A few minutes. The technician puts an IV in your arm and you lay flat on a narrow table. The table slides into a large donut shaped xray tube. You hold your breath for a few seconds, then you feel a hot sensation all over, and it's all done.
1 hour or so. Need to check in. Get IV and labs. Once labs come back go to the scanner. Cta takes 5 minutes. Some places will watch you for 15 minutes to make sure no reaction to the dye or contrast. Not to bad.
The scan itself. Does not take long as dr. Pak said. You need time to register and get lab tests before your scan. Schedule plenty of time.