Validity Of Lower Leg Muscle Cross-sectional Area Measurements Using Ultrasound Imaging Compared To MRI

Abstract

Quantification of muscle size can enhance assessment of musculoskeletal conditions in both clinical and research settings. Magnetic resonance imaging (MRI) is often considered a gold standard for assessing muscle morphology, while ultrasound imaging (US) is gaining recognition for its utility in musculoskeletal imaging. In the lower leg and foot, there is a need to validate US based assessment of muscle size compared to MRI in musculoskeletal imaging. PURPOSE: To validate muscle size measured from US images compared to images captured using MRI. METHODS: Eighteen people (female n = 10, age = 31 ± 15 y, ht =176 ± 11 cm, wt = 76 ± 18 kg) had their leg muscle size of the tibialis anterior (TA), tibialis posterior (TP), and fibularis longus (FL) assessed with both US and MRI at 30% of the distance from the knee joint line to the lateral malleolus, while the flexor digitorum longus (FDL) and fibularis brevis (FB) were assessed at the 50% point along the same line. Cross sectional area (CSA) was manually traced from two separate US and MRI images for each muscle and averages were calculated. Statistical analysis included comparison of MRI and US measures using the Pearson product correlation. RESULTS: High correlations were seen between US and MRI size measurements (TA r = 0.90, p=0.003; TP r = 0.94, p=0.000; FL r = 0.97, p=0.000; FDL r = 0.86, p=0.000; FB FDL r = 0.94, p=0.000. CSAs from MRI were larger than those measured from US by an average of 0.17 cm2. CONCLUSION: Measurements of CSA using US in selected leg muscles were comparable to those on MRI scans with MRI assessment larger than US. This difference may be due to difficulty in seeing fascial borders in the MRI images. Muscle CSA measurements from US appear to provide valid assessment of leg muscle size and may be used in clinical and research settings to quantify muscle morphology.