Magnetic_Resonance_Imaging RSS : Gourt

Multichannel transceiver dual-tuned RF coil for proton/sodium MR imaging of knee cartilage at 3 T.

Multichannel transceiver dual-tuned RF coil for proton/sodium MR imaging of knee cartilage at 3 T. Magn Reson Imaging. 2012 Jan 30; Authors: Kim JH, Moon CH, Park BW, Furlan A, Zhao T, Bae KT Abstract Sodium magnetic resonance (MR) imaging is a promising technique for detecting changes of proteoglycan (PG) content in cartilage associated with knee osteoarthritis. Despite its potential clinical benefit, sodium MR imaging in vivo is challenging because of intrinsically low sodium concentration and low MR signal sensitivity. Some of the challenges in sodium MR imaging may be eliminated by the use of a high-sensitivity radiofrequency (RF) coil, specifically, a dual-tuned (DT) proton/sodium RF coil which facilitates the co-registration of sodium and proton MR images and the evaluation of both physiochemical and structural properties of knee cartilage. Nevertheless, implementation of a DT proton/sodium RF coil is technically difficult because of the coupling effect between the coil elements (particularly at high field) and the required compact design with improved coil sensitivity. In this study, we applied a multitransceiver RF coil design to develop a DT proton/sodium coil for knee cartilage imaging at 3 T. With the new design, the size of the coil was minimized, and a high signal-to-noise ratio (SNR) was achieved. DT coil exhibited high levels of reflection S11 (∼-21 dB) and transmission coefficient S12 (∼-19 dB) for both the proton and sodium coils. High SNR (range 27-38) and contrast-to-noise ratio (CNR) (range 15-21) were achieved in sodium MR imaging of knee cartilage in vivo at 3-mm(3) isotropic resolution. This DT coil performance was comparable to that measured using a sodium-only birdcage coil (SNR of 28 and CNR of 20). Clinical evaluation of the DT coil on four normal subjects demonstrated a consistent acquisition of high-resolution proton images and measurement of relative sodium concentrations of knee cartilages without repositioning of the subjects during the same MR scanning session. PMID: 22297242 [PubMed - as supplied by publisher]

Minimization of spectral pattern changes during HRMAS experiments at 37 degrees celsius by prior focused microwave irradiation

Abstract Object High-resolution magic angle spinning (HRMAS) magnetic resonance spectroscopy provides detailed metabolomic information from intact tissue. However, long acquisition times and high rotation speed may lead to time-dependent spectral pattern changes, which may affect proper interpretation of results. We report a strategy to minimize those changes, even at physiological recording temperature. Materials and methods Glioblastoma (Gbm) tumours were induced in 12 mice by stereotactic injection of GL261 cells. Animals were sacrificed and tumours were removed and stored in liquid N2. Half of the samples were exposed to focused microwave (FMW) irradiation prior to HRMAS while the other half was not. Time-course experiments (374 min at 37°C, 9.4T, 3,000 Hz spinning rate) were carried out to monitor spectral pattern changes. Differences were assessed with Unianova test while post-HRMAS histopathology analysis was performed to assess tissue integrity. Results Significant changes (up to 1.7 fold) were observed in samples without FMW irradiation in several spectral regions e.g. mobile lipids/lactate (0.90–1.30 ppm), acetate (1.90 ppm), N-acetyl aspartate (2.00 ppm), and Choline-containing compounds (3.19–3.25 ppm). No significant changes in the spectral pattern of FMW-irradiated samples were recorded. Conclusion We describe here a successful strategy to minimize spectral pattern changes in mouse Gbm samples using a FMW irradiation system. Content Type Journal ArticleCategory Research ArticlePages 1-10DOI 10.1007/s10334-012-0303-1Authors Myriam Davila, Departament de Bioquímica i Biologia Molecular, Unitat de Bioquímica de Biociències, Edifici Cs, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, SpainAna Paula Candiota, Departament de Bioquímica i Biologia Molecular, Unitat de Bioquímica de Biociències, Edifici Cs, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, SpainMartí Pumarola, Murine Pathology Unit, Centre de Biotecnologia Animal i Teràpia Gènica (CBATEG), Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, SpainCarles Arus, Departament de Bioquímica i Biologia Molecular, Unitat de Bioquímica de Biociències, Edifici Cs, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

MR perfusion imaging by alternate slab width inversion recovery arterial spin labeling (AIRASL): a technique with higher signal-to-noise ratio at 3.0 T

Abstract Object To propose a new arterial spin labeling (ASL) perfusion-imaging method (alternate slab width inversion recovery ASL: AIRASL) that takes advantage of the qualities of 3.0 T. Materials and methods AIRASL utilizes alternate slab width IR pulses for labeling blood to obtain a higher signal-to-noise ratio (SNR). Numerical simulations were used to evaluate perfusion signals. In vivo studies were performed to show the feasibility of AIRASL on five healthy subjects. We performed a statistical analysis of the differences in perfusion SNR measurements between flow-sensitive alternating inversion recovery (FAIR) and AIRASL. Results In signal simulation, the signal obtained by AIRASL at 3.0 and 1.5 T was 1.14 and 0.85%, respectively, whereas the signal obtained by FAIR at 3.0 and 1.5 T was 0.57 and 0.47%, respectively. In an in vivo study, the SNR of FAIR (3.0 T) and FAIR (1.5 T) were 1.73 ± 0.49 and 1.02 ± 0.20, respectively, whereas the SNRs of AIRASL (3.0 T) and AIRASL (1.5 T) were 3.93 ± 1.65 and 1.34 ± 0.31, respectively. SNR in AIRASL at 3.0 T was significantly greater than that in FAIR at 3.0 T. Conclusion The most significant potential advantage of AIRASL is its high SNR, which takes advantage of the qualities of 3.0 T. This sequence can be easily applied in the clinical setting and will enable ASL to become more relevant for clinical application. Content Type Journal ArticleCategory Research ArticlePages 1-9DOI 10.1007/s10334-011-0301-8Authors Yasuhiro Fujiwara, Radiological Center, University of Fukui Hospital, Fukui, JapanHirohiko Kimura, Department of Radiology, Faculty of Medical Science, University of Fukui, 23-3, Shimoaizuki, Matsuoka, Eiheiji-tyo, Yoshida-gun, Fukui, 910-1193 JapanTosiaki Miyati, Division of Health Sciences, Kanazawa University Graduate School of Medical Science, Kanazawa, JapanHiroyuki Kabasawa, Applied Science Laboratory Japan, GE Healthcare Japan Corporation, Tokyo, JapanTsuyoshi Matsuda, Advanced Application Center, GE Healthcare Japan Corporation, Tokyo, JapanYoshiyuki Ishimori, Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, Ibaraki, JapanIsao Yamaguchi, Department of Radiological Technology, Osaka Butsuryo College, Osaka, JapanToshiki Adachi, Radiological Center, University of Fukui Hospital, Fukui, Japan Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Repeatability of renal arterial spin labelling MRI in healthy subjects

