ISSN:1053-1807    

DOI:10.1002/jmri.1880010602

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe potential of new high‐field‐strength magnetic resonance (MR) imaging sequences to evaluate bowel disease was investigated and compared with computed tomographic (CT) studies. Thirty‐two patients were studied, 14 with known or suspected gastrointestinal tumors and 18 with known or suspected bowel inflammatory conditions. T1‐weighted fat‐suppressed spinecho and breath‐hold FLASH (fast low‐angle shot) images were obtained before and after intravenous injection of 0.1 mmol/kg gadopentetate dimeglumine. Pathologic confirmation was obtained by biopsy (n = 18), surgical excision (n= 8), or endoscopy (n= 6). CT and MR images were analyzed separately in a prospective fashion and reviewed by consensus. Information from CT and MR images was comparable in cases of confirmed bowel neoplasia. CT scans had better spatial resolution, while fat‐suppressed gadolinium‐enhanced MR images had better contrast resolution. In the 18 cases of bowel inflammation, CT scans showed concentric wall thickening in 16, while MR images showed concentric wall thickening in 14 and increased contrast enhancement in 17. Contrast enhancement was better appreciated on fat‐suppressed images than on FLASH images. The results suggest that MR imaging may play a role in the evaluati

ISSN:1053-1807    

DOI:10.1002/jmri.1880010603

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

年代:1991

数据来源: WILEY

摘要:

AbstractA novel method for “ghost” artifact suppression is introduced. It suppresses ghosts induced by motion in any direction, as well as other types of quasi‐periodic signal modulation. Because it requires neither special hardware nor intensive data processing, it can be easily implemented on conventional magnetic resonance (MR) imagers. The method is based on the concept of decomposition of a ghosted complex image into a ghost mask and ideal image. A set of deliberately designed acquisitions are used to generate a set of ghosted complex images in which the ghost components are related in a simple manner. With use of equations describing image decomposition and ghost correlation, the ideal image can be calculated pixel by pixel. The ideal image obtained (representing the time‐averaged spin‐density distribution) is shown to be a truer representation of physical reality than the ghost‐free image obtained with ordered phase encoding. In this technique, both interview and intraview effects are taken into account. The technique is also useful in simultaneously suppressing ghosts from multifrequency signal modulations such as respiratory and cardiac motions. The method was successfully tested with three time‐interleaved, phase‐encoding‐order‐shifted acquisitions. Experimental results have shown that it is a simple but

ISSN:1053-1807    

DOI:10.1002/jmri.1880010604

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

年代:1991

数据来源: WILEY

摘要:

AbstractMagnetic resonance (MR) imaging can be performed on or below the time scale of most anatomic motion via echo‐planar imaging (EPI) techniques and their derivatives. The goal is to image rapidly and reduce artifacts that typically result from view‐to‐view changes in the spatial distribution of spins due to motion. However, the required time‐dependent magnetic field gradient waveforms remain sensitive to the dephasing effects of motion. Sources of motion artifact are simulated for spins moving along the imaging axes and are shown to be an important source of reduced image quality in EPI. A novel method of EPI is proposed that (a) refocuses single or multiple derivatives of motion at all echoes and (b) prevents accumulation of velocity (or higher derivative)‐induced dephasing along the phase‐encoding axis by moment nulling all phase‐encoding‐step waveforms about a single instant of time. Theoretical EPI sequences with considerable reductions in ghosts, blurring, and signal loss due to motion sensitivity are produced and compared with other EPI methods. Their time efficiency is presented as a function of available (relative) gradient strength for a variety of seq

ISSN:1053-1807    

DOI:10.1002/jmri.1880010605

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

年代:1991

数据来源: WILEY

摘要:

AbstractA custom‐built small‐animal transceiver was used for in vivo imaging of normal rat brain at 0.35 T, with the objective of identifying anatomic components by comparison of images with corresponding histologic sections. The cerebrum, cerebellum, brain stem, ventricles, hippocampus, and subarachnoid space were identified and cerebrospinal fluid (CSF) was differentiated from gray matter and white matter on coronal and transaxial magnetic resonance (MR) images. These images compare favorably with those obtained by others at higher field strengths in regard to delineating major neuroanatomic structures. It is concluded that this technique will be useful for investigating smallanimal models of human neurologic disease involving morphologic and morphometric changes in gray matter, white matter, and CSF‐filled s

