Live Pulse-Echo Speed-of-Sound Estimation for Quality Assessment of Large Muscles in Humans

OBJECTIVE: Muscle quality is broadly regarded as an indicator of physical health. Conventionally, ultrasound metrics such as echogenicity have been derived to assess muscle quality, but these measures are prone to changes in ultrasound hardware and operator skill. In contrast, tissue speed-of-sound (SoS) is an intrinsic property that can potentially act as a more robust biomarker for muscle quality. In this work, we demonstrate that muscle SoS can be effectively assessed in real-time via a novel pulse-echo ultrasound technique. METHODS: We conducted a study on the biceps, quadriceps, and calf muscles of 40 human volunteers (Sex: 21 M, 19 F; Age 30.3 ± 10.4 years) and compared muscle SoS to anthropometric and demographic factors [body-mass index (BMI), sex, physical activity]. SoS measurements were obtained using an image-guided global SoS estimation tool that was implemented on a portable research scanner (US4R-Lite). RESULTS: Significant linear correlations were observed between BMI and muscle SoS in the biceps (M: r = -0.75, F: r = -0.75), quadriceps (M: r = -0.54, F: r = -0.70), and calf (M: r = -0.59, F: r = -0.77). Unpaired t-tests demonstrated SoS differences between male and female muscles for all muscle groups measured (p < 0.001 for all muscles). A significant correlation was found for males only (biceps: M: r = 0.50, F: r = 0.009) between SoS and self-reported physical activity. CONCLUSION: Our study is the first to report muscle SoS in the biceps and quadriceps, as pulse-echo SoS estimation permits measurement in muscles inaccessible to previous devices. Overall, our study demonstrates the potential for clinical translation and application of the tissue SoS as a robust muscle quality biomarker with real-time performance.