Magnetic resonance imaging (MRI) was performed on 16 muscle flaps and eight jejunal segments in dogs to assess its usefulness in detecting vascular occlusion. Arterial or venous occlusion was carried out in 11 muscles and six bowel segments, with the remaining sham flaps serving as controls. Imaging was performed over 2 hours using a spin echo pulse sequence with T2 weighting. Arterial occlusions in muscles resulted in T2 values 15-30% higher than controls, while venous occlusion produced T2 values 55-75% higher than controls. Differences became significant (p less than 0.05) at 10 minutes after venous occlusion and at 35 minutes after arterial occlusion. Differences between occluded and control bowel segments, although demonstrating a similar trend, failed to reach statistical significance in this preliminary study. The authors conclude that magnetic resonance imaging may be a valuable method for early detection of venous and arterial occlusion in muscle flaps. Further study may also demonstrate this technique to be useful in the diagnosis of ischemic bowel.
A totally automated rule-based expert system has been developed for interpreting three-dimensional (3D) myocardial perfusion distributions obtained from thallium-201 tomographic images. Over two hundred heuristic rules have been generated for interpreting stress perfusion defects and their characteristics. Perfusion defects were identified in terms of pixels below gender-matched "normal" patient distributions; perfusion defects which reversed with time were identified in terms pixels above gender-matched "normal" patient distributions. The expert system automatically calculates certainty factors from each perfusion defect to provide the relative certainty associated with the location and shape of each myocardial perfusion defect, as well as with the presence, location, and character of each coronary lesion.The current expert system, which was developed after reviewing 294 nuclear tomographic perfusion studies, is being tested and refined using a pilot group of 20 patients.
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