A lot of CT technicians don't make the connection between a patient coming in for a thymus scan for MG and the possibility that they might have a reaction to the dye.

If I recall correctly, they did my CT scan without the dye precisely because I questioned the need for them to use it. They contacted my neurologist and she told them in no uncertain terms NOT to use it.

When I had to have an angiogram a few months later, I was put on a mega-dose of steroids a day before because the dye had to be used (and I was the one who brought up the possibility of a reaction in the first place). Thankfully, I had no adverse reactions.