical power. Voxelwise multivariate statistical mapping is expected to address both of these issues, but it has not been previously employed for spectroscopic imaging (SI) studies of brain. The aims of this study were to () develop and validate multivariate voxel-based statistical mapping for magnetic resonance spectroscopic imaging and () demonstrate that multivariate tests can be more powerful than univariate tests in identifying patterns of altered brain metabolism. Specifically, we compared multivariate to univariate tests in identifying known regional patterns in simulated data and regional patterns of metabolite alterations due to amyotrophic lateral sclerosis, a devastating brain disease of the motor neurons. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

Quantitative susceptibility map reconstruction from MR phase data using bayesian regularization: Validation and application to brain imaging

The diagnosis of many neurologic diseases benefits from the ability to quantitatively assess iron in the brain. Paramagnetic iron modifies the magnetic susceptibility causing magnetic field inhomogeneity in MRI. The local field can be mapped using the MR signal phase, which is discarded in a typical image reconstruction. The calculation of the susceptibility from the measured magnetic field is an ill-posed inverse problem. In this work, a bayesian regularization approach that adds spatial priors from the MR magnitude image is formulated for susceptibility imaging. Priors include background regions of known zero susceptibility and edge information from the magnitude image. Simulation and phantom validation experiments demonstrated accurate susceptibility maps free of artifacts. The ability to characterize iron content in brain hemorrhage was demonstrated on patients with cavernous hemangioma. Additionally, multiple structures within the brain can be clearly visualized and characterized. The technique introduces a new quantitative contrast in MRI that is directly linked to iron in the brain. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

Quantification of punctate iron sources using magnetic resonance phase

Iron-mediated tissue damage is present in cerebrovascular and neurodegenerative diseases and neurotrauma. Brain microbleeds are often present in these maladies and are assuming increasing clinical importance. Because brain microbleeds present a source of pathologic iron to the brain, the noninvasive quantification of this iron pool is potentially valuable. Past efforts to quantify brain iron have focused on content estimation within distributed brain regions. In addition, conventional approaches using "magnitude" images have met significant limitations. In this study, a technique is presented to quantify the iron content of punctate samples using phase images. Samples are modeled as magnetic dipoles and phase shifts due to local dipole field perturbations are mathematically related to sample iron content and radius using easily recognized geometric features in phase images. Phantoms containing samples of a chitosan-ferric oxyhydroxide composite (which serves as a mimic for hemosiderin) were scanned with a susceptibility-weighted imaging sequence at 11.7 T. Plots relating sample iron content and radius to phase image features were compared to theoretical predictions. The primary result is the validation of the technique by the excellent agreement between theory and the iron content plot. This research is a potential first step toward quantification of punctate brain iron sources such as brain microbleeds. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

Enhancement of gas-filled microbubble R2* by iron oxide nanoparticles for MRI

Gas-filled microbubbles have the potential to become a unique intravascular MR contrast agent due to their magnetic susceptibility effect, biocompatibility, and localized manipulation via ultrasound cavitation. However, microbubble susceptibility effect is relatively weak when compared with other intravascular MR susceptibility contrast agents. In this study, enhancement of microbubble susceptibility effect by entrapping monocrystalline iron oxide nanoparticles (MIONs) into polymeric microbubbles was investigated at 7 T in vitro. Apparent T2 enhancement ([Delta]R2*) induced by microbubbles was measured to be 79.2 ± 17.5 sec-1 and 301.2 ± 16.8 sec-1 for MION-free and MION-entrapped polymeric microbubbles at 5% volume fraction, respectively. [Delta]R2* and apparent transverse relaxivities (r2*) for MION-entrapped polymeric microbubbles and MION-entrapped solid microspheres (without gas core) were also compared, showing the synergistic effect of the gas core with MIONs. This is the first experimental demonstration of microbubble susceptibility enhancement for MRI application. This study indicates that gas-filled polymeric microbubble susceptibility effect can be substantially increased by incorporating iron oxide nanoparticles into microbubble shells. With such an approach, microbubbles can potentially be visualized with higher sensitivity and lower concentrations by MRI. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

Temporal and noninvasive monitoring of inflammatory-cell infiltration to myocardial infarction sites using micrometer-sized iron oxide particles

Micrometer-sized iron oxide particles (MPIO) are a more sensitive MRI contrast agent for tracking cell migration compared to ultrasmall iron oxide particles. This study investigated the temporal relationship between inflammation and tissue remodeling due to myocardial infarction (MI) using MPIO-enhanced MRI. C57Bl/6 mice received an intravenous MPIO injection for cell labeling, followed by a surgically induced MI seven days later (n = 7). For controls, two groups underwent either sham-operated surgery without inducing an MI post-MPIO injection (n = 7) or MI surgery without MPIO injection (n = 6). The MRIs performed post-MI showed significant signal attenuation around the MI site for the mice that received an intravenous MPIO injection for cell labeling, followed by a surgically induced MI seven days later, compared to the two control groups (P < 0.01). The findings suggested that the prelabeled inflammatory cells mobilized and infiltrated into the MI site. Furthermore, the linear regression of contrast-to-noise ratio at the MI site and left ventricular ejection function suggested a positive correlation between the labeled inflammatory cell infiltration and cardiac function attenuation during post-MI remodeling (r2 = 0.98). In conclusion, this study demonstrated an MRI technique for noninvasively and temporally monitoring inflammatory cell migration into the myocardium while potentially providing additional insight concerning the pathologic progression of a myocardial infarction. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

Globally optimal, minimum stored energy, double-doughnut superconducting magnets

The use of the minimum stored energy current density map-based methodology of designing closed-bore symmetric superconducting magnets was described recently. The technique is further developed to cater for the design of interventional-type MRI systems, and in particular open symmetric magnets of the double-doughnut configuration. This extends the work to multiple magnet domain configurations. The use of double-doughnut magnets in MRI scanners has previously been hindered by the ability to deliver strong magnetic fields over a sufficiently large volume appropriate for imaging, essentially limiting spatial resolution, signal-to-noise ratio, and field of view. The requirement of dedicated interventional space restricts the manner in which the coils can be arranged and placed. The minimum stored energy optimal coil arrangement ensures that the field strength is maximized over a specific region of imaging. The design method yields open, dual-domain magnets capable of delivering greater field strengths than those used prior to this work, and at the same time it provides an increase in the field-of-view volume. Simulation results are provided for 1-T double-doughnut magnets with at least a 50-cm 1-ppm (parts per million) field of view and 0.7-m gap between the two doughnuts. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

The impact of the relaxivity definition on the quantitative measurement of glycosaminoglycans in cartilage by the MRI dGEMRIC method

The relaxivities (R-values) of the gadolinium diethylene triamine pentaacetic acid (Gd(DTPA)2-) ions in a series of skim-milk solutions at 0-40% milk concentrations were measured using NMR spectroscopy. The R-value was found to be approximately linearly proportional to the concentration of the solid component in the milk solution. Using the R-value at 20% solid component (approximately the solid concentration in bovine nasal cartilage), the glycosaminoglycan concentration in bovine nasal cartilage can be quantified using the MRI delayed gadolinium-enhanced MRI of cartilage method without the customary scaling factor of 2. This finding is also supported by the measurements using 23Na NMR spectroscopy, 23Na inductively coupled plasma analysis, and biochemical assay. The choice of the R-value definition in the MRI delayed gadolinium-enhanced MRI of cartilage method is discussed, and the definition of Gd(DTPA)2- ions as "millimole per volume of tissue (or milk solution for substitution)" should be used. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Magnetic field homogenization of the human prefrontal cortex with a set of localized electrical coils

The prefrontal cortex is a common target brain structure in psychiatry and neuroscience due to its role in working memory and cognitive control. Large differences in magnetic susceptibility between the air-filled sinuses and the tissue/bone in the frontal part of the human head cause a strong and highly localized magnetic field focus in the prefrontal cortex. As a result, image distortion and signal dropout are observed in MR imaging. A set of external electrical coils is presented that provides localized and high-amplitude shim fields in the prefrontal cortex, with minimum impact on the rest of the brain when combined with regular zero- to second-order spherical harmonics shimming. The experimental realization of the new shim method strongly minimized or even eliminated signal dropout in gradient-echo images acquired at settings typically used in functional magnetic resonance at 4 T. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

