Positron Emission Tomography-Computed Tomography, also known as Positron Emission Tomography or PET-CT scan, is a combined examination of both cellular structures and functions of the body. Apart from detecting pathological changes of tumour cells in the early stages and assessing the extent of metastasis, PET-CT scan can also be used to diagnose cardiovascular and neurological diseases, such as primary brain tumour, Alzheimer’s diseases and seizure.
PET-CT scan can display metabolic state of body cells. Prior to the scanning examination, radiotracers, commonly F-18 Fluorodeoxyglucose (FDG) that is a molecule similar to glucose, are injected intravenously. As tumour cells are more metabolically active and may absorb glucose at a higher rate, the rate of FDG uptake and emission of gamma rays can be detected by the gamma camera, which facilitates the localization of tumour cells. In case of infectious and inflammatory diseases, PET-CT also has the ability to detect the FDG uptake in granulomatous cells producing the inflammation.
On the other hand, CT uses a narrow X-ray beam operating at a high energy level to capture cross-sectional images of inside organs. By superimposing PET images with CT to produce special views, it allows doctors to better correlate and interpret both functional and anatomical information, leading to more precise and accurate diagnoses.
Below is the information regarding the uses, safety issues, concerns of undergoing a PET-CT examination and its advantages and limitations in comparison with other types of imaging modalities.
With the ability to pinpoint molecular activity, PET-CT is particularly useful in the detection of early pathological changes of cancer cells, fostering early diagnosis and hence early treatment.
Its clinical applications include:
PET-CT is applicable to detect most tumours, such as lung, liver, colorectal, breast, lymphoma, head and neck, pancreas, prostate, cervix, gastrointestinal, skin, thyroid, bone and brain tumours.
The amount of radiation involved in both radiotracers and CT scan is minimal. Rarely do severe allergic reactions to radiotracers occur. Therefore, it is generally safe and seldom associated with any significant side effects. Reducing radiation exposure without comprising the diagnostic quality of images has been made possible with the team’s effort at our centre.
Based on previous studies, significant health impacts posed by radiation exposure in undergoing a PET-CT examination have not yet been found. For patients who need regular scanning for disease surveillance, there might be a risk of getting cancer and thus individual advice will be given accordingly upon an appointment with doctors.
Food intake is not allowed for 6 hours and only water is allowed before the procedure. Patients are advised to drink at least 6 to 8 bottles of water 1 day before to ensure enough hydration.
Patients should not have undergone any barium examination within 10 days before the procedure. Patients should inform us of the past medical history, current medications, history of drug allergy or other health conditions such as pregnancy. For diabetic patients, medication can be taken as usual 1 day before the procedure but should be suspended from midnight til the end of examination. To avoid hypoglycaemia, patients are advised to resume normal diet right after the procedure and have half dose of IV insulin or full dose of oral medication. Pregnant women are generally not advised to undergo PET-CT.
Intense muscular activities such as weight-lifting, heavy exercise should not be performed in 24 hours preceding injection to avoid inaccurate result.
Should there be any issues, radiographers are there to provide as much assistance as possible.
Common tests for diagnosing cancer includes blood test, urine test, imaging test, biopsy and genetic test. Apart from diagnosing cancer, these investigations can also localise the primary site, differentiate the specific cancer cell type, perform cancer staging, identify whether there is metastasis, formulate treatment plan, monitor disease progression and detect recurrence. Below is the information regarding different tests.
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