Panoramic ultrasound requires a trained operator and specific evaluation sites to maximize its sensitivity: A comprehensive analysis of the measurement errors

•Validity and repeatability of panoramic ultrasound to measure the ACSA of muscles that make up the quadriceps femoris are highly dependent on the operator's experience and the region of the thigh.•The implementation of this technique by a trained operator minimizes the measurement errors, which are mainly made during the image acquisition.•Operators are encouraged to measure quadriceps femoris ACSA at the central thigh regions (40–50%) if single-site evaluations.•Evaluations composed by multiple assessment sites or focused only on a single muscle within the quadriceps femoris would benefit from specific evaluation regions: VMVI (30–40%), VL (40–50%), and RF (50–60%). This study aimed to examine the validity and repeatability of panoramic ultrasound to evaluate the anatomical cross-sectional area (ACSA) of quadriceps femoris muscles. Specifically, we aimed to quantify the errors generated during the image acquisition and analysis (repeatability), as well as when comparing with magnetic resonance imaging (MRI) (validity). Moreover, we analyzed the influence of the operator's experience and the region of the thigh, on these errors. Both thighs of 16 subjects were included. The validity and repeatability study quantified the errors made by two operators (trained and novice) when measuring ACSA of vastus lateralis (VL), vastus medialis-intermedius (VMVI), and rectus femoris (RF), in six thigh regions (from 20 to 70%). Two ACSA images were acquired 5 min apart to examine acquisition errors, whereas acquisition #1 was analyzed twice to quantify analysis errors. Thereafter, ACSA of acquisition #1 was compared with that measured by MRI. Statistics included the standard error of measurement (SEM) expressed in absolute (cm2) and relative terms (%) as a coefficient of variation (CV). Measurement errors were lower for the trained operator than for the novice: Acquisition (SEM = 0.05 – 0.78 vs. 0.25 – 1.42 cm2), analysis (SEM = 0.13 – 1.93 vs. 0.30 – 3.05 cm2) and compared-with-MRI (SEM = 0.13 – 1.93 vs. 0.30 – 3.05 cm2). Regions with the lowest errors were those located at the middle of the thigh (40–50%), although slight between-muscle differences were found: VMVI (30–40%), VL (40–50%), RF (50–60%). These findings suggest that the accurate implementation of panoramic ultrasound to measure ACSA of quadriceps femoris muscles requires a trained operator and specific evaluation sites.