Assessment of quadriceps muscle cross-sectional area by ultrasound extended-field-of-view imaging.

This study aimed to test the validity and reliability of an extended-field-of-view ultrasonography (EFOV) method for quadriceps muscle cross-sectional area (CSA) assessment. The CSA was measured at 10, 20, 30, 40 and 50% of the distance from the superior border of the patella to the medial aspect of anterior superior iliac spine by EFOV imaging and compared to the CSA measured by computed tomography (CT). Validity was tested by intra-class correlation (ICC) between the two methods and intra- and inter-experimenter and inter-day reliability were also examined. The ICC computed between the two techniques ranged between 0.951 and 0.998 (P < 0.000), but the 95% confidence intervals of the ICCs were in the acceptable range only for 30, 40 and 50% sections (0.842-0.999, 0.943-0.997 and 0.992-0.999, respectively). The standard error of the EFOV technique when compared to CT was 2.4, 4.3, 1.2, 1.2 and 0.6%, for 10, 20, 30, 40 and 50% sections, respectively. The coefficient of variation, showing intra- and inter-experimenter reliability, ranged from 0.6 to 2.7%. ICCs computed to assess the inter-day reliability were between 0.982 and 0.998 (95% confidence interval 0.892-1). When CSA was compared between sections statistically significant differences were found between them, regardless of the imaging technique used. Small standard errors of the measurement and high ICCs with the small confidence intervals suggest that, at proximal and mid-thigh sections, EFOV is a valid and reliable method to measure quadriceps muscle size.