PET CT Scan: Purpose, Procedure, Benefits

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.

PET CT 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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So what is a PET CT Scan?

As the name implies, a PET-CT is a combination of two different methods and technologies: PET – positron emission tomograph – 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.

How does it work?

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.

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 must follow some rules before taking a PET CT test:

• Patients should not eat anything starting at 18.00 on the day before the analysis
• They are not allowed to eat sweets, pastas, cereals, leaves
• You don’t have to make an effort
• Do not drink coffee or alcohol
• You must avoid the cold

In addition, 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:

• To consume as much fluid as possible in the next 24 hours – the substance used is naturally eliminated from the body in this interval through urine, sweat and feces
• Avoid physical closeness of children under the age of 7, as well as pregnant women
• Preferably stay in a separate room from the other family members

Main PET CT focuses:

The diagnostic method using PET-CT can be successfully applied in a variety of serious tumors: [4] [5]

• Lung cancer (bronchial carcinoma)
• Breast cancer (Breast carcinoma)
• Cervical cancer (Cervical carcinoma, endometrial carcinoma)
• Ovarian cancer (Ovarian carcinoma)
• Larynx / throat cancer
• Cancer of the esophagus (Esophageal carcinoma)
• Head cancer (brain tumor)
• Colon cancer (Carcinoma of the colon – large intestine)
• Pancreatic cancer (Pancreatic carcinoma)
• Black skin cancer (Melanoma)
• Cancer of the thyroid gland (Carcinoma of the thyroid gland)
• Cancer of the bladder (Carcinoma of the bladder)
• Prostate Cancer (Prostate Carcinoma)
• Malignant lymphoma (cancer of the lymph glands)

The advantages of a PET-CT

• By diagnosing with the help of a PET-CT, the advantages of the two individual methods are combined, and the result considerably exceeds images obtained by the two devices taken separately.
• The method allows identification of all cancerous formations in the body, regardless of their size or degree of development.
• The diagnosis time is short, the doctor can thus save precious time in the fight with the disease [6]
• The substance used, although it is radioactive, presents a very low degree of risk, it is naturally eliminated by the body within a maximum of 24 hours after administration

What risks does a PET scan entail?

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.

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References:

[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