You may be asked to drink a contrast solution or receive an IV (intravenous) line through which a different contrast dye is put in. This helps better outline structures in your body. This might cause some flushing (a feeling of warmth). Some people are allergic and get hives. Rarely, more serious problems like trouble breathing or low blood pressure can happen. Be sure to tell the doctor if you have any allergies or have ever had any problems from contrast dye used for x-rays.
CT scans take longer than normal x-rays. You need to lie still on a table while they are being done. During the test, the table slides in and out of the scanner, a ring-shaped machine that surrounds the table. You might feel a bit confined by the ring you have to lie in while the pictures are being taken. Spiral CT (also known as helical CT) is now used in many places. This type of CT scan uses a faster machine.
The CT scan can help show the place and size of thyroid cancers and whether they have spread to nearby areas. A CT scan can also be used to look for spread into distant organs like the lungs. In some cases, a CT scan can be used to guide a biopsy needle right into a suspected area of cancer spread.
Because the CT contrast dye contains iodine, (which can cause problems with radioiodine scans described below), many doctors prefer MRI scans instead of CT scans.