TOMOGRAPHY BY EMISSION OF POSITRONS

 

Tomography by emission of positrons allows for the observation of consumption and/or distribution of certain molecules in the organs of the body. To observe this, a nurse injects a specifique solution into the patient. This solution contains a radio pharmacutique. The solution contains a molecule (or a chemical molecule) that allows for observation using a marker which contains a radioactive element and which allows for the emission of positrons.

Following the injection the patient is placed in the line of view of a positron camera which will show the presence of elements and allow for the localisation and quantification of the radio-pharmacutique element.

Thanks to a mathematical programme the information gathered is registered for analysis and transformed into a series of images corresponding to the organ that has been imaged. By viewing all the images rapidly the doctor can build up a 3D image of the organ observer.

 

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Click on the images to enlarge

 

What equipment is used for a PET
The radiopharmacutique is the principal tool of the PET, more often than not a 18FDG (Fluoro-Deoxy-Glucose). The 18 FDG is disintigrated by the cells (consumption of glucose)

During the radioactive disintigration, the Fluor atom gives off a Positron (an electron anti-particle). This positron will after a short time will met with its particle sister or electron.
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This meeting of electron – positron creates a reaction of destruction that will provoque the emission of two photons with the same energy and given off in two directions diametrically opposite. In general, the presence of the tracer is brief (two minutes to several hours) and is inoffensive to the patient.
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The cyclotron is an electromagnetic accelerator with a high frequency which allows for the production of isotopes. By accelerating the particles several effects can be seen - it allows for transmutations and the disintegration of atoms and also the incorporation of isotopes in the molecule. The cyclotron is invaluable to the production for the emitting of isotopes in positrons. In the case of 18FDG, the life span is very short (109 minutes) and necessitates that the patient is close to a PET scanner facility (less than two hours of transport).
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PET Scanners : allow for the detection of the two photons created during the destruction of the positron. The principle of the PETSCAN is the detection by coincidence of the deux positrons. The mathematical model allows for the readings of radioactivity to be translated into : blood levels, chemical reaction speed, the density of the neurotransmitter receptors....
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