Journal of Magnetic Resonance Imaging
SCIE-ISI SCOPUS (SonsInc.)
1522-2586
1053-1807
Mỹ
Cơ quản chủ quản: WILEY , John Wiley & Sons Inc.
Lĩnh vực:
Radiology, Nuclear Medicine and Imaging
Các bài báo tiêu biểu
Diffusion tensor imaging: Concepts and applicationsAbstract The success of diffusion magnetic resonance imaging (MRI) is deeply rooted in the powerful concept that during their random, diffusion‐driven displacements molecules probe tissue structure at a microscopic scale well beyond the usual image resolution. As diffusion is truly a three‐dimensional process, molecular mobility in tissues may be anisotropic, as in brain white matter. With diffusion tensor imaging (DTI), diffusion anisotropy effects can be fully extracted, characterized, and exploited, providing even more exquisite details on tissue microstructure. The most advanced application is certainly that of fiber tracking in the brain, which, in combination with functional MRI, might open a window on the important issue of connectivity. DTI has also been used to demonstrate subtle abnormalities in a variety of diseases (including stroke, multiple sclerosis, dyslexia, and schizophrenia) and is currently becoming part of many routine clinical protocols. The aim of this article is to review the concepts behind DTI and to present potential applications. J. Magn. Reson. Imaging 2001;13:534–546. © 2001 Wiley‐Liss, Inc.
Tập 13 Số 4 - Trang 534-546 - 2001
4D flow MRIAbstract Traditionally, magnetic resonance imaging (MRI) of flow using phase contrast (PC) methods is accomplished using methods that resolve single‐directional flow in two spatial dimensions (2D) of an individual slice. More recently, three‐dimensional (3D) spatial encoding combined with three‐directional velocity‐encoded phase contrast MRI (here termed 4D flow MRI) has drawn increased attention. 4D flow MRI offers the ability to measure and to visualize the temporal evolution of complex blood flow patterns within an acquired 3D volume. Various methodological improvements permit the acquisition of 4D flow MRI data encompassing individual vascular structures and entire vascular territories such as the heart, the adjacent aorta, the carotid arteries, abdominal, or peripheral vessels within reasonable scan times. To subsequently analyze the flow data by quantitative means and visualization of complex, three‐directional blood flow patterns, various tools have been proposed. This review intends to introduce currently used 4D flow MRI methods, including Cartesian and radial data acquisition, approaches for accelerated data acquisition, cardiac gating, and respiration control. Based on these developments, an overview is provided over the potential this new imaging technique has in different parts of the body from the head to the peripheral arteries. J. Magn. Reson. Imaging 2012;36:1015–1036. © 2012 Wiley Periodicals, Inc.
Tập 36 Số 5 - Trang 1015-1036 - 2012
Một khuôn khổ cho chỉ số xác suất kết nối dựa trên dòng chảy (PICo) thông qua việc giải thích cấu trúc của các phép đo khuếch tán MRI Dịch bởi AI Tóm tắt Mục đích: Thiết lập một phương pháp tổng quát để định lượng các phương pháp theo dõi sợi dựa trên dòng chảy về xác suất kết nối giữa các điểm và/hoặc các vùng. Nguyên liệu và Phương pháp: Phương pháp dòng chảy thường được sử dụng được điều chỉnh để tận dụng sự không chắc chắn trong định hướng của phương hướng khuếch tán chính được xác định cho mỗi voxel ảnh. Việc chạy quy trình dòng chảy lặp lại sử dụng các phương pháp Monte Carlo để khai thác sự không chắc chắn vốn có này tạo ra các bản đồ xác suất kết nối. Sự không chắc chắn được định nghĩa bằng cách diễn giải hình dạng của hồ sơ định hướng khuếch tán do tensor khuếch tán cung cấp theo cấu trúc vi mô cơ bản. Kết quả: Hai ứng cử viên để mô tả sự không chắc chắn trong tensor khuếch tán được đề xuất và các bản đồ xác suất kết nối với các điểm xuất phát hoặc các vùng đã chọn được tạo ra trong một số lộ trình chính. Kết luận: Các phương pháp được trình bày cung cấp một khung tổng quát cho việc sử dụng các phương pháp dòng chảy để tạo ra các bản đồ xác suất kết nối. J. Magn. Reson. Imaging 2003;18:242–254. © 2003 Wiley‐Liss, Inc.