T2 relaxation time abnormalities in bipolar disorder and schizophrenia

There are substantial abnormalities in the number, density, and size of cortical neurons and glial cells in bipolar disorder and schizophrenia. Because molecule-microenvironment interactions modulate metabolite signals characteristics, these cellular abnormalities may impact transverse (T2) relaxation times. We measured T2 relaxation times for three intracellular metabolites (N-acetylaspartate + N-acetylaspartylglutamate, creatine + phosphocreatine, and choline-containing compounds) in the anterior cingulate cortex and parieto-occipital cortex from 20 healthy subjects, 15 patients with bipolar disorder, and 15 patients with schizophrenia at 4 T. Spectra used in T2 quantification were collected from 8-cc voxels with varying echo times (30 to 500 ms, in 10-ms steps). Both bipolar disorder and schizophrenia groups had numerically shorter T2 relaxation times than the healthy subjects group in both regions; these differences reached statistical significance for creatine + phosphocreatine and choline-containing compounds in bipolar disorder and for choline-containing compounds in schizophrenia. Metabolite T2 relaxation time shortening is consistent with reduced cell volumes and altered macromolecule structures, and with prolonged water T2 relaxation times reported in bipolar disorder and schizophrenia. These findings suggest that metabolite concentrations reported in magnetic resonance spectroscopy studies of psychiatric conditions may be confounded by T2 relaxation and highlight the importance of measuring and correcting for this variable. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Motion correction using an enhanced floating navigator and GRAPPA operations

A method for motion correction in multicoil imaging applications, involving both data collection and reconstruction, is presented. The floating navigator method, which acquires a readout line off center in the phase-encoding direction, is expanded to detect translation/rotation and inconsistent motion. This is done by comparing floating navigator data with a reference k-space region surrounding the floating navigator line, using a correlation measure. The technique of generalized autocalibrating partially parallel acquisition is further developed to correct for a fully sampled, motion-corrupted dataset. The flexibility of generalized autocalibrating partially parallel acquisition kernels is exploited by extrapolating readout lines to fill in missing "pie slices" of k-space caused by rotational motion and regenerating full k-space data from multiple interleaved datasets, facilitating subsequent rigid-body motion correction or proper weighting of inconsistent data (e.g., with through-plane and nonrigid motion). Phantom and in vivo imaging experiments with turbo spin-echo sequence demonstrate the correction of severe motion artifacts. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

An expandable catheter loop coil for intravascular MRI in larger blood vessels

The present study proposes a catheter system with an expandable coil etched on a polyimide foil. The catheter system combines the advantages of a small insertion diameter when the coil is rolled up in a protective carrier sheath with an increased signal-to-noise ratio (SNR) and penetration depth when the coil is pushed out. After imaging, the coil can be retracted into the sheath and folded back into the initial rolled-up configuration due to the tapered geometry of the carrier foil. The catheter system was tested on two healthy anesthetized pigs, including tracking and high-resolution intravascular imaging. To reduce artifacts in high-resolution images induced by catheter motion in the pulsatile blood flow, a motion-gating method was implemented that combines a flow-compensated two-dimensional fast low angle shot (FLASH) imaging sequence with the acquisition of projection data for retrospective gating. Using the projection data for motion detection, image SNR was increased by up to 500% over uncorrected images, and anatomic structures of 150 [mu]m size could be differentiated in the aorta. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Change in the proton T1 of fat and water in mixture

This work describes observed changes in the proton T1 relaxation time of both water and lipid when they are in relatively homogeneous mixtures. Results obtained from vegetable oil-water emulsions, pork kidney and lard mixtures, and excised samples of white and brown adipose tissues are presented to demonstrate this change in T1 as a function of mixture fat fraction. As an initial proof of concept, a simpler acetone-water experiment was performed to take advantage of complete miscibility between acetone and water and both components' single chemical shift peaks. Single-voxel MR spectroscopy was used to measure the T1 of predominant methylene spins in fat and the T1 of water spins in each setup. In the vegetable oil-water emulsions, the T1 of fat varied by as much as 3-fold when water was the dominant mixture component. The T1 of pure lard increased by 170 msec (+37%) when it was blended with lean kidney tissue in a 16% fatty mixture. The fat T1 of lipid-rich white adipose tissue was 312 msec. In contrast, the fat T1 of leaner brown adipose tissue (fat fraction 53%) was 460 msec. A change in the water T1 from that of pure water was also observed in the experiments. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Longitudinal analysis of MRI T2 knee cartilage laminar organization in a subset of patients from the osteoarthritis initiative

The purpose of this pilot study was to longitudinally quantify the T2 laminar integrity of knee cartilage in a subset of subjects with osteoarthritis from the Osteoarthritis Initiative at baseline, 1-year follow-up, and 2-year follow-up. Cartilage from 13 subjects was divided into six compartments and subdivided into deep and superficial layers. At each time point, mean T2 values in superficial and deep layers were compared. Longitudinal analysis included full-thickness mean T2, mean deep T2, mean superficial T2, mean T2 laminar difference, mean percentage T2 laminar difference, and two-dimensional measures of cartilage thickness. More compartments showed significantly higher superficial T2 than deep T2 values at baseline and 1-year follow-up compared to 2-year follow-up. No significant longitudinal changes of full-thickness mean T2 and superficial T2 values were observed. Significant longitudinal changes were observed in the deep T2 values, T2 laminar difference, and percentage T2 laminar difference. Cartilage thickness had no influence on T2 analysis. Results of this study suggest that laminar analysis may improve the sensitivity to detect longitudinal T2 changes and that disruption of the T2 laminar organization of knee cartilage may be present in knee osteoarthritis progressors. Further investigation is warranted to evaluate the potential of the presented methodology to better characterize evolution and pathophysiology of osteoarthritis. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Phase-unwrapping algorithm for translation extraction from spherical navigator echoes

Spherical navigator echoes have been shown to determine rigid-body rotation and translation simultaneously. Following the determination of rotation, translations are determined from the phase change between the baseline and transformed spherical navigator echoes. Because the measured phase change is limited in the interval (-[pi], [pi]), a phase-unwrapping algorithm is required to recover the true phase change in absolute values. The unwrapping algorithm presented in this article is based on a priori information about the true translation-induced phase-change function. The algorithm is verified using simulation and in vivo experiments, and the accuracy and precision of translation determination are evaluated. Specifically, the effects of background and off-resonance-induced phase noise are explored. When the proposed phase-unwrapping algorithm was used, translations up to 15 mm were measured, with accuracy better than 5%; for translations up to 40 mm, an error of approximately 10% was observed. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Improved signal to noise in proton spectroscopy of the human calf muscle at 7 T using localized B1 calibration

Large variations of tip angle within a slice can lead to suboptimal pulse power optimization using standard techniques, which measure the average tip angle over a slice; this effect is especially pronounced at fields of 7 T and above. A technique was introduced that performed a volume-selective power optimization in less than 10 sec and automatically calibrates the radiofrequency pulses for subsequent spectroscopy scans. Using this technique, MR spectra were acquired in the human calf of seven healthy volunteers with a partial volume Tx/Rx coil. Increases in signal-to-noise ratio based upon the unsuppressed water signal between 22 ± 5% and 166 ± 42%, compared to spectra obtained with the conventional power calibration technique, were measured in different regions of the calf muscle. This new technique was able to measure the inhomogeneous radiofrequency field at 7 T and its use resulted in a considerable signal-to-noise ratio increase. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

A multislice gradient echo pulse sequence for CEST imaging

Chemical exchange-dependent saturation transfer and paramagnetic chemical exchange-dependent saturation transfer are agent-mediated contrast mechanisms that depend on saturating spins at the resonant frequency of the exchangeable protons on the agent, thereby indirectly saturating the bulk water. In general, longer saturating pulses produce stronger chemical and paramagnetic exchange-dependent saturation transfer effects, with returns diminishing for pulses longer than T1. This could make imaging slow, so one approach to chemical exchange-dependent saturation transfer imaging has been to follow a long, frequency-selective saturation period by a fast imaging method. A new approach is to insert a short frequency-selective saturation pulse before each spatially selective observation pulse in a standard, two-dimensional, gradient-echo pulse sequence. Being much less than T1 apart, the saturation pulses have a cumulative effect. Interleaved, multislice imaging is straightforward. Observation pulses directed at one slice did not produce observable, unintended chemical exchange-dependent saturation transfer effects in another slice. Pulse repetition time and signal-to noise ratio increase in the normal way as more slices are imaged simultaneously. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Navigator accuracy requirements for prospective motion correction

