It could be a problem. I found this:
http://imaginis.com/ct-scan/contrast.asp
"Patients should inform the radiologist or technologist if they have a history of allergies (especially to medications, previous iodine injections, or shellfish), diabetes, asthma, a heart condition, kidney problems, or thyroid conditions. These conditions may indicate a higher risk of iodine reactions or problems with eliminating the iodine after the exam."
http://thyroid.about.com/od/thyroidbasicsthyroid101/a/riskfactors.htm
"Having a medical test in which an iodine-based contrast agent is used slightly increases the risk of developing a temporary thyroiditis, hypothyroidism or hyperthyroidism. (Note: Those with underlying thyroid antibodies and a tendency toward autoimmunity appear to be at more risk)"
And here is a link to a thread on MedHelp about the issue:
http://www.medhelp.org/posts/show/17462
Be careful.