ISSN:1053-1807    

DOI:10.1002/jmri.1880020402

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.1880020403

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

年代:1992

数据来源: WILEY

摘要:

Abstract“Single shot” magnetic resonance (MR) diffusion imaging was used to study the details of signal decay curves in experimental perturbations of cerebral perfusion induced by hypercapnia or death. Despite large perfusion increases observed with dynamic susceptibility‐contrast MR imaging, no correlation with these changes was seen in either the diffusion coefficient or any other intravoxel incoherent motion (IVIM) model parameters in dog gray matter as arterial carbon dioxide pressure increased. Non‐monoexponential signal decay in cat gray matter was seen both before and after death. In addition, cat gray matter demonstrated a steady decrease in the diffusion coefficient after death. These data are strong evidence that the fast component of the non‐monoexponential diffusion‐related signal decay is not due solely to perfusion. The authors believe that a second compartment of nonex‐changing spins, most likely cerebrospinal fluid, accounts for the non‐monoex

ISSN:1053-1807    

DOI:10.1002/jmri.1880020404

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn vivo sodium‐23 and hydrogen‐1 magnetic resonance (MR) imaging and spectroscopy of the rat brain during infusion of the shift reagent thulium DOTP5−(1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetra[methylene phosphonate]) was performed to assign the various peaks observed during infusion and to evaluate the shift reagent in discriminating tissue compartments. Na‐23 spectra collected during the infusion showed two shifted peaks that were assigned to intravascular Na+and extracellular muscle Na+, respectively, and one unshifted peak assigned to intra‐ and extracellular brain Na+and cerebrospinal fluid Na+. These assignments were validated with H‐1 and Na‐23 MR imaging and Na‐23 chemical shift imaging (CSI). The H‐1 and Na‐23 images showed that a surface coil placed on a rat head can detect a substantial amount of signal from muscle surrounding the skull. Na‐23 CSI spectra from successive 1‐mm‐thick coronal sections indicated that the shift reagent did not cross the blood‐brain barrier. The study also showed that bulk susceptibility shifts are quite small with Tm‐DOTP5−. This reagent may be useful in determining compartmental Na+concentrations and blood flow kinetics in brain and in examining the

ISSN:1053-1807    

DOI:10.1002/jmri.1880020405

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.1880020406

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe brains of anesthetized 7‐month‐old male hooded rats were imaged in coronal, sagittal, and horizontal planes at 4.7 T. Images were obtained with a section thickness of 0.6 mm and in‐plane pixel size of 0.18‐0.20 mm, resulting in finer combined spatial and contrast resolution than in most previously published reports. This allowed detailed anatomic assignment of many brain structures on the basis of comparison with a histologic brain atlas. T1, apparent T2, and water proton density values of gray matter, white matter, and cerebrospinal fluid (CSF) were derived from saturation‐recovery and multiecho measurements. These values were used to calculate expected contrast‐to‐noise ratios as a function of TR and TE in spin‐echo imaging sequences. The optimal simultaneous contrast between gray and white matter and between CSF and gray matter was obtained on images with moderate T2 weighting, with a TR of 3.6 seconds and a TE of 45 msec. The use of thin sections was found to be essential for resolving many fine structures, and the improved sensitivity provided by the high magnetic field strength was crucial for imaging such thin sections at adequate signal

