What Is a PET-CT Scan?
Diagnostic radiology is an advancing field. Various novel diagnostic tools are being devised periodically. Most of them are adept at providing images related to the tissues, organs, and their structural problems but not the working system of the body. A positron emission tomography (PET) scan is a nuclear imaging test that uses radioactive material to determine the metabolic and biochemical functioning of the tissues. The radioactive material is injected into the vein, and areas with abnormal metabolic activity will show increased uptake of the material, thus indicating the possibility of a disease. Changes in the biochemical properties can help identify the disease earlier before any structural or anatomic changes have happened in the tissues, which appear only later in an imaging process.
PET scan has been widely used in the field of oncology, though other areas are also benefiting from the advances in PET. PET scans are usually combined with computed tomography (CT) or magnetic resonance imaging (MRI) to form a combined PET-CT or PET-MRI scan for enhanced imaging.
Why Is a Combined PET-CT Preferred Over a PET Scan?
A PET scan displays the functioning details of the organs and tissues based on biochemical and metabolic activities. CT scan shows detailed images of the organs and structures within the body about the size, shape, anatomical abnormalities, and structural problems. A PET scan provides low-resolution anatomical details, whereas a CT scan can provide high-resolution images of the anatomical location of the disease. Hence a combination of these two procedures, that is, a PET-CT scan can help acquire both anatomical and functional images in a single procedure, thus providing better efficacy and accuracy in diagnosis.
What Is the Working Principle of a PET-CT Scan?
A PET-CT scan is most commonly used in cancer detection. The radioactive material commonly used is F-18 fluorodeoxyglucose (FDG) which is similar to a glucose molecule. This radioactive material tends to accumulate in various parts of the body depending on the molecular activity and metabolic rates of the tissues. Tumor cells are metabolically more active as they are rapidly dividing, and their growth rate is exponential; hence they attract glucose at a higher rate. Thus, an increased uptake of FDG, which appears as a bright spot on a PET scan, can indicate the possibility of malignancy.
What Are the Common Uses of PET-CT Scans?
A PET-CT scan is indicated in the following conditions:
Oncology:
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To diagnose cancer and determine its stage.
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To check for the spread of cancer in the body.
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To check if cancer has recurred.
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To evaluate the efficiency of the cancer treatment and its prognosis.
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To help differentiate active cancer from scar tissue, left post-cancer treatment.
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To check for disease progression.
Neurology:
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It can be used to diagnose conditions such as Parkinson’s and Alzheimer’s disease. It can help to assess the metabolic and biochemical activities of the nerves in the brain, thereby aiding in the diagnosis.
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Also, certain tumors, strokes, and seizures can be diagnosed using a PET-CT scan.
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It can help to determine the blood flow and oxygen supply to the brain tissues after trauma.
Heart:
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PET scan may aid in determining the blood flow to the heart muscles and if a surgical intervention such as angioplasty or bypass may help restore the blood supply.
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To ascertain the heart muscle function after a heart attack.
What Are the Preparations Done Before the Procedure?
- Patients should preferably wear comfortable clothes while going for this procedure.
- Female patients should inform the doctor if they are pregnant or could be pregnant.Lactating mothers should also notify the doctor as they may be required to stop breastfeeding for a few hours after the procedure. Inform the doctor of any history of allergy. Patients should report to the doctor about the medications, supplements, and over-the-counter medicines taken by them. They should give a detailed medical history.
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Claustrophobic patients (fear of closed spaces) should also inform the doctor of the same. Patients should remove any jewelry, accessories, or metallic objects such as pins, belts, and eyeglasses at home before the procedure. They should also remove their hearing aids and removable dentures before the procedure.
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Patients should fast, that is, do not eat or drink four to six hours before the procedure.
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Patients should avoid sugary drinks and food as they can alter the glucose level in the body resulting in faulty reports.
