PET Scan

A PET scan works differently from an X-ray or MRI. Instead of showing the structure of your tissues, it shows how actively those tissues are working — their metabolic function. Before the scan, you receive an injection of a radioactive tracer, most commonly a form of glucose (sugar) that's been tagged with a tiny radioactive particle called a positron. The scanner then detects where in your body that tracer accumulates.

Cancer cells divide rapidly and consume a great deal of energy, so they tend to absorb glucose at a much higher rate than surrounding normal tissue. On a PET scan, these areas show up as bright spots — called "hot spots" — that flag areas of high metabolic activity. This makes PET scanning particularly valuable in cancer care for finding tumors that might be too small or too scattered to show up clearly on a CT scan or MRI alone.

PET scans are often performed in combination with a CT scan (as a PET/CT), allowing doctors to see both the functional activity and the structural anatomy in the same session. The test itself is generally painless — you lie still on a table while the scanner moves around you — and the radioactive tracer leaves your body through normal urination within a day.

PET scans are one of the most powerful tools available for cancer staging — determining how far a cancer has spread — and for monitoring treatment response. If a tumor is responding to chemotherapy or radiation, its metabolic activity will decrease, and that change shows up on a follow-up PET scan before the tumor even visibly shrinks. This allows oncologists to adjust treatment strategies in real time.

PET scans are also used to help distinguish between scar tissue and active tumor after treatment, which can be difficult to tell apart on structural imaging alone. If your oncologist recommends a PET scan, it's typically because the metabolic picture it provides will add meaningful information to your care plan.