ISSN:1053-1807    

DOI:10.1002/jmri.1880020407

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe magnetization transfer contrast (MTC) technique was used in low‐field‐strength (0.1 T) magnetic resonance (MR) imaging of 28 patients with intracranial tumors. MTC images were generated with an off‐resonance, low‐power radio‐frequency pulse applied during the interpulse delay period of a gradient‐echo partial‐saturation sequence (TR msec/TE msec = 200/20). Images in the presence and absence of the MTC pulse were concurrently acquired before and after injection of gadopen‐tetate dimeglumine at a dose of 0.1 mmol/kg. The contrast agent enhanced 27 of 28 tumors. Application of the MTC pulse improved the contrast‐to‐noise ratio (C/N) between tumor and normal white matter in 26 of 28 cases on the preinjection images and in 25 of 28 cases on the postinjection images. On the gadolinium‐enhanced images, the mean C/N was 2.6 ± 1.7 without the MTC pulse and 3.2 ± 1.9 with the MTC pulse. The greatest contrast improvement with the MTC technique was obtained in tumors showing the strongest paramagnetic enhancement. The results indicate that MTC can improve contrast between normal brain and some intracranial neoplasms. The use of gadopentetate dimeglumine generally

ISSN:1053-1807    

DOI:10.1002/jmri.1880020408

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

年代:1992

数据来源: WILEY

摘要:

AbstractAn ischemic clamp model of exercise was used to evaluate the potential role of blood flow in mediating changes in the magnetic resonance imaging appearance of skeletal muscle. Proton relaxation times of muscle were serially estimated in 10 healthy subjects (a) before exercise, (b) after exercise in the presence of vascular occlusion (VO1), (c) during vascular reocclusion after 1 minute of reperfusion (VO2), and (d) after reinstitution of continuous flow. T1 and T2 of active muscles were increased during VO1. During VO2, there were additional increases in relaxation times of active muscles. Reinstitution of continuous flow was associated with a continuous decrease in the T2 of exercised muscle. Hence, blood flow was not required for increases in T1 and T2 with exercise. Additional relaxation time increases occurred after a brief period of reperfusion; however, continuous flow was associated with a decrease in T2.

ISSN:1053-1807    

DOI:10.1002/jmri.1880020409

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

年代:1992

数据来源: WILEY

摘要:

AbstractFifteen patients with cardiac or paracardiac masses underwent magnetic resonance (MR) imaging with spin‐echo (n = 15), cine gradient‐echo (n = 15), gadopentetate dimeglumine‐enhanced spin‐echo (n = 15), and TurboFLASH (fast low‐angle shot) (n = 7) sequences. All masses had either histologic confirmation (n = 11) or confirmation with other imaging modalities (n = 4). Myxomas (n = 6) were characterized by an intermediate signal intensity (SI) on spin‐echo (n = 6) and low SI on cine gradient‐echo (n = 6) images and moderately high‐SI contrast enhancement (n = 5). Percent contrast enhancement for myxomas was 57% ± 11%. Thrombus (n = 4) had intermediate (n = 3) or high (n = 1) SI on spin‐echo images and low (n = 2) or intermediate (n = 2) SI on gradient‐echo images and did not show substantial contrast enhancement. Postcontrast first‐pass TurboFLASH images were useful by clearly demonstrating the nonen‐hancing mass lesion in a high‐SI blood pool. Other cardiac and paracardiac tumors (n = 5) showed variable pre‐and postcontrast spin‐echo SI; however, no other tumor showed low S

ISSN:1053-1807    

DOI:10.1002/jmri.1880020410

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

年代:1992

数据来源: WILEY

摘要:

AbstractA method for producing high‐resolution magnetic resonance (MR) images of blood vessel walls is described. The authors review a theoretical analysis of receiver‐coil design and present a coil well suited for intravascular MR imaging. The design is based on two coaxial solenoids separated by a gap region and with current driven in opposite directions. Placement of this receiver coil within the vascular space is shown to provide a substantial increase in sensitivity over that of external surface coils. Experimental verification of these predictions was obtained in a vessel phantom in which a 13‐cm surface coil was compared with a 3.5‐mm‐diameter opposed‐solenoid intravascular coil. This intravascular coil had a cylindric region of high sensitivity that offered a 10‐fold improvement in signal‐to‐noise ratio over that of an external coil near the vessel wall. The performance of this coil was also tested in the jugula

ISSN:1053-1807    

DOI:10.1002/jmri.1880020411

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

年代:1992

数据来源: WILEY