QUANTITATIVE ECHOTEXTURE ANALYSIS OF BOVINE OVARIAN FOLLICLES

Computer-assisted image analysis was used to evaluate ultrasound image s of bovine ovarian follicles. The ovaries of 8 sexually mature heifer s were examined daily by transrectal ultrasonography for 2 estrous cyc les. Ultrasonographic examinations of the ovaries were then videotaped , and the dominant and subordinate follicles of successive waves were individually identified and monitored. Recorded images of the dominant anovulatory follicle of the first wave (n = 15) and the ovulatory fol licle of the last wave (n = 15) of the estrous cycle were subsequently digitized for computer analysis of echotexture (mean pixel value and pixel heterogeneity). Regions of the image spanning the breadth of the follicle wall were selected, and image analysis revealed that mean pi xel value of the dominant anovulatory follicle changed over time (P = 0.0005). Mean pixel value decreased (P = 0.0005) dramatically during t he early static phase (Days 6 to 8, Day 0 = day of ovulation), increas ed (P = 0.0005) at the onset of the regressing phase (Day 12), and rea ched maximal levels (P = 0.0005) on Day 14. Similarly, image echotextu re of the ovulatory follicle revealed a time-dependent effect (P = 0.0 001) due to a rapid decrease in mean pixel values between 7 and 4 d be fore ovulation, followed by an increase until the day before ovulation . The echotexture of images of the follicular antrum were also evaluat ed and with regard to the dominant anovulatory follicle, a time-depend ent effect was not detected for mean pixel value (P = 0.62) but was ob served for pixel heterogeneity (P = 0.02). In addition, there was a po sitive correlation between mean pixel value and heterogeneity (r = 0.6 1, P = 0.0001). Heterogeneity initially decreased (P = 0.02) and remai ned low until the emergence of the second follicular wave (mean Day 9) . Values subsequently increased and became variable during the late st atic and regressing phases (> Day 9). Mean pixel value of the antrum o f the dominant ovulatory follicle increased (P = 0.0001) as the day of ovulation approached. Heterogeneity did not change (P = 0.14), nor wa s there any correlation between mean pixel value and heterogeneity for the antrum of the ovulatory follicle (r = 0.06, P = 0.49). We conclud ed that changes in echotexture (mean pixel value and heterogeneity) of bovine ovarian follicles assessed by computer analysis of ultrasound images were temporally related to functional status (i.e., anovulatory versus ovulatory; growing, static or regressing). The results were st rongly supportive of the concept that ultrasonographically detected im age attributes are a reflection of physiologic status. (C) 1998 by Els evier Science Inc.