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 (ICC3,2), within-subject coefficient of variation CVw-s$$ \left({\mathrm{CV}}_{\mathrm{w}-\mathrm{s}}\right) $$, standard error of measurement (SEM), and minimal detectable change (MDC). Mean mCSA for RF was mean +/- SD, 7.5 +/- 2.7 cm2 on both test days, with a numeric difference of 0.8%. Mean VL mCSA was 20.6 +/- 6.6 cm2 and 20.5 +/- 6.5 cm2 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. CVw-s$$ {\mathrm{CV}}_{\mathrm{w}-\mathrm{s}} $$ was 2.6% for RF and 2.4% for VL. SEM was 0.2 cm2 for RF and 0.5 cm2 for VL. MDC was 0.4 cm2 for RF and 1.3 cm2 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.