Magnetic resonance image attributes of the bovine ovarian follicle antrum during development and regression

The magnetic resonance images and maps of bovine ovaries acquired at define d phases of follicular development and regression were studied to determine whether magnetic resonance image attributes of the follicular antrum refle ct the physiological status of dominant and subordinate ovarian follicles. Ovariectomies were performed at day 3 of wave one, day 6 of wave one, day 1 of wave two and at greater than or equal to day 17 after ovulation. The ti mings of ovariectomies were selected to acquire growing, early static, late static and regressing follicles of the first wave and preovulatory follicl es of the ovulatory wave. Pre-selection and subordinate follicles were also available for analysis. Serum samples were taken on the day of ovariectomy and follicular fluid samples were taken after imaging. Numerical pixel val ue and pixel heterogeneity in a spot representing approximately 95% of the follicular antrum were quantified in T-1- and T-2-weighted images. T-1 and T-2 relaxation rates (T-1 and T-2), proton density, apparent diffusion coef ficients and their heterogeneities were determined from the computed magnet ic resonance maps. The antra of early atretic dominant follicles showed hig her T-2 weighted mean pixel value (P < 0.008) and heterogeneity (P < 0.01) and lower T-2 heterogeneity (P < 0.008) than growing follicles. Subordinate follicles in the presence of a preovulatory dominant follicle had higher T -1, T-1 heterogeneity, proton density, proton density heterogeneity, and lo wer mean pixel value in T-1-weighted images than subordinate follicles of t he anovulatory wave (P < 0.04). T-1 relaxation rate heterogeneity and proto n density heterogeneity were positively correlated with follicular fluid oe stradiol concentration (r = 0.4 and 0.3; P < 0.04). T-2 relaxation rate het erogeneity was positively correlated with follicular fluid progesterone con centration (r = 0.4; P < 0.008). Quantitative differences in magnetic reson ance image attributes of the antrum observed among phases of follicular dev elopment and regression coincided with changes in the ability of the domina nt follicle to produce steroid hormones and ovulate, and thus were indicati ve of physiological status and follicular health.