On a pet/ct preliminary report came out on 11/22 they said final report will follow. generally is there much difference in info on prelim vs final?

No: Preliminary means that the dictated report has not been reviewed since it was typed. The doctor will review the dictation for any errors before it is finalized.

Usuallly similar: The preliminary report often has less details. It may include what the radiologist has grossly observed but not interpretated. The full report usually includes details of how the study was performed, objectively what was seen, an impression (the meaning of findings), and a diagnosis stated as "most consistent with". Even with little difference between reports, rely on the final one.

Depends...: Ultimately it depends on the type of preliminary and who read it. However, in my experience, there are frequently minor findings that will be added and or different from the prelim report and there are only occasionally significant discrepancies between the two reports. I hope this helps answer your question.