Positron emission tomography (PET) is a non-invasive diagnosis technique which allows the acquisition of images showing metabolism and the function of tissues and organs.

The main feature of this technique is the use of positron emitting isotopes, that is, positive electrons. The positrons leave the nucleus and interact (crash) with the electrons present on the outer layer of the atom, which is when the phenomenon known as annihilation occurs.

This phenomenon gives rise to gamma radiation which is emitted in opposite directions at an angle of 180º. The simultaneous detection of this radiation by means of detectors placed in coincidence, i.e., opposite each other, makes it possible to pinpoint its origin. Thus, it is possible to locate the point in the body from which the radiation is being emitted, which reveals where the tracer injected into the patient is accumulating and therefore where the disease is.

The scientific basis of this process is that a property of tumour cells is being used to identify them. It has been known for a long time that tumour cells grow faster than normal ones. To do this, they require more "fuel" than other cells. The "fuel" used by our body cells is glucose, also known as sugar.

For this reason, the patient is injected with a tracer containing glucose which has been combined with a substance which will enable it to be located externally. This substance consists of positron emitting isotopes, normally fluorine 18.

Here we expose a table of diseases in which it is indicated PET-CT scan by MUFACE society.

Is a PET study in any way dangerous for patients?

The fundamental characteristic of positron emitting radiopharmaceuticals is their short half-life. For this reason the amount of radiation emitted and received by the patient is extraordinarily low, similar to the amount received during an abdominopelvic CT scan.

Moreover, with respect to the pharmacological molecule used (regardless of its half-life), the amount injected is so small that there is absolutely no danger of any reaction.

The only contraindications for carrying out the scan are for female patients that are pregnant or for extremely overweight patients as they might have difficulties accessing the scanner. If in doubt, contact our specialists at the PET centre.

Scanning step by step

1.-Medical prescription

To have this test performed it should ALWAYS be prescribed by a physician, and it is to them that the results are normally sent. Your doctor should have reasons to believe that this technique will be useful to you, generally keeping to the existing indications for it to be carried out.

Medical prescription

2.-Making an appointment

Once your doctor has prescribed the test, you should get in touch with the centre where the PET scan will be done. There you will be given an appointment for a certain day and time, and you will be helped with any questions you may have. It is very important to be punctual, as the isotopes used in this test have a short lifespan, that is, they disappear after a short time. Therefore, if the delay is excessive, in extreme cases it may be necessary to postpone the test for a later date. You will also be asked if you are on any medication and if you are diabetic, in which case it is necessary to follow a slightly different procedure.

Before the exam

3.-Before the exam

When you make the appointment, you will be explained about the precautions that should be taken into account before the PET scan. It is important to follow them correctly. First of all, it is necessary not to eat anything for at least 6 hours before the test. Also, it is important not to do any intense physical exercise during the days prior to the test.

You will be asked if you are on any medication, as, although it is normally possible to continue taking it, occasionally it may be necessary to stop certain medications. It is also advisable to drink plenty of water (about one and a half litres) the day of the PET scan, as this will promote hydration and the elimination of the radiopharmaceutical when the test has finished, which occurs through the genitourinary system.

When you are at the PET centre, your weight and measurements are taken and your glycaemia level is checked, which should be within normal levels. Afterwards, you are administered intravenously the radiopharmaceutical (FDG). This injection is completely painless and harmless, and it has neither known side effects nor danger of causing allergies. Once the FDG has been administered, you must lay comfortably in a room for 45 minutes, the time required for the FDG to distribute adequately throughout the body.

4.-Into the PET-CT scanner

After the 45 minutes it takes for the radiopharmaceutical to distribute, you are taken to the PET scanner. Once on the bed, the scan begins. A PET scan takes longer than a CT scan; it lasts between 30 and 90 minutes depending on the type of study. The only precaution is to try not to move while the scan takes place.

This test has no dangers or side effects; it is absolutely harmless.

Exploraciones PET
Exploraciones PET

5.-After the scan

Once the scan has finished, you may eat and drink normally. During the day of the scan, it is advisable not to remain for too long next to pregnant women or small children, as they are more sensitive to the radiation. This is only necessary during the day of the scan, given that the radiopharmaceutical will have been eliminated completely by the following day, being able to go about life normally as from then.


The results are not immediately available after the scan has finished. Powerful computers have to process all the data that has been obtained for it to be possible to achieve finally the images that specialists in nuclear medicine will evaluate.

Exploraciones PET


PET-CT scan studies are used especially in certain psychiatric, neurological and cardiological diseases, but unquestionably its main field of application is in oncology, where the introduction of whole body PET and the FDG radiopharmaceutical has achieved extraordinary clinical results.

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Currently CADPET has service agreements with leading medical companies National and European market. Depending on the type of policy you have, the service will be covered or not so you should first consult your insurance company .