Age‐related differences in diffusion tensor indices and fiber architecture in the medial and lateral gastrocnemius

Abstract

Purpose To investigate age related changes in diffusion tensor indices and fiber architecture of the medial and lateral gastrocnemius (MG and LG) muscles using diffusion tensor imaging (DTI). Materials and Methods The lower leg of five young and five senior subjects was scanned at 3T and DTI indices extracted using three methods: ROI, histogram and tract based. Tracked fibers were automatically edited to ensure physiologically relevant tracks. Pennation angles were measured with respect to the deep and superficial aponeuroses of both muscles. Results The three methods provided internally consistent measures of the DTI indices (correlation coefficient in the range of 0.90-0.99). The primary, secondary and tertiary eigenvalues in the MG and LG increased significantly in the senior cohort (p<0.05), while the small increase in fractional anisotropy (FA) with age was not significant (MG/LG: p=0.39/0.85; 95% CI:[ −0.059/-0.056, 0.116/0.064]). Fiber lengths of MG fibers originating distally were significantly decreased in seniors (p<0.05) while pennation angles decreased with age in the MG and LG but this was not significant. Conclusion Fiber atrophy and increased fibrosis have opposing effects on the diffusion indices resulting in a complicated dependence with aging. Fiber architectural changes could play a role in determining aging muscle function.

Age-related differences in the response of leg muscle cross-sectional area and water diffusivity measures to a period of supine rest

“…In agreement with previous work that documented higher eigenvalues in women compared to men, our sample had higher mean k 1 , k 2 , and k 3 values at the TibA, SOL, MG, and LG, compared men [14]. Likewise, our findings are in line with a recent study that compared DTI measures in MG and LG of five young (mean age = 31.6 years) and five older (mean age = 83.4 years) Japanese women [15]. Sinha et al [15] reported higher eigenvalues in older women that were explained using a model that builds upon the existing interpretation of DTI measures [40,41].…”

“…Likewise, our findings are in line with a recent study that compared DTI measures in MG and LG of five young (mean age = 31.6 years) and five older (mean age = 83.4 years) Japanese women [15]. Sinha et al [15] reported higher eigenvalues in older women that were explained using a model that builds upon the existing interpretation of DTI measures [40,41]. Within the revised model, eigenvalues represent diffusion occurring in both intracellular and extracellular spaces [15].…”

“…This observation may be attributed to the complex architecture of the SOL and the inclusion of more slices for analysis, which capture the changes in muscle fiber orientation with the five-slice ROI [36]. A consideration for measuring aged muscle is fat infiltration, which leads to partial volume effects and influences the quantification of DTI measures by bringing ADC closer to zero and inflating FA values [15,37]. Although our ROIs were carefully selected to exclude visible fat that was apparent among the older women, membrane permeability, connective tissue, and other macromolecules are known to affect water diffusivity [15,37,38].…”

“…A consideration for measuring aged muscle is fat infiltration, which leads to partial volume effects and influences the quantification of DTI measures by bringing ADC closer to zero and inflating FA values [15,37]. Although our ROIs were carefully selected to exclude visible fat that was apparent among the older women, membrane permeability, connective tissue, and other macromolecules are known to affect water diffusivity [15,37,38]. The distribution of these morphological attributes is less homogenous within aging muscle compared to young adult muscle.…”

“…A study of age-related changes in DTI measures found lower eigenvalues and reduced FA in the tibialis anterior in older men [14]. In contrast, a more recent study reported that older women had higher eigenvalues and FA in the medial and lateral heads of the gastrocnemius compared to young women [15]. The discrepancy in these reports suggests that there is a need to extend our knowledge related to agerelated change in muscle microstructure using DTI.…”