Ovarian follicles. Coloured 3-D ultrasound scan of an ovary showing multiple follicles (dark regions). These are unruptured follicles, which still contain developing ova (eggs). Usually, only one ovum matures and is released from an ovary during each cycle of ovulation. This patient has received hormonal treatment to stimulate the ripening of multiple follicles. The ova will be harvested for use in fertility treatment, such as in-vitro fertilisation. Ultrasound scanning is a diagnostic technique that sends high- frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure.