Acoustic radiation force impulse quantification: repeatability of measurements in selected liver segments and influence of age, body mass index and liver capsule-to-box distance.

OBJECTIVE: To assess the inter- and intra-observer variability of acoustic radiation force impulse (ARFI) quantification in liver segments with influence of age, body mass index (BMI) and liver capsule-to-box (CB) distance. METHODS: 10 healthy volunteers were examined twice, by three experienced operators, separated by a 1-week interval. 10 readings were obtained, from segments 3, 5/6 and 7/8. Age, BMI and the CB distance were noted. The Cronbach α statistic for analysis of reliability was performed for the inter- and intra-observer studies. Multivariate linear regression models determined significance of the other parameters. RESULTS: 1800 velocity measurements were recorded. Mean values±standard deviation: segment 3, 1.31±0.19 m s(-1); segment 5/6, 1.12±0.22 m s(-1); segment 7/8, 1.12±0.17 m s(-1). For both the inter- and intra-observer study, the Cronbach α statistic was ≥0.7 (reliable) when taken from segments 5/6 and 7/8 but <0.7 (unreliable) for segment 3. BMI and age showed significant (p<0.0001) but contrasting correlation (segment 5/6: BMI r=0.02, age r=-0.02; segment 7/8: BMI r=-0.01, age r=0.01) with ARFI velocities when analysed for the segments deemed reliable. A weak negative correlation between ARFI velocities and liver CB distance was demonstrated for both assessed segments (segment 5/6, r=-0.08; segment 7/8, r=-0.06; p<0.001). CONCLUSION: With trained operators, ARFI is a reliable and reproducible method of liver stiffness quantification in segments 5/6 and 7/8 but acquisition of measurements from segment 3 should be avoided. Values obtained deeper to the liver capsule allow more reliable liver stiffness quantification.