Magnetic Resonance Diffusion Tensor Imaging Study Of Skeletal Muscle With Ischemia Injury

Diffusion tensor imaging (DTI) is a powerful tool to evaluate skeletal muscle structure by monitoring alterations of DTI indices, such as fractional anisotropy (FA), mean (MD), axial (λ∥) and radial (λ⊥) diffusivities, and fiber architecture. However, most of the previous studies were performed on adult species and the impact of age on injured muscle regeneration remains unclear. In this study, microstructural alterations of skeletal muscle with ischemia damage were evaluated in young and old rats using DTI, which may facilitate better understanding of muscle repair process.Ten old (～11months), three adult (-3months) and ten young (～4weeks) rats were induced ischemia in hind limbs by permanently ligating the abdominal aorta. MRI studies were performed before,2hours, and2,9, and21days after the surgery with multi-slice readout-segmented EPI DTI sequence on a3T MR imager. For each time point,6young and old rats were scanned and1was sacrificed after imaging for H&E histological analysis in each group. FA, mean and directional diffusivities, and the extent of fiber disarray (DA) were calculated on each slice with bones and large vessels excluded. ANOVA with post hoc Bonferroni’s multiple comparison tests were performed with p<0.05as significance.3D fiber tracts were reconstructed using MedINRIA. Fiber number and length were measured and normalized to those of control in each adult rat.For young group, DA and FA increased significantly after the surgery at day2, and mean and directional diffusivities substantially decreased2hours after ischemia induction. The DTI indices then started to recovery. Specifically, DA and λ∥at day9, and FA, MD and λ⊥at day21renormalize to normal values. For old group, FA and DA increased apparently at day9, and mean and directional diffusivities reduced continuously after ischemia surgery till day9. Then, all these DTI indices became normal at day21.In current study, increase of FA was observed in both groups after the ischemia surgery, which may be related with the augmentation of intracellular space caused by edema or inflammation. Mean and directional diffusivities were found to decrease which may arise from the shrinkage of extracellular space. DA increment may result from disorganized fiber architecture after ischemia damage. Young group was observed to be more sensitive to ischemia and recovered more rapidly than the old one, confirming the age-related variation of muscle regeneration process. These findings may provide additional information for understanding of muscle recovery evolution as well as developing new clinical treatment strategies.