Positron Emission Tomography (PET) Advanced Technique for Diagnosing Tumors
What is Positron Emission Tomography (PET) Scan?
A positron emission tomography (PET) scan is a type of test that can be used in cancer treatment. It can be done alongside a computed tomography (CT) scan. For some types of cancer, PET scanning is a way to help find the cancer and determine its stage.
The stage is a way to describe where the cancer is and whether it has spread. This also helps doctors understand how the cancer affects body functions. Knowing the stage of cancer helps choose the best treatment.
It also helps the doctor predict the patient’s chance of recovery. Doctors frequently use PET scans to help diagnose cancer and evaluate cancer treatment. They can also assess some heart and brain problems during the scan.
How does PET differ from CT?
CT scans show detailed images of the organs and tissues inside your body. PET scans can find abnormal activity and can be more sensitive than other imaging tests. They may also show changes in your body earlier.
Doctors use PET-CT scans to provide more information about cancer. In addition to determining the stage of cancer, a PET-CT scan can help the doctor to:
- Searching for the Right Spot for a Biopsy
- Determining if Cancer Treatment is Effective
- Checking for New Cancer Growth After Treatment Ends
- Planning Radiation Therapy
How Positron Emission Tomography (PET) Works
Before a PET scan, you will receive an injection of a small amount of radioactive sugar called fluorodeoxyglucose-18. This substance is sometimes referred to as FGD-18, radioactive glucose, or the tracer. Cells in your body absorb the sugar.
Areas that use more energy take up more sugar. Cancer cells tend to use more energy than healthy cells. The PET scan shows where the radioactive tracer is located in your body.
A CT scan takes X-rays of your body from different angles. You might get an injection of dye before the X-rays to help certain details appear better.
Finally, a computer combines the PET and CT images. Your doctor gets a detailed 3D result showing anything abnormal, including tumors.
Are PET Scans Safe?
PET-CT scans carry a radiation risk. This type of scan uses some radiation from the X-rays, the substance used in the PET scan, or both. Scanning a smaller area of the body means less radiation. The same goes for CT scans without the dye that helps show details.
Typically, the benefits of these tests outweigh the risks. During these tests, you will be exposed to small amounts of radiation. This low dose of radiation has not been shown to cause harm. For children or other people who need multiple PET-CT scans, CT scans, or X-rays, there may be a slight chance of an increased risk of cancer in the future.
Doctors can use lower-dose scans or limit the areas that need to be scanned. Make sure all your doctors know how many imaging scans you have had, including the number and type.
This information can help them decide which scans to use in the future to help minimize risks.
If you are concerned about radiation exposure, talk to your doctor, including asking if you can have another type of test that uses less radiation instead
Why is Positron Emission Tomography (PET) Performed?
A PET-CT scan is a type of nuclear medicine imaging. Nuclear medicine imaging systems aim to detect changes in the body using small amounts of radioactive materials. Thanks to nuclear medicine, changes at the cellular level can be detected, providing early diagnosis of diseases.
Nuclear medicine can also be used to detect if patients are responding to treatments and is used for the following purposes:
- Diagnosing cancer
- Determining if cancer has spread in the body
- Assessing the effectiveness of treatments
- Checking if cancer has recurred after treatments
- Detecting inflammation and inflammatory changes
- Evaluating neurological problems such as reduced blood supply in the brain
- Showing areas of reduced blood flow in the heart muscle
Preparing for a PET-CT Scan
When you schedule a PET-CT scan, the specialist will inform you how to prepare. Be sure to follow the instructions carefully to avoid affecting the test results.
Depending on the part of your body being scanned, you may be asked to drink only fluids after midnight the night before the scan. You may need to stop eating and drinking four hours before the scan. For some scans, you can eat and drink normally.
Medications and Health History: Ask whether you should take your usual medications or supplements on the day of the test. Also, inform them if you have diabetes or other medical conditions. Diabetes can alter test results, and the radioactive tracer can affect blood sugar levels. If you are breastfeeding or might be pregnant, inform the doctor, as these scans can pose a risk to the baby.
