Ultrasound image resolution influences analysis of skeletal muscle composition

INTRODUCTION: Analysis of muscle composition using ultrasound requires standardization of several equipment settings (i.e. gain). However, the influence of image resolution, which is altered by imaging depth, on measures of muscle composition is unknown. METHODS: We analysed rectus femoris muscle composition using ultrasound images captured from 32 males and females (aged 28 ± 5 years) at depths of 9.0, 7.3, 5.9 and 4.7 cm. The transducer's orientation was fixed using a clamp during image acquisition to minimize movement. Across each image resolution, a region of interest encompassing the same anatomical area within the muscle was used for muscle composition analysis. Muscle composition was analysed using a combination of first-, second- and higher-order texture features. Muscle composition agreement across image resolutions was evaluated using a one-way ANOVA and intraclass correlation coefficients (ICC). RESULTS: Most muscle composition features displayed differences due to image resolution (p < .05). ICCs demonstrated poor-to-good agreement across different image resolutions. In general, higher resolution images (i.e. shallower imaging depth) demonstrated better agreement (ICC > 0.90) compared to lower resolution images. CONCLUSIONS: Ultrasound image resolution influences muscle composition analysis. Image resolution should be fixed within and between individuals when evaluating muscle composition using ultrasound.