Tuesday, March 23, 2021
MEDICALLY REVIEWED BY
Andrada Costache, MD
Dr. Costache is a radiologist with over 10 years of experience. She specializes in thoracic radiology.
A PET-CT scan is a relatively new medical imaging diagnostic method that is successfully used to accurately identify certain types of cancer, as well as their metastases. Besides PET-CT scan also detect body's responses to any infection by lighting up inflammatory responses with the use of radiolabeled tracers.
The scan enables both locating the tumor with maximum accuracy and tracking its evolution over time. [1]
Thanks to the possibility of accurately tracking its evolution, it’s widely used in assessing treatment success and efficiency, including the evolution and spreading of cancer throughout the body.
With its help, the size of each formation is also measured, the response to treatments – so the evolution over time during the administration of different types of treatment, and whether and how the cancer spreads or not throughout the body. A PET-CT can identify the exact localization of both the metastases and the smallest tumor formations in its early phases.
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PET-CT is a combination of two different methods and technologies: PET (Positron Emission Tomography) and CT(Computerized Tomography). The two methods, taken individually, have their own undeniable advantages, but the results they offer are of a different nature and provide different visual data. This is why these two methods work very well together for certain types of cancer and are widely used. [2]
A PET-CT is essentially a combination of these two that enables much clearer and accurate means of diagnosis.
Positron emission tomography (PET ) represents a diagnostic radionuclide imaging technique that uses isotopes with short half-lives. In other words, in order to use this technique, certain radioactive labeled substances, known as tracers, are introduced into the body. Their distribution in the body depends on the tissues they encounter and the interaction with them. These particularities are precisely detected by the camera and then rendered graphically.
Computed tomography (CT ) performs a complete tissue scan and recreates medical images of the entire body section – high accuracy radiographs.
Therefore, a PET-CT combines the two methods into one device. Alone, a PET cannot accurately locate a tumor, as well as its displacement or the way it develops or decreases. The CT is the one who offers this tissue mapping, and the PET-CT combines the two types of cameras to provide data in a single image of maximum precision.
In the detection and correct diagnosis of a tumor there is a wide range of tests to be performed besides a PET CT- clinical examination, blood tests, tomography, mammography, tumor markers, magnetic resonance imaging, or biopsy.
Patient’s blood glucose levels should be measured prior to the PET CT and should not exceed 200 units. After this procedure the patient is injected with glucose and will have to wait quietly, lying in bed, for a minimum of 45 minutes or one hour for it to take effect.
The actual scan has a duration of about 20 minutes (it may take longer, depending on the type of analysis and the scanned area). The result of the PET CT scan consists of a series of standardized medical images, which can be saved locally or in a cloud PACS for later analysis or comparison with other studies using a DICOM viewer.
After completing the procedure, the patient can go home, but it is good to take into account some recommendations:
The PET-CT scan is preceded by the patient’s injection with glucose mixed with radioactive fluoride. After the injection, the respective glucose is absorbed much faster by the cancer cells, as their particular appetite for glucose is higher than in normal cells. Due to the radioactive fluoride attached to the glucose, the substance makes the tumor cells visible to the PET-CT scanner. [3]
This is why this scan is so useful to physicians in correctly detecting all cancer cells, as well as observing their evolution and aggressiveness. Also, this procedure is used when doctors have found metastases in the body, but they have not yet been able to locate the main tumor.
Because this glucose uptake process is a natural one and can be influenced by blood glucose level, patients should not eat anything starting at 6:00 PM on the day before the analysis.
The recommended PET scan prep diet should be high-fat and low-carb. Include high protein items like meat, eggs, and low-starch vegetables along with hard cheese, tofu, and butter. Avoid any foods that are high in carbohydrates like breads, pasta, soda pop, and alcoholic beverages.
Drink plenty of water and avoid exercise te day before the scan. You should not take any OTC cough syrups, cough drops, or antacids on the day of scan. Unless necessary, avoid taking any supplements.
Caffeine can interfere with the PET scan accuracy by disrupting the radioactive tracers distribution in your body. The effect of caffeine is significant in case of heart and can impacts the cardiac pet scan interpretation.
Research shows that patients who consumed coffee before the scans had a "significantly higher" myocardial uptake than those with low or no caffeine intake.
The diagnostic method using PET-CT can be successfully applied in a variety of serious tumors: [4] [5]
PET scanning involves radioactive contrast substance, but exposure to harmful radiation is minimal. The amount of radiation from the contrast substance is small, so the risks to the body are very small. Risk tests are also much smaller and not compared to how beneficial the results can be in a diagnosis of serious medical conditions.
People with allergies may be prone to allergic reactions, so it is advisable to notify their doctor about their condition, especially those with allergies to iodine, aspartame or saccharin. [7]
In the case of those with iodine allergy, the respective substance is replaced by another, based on diluted barium. Among those most likely to have an allergic reaction to iodine include: those with heart problems, other allergies, asthma, kidney disease, blood cell disorders such as sickle cell anemia, polycythemia vera and multiple myeloma.
Pregnant women are a separate category altogether. Because radiation is not considered safe for the fetus, PET-CT scanning does not apply to pregnant women or those who are expecting a pregnancy.
Also, breastfeeding women should take measures before the procedure, as they will not be able to breastfeed within the next 24 hours after the investigation.
[1] https://www.cancer.net/navigating-cancer-care/diagnosing-cancer/tests-and-procedures/positron-emission-tomography-and-computed-tomography-pet-ct-scans
[2] https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/positron-emission-tomography-pet
[3] https://www.radiologyinfo.org/en/info.cfm?pg=pet#how-its-performed
[4] https://www.medicalnewstoday.com/articles/154877#uses
[5] https://www.mayoclinic.org/tests-procedures/pet-scan/about/pac-20385078
[6] https://stanfordhealthcare.org/medical-tests/p/pet-ct-scan/what-to-expect.html
[7] https://www.healthline.com/health/pet-scan
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