PET-CT examination, challenges, management, patient preparation before and after the examination

PET-CT (Positron Emission Tomography Fused with Computed Tomography) is a non-invasive imaging method that allows functional and anatomical evaluation of tissues and organs in the human body.

Msc. Fesal Selimi, PhDc.
Medical Physics Expert & Radiation Protection Expert

This technology is widely used for the diagnosis, staging, and monitoring of several diseases such as: cancer, cardiac pathologies, and neurological disorders.

For this imaging procedure, an active radiopharmaceutical 18F-FDG (Fluorideoxyglucose) is used, which is a combination of glucose with the radionuclide Fluorine-18 (¹⁸F). Fluorine-18 is a positron emitter with a half-life of 109.77 minutes.

After intravenous injection of 18F(FDG), the molecule is selectively taken up by metabolically active cells, especially tumor cells that have a high glucose consumption. The positrons emitted by 18F immediately interact with electrons in the tissue, causing annihilation, a physical process during which a positron and an electron are released, producing two gamma photons of equal energy of 511 KeV that travel in opposite directions (180°).

PET's circular detectors detect these pairs of photons emitted simultaneously within a short time window, through a process called tomographic reconstruction, where the computer then determines the exact location of the annihilation source in the body, creating three-dimensional functional images.

At the same time, the CT (Computed Tomography) scan provides detailed anatomical information, enabling the fusion of metabolic data with the structural map of the body, which significantly improves diagnostic accuracy.

Instructions for patient safety and preparation before performing a PET-CT examination

Before each PET-CT examination, you must inform the medical staff if: you have allergies to drugs or other substances, you are pregnant or suspect that you may be pregnant, you have diabetes, heart disease, kidney disease or other chronic disorders. Bring all medications you use regularly. Always measure your glucose, urea and creatinine levels at least 2 days before the examination and inform the staff of the results, measure your glucose levels at least 24 hours before the examination, stop consuming foods with carbohydrates: sugar, potatoes, rice, bread, alcohol, carbonated drinks and tobacco. During this time, the consumption of foods rich in protein and without fat is allowed: white meat (chicken, fish), lean beef, eggs, fresh cheese. Keep in mind that 6-8 hours before the examination, the consumption of food or drinks other than plain water is prohibited.

Routine medications may be taken 6-8 hours before the examination, unless otherwise instructed by the staff. If you are diabetic, you may take your diabetes medication at least 8 hours before the examination, please consult your doctor the day before the examination if you use insulin.

In certain specific situations, the doctor may order the patient for additional laboratory tests before the examination is performed.

The patient is prohibited from physical exercise at least 48 hours before the examination and the stomach must also be empty before the examination, you should not use gum, candy or sweeteners. Do not use carbonated drinks or juices containing sugar.

Preparation and instructions to be given to the patient during the PET-CT examination

The total duration of the examination for a patient is about 2-4 hours. Initially, the patient stays for about 30-60 minutes in a separate room before the examination, after this time of stay the Nurse/Technician will place an intravenous (IV) line for the injection of the radiopharmaceutical and contrast if necessary. After the injection of the radioisotope, the patient is recommended to drink about 0,5-2 liters of water in 45 minutes to 1 hour.

The PET-CT examination takes 25-40 minutes, depending on body size and the type of examination. The patient should be positioned comfortably and you will be asked to remain still during the examination. The staff will inform and assist you at every step of the procedure.

Patient preparation and instructions after PET-CT examination

After the examination, patients are recommended to:

1. Drink as much water as possible to help eliminate the radioisotope from the body.
2. Avoid close contact with pregnant women and children for 24 hours after the procedure, and maintain a distance of at least 3 meters from other family members.
3. Eat normally after the examination and prefer protein-rich foods after the examination for quick recovery.
4. Take care of your personal hygiene by showering after the examination.

Risks and complications that may occur during a PET CT examination

While PET-CT examinations are generally safe, there are some potential risks and considerations:

• Radiation exposure: Although the amount of radiation in a PET scan is relatively low, it is still a form of ionizing radiation. Radiation exposure from a single scan is generally considered safe for most individuals, but it is important to avoid unnecessary scans, especially during pregnancy.

• Allergic reactions: Although rare, some individuals may have allergic reactions to radiopharmaceuticals. Symptoms may include redness, itching, or swelling. Always inform your doctor if you experience any of these symptoms.

• Claustrophobia: Some people may experience anxiety or claustrophobia from the PET-CT, which is an enclosed machine. If you feel nervous, let your doctor know in advance, as there may be ways to help you manage these feelings.

The most frequently asked questions by patients for PET-CT staff

What is a PET-CT and why is this examination performed?

PET-CT (Positron Emission Tomography) is an imaging examination that measures the metabolic activity of organs and tissues in the body, which is used for: diagnosing and staging cancer, evaluating heart disease, diagnosing neurological disorders (such as Alzheimer's), and monitoring the effectiveness of treatment after RT.

How long does a PET-CT examination take?

The scan itself takes 20 to 45 minutes. The entire procedure (preparation and waiting for the radioisotope to be absorbed) can take about 2 to 4 hours.

Is the PET-CT examination painful?

No. The scan is painless and non-invasive. You may only feel a little discomfort during the insertion of the cannula, which is temporary.

How should I prepare for a PET-CT examination?

Fast for 6-8 hours before the examination (only water is allowed), avoid intense exercise 24 hours before the examination, inform the doctor about all medications you use (especially medications that affect glucose metabolism), diabetic patients should receive specific instructions from the doctor before the examination.

Is PET-CT examination safe?

Yes. PET-CT involves a small dose of radiation, but is considered safe for most patients. The benefits of accurate diagnosis outweigh the risks in most cases.

Can PET-CT detect all types of cancer?

PET-CT is very accurate in detecting many types of cancer, however, some tumors with low metabolic activity may not show up clearly and in certain cases, additional tests may be needed.

How accurate is a PET-CT examination?

PET-CT offers high accuracy, but like any other medical test it can have positive or negative sides. Usually when there are doubts it is used in combination with CT, MRI or other laboratory tests for a more complete diagnosis.

Can I eat or drink before a PET-CT examination?

No food or drinks (except water) for 6-8 hours before the examination, plain water is recommended and beneficial, avoid sugary and caffeinated drinks, which can affect the quality of the images.

Read too Treatment of skin cancer with electrons and the role of the Medical Physicist in Radiotherapy

What happens after the PET-CT examination?

You can resume your usual activities, drink plenty of water to help the body eliminate the radioisotope, avoid close contact with children and pregnant women for 24 hours after the procedure, hygienic cleaning recommended. /Telegraph/