Magnetic Resonance in Medicine
0740-3194
1522-2594
Mỹ
Cơ quản chủ quản: John Wiley & Sons Inc. , WILEY
Lĩnh vực:
Radiology, Nuclear Medicine and Imaging
Phân tích ảnh hưởng
Thông tin về tạp chí
Magnetic Resonance in Medicine (Magn Reson Med) is an international journal devoted to the publication of original investigations concerned with all aspects of the development and use of nuclear magnetic resonance and electron paramagnetic resonance techniques for medical applications. Reports of original investigations in the areas of mathematics, computing, engineering, physics, biophysics, chemistry, biochemistry, and physiology directly relevant to magnetic resonance will be accepted, as well as methodology-oriented clinical studies.
Các bài báo tiêu biểu
Three‐dimensional whole‐heart T<sub>2</sub> mapping at 3T Purpose Detecting variations in myocardial water content with T2 mapping is superior to conventional T2 ‐weighted MRI since quantification enables direct observation of complicated pathology. Most commonly used T2 mapping techniques are limited in achievable spatial and/or temporal resolution, both of which reduce accuracy due to partial‐volume averaging and misregistration between images. The goal of this study was to validate a novel free breathing T2 mapping sequence that overcomes these limitations. Methods The proposed technique was made insensitive to heart rate variability through the use of a saturation prepulse to reset magnetization every heartbeat. Respiratory navigator‐gated, differentially T2 ‐weighted volumes were interleaved per heartbeat, guaranteeing registered images and robust voxel‐by‐voxel T2 maps. Free breathing acquisitions removed limits on spatial resolution and allowed short diastolic windows. Accuracy was quantified with simulations and phantoms. Results Homogeneous three‐dimensional (3D) T2 maps were obtained from normal human subjects and swine. Normal human and swine left ventricular T2 values were 42.3 ± 4.0 and 43.5 ± 4.3 ms, respectively. The T2 value for edematous myocardium obtained from a swine model of acute myocardial infarction was 59.1 ± 7.1 ms. Conclusion Free‐breathing accurate 3D T2 mapping is feasible and may be applicable in myocardial assessment in lieu of current clinical black blood, T2 ‐weighted techniques. Magn Reson Med 74:803–816, 2015. © 2014 Wiley Periodicals, Inc.
Tập 74 Số 3 - Trang 803-816 - 2015
The effects of isoflurane and halothane on blood flow and <sup>31</sup>P NMR spectra in murine RIF‐1 tumors Abstract The principal aim of these studies was to evaluate the utility of isoflurane and halothane for NMR investigations of tumor physiology. In vivo 31 P and 2 H NMR were used to examine RIF‐1 tumors before, during, and (for 31 P) after anesthesia. In tumors, halothane decreases blood flow, [PCR]:[NTP], and pH indicated by the P 1 chemical shift (pHnmr ), while it increases [P 1 :[NTP]; effects consistent with well‐established cardiovascular effects of halothane. Isoflurane does not affect tumor blood flow or [PCr]:[NTP], but increases tumor [P 1 :[NTP] and decreases tumor pHnmr . In vivo 31 P NMR measurements of normal mouse liver (upper abdomen) indicate that isoflurane has a similar effect in the liver. Although the mechanism for these effects is unknown, observation of a split P 1 peak during isoflurane anesthesia suggests that a pool of P 1 in a lower pH environment may become evident under isoflurane anesthesia. Regardless of the cause for increased [P 1 :[NTP] and decreased pHnmr the utility of isoflurane anesthesia for 31 P NMR studies of energy metabolism is limited.
