摘要:

AbstractSpectroscopic images of the brain have great potential in disease diagnosis and treatment monitoring. Unfortunately, interfering lipid signals from subcutaneous fat and poor water suppression due to magnetic field inhomogeneities can make such images difficult to obtain. A pulse sequence that uses inversion recovery for lipid suppression and a spectral‐spatial refocusing pulse for water suppression is introduced. In contrast to methods that eliminate fat signal by restricting the excited volume to lie completely within the brain, inversion‐recovery techniques allow imaging of an entire section without such restrictions. In addition, the spectral‐spatial pulse was designed to provide water suppression insensitive to a reasonable range of B0and B1inhomogeneities. Several data processing algorithms have also been developed and used in conjunction with the new pulse sequence to produce metabolite maps covering large volumes of the human brain. Images from single‐ and multisection studies demonstrate the performance of these tec

ISSN:1053-1807    

DOI:10.1002/jmri.1880020302

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

年代:1992

数据来源: WILEY

摘要:

AbstractMagnetic resonance (MR) imaging and proton MR spectroscopy were performed in 14 patients with clinically definite multiple sclerosis (MS). Prominent resonances in the 0.5‐2.0‐ppm region were seen in the spectra of six of nine gadopentetate dimeglumine‐enhanced plaques in seven patients. These resonances were presumed to originate in lipids and other myelin breakdown products. Similar resonances were detected in only seven of 21 unenhancing plaques. The more frequent presence of such signals in the gadolinium‐enhanced regions indicates that myelin breakdown is often associated with the inflammation that occurs in early stages of MS plaque evolution. It remains uncertain, however, whether active inflammation as indicated by gadolinium enhancement is a necessary precursor of myelin breakdown as detected at MR spectroscopy. Quantitative spectral analysis did not indicate statistically significant differences in N‐acetyl aspartate and choline levels relative to creatine plus phosphocreatine between healthy volunteers and MS

ISSN:1053-1807    

DOI:10.1002/jmri.1880020303

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

年代:1992

数据来源: WILEY

摘要:

AbstractMagnetic susceptibility variation caused by calcium permits limited detection of intracranial calcificatios and/or their distinction from iron‐laden lesions with spin‐echo or gradient‐echo magnetic resonance (MR) techniques. The magnetic susceptibility sensitivity of phase imaging has been used to detect iron‐laden lesions. A new approach that combines the magnetic susceptibility sensitivity of both gradient‐echo and phase imaging to yield greater imaging sensitivity to calcium is presented. Two‐dimensional fast low‐angle shot (FLASH) gradient‐echo imaging with phase image reconstruction (gradient‐echo phase [GEP]) was used at 1.0 and 1.5 T. Twelve patients with computed tomography‐proved calcified intracranial lesions (≥200 HU) and seven patients with iron‐laden intracranial lesions having a characteristic appearance on T1‐and T2‐weighted and FLASH MR images were studied. The GEP imaging technique helped detect calcified intracranial lesions (≥200 HU) and helped distinguish

ISSN:1053-1807    

DOI:10.1002/jmri.1880020304

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

年代:1992

数据来源: WILEY

摘要:

AbstractTo overcome problems associated with poor contrast between vessels and background tissue in time‐of‐flight magnetic resonance angiography, the role of intravenous gadopentetate dimeglumine in conjunction with a postprocessing adaptive vessel tracking scheme was studied. Vessel tracking makes it possible to discriminate arteries from veins, to prevent problems associated with other bright tissues on maximum‐intensity projections, and to increase the signal‐to‐noise ratio. Short, asymmetric, velocity‐compensated field echoes were used in conjunction with high‐resolution imaging techniques to spatially discriminate between adjacent vessels and stationary background tissue. Gadopentetate dimeglumine was shown to be useful for visualization of small vessels, aneurysms, and regions of slow flow, when used with this post proc

