I've had invisible blood and had cystoscopy. Also had CT scan when I was in hospital for an infection. It's iodine I think and you just get a warm feeling. Hardly anything at all. It's so that they can locate things, almost like a map. If you managed the cystoscopy ok, the contrast dye would have been ok. Well done for getting through the cystoscopy. It's a bit daunting. I was so nervous but found it was fine. Often the worry is the worst.