Watch for these key lung scan terms -- in addition to the terms used in the CPT descriptors -- to help you pinpoint whether you should code ventilation studies, perfusion studies, or combined studies in the 78580-78594 range. (Chart based on one by Bruce W. Hammond CRA, CNMT, executive vice president of Diagnostic Health Services.) Remember: These terms are a starting point, but because the same abbreviation may have different meanings to different providers, always look further into the documentation to pinpoint the precise procedure performed.