Cardiac transplantations in dogs: evaluation with MR

To assess the potential of magnetic resonance (MR) imaging as an early predictor of cardiac transplant rejection, electrocardiogram-gated (ECG-gated) MR imaging was performed in 12 dogs with heterotopic cardiac transplants. Twenty-two examinations were performed in vivo, and ten postmortem examinations were performed immediately after the dogs were killed. Examinations were performed from 3 days to 14 weeks after transplantation. A 0.35-T superconducting magnet was used with the spin-echo pulse sequence. There was a significant increase (P less than .02 to P less than .001) in T2 relaxation times and intensity values for the transplanted hearts compared with native hearts at all time intervals after transplantation. T1 relaxation times of native and transplanted hearts showed no significant difference on the in vivo ECG-gated studies. However, T1 values calculated on post-mortem studies were significantly longer (P less than .005) in the transplanted compared with the native hearts. With longer pulse repetition and echo delay times, there was an increase in the contrast between the rejecting transplanted heart and the native heart. Thus, ECG-gated MR imaging using the spin-echo technique displays cardiac allograft rejection in vivo. The rejected myocardium in vivo is characterized by a prolonged T2 relaxation time.