Out of the horror novels, I have read the Wasp Factory, basically because when I was at a crime fiction event a few authors praised it. I didn't really care for it but maybe you will.
Also, that seems an odd thing for them to request at the mammogram place. Where I go, you get let into a small dressing room that locks behind you and only they can open on the other side, so you leave your purse and clothes there and they bring you through to the machine. It all seems quite secure since the other people waiting in the waiting room can’t get in there.