摘要:

AbstractThe purpose of the present study was to demonstrate the frequency of occurrence of transient increased segmental hepatic enhancement distal to portal veto obstruction in patients with a lobar (main branch) portal vein obstruction. MR images of all patients with main and lobar branch portal vein obstruction examined by dynamic gadolinium enhanced gradient echo MR images between December 1990 and July 1994 were reviewed retrospectively. All studies included T2‐weighted imaging, Tl‐weighted spoiled gradient echo‘fast low angle shot ([FLASH])’ and postgadolinium enhanced PLASH imaging at 1, 45, and 90 sec and 10 min. Fourteen patients were identified with portal vein obstruction which Included: six with main portal and right and left branch occlusion, six with right lobar, and two with left lobar. In the six patients with main portal vein obstruction, enhancement on 1‐sec postgadolinium FLASH images was homogenous (three patients), diffusely heterogeneous (two patients), or peripherally hyperintense (one patient). In eight of eight patients with isolated obstruction of the right or left lobar portal vein, transient‐increased segmental enhancement distal to portal vein occlusion was observed on immediate postcontrast images. Relatively high signal intensity of the involved segments was present on 1‐sec images and liver parenchymal enhancement became more homogeneous by 45 to 90 sec in all cases. In conclusion, transient‐increased segmental enhancement occurred in eight of eight patients with isolated right or left portal vein occlusion. We postulate that this effect occurs due to increased hepatic arterial blood flow in the presence of portal v

ISSN:1053-1807    

DOI:10.1002/jmri.1880050402

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.1880050422

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe purpose of our study was to perform a prospective comparative analysis of three‐dimensional (3D) steady‐state free precession (SSFP) and two‐dimensional (2D) fast spin‐echo (FSB) imaging in the evaluation of 26 patients with suspected bile duct obstruction. SSFP and highly T2‐weighted FSB sequences were obtained for each patient in multiple planes. Both sequences were reviewed independently and results were compared with findings from direct cholangiography (n = 17) or from a combination of sonography and CT (n = 9). The extrahepatic bile duct (EHBD) and intrahepatic bile duct (IHBD) were dilated In 32% and 54% of patients, respectively. The EHBDs were visualized in 44% of patients with SSFP. versus in 96% with FSE. One or more IHBD segments were seen In 42% of the SSFP sequences and in 100% of the FSB sequences. A portion of, or the entire, pancreatic duct was seen in 23% of the SSFP sequences and in 65% of the FSE sequences. Our findings lead us to conclude that T2‐weighted FSE sequences are superior to SSFP sequences In visualizing the biliary tree and pancreatic duct and that they should replace gradient‐echo sequences in MR Cholangiopa

ISSN:1053-1807    

DOI:10.1002/jmri.1880050403

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to determine the tolerance and the efficacy of the oral contrast agent ferumoxsil in the assessment of gynecologic diseases. Twenty patients underwent MR imaging at 1.5 T. T1‐weighted spin‐echo (SE) and T2‐weighted fast SE images were obtained before and after ingestion of 600900 mL of the Superparamagnetic negative contrast agent ferumoxsil. No side effects were observed. No statistically significant increase in artifact generation was present in the postcontrast images. The efficacy in bowel marking was significant for the small bowel (P= 0.0001) and the cecum (P<0.01), but not significant in all sequences for the sigmoid. In the postcontrast images, delineation of the uterus, the right‐sided adnexa, the lymph nodes, and the pathologic lesions was significantly better(P<.01), but not all sequences showed an improvement in delineation of the other pelvic organs. After administration of ferumoxsil, the level of confidence in diagnosis was significantly higher(P= .0001), but no change in diagnosis was made from the preto the postcontrast images. We found the oral contrast agent ferumoxsil to be well tolerated and effective in marking the bowel and in delineating the normal organs as well as the pathologic lesions on pelvic MR

ISSN:1053-1807    

DOI:10.1002/jmri.1880050404

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

年代:1995

数据来源: WILEY

摘要:

AbstractTwo Important prerequisites for MR velocity mapping of pulsatile motion are synchronization of the sequence execution to the time course of the flow pattern and robustness toward loss of signal in complex flow fields. Synchronization is normally accomplished by using either prospective ECG triggering or so‐called retrospective gating. However, if the studied vessel moves periodically in space as a result of respiratory motion, as in the case of renal arteries, a second synchronization with respect to the vessel motion in space may be necessary. One method to overcome this problem is to use the segmented k‐space technique, in which the entire data acquisition can be made within a breath‐hold by the sampling of several phase‐encoding lines within a small time window during each heart cycle. The aim of this study was to investigate the performance of a segmented k‐space velocity mapping protocol for renal artery flow determination. The protocol uses 16 phase‐encoding lines per heart beat during 16 heart cycles and gives a temporal velocity resolution of 160 msec. Comparison with a conventional ECG‐triggered velocity mapping protocol was made in phantoms as well as in volunteers. In our study, both methods showed sufficient robustness toward complex flow in a phantom model. In comparison with the ECG technique, the segmentation technique reduced vessel blurring and pulsatility artifacts caused by respiratory motion, and average flow values obtained in vivo in the left renal artery agreed between the two methods studied. Although presently hampered by a relatively low temporal resolution, velocity mapping with k‐space segmentation In combination with breath‐holding will benefit from future increased gradient quality, and we assume that in the future the method will become an attractive choice for noninvasive renal artery f

