The influence of ultrasound image depth and gain on skeletal muscle echo intensity

Echo intensity may associate with indicators of skeletal muscle quality, but investigators often use different methodological approaches that may alter echo intensity when acquiring B-mode ultrasound images. We examined the influence of image depth and gain settings on the interpretation of echo intensity. Thirty-six college-aged males and females participated. Ultrasound images of the vastus lateralis were captured in the sagittal plane. Images were captured at depths of 3.0, 3.5, 4.0, 4.5, 5.0, 6.0, and 7.0 cm and gain settings of 50 and 60 dB in random order. For both gain settings, echo intensity values were similar between 4.0 and 6.0 cm. At a gain of 50 dB, 7.0 cm demonstrated greater values than all other depths. At a gain of 60 dB, 7.0 cm displayed greater values compared to all other depths, but 3.0 cm displayed lower echo intensity values than other depths. Echo intensity was substantially higher when using a gain of 60 dB compared to 50 dB (mean difference ≥ 21.7 arbitrary units, d ≥ 3.47). When planning investigations in new research areas, researchers should carefully consider their study-specific image depth. Echo intensity values are stable between depths of 4.0 and 6.0 cm, suggesting that changing image depth may not be problematic. Image gain must be kept constant.