Unbiased and efficient estimation of the volume of the fibroid uterus using the Cavalieri method and magnetic resonance imaging.

The aim of our study was to develop a reliable technique for measuring volume of the fibroid uterus using Magnetic Resonance Imaging. We applied the Cavalieri method and standard calliper technique to measure the volume of the uterus and largest fibroid in 26 patients, and results were compared with "gold-standard" planimetry measurements. We found Cavalieri measurements to be unbiased, while calliper measurements systematically underestimated uterine volume (- 13.2%, P < 10(-5)) and had greater variance. Repeatability was similar for the 2 techniques (standard deviation [SD] = 4.0%-6.9%). Reproducibility of Cavalieri measurements was higher for measurement of uterine (SD = 9.0%) than fibroid volume (SD = 19.1%), whereas the reproducibility of calliper measurements was higher for fibroid (SD = 9.1%) than uterine volume (SD = 15.9%). The additional measurement time for the Cavalieri method was approximately 1 to 2 minutes. In conclusion, the Cavalieri method permits more accurate measurement of uterine and fibroid volumes and is suitable for application in both clinical practice and scientific research.