Abstract Object Arterial spin labelling (ASL) can be used to measure renal perfusion non-invasively. The aim of this study was to determine the repeatability of this technique in healthy kidneys to vindicate its use in clinic. Materials and methods Two groups of healthy volunteers were imaged two different days to assess intra- and inter-session repeatability. Oblique-coronal data volumes were acquired on a 1.5 T scanner with a dedicated abdominal 32-channel body phased array coil. ASL was performed using a multi-TI FAIR labelling scheme and 3D GRASE imaging module. Background suppression and respiratory triggering were used. T1 maps of the kidney were acquired using the same sequence with background suppression disabled. Results For the group with multiple intra-session ASL measurements, the average cortical perfusion was 197 mL min−1100 g−1 and average cortical T1 was 1265 ms. For both perfusion and T1 the variation shown by the within-subject standard deviation (SDws) (14.6 mL min−1100 g−1 and 33.4 ms) and coefficient of variation (CVws) (7.52 and 2.69%, respectively) was small for all the analyses carried out. Bland–Altman plots were also used to visualise the variation between the same parameters collected from the different scanning sessions in both groups, and demonstrated good reproducibility. Conclusion We have shown that in healthy volunteers, ASL parameters are repeatable over a short and long period. This supports the overall aim of using ASL in the clinic to assess longitudinal renal perfusion changes in patients. Content Type Journal ArticleCategory Research ArticlePages 1-9DOI 10.1007/s10334-011-0300-9Authors Marica Cutajar, Imaging and Biophysics Unit, UCL Institute of Child Health, 30 Guilford Street, London, WC1N 1EH UKDavid L. Thomas, Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, Queen Square, London, WC1N 3BG UKTina Banks, Department of Radiology, Great Ormond Street Hospital, London, WC1N 3JH UKChristopher A. Clark, Imaging and Biophysics Unit, UCL Institute of Child Health, 30 Guilford Street, London, WC1N 1EH UKXavier Golay, Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, Queen Square, London, WC1N 3BG UKIsky Gordon, Imaging and Biophysics Unit, UCL Institute of Child Health, 30 Guilford Street, London, WC1N 1EH UK Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Blind detection of vascular sources and territories using random vessel encoded arterial spin labeling

Abstract Object The goal of this work is to use vessel encoded arterial spin labeling (VEASL) methods to detect feeding arteries without prior knowledge of their positions, and map the vascular territory of each. Materials and methods Five healthy subjects were scanned, each with four different tagging planes. The VEASL tagging method was modified to use 60 different pairs of encoding steps with random orientation and spacing. A signal model was developed to calculate the theoretical ASL signal resulting from a vessel in any position in the tagging plane. For each voxel, the location of the feeding vessel was estimated by finding the theoretical signal that correlates most closely with the data. Results The main intracranial arteries, including carotid, vertebral, basilar, and cerebral arteries above the Circle of Willis were identified and localized from the ASL data in all subjects. In addition, external carotid branches were detected in all subjects. Conclusions Randomly encoded VEASL provides data that allows for blind detection of source vessels. This method simplifies the VEASL prescription process and allows for efficient detection of atypical or collateral circulation. Content Type Journal ArticleCategory Research ArticlePages 1-7DOI 10.1007/s10334-011-0302-7Authors Eric C. Wong, Departments of Radiology and Psychiatry, UCSD Center for Functional MRI, 9500 Gilman Drive, MC 0677, La Jolla, CA 92093-0677, USAJia Guo, Department of Bioengineering, University of California, San Diego, CA, USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Measuring temperature using MRI: a powerful and versatile technique

Abstract The Larmor frequency of water protons has reliably linear temperature dependence. Since this frequency shift is easily measurable using relatively simple MRI techniques, a remarkable opportunity arises for uniquely non-invasive and accurate temperature evaluation, deep within any water-containing object. Major applications are appearing in the field of image-guided surgery. The cutting-edge papers collected in this Special Issue demonstrate both the versatility and the power of MRI thermometry. Content Type Journal ArticleCategory EditorialPages 1-3DOI 10.1007/s10334-011-0299-yAuthors Robert Turner, Max-Planck Institute for Human Cognitive and Brain Sciences, Stephanstraße 1A, 04103 Leipzig, GermanyMarkus Streicher, Max-Planck Institute for Human Cognitive and Brain Sciences, Stephanstraße 1A, 04103 Leipzig, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 25 Journal Issue Volume 25, Number 1

Magnetisation transfer effects of Q2TIPS pulses in ASL

Abstract Object In pulsed arterial spin labelling (ASL), Q2TIPS saturation pulses are used to actively control the temporal width of the labelled bolus. However, these Q2TIPS pulses also induce magnetisation transfer (MT) effects in the adjacent tissue. In this work, we investigated how Q2TIPS-related MT alters tissue signal in pulsed ASL and, consequently, CBF quantification. Materials and methods Seven volunteers were studied at 3 tesla using a multi-TI FAIR sequence and 3D-GRASE readout with background suppression. Q2TIPS pulses were used and the spacing between RF pulses was varied to modulate MT effects. Computer simulations were designed to mimic in-vivo signals at multiple TI values. Results Q2TIPS-associated MT was found to reduce tissue T1 and M0 values by up to 42 and 50% respectively; leading to a reduction of up to 40% in the effectiveness of background suppression and, therefore, increased sensitivity to motion for the longest TI values. In addition, greater MT effects were associated with reduced grey matter CBF estimates of up to 15%. Conclusions The MT effect associated with the Q2TIPS pulse train has a significant effect on tissue signal. It is recommended that MT effects are characterised and both background suppression and Q2TIPS schemes are accordingly optimised to reduce the effects of MT on accuracy and precision of CBF estimation. Content Type Journal ArticleCategory Research ArticlePages 1-14DOI 10.1007/s10334-011-0298-zAuthors Enrico De Vita, Lysholm Department of Neuroradiology, National Hospital for Neurology and Neurosurgery, University College London Hospitals NHS Foundation Trust, Queen Square, Box 65, London, WC1N 3BG UKMatthias Günther, Mediri GmbH, Heidelberg, GermanyXavier Golay, Lysholm Department of Neuroradiology, National Hospital for Neurology and Neurosurgery, University College London Hospitals NHS Foundation Trust, Queen Square, Box 65, London, WC1N 3BG UKDavid L. Thomas, Academic Neuroradiological Unit, Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, Queen Square, London, WC1N 3BG UK Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Feasibility of pseudocontinuous arterial spin labeling at 7 T with whole-brain coverage

Abstract Object We studied the feasibility of pseudocontinuous arterial spin labeling (pCASL) at 7 T. Materials and methods Simulations were performed to find the optimal labeling parameters for pCASL, with particular attention to the maximum-allowed specific absorption rate (SAR). Subsequently, pCASL experiments (four volunteers) were performed to find the B1 efficiency at the labeling position with and without high-permittivity pads placed around the head, and to study the optimal labeling duration (four separate volunteers). Finally, feasibility of whole-brain pCASL imaging was tested. Results Simulations showed that a lower B1 efficiency should be compensated by a lower effective flip angle of the labeling, a moderately shorter labeling duration, and a longer repetition time. B1 efficiency in the internal carotid arteries just below the carotid siphon was approximately 55% and 35% with and without high-permittivity pads, respectively. In vivo experiments showed an optimal labeling duration of 1,500 ms, although longer labeling durations up to 2,500 ms resulted in similar signal-to-noise efficiency. Whole-brain pCASL imaging was demonstrated in a single volunteer. Conclusion Despite decreased B1 efficiency, sufficient labeling efficiency can be achieved for whole-brain pCASL at 7 T with high-permittivity pads. However, image quality is still limited compared with 3 T, probably due to imaging instabilities, and further research is needed to elucidate this. Content Type Journal ArticleCategory Research ArticlePages 1-11DOI 10.1007/s10334-011-0297-0Authors Eidrees Ghariq, Department of Radiology, C.J. Gorter Center for High Field MRI, Leiden University Medical Center (LUMC), C3-Q, Albinusdreef 2, 2333 ZA Leiden, The NetherlandsWouter M. Teeuwisse, Department of Radiology, C.J. Gorter Center for High Field MRI, Leiden University Medical Center (LUMC), C3-Q, Albinusdreef 2, 2333 ZA Leiden, The NetherlandsAndrew G. Webb, Department of Radiology, C.J. Gorter Center for High Field MRI, Leiden University Medical Center (LUMC), C3-Q, Albinusdreef 2, 2333 ZA Leiden, The NetherlandsMatthias J. P. van Osch, Department of Radiology, C.J. Gorter Center for High Field MRI, Leiden University Medical Center (LUMC), C3-Q, Albinusdreef 2, 2333 ZA Leiden, The Netherlands Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Comparison between different implementations of the 3D FLASH sequence for knee cartilage quantification

