Influence of Inward Pressure of the Transducer on Thickness and Echo Intensity of the Rectus Femoris Muscle During Ultrasonography

Muscle ultrasonography (US) can be used to evaluate muscle quantity and quality affected by a neuromuscular disease and aging. The evaluation of muscle thickness and echo intensity using US are useful ways of estimating muscle mass and composition. During US, diligent attention to steadying the position, orientation, and inward pressure of a transducer is required; however, little is known about the quantitative influence of different inward pressures of the transducer on muscle thickness and echo intensity during US. The purpose of this study was to quantify the changes in muscle thickness and echo intensity induced by different inward pressures of the transducer during US. Fifteen healthy male volunteers (mean ± SD, 20.7 ± 0.7 years old) participated in the study. Thickness and echo intensity of the right rectus femoris muscle (RF) was measured by US in the following three conditions: inward pressures of 0.5 N, 1.0 N, and 2.0 N. A repeated-measures ANOVA was utilized to determine the influence of inward pressure on the thickness and echo intensity of the RF. Muscle thickness was significantly decreased during increased inward pressures of the transducer among the three conditions (P < 0.001). On the other hand, echo intensity from the 0.5-N to 1.0-N condition was significantly decreased (P = 0.002), and from the 1.0-N to 2.0-N condition, it was significantly increased (P = 0.019). Our results indicate that changes in muscle thickness and echo intensity are induced by different inward pressures of the transducer during US. When using a technique that involves a handheld transducer, the examiner should attempt to maintain consistent inward pressure of the transducer during US, to quantify the minimal change of the RF mass and composition.