Identification of cardiac rejection with magnetic resonance imaging in heterotopic heart transplantation model.

It is important to evaluate the severity and extent of cardiac rejection in heart transplantations. Eight heterotopic heart transplantations using mongrel dogs were performed, and grated magnetic resonance imaging (MRI) of the donor hearts was carried out. High signal intensity was obtained in the rejected myocardium at the time of cardiac rejection, especially from the right ventricular wall to the intraventricular septal wall compared with the left ventricular posterolateral wall. In addition, MRI was performed in the excised heart. High signal intensity was also observed in the same region of the excised donor hearts. The histopathological rejection scores were well in agreement with prolonged T1 and T2 relaxation times; severe and mild rejection of the myocardium were distinguished by the T1 and T2 relaxation times. Our results suggest that MRI is able to visualize the transplanted myocardium undergoing rejection and that the right ventricular wall is more sensitive to cardiac rejection than the left. MRI may allow noninvasive evaluation of the severity and extent of cardiac rejection.