Magnetic resonance imaging (MRI), formerly referred to as magnetic resonance tomography (MRT) or nuclear magnetic resonance (NMR), is a method used to visualize the inside of living organisms as well as to detect the composition of geological structures. It is primarily used to demonstrate pathological or other physiological alterations of living tissues and is a commonly used form of medical imaging. MRI has also found many novel applications outside of the medical and biological fields such as rock permeability to hydrocarbons and certain non-destructive testing methods such as produce and timber quality characterization. ^* The devices used in medicine are expensive, costing approximately $1 million USD per tesla for each unit (common field strength ranges from 0.3 to 3 teslas), with several hundred thousand dollars per year of upkeep costs.

Background

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Nomenclature

Magnetic resonance imaging was developed from knowledge gained in the study of nuclear magnetic resonance. The original name for the medical technology is nuclear magnetic resonance imaging (NMRI), but the word nuclear is almost universally dropped. This is done to avoid the negative connotations of the word nuclear, and to prevent patients from associating the examination with radiation exposure, which is not one of the safety concerns for MRI. Scientists still use NMR when discussing non-medical devices operating on the same principles.

More on [ Magnetic resonance imaging ]

pubmed: 0730-725X

Optimal real-time estimation in diffusion tensor imaging.
Casaseca-de-la-Higuera P, Tristán-Vega A, Aja-Fernández S, Alberola-López C, Westin CF, San José Estépar R Optimal real-time estimation in diffusion tensor imaging. Magn Reson Imaging. 2012 Feb 1; Authors: Casaseca-de-la-Higuera P, Tristán-Vega A, Aja-Fernández S, Alberola-López C, Westin CF, San José Estépar R Abstract Diffusion tensor imaging (DTI) constitutes the most used paradigm among the diffusion-weighted magnetic resonance imaging (DW-MRI) techniques due to its simplicity and application potential. Recently, real-time estimation in DW-MRI has deserved special attention, with several proposals aiming at the estimation of meaningful diffusion parameters during the repetition time of the acquisition sequence. Specifically focusing on DTI, the underlying model of the noise present in the acquired data is not taken into account, leading to a suboptimal estimation of the diffusion tensor. In this paper, we propose an optimal real-time estimation framework for DTI reconstruction in single-coil acquisitions. By including an online estimation of the time-changing noise variance associated to the acquisition process, the proposed method achieves the sequential best linear unbiased estimator. Results on both synthetic and real data show that our method outperforms those so far proposed, reaching the best performance of the existing proposals by processing a substantially lower number of diffusion images. PMID: 22305020 [PubMed - as supplied by publisher]
Signal evolution in the local magnetic field of a capillary - analogy to the damped driven harmonic oscillator.
Ziener CH, Kampf T, Melkus G, Jakob PM, Schlemmer HP, Bauer WR Signal evolution in the local magnetic field of a capillary - analogy to the damped driven harmonic oscillator. Magn Reson Imaging. 2012 Feb 1; Authors: Ziener CH, Kampf T, Melkus G, Jakob PM, Schlemmer HP, Bauer WR Abstract The temporal behavior of the magnetization decay caused by the local inhomogeneous magnetic field of a capillary is analyzed. Respecting the diffusion of the spins surrounding the capillary and the strength of the susceptibility difference between the capillary and the surrounding medium, it is possible to distinguish different dephasing regimes. Each dephasing regime can be related to a certain characteristic form of the magnetization decay. If the influence of the diffusion dominates, the magnetization exhibits a monotonic decay. In the opposite case of dominating influence of the susceptibility effects, the magnetization shows an oscillating behavior. It can be shown that the dephasing process is closely related to the behavior of a damped driven harmonic oscillator. PMID: 22305019 [PubMed - as supplied by publisher]

Magnetic Resonance Materials in Physics, Biology and Medicine (Online Firstâ„¢)

Minimization of spectral pattern changes during HRMAS experiments at 37 degrees celsius by prior focused microwave irradiation
Sat, 28 Jan 2012 16:50:48 -0000
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
Fri, 13 Jan 2012 17:15:50 -0000
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 Â± 0.49 and 1.02 Â± 0.20, respectively, whereas the SNRs of AIRASL (3.0 T) and AIRASL (1.5 T) were 3.93 Â± 1.65 and 1.34 Â± 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
Fri, 13 Jan 2012 17:15:46 -0000
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

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Magnetic resonance imaging: Referred to as magnetic resonance tomography (MRT) or, in chemistry nuclear magnetic resonance (NMR), is a non-invasive method used to render images of the inside of an object. The scanners used in medicine cost approximately US$ 1 million per tesla (T) and have a typical field strength of 0.3 to 3 T, with several hundred thousand dollars paid per year just for maintenance.