The laboratory mouse is a well-accepted model for reproductive<br>biology studies and findings made in mice have been commonly<br>translated to humans. C57BL/6J and BALB/c strains provide a<br>robust experimental platform for polycystic ovary syndrome and<br>ovarian cancer research in women. Serial assessment of ovarian<br>morphometry and follicle dynamics may be performed non-invasively<br>and reliably in mice by Ultrasound Biomicroscopy (UBM),<br>with a near microscopic resolution. Our pilot study focused on<br>the utility of UBM in murine models to measure size of ovaries<br>and to count ovarian follicles over time. Three C57Bl/6J and two<br>BALB/c adult mice (>8 weeks of age) were housed in standard<br>conditions, with free access to food and water. Spontaneous<br>estrous cycle was longitudinally evaluated by transcutaneous<br>UBM (Vevo 770, VisualSonics, Toronto, Canada; center frequency<br>of 40 MHz; focal depth of 6 mm, spatial resolution of 30 um) on<br>a time period of 8-15 consecutive days. Mice were anesthetized<br>with 1.5% isoflurane in oxygen and fixed in sternal recumbency<br>on a heated stage. Trichotomy was performed over the thoracolumbar<br>area, and acoustic gel was applied to the skin. Images<br>of both ovaries were obtained in sagittal and axial scans, and<br>processed offline using ImageJ software. Ovarian diameters, area,<br>volume and follicles identification were obtained. To imaging<br>results comparison, the phase of the estrous cycle was assessed<br>in BALB/c mice by vaginal cytology. Ovaries were consistently<br>localized in all mice, with a 10 minutes scan time. The changes of<br>the follicles pattern and number overtime have wave-like fashion.<br>In conclusion, UBM is a suitable method for measuring and for<br>identifying the patterns in follicle development, ovulation and<br>regression in mice in vivo, and to monitor the potential efficacy<br>of novel therapies in murine models of ovarian pathologies.