Ordering (test) physician, interpreting radiologists, and radiology techinicians, whose ultimate responsibility is it if something is missed?

The radiologist. The radiologist is responsible for the interpretation of a imaging study.
Radiology. The ultimate responsibility for findings of a radiology exam falls on the radiologist. It is important for the ordering physician to follow up on results of exams. If there is something critical the radiologist should also directly contact the ordering physician.
Consult. Sounds like a legal issue.I would request a copy of the cat scan and then get an independent radiologist and practitioner to interpret them.