76942 Documentation

We are a ASC that bills for an anesthesiologist who regularly administers post-op pain management injections using ultra sound guidance. We are trying hard to get a hang of all the technicalities involved with this billing process, so any and all advice is deeply appreciated! But I'll start with a specific question:

Is there any sort of documentation required in conjunction with billing 76942? I've read that a "permanent image" is require, but I've also read that this is not the case and that no documentation is necessary.

Thanks in advance for the help!