Abstract Objective To compare several sequence implementations of the 3D FLASH sequence in the context of quantitative cartilage imaging. Materials and methods Test–retest coronal fast low angle shot (FLASH) sequences with water excitation were acquired in knees of 12 healthy participants, using two 1.5 T scanners from the same manufacturer. On one of the scanners, the FLASH was additionally compared with a FLASH VIBE, 75% with 100% slice resolution, a non-selective with a conventional spatial pulse, and “asymmetric echo allowed” with “not allowed”. Results Implementations of the FLASH showed systematic differences of up to 3.3%, but these were not statistically significant. Precision errors were similar between protocols, but tended to be smallest for the FLASH VIBE with 100% slice resolution (0.6–6.7%). In the medial tibia cartilage volume and thickness differed significantly (P < 0.01; 6.2 and 5.9%) between the two scanners. Conclusion Using a validated FLASH sequence, one can reduce slice resolution to 75% and allow asymmetric echo without sacrificing precision, in order to reduce the total acquisition time. However, in longitudinal studies, the scanner and the specific sequence implementation should be kept constant between baseline and follow-up, in order to avoid systematic off-sets in the measurements. Content Type Journal ArticleCategory Research ArticlePages 1-8DOI 10.1007/s10334-011-0296-1Authors Martin Hudelmaier, Institute of Anatomy and Musculoskeletal Research, Paracelsus Medical University, Strubergasse 21, 5020 Salzburg, AustriaChristian Glaser, Institut für Klinische Radiologie, Klinikum der LMU München, Marchioninistr. 15, 81377 Munich, GermanyChristian Pfau, Muskuloskeletal Research Group, Anatomische Anstalt, LMU München, Pettenkoferstr. 11, 80336 Munich, GermanyFelix Eckstein, Institute of Anatomy and Musculoskeletal Research, Paracelsus Medical University, Strubergasse 21, 5020 Salzburg, Austria Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Quantification and localization of contrast agents using delta relaxation enhanced magnetic resonance at 1.5 T

Abstract Object Delta relaxation enhanced magnetic resonance (dreMR) is a new imaging technique based on the idea of cycling the magnetic field B 0 during an imaging sequence. The method determines the field dependency of the relaxation rate (relaxation dispersion dR 1/dB). This quantity is of particular interest in contrast agent imaging because the parameter can be used to determine contrast agent concentrations and increases the ability to localize the contrast agent. Materials and methods In this paper dreMR imaging was implemented on a clinical 1.5 T MR scanner combining conventional MR imaging with fast field-cycling. Two improvements to dreMR theory are presented describing the quantification of contrast agent concentrations from dreMR data and a correction for field-cycling with finite ramp times. Results Experiments demonstrate the use of the extended theory and show the measurement of contrast agent concentrations with the dreMR method. A second experiment performs localization of a contrast agent with a significant improvement in comparison to conventional imaging. Conclusion dreMR imaging has been extended by a method to quantify contrast agent concentrations and improved for field-cycling with finite ramp times. Robust localization of contrast agents using dreMR imaging has been performed in a sample where conventional imaging delivers inconclusive results. Content Type Journal ArticleCategory Research ArticlePages 1-9DOI 10.1007/s10334-011-0291-6Authors Uvo Christoph Hoelscher, Research Center for Magnetic Resonance Bavaria (MRB), Würzburg, GermanySteffen Lother, Research Center for Magnetic Resonance Bavaria (MRB), Würzburg, GermanyFlorian Fidler, Research Center for Magnetic Resonance Bavaria (MRB), Würzburg, GermanyMartin Blaimer, Research Center for Magnetic Resonance Bavaria (MRB), Würzburg, GermanyPeter Jakob, Research Center for Magnetic Resonance Bavaria (MRB), Würzburg, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Using the biophysical CHARMED model to elucidate the underpinnings of contrast in diffusional kurtosis analysis of diffusion-weighted MRI

Abstract Object The aim of this work was to understand biophysical substrate underpinning contrast in diffusional kurtosis imaging (DKI) in white matter, using the composite hindered and restricted model of diffusion (CHARMED). Materials and methods A theoretical relationship between the kurtosis function K and the CHARMED parameters, i.e., the restricted volume fraction RF and the axonal longitudinal diffusivity D was derived for the propagator used in the CHARMED model. Evidence for a similar correlation between these measures was then investigated in vivo across different WM regions in five healthy young subjects that underwent a CHARMED protocol at 3T. Results Our theoretical treatment shows that K has an increasing trend for both increasing RF values and increasing D. In vivo, a significant positive correlation (P < 0.001) was found between the kurtosis orthogonal to the fibre orientation K ⊥ and RF. A multilinear regression showed that K ⊥ values are better explained by a mixed contribution of both RF and D. Conclusions The CHARMED model was used to understand whether and where DKI contrast can be explained in terms of the underlying axonal geometry. This work demonstrates that the information contained in DKI overlaps with the information extracted by CHARMED in areas of higher intra-voxel directional coherence. Content Type Journal ArticleCategory Research ArticlePages 1-10DOI 10.1007/s10334-011-0292-5Authors Silvia De Santis, CUBRIC, School of Psychology, Cardiff University, Cardiff, UKYaniv Assaf, Department of Neurobiology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, IsraelDerek K. Jones, CUBRIC, School of Psychology, Cardiff University, Cardiff, UK Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Diffusion time dependence of magnetic resonance diffusion signal decays: an investigation of water exchange in human brain in vivo

Abstract Object To understand the behavior of diffusion signal decays of water in white matter of human brain in vivo and to estimate tissue microstructure parameters such as exchange time of diffusing water molecules in human brain. Materials and methods Diffusion decays were measured over an extended range of diffusion weightings (b-values) up to a maximum of 12,500 s/mm2 and diffusion times between 19.9 and 53.8 ms in eight healthy human subjects using MRI scans. The diffusion signal decays were all Rician noise corrected and then analyzed using multi-component non-negative least squares (NNLS) data analysis. Results Three diffusion coefficients including one at (0.930 ± 0.003) × 10−3 (80 ± 1%) mm2/s, another at (0.067 ± 0.002) × 10−3 (19 ± 1%) mm2/s and a small contribution at (1.20 ± 0.02) × 10−2 (1.00 ± 0.01%) mm2/s were observed in the diffusion decay using the highest b-value. The diffusion decays show diffusion time dependence for the slow diffusion coefficient which has not previously been reported. Conclusion This study presents the accurate diffusion parameters by the use of very large b-values along with Rician noise correction and multi-component data analysis. The experimental results are consistent with the theoretical predictions used to estimate the exchange time of diffusing water molecules for a model of human brain tissue. Content Type Journal ArticleCategory Research ArticlePages 1-12DOI 10.1007/s10334-011-0295-2Authors Marzieh Nezamzadeh, Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

The response to rapid infusion of fentanyl in the human brain measured using pulsed arterial spin labelling

