Magnetic Resonance Imaging of Ovarian Activity in Microminipigs Showing Normal Estrous Cycles.

We investigated whether magnetic resonance imaging (MRI) might be applicable to evaluation of the ovarian activity of microminipigs. Firstly, using three mature microminipigs, we confirmed ovarian position and morphology by laparotomy or laparoscopy, and then acquired MRI images in various patterns to determine the most suitable condition for the acquisition. Next, using four microminipigs, we performed daily MRI, starting 10 days after ovulation and ending 10 days after the subsequent ovulation, as the starting day of standing estrus was taken as day 0. While the ovarian structure could not be discriminated on T1-weighted imaging, it was possible to confirm the follicles during estrus as hyperintense regions on T2-weighted imaging. With chronological MRI, 3-5 follicles were visible on T2-weighted imaging during the interval from day -2 to day 1, and their size immediately prior to ovulation was 3-5 mm. However, confirmation of the presence of small follicles and the corpus luteum was difficult.