A little while. If it becomes to uncomfortable for you to hold the urine, they will allow you to release a little uring from your bladder. They do need some fluid so they can get more accurate pictures.

I have worked in the radiology field and have had a few pelvic sono's for cysyts. It is physically painless, but it made me feel very uncomfortable, mentally, for other reasons.

I wish you luck.

Jen