Prospective motion correction in MRI is becoming increasingly popular to prevent the image artifacts that result from subject motion. Navigator information is used to update the position of the imaging volume before every spin excitation so that lines of acquired k-space data are consistent. Errors in the navigator information, however, result in residual errors in each k-space line. This paper presents an analysis linking noise in the tracking system to the power of the resulting image artifacts. An expression is formulated for the required navigator accuracy based on the properties of the imaged object and the desired resolution. Analytical results are compared with computer simulations and experimental data. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

MRI using radiofrequency magnetic field phase gradients

Conventionally, MR images are formed by applying gradients to the main static magnetic field (B0). However, the B0 gradient equipment is expensive, power-hungry, complex, and noisy and can induce eddy currents in nearby conducting structures, including the patient. Here, we describe a new silent, B0 gradient-free MRI principle, Transmit Array Spatial Encoding (TRASE), based on phase gradients of the radio-frequency (RF) field. RF phase gradients offer a new method of k-space traversal. Echo trains using at least two different RF phase gradients allow spin phase to accumulate, causing k-space traversal. Two such RF fields provide one-dimensional imaging and three are sufficient for two-dimensional imaging. Since TRASE is a k-space method, analogues of many conventional pulse sequences are possible. Experimental results demonstrate one-dimensional and two-dimensional RF MRI and slice selection using a single-channel, transmit/receive, 0.2 T, permanent magnet, human MR system. The experimentally demonstrated spatial resolution is much higher than that provided by RF receive coil array sensitivity encoding alone but lower than generally achievable with B0 gradients. Potential applications are those in which one or more of the features of simplified equipment, lower costs, silent MRI, or the different physics of the image formation process are particularly advantageous. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

RF shimming for spectroscopic localization in the human brain at 7 T

Spectroscopic imaging of the human head at short echo times ([le]15 ms) typically requires suppression of signals from extracerebral tissues. However, at 7 T, decreasing efficiency in B1+ generation (hertz/watt) and increasing spectral bandwidth result in dramatic increases in power deposition and increased chemical shift registration artifacts for conventional gradient-based in-plane localization. In this work, we describe a novel method using radiofrequency shimming and an eight-element transceiver array to generate a B1+ field distribution that excites a ring about the periphery of the head and leaves central brain regions largely unaffected. We have used this novel B1+ distribution to provide in-plane outer volume suppression (>98% suppression of extracerebral lipids) without the use of gradients. This novel B1+ distribution is used in conjunction with a double inversion recovery method to provide suppression of extracerebral resonances with T1s greater than 400 ms, while having negligible effect on metabolite ratios of cerebral resonances with T1s > 1000 ms. Despite the use of two adiabatic pulses, the high efficiency of the ring distribution allows radiofrequency power deposition to be limited to 3-4 W for a pulse repetition time of 1.5 sec. The short echo time enabled the acquisition of images of the human brain, displaying glutamate, glutamine, macromolecules, and other major cerebral metabolites. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

A short-breath-hold technique for lung pO2 mapping with 3He MRI

A pulse-sequence strategy was developed for generating regional maps of alveolar oxygen partial pressure (pO2) in a single 6-sec breath hold, for use in human subjects with impaired lung function. Like previously described methods, pO2 values are obtained by measuring the oxygen-induced T1 relaxation of inhaled hyperpolarized 3He. Unlike other methods, only two 3He images are acquired: one with reverse-centric and the other with centric phase-encoding order. This phase-encoding arrangement minimizes the effects of regional flip-angle variations, so that an accurate map of instantaneous pO2 can be calculated from two images acquired a few seconds apart. By combining this phase-encoding strategy with variable flip angles, the vast majority of the hyperpolarized magnetization goes directly into the T1 measurement, minimizing noise in the resulting pO2 map. The short-breath-hold pulse sequence was tested in phantoms containing known O2 concentrations. The mean difference between measured and prepared pO2 values was 1 mm Hg. The method was also tested in four healthy volunteers and three lung-transplant patients. Maps of healthy subjects were largely uniform, whereas focal regions of abnormal pO2 were observed in diseased subjects. Mean pO2 values varied with inhaled O2 concentration. Mean pO2 was consistent with normal steady-state values in subjects who inhaled 3He diluted only with room air. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

An MR-compatible bicycle ergometer for in-magnet whole-body human exercise testing

An MR-compatible ergometer was developed for in-magnet whole-body human exercise testing. Designed on the basis of conventional mechanically braked bicycle ergometers and constructed from nonferrous materials, the ergometer was implemented on a 1.5-T whole-body MR scanner. A spectrometer interface was constructed using standard scanner hardware, complemented with custom-built parts and software to enable gated data acquisition during exercise. High-quality 31P NMR spectra were reproducibly obtained from the medial head of the quadriceps muscle of the right leg of eight healthy subjects during two-legged high-frequency pedaling (80 revolutions per minute) at three incremental workloads, including maximal. Muscle phosphocreatine content dropped 82%, from 32.2 ± 1.0 mM at rest to 5.7 ± 1.1 mM at maximal workload (mean ± standard error; n = 8), indicating that the majority of quadriceps motor units were recruited. The cardiovascular load of the exercise was likewise significant, as evidenced by heart rates of 150 (±10%) beats per minute, measured immediately afterward. As such, the newly developed MR bicycling exercise equipment offers a powerful new tool for clinical musculoskeletal and cardiovascular MR investigation. The basic design of the ergometer is highly generic and adaptable for application on a wide selection of whole-body MR scanners. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Quantification of T2 in the abdomen at 3.0 T using a T2-prepared balanced turbo field echo sequence

The T2-prepared balanced turbo field echo sequence has been used to measure T2 in phantoms and in vivo in the abdomen with low sensitivity to radiofrequency pulse errors. The effects of noise, errors in the pulse flip angles, and off resonance effects on the results have been simulated. It was found from simulations that for normal conditions, including the flip angle in the fit improved the systematic errors due to radiofrequency pulse errors and noise in the results to less than 1% without significantly increasing the random errors. For a 0.3% noise level, the standard deviation in the measured T2 was approximately 0.003 ms. Off-resonance effects had a minimal effect on the measured T2 value. The T2 at 3.0 T of various abdominal organs was measured, in particular the liver (31 ± 6 ms), spleen (54 ± 15 ms), kidney cortex (76 ± 6 ms), kidney medulla (61 ± 8 ms), and pancreas (42 ± 20 ms). Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Investigation and modeling of magnetization transfer effects in two-dimensional multislice turbo spin echo sequences with low constant or variable flip angles at 3 T

Magnetization transfer effects represent a major source of contrast in multislice turbo spin echo sequences (TSE)/fast spin echo sequences. Generally, low refocusing flip angles have become common in such MRI sequences, especially to mitigate specific absorption rate problems. Since the strength of magnetization transfer effects is related to the radiofrequency power and therefore specific absorption rate applied, magnetization transfer induced signal attenuations are investigated for a variety of TSE sequences with low constant and variable flip angles. Noticeable differences between the sequences have been observed. In particular, fewer signal attenuations are observed for TSE with low flip angles such as hyperecho-TSE and smooth transitions between pseudo steady states-TSE, leading to contrast that is less dependent on the number of slices. It is shown that the strength of the magnetization transfer-induced signal attenuations can be understood and described by a physical framework, which is based on the mean square flip angle of a given TSE sequence. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

A 2D MTF approach to evaluate and guide dynamic imaging developments

As the number and complexity of partially sampled dynamic imaging methods continue to increase, reliable strategies to evaluate performance may prove most useful. In the present work, an analytical framework to evaluate given reconstruction methods is presented. A perturbation algorithm allows the proposed evaluation scheme to perform robustly without requiring knowledge about the inner workings of the method being evaluated. A main output of the evaluation process consists of a two-dimensional modulation transfer function, an easy-to-interpret visual rendering of a method's ability to capture all combinations of spatial and temporal frequencies. Approaches to evaluate noise properties and artifact content at all spatial and temporal frequencies are also proposed. One fully sampled phantom and three fully sampled cardiac cine datasets were subsampled (R = 4 and 8) and reconstructed with the different methods tested here. A hybrid method, which combines the main advantageous features observed in our assessments, was proposed and tested in a cardiac cine application, with acceleration factors of 3.5 and 6.3 (skip factors of 4 and 8, respectively). This approach combines features from methods such as k-t sensitivity encoding, unaliasing by Fourier encoding the overlaps in the temporal dimension-sensitivity encoding, generalized autocalibrating partially parallel acquisition, sensitivity profiles from an array of coils for encoding and reconstruction in parallel, self, hybrid referencing with unaliasing by Fourier encoding the overlaps in the temporal dimension and generalized autocalibrating partially parallel acquisition, and generalized autocalibrating partially parallel acquisition-enhanced sensitivity maps for sensitivity encoding reconstructions. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Tailored RF pulse for magnetization inversion at ultrahigh field

