Diffusion tensor imaging and diffusion modeling: Application to monitoring changes in the medial gastrocnemius in disuse atrophy induced by unilateral limb suspension.

BACKGROUND:Diffusion tensor imaging (DTI) assesses underlying tissue microstructure, and has been applied to studying skeletal muscle. Unloading of the lower leg causes decreases in muscle force, mass, and muscle protein synthesis as well as changes in muscle architecture. PURPOSE:To monitor the change in DTI indices in the medial gastrocnemius (MG) after 4-week unilateral limb suspension (ULLS) and to explore the feasibility of extracting tissue microstructural parameters based on a two-compartment diffusion model. STUDY TYPE:Prospective cohort study. SUBJECTS:Seven moderately active subjects (29.1 ± 5.7 years). FIELD STRENGTH/SEQUENCE:3T, single-shot fat-suppressed echo planar spin echo sequence. ASSESSMENT:Suspension-related changes in the DTI indices (eigenvalues: λ1 , λ2 , λ3 , fractional anisotropy; coefficient of planarity) were statistically analyzed. Changes in model-derived tissue parameters (muscle fiber circularity and diameter, intracellular volume fraction, and residence time) after suspension are qualitatively discussed. STATISTICAL TESTS:Changes in the DTI indices of the MG between pre- and postsuspension were assessed using repeated-measures two-way analysis of variance (ANOVA). RESULTS:All the eigenvalues (λ1 : P = 0.025, λ2 : P = 0.035, λ3 : P = 0.049) as well as anisotropic diffusion coefficient (P = 0.029) were significantly smaller post-ULLS. Diffusion modeling revealed that fibers were more circular (circularity index increased from 0.55 to 0.95) with a smaller diameter (diameter decreased from 82-60 μm) postsuspension. DATA CONCLUSION:We have shown that DTI indices change with disuse and modeling can relate these voxel level changes to changes in the tissue microarchitecture. LEVEL OF EVIDENCE:2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018.