G.P.117: NMR based biomarkers to study age-related degenerative changes in the human quadriceps

Abstract

Age-related sarcopenia is a major health issue. To improve the quality of life of elderly persons, it is important to characterize and understand age-associated structural changes in the skeletal muscle. In this work, we used several NMR biomarkers to monitor the effect of age as well as physical activity on the quadriceps muscle properties. We scanned 96 subjects composed of 34 young adults between 19 and 27 yrs old and 63 older adults between 69 and 80 yrs old. For the elderly group, we considered two sub-groups, active (<i>n</i>=31) and sedentary (<i>n</i>=32). To compute T2 maps, we run, a standard multi-slice multi-echo (MSME) sequence with: TR=3000ms, 17 echoes train with TEs ranging from 9.5ms to 161ms, pixel size=1.4 mm², slices thickness=10mm. Water T2 maps were generated using a tri-exponential fit model. For 3-point Dixon fat quantification, we acquired three 3D gradient echo volumes with (TR=10ms, TE=2.75/3.95/5.15ms, flip angle=3°, voxel size=1×1×5mm³). In each quadriceps muscle, we calculated: water T2 mean value, water T2 heterogeneity and the fat ratio. Results of statistical analysis (ANOVA) showed that water T2 values, were higher in the elderly group (<i>p</i><0.05). Furthermore, a regular physical activity maintained lower muscle T2 values (<i>p</i><0.05). Regarding the coefficient of variation of water T2, it was higher for the older group and also for sedentary when compared to the active ones. The same trend was observed for fat ratio. It is tempting to relate T2 increase with age to the progressive atrophy and rarefaction of type II fibers and to the higher proportion of extracellular space in progressively predominant type I oxidative fibers. It also would make sense to attribute increased T2 heterogeneities to some degree of tissue disorganisation, such as the development of interstitial fibrosis. It would be the case with aging, as indicated by higher heterogeneity indices in the elderly group. These processes were partly slowed down by physical activity.