Abstract Objective We evaluated the sensitivity of pulsed Arterial Spin Labelling (pASL) for the detection of changes in regional cerebral blood perfusion (CBP) during and after intra-venous (i.v.) infusion of an opioid agonist (fentanyl) and an opioid antagonist (naloxone). Materials and methods Twenty-three subjects were scanned four times, receiving i.v. infusion of fentanyl, naloxone, placebo and a second fentanyl administration, in four separate scanning sessions in randomised order. End-tidal CO2, respiration rate and heart rate were recorded continuously throughout each scan. pASL time series were collected using single shot EPI for 15 min (including 5 min of baseline prior to infusion). Results Significant increases in CBP were detected during and after administration of fentanyl, (when compared to placebo and naloxone), in most areas of high concentration of mu-opioid receptors (thalamus, lingual gyrus, para-hippocampal gyrus, and insula); near-significant increases were also observed in the insula. No increases in perfusion were observed during or after naloxone infusion. No correlation was found between regional rCBF changes and end-tidal CO2, respiration rate or heart rate. Good reliability was found between the first and second fentanyl sessions but the regions of high reliability did not overlap completely with those of highest perfusion change. Conclusion pASL is a suitable method for examining rapid, dynamic effects of opioid administration on brain physiology. Content Type Journal ArticleCategory Research ArticlePages 1-13DOI 10.1007/s10334-011-0293-4Authors Fernando O. Zelaya, Department of Neuroimaging, Centre for Neuroimaging Sciences, Institute of Psychiatry, King’s College London, De Crespigny Park, London, SE5 8AF UKEvangelos Zois, Department of Addictive Behavior and Addiction Medicine, J5, 68159 Mannheim, GermanyChristopher Muller-Pollard, Department of Addictions, Institute of Psychiatry, King’s College London, De Crespigny Park, London, UKDavid J. Lythgoe, Department of Neuroimaging, Centre for Neuroimaging Sciences, Institute of Psychiatry, King’s College London, De Crespigny Park, London, SE5 8AF UKSarah Lee, Department of Neuroimaging, Centre for Neuroimaging Sciences, Institute of Psychiatry, King’s College London, De Crespigny Park, London, SE5 8AF UKCaroline Andrews, Department of Neuroimaging, Centre for Neuroimaging Sciences, Institute of Psychiatry, King’s College London, De Crespigny Park, London, SE5 8AF UKTrevor Smart, Pfizer Global Research and Development, Sandwich, Kent, UKPatricia Conrod, Department of Addictions, Institute of Psychiatry, King’s College London, De Crespigny Park, London, UKWilliam Vennart, Pfizer Global Research and Development, Sandwich, Kent, UKSteven C. R. Williams, Department of Neuroimaging, Centre for Neuroimaging Sciences, Institute of Psychiatry, King’s College London, De Crespigny Park, London, SE5 8AF UKMitul A. Mehta, Department of Neuroimaging, Centre for Neuroimaging Sciences, Institute of Psychiatry, King’s College London, De Crespigny Park, London, SE5 8AF UKLaurence J. Reed, Neuropsychopharmacology Unit, Imperial College London, London, UK Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Diffusion property differences of the lower leg musculature between athletes and non-athletes using 1.5T MRI

Abstract Object To compare the differences in diffusion properties—namely fractional anisotropy (FA), three eigenvalues of the diffusion tensor (λ1, λ2, and λ3), and apparent diffusion coefficient (ADC)—between athletically-trained and untrained lower leg musculature. Materials and methods Twelve athletes (Group A) and 11 non-athletes (Group B) were recruited. All were females in their 20s. We scanned diffusion tensor images of both calves and compared FA, the three eigenvalues, and ADC in the gastrocnemius medialis, gastrocnemius lateralis, soleus (SOL), and anterior tibialis muscles between Groups A and B, and between the right and left sides, using two-factor fractional ANOVA. Results In all muscles of bilateral calves, all three eigenvalues and ADC were lower in Group A than in Group B, with statistically significant differences in all muscles for λ1, λ2, and λ3 and ADC, with a P value of <0.01. Moreover, statistical differences were also found between right and left for λ1, λ2, and λ3 (P < 0.05), and ADC (P < 0.01) of the SOL muscle. FA showed no statistically significant differences in any muscles. Conclusions Our results indicate that training causes a decrease of the three eigenvalues and ADC, which we hypothesize is due to an increase of density of myofilaments in the intracellular space, and deformation of the cell induced by enlargement of extracellular components. Content Type Journal ArticleCategory Research ArticlePages 1-8DOI 10.1007/s10334-011-0294-3Authors Yoshikazu Okamoto, Department of Radiology, Institute of Clinical Medicine, University of Tsukuba Hospital, 2-1-1 Amakubo, Tsukuba, Ibaraki 305-8576, JapanShintaro Mori, Doctoral Program of Sports Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, JapanYuka Kujiraoka, Department of Radiology, Tsukuba Memorial Hospital, Tsukuba, JapanKatsuhiro Nasu, Department of Radiology, Institute of Clinical Medicine, University of Tsukuba Hospital, 2-1-1 Amakubo, Tsukuba, Ibaraki 305-8576, JapanYuji Hirano, Department of Radiology, University of Tsukuba Hospital, Tsukuba, JapanManabu Minami, Department of Radiology, Institute of Clinical Medicine, University of Tsukuba Hospital, 2-1-1 Amakubo, Tsukuba, Ibaraki 305-8576, Japan Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

A highly parallelized framework for computationally intensive MR data analysis

Abstract Object The goal of this study was to develop a comprehensive magnetic resonance (MR) data analysis framework for handling very large datasets with user-friendly tools for parallelization and to provide an example implementation. Materials and methods Commonly used software packages (AFNI, FSL, SPM) were connected via a framework based on the free software environment R, with the possibility of using Nvidia CUDA GPU processing integrated for high-speed linear algebra operations in R. Three hundred single-subject datasets from the 1,000 Functional Connectomes project were used to demonstrate the capabilities of the framework. Results A framework for easy implementation of processing pipelines was developed and an R package for the example implementation of Fully Exploratory Network ICA was compiled. Test runs on data from 300 subjects demonstrated the computational advantages of a processing pipeline developed using the framework compared to non-parallelized processing, reducing computation time by a factor of 15. Conclusion The feasibility of computationally intensive exploratory analyses allows broader access to the tools for discovery science. Content Type Journal ArticleCategory Research ArticlePages 1-8DOI 10.1007/s10334-011-0290-7Authors Roland N. Boubela, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, AustriaWolfgang Huf, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, AustriaKlaudius Kalcher, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, AustriaRonald Sladky, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, AustriaPeter Filzmoser, Department of Statistics and Probability Theory, Vienna University of Technology, Wiedner Hauptstraße 8-10, 1040 Vienna, AustriaLukas Pezawas, Department of Psychiatry and Psychotherapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, AustriaSiegfried Kasper, Department of Psychiatry and Psychotherapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, AustriaChristian Windischberger, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, AustriaEwald Moser, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Orientational dependent sensitivities of T2 and T1ρ towards trypsin degradation and Gd-DTPA2− presence in bovine nasal cartilage

Abstract Objective To study the orientational dependencies of T2 and T1ρ in native and trypsin-degraded bovine nasal cartilage, with and without the presence of 1 mM Gd-DTPA2−. Materials and methods Sixteen specimens were prepared in two orthogonal fibril directions (parallel and perpendicular), treated using different protocols (native, Gd treated, trypsin-treated, and combination), and imaged using μMRI at 0° and 55° (the magic angle) fibril orientations with respect to the magnetic field B0. Two-dimensional (2D) T2 and T1ρ images were then calculated quantitatively. Results Without Gd, native perpendicular tissues demonstrated significant T1ρ dispersion (including T2 at the zero spin-lock field) at 0° and less dispersion at 55°, while native parallel specimens exhibited smaller T1ρ dispersion at both 0° and 55°. Trypsin degradation caused a minimum 50% increase in T1ρ. With Gd, trypsin degradation caused significant reduction in T1ρ values up to 60%. Conclusion The collagen orientation in nasal cartilage can influence T2 and T1ρ MRI of cartilage. Without Gd, T1ρ was sensitive to the proteoglycan content and its sensitivity was nearly constant regardless of fibril orientation. In comparison, the T2 sensitivity to proteoglycan was dependant upon fibril orientation, i.e., more sensitive at 55° than 0°. When Gd ions were present, both T2 and T1ρ became insensitive to the proteoglycan content. Content Type Journal ArticleCategory Research ArticlePages 1-8DOI 10.1007/s10334-011-0288-1Authors Nian Wang, Department of Physics and Center for Biomedical Research, Oakland University, Rochester, MI 48309, USAYang Xia, Department of Physics and Center for Biomedical Research, Oakland University, Rochester, MI 48309, USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Blood longitudinal (T1) and transverse (T2) relaxation time constants at 11.7 Tesla

