Do you need contrast material for a sinus CT scan?

No. Except for rare cases the sinus ct is performed without contrast.
Not usually. A sinus ct looks at the bone and soft tissue of the several facial sinus cavities. In general, intravenous contrast material is not necessary. However, there are certain circumstances under which contrast media may be helpful, particularly if they're looking for a tumor or cancer. But for general sinus symptoms, it's not usually indicated.