EARLY DETECTION OF REGIONAL MYOCARDIAL-ISCHEMIA IN EX-VIVO PIGLET HEARTS - MR-IMAGING WITH MAGNETIZATION-TRANSFER

The effects of regional myocardial ischemia and reperfusion on magneti zation transfer (MT) contrast were investigated in an ex vivo perfused piglet heart model. The extent of the ischemic area was defined with perfusion magnetic resonance (MR) studies performed with use of extrac ellular contrast agents. Relative MT contrast was calculated for a tot al of 106 regions of interest in nine hearts. In the areas defined as being severely ischemic in the perfusion studies, a small but signific ant increase in the MT contrast of 18% +/- 9 (standard deviation) (n = 35) was found as early as 10 minutes after the start of ischemia. Thi s contrast difference was reduced to 11% +/- 10 after 2 hours of total occlusion. The contrast between normal and ischemic tissue can be exp lained in part by the effect of inflowing blood, which leads to change s in both equilibrium magnetization and the apparent T1 of the perfuse d tissue. However, theoretical estimation suggests that these flow-rel ated changes would produce a maximal relative change in MT contrast of approximately 4%. The most likely explanation for the rest of the obs erved changes is alteration in the distribution of cellular water rela ted to the so-called intracellular edema that is known to be associate d with the acute phase of myocardial ischemia.