Background: Skeletal muscle experiences both quantitative and qualitative changes with aging. Echo intensity (EI) of the skeletal muscle obtained by ultrasonography (US) has been considered to reflect muscle quality. This technique is noninvasive, easily accessible, and is relatively inexpensive than that of other imaging techniques such as computed tomography (CT). Previous studies have reported that EI is related to several physical performances. However, few studies have investigated the validity of EI against other imaging methods in case of imaging of the skeletal muscle. We compared quantitative and qualitative indices evaluated by the US and CT imaging systems to strengthen their validity.
Participants and methods: A total of 40 adults participated in this study: 19 young (10 men and 9 women; their mean (±SD) age was 22.7±1.5 years) and 21 older adults (13 men and 8 women; their mean age was 70.6±4.8 years). Both thighs of each participant were evaluated using US and CT imaging systems.
Results: With respect to the US indices, the young group had significantly higher muscle thickness (MT) of the front thigh (P<0.001) and lower EI (P=0.001) than that of the older group. With respect to the CT indices, the cross-sectional area (CSA) and mean CT value (Hounsfield unit [HU]) of the muscle were found to be significantly higher in the young group (P<0.001) than that of the older group, whereas the percentage of low-density muscle area (%LDMA) was found to be significantly higher in the older group (P<0.001) than that of the young group. A significant, strong, and positive correlation was observed between MT and CSA, which reflects the muscle quantity (r=0.774; P<0.001). With respect to the indices of muscle quality, we found significant and moderate correlations between EI and CT values (r=-0.502; P<0.001) and between EI and %LDMA (r=0.441; P<0.001). However, these correlations were found to be decreased in the older group [between EI and CT value (r=-0.363; P=0.018) and between EI and %LDMA (r=0.257; P=0.100)].
Conclusion: Results of this study indicate that the EI is moderately associated with muscle attenuation as assessed by CT, which means that higher EI at least partly reflects intramuscular lipid infiltration.
Keywords: CT value; echogenicity; low-density muscle area; muscle composition; muscle quality; ultrasound imaging.