ISSN:1053-1807    

DOI:10.1002/jmri.1880010102

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

年代:1991

数据来源: WILEY

摘要:

AbstractRecent developments in the use of magnetic resonance (MR) to measure and image diffusion and blood microcirculation (“perfusion”) are summarized. After a brief description of the effects of diffusion and perfusion on the MR signal, the different methods (conventional spin‐echo, stimulated‐echo, gradient‐echo, and echo‐planar imaging) that have been proposed and used to image and measure diffusion and perfusion by gradient sensitization are presented, along with their advantages and limitations. The difficulties of diffusion/ perfusion imaging related to both hardware and software are then discussed. Special attention is given to specific problems encountered with in vivo studies and data analysis. Finally, the potential biologic and clinical applications are outlined, and some examples ar

ISSN:1053-1807    

DOI:10.1002/jmri.1880010103

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

年代:1991

数据来源: WILEY

摘要:

AbstractDEGENERATION OF THE INTERVERTEBRAL disk is a ubiquitous process, seen at autopsy in 97% of adults by age 49 years (1). Low back pain is the most expensive health care problem in patients 20–50 years old, with $14 billion spent yearly on treatment and compensation (2). The greatest costs connected with low back pain occur in patients who have pain longer than 3 months and in those with recurrent pain episodes (3). Approximately 5.2 million people are disabled by back pain (3–5).These statistics indicate that the accurate diagnosis of back pain disease is obviously of great importance. In the diagnosis of disk degeneration and its sequelae, magnetic resonance (MR) imaging has become a key ingredient. The utility of conventional two‐dimensional spin‐echo MR imaging of the spine has been firmly established for extradural disease (6–8). Gradient‐echo techniques have more recently been used to enhance the cerebrospinal fluid (CSF)‐extradural interface in the evaluation of degenerative disease (9–13). Some of the new imaging findings and concepts regarding the use of contrast material and three‐dimensional techniques in the evaluation of degenerative disease of the s

ISSN:1053-1807    

DOI:10.1002/jmri.1880010104

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

年代:1991

数据来源: WILEY

摘要:

AbstractOptimization of the contrast‐to‐noise ratio (CNR) is described for microcirculation magnetic resonance (MR) imaging techniques based on flow‐compensated/flow‐dephased sequences, both with and without even‐echo rephasing. The authors present the most advantageous manner of applying flow‐dephased gradients, such that de‐phasing is maximal while diffusion losses are minimal. The theoretical considerations include phase, diffusion, echo time, and bandwidth in the determination of the optimal parameters for microcirculation imaging. Studies in phantoms consisting of stationary and flowing copper sul‐fate in Sephadex columns demonstrate the validity of the calculations. Optimized in vivo images of a rat stroke model demonstrate the potential of the flow‐compensated/flow‐dephased technique and the importanc

ISSN:1053-1807    

DOI:10.1002/jmri.1880010105

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

年代:1991

数据来源: WILEY

摘要:

AbstractAs part of a phase III clinical trial, 25 patients with suspected intracranial or spinal disease underwent magnetic resonance (MR) imaging before and after intravenous injection of 0.1 mmol/ kg Gd‐HP‐DO3A (1,4,7‐tris[carboxymethy1]‐10‐[2′hydroxypropy1]‐1,4,7,10‐tetraazacyclodode‐cane), a neutral (nonionic) gadolinium chelate. Laboratory analysis included a complete blood count; blood chemistry; measurement of electrolyte levels; hepatic function, clotting function, and iron metabolism panels; and urinalysis both before and 24 hours after contrast agent administration. No statistically significant changes related to contrast agent administration were noted in laboratory values after administration of the contrast agent. In this selected group of patients, the contrast agent‐enhanced study provided greater diagnostic information than did the precontrast study in 69% of head cases and 67% of spine cases. These initial clinical trials demonstrate that Gd‐HP‐DO3A is a safe, efficacious agent for head