Abstract Object The goal of the study was to determine blood T 1 and T 2 values as functions of oxygen saturation (Y), temperature (Temp) and hematocrit (Hct) at an ultrahigh MR field (11.7 T) and explore their impacts on physiological measurements, including cerebral blood flow (CBF), blood volume (CBV) and oxygenation determination. Materials and methods T 1 and T 2 were simultaneously measured. Temperature was adjusted from 25 to 40°C to determine Temp dependence; Hct of 0.17–0.51 to evaluate Hct dependence at 25 and 37°C; and Y of 40–100% to evaluate Y dependence at 25 and 37°C. Comparisons were made with published data obtained at different magnetic field strengths (B 0). Results T 1 was positively correlated with Temp, independent of Y, and negatively correlated with Hct. T 2 was negatively correlated with Temp and Hct, but positively correlated with Y, in a non-linear fashion. T 1 increased linearly with B 0, whereas T 2 decreased exponentially with B0. Conclusion This study reported blood T 1 and T 2 measurements at 11.7 T for the first time. These blood relaxation data could have implications in numerous functional and physiological MRI studies at 11.7 T. Content Type Journal ArticleCategory Research ArticlePages 1-5DOI 10.1007/s10334-011-0287-2Authors Ai-Ling Lin, Research Imaging Institute, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78229, USAQin Qin, The Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USAXia Zhao, Research Imaging Institute, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78229, USATimothy Q. Duong, Research Imaging Institute, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78229, USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

A correction method for streak artifacts in gradient-echo EPI using spin-echo EPI reference data

Abstract Objective To analyze the streak artifacts in a gradient-echo echo planar imaging (GE-EPI) sequence and to propose a correction method for the Nyquist ghost artifacts that does not cause streak artifacts in the GE-EPI imaging. Materials and methods Several GE-EPI imaging experiments with various reference scans, using both GE-EPI and SE-EPI scan data, were performed to analyze the streak artifacts and to investigate the spin dephasing phenomena of the GE-EPI reference scan. In addition, the analysis based on the spin dephasing was undertaken in order to demonstrate that the SE-EPI reference data can be used for the correction of the GE-EPI main scan data. Results The experimental results confirmed that the improvement of the reference data using either signal averaging or a large flip angle cannot guarantee perfect correction of the streak artifact if the noise is not completely removed. Due to the main field inhomogeneity, the spins of the GE-EPI reference data were dephased in multiple echo signals. The proposed correction method, which uses a SE-EPI reference scan for the GE-EPI images, eliminates the N/2 ghost artifacts without producing streak artifacts. Conclusion It is believed that the proposed phase error correction scheme can improve the EPI performance in high field MRIs with higher magnetic field inhomogeneities. Content Type Journal ArticleCategory Research ArticlePages 1-9DOI 10.1007/s10334-011-0289-0Authors Jun-Young Chung, Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Republic of KoreaYeji Han, Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701 Republic of KoreaZang-Hee Cho, Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Republic of KoreaHyunWook Park, Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701 Republic of Korea Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Possibilities and limitations for high resolution small animal MRI on a clinical whole-body 3T scanner

Abstract Object To investigate the potential of a clinical 3 T scanner to perform MRI of small rodents. Materials and methods Different dedicated small animal coils and several imaging sequences were evaluated to optimize image quality with respect to SNR, contrast and spatial resolution. As an application, optimal grey-white-matter contrast and resolution were investigated for rats. Furthermore, manganese-enhanced MRI was applied in mice with unilateral crush injury of the optic nerve to investigate coil performance on topographic mapping of the visual projection. Results Differences in SNR and CNR up to factor 3 and more were observed between the investigated coils. The best grey-white matter contrast was achieved with a high resolution 3D T 2-weighted TSE (SPACE) sequence. Delineation of the retino-tectal projection and detection of defined visual pathway damage on the level of the optic nerve could be achieved by using a T 1-weighted, 3D gradient echo sequence with isotropic resolution of (0.2 mm)3. Conclusions Experimental studies in small rodents requiring high spatial resolution can be performed by using a clinical 3 T scanner with appropriate dedicated coils. Content Type Journal ArticleCategory Research ArticlePages 1-12DOI 10.1007/s10334-011-0284-5Authors Karl-Heinz Herrmann, Medical Physics Group, Institute for Diagnostic and Interventional Radiology I, Jena University Hospital, Philosophenweg 3, Gebäude 5, 07743 Jena, GermanySilvio Schmidt, Hans Berger Department of Neurology, Jena University Hospital, Erlanger Allee 101, 07747 Jena, GermanyAlexandra Kretz, Hans Berger Department of Neurology, Jena University Hospital, Erlanger Allee 101, 07747 Jena, GermanyRonny Haenold, Leibniz Institute for Age Research, Fritz Lipmann Institute, Beutenberger Str.11, 07745 Jena, GermanyInes Krumbein, Medical Physics Group, Institute for Diagnostic and Interventional Radiology I, Jena University Hospital, Philosophenweg 3, Gebäude 5, 07743 Jena, GermanyMartin Metzler, Hans Berger Department of Neurology, Jena University Hospital, Erlanger Allee 101, 07747 Jena, GermanyChristian Gaser, Hans Berger Department of Neurology, Jena University Hospital, Erlanger Allee 101, 07747 Jena, GermanyOtto W. Witte, Hans Berger Department of Neurology, Jena University Hospital, Erlanger Allee 101, 07747 Jena, GermanyJürgen R. Reichenbach, Medical Physics Group, Institute for Diagnostic and Interventional Radiology I, Jena University Hospital, Philosophenweg 3, Gebäude 5, 07743 Jena, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Lateralization of amygdala activation in fMRI may depend on phase-encoding polarity

Abstract Object Susceptibility artifacts along the phase-encoding (PE) direction impact the activation pattern in the amygdala and may lead to systematic asymmetries. We implemented a triple-echo echo-planar imaging (EPI) sequence, acquiring opposite PE polarities along left–right PE direction in a single shot, to investigate its effects on amygdala lateralization. Materials and Methods Twelve subjects viewed emotional faces to evoke amygdala activation. Results and Conclusion A region of interest analysis revealed that the lateralization of amygdala responses depended on the PE polarity thus representing a pure method artifact. Alternating PE with multi-echo EPI reduced the artifact. Lateralized fMRI activation in areas with magnetic field inhomogeneities need to be interpreted with caution. Content Type Journal ArticleCategory Short CommunicationPages 1-6DOI 10.1007/s10334-011-0285-4Authors Krystyna A. Mathiak, Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, RWTH Aachen University, Neuenhofer Weg 21, 52074 Aachen, GermanyMikhail Zvyagintsev, Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH Aachen University, Aachen, GermanyHermann Ackermann, Center for Neurology, Hertie Institute, University of Tübingen, Tübingen, GermanyKlaus Mathiak, Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH Aachen University, Aachen, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Optimization of background suppression for arterial spin labeling perfusion imaging

Abstract Object To present an algorithm for optimization of background suppression pulse timing for arterial spin labeling (ASL) perfusion imaging. Materials and methods An algorithm for optimization of background suppression pulse timing is proposed. Numerical optimization of timing of the background suppression pulses is investigated in both constrained and unconstrained ASL sequences. The performance of the parameters from the algorithm is evaluated in phantom and also in vivo in five human subjects. Results The background signal is suppressed to less than 1% across a broad range of T1s with a modest number of inversion pulses using the timings acquired from the numerical optimization algorithm proposed in this study. The performance of the parameters from the algorithm is also confirmed in vivo. Conclusion Successful background suppression over a broad range of tissues is achievable. Values for optimal pulse timing in both pulsed and continuous ASL studies are reported to facilitate sequence design with different labeling parameters. Content Type Journal ArticleCategory Research ArticlePages 1-7DOI 10.1007/s10334-011-0286-3Authors Nasim Maleki, Department of Radiology, Children’s Hospital Boston, 300 Longwood Ave, Boston, MA 02115, USAWeiying Dai, Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USADavid C. Alsop, Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Contrast agent derived determination of the total circulating blood volume using magnetic resonance

