What happens during a CT of my sinuses?

Quick and safe. You lay on the ct gantry table and the technologist does a scout scan of your head. Using the appropriate landmarks, the technologist then tells the scanner which part of the head to scan to include the sinuses. You may or may not receive intravenous contrast. On older scanners you may be asked to lay on your stomach with your head oriented such that you are looking through the bore of the scanner.
Also. It will take about 5 minutes, lying on a firm surface, with your head in a scanner.