If my child needs a ct scan of his head and i hold his head with my hands during the scan, will my hands interfere with the scan? also, what if i had a ring on one of my fingers.

Likely: The added bony and metallic structures can cause artifacts/irregularities in any scan. You would also likely add subtle movement artifact. They have restraints built to cushion a babies head and you are an unnecessary add on. To comfort baby sitting nearby and consoling the kid is a positive role.

Ask the technician: The technician who performs the test will be the one who can advise you on hand placement and whether the ring should be removed in a CT scan.