Abstract Object Knowledge of the total circulating blood volume (TCBV) is essential for the treatment of a variety of medical conditions and blood disorders. To date, blood volume analysis is rarely carried out due to the disadvantages of available methods. Our aim was to develop a widely available, simple, fast, yet accurate method for the determination of the total circulating blood volume. Materials and methods Magnetic resonance (MR) is a well-established, non-invasive technique. In this article, we present a method that uses MR contrast agents for the determination of the blood volume. The dependence of MR relaxation times on the concentration of MR contrast agents allows the calculation of the volume the contrast agent has been diluted in. Results In phantom and in vivo experiments we could demonstrate that TCBV can be determined with high accuracy and precision. Conclusion This work introduces a novel method for the determination of the total circulating blood volume using magnetic resonance contrast agents as tracers. Content Type Journal ArticleCategory Research ArticlePages 1-8DOI 10.1007/s10334-011-0282-7Authors Kerstin Pannek, Research Center Magnetic-Resonance-Bavaria, Am Hubland, 97074 Wuerzburg, GermanyFlorian Fidler, Research Center Magnetic-Resonance-Bavaria, Am Hubland, 97074 Wuerzburg, GermanyRalf Kartäusch, Research Center Magnetic-Resonance-Bavaria, Am Hubland, 97074 Wuerzburg, GermanyPeter M. Jakob, Research Center Magnetic-Resonance-Bavaria, Am Hubland, 97074 Wuerzburg, GermanyKarl-Heinz Hiller, Research Center Magnetic-Resonance-Bavaria, Am Hubland, 97074 Wuerzburg, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Local SAR management by RF Shimming: a simulation study with multiple human body models

Abstract Object Parallel transmission facilitates a relatively direct control of the RF transmit field. This is usually applied to improve the RF field homogeneity but might also allow a reduction of the specific absorption rate (SAR) to increase freedom in sequence design for high-field MRI. However, predicting the local SAR is challenging as it depends not only on the multi-channel drive but also on the individual patient. Materials and methods The potential of RF shimming for SAR management is investigated for a 3 T body coil with eight independent transmit elements, based on Finite-Difference Time-Domain (FDTD) simulations. To address the patient-dependency of the SAR, nine human body models were generated from volunteer MR data and used in the simulations. A novel approach to RF shimming that enforces local SAR constraints is proposed. Results RF shimming substantially reduced the local SAR, consistently for all volunteers. Using SAR constraints, a further SAR reduction could be achieved with only minor compromises in RF performance. Conclusion Parallel transmission can become an important tool to control and manage the local SAR in the human body. The practical use of local SAR constraints is feasible with consistent results for a variety of body models. Content Type Journal ArticleCategory Research ArticlePages 1-12DOI 10.1007/s10334-011-0281-8Authors Hanno Homann, Karlsruhe Institute of Technology, Institute of Biomedical Engineering, Kaiserstr. 12, 76131 Karlsruhe, GermanyIngmar Graesslin, Philips Research Laboratories, Department of Tomographic Imaging Systems, Hamburg, GermanyHolger Eggers, Philips Research Laboratories, Department of Tomographic Imaging Systems, Hamburg, GermanyKay Nehrke, Philips Research Laboratories, Department of Tomographic Imaging Systems, Hamburg, GermanyPeter Vernickel, Philips Research Laboratories, Department of Tomographic Imaging Systems, Hamburg, GermanyUlrich Katscher, Philips Research Laboratories, Department of Tomographic Imaging Systems, Hamburg, GermanyOlaf Dössel, Karlsruhe Institute of Technology, Institute of Biomedical Engineering, Kaiserstr. 12, 76131 Karlsruhe, GermanyPeter Börnert, Philips Research Laboratories, Department of Tomographic Imaging Systems, Hamburg, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Correction of susceptibility-induced GRE phase shift for accurate PRFS thermometry proximal to cryoablation iceball

Abstract Introduction The susceptibility contrast between frozen and unfrozen tissue disturbs the local magnetic field in the proximity of the ice-ball during cryotherapy. This effect should be corrected for in real time to allow PRFS-based monitoring of near-zero temperatures during intervention. Material and methods Susceptibility artifacts were corrected post-processing, using a rapid numerical algorithm. The difference in bulk magnetic susceptibility between frozen and non-frozen tissue was approximated to be uniform over the ice-ball volume and was determined from the isothermal principle applied to the phase-transition frontier of compartments. Subsequently, the magnetic perturbation field was calculated rapidly in 3D using a Fourier-convolution. Experimental studies were performed for two scenarios: tissue defrosting in a water bath and induction of an ice-ball by a MR-compatible cryogenic probe. Results The susceptibility artifacts yielded PRFS temperature errors as high as 10–12°C proximal to the ice-ball, positive or negative depending on the relative orientation of the position vector from the B o direction. These effects were fully corrected for to within the noise range. The susceptibility-corrected PRFS temperature values were consistent with the phase-transition isothermal condition, irrespective of the local orientation of the position vector. Conclusion By implementing on-line the post processing algorithm, PRFS MRT may be used as a safety tool for non-invasive and accurate monitoring of near-zero temperatures during MR-guided clinical cryotherapy. Content Type Journal ArticleCategory Research ArticlePages 23-31DOI 10.1007/s10334-011-0277-4Authors Antje Kickhefel, Eberhard-Karls-University Tübingen, Tübingen, Badem-Württenberg, GermanyClifford Weiss, Johns Hopkins University, Baltimore, USAJoerg Roland, Siemens Healthcare, Erlangen, GermanyPatrick Gross, Siemens Healthcare, Erlangen, GermanyFritz Schick, Eberhard-Karls-University Tübingen, Tübingen, Badem-Württenberg, GermanyRares Salomir, University Hospitals of Geneva, Geneva, Switzerland Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 25 Journal Issue Volume 25, Number 1

Comparison of arterial transit times estimated using arterial spin labeling

Abstract Objective To compare arterial transit time estimates from two efficient transit time mapping techniques using arterial spin labeling (ASL)—flow encoded arterial spin tagging (FEAST) and Look-Locker ASL (LL-ASL). The effects of bipolar gradients and label location were investigated. Materials and methods Six healthy subjects were scanned with pseudo-continuous ASL (pCASL) FEAST and pulsed (PASL) and pCASL variants of LL-ASL at different labeling locations with and without bipolar gradients. Application of transit time mapping was demonstrated in a clinical case. Results Mean (±SD) macrovascular transit times were 363 ± 39, 676 ± 73 and 908 ± 170 ms for LL-PASL, LL-pCASL with labeling offsets of 60 and 90 mm respectively, showing linear dependence on labeling locations. Mean microvascular transit time for LL-pCASL was 1,463±135 ms, in good agreement with the FEAST estimate of 1,444 ± 128 ms. Data acquired from a patient with stroke demonstrate how transit time and CBF maps provide complementary information for clinical diagnosis. Conclusion Both FEAST and LL-ASL provide transit time information in clinically acceptable scan times. Bipolar gradients can be used to tailor transit time estimates for different experimental and clinical situations. Content Type Journal ArticleCategory Research ArticlePages 1-10DOI 10.1007/s10334-011-0276-5Authors Yufen Chen, Center for Advanced MRI, Department of Radiology, Northwestern University, 737 N Michigan Ave. 16th Flr., Chicago, IL 60611, USADanny J. J. Wang, Department of Neurology, University of California Los Angeles, Los Angeles, CA, USAJohn A. Detre, Center of Functional Neuroimaging, University of Pennsylvania, Philadelphia, PA, USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Highly accelerated PSF-mapping for EPI distortion correction with improved fidelity

