Localization of ischemia in canine hearts using tagged rotated long axis MR images, endocardial surface stretch and wall thickening.

Tagged magnetic resonance imaging allows the noninvasive measurement of regional systolic myocardial deformations and helps localize ischemic regions in the left ventricle (LV). The objective of this study was to evaluate the potential accuracy of localizing ischemic regions in the LV using endocardial and epicardial data obtained from tagged rotated long axis images. Nine canine hearts with acute ischemia induced by coronary artery ligation were imaged along four long axis planes rotated around the LV long axis, at end diastole and end systole. Each plane was tagged by four parallel lines perpendicular to the LV long axis. Tracing the endocardial and epicardial intersection points of the tag lines, 24 myocardial cuboids were reconstructed for each LV at end diastole and end systole. Endocardial surface stretch and transmural systolic thickening were calculated for each cuboid. The functional data were compared to perfusion data obtained from postmortem monastral blue staining of the heart. The ability of each functional index to discriminate between ischemic and non-ischemic regions was assessed using the "t"-statistic. The potential accuracy in localizing ischemia was evaluated by studying the corresponding sensitivity-specificity curves. The results demonstrate that adequate discrimination and localization can be obtained with both functional indices. However, endocardial surface stretch is advantageous as it uses only endocardial data and can save 50% of the post-processing time.