A brain PET scan involves the use of a small amount of radioactive material to create detailed images of the brain’s metabolic activity. The radiation dose from a brain PET scan typically ranges around 5 to 7 millisieverts (mSv), which is a measure of the radiation absorbed by the body.
To understand this better, it helps to know what a PET scan is and how it works. PET stands for Positron Emission Tomography. During the scan, a radioactive tracer—usually a form of glucose tagged with a radioactive isotope like fluorine-18—is injected into the bloodstream. Because brain cells consume glucose for energy, the tracer accumulates in areas with higher metabolic activity. The PET scanner detects the radiation emitted by the tracer as it decays, producing images that show how different parts of the brain are functioning.
The amount of radiation in a brain PET scan is relatively low but higher than that of a standard X-ray. For context, the average person is exposed to about 3 mSv of natural background radiation annually from the environment. A brain PET scan’s 5 to 7 mSv dose is roughly equivalent to a couple of years’ worth of natural background radiation. This level is considered safe for most adults when medically necessary, but it is still important to limit exposure to radiation when possible.
Radiation exposure from PET scans is carefully controlled. The radioactive tracer used has a short half-life, meaning it decays quickly and reduces radiation exposure over time. The total radiation dose depends on the specific tracer used and the amount administered, but protocols are designed to use the minimum dose needed to obtain clear images.
When a PET scan is combined with a CT scan (called a PET-CT), the total radiation dose increases because the CT scan adds its own radiation, typically between 2 to 10 mSv depending on the body part scanned. For brain imaging, the combined PET-CT dose might be higher but still within safe limits for diagnostic procedures.
The risks associated with this radiation are generally low but not zero. Ionizing radiation can potentially damage cells and DNA, which in rare cases might increase the risk of cancer later in life. This risk is considered very small compared to the benefits of accurate diagnosis and treatment planning that PET scans provide. Special caution is taken with children and pregnant women, as they are more sensitive to radiation. Alternative imaging methods like MRI or ultrasound, which do not use ionizing radiation, may be preferred in those cases.
In summary, a brain PET scan exposes a patient to about 5 to 7 mSv of radiation, which is a controlled and relatively low dose designed to balance safety with the need for detailed metabolic imaging. This radiation dose is higher than a typical X-ray but comparable to a few years of natural background radiation, and it is generally considered safe when used appropriately in medical diagnostics.