Let the doctor know of any medication or food allergies, including any past allergic reactions to iodine.
Do not engage in heavy exercise such as running, jogging, or weightlifting 24 hours before the scan. Exercise can make your scans less accurate.
Wear loose, comfortable clothing without zippers or metal buttons. You will need to remove any clothing containing metal, as metal can affect the scan. This includes belts, earrings, zippered shirts, bras, and glasses. If your clothing is not suitable for the scan, you may wear a hospital gown.
By adhering to these preparation steps, you can ensure the accuracy and effectiveness of your PET-CT scan.
During the PET-CT Scan
The specialist will insert a thin tube with a connected needle into your vein, which contains the radioactive tracer for the scan. You will not feel anything from the radioactive material.
After the injection, you should limit your movement and avoid activity, but you can sit comfortably in a chair. Moving too much can cause the tracer to spread to areas not being studied, making it difficult for doctors to read the scan.
The radioactive material takes about 30 to 90 minutes to reach the parts of your body being scanned.
You may also be asked to drink a contrast liquid that helps make the images clearer. Just before the test starts, you will be asked to empty your bladder.
This liquid can make the area around your vein feel warm or itchy. You might also have a metallic taste in your mouth. These feelings should go away within a few minutes.
If you have a more serious reaction, such as difficulty breathing, inform the staff immediately.
When it is time to start the scan, the technician will help you position your body comfortably on a table. You will likely lie on your back, but you may need to lie on your stomach or side, depending on which part of your body needs to be scanned.
Sometimes PET-CT is used to plan radiation therapy for cancer treatment. In this case, your body position will be very important.
Will I Be Comfortable During the Scan?
The specialist will make you as comfortable as possible. The PET-CT scan itself does not hurt. However, some positions may be uncomfortable or tiring. You need to remain still for the entire scan. You may also need to keep your arms above your head. The specialist might ask you to hold your breath at times, as movement from breathing can cause blurry images.
The staff might also raise, lower, or tilt the table during the scan to get images from different angles. Ask them to inform you when the table will move.
You can expect to hear buzzing or clicking sounds from the machine. Some machines are noisier than others.
The entire process will last from one to three hours once the radioactive material reaches the right area, with the scan itself usually taking about 30 minutes. If the machine scans a large area, the test may take longer. The specialist can tell you how long it will take.
Once the scan is finished, you may need to stay on the table while the doctor checks the images to ensure they are not blurry. If they are not clear, you might need another scan.
After the PET-CT Scan
You can resume your normal activities after the scan, including driving. The specialist will ask you to drink several cups of water to help flush the radioactive material and contrast dye from your body.
Abnormal Results in PET-CT Scans
Abnormal results in a PET-CT scan indicate noticeable changes in the size, shape, or position of the organ being studied. These abnormal results can be due to several reasons, including:
- Signs of cancer or malignant tumors.
- Inflammation or infection in the studied organ.
- Dysfunction of the organ or system being imaged.
- Pathological changes or abnormalities in the organ.
- If abnormal results appear, the doctor must determine the cause of the deviation from the normal pattern and provide appropriate guidance to the patient accordingly.
Risks of PET-CT Scans
- Radiation Exposure: PET scans use short-term radioactive materials, which can increase the risk of cancer over time. However, this risk is generally considered small and is balanced against the medical benefits of obtaining an accurate diagnosis.
- Allergy to Radioactive Materials: Some individuals may experience allergic reactions to the radioactive materials used in the scan, resulting in symptoms such as itching, rash, and difficulty breathing. It is advisable to inform the doctor of any previous allergies to ensure safety.
- Potential Side Effects of the Injection: The process of injecting radioactive materials may cause temporary side effects such as bleeding, bruising, and swelling at the injection site.
- Psychological Discomfort: Some individuals may feel psychological discomfort during the scan, especially if they have an excessive fear of needles or medical devices.
Please note that these risks depend on the individual’s health condition and personal circumstances. It is always advisable to consult the treating physician for appropriate advice and decision-making.
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