Intra-Rater Reliability of Panoramic Ultrasound Imaging for Determining Quadriceps Muscle Cross-Sectional Area in Middle-Aged and Elderly Adults

Panoramic ultrasound (US) is an extended field-of-view (EFOV) imaging technique that enables visualization of large-scale skeletal muscles. This technique has previously been found to produce valid and reliable quantifications of muscle morphology in primarily young male subjects. The purpose was to investigate the intra-rater between-session test–retest reliability of panoramic US imaging for determining vastus lateralis (VL) and rectus femoris (RF) cross-sectional area (mCSA) in healthy middle-aged to elderly adults. In this cross-sectional study, axial panoramic US images of the RF and VL muscles were captured in 23 healthy females and males aged 47 to 78. Assessed across two sessions 3–7 days apart, intra-rater reliability was evaluated by intraclass correlation coefficients (ICC _3,2), within-subject coefficient of variation (Formula presented.), standard error of measurement (SEM), and minimal detectable change (MDC). Mean mCSA for RF was mean ± SD, 7.5 ± 2.7 cm ² on both test days, with a numeric difference of 0.8%. Mean VL mCSA was 20.6 ± 6.6 cm ² and 20.5 ± 6.5 cm ² on test days 1 and 2, respectively. Test–retest ICC were: 0.997 (95% CI: 0.994–0.999) for RF and 0.995 (95% CI: 0.989–0.998) for VL. (Formula presented.) was 2.6% for RF and 2.4% for VL. SEM was 0.2 cm ² for RF and 0.5 cm ² for VL. MDC was 0.4 cm ² for RF and 1.3 cm ² for VL. In conclusion, panoramic EFOV US is a highly reliable imaging technique for assessing RF and VL mCSA in middle-aged and elderly adults. These findings endorse the clinical and research utility of EFOV US and its sensitivity for detecting even minor changes in skeletal muscle size.