Volumetric tumor measurement using three-dimensional ultrasound: in vitro phantom study on measurement accuracy under various scanning conditions.

Factors influencing volumetric tumor measurement using 3-D ultrasound (US) were investigated. A 3-D US unit equipped with 4- to 8-MHz curved-array and 5- to 10-MHz linear-array mechanical volume transducers, and a US phantom made of 20 ham pieces (8.6 approximately 10.5 mL) embedded in agar gel that simulated hyperechoic tumors, were used. Volumetric tumor measurement was significantly affected by the position of US focus and tumor depth. When focus was at 2 cm and 8 cm below the transducer, 5-cm-deep tumors were measured 5.6% +/- 2.8% (mean +/- SD) and 8.3% +/- 2.2% bigger, respectively, than when focus was at 5 cm below the transducer, the same position as tumors (p < 0.01). Tumors were measured 11.8% +/- 2.9% bigger when they were 8-cm deep below the transducer than when they were 5-cm deep below the transducer (p < 0.001). Setting focus at the same position as tumors and keeping tumor depth consistent during serial 3-D US examinations may be necessary for reliable volumetric assessment of tumors.