The radiofrequency (RF) transmit field is severely inhomogeneous at ultrahigh field due to both RF penetration and RF coil design issues. This particularly impairs image quality for sequences that use inversion pulses such as magnetization prepared rapid acquisition gradient echo and limits the use of quantitative arterial spin labeling sequences such as flow-attenuated inversion recovery. Here we have used a search algorithm to produce inversion pulses tailored to take into account the heterogeneity of the RF transmit field at 7 T. This created a slice selective inversion pulse that worked well (good slice profile and uniform inversion) over the range of RF amplitudes typically obtained in the head at 7 T while still maintaining an experimentally achievable pulse length and pulse amplitude in the brain at 7 T. The pulses used were based on the frequency offset correction inversion technique, as well as time dilation of functions, but the RF amplitude, frequency sweep, and gradient functions were all generated using a genetic algorithm with an evaluation function that took into account both the desired inversion profile and the transmit field inhomogeneity. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

T2 measurement in articular cartilage: Impact of the fitting method on accuracy and precision at low SNR

T2 relaxation time is a promising MRI parameter for the detection of cartilage degeneration in osteoarthritis. However, the accuracy and precision of the measured T2 may be substantially impaired by the low signal-to-noise ratio of images available from clinical examinations. The purpose of this work was to assess the accuracy and precision of the traditional fit methods (linear least-squares regression and nonlinear fit to an exponential) and two new noise-corrected fit methods: fit to a noise-corrected exponential and fit of the noise-corrected squared signal intensity to an exponential. Accuracy and precision have been analyzed in simulations, in phantom measurements, and in seven repetitive acquisitions of the patellar cartilage in six healthy volunteers. Traditional fit methods lead to a poor accuracy for low T2, with overestimations of the exact T2 up to 500%. The noise-corrected fit methods demonstrate a very good accuracy for all T2 values and signal-to-noise ratio. Even more, the fit to a noise-corrected exponential results in precisions comparable to the best achievable precisions (Cramér-Rao lower bound). For in vivo images, the traditional fit methods considerably overestimate T2 near the bone-cartilage interface. Therefore, using an adequate fit method may substantially improve the sensitivity of T2 to detect pathology in cartilage and change in T2 follow-up examinations. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

IIR GRAPPA for parallel MR image reconstruction

Accelerated parallel MRI has advantage in imaging speed, and its image quality has been improved continuously in recent years. This paper introduces a two-dimensional infinite impulse response model of inverse filter to replace the finite impulse response model currently used in generalized autocalibrating partially parallel acquisitions class image reconstruction methods. The infinite impulse response model better characterizes the correlation of k-space data points and better approximates the perfect inversion of parallel imaging process, resulting in a novel generalized image reconstruction method for accelerated parallel MRI. This k-space-based reconstruction method includes the conventional generalized autocalibrating partially parallel acquisitions class methods as special cases and has a new infinite impulse response data estimation mechanism for effective improvement of image quality. The experiments on in vivo MRI data show that the proposed method significantly reduces reconstruction errors compared with the conventional two-dimensional generalized autocalibrating partially parallel acquisitions method, particularly at the high acceleration rates. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Improved technique for measurement of regional fractional ventilation by hyperpolarized 3He MRI

Quantitative measurement of regional lung ventilation is of great significance in assessment of lung function in many obstructive and restrictive pulmonary diseases. A new technique for regional measurement of fractional ventilation using hyperpolarized 3He MRI is proposed, addressing the shortcomings of an earlier approach that limited its use to small animals. The new approach allows for the acquisition of similar quantitative maps over a shortened period and requires substantially less 3He gas. This technique is therefore a better platform for implementation in large species, including humans. The measurements using the two approaches were comparable to a great degree, as verified in a healthy rat lung, and are very reproducible. Preliminary validation is performed in a lung phantom system. Volume dependency of measurements was assessed both in vivo and in vitro. A scheme for selecting an optimum flip angle is proposed. In addition, a dead space modeling approach is proposed to yield more accurate measurements of regional fractional ventilation using either method. Finally, sensitivity of the new technique to model parameters, noise, and number of included images were assessed numerically. As a prelude to application in humans, the technique was implemented in a large animal study successfully. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

3D steady-state diffusion-weighted imaging with trajectory using radially batched internal navigator echoes (TURBINE)

While most diffusion-weighted imaging (DWI) is acquired using single-shot diffusion-weighted spin-echo echo-planar imaging, steady-state DWI is an alternative method with the potential to achieve higher-resolution images with less distortion. Steady-state DWI is, however, best suited to a segmented three-dimensional acquisition and thus requires three-dimensional navigation to fully correct for motion artifacts. In this paper, a method for three-dimensional motion-corrected steady-state DWI is presented. The method uses a unique acquisition and reconstruction scheme named trajectory using radially batched internal navigator echoes (TURBINE). Steady-state DWI with TURBINE uses slab-selection and a short echo-planar imaging (EPI) readout each pulse repetition time. Successive EPI readouts are rotated about the phase-encode axis. For image reconstruction, batches of cardiac-synchronized readouts are used to form three-dimensional navigators from a fully sampled central k-space cylinder. In vivo steady-state DWI with TURBINE is demonstrated in human brain. Motion artifacts are corrected using refocusing reconstruction and TURBINE images prove less distorted compared to two-dimensional single-shot diffusion-weighted-spin-EPI. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Optimization of k-space trajectories for compressed sensing by Bayesian experimental design

The optimization of k-space sampling for nonlinear sparse MRI reconstruction is phrased as a Bayesian experimental design problem. Bayesian inference is approximated by a novel relaxation to standard signal processing primitives, resulting in an efficient optimization algorithm for Cartesian and spiral trajectories. On clinical resolution brain image data from a Siemens 3T scanner, automatically optimized trajectories lead to significantly improved images, compared to standard low-pass, equispaced, or variable density randomized designs. Insights into the nonlinear design optimization problem for MRI are given. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Robust water/fat separation in the presence of large field inhomogeneities using a graph cut algorithm

Water/fat separation is a classical problem for in vivo proton MRI. Although many methods have been proposed to address this problem, robust water/fat separation remains a challenge, especially in the presence of large amplitude of static field inhomogeneities. This problem is challenging because of the nonuniqueness of the solution for an isolated voxel. This paper tackles the problem using a statistically motivated formulation that jointly estimates the complete field map and the entire water/fat images. This formulation results in a difficult optimization problem that is solved effectively using a novel graph cut algorithm, based on an iterative process where all voxels are updated simultaneously. The proposed method has good theoretical properties, as well as an efficient implementation. Simulations and in vivo results are shown to highlight the properties of the proposed method and compare it to previous approaches. Twenty-five cardiac datasets acquired on a short, wide-bore scanner with different slice orientations were used to test the proposed method, which produced robust water/fat separation for these challenging datasets. This paper also shows example applications of the proposed method, such as the characterization of intramyocardial fat. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Quantitative T2 analysis: The effects of noise, regularization, and multivoxel approaches

Typical quantitative T2 (qT2) analysis involves creating T2 distributions using a regularized algorithm from region-of-interest averaged decay data. This study uses qT2 analysis of simulated and experimental decay signals to determine how (a) noise-type, (b) regularization, and (c) region-of-interest versus multivoxel analyses affect T2 distributions. Our simulations indicate that regularization causes myelin water fraction and intra/extracellular water geometric mean T2 underestimation that worsens as the signal-to-noise ratio decreases. The underestimation was greater for intra/extracellular water geometric mean T2 measures using Rician noise. Simulations showed significant differences between myelin water fractions determined using region-of-interest and multivoxel approaches compared to the true value. The nonregularized voxel-based approach gave the most accurate measure of myelin water fraction and intra/extracellular water geometric mean T2 for a given signal-to-noise ratio and noise type. Additionally, multivoxel analysis provides important information about the variability of the analysis. Results obtained from in vivo rat data were similar to our simulation results. In each case, a nonregularized, multivoxel analysis provided myelin water fractions significantly different from the regularized approaches and obtained the largest myelin water fraction. We conclude that quantitative T2 analysis is best performed using a nonregularized, multivoxel approach. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Radial k-t FOCUSS for high-resolution cardiac cine MRI

