Will a 6mm lung nodule show up on a pet scan?

Borderline to nope: It would be seen on the ct component of the scan but may not uptake enough FDG to make it light up. Many centers use 8 mm as cutoff but i guess it will vary a bit from place to place. I would not call such nodule negative if it did not light up on pet.

Borderline: Pet ct likely will show. Pet could be negative if benign also.

Maybe: Lung nodules smaller than 10 mm (3/8 inch) can be falsely negative on pet because of limitations of the technology. That means the uptake on the scan is not high enough to be suspicious even though the nodule is actually worrisome. However, some small nodules have enough uptake despite their small size. The pet is not a bad idea for a 6 mm nodule, and if positive, means aggressive evaluation.

Usually not: There are exceptions, and they CAN "show up", but the real question to ask is not if it will show up, its what will you do if it doesn't? At this size, a negative PET is not very helpful and the utility of the PET is greatest when it is negative, but not at this size.