PET / CT - what is this study?

Many already know, when talking about PET / CT, that this is a new, very accurate way of early diagnosis of oncology, neurological diseases and cardiovascular pathologies. He, unlike CT or MRI, does not show a picture of the anatomical features of the patient's body, but records the process of functioning of certain organs and tissues. How PET scanning is done and how you need to prepare for it, we'll cover in this article.

What diseases are diagnosed with PET / CT?

Positron emission tomography is a complex study by which it is possible to diagnose tumors that do not produce clinical manifestations and cancer metastases in the initial stage. In addition, it allows you to monitor the course of the disease, the results and effectiveness of therapy.

In cardiology, PET / CT scan is used in cases of coronary heart disease and before aortocoronary bypass surgery. In neurology, with its help, multiple sclerosis is diagnosed, and in psychiatry - Alzheimer's disease at an early stage, when external manifestations of the beginning of pathology are not yet observed. By the way, this examination makes it possible to distinguish Alzheimer's disease from other pathologies leading to senile dementia (Parkinson's or Huntington 's disease ).

With the help of PET, brain function is evaluated after a stroke and seizures are diagnosed with epilepsy.

PET / CT: reviews of the benefits of this diagnostic method

Before other modern methods of diagnosis, PET has many advantages. First of all, this method is the most accurate of all existing ones, and besides it can replace several traditional surveys. In addition, PET does not cause painful sensations, does not have harmful side effects on the human body and allows to detect the pathological process already at early stages.

The reviews available among doctors about PET / CT allow us to talk about this method as a way to obtain reliable information at a stage in which the visible to the eye of structural changes in the organ does not yet exist. And this, as you understand, allows you to start treatment at the earliest stages of the disease, which greatly increases the effectiveness of therapy.

Principle of PET examination

It is worth mentioning, talking about the features of PET / CT, that this examination allows you to record the flow of blood in organs and tissues, as well as the consumption of glucose by the latter.

In the body of the examinee, a small, harmless for human, a quantity of radioactive substance, which is carried by blood through the tissues. The weak radiation coming from it is fixed by PET and transmitted to the computer. There is information processing and image creation. And the more radioactive material appears in the tissues, the brighter they look in the picture - these are the so-called "hot" areas, and places where the substances are small, look dull - these are "cold" areas.

Developing cancer cells especially need glucose, they have an active metabolism, which gives them in the photos after PET / CT with a bright ("hot") image. Thus, with PET diagnostics, it is possible to detect only cancer cells that have begun their pathological growth and even to specify the forecast of their growth.

Methods of PET / CT

Depending on what are the tasks of the examination, the doctor may need some or other methods of carrying out the described diagnostics with different radiopharmaceuticals:

• PET with 11C-choline;
• PET with 18F-fluorodeoxyglucose;
• PET with 11C-methionine;
• PET with 13N-ammonium.

For example, the diagnosis of malignant glioma (brain tumor) requires the results of PET / CT with methionine, which allow an assessment of the degree of its malignancy.

For the results to be as reliable as possible, the day before the study, the patient is recommended to exclude from the diet all protein-containing foods: meat, fish, milk and soy. You can eat only fruits and vegetables. The clinic should come on an empty stomach, and water is allowed to drink in unlimited quantities (but not fizzy or sweet).

In what cases is the diagnosis with choline

To assess the state of the body in prostate cancer, as well as tumors of the liver and brain, PET / CT with choline is most often performed.

This substance is involved in the construction of cell walls, therefore, when a radionuclide is introduced into it, it makes it possible to visualize the presence of even small metastases that can be seen in the images as luminous points.

These studies are conducted in 2 stages - immediately after the introduction of the radiopharmaceutical and after 40 minutes. Scanning is done on an empty stomach and without the use of liquid (it is completely excluded in the morning).