Abstract Objective This study presents an improved point-spread-function (PSF) mapping-based distortion correction method and accelerated PSF acquisition for distortion correction in EPI without loss of quality or reliability compared to full encoding. Materials and methods To correct geometric distortions accurately, the PSF in the EPI phase-encoding coordinates (EPI-PSF) was measured and used as a kernel for distortion correction. FOV reduction was applied in the PSF mapping dimension for highly accelerated PSF acquisition. A novel approach for fold-over artifact correction in this reduced dimension is introduced. Conventional gradient-echo EPI and corresponding full PSF reference data were acquired in phantoms and in human brain at 7 T. The distortion corrected EPI data with the proposed acceleration were compared to result with full encoding. Previously published interpolation methods based on shift maps, non-uniform Fourier transformation and a b-spline interpolation were compared with the proposed method. Results The results demonstrate that the proposed method corrects geometric distortions in EPI with high accuracy and quality despite the high acceleration. In contrast to partial parallel imaging acceleration, no noise enhancement is introduced. Conclusion The proposed EPI-PSF-based distortion correction improves correction of EPI and accelerates PSF reference data acquisition and computation. Content Type Journal ArticleCategory Research ArticlePages 1-10DOI 10.1007/s10334-011-0275-6Authors Myung-Ho In, Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Leipziger Strasse 44, 39120 Magdeburg, GermanyOliver Speck, Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Leipziger Strasse 44, 39120 Magdeburg, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Ultrafast 1D MR thermometry using phase or frequency mapping

Abstract Object To develop an ultrafast MRI-based temperature monitoring method for application during rapid ultrasound exposures in moving organs. Materials and methods A slice selective 90° − 180° pair of RF pulses was used to solicit an echo from a column, which was then sampled with a train of gradient echoes. In a gel phantom, phase changes of each echo were compared to standard gradient-echo thermometry, and temperature monitoring was tested during focused ultrasound sonications. Signal-to-noise ratio (SNR) performance was evaluated in vivo in a rabbit brain, and feasibility was tested in a human heart. Results The correlation between each echo in the acquisition and MRI-based temperature measurements was good (R = 0.98 ± 0.03). A temperature sampling rate of 19 Hz was achieved at 3T in the gel phantom. It was possible to acquire the water frequency in the beating heart muscle with 5-Hz sampling rate during a breath hold. Conclusion Ultrafast thermometry via phase or frequency monitoring along single columns was demonstrated. With a temporal resolution around 50 ms, it may be possible to monitor focal heating produced by short ultrasound pulses. Content Type Journal ArticleCategory Research ArticlePages 5-14DOI 10.1007/s10334-011-0272-9Authors Chang-Sheng Mei, Department of Physics, Boston College, Chestnut Hill, MA, USARobert V. Mulkern, Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USAKoichi Oshio, Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USANan-kuei Chen, Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, USABruno Madore, Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USALawrence P. Panych, Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USAKullervo Hynynen, Department of Imaging Research, Sunnybrook Research Institute, Toronto, CanadaNathan J. McDannold, Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 25 Journal Issue Volume 25, Number 1

Non-invasive pulmonary perfusion assessment in young patients with cystic fibrosis using an arterial spin labeling MR technique at 1.5 T

Abstract Object To assess lung perfusion in young patients with cystic fibrosis (CF) using an arterial spin labeling (ASL) technique. Materials and methods Perfusion imaging was performed in 5 healthy volunteers and 33 pediatric patients (13 ± 5 years) with CF using an ASL technique. Image quality was evaluated on a five-point scale (1 = excellent). Quantitative perfusion maps were calculated based on the modified Bloch equations. Perfusion differences between volunteers and CF patients and regional differences between lobes were analyzed using Student’s t test. The association of perfusion values and forced expiratory volume in 1 s (FEV1) was analyzed using univariate regression analysis. Results Mean lung perfusion was 698 ± 67 ml/100g/min (range: 593–777 ml/100g/min) in volunteers and 526 ± 113 ml/100g/min (range: 346–724 ml/100g/min) in CF patients. Median image quality was 2 in volunteers and 3 in CF patients. In CF patients, significantly lower perfusion was observed in the upper lobes compared to healthy volunteers. Mean perfusion values significantly correlated with FEV1 (r = 0.84, P < 0.0001). Conclusion ASL perfusion imaging provides lung perfusion assessment in young CF patients. This non-invasive functional imaging technique is worth being evaluated in the clinical monitoring of CF patients. Content Type Journal ArticleCategory Research ArticlePages 1-8DOI 10.1007/s10334-011-0271-xAuthors Christina Schraml, Department of Diagnostic and Interventional Radiology, University Hospital of Tuebingen, Hoppe-Seyler-Str. 3, 72076 Tuebingen, GermanyNina F. Schwenzer, Department of Diagnostic and Interventional Radiology, University Hospital of Tuebingen, Hoppe-Seyler-Str. 3, 72076 Tuebingen, GermanyPetros Martirosian, Section on Experimental Radiology, University Hospital of Tuebingen, Tuebingen, GermanyAndreas Boss, Department of Diagnostic and Interventional Radiology, University Hospital of Tuebingen, Hoppe-Seyler-Str. 3, 72076 Tuebingen, GermanyFritz Schick, Section on Experimental Radiology, University Hospital of Tuebingen, Tuebingen, GermanySusanne Schäfer, Department of Diagnostic and Interventional Radiology, University Hospital of Tuebingen, Hoppe-Seyler-Str. 3, 72076 Tuebingen, GermanyMartin Stern, Hoppe-Seyler-Str. 1, 72076 Tuebingen, GermanyClaus D. Claussen, Department of Diagnostic and Interventional Radiology, University Hospital of Tuebingen, Hoppe-Seyler-Str. 3, 72076 Tuebingen, GermanyJürgen F. Schäfer, Department of Diagnostic and Interventional Radiology, University Hospital of Tuebingen, Hoppe-Seyler-Str. 3, 72076 Tuebingen, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Residual tumor after laser ablation of human non-small-cell lung cancer demonstrated by ex vivo staining: correlation with invasive temperature measurements

Abstract Object Histology is the gold standard for confirming thermally induced necrosis. Generally, however, no specimen is obtained from thermal ablation therapy for pathological examination. The aim of this study was to provide evidence for the relationship between temperatures reached and resulting tissue coagulation during laser ablation in a near-physiological ex vivo lung tumor model by combining viability staining and direct temperature measurement. Materials and methods In all, 17 human lung specimens with primary non-small-cell lung cancer (NSCLC) were examined in this study. Organs were resected with curative intent from patients of either gender (5 female, 12 male) with an average age of 65 years (51–78). Here, 11/17 specimens were subjected to interstitial laser thermal ablation in an ex vivo lung perfusion and ventilation model after surgery. A control group of 6/17 specimens was tested for viability without laser ablation. Tissue temperature was measured invasively in real-time during the ablation process using thermocouples. Afterwards, representative slices of all 17 specimens were tested for viability with triphenyltetrazolium chloride (TTC). Maximum tissue temperature Tmax[°C] measured at a distance of 10 and 20 mm from the laser tip and time of temperature exposure were correlated with the diameter of the induced coagulation as ascertained with viability staining. CH evaluated the results. Results Mean maximum temperature was 75.9°C ± 14.4°C at a distance of 10 mm from the laser tip and 50.3°C ± 14.6°C at a distance of 20 mm, respectively. The mean distance between the coagulation margin and the laser tip was 17.8 mm ± 7.3 mm. Conclusion We found that coagulation size correlated positively with temperature. There was a clear trend towards the correlation of time over 44°C and ablation depth. Maximum temperatures did not significantly correlate with coagulation size. Laser ablation of lung tumors using the IHLP (isolated human lung perfusion) model represents a possible method for evaluating ex vivo the interrelationships of temperature, time of temperature exposure, and resulting coagulation. Content Type Journal ArticleCategory Research ArticlePages 63-74DOI 10.1007/s10334-011-0261-zAuthors Christian Oliver Martin Hoffmann, Department of Diagnostic Radiology and Neuroradiology, Ernst-Moritz-Arndt-Universitaet Greifswald, Sauerbruchstraße, 17487 Greifswald, GermanyChristian Rosenberg, Department of Diagnostic Radiology and Neuroradiology, Ernst-Moritz-Arndt-Universitaet Greifswald, Sauerbruchstraße, 17487 Greifswald, GermanyAlbert Linder, Department of Thoracic Surgery, Klinikum Bremen-Ost, Zuericher Straße 40, 28325 Bremen, GermanyNorbert Hosten, Department of Diagnostic Radiology and Neuroradiology, Ernst-Moritz-Arndt-Universitaet Greifswald, Sauerbruchstraße, 17487 Greifswald, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 25 Journal Issue Volume 25, Number 1