ISSN:1053-1807    

DOI:10.1002/jmri.1880050405

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.1880050423

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

年代:1995

数据来源: WILEY

摘要:

AbstractWe show the feasibility of single breath‐hold volumetric imaging of the heart using a three‐dimensional (3D) segmented echo planar Imaging (EPI) pulse sequence. Fifteen healthy subjects were evaluated using three magnetization preparation schemes: (a) a driven equilibrium T2‐weighted preparation for bright blood and dark myocardium; (b) a STEAM magnetization preparation for dark blood; and (c) fat suppression for coronary artery Imaging. An interleaved EPI trajectory encoding six echoes per Interleave with a 1090 Hz/pixel readout bandwidth was used to collect a 126 × 256 matrix in 22 heartbeats with data acquisition windows per cardiac cycle of 71–285 msec for 8–32 sections. Multiplanar reconstructions could be used if thin (1–3 mm) sections were acquired. Breath‐hold volumetric imaging with 3D segmented EPI holds promise for rapid volumetric evaluation of c

ISSN:1053-1807    

DOI:10.1002/jmri.1880050406

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

年代:1995

数据来源: WILEY

摘要:

AbstractFirst‐pass MR myocardial perfusion measurements require a well‐defined left ventricular (LV) blood pool input function. We used a peripheral intravenous (IV) injection of a gadolinium (Gd) chelate to obtain a well‐characterized LV time‐intensity curve. Using a strongly T1‐weighted subsecond MR sequence, we performed cardiac MR imaging after administering an IV bolus injection of one of three different doses of the Gd chelate: a standard dose (0.1 mmol/kg, group I, n = 8); a low dose with two bolus volumes (0.01 mmol/kg, l/10e bolus volume, group n, n = 7, and 0.01 mmol/kg diluted in saline, same bolus volume as group I, group III, n = 3); and an intermediate dose (0.05 mmol/kg, group IV, n = 5). Unlike in group I (high dose), in groups n and m (low dose), the LV curve had a well‐defined first peak, followed by a downslope and a recirculation peak. With the intermediate dose (group IV), a saturation effect still remained on the LV curve. The signal intensity (SI) enhancement of the myocardium was respectively 580 ± 77% at 0.1 mmol/kg, 362 ± 95% at 0.05 mmol/kg, and at 0.01 mmol/kg, it was 184 ± 33% in group II and 272 ± 8% in group m. In conclusion, with subsecond T1‐weighted MR imaging and a low dose of Gd chelate (i.e., 0.01 mmol/kg). the LV input function is a well‐defined first step for MR

ISSN:1053-1807    

DOI:10.1002/jmri.1880050407

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

年代:1995

数据来源: WILEY

摘要:

AbstractAn RF excitation pulse for three‐dimensional (3D) time‐of‐flight (TOP) MR angiography (MRA) with a nonlinear excitation profile was numerically calculated under the condition of uniform vessel signal across the excitation volume (slab), and the superiority of the optform pulse as compared with conventional RF pulses and TONE pulses was demonstrated. For this purpose we acquired MRA of the lower leg and of the carotid and vertebral arteries in a 30‐year‐old healthy volunteer. Although the flow velocity ranges in these two anatomic locations are different by about a factor of 10, in both cases the corresponding optform pulse provided the best signal homogeneity at the high

ISSN:1053-1807    

DOI:10.1002/jmri.1880050408

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

年代:1995

数据来源: WILEY

摘要:

AbstractA spatially asymmetric RF pulse that improves the uniformity of blood signal intensity and vascular contrast in three‐dimensional (3D) MR angiorpgphy [MRA] is presented. The pulse, called variable‐angle uniform signal excitation (VUSE), was designed to provide uniform signal response and improved contrast for blood flowing through a 3D imagine volume during a FLASH sequence. The VUSE excitation proffle was optimized on the bash of the number of pulses seen by the blood, which varied with the velocity of through‐plane flow, repetition time, and slab thickness with the maximum flip angle at the flow udt constrained at 90°. The theoretical results show that the optimal RF pulse gives more uniformity for flow signal than does a linear ramp excitation proffle or a Gaussian pulse combined with a presaturation pulse. After truncation and ffltering of the VUSE pulse in the time domain, the general shape of the VUSE RF excitation profile is maintained. but the maximum flip angle is reduced. The arteries of the neck in a healthy volunteer were imaged with the VUSE pulse, a constant flip angle (flat) pulse, and a linear ramp pulse in flow‐compensated 3D MRA requences. The WSE pulse produced the most uniform signal as evidenced by the lowest relative dispersion of signal along the left vertebral artery (18.0 versus 26.4 to 23.6 for the other studies). F‐distribution tests also showed that the signal distribution obtained with the VUSE pulse in a 3D FLASH sequence was statistically different from that for the flat and the linear r

ISSN:1053-1807    

DOI:10.1002/jmri.1880050409

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

年代:1995

数据来源: WILEY