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For comparison, radiation dosage for other medical procedures range from 0.02 mSv for a chest X-ray and 6.5–8 mSv for a CT scan of the chest. [ 42 ] [ 43 ] Average civil aircrews are exposed to 3 mSv/year, [ 44 ] and the whole body occupational dose limit for nuclear energy workers in the US is 50 mSv/year. [ 45 ]
Positron emission tomography–computed tomography (better known as PET-CT or PET/CT) is a nuclear medicine technique which combines, in a single gantry, a positron emission tomography (PET) scanner and an x-ray computed tomography (CT) scanner, to acquire sequential images from both devices in the same session, which are combined into a single superposed (co-registered) image.
Cardiac PET (or cardiac positron emission tomography) is a form of diagnostic imaging in which the presence of heart disease is evaluated using a PET scanner. Intravenous injection of a radiotracer is performed as part of the scan. Commonly used radiotracers are Rubidium-82, Nitrogen-13 ammonia and Oxygen-15 water. [1]
In addition, there are nuclear medicine studies that allow imaging of the whole body based on certain cellular receptors or functions. Examples are whole body PET scans or PET/CT scans, gallium scans, indium white blood cell scans, MIBG and octreotide scans. Iodine-123 whole body scan for thyroid cancer evaluation.
The embryo and fetus are considered highly sensitive to radiation exposure. [8] Complications from radiation exposure include malformation of internal organs, reduction of IQ, and cancer formation. [8] The SI unit of exposure is the coulomb per kilogram (C/kg), which has largely replaced the roentgen (R). [9]
Technetium-99m (99m Tc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99m Tc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used medical radioisotope in the world.
The amount of radiation a patient is exposed to in a PET scan is relatively small, comparable to the amount of environmental radiation an individual is exposed to across a year. PET radioisotopes have limited exposure time in the body as they commonly have very short half-lives (~2 hours) and decay rapidly. [38]
In Alzheimer's disease, MRI scans of the entire brain can accurately assess the rate of hippocampal atrophy, [38] [39] while PET scans can measure the brain's metabolic activity by measuring regional glucose metabolism, [33] and beta-amyloid plaques using tracers such as Pittsburgh compound B (PiB).