I was in that situation with a CS one time to have a spot checked either on my liver or kidney. The ultrasound had mentioned one time the left side and another time the right side.
So they wanted to inject me too, to see it better, but I had to sign a consent forum and there it said all the side effects etc.
I did not want to sign, of course the nurse was in shock, but I told her I would do without it. They put in big letters Patient Refused on the form.