摘要:

AbstractThis work demonstrates the effects of through‐plane motion due to respiration on contrast and sharpness of liver lesions in MRI. The effects of slice coverage with and without such respiratory motion is also reported. This work is comprised of two parts: a theoretical prediction of liver‐lesion contrast and blur with and without respiration and an experimental validation using gel phantoms of the predicted results. Both theory and experiment show a loss of contrast, increasing with amplitude of the peak‐to‐peak motion. The loss of contrast for a 5‐mm lesion at normal respiration of 15 mm peak‐to‐peak superior‐inferior motion is ≈ 10% with a low order sorted respiratory ordered phase encoding acquisition and ≈ 50% for an unsorted acquisition. Lesion blur is greatest for the low order sorted acquisition while the unsorted and high sort acquisitions maintain edge definition. Breath‐hold imaging is potentially superior to nonbreath‐hold imaging in liver lesion contrast and edge definition, but is more sensitive to in

ISSN:0740-3194    

DOI:10.1002/mrm.1910330102

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

年代:1995

数据来源: WILEY

摘要:

Abstract1H NMR localized spectroscopy (STEAM), combined with echocardiography (ECG), respiratory gating, and water and fat suppression, was used to quantify silicone concentrations in the liver of women with silicone gel‐filled breast implants. Localized spectroscopy was performed on 15 patients with silicone gel‐filled breast prostheses and on eight volunteers with no implants. The1H spectra in the liver of patients showed silicone resonances from 0.3 to −0.8 ppm, attributable to protons in the methyl groups of silicone. The presence of silicone in the liver could first be detected 3–4 years after breast prostheses implantation. No correlation between silicone concentrations and implantation times was observed. However, our results indicated that silicone concentrations may reflect implant integrity: detectable silicone concentrations in the liver appeared to be higher when the implants were ruptured than when the implants appeared intact. Moreover, new resonances in the range of −2.6 to −4 ppm were observed in most patients after long‐term implantation. As these species increase with implantation time, the new resonances may reflect chemically changed silicone (paramag‐netically shifted silicon complexes bound to iron) accumulated over time. The sensitivity of1H NMR localized spectroscopy is sufficient to detect silicon concentrations as low as 0.20 mM.Results from one patient whose implants had been removed 14 months prior to the NMR examination showed no detectable silicone in the liver, indicating that it may have been excreted via bile or degraded to silica and high coordinated silicon complexes. Quantitative1H localized spectroscopy of the liver in women with silicone gel‐filled breast implants may provide valuable information concerning silicone accumulation and degradationin vivo, as well as about the kinetics of its elimination from the body afte

ISSN:0740-3194    

DOI:10.1002/mrm.1910330103

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

年代:1995

数据来源: WILEY

摘要:

AbstractBreath‐hold MR cholangio‐pancreaticography using the RARE method was evaluated as a noninvasive alternative to direct cholangio‐pancreaticography in 30 healthy volunteers and in 30 patients with various diseases of the respective duct systems. In contrast to 3D MR cholangiography, RARE MRCP generates projection images requiring a 4‐s acquisition time and no postprocessing. Diagnostic information gained from the cholangio‐pancreaticograms was fully equivalent to that of conventional x‐ray imaging by invasive procedures. Additional information was gained whenever endoscopic access was impossible and/or cystic malformations w

ISSN:0740-3194    

DOI:10.1002/mrm.1910330104

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

年代:1995

数据来源: WILEY

摘要:

AbstractApplication of a slice‐selective frequency modulated radio‐frequency excitation pulse in a magnetic resonance (MR) imaging experiment creates a quadratic phase profile along the direction of slice selection. This quadratic phase profile inherently localizes the signal contribution to its vertex, which can be shifted with the application of a linear magnetic field gradient. Different methods for reconstruction of the spatial profile are discussed. The point spread functions of these reconstructions are similar to that of conventional Fourier transforms; one important difference is the elimination of aliasing at the expense of MR signal amplitude when performing ‘local,’ or limited, reconstruction. Limited reconstruction together with spatially limited excitation combines some of the advantages of both three‐dimensional phase‐encoded and two‐dimensional multislice techniques in appropriate situations. Applications discussed are three‐dimensional gradient echo experiments applied to time of flight MR angiography andT2‐weighte

ISSN:0740-3194    

DOI:10.1002/mrm.1910330105

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

年代:1995

数据来源: WILEY

摘要:

AbstractWe introduce a fast and robust spatial‐spectral encoding method, which enables acquisition of high resolution short echo time (13 ms) proton spectroscopic images from human brain with acquisition times as short as 64 s when using surface coils. The encoding scheme, which was implemented on a clinical 1.5 Tesla whole body scanner, is a modification of an echo‐planar spectroscopic imaging method originally proposed by MansfieldMagn. Reson. Med.1, 370–386 (1984), and utilizes a series of read‐out gradients to simultaneously encode spatial and spectral information. Superficial lipid signals are suppressed by a novel double outer volume suppression along the contours of the brain. The spectral resolution and the signal‐to‐noise per unit time and unit volume from resonances such as N‐acetyl aspartate, choline, creatine, and inositol are comparable with those obtained with conventional methods. The short encoding time of this technique enhances the flexibility ofin vivospectroscopic imaging by reducing motion artifacts and allowing acquisition of multiple data sets with different param

