ABSTRACT
Objective To assess the inlfuence of depth on liver stiffness measurement with real-time shear wave elastography (SWE) and determine the optimal depth for SWE in liver. Methods SWE of liver was performed on 89 healthy volunteers between May 2012 and November 2012. The depths of each liver were varied from 0 cm to 7 cm (from the liver capsule) in 1 cm increment and there were 8 depth groups in total. Then the elastic modulus of liver in each depth group were measured three times by SWE. The body mass index (BMI) and the distance from body surface to liver capsule were documented. The success rates and the mean elastic modulus of each group were calculated. Results The success rates of 0-7 cm were 0, 98.9%(88/89), 98.9%(88/89), 98.9%(88/89), 71.9%(64/89), 24.7%(22/89), 3.4%(3/89) and 0, respectively. The success rates were highest in 1 cm, 2 cm and 3 cm groups but signiifcant decreased with the increasement of depths in 4 cm, 5 cm and 6 cm groups ( 3 cm vs 4 cm, χ2=25.94, P<0.001; 4 cm vs 5 cm, χ2=39.68, P<0.001;5 cm vs 6 cm,χ2=16.79, P<0.001). The mean elastic modulus of 1 cm, 2 cm, 3 cm, 4 cm and 5 cm groups were (4.77±0.99), (4.68±0.99), (4.76±0.95), (5.19±1.10) and (5.41±0.95) kPa, respectively. The mean elastic modulus of 4 cm and 5 cm groups were signiifcant higher than those of 1 cm, 2 cm, 3 cm groups (4 cm vs 1 cm, t=-2.85, P=0.005;4 cm vs 2 cm, t=-3.49, P=0.001;4 cm vs 3 cm, t=-2.76, P=0.006;5 cm vs 1 cm, t=-3.13, P=0.002;5 cm vs 2 cm, t=-3.66, P=0.000;5 cm vs 3 cm, t=-3.05, P=0.003). In the group of 4 cm, the BMI and the distance from body surface to liver capsule of the volunteers performed successfully and unsuccessfully were (20.70±2.87), (22.07±2.42) kg/m2 and (1.45±0.25 ), (1.60±0.29) cm, respectively. In the group of 5 cm, the BMI and the distance from body surface to liver capsule of the volunteers performed successfully and unsuccessfully were (19.82±2.76), (21.49±2.72) kg/m2 and (1.35±0.21), (1.54±0.26) cm respectively. The BMI had no signiifcant difference between the successful and unsuccessful groups (t=-2.83, P=0.108 for 4 cm;t=0.77, P=0.709 for 5 cm), but the distance from body surface to liver capsule was signiifcantly different (t=26.51, P=0.012 for 4 cm;t=79.57, P=0.004 for 5 cm). Conclusions The success rates and elastic modulus were different at different depths. SWE should be performed at the depths of 1-3 cm from the liver capsule.