Ultrasound biomicroscopy: a non-invasive approach for in vivo evaluation of oocytes and small antral follicles in mammals

Abstract

The use of ultrasonography has changed our understanding of the ovarian function in live animals. However, most of the studies that have used ultrasonography to image the ovary have provided data only of structures >1 mm in diameter. The recent availability of high-resolution ultrasound technology with high-frequency transducers (25–70 MHz), offers the potential to examine the developmental dynamics of small antral follicles and the cumulus–oocyte complex (COC) in vivo. In this review we provide data from a series of studies performed by Veterinary Biomedical Sciences Laboratory describing the advantages and disadvantages, as well as image characteristics, of ultrasound biomicroscopy (UBM) to study ovarian biology in mammals. Data and images of small ovarian structures in rabbits, cattle, mice and humans are shown. The UBM technique allowed visualisation of small antral follicles ranging in size from 300 to 700 μm in all species examined, as well as COC within follicles in rabbits, cattle and humans. Furthermore, UBM permitted clear distinction of the follicular wall from the surrounding ovarian stroma in cattle and humans. At present, the limited depth of penetration of UBM restricts the use of this technique to an experimental setting. In that regard, further studies using UBM will probably result in a greater understanding of the pattern and control of early antral folliculogenesis and oogenesis.