As a radiologist, a challenge is to clearly explain the limitations of the imaging modalities we use to diagnose disease. For instance, people think of a PET scan as the best way to diagnose a cancer. If a "spot" is "bright," i.e. "hot," it must be cancer right?

Wrong.

Here is an excerpt from "Radiologic Clinics of North America: PET/CT," September 2013, which nicely sums up the limitations of PET scans for "patients with known or suspected lung cancer:"

"Information can mimic malignant tissue on FDG-PET, and this must always be kept in mind. For example, small spiculated nodules can because by pneumonitis, and present a management dilemma as they are not generally suitable for biopsy. Radiation pneumonitis can be FDG-PET positive, making it difficult to assess possible residual or recurrent lung cancer after radiation treatment. A pulmonary abscess can be indistinguishable from a pulmonary cancer based on CT and FDG-PET findings. Not all malignant neoplasms are FDG avid, and, in the lungs, well-differentiated adenocarcinoma and carcinoid tumors can be minimal or essentially negative on FDG-PET images. Small foci of FDG tracer activity in the skeleton can be caused by degenerative joint changes or healing fractures, or even Schmorl's nodes and vertebral body end plates and mimic small metastatic deposits. Benign adrenal adenomas can present modest FDG uptake. In contrast, certain benign tumors such as Warthin's tumor in the parotid gland or pituitary adenomas at the skull base can be very FDG avid and be mistaken for distant metastases based on the PET images alone. Patients with lung cancer can have additional unrelated neoplasms, and incidental thyroid and early colon cancers are commonly seen on FDG-PET images."

So if you or a loved one or a friend needs or has undergone a PET scan, please make sure you understand the findings and discuss them fully with either your doctor or, if possible, the radiologist who interpreted the study.