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Diabetic patients have to follow certain special instructions. They can take all the medicines till the day before the procedure. They need to preferably schedule an early morning appointment. Patients need to give a gap of four to six hours between their diabetic medicines or insulin and the PET-CT scan procedure.
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If patients are wearing an insulin pump or continuous glucose monitor, they should be removed before the procedure. The blood sugar level is supposed to be between 70 to 200mg/dl.
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No strenuous physical activity for a day before the exam.
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Patients might be required to do some blood tests before the procedure.
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They should ensure to carry all their recent reports to the scan center on the day of their procedure.
How Is the Procedure Done?
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A PET-CT scan is done on an outpatient basis, and no hospital stay will be required.
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The entire procedure takes about two hours to complete.
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The patient will be asked to change into a hospital gown and will be taken to the examination room. They will be asked to empty the bladder before the procedure.
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The patient’s medical history will be assessed in detail before the procedure begins.
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An Intravenous (I.V) line would be inserted into the vein of your arm through which the radioactive material F-18 fluorodeoxyglucose (FDG) would be injected. The patient might experience a cold feeling when the radioactive material is injected.
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The patient will have to wait for 30 to 45 minutes while the radioactive material is dispersed throughout the body.
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Iodinated contrast material will also be injected through the I.V line.
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The patient would then be taken to a PET-CT scanner, where they would be made to lie down.
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Patients are required to remain very still while the scanning is in progress.
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The scanning machine would record the energy transmitted by the radioactive material, which would then be processed by a computer into the images.
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For a cardiac PET-CT, images will be obtained initially after injecting the radioactive material, which will be known as resting images. Later a vasodilator medication would be injected through the I.V, which would stimulate the heart, causing it to beat rapidly. Further radioactive materials may be injected and the images obtained are known as active images. These two scans would be compared to assess the cardiac blood flow.
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Once the desired images are obtained, the I.V line will be removed, and the patient will be asked to wait in the recovery room for 30 minutes after the procedure is complete.
What Are the Instructions After the Procedure?
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Patients can resume their normal activities after the procedure unless otherwise instructed by their doctor.
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They should drink lots of water to flush out the radioactive material from their body. The radioactive material is expelled from the body either as urine or feces.
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Patients will be asked to flush twice after urinating.
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Do not come in close contact with pregnant ladies or infants and kids for at least 12 hours after the procedure.
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Breastfeeding should be stopped for 12 hours after the procedure, during which the breast milk may be pumped and thrown or stored for 24 hours, after which it can be fed to the baby. Breastfeeding can be resumed after 12 hours.
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Patients air-traveling within a week of the procedure should carry the report showing a PET-CT scan has been done; the radiation monitors at the airport are sensitive enough to pick up any remnant radiation left in the body.
What Are the Benefits of the Procedure?
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PET-CT provides double diagnostic clarity by giving information on the structural as well as functional issues of the body.
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Painless and less invasive.
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No recovery time is required after the procedure.
What Are the Risks Associated With the Procedure?
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Allergic reaction to the contrast material.
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Low risk of radiation exposure.
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The injection site may have some redness, swelling, or pain.
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Possibility of the radioactive material leaking outside the vein resulting in some swelling which would be temporary.
What Are the Limitations of the Procedure?
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The procedure may be time-consuming as it takes time for the radioactive material to accumulate and disperse throughout the body.
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Altered blood sugar levels, especially in diabetic patients, can hamper the test results as the radioactive material is also a glucose analog. Hence, it is essential to monitor the blood glucose level in diabetic patients, and the procedure is carried out with certain precautions.
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The radioactive material needs to be prepared for every procedure as they are effective only for a short period. Hence, patients need to report at the scheduled time.
Conclusion:
Oncological imaging has been redefined with the introduction of the PET-CT scan. A PET-CT scan is proved to be a synergistic combination providing superior diagnostic accuracy and high-resolution images in a single procedure. The accurate diagnosis and staging and determining the spread of disease is the key to successful management and better prognosis. With further advances, PET-CT will be an indispensable diagnostic tool in the field of radiology.
