Y
yolk sac a circular structure seen on ultrasound scans at 6 weeks which supplies the fetal pole with nutrients; it is used to confirm an intrauterine pregnancy.
yttrium-90 (90Y) a substance emitting beta particles with a half-life of 64 hours. Implantations of this in bone wax are left in the pituitary fossa after hypophysectomy for breast cancer. Also used in a number of interstitial cancer treatments.
