摘要:

AbstractMagnetic resonance (MR) phase‐difference methods work well for measuring volumetric flow rates when the vessel diameter is large compared with the in‐plane voxel dimensions. For small vessels (eg, coronary arteries), partial‐volume effects introduce substantial errors in the measured volume flow rate. To correctly measure flow rates through a voxel, both the fraction of the voxel containing moving spins and the phase shift imparted to those spins must be known. The authors propose a flow measurement method that combines information obtained with both the complex‐difference and phase‐difference processing techniques and thereby provides the fractional volume occupied by the moving spins and the phase of those spins. The complex‐difference flow map method proposed results in improved accuracy of MR phase‐contrast flow measurements in the presence of partial

ISSN:1053-1807    

DOI:10.1002/jmri.1880050202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:1053-1807    

DOI:10.1002/jmri.1880050203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractAn analytic correction method was developed and applied to correct the signal intensity nonuniformity caused by the inhomogeneous reception profile of surface coils used—because of their higher sensitivity—for magnetic resonance imaging of the brain at 1.5 T. The reception profile was analytically modeled by using the Blot–Savart law. The correction considerably improved visual interpretation of the images by modeling and removing the dependence of signal intensity on distance from the coil. The method can be used for single or multiple coils of any planar geometry and in any orientation. Application of this technique allows imaging of the brain with surface coils, yielding increased resolution and signal‐to‐noise ratio, without the penalty of image nonu

ISSN:1053-1807    

DOI:10.1002/jmri.1880050204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe authors retrospectively evaluated magnetic resonance Images of the abdomen obtained In 52 consecutive patients. All cases included fast spinecho (FSE) T2‐weighted images acquired with a frequency‐selective fat saturation technique. All imaging was performed with a 1.5‐T unit. In 42 patients (81%), fat was not suppressed in the right anterior diaphragmatic region on the T2‐welghted FSE images with fat suppression. In 11 (26%) of these 42 patients, subcutaneous fat adjacent to the unsuppressed anterior diaphragmatic fat was well suppressed. Hence, the fat In the diaphragmatic region mimicked fluid or peritoneal implants. The cause of the artifact appears to be the juxtaposition of liver, fat, and lung parenchymal air within a small anatomic space, creating a localized inhomogeneity of the magnetic field and susceptibility effects. Radiologists should be aware of this phenomenon to prevent confusion of an artifact with fluid or ne

ISSN:1053-1807    

DOI:10.1002/jmri.1880050205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:1053-1807    

DOI:10.1002/jmri.1880050206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractFor a variety of reasons, small vessels have low signal Intensity in magnetic resonance angiography. When the vessel signal intensity is lower than the signal intensity of background tissues, these vessels tend not to be visible on maximum‐intensity‐projection images. The authors developed a nonlinear second‐difference spatial filtering technique that enhances the details of small vessels while suppressing both noise and uniform background tissue. Two similar nonlinear second‐difference filters are presented and compared with the linear Laplacian second‐difference filter. To evaluate the performance of these filters, they were applied to intracranial three‐dimensional time‐of‐flight MR angiographic data and the results compared with the vessel enhancement obtained with a simple second‐difference Laplacian filter and with magnetization transfer contrast (MTC) techniques. The comparisons demonstrated that nonlinear filtering and MTC techniques result in similar Improvement in small‐vessel visibility and apparent continuity. A quantitative comparison demonstrated that the improvement in the contrast‐to‐noise ratio is much greater with the nonlinear filters th

ISSN:1053-1807    

DOI:10.1002/jmri.1880050207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:1053-1807    

DOI:10.1002/jmri.1880050208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractSpiral echo‐planar magnetic resonance (MR) velocity mapping was used to measure exercise‐related changes in flow in the descending thoracic aorta in 10 healthy volunteers. Flow was measured at rest and Immediately after dynamic exercise, with a 0.5‐T imager with a surface receiving coil and electrocardiographic triggering. Supine exercise was performed with a home‐built pedaling apparatus. Spiral velocity mapping was performed in a transverse plane through the descending thoracic aorta with the subject at rest. The subject was then asked to perform maximum exercise, stop, and hold his breath during a four‐heartbeat acquisition time. Eight cine frames with a temporal resolution of 50 msec were acquired through systole. Each image was acquired in 40 msec during spiral acquisition of k‐space data, starting at the center, 6 msec after the excitation pulse. Reproduclbility of the technique was established by repeating the flow measurement in four consecutive heartbeats. At rest, the heart rate (mean ± standard deviation), mean aortic flow, peak aortic flow, and time to peak flow were 68 beats per minute ± 6, 41 mllliliters per beat ±8, 107 mL/sec ± 20, and 175 msec ± 25, respectively. After exercise, the heart rate and mean and peak aortic flow were significantly increased (P<0.001), measuring 101 beats per minute ±12, 57 milliliters per beat ± 11, and 158 mL/sec ±29, respectively, while the time to peak flow (115 msec ±32) was significantly reduced (P<0.001). The four sets of values obtained for the first four consecutive heartbeats measured at rest were similar, as were those obtained for the first four heart

ISSN:1053-1807    

DOI:10.1002/jmri.1880050209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe authors describe the enhanced magnetic resonance (MR) imaging appearance of intrahepatic Cholangiocarcinoma. The MR Images of eight patients with intrahepatlc Cholangiocarcinoma who underwent MR examination within 3 weeks before partial hepatectomy were retrospectively studied. The MR images, including a dynamic study, were compared directly with pathologic and histologic findings. The peripheral region of the medullary subtype of Cholangiocarcinoma, with many tumor cells, showed greater enhancement relative to liver parenchyma in the early phase. The peripheral region of the scirrhous subtype, with fewer tumor cells showed less enhancement in the early phase. In one patient, the thin rim of the medullary tumor showed less enhancement in the late phase, and this rim corresponded to the peripheral region of the medullary tumor with many tumor cells. The central region of tumors with a large amount of fibrous tissue showed prolonged enhancement in the late and delayed phases. The thin rim of liver parenchyma around the tumor showed less enhancement in the early phase and greater enhancement in the late phase; this rim corresponded to congestive liver parenchyma with dilated sinusoids. Intrahepatic Cholangiocarcinoma shows various enhancement patterns, which depend on both the histologic subtype and the degree and distribution of flbrosis within the tumor.

ISSN:1053-1807    

DOI:10.1002/jmri.1880050210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe purpose of the study was to define the magnetic resonance (MR) imaging appearance of adrenocortical carcinoma (ACC) with current MR techniques. Eight patients with ACC underwent high‐field‐strength MR imaging with the following sequences: axial T1‐weighted gradient echo, fat‐suppressed T1‐weighted spin echo, fat‐suppressed T2‐weighted spin echo, and gadolinium‐enhanced T1‐weighted gradient echo and fat‐suppressed T1‐weighted spin echo. Postcontrast images were also acquired in the sagittal (six patients) and coronal (three patients) planes. Out‐of‐phase gradient‐echo images were obtained in two patients. Lesion morphology, signal intensity features, and presence of metastatic disease were retrospectively evaluated. MR imaging features of ACC included internal hemorrhage (seven of eight patients), central necrosis (seven of eight), and peripheral enhancing nodules (seven of eight). Out‐of‐phase images in two of two patients demonstrated signal loss compared with in‐phase images, which may be a common feature of these tumors. Liver metastases were present in four patients. Consistent

ISSN:1053-1807    

DOI:10.1002/jmri.1880050211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY