Reliability and validity of in vitro volume calculations by 3-dimensional ultrasonography using the multiplanar, virtual organ computer-aided analysis (VOCAL), and extended imaging VOCAL methods.

OBJECTIVE: The purpose of this study was to assess the reliability and validity of in vitro volume calculations by 3-dimensional ultrasonography. METHODS: This observational study was performed by 2 examiners to obtain volumes of 3 objects of different shapes and sizes filled with ultrasound gel and immersed in water. The examiners used the multiplanar (5-mm interval), virtual organ computer-aided analysis (VOCAL, 30 degrees) and extended imaging (XI) VOCAL (5, 10, 15, and 20 planes) methods to estimate the volumes of each object. A paired Student t test (P) and intraclass correlation coefficients (ICCs) were used to assess reproducibility of the methods. Validity was assessed comparing the percent differences between the estimated and the real volumes using the P value, mean differences, and ICC for each method. RESULTS: All methods were highly reliable and valid. There were no significant differences in interobserver variability; there was a strong interobserver correlation. There were no significant differences in the percent differences between the estimated and real volumes of the objects using the 3 methods. The XI VOCAL method was superior to the multiplanar and VOCAL methods in the measurement of irregularly shaped objects. The XI VOCAL method with 10 planes estimated volumes closest to the real volumes. CONCLUSIONS: All 3 methods were reliable and valid; however, XI VOCAL was superior to the other methods in the measurement of irregularly shaped objects.