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Magnetic Resonance Image Attributes of the Ovarian Follicle Wall During Development and Regression¹

^a Departments of Obstetrics, Gynecology and Reproductive Sciences and ^b Medical Imaging, ^c College of Medicine, and Veterinary Medical Biosciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W8

ABSTRACT

We analyzed image characteristics in T₁-, T₂-, and diffusion-weighted in vitro magnetic resonance (MR) images acquired at predefined stages of the ovarian cycle in 36 heifers to test the hypothesis that MR image attributes of the follicle wall reflect the physiologic status of ovarian follicles (viable, atretic, dominant, subordinate). Numerical pixel values (NPV), standard deviation of pixel values (heterogeneity), and area under the curve were used to assess images of follicle walls. Pixel values of the wall were used to calculate a regression line from which intercept, slope, and coefficient of determination were calculated. In T₁ images, NPV of dominant follicles were less likely to fit a regression line at the preovulatory phase than at any other phase (P < 0.1). Preovulatory dominant follicles had lower area under the curve in diffusion-weighted images than early and late static dominant follicles of the anovulatory wave (P < 0.02). Subordinate follicles in the presence of a preovulatory dominant follicle had lower mean NPV in T₁- and T₂-weighted images and lower intercepts in T₁-weighted images than subordinate follicles of the anovulatory wave (P < 0.02). Early atresia of dominant follicles was identified at the late static phase by greater area, mean NPV, and slope in T₂-weighted images (P < 0.02). Preovulatory dominant follicles had poor fit of NPV to a regression line in T₁-weighted images and lower area under the curve in diffusion images. Atretic follicles had brighter walls with more acute transitions from follicular fluid to stroma in T₂-weighted images and more heterogeneous walls in diffusion images. The MR image attributes of the follicle wall reflected the physiologic status of dominant and largest subordinate follicles.

FOOTNOTES

First decision: 22 January 2001.

¹ Supported by grants from the Canadian Institutes for Health Research (R.A.P./G.E.S.) and the Natural Sciences and Engineering Research Council of Canada (G.P.A.).

² Correspondence: R.A. Pierson, Department of Obstetrics and Reproductive Sciences, College of Medicine, University of Saskatchewan, Royal University Hospital, 103 Hospital Drive, Saskatoon, SK, Canada S7N 0W8. FAX: 306 966 8796; pierson{at}erato.usask.ca