What to Know About a PET Scan

In cancer care, it may help locate active disease, assess its extent, guide a biopsy, or show how tissue responds to treatment. PET is often combined with CT so metabolic activity can be matched to detailed anatomy. An active area on the image is not, by itself, a cancer diagnosis.

The tracer most often used in oncology behaves similarly to glucose. Cells that take up more tracer appear as areas of increased activity, sometimes called uptake. Cancer can cause uptake, but inflammation, infection, healing tissue, and normal organ activity can also do so. A radiologist interprets the pattern alongside the CT images, your history, earlier scans, and any biopsy findings.

A report may describe the location and intensity of uptake and compare it with previous imaging. The result can narrow the next decision, but tissue sampling may still be needed when the diagnosis remains uncertain.

Follow the imaging centre's instructions about food, drinks, exercise, and medicines. Tell the team before the appointment if you have diabetes, are pregnant or could be pregnant, are breastfeeding, have difficulty lying still, or have had a recent infection, procedure, or treatment. These details can affect preparation or image interpretation.

After the tracer injection, you will rest quietly while it circulates. The scan itself requires lying still on a moving table. Unless the clinical team gives different advice, drinking fluids afterward helps clear the tracer through urine. Keep the written report and images available for the clinician who requested the test.

Tell staff immediately if you develop trouble breathing, facial or throat swelling, faintness, or widespread hives during or soon after an injection. These symptoms can signal a serious reaction and need urgent assessment. Contact the imaging centre if the injection site becomes increasingly painful, swollen, or red after you leave.

The scan does not replace assessment of new or worsening symptoms. Seek prompt care for severe breathlessness, new weakness, confusion, uncontrolled pain, or another symptom your cancer team has identified as urgent.

Ask what specific decision the PET-CT is intended to inform, whether contrast will also be used, how your medicines should be managed beforehand, and when the report will be discussed. If uptake is found, ask whether it can be explained by infection or recent treatment and whether comparison imaging, another scan, or a biopsy is needed.