The PET scan (positron emission tomography) is a medical imaging examination which uses radiotracers to detect cells in the body that consume more energy than others. It is mainly used as a second-line in the context of cancer screening, since cancer cells tend to consume more energy. When and how to do it? How is it going? Lighting from Dr Aurelien Dupresurgeon specializing in digestive oncology at the Léon Bérard cancer center (Lyon) & du Dr Lucas Spindlerproctologist and hepato-gastroenterologist at St Joseph Hospital and member of the SNFCP (French National Society of Colo-Proctology).
Definition: what is a PET scan? What do we see?
“The PET scan is a medical imaging technique which makes it possible to study the metabolic activity of cells thanks to the injection of a radioactive product into the patient”, indicates Dr. Dupré. In concrete terms, the patient is injected a weakly radioactive productwhich serves as a radiotracerr and whose lifespan in the body does not exceed two hours. Most often it is the FDG (fluoro-deoxy-glucose), a glucose derivative labeled with a fluorine-18 molecule.
Thanks to this examination, doctors can observe the anatomical structure of the organs, but also their metabolic functioning. “Concretely, the PET scan allows to map the cells that consume the most glucose in our body”, explains Dr. Spindler. And to specify: “All our cells need glucose to function, but certain cells, in particular cancer cells need it more. The PET scan therefore makes it possible toidentify the areas that consume the most glucosewhich correspond to potential tumors and/or their metastases.”
Thanks to the PET scan, we can detect anomalies that would go unnoticed with other anatomical imaging techniques (scanner, X-rays, etc.), insists Dr. Dupré.
What is the difference between a PET scan and a PET scan?
The letters PET are simply the English initials of TEP in French, which means positron emission tomography. The names PET scan and PET scan therefore refer to the same examination.
Cancer, neurology, cardiology… When should this type of scan be done? And why ?
The PET scan is mainly used in oncology. It is recommended as a second intention in the context of diagnostic de cancers, to detect the possible presence of tumors and measure their extent. But doctors also use it to measure the body’s response current treatments and prevent recurrences, say the experts.
More rarely, this examination can also be used in neurology, to assess brain functions in the context of neurodegenerative pathologies such as Alzheimer’s disease or Parkinson’s disease
It is also sometimes used in cardiology to assess blood flow in the coronary arteries or heart chambers. Thus, the medical teams can for example visualize the extent of the damage after a myocardial infarction.
Positron emission tomography: before the examination, what precautions to take?
As with many medical examinations, you must follow certain rules:
- fasting so as not to interfere with the fixation of the radiotracer (drinking water is still allowed). Generally, if you have an appointment before noon, you must stop eating the night before at midnight. And if you have an appointment in the afternoon, you’re allowed to have a light breakfast before 8 a.m., says Dr. Spindler.
- do not smoke, chew gum or lozenges before the exam;
- not having made too intense a physical effort the day before ;
- continue their usual treatments ;
- plan a snack for the post-exam and a bottle of water;
- provide clothes without metallic elements and remove her jewelry.
What documents to bring?
On D-Day, bring:
- of your vital card ;
- of your mutual card ;
- of one ID ;
- and of your medical file including your latest examinations (scanner, MRI, scans, x-rays, etc.).
What precautions if you are diabetic?
First of all, know that the exam will not be realized if your diabetes is out of balance. This could skew the results: “high blood glucose levels can affect test results because glucose can compete with the radioactive tracer used“, explains Dr. Dupré. Otherwise, follow these few precautions to ensure that the examination is as relevant as possible:
- inform the medical staff your circumstances;
- control your blood sugar before the examination (if your glucose level is too high, the PET scan may be postponed);
- most often, diabetic patients are allowed a light breakfast — and their treatment (oral medication or insulin) before the exam. The date is set at the most suitable time for each patient, depending on the type of diabetes. Either way, get in touch with the team in charge of giving you the exam and apply their advice.
Are there any contraindications to the PET scan?
The PET scan is a painless examination that does not present any danger or risk of allergy. It is however contraindicated in pregnancy and lactation (except in special cases). Indeed, this examination involves the injection of a radiopharmaceutical product into the body, which can potentially cross the placenta and affect the fetus. Not to mention that the PET scan uses ionizing radiationalso likely to affect fetal development.
As far as possible, to limit the risk of potential pregnancy, the PET scan is performed during the first half of menstrual cycle women. And in the event of a risky report, patients may be required to perform a pregnancy test. As for breastfeeding patients, they are invited to pump their milk upstreambecause they will not be able to breastfeed their baby within twelve hours of the injection of FDG (i.e. the time that their body has eliminated the radiotracer).
Procedure: how is a PET scan performed? How long does it last?
Le TEP scan dure on average 2h30. Once you arrive on site, you will be taken care of by a team of radio manipulators. You will be asked to empty your bladder and then the professionals will begin by check your blood sugar before setting up an infusion to inject the radiotracer (FDG). Note: the dose of FDG is adapted to the patient’s weight. Once the injection is done, you will need to lying down for about an hourthe time that the product diffuses in your body.
Once this time has passed, you will be installed on the table of the device, which looks like a scanner and MRI – but less oppressive all the same. You will then slide into the “tunnel” of the machine for about twenty minutes and a camera will take care of capturing targeted shots depending on the area to be explored. Note: you will need to stay perfectly still throughout the exam to ensure image quality, says Dr. Spindler.
In video: How does a PET scan take place? (source 1)
What precautions should I take after a PET scan? What side effects should you expect?
The PET scan does not cause any side effects, since the amount of radiotracer injected is really very low, agree the two doctors. As for FDG, it does not cause an allergic reaction, nausea, vomiting or drowsiness, insists Dr. Spindler.
In other words, you can resume your normal life: drink, drive, eat, etc. The results will be transmitted within 24 to 48 hours to your prescribing physician.
Is the exam dangerous?
The question is legitimate, but no, the injected radiopharmaceutical is not toxic. And all the less so when the quantity of product administered is extremely low.
Only downsides? The length of the procedure and having to remain still during the examination.
You will remain slightly radiant for a few hours after the exam (but nothing alarming!). Once the PET scan has been taken, remember to hydrate yourself well to eliminate FDG. Doctors also ask foravoid contact with young children and pregnant women within twelve hours of the examination.
The PET scan is not a medical examination. It is carried out as a last resort in the face of a serious health problem, the hypothetical ‘risk’ is therefore more than justified, believes Dr. Dupré.