What is PET scan?
Positron emission tomography ( PET) is a sophisticated radiology technique that has been used to analyze different body tissues to distinguish diseases. PET can also be used to monitor the progress of such diseases in treating. While PET is most widely used in the fields of neurology, oncology and cardiology, applications are currently being studied in other areas.
PET is a type of procedure in nuclear medicine. This indicates that during the treatment, a small amount of a radioactive material, called a radionuclide (radiopharmaceutical or radioactive tracer), is used to aid in the examination of the tissue being studied. In particular, PET studies examine the metabolism of a specific organ or tissue, so that knowledge on the organ or tissue’s physiology (functionality) and anatomy (structure) and its biochemical properties are evaluated. PET can thus detect biochemical changes in an organ or tissue that can define the initiation of a disease process before other imaging methods such as computed tomography (CT) or magnetic resonance imaging (MRI) can show anatomical changes related to the disease.
PET is most widely used by oncologists (doctors specializing in cancer care), neurologists and neurochirurgians (doctors specializing in brain and nervous system care and surgery), and cardiologists (doctors specializing in cardiac treatment). However, this technique is starting to be used more commonly in other areas as developments in PET technology continue. Along with other Diagnostic Tests such as computed tomography (CT), PET is often used to provide more reliable knowledge about malignant (cancerous) tumours and other lesions. The combination of PET and CT demonstrates a particular promise in the diagnosis and treatment of several cancers.
PET procedures are performed in dedicated PET centres. The equipment is very expensive. However, a new technology called gamma camera systems (devices used to scan patients that have been treated with small quantities of radionuclides and are currently in use for other procedures in nuclear medicine) is now being modified for use in PET scanning. The gamma camera system can complete a scan faster than a conventional PET scan, and at less expense.
How does PET scan work?
PET acts to detect positrons (subatomic particles) released by a radionuclide in the organ or tissue being investigated by using a scanning system (a computer with a large hole at its centre). The radionuclides used in PET scans are created by adding a radioactive atom to chemical substances which the individual organ or tissue use naturally during its metabolic process. For instance, a radioactive atom is added to glucose (blood sugar) to produce a radionuclide called fluorodeoxyglucose (FDG) in brain PET scans, since the brain uses glucose for its metabolism. FDG is used extensively in PET scans. Depending on the intent of the scan, other substances can be used for PET scanning. Where blood flow and perfusion are of concern to an organ or tissue, the radionuclide may be a form of radioactive oxygen, carbon, nitrogen or gallium. The radionuclide is administered via intravenous ( IV ) line into a vein. The PET scanner then travels slowly across the part of the body that is being investigated. The radionuclide breakdown emits positrons. Gamma rays are produced during positron emission, and the gamma rays are then detected by the scanner. A computer analyzes the gamma rays and makes use of the knowledge to create a picture map of the studied organ or tissue. The amount of radionuclide contained in the tissue determines how brightly the tissue appears on the picture, and shows the degree of function of the organ or tissue. Other potential associated procedures include computed tomography (CT scan) and magnetic resonance imaging ( MRI). For more details, please see these procedures.
Reason for the PET scan procedure?
In general, PET scans can be used to determine the existence of the disease or other diseases in organs and/or tissues. PET can also be used to measure the function of such organs like the heart or brain. Another use of PET scans is in evaluating cancer care. More precise explanations for PET scans include the following but are not limited to:
- To diagnose dementias such as Alzheimer’s disease, as well as other neurological disorders such as Parkinson’s disease (a progressive nervous system disorder in which fine tremor, muscle weakness, and an unusual form of gait are observed), Huntington’s disease (an inherited nervous system disease that induces increased dementia, strange involuntary movements, and irregular posture)
- The relevant surgical site to be found before brain surgery
- To examine the brain after trauma to identify the hematoma (blood clot), bleeding, and/or perfusion (blood and oxygen flow)
- To detect cancer spread from the original cancer site into other parts of the body
- Assessing the success of cancer therapy
- To measure myocardial perfusion (heart muscle) as an aid in assessing the effectiveness of a therapeutic procedure to enhance myocardial blood flow
- To classify more lung lesions or masses found on X-Ray torso and/or chest CT
- Helps control and treat Lung Cancer by staging lesions and monitoring the development of lesions during treatment
- To detect tumour recurrence earlier than with other methods of diagnosis
Your doctor might come up with other reasons to prescribe a PET scan.
