Tennessee Subscriber
Answer: You can report 78465 (Myocardial perfusion imaging; tomographic [SPECT], multiple studies, at rest and/or stress [exercise and/or pharmacologic] and redistribution and/or rest injection, with or without quantification) only if you address the cardiovascular system. Your lower-extremity SPECT study would not meet the requirements to report 78465, so you should instead opt for 78399 (Unlisted musculoskeletal procedure, diagnostic nuclear medicine).
As with all unlisted-procedure codes, you should submit the procedure note to the insurer with your claim, along with a short letter explaining what you performed and why it was medically necessary.