Tập 33 Số 5 - Trang 610-618 - 1995
Experimental performance evaluation of multi‐echo ICNE pulse sequence in magnetic resonance electrical impedance tomography Abstract Latest experimental results in magnetic resonance electrical impedance tomography (MREIT) demonstrated high‐resolution in vivo conductivity imaging of animal and human subjects using imaging currents of 5 to 9 mA. Externally injected imaging currents induce magnetic flux density distributions, which are affected by a conductivity distribution. Since we extract the induced magnetic flux density images from MR phase images, it is essential to reduce noise in the phase images. In vivo human and disease model animal experiments require reduction of imaging current amplitudes and scan times. In this article, we investigate a multi‐echo based MREIT pulse sequence where we utilize a remaining time after the first echo within one TR to obtain more echo signals. It also allows us to prolong the total current injection time. From phantom and animal imaging experiments, we found that this method significantly reduces the noise level in measured magnetic flux density images. We describe experimental validation of the multi‐echo sequence by comparing its performance with a single‐echo method using 3 mA imaging currents. The proposed method will be advantageous for an imaging region with long T2 values such as the brain and knee. Depending on T2 values, we suggest using two or three echoes in future experimental studies. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Tập 66 Số 4 - Trang 957-965 - 2011
Three‐point dixon technique for true water/fat decomposition with <i>B</i><sub>0</sub> inhomogeneity correction Abstract An enhancement to Dixon's technique is described which can provide error‐free decomposition of water and fat proton images even in the presence of off‐resonance conditions which result from susceptibility differences, demagnetization, or shim errors. The method uses three measurements with phase shifts of 0, π and − π between the fat and water resonances. The additional information provided by the third measurement is used to calculate an image of the field inhomogeneity in addition to true water and fat images. The signal‐to‐noise ratio (SNR) in the decomposed images is equivalent to that of a 2.7 NEX acquisition (instead of 3 NEX), yielding an SNR imaging efficiency of 95%. In addition, the B 0 image which is provided may have diagnostic value in its own right. Examples of head and body scans often portray surprisingly large B 0 shifts near interfaces between air or bone and soft tissue. © 1991 Academic Press. Inc.
Tập 18 Số 2 - Trang 371-383 - 1991
Localized high‐resolution proton NMR spectroscopy using stimulated echoes: Initial applications to human brain <i>in vivo</i> Abstract Water‐suppressed localized proton NMR spectroscopy using stimulated echoes has been successfully applied to detect metabolites in the human brain in vivo . The STEAM spectroscopy sequence allows single‐step localization by exciting three intersecting slices. Water suppression is achieved by preceding chemical‐shift‐selective (CHESS) rf pulses. High‐resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been obtained on a conventional 1.5‐T whole‐body MRI system (Siemens Magnetom). Volumes‐of‐interest (VOI) of 64 ml(4 × 4 × 4 cm3 ) were localized in the occipital area of the brain and spectra were recorded within measuring times ranging from I s (single scan) to about 10 min. The experimental procedure is described in detail. Resonance assignments include acetate, N ‐acetyl aspartate, γ‐amino butyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline‐containing compounds, taurine, and inositols. Cerebral lactate was found to be at a maximum concentration of 0.5 mM when assuming N ‐acetyl aspartate in white matter to be 6 mM . © 1989 Academic Press, Inc.
Tập 9 Số 1 - Trang 79-93 - 1989
<i>In vivo</i> visualization of myelin water in brain by magnetic resonance Abstract We exploit the intrinsic difference in magnetic resonance spin‐spin relaxation time, T 2 , between water associated with myelin sheaths and water in other central nervous system tissue in order to measure myelin water content within any region of an image or to generate indirectly a myelin map of the brain. In normal volunteers, myelin water maps give the expected myelin distribution. In multiple sclerosis patients, lesions exhibit different myelin water contents providing insight into the de‐myelination process unavailable from conventional magnetic resonance images. In vivo myelin measurement has important applications in the clinical management of multiple sclerosis and other white matter diseases.