A compressed sensing dynamic MR technique called k-t FOCUSS (k-t FOCal Underdetermined System Solver) has been recently proposed. It outperforms the conventional k-t BLAST/SENSE (Broad-use Linear Acquisition Speed-up Technique/SENSitivity Encoding) technique by exploiting the sparsity of x-f signals. This paper applies this idea to radial trajectories for high-resolution cardiac cine imaging. Radial trajectories are more suitable for high-resolution dynamic MRI than Cartesian trajectories since there is smaller tradeoff between spatial resolution and number of views if streaking artifacts due to limited views can be resolved. As shown for Cartesian trajectories, k-t FOCUSS algorithm efficiently removes artifacts while preserving high temporal resolution. k-t FOCUSS algorithm applied to radial trajectories is expected to enhance dynamic MRI quality. Rather than using an explicit gridding method, which transforms radial k-space sampling data to Cartesian grid prior to applying k-t FOCUSS algorithms, we use implicit gridding during FOCUSS iterations to prevent k-space sampling errors from being propagated. In addition, motion estimation and motion compensation after the first FOCUSS iteration were used to further sparsify the residual image. By applying an additional k-t FOCUSS step to the residual image, improved resolution was achieved. In vivo experimental results show that this new method can provide high spatiotemporal resolution even from a very limited radial data set. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Reconstruction from free-breathing cardiac MRI data using reproducing kernel Hilbert spaces

This paper describes a rigorous framework for reconstructing MR images of the heart, acquired continuously over the cardiac and respiratory cycle. The framework generalizes existing techniques, commonly referred to as retrospective gating, and is based on the properties of reproducing kernel Hilbert spaces. The reconstruction problem is formulated as a moment problem in a multidimensional reproducing kernel Hilbert spaces (a two-dimensional space for cardiac and respiratory resolved imaging). Several reproducing kernel Hilbert spaces were tested and compared, including those corresponding to commonly used interpolation techniques (sinc-based and splines kernels) and a more specific kernel allowed by the framework (based on a first-order Sobolev RKHS). The Sobolev reproducing kernel Hilbert spaces was shown to allow improved reconstructions in both simulated and real data from healthy volunteers, acquired in free breathing. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Experimental and numerical assessment of MRI-induced temperature change and SAR distributions in phantoms and in vivo

It is important to accurately characterize the heating of tissues due to the radiofrequency energy applied during MRI. This has led to an increase in the use of numerical methods to predict specific energy absorption rate distributions for safety assurance in MRI. To ensure these methods are accurate for actual MRI coils, however, it is necessary to compare to experimental results. Here, we report results of some recent efforts to experimentally map temperature change and specific energy absorption rate in a phantom and in vivo where the only source of heat is the radiofrequency fields produced by the imaging coil. Results in a phantom match numerical simulation well, and preliminary results in vivo show measurable temperature increase. With further development, similar methods may be useful for verifying numerical methods for predicting specific energy absorption rate distributions and in some cases for directly measuring temperature changes and specific energy absorption rate induced by the radiofrequency fields in MRI experiments. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Absolute quantification of perfusion using dynamic susceptibility contrast MRI: pitfalls and possibilities

Abstract Absolute quantification of cerebral blood flow, cerebral blood volume and mean transit time is desirable in the determination of tissue viability thresholds and tissue at risk in acute ischaemic stroke, as well as in cases where a global reduction in cerebral blood flow is expected, for example, in patients with dementia or depressive disorders. Absolute values are also useful when comparing sequential examinations of tissue perfusion parameters, for example, in the monitoring and follow-up of various kinds of therapy. Regardless of the method employed, a number of assumptions and approximations must be made to obtain absolute measures of perfusion. Furthermore, the different stages of data acquisition and processing are associated with various degrees of uncertainty. In this review, the problems of particular relevance to absolute quantification of cerebral perfusion parameters using dynamic susceptibility contrast magnetic resonance imaging are discussed, and possible solutions are outlined. Content Type Journal ArticleCategory Review ArticleDOI 10.1007/s10334-009-0190-2Authors Linda Knutsson, Lund University, Lund University Hospital Department of Medical Radiation Physics 221 85 Lund SwedenFreddy Ståhlberg, Lund University, Lund University Hospital Department of Medical Radiation Physics 221 85 Lund SwedenRonnie Wirestam, Lund University, Lund University Hospital Department of Medical Radiation Physics 221 85 Lund Sweden Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

3D T1-mapping for the characterization of deep vein thrombosis

Abstract Purpose The aim of this work was to investigate fast T 1-mapping for the characterization of deep vein thrombosis (DVT). Methods The accuracy and reproducibility of the T 1-mapping sequence was tested in phantoms and in 8 healthy volunteers on a 1.5 T clinical scanner using a 32-channel array coil. Furthermore, the feasibility of the technique was tested in 5 patients diagnosed with DVT by measuring the volume and T 1 values of the thrombus at 5 time points over a period of 6 months. Results The results of the phantom and volunteer study showed a high accuracy and reproducibility for the quantification of T 1. The resolution of the T 1-maps was high enough to identify small anatomical structures. T 1 values derived for normal blood and various other tissues were comparable to those reported in the literature. In all patients, the T 1 times of thrombi showed decreased values (T 1 = 843 ± 91 ms) in the acute phase and recovered back to normal values of blood (T 1 = 1,317 ± 36 ms) after 6 months. Conclusions Measurement of all relevant T 1 values of acute thrombi and normal blood achieved accurate and reproducible results in vivo. Fast T 1 quantification of the thrombus can provide information about tissue characteristics such as thrombus resolution. Such a quantitative MRI technique may be valuable in studying the factors that influence natural resolution and in evaluating treatment effects that enhance this process. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0189-8Authors Ulrike Blume, King’s College London, St Thomas Hospital Division of Imaging Sciences, The Rayne Institute 4th Floor Lambeth Wing London SE1 7EH UKJames Orbell, St Thomas Hospital Academic Department of Surgery, Cardiovascular Division London UKMatthew Waltham, St Thomas Hospital Academic Department of Surgery, Cardiovascular Division London UKAlberto Smith, St Thomas Hospital Academic Department of Surgery, Cardiovascular Division London UKReza Razavi, King’s College London, St Thomas Hospital Division of Imaging Sciences, The Rayne Institute 4th Floor Lambeth Wing London SE1 7EH UKTobias Schaeffter, King’s College London, St Thomas Hospital Division of Imaging Sciences, The Rayne Institute 4th Floor Lambeth Wing London SE1 7EH UK Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

High-resolution 3D magnetic resonance imaging and quantification of carious lesions and dental pulp in vivo

Abstract Objective The purpose of the study was to assess the feasibility of MRI of three-dimensional visualization and quantification of carious lesions, as well as measurement of the distance between the lesion and dental pulp in vivo. Materials and methods High-resolution 3D MRI was performed to measure seven carious lesions in vivo using gelatinous gadolinium-based oral contrast medium in combination with an intraoral radio frequency receiver coil on a clinical 1.5 T MRI scanner. Extension of the carious lesion in three spatial dimensions and the minimum distance between the lesion and dental pulp were quantified. When possible, the result was compared to an X-ray projection and an impression of the lesion taken using a plastic impression material before and after dental treatment. Results Carious lesions, including pit and fissure, approximal lesions, and occult dentin caries, could be visualized due to the MRI signal rise in the porous affected dentin. The minimum distance between the carious lesion and dental pulp could be determined in all cases. Conclusion The results presented demonstrate the feasibility of high-resolution dental MRI to three-dimensionally visualize and quantify carious lesions, including approximal and occult caries lesions, and measure the minimum distance to the dental pulp. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0188-9Authors Olga Tymofiyeva, University of Wuerzburg Department of Experimental Physics 5 Am Hubland 97074 Wuerzburg GermanyJulian Boldt, University of Wuerzburg Department of Prosthodontics, Dental School Pleicherwall 2 97070 Wuerzburg GermanyKurt Rottner, University of Wuerzburg Department of Prosthodontics, Dental School Pleicherwall 2 97070 Wuerzburg GermanyFlorian Schmid, University of Wuerzburg Department of Experimental Physics 5 Am Hubland 97074 Wuerzburg GermanyErnst-Juergen Richter, University of Wuerzburg Department of Prosthodontics, Dental School Pleicherwall 2 97070 Wuerzburg GermanyPeter M. Jakob, University of Wuerzburg Department of Experimental Physics 5 Am Hubland 97074 Wuerzburg Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Detection of polyunsaturated omega-6 fatty acid in human malignant prostate tissue by 1D and 2D high-resolution magic angle spinning NMR spectroscopy

