Accuracy of in-vitro volume estimation of small structures using three-dimensional ultrasound

We describe an ultrasound probe for three-dimensional transvaginal imaging. The transducer was an annular array with a center frequency of 7.5 MHz whi ch was rotated with an internal stepper motor. The probe had no external mo ving parts, and the total volume covered by a full rotation defined a half sphere. The raw digital data from the scanner were transferred to an extern al PC for three-dimensional reconstruction. We evaluated the three-dimensio nal imaging system by measuring the volumes of phantoms (range 24.8-3362.5 mm(3)) in a water tank, and found good correlation with true volumes (two o bservers' measurements gave a linear regression with a slope of 1.010 and R -2 = 0.993, and a slope of 0.956 and R-2 = 0.993, respectively). The size o f the point-spread function was used in the calculations to eliminate the e ffect of under- or overestimation due to the limited ultrasound beam resolu tion. An example of data acquisition, volume estimation and imaging of an e mbryo less than 8 weeks old in vivo with the brain cavities and body is giv en. We conclude that the three-dimensional reconstruction and volume estima tion were accurate and repeatable. (C) 2000 World Federation for Ultrasound in Medicine & Biology.