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PET / CT explained

PET-CT (positron emission tomography and computerised tomography) is a scanning method that allows us to see how organs are working. PET / CT helps us identify organs or tissues that are not working normally.

The body is imaged following the injection of a radioactive tracer (most commonly 18FDG; a form of slightly radioactive sugar.) This provides important information about many conditions affecting different organs and these images allow your doctor to plan your treatment more accurately.

Radioactive tracer injections

To perform a PET scan, a very short lived radioactive tracer is first injected into a patient, commonly in the form of radioactive glucose (18F fluoro-deoxyglucose or FDG.) The amount of tracer administered is very small, usually under 2mls. After injection, the patient will rest for 60 to 90 minutes allowing time for the tracer to be metabolised in the body. It was found that most cancer cells have a higher glucose uptake than the adjacent healthy cells. With this information in mind, the cancer and its metabolic activity can be easily identified on the images.  

While FDG is our most common radioactive tracer used; Addenbrooke’s has an onsite radiopharmacy which is able to produce 68Ga DOTATATE and 68Ga PSMA for us. These tracers are able to image different metabolic processes in the body to FDG, therefore in some cases you may find you have been referred for one of these scans instead.

A close collaboration has been formed with the Wolfson Brain Imaging Radiochemistry Department (WBIC) within Addenbrooke’s Hospital to supply radiopharmaceuticals for both clinical and research purposes. The Wolfson Brain Imaging Department has a cyclotron which produces a wide range of positron emitting tracers including 18F CETO and 11C Methionine, Metomidate, and PiB.

Combining a PET scanner with a computer tomography (CT) scanner

PET images do not give good anatomical detail which is required for treatment planning. The combination of a PET scanner with a computer tomography scanner compensated for this by allowing anatomical images to be obtained at the same time, thus allowing the co registration of both sets of images. Computed tomography uses multiple x-rays to generate a three dimensional image. Images obtained in this way show exquisite anatomical detail.

Combining these two technologies, the PET / CT provides us with information on where the cancer is and its relationship with the adjacent healthy tissue. We are also able to identify any distant spread of the cancer much earlier than any other imaging methods.

Cardiology and neurology diagnostics

PET / CT has other clinical uses than just cancer imaging. It can look at the elevated glucose metabolism in inflammatory cells in arterial walls (arteritis) and for sources of infection. This imaging can also determine blood flow to the heart muscle and therefore the effects of a myocardial infarction on areas of the heart. PET / CT can assist in areas of epilepsy, alzheimer's disease and other neurology diseases.