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Positron Emission Tomography (PET) | Diseases and conditions: Medical tests.


What is a PET

Positron Emission Tomography (PET by its English name, positron emission tomography) is a diagnostic test which, through the use of a small amount of a radioactive substance, allows to obtain images of the inside of the body.
Unlike other techniques such as computed tomography (CT) or magnetic nuclear (NMR), the PET resonance not gives anatomical information of the organism, but it detects the metabolic activity of cells you want to study. For example, you can determine the blood flow, oxygen consumption, or the consumption of sugar, certain cells. For this reason, used mainly for diagnosis and follow-up of patients with cancer, because the tumor cells have a different healthy cells metabolism.
PET can also be used in other fields in cardiology or Neurology. Using radioactive substances, is a technique that is included in a part of the so-called medicine nuclear medicine.
The PET machine is very similar to that used to make a TAC. It is a large machine shaped donut and a stretcher inside where the patient lies down. Prior to the taking of images is given a radioactive substance, called a radiopharmaceutical or liner, intravenous, oral or inhaled via, depending on the suspected diagnosis. This radiopharmaceutical circulates through the body and sticks to the tumor cells, which begin to emit a small amount of radiation. This radiation is detected by the machine's PET, which produces an image that highlight areas of the body where it has accumulated the radiopharmaceutical and that they may correspond to tumors.
In many occasions is a TAC while the PET is made. This allows to see images of the body by two different techniques, which can be merged into a single image and offers a very precise information about the possible pathology. Devices that have incorporated both technologies are used for this.

In which cases is performed tomography (PET) positron emission?

The most common reasons for which you can request the realization of PET are as follows:
· Detect a cancer.
· Detect if a cancer has spread through the body, i.e. If metastasis has occurred.
· To determine the efficacy of a treatment against cancer, i.e., if the treatment has achieved a reduction or disappearance of tumors or metastases.
· To determine if cancer has come back after having been eliminated with treatment.
Less frequently, and outside the field of cancer, it can be used for the following:
  • Study of blood flow to the heart and see the effect of myocardial infarction on the cardiac muscle. After a heart attack, the PET can identify areas of the heart muscle that are still viable and that can benefit from revascularization treatment.
  • Evaluate the functioning of the brain in disorders such as the problems of memory, epilepsy and other neurological diseases.

Preparation for the (PET) Positron Emission Tomography

These are the issues that you must consider when you undergo a Tomography (PET) positron emission:
Duration: the imaging within the PET machine can last about 20-30 minutes. The radiopharmaceutical will manage about 60 minutes before the shooting.
Entry: the test can be done on an outpatient basis.
Is necessary to be accompanied?: don't have to be accompanied by, although it might help if it makes you feel more relaxed.
Drugs: is not necessary to take any prior medication
Food: must be that it do not eat neither food nor water for hours before the test.
Clothing: you can wear any clothes you want, but it is preferable that it is easy to remove. You don't want to carry metal objects (earrings, bracelets, etc.) because they will be asked to remove them during the test.
Documents: should be informed consent, which is a role where they explain you what is the test and its potential risks. You should read it carefully and take it signed. You must take the wheel of the test request.
Contraindications: It should not do an enema in the following cases:
  • If you perform a CT and PET, contraindications to the test will be those of the TAC, as for example the allergy to iodinated contrast.
  • In pregnancy, because technique is done with x-rays, which may harm the fetus.
Pregnancy and lactation: should be avoided during pregnancy, especially in the first trimester, the risk of radiation to the fetus. Some radiopharmaceuticals can be removed by breast milk, so it is advisable to inform your doctor that you are giving suck before performing the procedure. To avoid problems, mothers who are giving breastfeeding can avoid breastfeeding during the hours following the test. During those hours the mother can remove the milk through a pump and discard. In anticipation of the space of time that won't be able to breast-feed, the mother can remove milk before testing and store enough to cover the needs of the child during this period. Time that should expect after the test depends on the radiopharmaceutical administered, but they are generally a few hours.
Other considerations
Not do exercise immediately before the test and be as relaxed as possible, because any movement can alter the result should.

How is tomography (PET) positron emission

The unit in which the test is donut-shaped and inside moves a stretcher that is where lies down the patient, usually face up. The couch moves on the inside hole of the CT scanner, and remains within 20-30 minutes while images are taken. Unlike MRI, this test does not usually cause claustrophobia, because the patient does not remain within a closed site. Noise is not heard. In general, it may be necessary to change the clothes by a hospital gown, but it depends on the centers. They will make you take off all metal objects, including dentures or the sonotones, because they may interfere with the images obtained.
About 60 minutes before the images you will be given the radiopharmaceutical orally, intravenously, or through inhaled. If the radiopharmaceutical is administered intravenously they will catch a vein via the arm to insert it.
During the procedure, a technician will be watching through a glass from an adjoining room, and will instruct you to not move. Where is done a CT with PET, usually first CT images are taken and then those of the PET. Sometimes, after the PET, repeats the TAC using contrast. Depending on the organ studied, may require a different procedure. For example, to study the heart you can be a PET before and after exercise, or before and after the administration of a drug that increases the cardiac blood flow.
After the test, you can tell him to wait a little bit to that technician see the quality of the images if it is necessary to repeat something. The fact of repeating the Imaging does not mean that they have found something wrong, so should not be cause for concern. After testing the intravenous arm, they withdraw unless you have to repeat some procedure that same day.
PET is a very safe test because the dose of radiation administered is very small. Allergic reactions to the radiopharmaceutical can occur, but are extremely rare. The injection of the radiopharmaceutical can cause mild discomfort in the arm, but very short. The radiopharmaceutical administered orally does not have any flavor, and the administration of the radiopharmaceutical inhaled via is no different from inhalation of ambient air.

Results of the (PET) Positron Emission Tomography

The images obtained by the CT scanner can be seen immediately. However, their interpretation requires much expertise and is carried out by physicians specializing in nuclear medicine. This specialist will make a written report that will give you a few days of the test along with the images obtained.
The result report will include data on the technique used, the radiopharmaceutical used and found finds. The type of discovery can vary greatly depending on the pathology and studied organ. The most frequent is to perform as part of the diagnosis or monitoring of a cancer, and that report of the presence or absence of lesions compatible with pathology, tumor, cancer cells have a different to normal cells metabolism, so it highlighted in the images obtained by the PET. Often compares the new study with previous studies, and are informed of possible changes in the lesions and the presence of new lesions. In the case of cardiac pathology it is reported the presence of metabolic activity of the cells of the heart, indicating their viability after myocardial infarction. In the case of the brain, inform you of possible sources that may be causing epilepsy, or alterations in the activity of the brain being related to any disease in particular. In the case that a TAC is completed while the PET inform you of findings from these images as tumors, inflammations, etc, and its coincidence or not with lesions that may appear in the PET.
It is advisable to go to pick up the result and not assume that everything is normal because the results you are not delivered in a few weeks. The physician who requested the test will give you the results, and will instruct you if it is necessary to other complementary examinations or to follow any treatment.
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