Magnetic resonance imaging and histopathological analysis of experimental muscle injuries in a rabbit.

OBJECTIVE To investigate the correlation of magnetic resonance imaging (MRI) with histopathological changes, and to evaluate T2 mapping in assessing muscle trauma in a rabbit model of muscle injury. METHODS We divided 35 rabbits into seven groups that each represented a different time point after intramuscular hemorrhage and muscle injury. Hemorrhage was created by injecting autologous blood into the left legs, and muscle injury was created by scalpel incision of the biceps femoris of the right legs. At different time points, the rabbits underwent T1-weighted imaging and T2-weighted imaging (T1WI and T2WI) and T2 mapping. T2 relaxation times were measured, and the corresponding samples were evaluated for pathological changes RESULTS After 2 h, the intramuscular hemorrhage model demonstrated an increased signal intensity on both T1WI and T2WI. Histological examination showed erythrocytes within the muscle bundle. On days 1 and 3, the MRI signals were decreased, and there were no significant changes after day 7. From 2 h to 3 days, the muscle-injury model showed a high signal on both T1WI and T2WI. Corresponding pathological changes included rupture and edema of muscle fibers, and inflammation. The abnormal signals were reduced on day 7. After day 14, the T2WI intensity remained high. T1WI showed no abnormal changes, but some models showed a high signal, representing fresh bleeding and fatty tissue. T2 relaxation times were significantly different between the central and marginal regions, and between the marginal and normal regions. CONCLUSION MRI clearly demonstrates intramuscular hemorrhage and muscle injury, which correlate well with histopathological changes. T2 mapping is useful in assessing the extent of injury.