ISSN:1053-1807    

DOI:10.1002/jmri.1880020305

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe effects on the phase of spins moving during echo‐planar imaging (EPI) acquisition were studied. Standard single‐shot and interleaved multishot blipped EPI acquisitions were considered, assuming either high gradient strength and slew rates or standard gradient strength and slew rates. A spiral k‐space trajectory was also considered. Flow components in the section‐select and phase‐ and frequency‐encoding directions were analyzed separately. While the effect of flow in the section‐select direction is identical to that in a standard two‐dimensional Fourier transform (2DFT) acquisition, flow in the phase‐ or frequency‐encoding directions can have substantial effects on the image, different from that in 2DFT imaging. The magnitude of these effects, which include displacement, distortion, and/or ghosting of vascular structures, is analyzed and predicted for a given velocity and direction of flow, the specific acquisition sequence, and the strength and slew rate of the gradients. For example, 50‐cm/sec flow along the phase‐encoding direction can cause a blurring of 1.25 cm full width at half maximum for blipped EPI with high‐strength gradients, assuming a 40‐cm field

ISSN:1053-1807    

DOI:10.1002/jmri.1880020306

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.1880020307

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

年代:1992

数据来源: WILEY

摘要:

AbstractWhen magnetic resonance phase mapping is used to quantitate valvular blood flow, the presence of higher‐order‐motion terms may cause a loss of phase information. To overcome this problem, a sequence with reduced encoding for higher‐order motion was used, achieved by decreasing the duration of the flow‐encoding gradient to 2.2 msec. Tested on a flow phantom simulating a severe valvular stenosis, the sequence was found to be robust for higher‐order motion within the clinical velocity range. In eight healthy volunteers, mitral and aortic volume flow rates and peak velocities were quantified by means of phase mapping and compared with results of the indicator‐dilution technique and Dop‐pler echocardiography, respectively. Statistically significant correlations were found between phase mapping and the other two techniques. Similar studies in patients with valvular disease indicate that phase mapping is also valid for pathologic conditions. Phase mapping may be used as a noninva‐sive clinical tool for flow quantification in hear

ISSN:1053-1807    

DOI:10.1002/jmri.1880020308

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

年代:1992

数据来源: WILEY

摘要:

AbstractNineteen patients underwent magnetic resonance (MR) angiography for evaluation of lower‐extremity arterial disease. The underlying conditions included atherosclerotic occlusive disease in 12 patients, femoral or popliteal aneurysms in four, and bypass graft stenoses or occlusion in four. In the patients with occlusive disease, the iliac and femo‐ropopliteal vessels were classified as patent, moderately stenotic, severely stenotic, or occluded. Fifteen of 16 occlusions (accuracy = 94%) were correctly classified. In the one missed case, there was a long delay between MR angiography and x‐ray angiography and it is likely that the occlusion occurred during the interval. Three of five severe stenoses were correctly classified with MR angiography. In two cases of iliac artery stenosis, there was a signal void at the point of maximal stenosis, which on the basis of anatomic features could be recognized as severe stenosis rather than an occlusion. Three of four moderate stenoses were correctly classified. Correlation with x‐ray angiography or surgery demonstrated the ability of MR angiography to accurately depict the status of runoff

ISSN:1053-1807    

DOI:10.1002/jmri.1880020309

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.1880020310

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe potential of magnetic resonance (MR) imaging enhanced with albumin‐(gadolinium diethylenetri‐aminepentaacetic acid [DTPA])35, a macromolecular blood pool marker, for detection of focal changes in renal perfusion was studied in a myoglobinuric acute renal failure (ARF) model in the rat. T1‐weighted spin‐echo postcontrast images of injured kidneys at 3 hours after glycerol injection showed three distinct zones: a strongly enhanced outer cortex, a low‐intensity inner cortex, and a strongly enhanced medulla. The distinct band of low intensity in the inner cortex indicated zonal decreased blood volume, corresponding to published microsphere data showing zonal low perfusion in the inner cortex. Contrast differences between parenchymal zones were significant for at least 30 minutes. No focal ischemic changes could be delineated on nonenhanced images. Enhanced and nonenhanced images of injured kidneys obtained at 24 hours after glycerol injection revealed no zonal differentiation. Contrast‐enhanced MR imaging data in this ARF model correlated well with pathologic data and microsphere perfusion results. Contrast‐enhanced characterization of the ischemic phase of renal injury with MR imaging may improve specificity for the diagnosis of ARF and may serve as a marker for therapeutic

ISSN:1053-1807    

DOI:10.1002/jmri.1880020311

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

年代:1992

数据来源: WILEY