This is one of the many places where computer people simplify other professions.

Legally yes, the rad is the one interpreting it, but it's a very active process by the technologist. The ultrasound tech is actively interpreting the scans as they do them, and then using the wand to chase down what they notice to get better shots of things. If they don't see something the rad won't either, so you need that expertise there to identify things that don't look right, it's very real time and you can't do it post hoc.