Comparison of two- and three-dimensional ultrasound for volume estimation of the meal-stimulated gallbladder

To compare two- and three-dimensional (2D and 3D) ultrasound of the gallbladder in an adult cohort.

In this observational, cross-sectional study, gallbladder volumes were measured using 2D and 3D ultrasound. Examinations were performed in the fasting state and at predefined time intervals after ingestion of a standardized nutritional drink. At each time point, measurements were performed twice using 2D and twice using 3D ultrasound. Volumes were calculated using the ellipsoid method for 2D ultrasound. For 3D, manual tracing was performed.

Sixty-two subjects were included, yielding 2,328 volume measurements. The mean age was 69 years (SD 6.6) and the median BMI was 24.3 kg/m² (IQR 22.9-28.6). The mean difference between 2D measurements was significantly larger than the difference between 3D measurements (3.3 cm³ vs. 1.9 cm³, p <0.001). The intraclass correlation coefficient (ICC) between two sequential 2D measurements was 0.94 (p <0.001, 95% CI 0.94-0.95), and between two sequential 3D measurements 0.96 (p <0.001, 95% CI 0.96-0.97). The ICC between 2D and 3D measurements was 0.85 (95% CI 0.74-0.91, p <0.001).

Our findings indicate that 3D ultrasound exhibits lower intra-observer variation when determining gallbladder volumes compared to 2D ultrasound. The discrepancy between the two methods increases with gallbladder volume.