Clamping the foley prior to an ultrasound to view the pelvis might be appropriate.
A Ct scan, never.
Clamping a CBI drainage catheter for a Ct scan is insane as it could result in a ruptured bladder. No no no.
Beware of radiology people who operate outside of your hospital's policies and want to play with the
ETT and have respiratory hyperinflate the lungs and play with other tubes and devices. It happens and you need to yell for help and order him to step away from your patient.
I would print that CT policy and notify the MD, especially the Urologist, write an incident report and make a whole lot of noise.