Multidetector CT Measurement of Myocardial Extracellular Volume in Acute Patchy and Contiguous Infarction: Validation with Microscopic Measurement

Purpose: To provide proof of concept that expansion of myocardial extracellular volume (MECV), measured at contrast material- enhanced multidetector computed tomography (CT), can be used as a (a) marker for viability based on histologic confirmation and (b) predictor of severity of myocardial injury. Materials and Methods: Animals cared for in compliance with Institutional Animal Care and Use Committee served as controls (group 1, n = 6) or were subjected to microinfarction by using 16- mm3 (60 000 count) microemboli (group 2) and 32mm3 (120 000 count) microemboli (group 3), contiguous infarct with left anterior descending artery (LAD) occlusion followed by reperfusion (group 4), or the combination of LAD occlusion and 32- mm3 microemboli followed by reperfusion (group 5) (n = 7 per group). MECV calculations were based on regional measurements of signal attenuation at contrast- enhanced multidetector CT and counterstaining of infarct at microscopy. Two- way analysis of variance and Student t tests were used to determine significant differences (P,.05). Data were presented as means 6 standard deviations. Results: Mean signal attenuation at equilibrium state of contrast media distribution (10 minutes) was significantly different among blood (137 HU 6 10), myocardial muscle (77 HU 6 12, P,.05), and skeletal muscle (35 HU 6 12, P,.05). Patchy microinfarct, contiguous infarct, and microinfarct with preexisting contiguous infarct can be differentiated on the basis of mean MECV (24% 6 3 [group 1] vs 36% 6 3 [group 2], P,.01, and 55% 6 5 [group 4], 56% 6 4 [group 5] vs 41% 6 3 [group 3], P,.05). Microscopy measurements confirmed multidetector CT quantitative measurements and differences in patterns of infarct caused by obstruction of major and minor coronary arteries. Regression analysis revealed excellent correlation between regional MECV using multidetector CT and microscopy (r2 = 0.92). Conclusion: Contrast- enhanced multidetector CT is a suitable noninvasive imaging technique for assessing MECV in acute patchy and contiguous infarct caused by obstruction of major and minor coronary vessels.