I assume you're referring to out-pt IV starts. We never had orders to start the IV, it was just part of the study if the Radiologist ordered IV contrast and the pt didn't have one (which most out-pts don't have). But, the RNs were starting most of the IVs. Don't know if you need an order -- hmmm, you're in TX . . . perhaps it's different there. Can you call around to area hospitals and see what their CT depts are doing? That might help direct you some.
If the Rad isn't going to see or sign the form, how do you have an order? Perhaps just writing a protocol for the out-pts. . . . just say what you do. eg, "out-patients scheduled for CT scans will have a peripheral IV started by the Radiology Nurse (or certified CT technologist) if the Radiologist orders IV contrast for the exam. The IV is to be started according to standard hospital procedure (may insert IV start procedure here) and is to be DC'd after the exam, if no s/sx of reaction are present." Something simple.
Sorry, that's all I have to offer!