Ovarian imaging in the mouse using ultrasound biomicroscopy (UBM): a validation study

The mouse is a well accepted model for studies of human reproduction despite little being known about follicle dynamics in this species. Longitudinal studies of mouse folliculogenesis have been hampered by the lack of an appropriate imaging tool. Ultrasound biomicroscopy (UBM) may overcome this obstacle as it confers near-microscopic resolution through the use of high-frequency ultrasound waves. The objective of the present study was to determine whether UBM could be used to count and measure ovarian follicles and corpora lutea (CL) reliably in mice. Ovaries of 25 adult CD-1 mice were imaged using a 55-MHz transducer and then excised and processed for histology. Follicles and CL were counted and measured from digitally stored UBM cine-loops and photographed histological sections. Differences between techniques were assessed by Bland-Altman agreement analyses. Follicle counts yielded by the two techniques varied by only +/-1 follicle when follicles ranged between 300 and 499 microm. Perfect agreement among counts was evident when follicles were >500 microm. The total number of CL was accurately estimated using UBM; however, the number of 350-699 microm CL was underestimated and the number of CL>or=700 microm was overestimated. In conclusion, UBM can be used reliably to count and measure follicles in mice.