Early pregnancy volume measurements: validation of ultrasound techniques and new perspectives.

OBJECTIVE: To investigate accuracy and reliability of four different ultrasound-related volume-measuring methods.
DESIGN: Observational study.
SETTING: Both in vitro and in vivo. POPULATION OR SAMPLE: Ten phantoms for in vitro measurements and 28 pregnancies with gestational ages ranging from 6 to 11 weeks for in vivo measurements were included.
METHODS: Three-dimensional (3D) ultrasound images of phantoms (with known variable contents) and yolk sacs were used to calculate volumes using four different methods: Virtual Organ Computed-Aided AnaLysis (VOCAL), inversion mode, Sono Automatic Volume Calculation (SonoAVC) and V-Scope. V-Scope is a newly developed 3D volume visualisation application using a Barco I-Space virtual reality system. Intra- and interobserver agreement was established by calculating intraclass correlation coefficients (ICC). MAIN OUTCOME MEASURE: Evaluation of accuracy and reliability by comparing the different techniques with true volumes (in vitro) and with each other (in vitro and in vivo).
RESULTS: In the in vitro study, volume measurements by VOCAL, inversion mode and V-Scope proved to be accurate. SonoAVC measurements resulted in a substantial systematic underestimation. Correlation coefficients of measured versus true volumes were excellent in all four techniques. For all techniques, an intra- and interobserver agreement of at least 0.91 was found. Yolk sac measurements by the different techniques proved to be highly correlated (ICCs>0.91).
CONCLUSIONS: We demonstrated that VOCAL, inversion mode and V-Scope can all be used to measure volumes of hypoechoic structures. The newly introduced V-Scope application proved to be accurate and reliable.