Abstract Object Polyunsaturated omega-6 fatty acids (PUFAs) have been shown to promote prostate cancer. Here, we describe the use of HRMAS NMR spectroscopy to detect omega-6 PUFA species in prostate tissues. Materials and methods Samples originating from non-malignant (n = 54) and malignant (n = 27) prostate tissues (from 27 prostatectomized men) were studied by 1D 1H, 2D 1H–1H and 1H–13C HRMAS NMR spectroscopy followed by histopathological characterization. Results HRMAS NMR proved to be a powerful, non-destructive method to identify and characterize PUFAs. The omega-6 PUFA was found in 15% of examined human prostate tumors. Conclusion It is possible to detect PUFAs in prostate tissues using our NMR-based spectroscopic approach. Content Type Journal ArticleCategory Short CommunicationDOI 10.1007/s10334-009-0187-xAuthors Katarina Stenman, Umeå University and University Hospital of Northern Sweden Department of Radiation Sciences, Diagnostic Radiology Umeå 901 87 SwedenJón B. Hauksson, Umeå University and University Hospital of Northern Sweden Radiation Physics Umeå SwedenGerhard Gröbner, Umeå University Department of Chemistry Umeå SwedenPär Stattin, Umeå University and University Hospital of Northern Sweden Department of Surgery and Perioperative Sciences, Urology and Andrology Umeå SwedenAnders Bergh, Umeå University and University Hospital of Northern Sweden Department of Medical Biosciences Pathology Umeå SwedenKatrine Riklund, Umeå University and University Hospital of Northern Sweden Department of Radiation Sciences, Diagnostic Radiology Umeå 901 87 Sweden Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Structural–acoustic modal analysis of cylindrical shells: application to MRI scanner systems

Abstract Object The acoustic noise in a magnetic resonance imaging (MRI) scanner bore is mainly introduced by the vibration of gradient coils. The interaction between acoustic modes in the scanner bore and structure modes in the coil structure leads to structural–acoustic coupling. In order to implement quiet MRI design, the structural–acoustic coupling mechanism in MRI machines needs to be fully investigated. Materials and method Structural analysis was first implemented using Love’s classical shell theory. The concept of a “virtually closed cavity” was used in the acoustic modal analysis of the gradient coil duct. The dispersion curves and the number of modes per frequency band were used to reveal modal distribution properties for both structural modes and acoustic modes. Structural–acoustic coupling modes were identified by superposition of the dispersion diagrams of the structural waves and acoustic waves. Experimental validation was implemented separately for the structural analysis and acoustic analysis. Results Independent structural modes and acoustic modes and their distribution patterns were calculated up to 3000Hz with various boundary conditions. Coupling modes were clearly revealed using the analysis procedures presented in this paper and were found to be in agreement with the ones identified from experimental measurements. Conclusion These methods are effective for coupled and uncoupled modal analysis of MRI scanner systems and can be used for quiet MRI design or sound absorber design for existing MRI systems. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0185-zAuthors Gemin Li, Queen’s University Department of Mechanical Engineering McLaughlin Hall Kingston ON K7L 3N6 CanadaChris K. Mechefske, Queen’s University Department of Mechanical Engineering McLaughlin Hall Kingston ON K7L 3N6 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Quantitative metabolic profiles of 2nd and 3rd trimester human amniotic fluid using 1H HR-MAS spectroscopy

Abstract Object To establish and compare normative metabolite concentrations in 2nd and 3rd trimester human amniotic fluid samples in an effort to reveal metabolic biomarkers of fetal health and development. Materials and methods Twenty-one metabolite concentrations were compared between 2nd (15–27 weeks gestation, N = 23) and 3rd (29–39 weeks gestation, N = 27) trimester amniotic fluid samples using 1H high resolution magic angle spinning (HR-MAS) spectroscopy. Data were acquired using the electronic reference to access in vivo concentrations method and quantified using a modified semi-parametric quantum estimation algorithm modified for high-resolution ex vivo data. Results Sixteen of 21 metabolite concentrations differed significantly between 2nd and 3rd trimester groups. Betaine (0.00846±0.00206 mmol/kg vs. 0.0133±0.0058 mmol/kg, P < 0.002) and creatinine (0.0124±0.0058 mmol/kg vs. 0.247±0.011 mmol/kg, P < 0.001) concentrations increased significantly, while glucose (5.96±1.66 mmol/kg vs. 2.41±1.69 mmol/kg, P < 0.001), citrate (0.740±0.217 mmol/kg vs. 0.399±0.137 mmol/kg, P < 0.001), pyruvate (0.0659±0.0103 mmol/kg vs. 0.0299±0.286 mmol/kg, P < 0.001), and numerous amino acid (e.g. alanine, glutamate, isoleucine, leucine, lysine, and valine) concentrations decreased significantly with advancing gestation. A stepwise multiple linear regression model applied to 50 samples showed that gestational age can be accurately predicted using combinations of alanine, glucose and creatinine concentrations. Conclusion These results provide key normative data for 2nd and 3rd trimester amniotic fluid metabolite concentrations and provide the foundation for future development of magnetic resonance spectroscopy (MRS) biomarkers to evaluate fetal health and development. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0184-0Authors Brad R. Cohn, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USABonnie N. Joe, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAShoujun Zhao, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAJohn Kornak, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAVickie Y. Zhang, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USARahwa Iman, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAJohn Kurhanewicz, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAKiarash Vahidi, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAJingwei Yu, University of California Department of Laboratory Medicine San Francisco CA USAAaron B. Caughey, University of California Department of Obstetrics & Gynecology San Francisco CA USAMark G. Swanson, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Thursday

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Thursday Content Type Journal ArticleDOI 10.1007/s10334-009-0175-1 Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Saturday

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Saturday Content Type Journal ArticleDOI 10.1007/s10334-009-0177-z Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Friday

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Friday Content Type Journal ArticleDOI 10.1007/s10334-009-0176-0 Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: EPOStm Posters / Paper Posters / Info-RESO

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: EPOStm Posters / Paper Posters / Info-RESO Content Type Journal ArticleDOI 10.1007/s10334-009-0178-y Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Author Index

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Author Index Content Type Journal ArticleDOI 10.1007/s10334-009-0179-x Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

A digital receiver with fast frequency- and gain-switching capabilities for MRI systems

Abstract Object In this article, two issues pertaining to MRI digital receivers are addressed. One is the maintenance of phase coherence between the transmitter and the receiver—an effective solution is proposed, in which the receiver frequency is switched synchronously with the transmitter frequency. The other is the dynamic range of the receiver—gain-switching technique is utilized to improve the dynamic range. To meet the hardware requirements of these solutions, a digital receiver with fast frequency- and gain-switching capabilities was implemented. Materials and methods The primary components of the proposed digital receiver are a variable gain amplifier, a high-speed analog-to-digital converter and a single-chip digital receiver core. The radio-frequency magnetic resonance signal is directly sampled by the analog-to-digital converter and processed in the digital receiver core. By pre-storing the receiver waveform in the on-board SDRAM, the frequency and gain of the receiver may be switched very quickly. Results The performance of the proposed digital receiver is verified by embedding it in an imaging spectrometer. It is then demonstrated by conducting experiments on a home-built 0.3-T magnetic resonance imaging system. Conclusion The results show that the phase coherence between the transmitter and the receiver and the dynamic range of the receiver are greatly improved. Consequently, the proposed digital receiver may be useful for obtaining multiple-slice two-dimensional magnetic resonance images with very high resolution. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0182-2Authors Ning Ruipeng, East China Normal University Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics 3663 North Zhong-Shan Road 200062 Shanghai People’s Republic of ChinaDai Yidong, East China Normal University Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics 3663 North Zhong-Shan Road 200062 Shanghai People’s Republic of ChinaYang Guang, East China Normal University Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics 3663 North Zhong-Shan Road 200062 Shanghai People’s Republic of ChinaLi Gengying, East China Normal University Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics 3663 North Zhong-Shan Road 200062 Shanghai People’s Republic of China Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Influence of cardiac motion on diffusion-weighted magnetic resonance imaging of the liver

