At this point CT is much faster than it used to be. It takes about as long to type in the Patient's info as it does to do a sinus scan. Many people are dissapointed when it takes so little time and complain that it's a lot of money for such a short nothing exam .Since fluid (or yuck) in the sinus is heavier than air it will sink and layer out on the scans, that's why you have to lay face down with your head back.Same reason why sinus and chest xrays are done sitting or standing up. Ct scans are always faster than MRI because they scan things 1 or 2 times. MRI does many different "series" of scans to "see" things differently. In general CT is better for bones and anything in the chest, abdomen or pelvis. MRI is better for brains, soft tissue back & neck injuries and joint injuries.