My dad 73 yr old quit smoking 18 yr old. his ct scan shows infection & one 7 mm nodule. should we go for pet scan or biopsy? any pros cons of each?

Biopsy first: He needs to have a biopsy of the nodule first to see what it is. The pet scan is useful if the nodule turns out to be cancer.

No PET at this point: If this is the only nodule, is 7 mm and associated with infectious pattern you should follow-up with ct to ensure resolution in 2-3 months. The nodule is too small to be metabolically characterize by most pet scanners and therefore a this point pet won't be helpful. In case this nodule has increased in size of follow-up ct and measures >=1 cm pet scan could be use for metabolic characterization.

Comparisons?: 1st, are there any old cds to compare? If so, is the nodule truly new? The 7 mm nodule could be infectious. Consider waiting a month and repeating the ct scan. Given remote smoking history and nodule size, would lean towards pet/ ct 1st. Biopsy may still be needed to prove cause.