Journal of Magnetic Resonance Imaging
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 applications Abstract 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 MRI Abstract 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
Encoding strategies for three‐direction phase‐contrast MR imaging of flow Abstract 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 contrast Abstract 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 steatosis Abstract 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 flow Abstract 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 data Abstract 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 protocol Abstract 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
Principles of cerebral perfusion imaging by bolus tracking Abstract The principles of cerebral perfusion imaging by the method of dynamic susceptibility contrast magnetic resonance imaging (DSC‐MRI) (bolus tracking) are described. The MRI signals underlying DSC‐MRI are discussed. Tracer kinetics procedures are defined to calculate images of cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT). Two general categories of numerical procedures are reviewed for deriving CBF from the residue function. Procedures that involve deconvolution, such as Fourier deconvolution or singular value decomposition (SVD), are classified as model‐independent methods because they do not require a model of the microvascular hemodynamics. Those methods in principle also yield a measure of the tissue impulse response function and the residue function, from which microvascular hemodynamics can be characterized. The second category of methods is the model‐dependent methods, which use models of tracer transport and retention in the microvasculature. These methods do not yield independent measures of the residue function and may introduce bias when the physiology does not follow the model. Statistical methods are sometimes used, which involve treating the residue function as a deconvolution kernel and optimizing (fitting) the kernel from the experimental data using procedures such as maximum likelihood. Finally, other hemodynamic indices that can be measured from DSC‐MRI data are described. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.
Tập 22 Số 6 - Trang 710-717 - 2005
Development, standardization, and testing of a lexicon for reporting contrast‐enhanced breast magnetic resonance imaging studies Abstract The purpose of this study was to develop, standardize, and test reproducibility of a lexicon for reporting contrast‐enhanced breast magnetic resonance imaging (MRI) examinations. To standardize breast MRI lesion description and reporting, seven radiologists with extensive breast MRI experience developed consensus on technical detail, clinical history, and terminology reporting to describe kinetic and architectural features of lesions detected on contrast‐enhanced breast MR images. This lexicon adapted American College of Radiology Breast Imaging and Data Reporting System terminology for breast MRI reporting, including recommendations for reporting clinical history, technical parameters for breast MRI, descriptions for general breast composition, morphologic and kinetic characteristics of mass lesions or regions of abnormal enhancement, and overall impression and management recommendations. To test morphology reproducibility, seven radiologists assessed morphology characteristics of 85 contrast‐enhanced breast MRI studies. Data from each independent reader were used to compute weighted and unweighted kappa (κ) statistics for interobserver agreement among readers. The MR lexicon differentiates two lesion types, mass and non‐mass‐like enhancement based on morphology and geographical distribution, with descriptors of shape, margin, and internal enhancement. Lexicon testing showed substantial agreement for breast density (κ = 0.63) and moderate agreement for lesion type (κ = 0.57), mass margins (κ = 0.55), and mass shape (κ = 0.42). Agreement was fair for internal enhancement characteristics. Unweighted kappa statistics showed highest agreement for the terms dense in the breast composition category, mass in lesion type, spiculated and smooth in mass margins, irregular in mass shape, and both dark septations and rim enhancement for internal enhancement characteristics within a mass. The newly developed breast MR lexicon demonstrated moderate interobserver agreement. While breast density and lesion type appear reproducible, other terms require further refinement and testing to lead to a uniform standard language and reporting system for breast MRI. J. Magn. Reson. Imaging 2001;13:889–895. © 2001 Wiley‐Liss, Inc.
Tập 13 Số 6 - Trang 889-895 - 2001