Tập 18 Số 2 - Trang 242-254 - 2003
Osteoporosis is associated with increased marrow fat content and decreased marrow fat unsaturation: A proton MR spectroscopy studyAbstract Purpose To use proton magnetic resonance spectroscopy (1 H‐MRS) to evaluate vertebral marrow fat, and to determine whether bone density correlates with fat content and fat unsaturation levels in postmenopausal women. Materials and Methods Fifty‐three women (mean age = 70 years) underwent dual energy x‐ray absorptiometry and 1 H‐MRS, and 12 young female controls (mean age = 28 years) underwent 1 H‐MRS of the lumber spine. Water and lipid peak amplitudes were measured to calculate fat content and fat unsaturation index. Spearman's correlation tests and a t‐test comparison of means were applied. Results 1 H‐MRS was successful in 15 normal, 15 osteopenic, and 20 osteoporotic subjects, and in all controls. Marrow fat content was significantly elevated in osteoporotic (65.5% ± 10%) and osteopenic (63.5% ± 9.3%) subjects compared to normal subjects (56.3% ± 11.2%) and young controls (29% ± 9.6%). The fat unsaturation index was significantly decreased in osteoporotic (0.091 ± 0.013) and osteopenic (0.097 ± 0.014) subjects compared to normal subjects (0.114 ± 0.016) and young controls (0.127 ± 0.031). A good inverse correlation was observed between the fat content and the unsaturation index (rs = −0.53, P < 0.0001).Conclusion Osteoporosis is associated with increased marrow fat. As marrow fat increases, saturated lipids appear to increase preferentially to unsaturated lipids. J. Magn. Reson. Imaging 2005;22:279–285. © 2005 Wiley‐Liss, Inc.
Tập 22 Số 2 - Trang 279-285 - 2005
Encoding strategies for three‐direction phase‐contrast MR imaging of flowAbstract Three encoding strategies for the measurement of flow velocities in arbitrary directions with phase‐contrast magnetic resonance imaging are presented; their noise and dynamic range performance are compared by means of theoretical analysis and computer simulation. A six‐point measurement strategy is shown to be quite inefficient in terms of velocity variance per unit time. A simple four‐point method exhibits equal dynamic range; its noise depends on flow direction but on average is equal to that of the six‐point method. An alternate, balanced four‐point method has noise that is direction independent and has, depending on implementation, possibly lower noise levels. Either four‐point method is more efficient and is preferred over the six‐point approach.
Tập 1 Số 4 - Trang 405-413 - 1991
Nephrotoxicity of high‐dose gadolinium compared with iodinated contrastAbstract To determine if high‐dose gadolinium chelates are less nephrotoxic than iodinated contrast. Records of 342 patients who had received high‐dose gadolinium (.2 to .4 mmol/kg) for magnetic resonance imaging were reviewed to identify patients who had also received iodinated contrast for radiographic examinations. Their clinical course and laboratory data were reviewed to identify changes in serum creatinine attributable to the contrast agents. In 64 patients, serum creatinine data were available pre and post both gadolinium and iodinated contrast. The mean change in serum creatinine after gadolinium in these 64 patients was −.07 mg/dL (−6 μmol/L). By comparison, the mean change in serum creatinine in the same patients after iodinated contrast was .35 mg/dL (+31 μmol/L) from 2.0 ± 1.4 to 2.3 ± 1.8 (P =.002). Eleven of the 64 patients had iodinated contrast‐induced renal failure (.5 mg/dL or greater rise in serum creatinine); none had gadolinium contrast‐induced renal failure despite the high gadolinium dose and high prevalence of underlying renal insufficiency. High‐dose gadolinium chelates are significantly less nephrotoxic than iodinated contrast.
