How common is the use of iodized salt in the USA?

[Daisy and Delilah]

Thank you everyone for your replies, very interesting!
Wow! That's sounds like a typical iodine allergy! But there's also iodine-free contrast dye, isn't it? They always inject me something when I have my MRTs, and they always say it doesn't contain iodine.
Kirsten

I think there is an iodine free dye. I've heard they can use it and the image isn't as clear.