Temperature dependence of the magnetic volume susceptibility of human breast fat tissue: an NMR study

Abstract Object Proton resonance frequency shift (PRFS)-based MR thermometry (MRT) is hampered by heat-induced susceptibility changes when applied in tissues containing fat, e.g., the human breast. In order to assess the impact of fat susceptibility changes on PRFS-based MRT during thermal therapy in the human breast, reliable knowledge of the temperature dependence of the magnetic volume susceptibility of fat, dχfat/dT, is a prerequisite. In this work we have measured dχfat/dT of human breast fat tissue, using a double-reference method to ensure invariance to temperature-induced changes in the proton electron screening constant. Materials and methods Ex vivo measurements were taken on a 14.1 T five mm narrow bore NMR spectrometer. Breast fat tissue samples were collected from six subjects, directly postmortem. The susceptibility was measured over a temperature range from 24°C to 65°C. Results A linear behavior of the susceptibility over temperature was observed for all samples. The resulting dχfat/dT of human breast fat ranged between 0.0039 and 0.0076 ppm/°C. Conclusion It is concluded that the impact of heat-induced susceptibility changes of fat during thermal therapy in the breast may not be neglected. Content Type Journal ArticleCategory Research ArticlePages 33-39DOI 10.1007/s10334-011-0250-2Authors Sara M. Sprinkhuizen, Image Sciences Institute/Department of Radiology, University Medical Center Utrecht, Room Q0S.459, Heidelberglaan 100, 3584 CX Utrecht, The NetherlandsChris J. G. Bakker, Image Sciences Institute/Department of Radiology, University Medical Center Utrecht, Room Q0S.459, Heidelberglaan 100, 3584 CX Utrecht, The NetherlandsJohannes H. Ippel, NMR Spectroscopy Research Group, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The NetherlandsRolf Boelens, NMR Spectroscopy Research Group, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The NetherlandsMax A. Viergever, Image Sciences Institute/Department of Radiology, University Medical Center Utrecht, Room Q0S.459, Heidelberglaan 100, 3584 CX Utrecht, The NetherlandsLambertus W. Bartels, Image Sciences Institute/Department of Radiology, University Medical Center Utrecht, Room Q0S.459, 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 25 Journal Issue Volume 25, Number 1

Effects of air susceptibility on proton resonance frequency MR thermometry

Abstract Object The temperature dependence of the proton resonance frequency (PRF) is often used in MR thermometry. However, this method is prone to even very small changes in local magnetic field strength. Here, we report on the effects of susceptibility changes of surrounding air on the magnetic field inside an object and their inferred effect on the measured MR temperature. Materials and methods MR phase thermometry was performed on spherical agar phantoms enclosed in cylindrical containers at 7 T. The air susceptibility inside the cylindrical container was changed by both heating the air and changing the gas composition. Results Changing the temperature of surrounding air from 23 to 69°C caused an apparent MR temperature error of 2 K. When ambient air was displaced by 100% oxygen, the MR temperature error increased to 40 K. The magnetic field shift and therefore error in inferred MR temperature scales linearly with volume susceptibility change and has a strong and nontrivial dependence on the experimental configuration. Conclusion Air susceptibility changes associated with oxygen concentration changes greatly affect PRF MR thermometry measurements. Air temperature changes can also affect these measurements, but to a smaller degree. For uncalibrated MR thermometry, air susceptibility changes may be a significant source of error. Content Type Journal ArticleCategory Research ArticlePages 41-47DOI 10.1007/s10334-011-0249-8Authors Markus N. Streicher, Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, GermanyAndreas Schäfer, Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, GermanyEnrico Reimer, Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, GermanyBibek Dhital, Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, GermanyRobert Trampel, Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, GermanyDimo Ivanov, Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, GermanyRobert Turner, Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 25 Journal Issue Volume 25, Number 1

Comprehensive analysis of the Cramer–Rao bounds for magnetic resonance temperature change measurement in fat–water voxels using multi-echo imaging

Abstract Object The aim of this paper is to characterize the noise propagation for MRI temperature change measurement with emphasis on finding the best echo time combinations that yield the lowest temperature noise. Materials and methods A Cramer–Rao lower-bound (CRLB) calculation was used to estimate the temperature noise for a model of the MR signal in fat–water voxels. The temperature noise CRLB was then used to find a set of echo times that gave the lowest temperature change noise for a range of fat–water frequency differences, temperature changes, fat/water signal ratios, and T2* values. CRLB estimates were verified by Monte Carlo simulation and in phantoms using images acquired in a 1.5 T magnet. Results Results show that regions exist where the CRLB predicts minimal temperature variation as a function of the other variables. The results also indicate that the CRLB values calculated in this paper provide excellent guidance for predicting the variation of temperature measurements due to changes in the signal parameters. For three echo scans, the best noise characteristics are seen for TE values of 20.71, 23.71, and 26.71 ms. Results for five and seven echo scans are also presented in the text. Conclusion The results present a comprehensive analysis of the effects of different scan parameters on temperature noise, potentially benefiting the selection of scan parameters for clinical MRI thermometry. Content Type Journal ArticleCategory Research ArticlePages 49-61DOI 10.1007/s10334-011-0247-xAuthors Cory Wyatt, Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710, USABrian J. Soher, Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710, USAKavitha Arunachalam, Department of Engineering Design, Indian Institute of Technology Madras, Chennai, IndiaJames MacFall, Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710, USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 25 Journal Issue Volume 25, Number 1

Velocity navigator for motion compensated thermometry

Abstract Object Proton resonance frequency shift thermometry is sensitive to breathing motion that leads to incorrect phase differences. In this work, a novel velocity-sensitive navigator technique for triggering MR thermometry image acquisition is presented. Materials and methods A segmented echo planar imaging pulse sequence was modified for velocity-triggered temperature mapping. Trigger events were generated when the estimated velocity value was less than 0.2 cm/s during the slowdown phase in parallel to the velocity-encoding direction. To remove remaining high-frequency spikes from pulsation in real time, a Kalman filter was applied to the velocity navigator data. A phantom experiment with heating and an initial volunteer experiment without heating were performed to show the applicability of this technique. Additionally, a breath-hold experiment was conducted for comparison. Results A temperature rise of ΔT = +37.3°C was seen in the phantom experiment, and a root mean square error (RMSE) outside the heated region of 2.3°C could be obtained for periodic motion. In the volunteer experiment, a RMSE of 2.7°C/2.9°C (triggered vs. breath hold) was measured. Conclusion A novel velocity navigator with Kalman filter postprocessing in real time significantly improves the temperature accuracy over non-triggered acquisitions and suggests being comparable to a breath-held acquisition. The proposed technique might be clinically applied for monitoring of thermal ablations in abdominal organs. Content Type Journal ArticleCategory Research ArticlePages 15-22DOI 10.1007/s10334-011-0245-zAuthors Florian Maier, Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, GermanyAxel J. Krafft, Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, GermanyJoshua P. Yung, Department of Imaging Physics, The University of Texas M. D., Anderson Cancer Center, Houston, TX, USAR. Jason Stafford, Department of Imaging Physics, The University of Texas M. D., Anderson Cancer Center, Houston, TX, USAAndrew Elliott, Department of Imaging Physics, The University of Texas M. D., Anderson Cancer Center, Houston, TX, USARüdiger Dillmann, Institute of Anthropomatics, Karlsruhe Institute of Technology, Karlsruhe, GermanyWolfhard Semmler, Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, GermanyMichael Bock, Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 25 Journal Issue Volume 25, Number 1