Abstract Purpose To assess cardiac motion-induced signal loss in diffusion-weighted magnetic resonance imaging (DWI) of the liver using dynamic DWI. Materials and methods Three volunteers underwent dynamic coronal DWI of the liver under breathholding, in the diastolic (DWIdiast) or systolic (DWIsyst) cardiac phase, and with motion probing gradients (MPGs) in phase encoding (P, left–right), frequency encoding (M, superior–inferior), or slice select (S, anterior–posterior) direction. Liver-to-background contrasts (LBCs) of DWIsyst were compared to those of DWIdiast, for both the left and right liver lobes, using nonparametric tests. Signal decrease ratios (SDRs) were calculated as (1−(LBCDWIsyst/LBCDWIdiast)) × 100%. DWIsyst was further analyzed to determine which direction of MPGs was most affected by cardiac motion. Results In the left liver lobe, LBCs of DWIsyst (median 3.35) were significantly lower (P < 0.0001) than those of DWIdiast (median 4.84). In the right liver lobe, LBCs of DWIsyst (median 4.17) were also significantly lower (P < 0.0001) than those of DWIdiast (median 5.35 ). SDRs of the left and right liver lobes were 25.5% and 17.3%, respectively. In DWIsyst, the significantly lowest (P < 0.05) LBCs were observed in the M direction (left liver lobe) and P direction (right liver lobe) of MPGs. Conclusion Signal intensity of both liver lobes are affected by cardiac motion in DWI. In the left liver lobe, signal loss especially occurs in the superior–inferior direction of MPGs, whereas in the right lobe, signal loss especially occurs in the left-right direction of MPGs. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0183-1Authors Thomas C. Kwee, University Medical Center Utrecht Department of Radiology Heidelberglaan 100 3584 CX Utrecht The NetherlandsTaro Takahara, University Medical Center Utrecht Department of Radiology Heidelberglaan 100 3584 CX Utrecht The NetherlandsTetsu Niwa, University Medical Center Utrecht Department of Radiology Heidelberglaan 100 3584 CX Utrecht The NetherlandsMarko K. Ivancevic, University of Michigan Medical Center Department of Radiology Ann Arbor MI USAGwenael Herigault, Philips Healthcare Best The NetherlandsMarc Van Cauteren, Philips Healthcare Asia Pacific Tokyo JapanPeter R. Luijten, University Medical Center Utrecht Department of Radiology Heidelberglaan 100 3584 CX Utrecht The Netherlands Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Rapid 3-D mapping of hyperpolarized 3He spin-lattice relaxation times using variable flip angle gradient echo imaging with application to alveolar oxygen partial pressure measurement in rat lungs

Abstract Objective The purpose of this work was to develop a rapid 3-D, variable flip angle (VFA) method for measurement of hyperpolarized 3He T 1 which accounts for the effects of radiofrequency (RF) pulses without the need for additional flip angle information. Materials and methods The 3-D, VFA method was validated in vitro over a range of oxygen partial pressures ranging from 0.04 to 0.52 atm. The approach was also tested in vivo in five healthy rats as a function of increasing number of wash-out breaths. The T 1 accuracy of the VFA method in the presence of flip angle mis-setting and RF field non-uniformity was compared with the CFA method using simulations and experiments. Results T 1 measurements were found to provide pAO2 estimates, both in vitro and in vivo consistent with those predicted based on gas dilution and/or ventilation para- meters. For the RF pulse mis-setting (4%) and RF field non-uniformity (3%) used here, the VFA method provided a T 1 accuracy of better than 5% compared to 12% for the CFA method. Conclusion With sufficient RF field homogeneity (3%) and proper calibration (4%), the VFA approach can provide rapid and reliable 3-D T 1 mapping of hyperpolarized 3He without the need for additional flip angle information. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0181-3Authors Alexei V. Ouriadov, Robarts Research Institute Imaging Research Laboratories P.O. Box 5015 100 Perth Drive London ON N6A 5K8 CanadaWilfred W. Lam, Sunnybrook Health Sciences Centre Imaging Research Toronto ON M4N 3M5 CanadaGiles E. Santyr, Robarts Research Institute Imaging Research Laboratories P.O. Box 5015 100 Perth Drive London ON N6A 5K8 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Utilizing different methods for visualizing susceptibility from a single multi-gradient echo dataset

Abstract Purpose Objects that cause a susceptibility gradient can generate regions of hypo-intensity in MRI. MR techniques developed for positive enhancement of such objects require sequence parameter optimization. Thus comparison of images acquired successively using different techniques is difficult since different parameter settings result in variations in signal and noise. A new method is presented that allows production of positive contrast images, a relaxation rate R2* -map and negative contrast images from a single dataset by post-processing. Methods Positive contrast techniques considered include the “white marker” technique, inversion-recovery on-resonance (IRON) and susceptibility gradient mapping (SGM). The new method was tested in phantoms of iron-oxide agent gel solutions and prostate marker seeds. Images produced by post-processing were compared with those obtained directly. The post-processing technique was applied in vivo for the visualization of iron-oxide contrast agent uptake in a balloon-injured swine carotid model. Results The images produced in the post-processing step allowed determination of optimal parameter settings for each technique. SGM was found to provide the greatest positive contrast, whilst the T2* -weighted images provide more sensitivity to regions that exhibited weaker susceptibility effects. Conclusions Combined T2* -weighted imaging and SGM using the same complex image data was found to provide complementary information and high sensitivity to detect distortion inducing agents. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0180-4Authors Gopal Varma, King’s College London, St Thomas’ Hospital Division of Imaging Sciences Westminster Bridge Road London SE1 7EH UKSteen Fjord Pedersen, University of Aarhus, Aarhus University Hospital The MR Research Centre Skejby, Brendstrupgaardsvej 8200 Aarhus N DenmarkMatthias Taupitz, Charite-Universitatsmedizin Berlin Department of Radiology Campus Charite Mitte, Chariteplatz 1 10117 Berlin GermanyRene Michael Botnar, King’s College London, St Thomas’ Hospital Division of Imaging Sciences Westminster Bridge Road London SE1 7EH UKHannes Dahnke, Philips Research Europe Roentgenstrasse 24-26 22335 Hamburg GermanyStephen Frederick Keevil, King’s College London, St Thomas’ Hospital Division of Imaging Sciences Westminster Bridge Road London SE1 7EH UKTobias Schaeffter, King’s College London, St Thomas’ Hospital Division of Imaging Sciences Westminster Bridge Road London SE1 7EH UK Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Influence of selecting EPI readout-encoding bandwidths on arterial spin labeling perfusion MRI

Abstract Object The objective of this study was to investigate effects of varying readout bandwidths on the arterial spin labeling (ASL)-perfusion MRI measurements at a high magnetic field MRI system. Materials and methods Brain perfusion studies were performed on nine volunteers (four males, five females) using flow sensitive alternating inversion recovery (FAIR) ASL single-shot echo-planar imaging (EPI)-MRI. To investigate EPI bandwidth effects on the time-series perfusion-weighted imaging (PWI) data, two regions-of-interest (ROI) were placed outside the brain to determine the level of noise and another ROI inside the brain to determine the level of signal. Coefficients of variations (CoV) were calculated for the time-series PWI data. One-way analysis of variance (ANOVA) was used to investigate voxel-wise differences in the time-series PWI data between two different bandwidth values. Results At the level of ROI, there was no significant effect of changing EPI bandwidths on the time-series PWI data in any of the volunteers (P > 0.031). In contrast, CoV values over the dynamic PWI data varied with depending on selecting EPI bandwidths and voxel-based tests showed that N2 ghosting, modulated by EPI bandwidth, can appear in some brain regions, especially in areas that overlap with the spatial distribution of N2 ghosting artifacts. Conclusions Although N2 ghosting can be reduced by adjusting the bandwidth of EPI on the time-series of PWI data, the effects cannot be entirely eliminated. In particular, N2 ghosting can bias CBF quantification if EPI control scans to determine the equilibrium-state signal are confounded by N2 ghosting. Therefore, careful tuning of the bandwidth of EPI is necessary to avoid artifacts in the ASL signal from N2-ghosting. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0174-2Authors Geon-Ho Jahng, Kyung Hee University Department of Radiology, School of Medicine, East-West Neo Medical Center 149 Sangil-dong, Gangdong-gu Seoul 134-090 South KoreaNorbert Schuff, University of California, San Francisco Department of Radiology, Center for Imaging of Neurodegenerative Diseases, VA Medical Center 4150 Clement Street, 114M San Francisco CA 94121 USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Echo-dephased steady state free precession