Tập 31 Số 6 - Trang 673-677 - 1994
Diffusion‐weighted imaging of the human optic nerve: A New approach to evaluate optic neuritis in multiple sclerosis Abstract The apparent diffusion coefficient (ADC) in the optic nerve was measured from diffusion‐weighted magnetic resonance imaging using an intravoxel incoherent motion (IVIM) sequence. The subjects were seven normal volunteers and eight patients with multiple sclerosis (MS) with a total of four optic nerves with acute neuritis and nine nerves with chronic neuritis. The mean ADC (4.18 ± 1.13 × 10−3 mm2 /s, n = 9) in the optic nerves with chronic neuritis was significantly higher than that in normal volunteers (1.56 ± 0.675 × 10−3 mm2 /s, n = 14) and that in the nerves with acute neuritis (0.94 ± 0.43 × 10−3 mm2 /s n = 4) (P < 0.001). The ADC is useful in assessing MS foci in the optic nerves.
Tập 38 Số 3 - Trang 484-491 - 1997
Magnetization transfer contrast (MTC) and tissue water proton relaxation <i>in vivo</i> Abstract In this study the exchange between 1 H magnetization in “free” water (1 Hf ) and that in a pool with restricted motion (1 Hr ) was observed in tissues in vivo using NMR saturation transfer methods. Exchange between these two pools was demonstrated by a decrease in the steady‐state magnetization and relaxation times of 1 Hf with radiofrequency irradiation of 1 Hr . The pseudo‐first‐order rate constant for the movement of magnetization from 1 Hf to 1 Hr was ∼ Is−1 in kidney and ∼3s−1 in skeletal muscle in vivo . Proton NMR imaging demonstrated that this exchange was tissue specific and generated a novel form of NMR image contrast. The extent of exchange between 1 Hf and 1 Hr as well as the topological correlation ofthe exchange with relaxation weighted images suggests that this pathway is a major determinant of the observed relaxation properties of water 1 H in vivo . © 1989 Academic Press. Inc.
Tập 10 Số 1 - Trang 135-144 - 1989
Novel ROC‐type method for testing the efficiency of multivariate statistical methods in fMRI Abstract The receiver operating characteristic (ROC) method is a useful and popular tool for testing the efficiency of various diagnostic tests applicable to functional MRI (fMRI) data. Typically, the diagnostic tests are applied on simulated and pseudo‐human fMRI data, and the area under the ROC curve is used as a measure of the efficiency of the diagnostic test. The effectiveness of such a method depends on how well the simulated data approximate the real data. For multivariate statistical methods, however, this technique is usually inadequate, as the spatial dependence among voxels is ignored for simulated data. In this work a modified ROC method using real fMRI data with a broader scope is proposed. This method can be applied to most fMRI postprocessing techniques, including multivariate analyses such as canonical correlation analysis (CCA). Also, the relationship of the modified ROC method with the conventional ROC method is discussed in detail. Magn Reson Med 49:1152–1162, 2003. © 2003 Wiley‐Liss, Inc.
Tập 49 Số 6 - Trang 1152-1162 - 2003
Estimation of metabolite concentrations from localized <i>in vivo</i> proton NMR spectra Abstract The LCModel method analyzes an in vivo spectrum as a Linear Combination of Model spectra of metabolite solutions in vitro. By using complete model spectra, rather than just individual resonances, maximum information and uniqueness are incorporated into the analysis. A constrained regularization method accounts for differences in phase, baseline, and lineshapes between the in vitro and in vivo spectra, and estimates the metabolite concentrations and their uncertainties. LCModel is fully automatic in that the only input is the time‐domain in vivo data. The lack of subjective interaction should help the exchange and comparison of results. More than 3000 human brain STEAM spectra from patients and healthy volunteers have been analyzed with LCModel. N ‐acetylaspartate, cholines, creatines, myo ‐inositol, and glutamate can be reliably determined, and abnormal levels of these or elevated levels of lactate, alanine, scyllo ‐inositol, glutamine, or glucose clearly indicate numerous pathologies. A computer program will be available.
Tập 30 Số 6 - Trang 672-679 - 1993