Is ultrasonic speed of sound estimation for liver fat quantification affected by measurement depth?

PURPOSE: Ultrasonic speed of sound (SS) estimation is one of the techniques that can be used to assess hepatic fat content. Current literature lacks of information for ultrasonic SS estimation technique in terms of depth dependence. We aimed to evaluate the impact of measurement depth on SS measurements. METHODS: A total of 90 patients who diagnosed with metabolic dysfunction-associated steatotic liver disease (MASLD) were included in the study. Upper edge of the region of interests (ROI) were positioned at 4 cm and 6 cm deep from the skin. Five measurements were obtained for both depths and the median values were noted for the analysis. Paired-t test was used to compare the measurements. RESULTS: The means of the SS measurements for 4 cm and 6 cm depths were 1514 ± 13.5 m/s and 1512.2 ± 15.1 m/s, respectively. There was a significant difference between the SS measurements obtained at 4 cm and 6 cm depths (P = 0.018). Subgroup analyses for BMI (< 30 kg/m2 vs. ≥ 30 kg/m2) and skin to liver capsule (SLC) distance (< 25 mm vs. ≥ 25 mm) revealed that there were significant differences in SS measurements between 4 cm and 6 cm depths in patients with high BMI (P = 0.047) and high SLC (P = 0.044), while there were no significant differences detected in patients with low BMI (P = 0.198) and low SLC (P = 0.140). CONCLUSION: Our results revealed that ultrasonic SS measurements are affected by the measurement depth in patients with high BMI and high SLC. These findings may be valuable for technical standardization of SS technique.