https://www.support.freestyle.abbot...5057-Can-I-keep-my-sensor-on-during-a-CT-scan <-- Abbott says yes, but the technician might not agree. With the scan area you're likely to have your arms raised above your head anyway, and not have that area scanned, so the metal inside shouldn't disturb the machine's pictures. With an MRI it would be problematic.
I live in France and 2 weeks ago I had an MRI. I was asked to remove my sensor (which was 1 week old). But they did give me a free prescription to replace it.