Risks of the PET scan procedure?
For the operation, the amount of radionuclide inserted into your vein is minimal enough to not require precautions against radioactive radiation. The radionuclide injection may cause some mild discomfort. Allergic radionuclide reactions are uncommon, but they can occur. For certain patients, it can cause certain discomfort or Pain to have to lie still on the scanning table for the duration of the operation. Patients resistant to or vulnerable to drugs, contrast dyes, iodine, or latex should inform their doctor. If you are pregnant or think you might be pregnant, you should alert your health care provider from a PET scan, because of the possibility of damage to the foetus. If you are lactating, or breastfeeding, your health care provider should be aware of the possibility of radionuclide contamination of breast milk. Depending on your particular medical condition, there may be other dangers. Be sure to speak with your doctor about any questions prior to the operation.
The accuracy of a PET scan can be compromised by certain variables or conditions. These considerations include the following but are not limited to:
- High levels of blood glucose among diabetics
- Ingested caffeine, Alcohol or nicotine within 24 hours of the treatment
- Medicines, such as morphine, sedatives and tranquilizers
If any of the above circumstances can apply to you, inform your doctor.
Before the PET scan procedure?
- Your doctor will describe the procedure and will give you the opportunity to ask any questions you might have about the procedure.
- You will be asked to sign a consent form allowing you to do the procedure. Carefully read the document, and ask questions if there is anything ambiguous.
- If you are allergic to latex and/or sensitive to medicine, contrast colouring, or iodine, notify the radiologist or technologist.
- Fasting is usually needed for a specified period of time before the operation. Your doctor will send you specific instructions in advance as to how many hours you will deprive of food and drink. You will also be told by your doctor about the use of drugs before the PET Scan.
- Notify your health care provider of all drugs (prescribed and over-the-counter) and herbal supplements you take.
- You should not drink any Alcohol or caffeine, or use Tobacco for at least 24 hours before the treatment.
- If you are a diabetic who uses insulin, you might be advised to take the insulin dose several hours before the treatment, with a meal. Your doctor will give you detailed instructions depending on the condition you are in. A fasting blood sugar test can also be obtained before the operation. If the blood sugar is high, insulin may be given to lower the blood sugar.
- Your doctor may order a further detailed preparation based on your medical condition.
During the PET scan procedure?
PET scans can be conducted on an outpatient basis or as part of your hospital stay. Procedures can differ according to your condition and the practices of your doctor.
A PET scan normally follows the process:
- You will be asked to remove any clothes, jewellery, or other items that could interfere with the scan. If you are asked to remove your pants, you will get to wear a robe.
- Before beginning the procedure, you will be asked to clear your bladder.
- For radionuclide injection one or two intravenous ( IV) lines will be initiated in the hand or arm.
- Some forms of abdominal or pelvic scans can involve the insertion of a urinary catheter into the bladder to drain urine throughout the procedure.
- In certain cases, an initial scan can be done before the radionuclide is injected, depending on the type of research being conducted. Within the scanner, you will be put on a padded table
- They will inject the radionuclide into your vein. The radionuclide would be able to accumulate for about 30 to 60 minutes in the organ or tissue. At that time you can stay in the room. You would not be harmful to anyone because the radionuclide releases less radiation than a normal X-Ray.
- The scan will begin after the radionuclide has been absorbed for the corresponding period of time. The scanner travels slowly across the section of the body being examined.
- Upon completion of the scan, the IV line will be removed. If a catheter is used, it will be removed.
Although the PET scan itself does not cause pain, having to lie still for the duration of the procedure can cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure, such as operation. The technologist will use every possible measure of comfort and complete the operation as soon as possible to reduce any discomfort or Pain.
After the PET scan procedure
When you get up from the scanner table, you can step slowly to prevent any dizziness or light headedness from lying flat for the duration of the operation.
After the test, you will be advised to drink plenty of water and periodically empty your bladder to help flush the excess radionuclide out of your body for 24 to 48 hours.
Any symptoms of redness or swelling will be tested at the IV Site. If you experience any discomfort, redness, and/or swelling at the IV site after returning home after your treatment, you should alert your doctor as this may suggest an infection or some kind of reaction.
After the procedure, your doctor can give you additional or alternative instructions, depending on your particular situation.