Abstract Objective To introduce a novel positive contrast method for passive localization and visualization of paramagnetic susceptibility markers. Materials and methods The novel approach is based on an echo-dephased steady-state free precession (SSFP) sequence. Gradients dephase any signal by ±π at the centered echo-time (TE = TR/2) and induce a total dephasing of ±2π per pixel within TR. This ensures that background tissues do not contribute to signal formation and thus appear dark. However, within the close vicinity of the paramagnetic marker, local gradient fields compensate for the intrinsic dephasing to form an echo. Conceptual issues of gradient compensation and its visualization characteristics are analyzed. The feasibility of the proposed technique for MR-guided intravascular interventions is demonstrated using flow phantom. Results Echo-dephased SSFP is able to localize and visualize paramagnetic marker with excellent suppression of the background signals. The flow phantom experiments concluded that reliable tracking of the interventional guidewire is feasible using echo-dephased SSFP. Conclusion With newly introduced echo-dephased SSFP approach, accurate and reliable visualization of paramagnetic interventional device is feasible. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0173-3Authors Sunil Patil, University of Basel Hospital Division of Radiological Physics, Department of Medical Radiology Petersgraben 4 4031 Basel SwitzerlandOliver Bieri, University of Basel Hospital Division of Radiological Physics, Department of Medical Radiology Petersgraben 4 4031 Basel SwitzerlandKlaus Scheffler, University of Basel Hospital Division of Radiological Physics, Department of Medical Radiology Petersgraben 4 4031 Basel Switzerland Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Monitoring the survival of islet transplants by MRI using a novel technique for their automated detection and quantification

Abstract Object There is a clinical need to be able to assess graft loss of transplanted pancreatic islets (PI) non-invasively with clear-cut quantification of islet survival. We tracked transplanted PI in diabetic mice during the early post-transplant period by magnetic resonance imaging (MRI) and quantified the islet loss using automatic segmentation technique. Materials and methods Magnetically labeled islet iso-, allo- and xenografts were injected into the right liver lobes. Animals underwent MRI scanning during 14 days after PI transplantation. MR images were processed using custom-made software, which automatically detects hypointense regions representing PI. It is based on morphological top-hat and bottom-hat transforms. Results Manually and automatically detected areas, corresponding to PI, differed by 4% in phantoms. Signal loss regions due to PI decreased comparably in all groups during the first week post transplant. Throughout the second week post-transplant, the signal loss area continued in a steep decline in case of allografts and xenografts, whereas the decline in case of isografts slowed down. Conclusion Automatic segmentation allows for the more reproducible, objective assessment of transplanted PI. Quantification confirms the assumption that a significant number of islets are destroyed in the first week following transplantation irrespective of allografts, xenografts or isografts. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0172-4Authors Daniel Jirak, Robarts Research Institute Imaging Research Laboratories London ON N6A 5K8 CanadaJan Kriz, Robarts Research Institute Imaging Research Laboratories London ON N6A 5K8 CanadaMichal Strzelecki, Technical University of Lodz Institute of Electronics Lodz PolandJiabi Yang, Robarts Research Institute Transplantation Group London ON CanadaCraig Hasilo, Robarts Research Institute Transplantation Group London ON CanadaDavid J. White, Robarts Research Institute Transplantation Group London ON CanadaPaula J. Foster, Robarts Research Institute Imaging Research Laboratories London ON N6A 5K8 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 4 / August, 2009

Detection and quantification of d-glucuronic acid in human bile using 1H NMR spectroscopy: relevance to the diagnosis of pancreatic cancer

Abstract Objective There are no specific biomarkers available for the definitive diagnosis of pancreatic cancer. Analysis of d-glucuronic acid (GlcUA) in bile could be valuable in this regard. Materials and methods Bile samples obtained from patients with pancreatic cancer (n = 4), chronic pancreatitis (n = 3) and control patients with biliary obstruction (n = 10) were analyzed by 1H NMR spectroscopy. GlcUA was quantified from the peak area of the α-1CH signal (at 5.24 ppm) obtained by deconvolution. Results GlcUA was detected in human bile by one-dimensional 1H NMR and two-dimensional 1H–1H COSY and TOCSY experiments. Quantification of GlcUA was achieved by measuring the peak area of the α-1CH signal using CPMG experiment, and the quantities of GlcUA were calibrated to account for the attenuation due to T 2 relaxation. GlcUA was observed at elevated levels in bile samples obtained from pancreatic cancer patients, whereas it was either absent or found in negligible amounts in control and chronic pancreatitis patients. The reason for the presence of elevated levels of GlcUA could be the hydrolysis of biliary bilirubin diglucuronide by β-glucuronidase, released excessively from pancreatic tissue during the course of malignancy. Conclusion Analysis of d-glucuronic acid in bile could be valuable in the detection of pancreatic cancer, and detecting GlcUA by in vivo 1H MRS has the potential to help in the non-invasive diagnosis of pancreatic cancer. Given that only four cancer patients have been studied so far, the new biomarker is regarded as a preliminary finding, but one that warrants further investigation. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0171-5Authors Tedros Bezabeh, National Research Council Institute for Biodiagnostics 435 Ellice Avenue Winnipeg MB R3B 1Y6 CanadaOmkar B. Ijare, National Research Council Institute for Biodiagnostics 435 Ellice Avenue Winnipeg MB R3B 1Y6 CanadaNils Albiin, CLINTEC, Karolinska Institutet Division of Radiology Stockholm SwedenUrban Arnelo, CLINTEC, Karolinska Institutet Division of Surgery Stockholm SwedenBo Lindberg, CLINTEC, Karolinska Institutet Division of Radiology Stockholm SwedenIan C. P. Smith, National Research Council Institute for Biodiagnostics 435 Ellice Avenue Winnipeg MB R3B 1Y6 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Extraction of the first bolus passage in dynamic susceptibility contrast perfusion measurements

Abstract Object The processing of dynamic susceptibility contrast perfusion measurements requires an extraction of the first bolus passage of the injected contrast agent. State-of-the-art methods employ the fit of a gamma variate function to the measured data. The use of a gamma variate function is motivated by its shape similarity to the expected relaxation rate time-course during the first bolus passage. However, the quality of this result is strongly influenced by the amount of overlap of the first and second bolus passage. In this work we present an alternative, data-driven method for the extraction of the first bolus passage from a measured relaxation time-course. Materials and methods By using prior knowledge of the injection function, the measured time-courses can be transformed to time-courses that would occur at a shorter injection duration where the two bolus passages have less overlap. This time-course is found by Tikhonov regularized deconvolution of the measured time-courses with an injection function that bases on the measurement protocol. A minimum search yields the cut-off point at which the first bolus can be extrapolated to zero. The gamma variate fit is performed using Powells algorithm. The proposed approach is compared to the gamma variate fit approach using simulations and an exemplary dataset from one healthy volunteer. Results The new method performs comparably stable as the gamma variate function fit approach in simulations. Both methods are superior to a simple exponential extrapolation approach. Applied to volunteer data, the new method performs much faster than the gamma variate fit approach. The results obtained from both methods correspond well. Conclusion The new method offers a conceptual understanding of the first bolus passage and yields similar results to the gamma variate function fit approach but performs much faster. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0170-6Authors Peter Gall, University Medical Center Freiburg Department of Diagnostic Radiology, Medical Physics Hugstetterstrasse 55 79106 Freiburg GermanyIrina Mader, University Medical Center Freiburg Department of Neuroradiology Breisacher Strasse 64 79106 Freiburg GermanyValerij G. Kiselev, University Medical Center Freiburg Department of Diagnostic Radiology, Medical Physics Hugstetterstrasse 55 79106 Freiburg Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 4 / August, 2009