Tập 6 Số 1 - Trang 162-166 - 1996
Proton MR spectroscopy in quantitative in vivo determination of fat content in human liver steatosisAbstract To demonstrate that the lipid volume fraction In liver steatosis can be accurately estimated with in vivo hydrogen‐1 magnetic resonance (MR) spectroscopy, the authors developed a calibration procedure based on in vitro MR spectroscopy of lipid extracts from steatotlc liver specimens. The lipid volume fractions determined with the calibration procedure were compared with the results of histomorphometry and with calibrated computed tomographic (CT) data. The volume fraction of fat determined with MR spectroscopy was in good agreement with the CT results, whereas histomorphometry underestimated the amount of hepatic fat. The results indicate that determination of the fat volume fraction in steatotic liver can be achieved noninvasively with MR spectroscopy.
Tập 5 Số 3 - Trang 281-285 - 1995
Time‐resolved 3D MR velocity mapping at 3T: Improved navigator‐gated assessment of vascular anatomy and blood flowAbstract Purpose To evaluate an improved image acquisition and data‐processing strategy for assessing aortic vascular geometry and 3D blood flow at 3T. Materials and Methods In a study with five normal volunteers and seven patients with known aortic pathology, prospectively ECG‐gated cine three‐dimensional (3D) MR velocity mapping with improved navigator gating, real‐time adaptive k‐space ordering and dynamic adjustment of the navigator acceptance criteria was performed. In addition to morphological information and three‐directional blood flow velocities, phase‐contrast (PC)‐MRA images were derived from the same data set, which permitted 3D isosurface rendering of vascular boundaries in combination with visualization of blood‐flow patterns. Results Analysis of navigator performance and image quality revealed improved scan efficiencies of 63.6% ± 10.5% and temporal resolution (<50 msec) compared to previous implementations. Semiquantitative evaluation of image quality by three independent observers demonstrated excellent general image appearance with moderate blurring and minor ghosting artifacts. Results from volunteer and patient examinations illustrate the potential of the improved image acquisition and data‐processing strategy for identifying normal and pathological blood‐flow characteristics. Conclusion Navigator‐gated time‐resolved 3D MR velocity mapping at 3T in combination with advanced data processing is a powerful tool for performing detailed assessments of global and local blood‐flow characteristics in the aorta to describe or exclude vascular alterations. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
Tập 25 Số 4 - Trang 824-831 - 2007
Semiautomated method for noise reduction and background phase error correction in MR phase velocity dataAbstract Background phase distortion and random noise can adversely affect the quality of magnetic resonance (MR) phase velocity measurements. A semiauto‐mated method has been developed that substantially reduces both effects. To remove the background phase distortion, the following steps were taken: The time standard deviations of the phase velocity images over a cardiac cycle were calculated. Static regions were identified as those in which the standard deviation was low. A flat surface representing an approximation to the background distortion was fitted to the static regions and subtracted from the phase velocity images to give corrected phase images. Random noise was removed by setting to zero those regions in which the standard deviation was high. The technique is demonstrated with a sample set of data in which the in‐plane velocities have been measured in an imaging section showing the left ventricular outflow tract of a human left ventricle. The results are presented in vector and contour form, superimposed on the conventional MR angiographic images.
Tập 3 Số 3 - Trang 521-530 - 1993
Report on a multicenter fMRI quality assurance protocolAbstract Temporal stability during an fMRI acquisition is very important because the blood oxygen level‐dependent (BOLD) effects of interest are only a few percent in magnitude. Also, studies involving the collection of groups of subjects over time require stable scanner performance over days, weeks, months, and even years. We describe a protocol designed by one of the authors that has been tested for several years within the context of a large, multicenter collaborative fMRI research project (FIRST‐BIRN). A full description of the phantom, the quality assurance (QA) protocol, and the several calculations used to measure performance is provided. The results obtained with this protocol at multiple sites over time are presented. These data can be used as benchmarks for other centers involved in fMRI research. Some issues with the various protocol measures are highlighted and discussed, and possible protocol improvements are also suggested. Overall, we expect that other fMRI centers will find this approach to QA useful and this report may facilitate developing a similar QA protocol locally. Based on the findings reported herein, the authors are convinced that monitoring QA in this way will improve the quality of fMRI data. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.
Tập 23 Số 6 - Trang 827-839 - 2006