| PURPOSE:To study the diagnostic value of morphological and functional MBA combined with Gd-DTPA contrast-enhancement and dobutamine stress test for viable myocardium after acute infarction and its basis of Quantitative Pathology. MATERIALS AND METHODS: 10 rabbits underwent in situ coronary occlusion for 24 hours and 7 rabbits after a 40 minutes coronary artery occlusion followed by 1-2 hours of reperflision were examined with MRI, T1 and T2 weighted images were acquired through Turbo SE sequences plain scan and delayed contrast enhancement scan. Dynamic contrast enhancement scan and cine-MRI at rest and during dobutamine infusion (10μg·kg-1·min-1)were performed with 2D-FLASH sequences. 6 dogs after 4 hours left anterior descending coronary artery occlusion were examined with Myocardial contrast echocardiography (MCE), and 4 isolated hearts of them were examined with MRI. Regional flood flow was measwred with radioactive microspheres (999Tc-MAA) . lschemic regions and infarcted regions were defined respectively as Even's blue and 2 , 3, 5 triphenyltetrazolium chloride (TTC) negative regions. The MRI and MCE intensity and the content of water of normal ischemic, and infarcted myocardium were measured, The time-intensity curves of contrast dynamic enhancement of MRI and MCE were described. The end-diastolic and end-systolic wall thickness and dobutamine-induced systolic wall thickening of normal and injured myocardium -3- were measured. The thickening rate of wall and ejection fraction of left ventricular were calculated. The light and electron microscopy samples were obtained from normals ischemic and infarcted regions to observe the changes of histopathology and ultramicrostructure. The quantitative changes of myocardial myocytes, mitochondria and myocardial microvessels were determined by using methods of stereology , and the myocardial ultramicrostructure ingury was scored and graded through electron micrographs. RESULTS: The direct signs of acute myoeardial infarction were the T2 signal intensity rising in the diseased area and the local cardiac wall motion abnormality . The indirect signs were local cardiac wall thinning and the abnormal flow high signal in the ventrical near the abnormal regions . There were no significant difference in T1 signal intensity between normal and diseased regions before and after operation. T2 signal intensity of the diseased areas were significant higher than that of the normal areas. There were marked difference the signal intensity of normal myocardium compared with ischemic and infarcted myocardium, but there were no significant difference between ischemic and infarcted areas in reperftised acute myocardial infarction. 10 minutes after bolus injection of 0.05 mmol/kg Gd-DTPA, the signal intensity were marked higher in diseased areas than in normal areas. The signal intensity of ischemic areas were marked higher than that of infarcted areas in occlusive acute myocardial infarction, but there were no significant difference in reperfused acute myocardial infarction. The dynamic enhancement time-signal internsity curves of nomal.. ischemic and infarcted myocardium were different, all of them showed hyperenhancement during the first-pass, but during the second-pass and the delayed enhancement were different, and the stimulation interval-acoustic intensity curves of them were different. The shape of Gd-DTPA perfused...
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