Influence of the ultrasound transducer tilt on muscle thickness and echo intensity of the rectus femoris muscle of healthy subjects

[Purpose] This study aimed to assess the influence of ultrasound (US) transducer tilt on muscle thickness and echo intensity of the rectus femoris muscle (RF) in healthy subjects. [Subjects and Methods] Fourteen healthy male subjects (20.8 ± 0.8 years) participated in this study. Transducer tilt was measured during US, with a digital angle gauge. Muscle thickness and echo intensity were measured in 4 transducer tilt conditions: reference angle; +3°; +6°; and +9° cranial from the reference angle. [Results] All differences in transducer tilt relative to the reference condition were larger than the minimal detectable change (MDC) of the reference condition. All differences in muscle thickness relative to the reference condition were not larger than the MDC of the reference condition. All differences in the echo intensity relative to the reference condition, except between the reference and the +3° condition, were larger than the MDC of the reference condition. [Conclusion] Our results indicated that an examiner should maintain a precise transducer tilt during repeated US measurements to quantify the minimal change in the echo intensity of the RF.