Author's personal copy Magnetic resonance imaging for the study of ovarian follicles in the mouse A.P. Stephenson a , D.J. Tyler b , C.A. Carr b , S.A. Williams a, * a Nuffield Department of Obstetrics & Gynaecology, University of Oxford, John Radcliffe Hospital, Oxford, UK b Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford, UK Received 5 December 2011; received in revised form 17 May 2012; accepted 22 May 2012 Abstract Additional tools to analyze follicle development would be highly advantageous because current methods require sacrifice of animals at specific times and time-consuming sectioning of tissues for histologic analysis. Magnetic resonance imaging (MRI) may provide a less involved, faster and more cost-effective method to analyze follicles in whole ovaries. Fixed ovaries were collected at different stages of the estrus cycle and after stimulation with gonadotrophins (24 and 48 h post pregnant mares serum (PMSG), and 10 and 24 h post human chorionic gonadotrophin (hCG)) with or without administration of the contrast agent gadodiamide. The MR images were generated using a vertical-bore, 11.7 Tesla MR system. Analysis of the MR images revealed large antral follicles in fixed ovaries with the oocyte and cumulus mass identifiable within preovulatory follicles. The use of gadodiamide had no impact on the quality of MR images obtained. The fixed ovaries were paraffin embedded, sectioned, and hematoxylin stained. Follicles were counted using the MR images and the histology sections. Preovulatory follicle numbers determined using MR images were comparable to those using histology; however counts of smaller follicles were inconsistent. MRI of gonadotrophin-stimulated ovaries in situ did not reveal discernable ovarian structures. Therefore, MRI is a useful tool for studying whole fixed ovaries leaving the ovary intact for additional analyses or for selection of samples based on morphology. The MRI is also useful for identifying preovulatory follicles, although analysis of smaller follicles is not possible, and thus the potential exists for cyst analysis in mouse models of polycystic ovarian syndrome (PCOS). © 2012 Elsevier Inc. All rights reserved. Keywords: Magnetic resonance imaging; MRI; ovary; follicle; mouse 1. Introduction To investigate the structural and functional changes that occur in the ovary as ovarian follicles develop, clear imaging of the ovaries is required. These images can be used to determine follicle numbers, a routine measure of follicle development, and are useful to gain insight into the dynamics of follicle development [1,2]. Although highly valuable for the data generated, cur- rent methods of follicle counting are time-consuming, with tissues requiring embedding, sectioning, staining and mounting prior to analysis. Moreover, in assessing follicle numbers using this technique, compromises have to be made because unless every section is analyzed, the counts generated provide only a representative sample of the follicle numbers actually present. In mice, although new methods of ascertaining fol- licle numbers have been explored to improve accuracy and reliability of results [3], they still rely on histologic sections. MRI is increasingly used in medicine and research. If MR images of whole ovaries could allow * Corresponding author. Tel.: +44 (0) 1865 221014; Fax: +44 (0) 1865 769141. E-mail address: suzannah.williams@obs-gyn.ox.ac.uk (S. Wil- liams). Available online at www.sciencedirect.com Theriogenology 78 (2012) 1190 –1198 www.theriojournal.com 0093-691X/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.theriogenology.2012.05.012