ISSN:0740-3194    

DOI:10.1002/mrm.1910330106

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe anisotropy of the water diffusion tensor inside brain causes contrast in diffusion images, which depends on the relative orientation of the diffusion gradients and the subject. Because the trace of a tensor is invariant upon rotation, measurement of this trace can reduce the orientation effect. A family of imaging pulse sequences is presented in which the signal intensity is weighted by the trace of the diffusion tensor in a single scan. The methods are demonstrated for chicken gizzard in several orientations with respect to the gradient frame of reference, and for ischemic injury in cat brain after middle cerebral artery occlusion. The sensitivity of the techniques to the presence of background gradients is measured and discussed in detail. As a result, pulse sequences are suggested that provide reliable diffusion constants in both homogeneous and inhomogeneous magnetic fields. The efficiency of the techniques for clinical application is also evaluated.

ISSN:0740-3194    

DOI:10.1002/mrm.1910330107

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

年代:1995

数据来源: WILEY

摘要:

AbstractA spin‐echo method is presented for obtaining high resolution,13C coupled, proton spectra of lactate and alanine in intact, beating rat hearts. All hearts were depleted of glycogen prior to prolonged perfusion with either 10 mM unenriched glucose or [1−13C]glucose to restore glycogen. These two groups of hearts were then examined by1H NMR during prolonged global (zero flow) or low pressure (low flow) ischemia. During global ischemia, lactate was derived from both glucose and glycogen, with endogenous glycogen contributing twice as much lactate as exogenous glucose. During low perfusion pressure ischemia, however, lactate was derived exclusively from exogenous glucose. The entire pool of lactate (both 12C and 13C) was visible by NMR in intact, glucose perfused hearts while alanine was not detected. However, upon adding 10 mM pyruvate to the perfusate, the entire alanine pool became NMR visible while some of the lactate became NMR invisible. These observations indicate that the NMR visibility of small, usually highly mobile metabolites such as alanine and lactate is not always 100% in intact hearts and that the NMR visibility of these molecules may depend upon which exogenous substrate is presented to the he

ISSN:0740-3194    

DOI:10.1002/mrm.1910330108

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn the elderly, asymptomatic white matter hyperintensities are common on T2‐weighted magnetic resonance imaging (MRI). Insymptomaticpatients, such MRI appearances correlate with varied postmortem findings including demyelination or stroke. What structural correlates underlie the T2hyperintensities in patients whose lesions are asymptomatic is controversial. Therefore, in order to investigate the underlying metabolism and perfusion in white matter lesions (exhibiting T2hyperintensity), 13 patients underwent proton magnetic resonance spectroscopy and dynamic gadolinium‐DTPA perfusion‐weighted MR imaging. N‐acetyl aspartate (NA) levels were reduced in the lesions compared with age‐matched controls (P = 0.031), implying neuronal/axonal loss. Creatine levels were also reduced (P = 0.001). Choline levels were unchanged in the lesions. Lactate was identified in the lesions of 5 of the 13 patients. Although not statistically significant, perfusion studies exhibited a trend toward lower cerebral blood volumes in patients with high grade extracranial carotid stenosis and lactate‐containing lesions. These findings suggest that neuronal/axonal loss underlies the majority of T2‐weighted asymptomatic lesions in the older population, and in many cases these changes may be due to chr

ISSN:0740-3194    

DOI:10.1002/mrm.1910330109

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

年代:1995

数据来源: WILEY

摘要:

AbstractHigh‐speed diffusion spectroscopic imaging based on an echo‐planar technique is presented. A pair of diffusion gradients is applied prior to a rapidly oscillating magnetic field gradient which encodes both chemical shift and spatial information. By applying this technique to a phantom consisting of acetone and water, a diffusion spectroscopic image is obtained in about 15 min, about 64 times faster than the time required in the conventional method. The measured diffusion coefficients show good agreement with previously reported values. This kind of diffusion spectroscopic imaging is expected to provide a way to observe more specific metabol

ISSN:0740-3194    

DOI:10.1002/mrm.1910330110

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe noninvasive thermometry method is based on the temperature dependence of the proton resonance frequency (PRF). High‐quality temperature images can be obtained from phase information of standard gradient‐echo sequences with an accuracy of 0.2°C in phantoms. This work was focused on thein vivocapabilities of this method. An experimental setup was designed that allows a qualitativein vivoverification. The lower‐leg muscles of a volunteer were cooled and afterwards reheated with an external water bolus. The temperature of the bolus water varied between 17°C and 37°C. Thein vivotemperature images can be used to extract the temperature in muscle tissue. The data in the fat tissue are difficult to interpret because of the predominance of susceptibility effects. The results confirm the method's potential for hyperthermia

ISSN:0740-3194    

DOI:10.1002/mrm.1910330111

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

年代:1995

数据来源: WILEY