摘要:

AbstractA method for the assessment of articular cartilage thickness based on MRI is presented and tts accuracy and reproducibil‐tty tested. Six specimens of human patellae were imaged, using a fat‐supressed FLASH 3D sequence, and sectioned with a high‐precision band saw. The reglonal dlstribution of articular cartilage thickness was determined from the MR images and from the anatomical sections (intervals of 0.5 mm). Wtth image analysis 50–90% of the image points were found to lie within exactly the same thickness interval in corresponding patterns, and tess than 17% deviated more than 0.5 mm. More than 85% of ali pixels were reproducible wtth MRI after new positioning of the Joint No influence of the read‐out direction and no important differences between areas of thin and thick cartilage could be detected. The authors conclude that MR chondro‐crassometry can provide accurate and reproducible Information on cartilag

ISSN:0740-3194    

DOI:10.1002/mrm.1910350112

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

年代:1996

数据来源: WILEY

摘要:

AbstractRelative perfusion, pO2, and bioreduction were measured simultaneouslyinwVo in tissues in mice by following changes in the intensity and shape of the EPR spectra of nitroxides injected directly into the tissues, using low frequency (1.1 GHz) localized EPR spectroscopy. Using normal and blood flow restricted gastrocnemius muscles it was shown that the decrease of the EPR signals of the nitroxides in tissues was due principally to perfusion, which redistributed the nitroxides. Changes in pO2were reflected by changes of the linewidth; only a perdeuterated nttroxide with a narrow line was an adequate indicator for this parameter. This technique was applied experimental murine tumors (MTG‐B and RIF‐1) to determine the perfusion and pO2in these relatively hypoxic model tumor systems. Using the paramagnetic properties of the nitroxides to enhance T1‐weighted MR images, heterogeneity in perfusion in individual tumors was demonst

ISSN:0740-3194    

DOI:10.1002/mrm.1910350113

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

年代:1996

数据来源: WILEY

摘要:

AbstractData obtained from functional magnetic resonance imaging are often limtted by a low signal‐to‐noise ratio. The time‐course data obtained from activated regions contain both system noise and physiological noise, primarily linked to the heart and respiratory rates, that are superimposed on task induced signals. Time averaging of a practical number of data sets is not very effective in improving the signal‐to‐noise ratio because netther system nor physiological noise is truly random. In this paper, a method is presented for fittering un‐wanted physiological fluctuations, including aliased signals that are formed as a result of long repetition time (TR) values. A pulse oximeter was used to obtain cardiac and respiratory Information during the scanning period. Fintte impulse response band‐reject digital fitters were designed to remove the physiological fluctuations. For comparison, cross‐correlation analyses were performed at the same tevel of statistical significance on both fittered and unfiltered data. We demonstrate that this method can improve the detection of weak signals without increasing the probability of

ISSN:0740-3194    

DOI:10.1002/mrm.1910350114

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

年代:1996

数据来源: WILEY

摘要:

AbstractA general model is developed for segmenting magnetic resonance images using vector decomposition and probabilfty techniques. Each voxel is assigned fractional volumes ofqtissues frompdifferently weighted images (q≤p+ 1) in the presence of partial‐volume mixing, random noise, and other tissues. Compared wtth the eigenimage method, fewer differently weighted images are needed for segmenting theqtissues, and the contrast‐to‐noise ratio in the calculated fractional volumes is improved. The model can produce com‐posrte tissue‐type images similar to that of the probability methods, by comparing the fractional volumes assigned to different tissues on each voxel. A three‐tissue (p= 2,q= 3) model is illustrated for segmenting three tissues from dual‐echo images. M provides statistical analysis to the algebraic method. A three‐compartment phantom is segmented for validation. Two clinical examp

ISSN:0740-3194    

DOI:10.1002/mrm.1910350115

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

年代:1996

数据来源: WILEY

摘要:

AbstractAnin vitrostudy was performed to investigate the effects of Boinhomogeneity on magnetic resonance images of flow. Controlled inhomogeneity gradients (G1) were applied and the magnitude of the artifacts produced was quantified for different echo delay times (TE). Both steady and pulsatile flows were examined. In the presence of an inhomogeneity gradient, signal loss is apparent if the flow is pulsatile and/or if the slice thickness is large. The signal loss increases with increasingTEand G1. With pulsatile flow, ghosting artifacts are also generated. These increase in intensity with increasingTEand G1.In vivo, field inhomogeneity due to susceptibility variations is large enough to produce these effects. Representative time‐of‐flight images obtained of a normal volunteer with two different TEs demonstrate the effectin vivo. Flow‐related signal loss and artifacts, therefore, increase with increasing TE independent of the moments of the applied grad

ISSN:0740-3194    

DOI:10.1002/mrm.1910350116

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

年代:1996

数据来源: WILEY

摘要:

AbstractTo detect reperfused ischemia of the rat intestine,T2‐weighted spin‐echo images were acquired, followed by T1‐weighted images before and after administration of polylysine‐Gd‐DTPA or Gd‐DTPA. Before administration of the contrast agent, the reperfused intestine was hyperintense onT2‐weighted images, and to a lesser extent on T1‐weighted images. After administration of polylysine‐Gd‐DTPA, the reperfused intestine enhanced more than the normal one, giving a significantly better contrast‐to‐noise (CNR) ratio than on unenhanced images. Gd‐DTPA induced the same enhancement of the reperfused and the normal intestine and the CNR was lower than on unenhancedT2‐weighted images. Reperfused intestinal ischemia could thus be better detected on polylysine‐Gd‐DTPA‐enhanced MR images than on unenhanced imag

ISSN:0740-3194    

DOI:10.1002/mrm.1910350117

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

年代:1996

数据来源: WILEY

摘要:

AbstractMany chemical solutions for use in magnetic resonance imaging phantoms have been reported in the literature. Each of these solutions has its application‐specific advantages and disadvantages. We propose a single reverse micelle phantom solution, which, although not a universal phantom solution, may find applications in testing of the radio frequency transmit and receive fields of an imaging coil, the homogeneity of the static magnetic field, and the suppression in a fat or water saturation imaging sequence. The solution is thermodynamically stable and biologically inert, it possesses a smaller standing wave artifact than water, and its overall spin lattice relaxation times may be adjuste

ISSN:0740-3194    

DOI:10.1002/mrm.1910350118

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

年代:1996

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910350119

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

年代:1996

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910350120

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

年代:1996

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910350101

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

年代:1996

数据来源: WILEY