ISSN:1053-1807    

DOI:10.1002/jmri.1880010106

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe safety and efficacy of a newly developed intravenous formulation of the nonionic contrast agent gadolinium diethylenetriaminepentaacetic acid‐bis(methylamide), formulated as gadodia‐mide injection, was investigated. In 30 patients who underwent spin‐echo magnetic resonance (MR) imaging before and after contrast agent enhancement, the enhanced images had characteristics judged similar to those of images enhanced by means of available gadolinium compounds. In 15 patients, contrast agent administration was of major diagnostic help, either revealing lesions not apparent without enhancement or providing important lesion characterization. In 12 patients, the lack of abnormal enhancement patterns was important in excluding the presence of disease. In three patients, the contrast agent did not provide information additional to that obtained with the unenhanced T1‐ and T2‐weighted images. No clinically significant changes were observed in vital signs, neurologic status, or laboratory results. The authors conclude that, in this limited series, gadodiamide injection proved to be a safe and useful MR imaging contrast agent for evaluation of the central nervous system and surrounding s

ISSN:1053-1807    

DOI:10.1002/jmri.1880010107

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

年代:1991

数据来源: WILEY

摘要:

AbstractTurboFLASH (fast low‐angle shot) sequences enable the acquisition of an image in a fraction of a second. However, unique to T1‐weighted ultra‐fast imaging, the magnetization variation during image acquisition can produce artifacts along the phase‐encoding direction. In this study, the signal behavior and nature of these artifacts were analyzed with various acquisition schemes to improve image contrast. The magnetization variation during image acquisition and its filtering effect on the image were simulated for three different approaches to T1‐weighted turboFLASH imaging: standard turboFLASH with (a) mono‐tonically ascending phase‐encoding steps, (b) reordered phase encoding, and (c) k‐space segmentation. Each of the modified data acquisition schemes has advantages. However, for sub‐second imaging, reordered phase encoding produced improved image contrast over that of standard turboFLASH, and segmented k‐space imaging gave superior tissue contrast compared with that of both standard and reordered turboFLASH, with imaging time that permits

ISSN:1053-1807    

DOI:10.1002/jmri.1880010108

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

年代:1991

数据来源: WILEY

摘要:

AbstractModeling of vocal tract behavior during speech production requires accurate measurements of the entire vocal tract. To accomplish this, magnetic resonance (MR) imaging was performed on a 0.5‐T system with a custom‐made, double‐loop, wraparound coil. A midsagittal section of the region from the glottis to the lips was imaged during sustained production of five American English vowels. A gradient‐spoiled gradient‐echo sequence was used to achieve a 4‐second imaging time. Images showed clear profiles of the entire vocal tract and exhibited essential articulatory features of vowel production. It was possible to measure midsagittal widths at various points along the vocal tract with 1‐mm resolution. The measurements were used to construct a tube model for prediction of the acoustic output of the vocal tract. It is concluded that risk‐free MR imaging promises to be an important means of acquiring data for vocal tract modeling, with applications to speech pathology, linguistics, and ar

ISSN:1053-1807    

DOI:10.1002/jmri.1880010109

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe influence of magnetic resonance (MR) imaging on the integrity and function of an implantable, programmable drug infusion pump and the distortion of the image by this device were tested. Six identical pumps were tested in magnetic fields of 1.5 T. Pump memory was not affected by the procedure. The pump rotor stalled (no infusion) as long as the device was within the magnetic field. Drug delivery resumed as programmed after the pump was removed from the field. No structural damage to the electrical or mechanical pump components was detected. The pump caused a circular image artifact (a signal dropout) within 8–10 cm of the device. The authors conclude that MR imaging is accurate if the area of interest is at least 10 cm from the pump, and that with awareness of temporary infusion cessation, it is safe to perform MR imaging in patients with this implanted pum

ISSN:1053-1807    

DOI:10.1002/jmri.1880010110

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

年代:1991

数据来源: WILEY

摘要:

AbstractWith a recently described rat model technique for direct hepatic injection of tumor cells for imaging research, there were concerns that the injection itself might produce lesions detectable with magnetic resonance (MR) imaging, thereby producing false‐positive results. To examine this possibility, the authors prospectively studied 14 Sprague‐Dawley rats after direct hepatic injection of cells from a rat hepatoma cell line. The rats were imaged with a variety of pulse sequences before and after intravenous injection of the contrast agent manganese dipyridoxal diphosphate at a dose of 8 μmol/kg. No intrahepatic lesions could be detected with MR imaging during the first 6 days after direct hepatic injection of the tumor cells. Therefore, the direct injection technique should be accurate for evaluating various MR imaging sequences and contrast agents for early hepatic tumor detec

ISSN:1053-1807    

DOI:10.1002/jmri.1880010111

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

年代:1991

数据来源: WILEY