ULTRASOUND IMAGE ATTRIBUTES OF BOVINE OVARIAN FOLLICLES AND ENDOCRINEAND FUNCTIONAL CORRELATES

Heifers were studied to determine whether computer-assisted quantitati ve echotexture analysis of ultrasound images reflect functional and en docrine characteristics of dominant and subordinate follicles at speci fic stages of development. Heifers were examined using transrectal ult rasonography each day until ovariectomy on day 3 (n = 8) and day 6 (n = 9) of wave 1, day 1 of wave 2 (n = 7), or after onset of pro-oestrus greater than or equal to 17 days after ovulation (n = 8) to obtain gr owing, early-static, late-static and regressing dominant follicles of wave 1, subordinate follicles, preselection follicles and preovulatory dominant follicles. Ultrasound images of the follicles were obtained in vitro and analysed using custom-developed computer algorithms. Mean pixel (picture element) values (grey-scale: black = 0, white = 255) f or the follicle wall and stroma increased (P < 0.05) progressively fro m the flowing to the regressing phases of the dominant follicle of wav e 1. The antrum and wall of subordinate follicles had higher (P < 0.05 ) mean pixel values than that of the corresponding dominant follicles. Pixel heterogeneity (a measure of: variation of grey-scale values of pixels) of images of the follicle antrum and wall increased (P < 0.05) progressively during the early-static to regressing phases. A progres sive increase (P < 0.05) in the slope of the regression line of pixel values for the follicle wall was detected from the growing to the regr essing phases of the dominant follicle of wave 1. The regression line of the wall of the preovulatory dominant follicle had the lowest (P < 0.05) slope. Oestradiol concentration in the follicular fluid decrease d (P < 0.05) from the growing to the late-static phase, while a marked decrease (P < 0.05) in the androstenedione concentration was recorded between the growing and the early-static phases of the dominant folli cle. Progesterone content did not increase until follicles were in the final stages of regression. Pixel heterogeneity of the antrum and wal l, and the slope of the follicle wall regression line were negatively correlated (P < 0.001) with oestradiol and the oestradiol:progesterone ratio in follicular fluid. The results of this study support the hypo thesis that echotexture characteristics of ultrasound images of the fo llicle antrum and wall are correlated with the functional and endocrin e status of a follicle.