Magnetic resonance imaging in ischemic injury after heart transplantation in rats

Magnetic resonance imaging with and without gadolinium (Gd)-DTPA has been shown to enable detection of coronary occlusive ischemic injury and heart transplant rejection. This study was performed to examine findings on magnetic resonance images associated with ischemic injury after heart transplantation in rats. Magnetic resonance imaging was performed immediately before death in 22 rats, between 1 and 90 days after isogeneic (Lewis grafts, Lewis host; or Fischer graft, Fischer host) heterotopic heart transplantation. Ischemic injury, characterized histologically by cellular infiltration or myocyte necrosis, correlated inversely with graft duration. It was graded as moderate to severe in 5 of 5 rats killed at 1 to 2 days, and in 0 of 9 animals killed at greater than or equal to 30 days. T2-weighted myocardial signal intensity (TR = 2.3 seconds; TE = 90 milliseconds) correlated inversely with graft duration and was significantly greater in grafts with moderate or severe histologic abnormalities than in grafts with absent or minimal changes. GD-DTPA-induced myocardial enhancement was judged on T1-weighted images (TR = 0.5 seconds, TE = 25 milliseconds). Areas of intense enhancement were present in all seven grafts with severe histologic abnormalities, but in only 3 of 15 grafts with absent to moderate histologic abnormalities. In conclusion, after heart transplantation in rats, ischemic injury causes increased T2-weighted signal intensity and Gd-DTPA-induced T1-weighted signal enhancement--findings similar to those described in transient coronary occlusive ischemia and in graft rejection. Abnormalities seen on magnetic resonance images during the first few posttransplant weeks may represent ischemic injury rather than rejection.