For 1-2 weeks before the examination the patient is recommended to be excluded from the ration:

• Eggs;
• peas;
• Soy, lentils and kidney beans;
• Liver (and other offal);
• spinach;
• Cabbage;
• peanut;
• Oatmeal;
• Orange juice and any vitamins (especially group B).

How is the examination conducted

In the room where the PET / CT examination is being conducted, the patient is asked to turn off the mobile devices and offer to go to the waiting room, where the patient must relax and calm for 20 minutes. This is necessary to improve the quality of the images.

After this, the patient is injected intravenously with a radiopharmaceutical and wait another half hour until the substance is distributed in the tissues of the body. By the way, if at that time there is a need to go to the toilet, you can not ignore it. Next, the patient is offered to go to a PET scanner that looks like an X-ray machine. The process of examination lasts about 45 minutes (brain scan, however, can take and 1.5 hours).

If necessary, during the procedure, someone from the medical staff may approach the patient. In the case of heart examination, the patient may be given a dosed physical load that will demonstrate the features of the blood supply and functioning of this organ.

It may take several hours to 2 days to process the material. It all depends on the type and complexity of the survey.

How is the whole body examination performed

The whole-body PET / CT procedure is usually performed to the bottom of the pelvis. The question of whether or not to capture the skull at this time remains controversial. In many centers this is not done. If it is necessary to examine anatomically complex areas, a targeted scan is performed with the introduction of a contrast agent (iodine preparations).

Scanning begins, as a rule, with the pelvic area to exclude the image change that appears as a result of the gradual filling of the bladder. Each position is scanned for at least 4 minutes (emission scan) plus another 2 minutes (transmission scan).

A full body PET scan allows you to make a complete operation plan to remove all affected tissue if possible.

Contraindications for PET / CT

It should be noted, speaking of PET / CT, that this examination in some cases is contraindicated, since the data may be distorted. For example, this happens in the early postoperative period after an open biopsy (in these cases, wait at least 4 weeks after the operation). Also, PET is contraindicated after recent chemotherapy or radiotherapy. In the latter case, a three-month break is recommended.

Inflammatory processes in the body: abscesses, infections and sarcosis - can give false positive results when scanning. In such situations it is necessary to be cautious about what PET / CT shows.

In some other cases (for example, with claustrophobia or if the patient has difficulty lying down), the scan protocol changes depending on the patient's condition.

Things to remember when preparing for PET / CT

In order for PET / CT diagnostics not to give you unpleasant sensations, and the results of it were of the highest quality, you must observe several general rules for any kind of procedure:

• PET / CT should be warm and comfortable.
• On clothes and body there should be no metal objects and ornaments.
• You can take 1 liter of unsweetened and non-carbonated drinking water.
• Women are obliged to inform the doctor about the available or possible pregnancy, as well as about breastfeeding, since in these situations scanning is strictly prohibited.
• It is necessary to mention the presence of allergic reactions.
• And for patients with diabetes, special preparation for PET / CT is required.
• In situations where the examination is performed in the pelvic area, an insertion into the bladder of the catheter may be necessary.
• Throughout the examination, the patient should be immobile, you can not change the pose.
• If no other recommendations are given, then immediately after the scan, the examinee can return to the usual way of life, and to accelerate the excretion of radiopharmaceuticals, he should drink as much liquid as possible.

How to interpret the results of PET / CT: what does this conclusion mean?

After the scan is carried out, the patient is given results. Immediately it is worthwhile to warn everyone who is assigned to this examination, from the attempts to treat them themselves - this is within the competence of the attending physician only (medical workers conducting PET also do not give any recommendations).

Lack of special knowledge can lead to incorrect interpretation of the results. They may seem heavier than it really is or, conversely, do not require medical intervention. The results of PET / CT can only be interpreted by the doctor who sent you to this examination. And if you decided on it yourself, then, no matter what the conclusion is from your point of view, it's best to demonstrate to his profile specialist for accurate diagnosis and the appointment of the necessary treatment.