What to know about a cancer PET scan machine

The scanner detects a small amount of radioactive tracer in the body. Cancer cells can use glucose differently from surrounding tissue, so areas with increased tracer uptake may appear brighter. Uptake is not specific to cancer: inflammation, infection, normal organs, and healing tissue can also appear active.

PET imaging maps tracer activity, while CT imaging shows detailed body structures. A computer aligns the two image sets so the radiologist can relate an active area to a particular organ, lymph node, bone, or soft tissue.

Clinicians may use PET-CT to assess the extent of lymphoma, help investigate cancer whose original site is unclear, check response during or after treatment, or look for signs that disease has returned. It is not suitable for every cancer, and results are interpreted alongside symptoms, examination findings, blood tests, previous scans, and sometimes a biopsy.

Follow the imaging centre’s instructions about food, drinks, medicines, and exercise because blood glucose and recent muscle activity can change tracer uptake. Tell the team beforehand if you have diabetes, might be pregnant, are breastfeeding, feel unable to lie flat, or become anxious in enclosed spaces.

At the centre, staff may check your blood glucose before injecting the tracer. You then rest quietly while it circulates. During imaging, you lie on a narrow table that moves through a wide, ring-shaped scanner. Remaining still reduces blurred images. The scan itself does not make you radioactive indefinitely; staff will give temporary precautions about close contact, hydration, and using the toilet after the appointment.

Tell staff immediately if you develop breathing difficulty, facial or throat swelling, widespread hives, faintness, or severe chest discomfort during or soon after the appointment. These symptoms need prompt assessment.

Contact the imaging centre if the injection site becomes increasingly painful, swollen, red, or hot. For new or worsening cancer-related symptoms, use the contact route provided by your oncology team rather than waiting for the scan report.

Useful questions include: What decision could this scan change? Do I need to adjust diabetes medicine or other medicines beforehand? How should I follow the food and activity instructions? Will the CT portion use an additional contrast agent? When and how will I receive the report? Ask what an unclear or unexpected area of uptake would mean for the next step, since another scan, follow-up imaging, or tissue sampling may be needed.