Department of Nuclear Medicine
What is nuclear medicine?
The Department of Nuclear Medicine carries out isotopic examinations, which means medical imaging examinations that use products (molecules) labelled with a radioactive atom (radioisotope). This is known as a labelled molecule or a tracer.
Depending on the kind of radioisotope, there are:
- conventional, or single-photon, scans, also known as single-photon emission computed tomography (SPECT),
- positron emission tomography (PET for short).
In both cases, the radioisotopes have the same properties:
- They are non-toxic and do not trigger allergic reactions (even those containing iodine), although some precautions need to be taken to protect certain organs (such as the thyroid).
- Once injected into the body, the equipment (SPECT camera or PET camera) tracks where it goes, produces images of the organ being examined and makes diagnoses. They are then eliminated by the body, generally in the urine.
- The radioisotope turns into a non-radioactive atom after a certain period of time. This process is known as radioactive decay. The time in which a radioisotope decays by half (meaning that its radioactivity has reduced by 50%) is known as its “half-life”. The half-life of the isotopes used in nuclear medicine are short, on the order of several hours. The half-life of fluorine-18, a component of 18 fluorodeoxyglucose (18FDG), is only two hours. It is therefore essential to arrive on time, as the products are delivered or made for you in advance.
- Being one hour late means losing 25% of the product, which affects image quality and so the quality of the diagnosis.
- The radioisotopes used in nuclear medicine are present in such tiny quantities that you have nothing to worry about with regard to your health. The radiation risk is very low. It is measured by a unit: the milliSievert (mSv), or the microSievert (µSv) which is equivalent to a thousandth of a milliSievert.
- As a guide, a CT scan of the chest, abdomen and pelvis in the radiology department delivers a radiation (X-photons) dose on the order of 10 to 20 mSv, which is comparable to the radiation delivered by an 18FDG PET scan. In some granitic regions of France, such as Brittany or Corsica, the natural radiation dose delivered every year is on the order of 3.5 mSv. A return transatlantic flight also delivers a radiation dose on the order of 0.2 mSv.
A CT scan (with or without injection of iodinated contrast medium) is an examination that visualises human anatomy, i.e. the shape and location of organs. An abnormality in shape (a tumour, for example) or structure (such as a fracture) can thus be detected. Nuclear medicine imaging uses a radioactive tracer that makes it possible to monitor the functioning of an organ, regardless of its shape. It is “functional” imaging, which complements “anatomical” radiological imaging.
Yes, there are two kinds of precautions:
- As regards the radiation risk, even though it’s very low, it should always be minimised. That means that unnecessary exposure to radiation should not be repeated and vulnerable people (pregnant women, young children) should not be exposed unnecessarily. These precautions mean that these examinations are avoided in pregnant women (except in the last trimester of pregnancy), ensuring that they are carried out in young women, either outside of ovulation (immediately after a period is the ideal time) or when they are using effective contraception or having protected sexual intercourse. Breastfeeding should be stopped 1 to 2 days before the examination. Lastly, a patient who has been injected with a radioisotope needs to be kept away from family members or those accompanying them. This is why there are two waiting rooms and friends should wait only in the “public” waiting room. After the examination, and depending on the radioisotope used, for several hours you may be required not to stay less than two metres away from children or pregnant women for prolonged periods. Feel free to ask for information in the department.
- As regards the “functional” nature of the examination. So as not to interfere with the examination, it is sometimes essential to avoid eating anything, eating no sugar for 18FDG PET scans, for example (no sugar AND no aspartame). For other examinations, coffee (including decaffeinated), tea, chocolate, bananas and cola drinks are prohibited. Some drugs may affect the scans.
- Explanatory sheets for PET scans, cardiological assessments and scintigraphy are available to download.
- Feel free to contact us for further information.