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A whole-body PET scan provides information about the body's chemistry and cell function (metabolism) rather than pictures of the body's anatomy or structure as shown by X-ray, ultrasound, CT scans, or MRI. As a result, PET scans may reveal abnormalities or tumours that would otherwise go undetected. In more situations than with any other imaging modality, a PET scan is key to early detection and accurate diagnoses.
You will be injected intravenously with a small amount of FDG (a form of glucose with a radioactive tracer). The amount of radiation received is less than from a typical CT scan. The FDG will distribute through the body and, because cancerous tissue aggressively feeds on glucose, the affected organ shows a concentration of FDG. After sitting quietly for 45 minutes, you will be asked to lie comfortably on a table that passes through the PET scanner. This will take about 45 minutes. Some patients who undergo PET may feel confined or claustrophobic and may require a sedative.
The FDG emits positrons that result in gamma rays that the scanner will record. A computer will process the information into a 3-dimensional picture of the body on a video screen. The PET scan will show images of your body metabolism (function), rather than pictures of your anatomy (structure) as shown in MRI and CT scans. This can uncover abnormalities or tumours that could otherwise go undetected. Early detection of cancer and recurring cancer is vital to its successful treatment.
A radiologist experienced in PET will analyze the scan and send a report with his or her interpretation to your physician. This should take only a few days or less.
You must fast for 8 hours prior to the PET scan. You may take your medications with a sip of water. If you are diabetic, you must fast for at least 4 hours before your scan and there should be a minimum of a three hour wait following the last dose of insulin. Oral medications may be taken as usual. All patients will have their blood sugar checked before the PET scan. If the blood sugar is too high the scan will have to be delayed and rescheduled. If you are a female with the potential to bear children, a blood test will be done to ensure that you are not pregnant.
A nuclear medicine technologist will explain the procedure to you and obtain your written consent for the PET scan. The technologist will also ask you if you have any drug allergies. You may be given a light sedative before the scan. This will be decided by the physician supervising the PET scan after discussion with you. If the physician thinks you need a sedative, a small tablet of lorazepam (Ativan) will be placed under your tongue to help you to relax during the scan. You may experience drowsiness and fatigue. If you have an allergy to lorazepam, you should not receive this drug. Please inform the technologist of this allergy.
You will then receive an injection of the PET imaging drug,18F-Fluorodeoxyglucose (FDG), through a vein in your arm. This is a radioactively-labelled sugar and where it collects in the body may represent areas of hidden cancer. Although FDG is not a new drug, Health Canada requires that we consider the use of FDG as investigational. There have been no adverse effects reported with its use.
Your heart rate, blood pressure and temperature will be monitored before the injection, before imaging and after imaging in order to monitor the safety of the FDG.
After the FDG is given you may also be given a diuretic called furosemide (Lasix) through a vein in your arm. This will help your body to get rid of the FDG through your urine. Furosemide does not normally cause any adverse reactions, however patients who are allergic to fursemide or sulfonamide antibiotics (sulpha) should not receive furosemide. If you have an allergy to one of these drugs, please inform the technologist.
The actual PET scan will be done 1 hour after the injection of the FDG. During the scan you must lie quietly on the scanning table. If you think this may be difficult for you, you may request a sedative to help you relax.