ISSN:1053-1807    

DOI:10.1002/jmri.1880020602

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

年代:1992

数据来源: WILEY

摘要:

AbstractA computerized system for processing spin‐echo magnetic resonance (MR) imaging data was implemented to estimate whole brain (gray and white matter) and cerebrospinal fluid volumes and to display three‐dimensional surface reconstructions of specified tissue classes. The techniques were evaluated by assessing the radiometric variability of MR volume data and by comparing automated and manual procedures for measuring tissue volumes. Results showed (a) the homogeneity of the MR data and (b) that automated techniques were consistently superior to manual techniques. Both techniques, however, were affected by the complexity of the structure, with simpler structures (eg, the intracranial cavity) showing less variability and better spatial correlation of segmentation results between raters. Moreover, the automated techniques were completed for whole brain in a fraction of the time required to complete the equivalent segmentation manually. Additional evaluations included interrater reliability and an evaluation that included longitudinal measurement, in which one subject was imaged sequentially 24 times, with reliability computed from data collected by three raters over 1 year. Results showed good reliability for the automated segmentation procedu

ISSN:1053-1807    

DOI:10.1002/jmri.1880020603

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

年代:1992

数据来源: WILEY

ISSN:1053-1807    

DOI:10.1002/jmri.1880020604

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

年代:1992

数据来源: WILEY

摘要:

AbstractPreliminary experience with phase‐contrast magnetic resonance (MR) angiography at 0.5 T applied in 12 cases of vascular malformations of the spinal cord is reported. There were six intramedullary arteriovenous malformations (AVMs), four perimedullary fistulas, and two dural arteriovenous fistulas with perimedullary drainage, all proved with x‐ray angiography. The small size of the vessels and their location within a bony structure presented a technical challenge. Serpentine vascular signal patterns were identified within the spinal canal in all cases, showing good correlation with the x‐ray angiographic pattern. Relative to spin‐echo images, MR angiograms allowed better visualization of the venous drainage. The nidus of intramedullary AVMs was more difficult to recognize. The ability to manipulate the velocity‐encoding value allows better characterization of flow speed. The results underline the two dimensions of the phase‐contrast technique, which provides both anatomic images and dynamic information about vascular malformations. MR angiography does not replace selective x‐ray angiography, which is indispensable for therapeutic strategy (endovascular procedure or surgery), but it can be considered a valuable alternative to x‐ray angiography d

ISSN:1053-1807    

DOI:10.1002/jmri.1880020605

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

年代:1992

数据来源: WILEY

摘要:

AbstractA method for cardiac‐phase–specific magnetic resonance (MR) angiography is presented. An electronics module permits incrementing of phase‐encoding gradients and storage of incoming data only during a chosen portion of the cardiac cycle. Suppression of stationary material is maintained by delivering radio‐frequency pulses at constant TR throughout the cycle. Imaging of a pulsatile flow phantom demonstrates that acquiring data only during systole substantially increases the signal intensity of flowing material. In addition, phase‐encoding ghost artifacts are eliminated from the neighborhood of the vessel. Image acquisition time is minimized by acquiring only the low‐frequency phase‐encoding lines in the cardiac‐phase–specific mode. In healthy volunteers, greatly improved MR angiograms of the lower extremities are obtained. Fat saturation and magnetization transfer further enhance vessel/background contrast. Acquiring data only during systole ensures rapid inflow for all phase‐encoding lines, permitting a near‐longitudinal section orientation without in‐plane saturation. This substantially reduces total acquisition time relati

ISSN:1053-1807    

DOI:10.1002/jmri.1880020606

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

年代:1992

数据来源: WILEY

ISSN:1053-1807    

DOI:10.1002/jmri.1880020607

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

年代:1992

数据来源: WILEY

摘要:

