Compatibility and Bias Between Ultrasound-Guided Attenuation Parameter and Controlled Attenuation Parameter for Ultrasound-Based Hepatic Steatosis Assessment

Purpose To develop a regression model for estimating the controlled attenuation parameter (CAP) from ultrasound-guided attenuation parameter (UGAP)-attenuation coefficient (AC) and to evaluate the agreement and interchangeability between the two measurements in a clinical setting. Methods This retrospective observational study included 85 patients who underwent both UGAP and CAP measurements. UGAP-AC values were converted to dB/m to match CAP units. Pearson’s correlation and linear regression analyses were performed to derive a prediction formula. Bland–Altman analysis and repeated-measures analysis of variance were used to assess fixed and proportional biases and the influence of body mass index (BMI). Results UGAP-AC and CAP showed a strong correlation ( r = 0.947, p < 0.0001). The regression equation was: CAP (dB/m) = 371.5 × UGAP-AC (dB/cm/MHz) + 12.3 ( R 2 = 0.8946). Bland–Altman analysis revealed a fixed bias of 28.6 dB/m and a BMI-dependent proportional bias. However, no significant proportional bias was observed within the clinically relevant CAP range (228–300 dB/m). Conclusion UGAP-AC can reliably estimate CAP using a simple regression formula. Although systematic biases exist, their clinical impact appears limited, supporting the interchangeable use of UGAP and CAP in routine practice.