ISSN:1053-1807    

DOI:10.1002/jmri.1880010606

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe value of inversion‐recovery (IR) sequences in the diagnosis and staging of prostatic carcinoma with magnetic resonance (MR) imaging was studied. Twenty‐six patients with carcinoma of the prostate were imaged at 1.5 T with an endorectal surface coil and with a variety of IR sequences and a set of spin‐echo (SE) sequences for comparison. Ex vivo prostate specimens were imaged again at the same field strength. The two images were correlated with histologic sections. Cancer was identified with MR imaging in 96% of patients. Of the tumors more than 4 mm in diameter, 87% were identified on T2‐weighted SE images, whereas only 26% were identified on IR images. However, IR images may be more useful in local staging of carcinoma. Gross capsular infiltration was present in only two patients; however, it was detectable (and excluded in five other patients) by means of IR images. It was not detectable on SE images. The high quality of images obtained with the endorectal coil was confirmed. The authors conclude that addition of the IR sequence to MR imaging with the endorectal coil may improve the usefulness of this exam

ISSN:1053-1807    

DOI:10.1002/jmri.1880010607

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe value of magnetic resonance (MR) imaging, with two‐dimensional (2D) spin‐echo and FISP (fast imaging with steady‐state precession) and FLASH (fast low‐angle shot) three‐dimensional (3D) gradient‐echo sequences, for the detection of hyaline cartilage defects of the femoral condyle and the tibial plateau, was investigated in an animal model. In eight dogs, the anterior cruciate ligament was transected in one knee joint, resulting in rapid development of osteoar‐thritis with degeneration of the hyaline cartilage. At autopsy, 24 cartilage lesions were found, which were classified into four grades. The overall detection of cartilage lesions with MR imaging was poor. Only five of the 24 lesions were visible on 2D spin‐echo images, while 11 of 24 were visible on 3D FISP images and 15 of 24 were seen on 3D FLASH images. The best results were obtained in advanced stages of cartilage degeneration, involving ulceration and complete abrasion of the cartilage layer. Signal loss or signal intensity increase in the cartilage layer was seen inconsistently in grades 3 and 4 degeneration. In this animal model, 2D spin‐echo imaging was inadequate for the diagnosis of hyaline cartilage lesions, while 3D gradient‐echo imaging permitted satisfactory diagnosis in only grade

ISSN:1053-1807    

DOI:10.1002/jmri.1880010608

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

年代:1991

数据来源: WILEY

摘要:

AbstractConsiderable interest has been shown in developing a magnetic resonance (MR) imaging technique with quantitative capability in the evaluation of tissue microcirculation (“perfusion”). In the present study, the flow‐dephased/flow‐compensated (FD/FC) technique is evaluated for measuring rat cerebral blood flow (CBF) under nearly optimal laboratory conditions. Imaging was performed on a 2.O‐T system equipped with shielded gradient coils. Rat CBF was varied by manipulating arterial carbon dioxide pressure (Paco2). In parallel experiments, optimized MR imaging studies (seven rats) were compared with laser Doppler flowmetry (LDF) studies (nine rats). LDF values showed a high degree of correlation between CBF and Paco2, agreeing with results in the literature. MR imaging values, while correlating with Paco2, showed considerable scatter. The most likely explanation is unavoidable rat motion during the requisite long imaging times. Because of this motion sensitivity, the FD/FC technique cannot provide a quantitative measure of CBF. It can, however, provide a qualitativ

ISSN:1053-1807    

DOI:10.1002/jmri.1880010609

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

年代:1991

数据来源: WILEY

ISSN:1053-1807    

DOI:10.1002/jmri.1880010610

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

年代:1991

数据来源: WILEY

摘要:

AbstractQuantitative errors (due to magnetic susceptibility artifacts) in the measurement of the cervical spinal neural foramina with fast gradient‐echo (GRE) magnetic resonance imaging were assessed. Cylindric phantoms of different materials were used to demonstrate the nature of magnetic susceptibility artifacts, emphasizing the dependence of the artifact on tissue geometry. Neural foramina diameters measured on thin, sagittal GRE and spin‐echo (SE) images through the neural foramina of a fresh human cervical spine specimen were then compared with direct measurements with calipers. The GRE images showed more apparent narrowing than did the SE images. The absolute distortion of seven neural foramina was rather constant (less than two pixels) on the GRE images; therefore, the relative distortion was inversely proportional to the size of the neural foramen, ranging up to 10% in the upper cervical region at a short TE. The absolute and relative distortion increased as TE increased. At a constant TE, the structural distortion did not change with different TRs or flip angles. The shortest possible TE is recommended in evaluation of the cervical sp

ISSN:1053-1807    

DOI:10.1002/jmri.1880010611

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

年代:1991

数据来源: WILEY