Muscle thickness and echo intensity measurements of the rectus femoris muscle of healthy subjects: Intra and interrater reliability of transducer tilt during ultrasound

This study aimed to assess the intra and interrater reliability of transducer tilt during the ultrasound (US) measurements of the muscle thickness and the echo intensity of the rectus femoris muscle (RF). Fourteen healthy male subjects (20.8 ± 0.8 years) participated in this study. The transducer tilt was measured using a digital angle gauge (°) during US. Two experimenters took two images to measure the muscle thickness (mm) and the echo intensity (a.u.: arbitrary unit). The intra and interclass correlation coefficient (ICC), standard error of measurement (SEM), and minimal detectable change (MDC) were also calculated. These measurements were immediately repeated. The ICC for the intrarater reliability for the transducer tilt, muscle thickness, and echo intensity were 0.96 (SEM: 0.9°, MDC: 2.6°), 0.99 (SEM: 0.4 mm, MDC: 0.1 mm), and 0.97 (SEM: 0.6 a.u., MDC: 1.7 a.u.), respectively. The ICC for the interrater reliability for the transducer tilt, muscle thickness, and echo intensity were 0.40 (SEM: 4.0°, MDC: 11.1°), 0.96 (SEM: 0.7 mm, MDC: 2.0 mm), and 0.95 (SEM: 0.9 a.u., MDC: 2.4 a.u.), respectively. The intrarater reliability of the transducer tilt was reliable, but the interrater reliability was questionable. Meanwhile, both the intra- and interrater reliability of the muscle thickness and the echo intensity were reliable.