Ovarian Volume Measurements in Mice with high resolution ultrasonography

The aim of our study was to evaluate the intraobserver and interobserver variability of ovar- ian volume measurements in mice with high-resolution 2-dimensional ultrasonography (2DUS) and 3-dimensional ultrasonography (3DUS). Methods. Ovaries of 10 nude mice were visualized with a small-animal ultrasound scanner and a 40-MHz probe. For each ovary, volume was measured 3 times by 2 independent readers using both 2DUS and 3DUS methods. The 2DUS method used a biplane ellipsoid model. The 3DUS method estimated the volume by integrating 10 to 12 parallel image planes of the ovary after semiautomated outlining of the boundaries. For each type of measurement, intraob- server and interobserver standard error of measurement (SEM) values and minimal detectable volume changes were calculated by analysis of variance. Results. Two-dimensional ultrasonography showed much poorer reproducibility, with higher absolute intraobserver and interobserver SEM values (0.50 and 0.61 mm3, respectively) than 3DUS (0.20 and 0.35 mm3; P < .01). Relative intraobserver and inter- observer SEM values were also much higher for 2DUS (12.20% and 14.88%) than for 3DUS (5.12% and 8.97%; P < .01). The minimal volume changes that could be detected with a 95% confidence level in successive measurements by the same (or different) observers were 33.90% (41.22%) for 2DUS and 14.10% (24.87%) for 3DUS. Conclusions. High-resolution 3DUS can provide a reliable tool for noninvasive, longitudinal ovarian volume measurements in mice. Key words: high-resolution ultra- sonography; ovary; small-animal imaging.