AbstractMuscle data from phosphorus‐31 magnetic resonance (MR) spectroscopy and hydrogen‐1 MR imaging and popliteal artery data from duplex Doppler ultrasound were compared during an exercise test of the anterior compartment of the leg, in nine healthy volunteers. Significant variations (mean ± standard deviation) were observed at the end of exercise versus rest in intracellular pH (pHi) (6.32 ± 0.02 vs 7.02 ± 0.04, P<.001), T2 (38.2 msec ± 2.3 vs 29.5 msec ± 1.1, P<.001), and popliteal output (652 mL/min ± 232 vs 149 mL/ min ± 65, P<.001). These variables showed the following significant correlations at the end of exercise: T2 and pHi (r = −.784, P<.01), T2 and popliteal output (r = −.737, P<.03), and pHi and popliteal output (r = −.902, P<.001). However, during recovery, the T2 curve was significantly different from those of pHi and popliteal output. This suggests that even if circulatory conditions play a role in the maximum T2 variation during exercise, they do not directly explain T2 changes. Furthermore, the correlations involving pHi suggest the role of the metabolism of exercising muscle in transcapillar

ISSN:1053-1807    

DOI:10.1002/jmri.1880020608

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

年代:1992

数据来源: WILEY

摘要:

AbstractMagnetization‐prepared magnetic resonance (MR) angiography (MPMRA) is an inflow‐based two‐dimensional (2D) imaging sequence in which a preparation phase precedes rapid image acquisition. For maximal blood/tissue contrast, an inversion‐recovery preparation nulls signal from static tissue. If needed, a second inversion suppresses signal from fat. Fully magnetized blood flows in after the inversion pulse (s), providing high signal intensity. The centric phase‐encoding order, which ensures that the initial contrast is reflected in the image set, requires the use of a modified venous saturation technique. The sequence is described and its performance assessed with regard to (a) depiction of in‐plane flow, (b) fat suppression, and (c) venous saturation. Phantom and volunteer studies showed good performance in all three areas. MPMRA images, acquired in just 2–4 seconds per image, had a blood/tissue contrast‐to‐noise ratio nearly twice that of standard 2D time‐of‐flight MR angiograms, acquired in 5–7 seconds. The technique is promising for restless patients and in anatomic areas plague

ISSN:1053-1807    

DOI:10.1002/jmri.1880020609

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

年代:1992

数据来源: WILEY

摘要:

AbstractAcceleration in blood flow can affect the accuracy of phase velocity measurements. Convective acceleration is due to changes in flow geometry and is independent of the time‐varying acceleration caused by flow pulsatility. To analyze the effects of convective acceleration on flow velocity measurements, phase velocity measurements were obtained in steady laminar flow in the convergent segment of a 90%, hourglass‐shaped stenosis phantom at a Reynolds number of 1,500. Measurements at the stenosis indicated that convective acceleration caused the measured values of average cross‐sectional velocity to deviate as much as 37% from the theoretical values. The magnitude of the error could be accounted for by including the convective acceleration term in the phase shift equation. Convective acceleration effects should not be ignored in flow velocity measurements through stenoses, even when time‐dependent acceleration due to flow pulsatility can be ne

ISSN:1053-1807    

DOI:10.1002/jmri.1880020610

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

年代:1992

数据来源: WILEY

摘要:

AbstractMagnetic resonance (MR) imaging–histopathologic correlation of thermal injuries induced with interstitial laser irradiation was performed in a chronic model up to 12 weeks after laser exposure. T2‐weighted MR images showed irreversible coagulative necrosis as a low‐signal‐intensity area. A higher‐intensity surrounding area, corresponding to edema, was also present in acute lesions on T2‐weighted images. Serial studies of the chronic model showed that a substantial portion of the interstitial edema zone progressed to coagulative necrosis up to 7 days after laser irradiation. This necrotic zone decreased in size beyond 2 weeks, presumably through biologic healing. MR imaging and pathologic findings correlated well in the chronic model. MR imaging has the potential to depict acute, irreversible thermal damage even before morphologic change is seen at the standard pathologic examination. Recognizing the dynamics of tissue response to interstitial laser irradiation on MR images is valuable for estimation of true le

ISSN:1053-1807    

DOI:10.1002/jmri.1880020611

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

年代:1992

数据来源: WILEY