Welcome to the BB and to Radiology Nursing!!
Re: informed consents. Our hospital policy (when I worked Radiology) was the same as yours: MD obtains informed consent. However, our Radiologists requested we "educate" the patient about the procedure, and then the Rads met the pt, asked if the pt had any questions, and handed the pt the form to sign

WE didn't have the pt sign the consent. I suggest you contact Risk Mgmt for guidelines/help changing current practice, this is a legal issue.
Have you tried a Google or Yahoo or Vivisimo search re: informed consent? Perhaps with key words "JCAHO informed consent" or something similar. Vivisimo is an interesting search engine, which will cluster the results for you, so you may not have to wade through as much unrelated material to reach the answers you want.
Re: SL's. that's a tough one. We nurses discussed amongst ourselves how we might document the out-pt SL's (for CT, IVP, etc) but never quite came up with a plan. What are your sister hospitals doing? for that matter, see what the other area hospitals are doing (I know, conducting polls in your "spare" time is hard, but it's always enlightening). What are the requirements? What would you chart as a floor or ICU nurse? Is there a generic template the hospital uses, or, you could develop your own (through forms committee, etc) -- make it simple (I love check-boxes!).
I work exclusively Cath Lab now, so am not "up" on Radiology anymore (but it's still interesting!). I hope someone else here can help you more. Good luck! --

-- D