The PET scan, or Positron Emission Tomography, was born in 1973 at Washington University. It was created by Edward Hoffman, Michael M. Ter-Pogossian, and Michael E. Phelps; Phelps is most often credited with the invention (History of PET and MRI, 2009). In preparation for a PET scan, radioactive tracers are injected into the body, inhaled, or ingested by the patient through a solution that they drink.
Then the scan will actually begin, as the patient lies on a table, which glides into the machine where all of the necessary images will be taken—this process will be described later in the paper—then the test will complete and the patient will slide back out of the machine. (See the image of the machine below). The PET scan is nuclear technology, and therefore has inherent risks associated with it. However, for the most part, these risks are neither likely nor significantly damaging.
The technology is scientifically complex and quite effective in certain situations. Thus, it’s important to understand how the Positron Emission Tomography works and the potential health threats that the nuclear technology poses. Positron emission, for which the technology is named, is a form of radioactive decay by which an unstable nucleus releases energy through radiation emission—so that the isotope can become stable, or nonradioactive—by emitting a positron.
A positron is a particle with the mass of an electron but with a positive charge; during positron emission, a proton from the unstable (with the tendency to continue to decay due to an inappropriate ratio of neutrons to protons or simply a nucleus that is too large) radioactive isotope changes from a proton to a neutron to alleviate imbalance when the ratio of neutrons to protons within the nucleus of a radioactive isotope is too low.
A sample decay process for positron emission is: (_28^59)Ni? (>+( ) ) (_27^59)Co+(_1^0)e . The problem that created the necessity for PET scans was that of largely undetectable and incurable cancer and other disorders, which appear globally. However, the use of PET scans is mainly limited to North America, Europe, Japan, Argentina, and Australia, due to the high cost of the machinery (Sabbatini, 1997).
The PET scan was developed in order to aid in the diagnostic medicine of a range of neurological diseases and disorders, in various cancers such as those found in the head, neck, and the gastrointestinal tract, as well as lymphomas, but it is approved mostly for the diagnosis of even the smallest and difficult-to-detect lung cancers (Scanning the scans, n. d. ). In a neurological setting, PET has been used to study stroke, epilepsy, Alzheimer disease, Parkinson disease, Huntington disease, schizophrenia, depression, obsessive-compulsive disorder (OCD), attention-deficit/hyperactivity disorder (ADHD), and Tourette syndrome (Christenson, 2014).
It is important to understand the scientific factors that allow PET to function. PET is used in conjunction with small amounts of radio-labeled compounds and a gamma camera to pick up and record the images that come from PET scans. A radioactive compound is inhaled or injected into the patient, and it accumulates in tissues. As the atoms in the compound decay, they release positrons, which, when they collide with electrons, both the electrons and positrons are annihilated, and two photons (light particles) are emitted. (See the image on the right).
The photons are picked up by a detector ring on the PET scanner, and the computer uses the information to generate three-dimensional images that represent the bioactivity where the compound accumulated and released light (Christenson, 2014). Most of the time, the injection received by patients who undergo PET scans is a radioactive form of F- fluorodeoyglucose (FDG), which is metabolized in the same way that glucose is. Malignant (harmful) cells have faster metabolisms than normal cells, so they require more sugar to fuel their rapid metabolism.
Thus, they use more of the F-FDG, emitting more of the photons detected by the gamma camera (Scanning the scans, n. d. ). F-FDG is the most common type of radioactive tracer used in PET scans, and it is manufactured in a cyclotron radioscope. A cyclotron body consists of electrodes in a vacuum chamber. It is flat, and the vacuum chamber sits in a gap between the poles of a large magnet, creating a perpendicular magnetic field. Then, a stream of charged particles is fed into the center of the chamber, while high, alternating energy stream is applied across the electrodes.
The voltage alternately attracts and repels the charged particles being fed into the center, so that they accelerate. The magnetic field causes the particles to spiral around the chamber so that they re-encounter the accelerating voltage many times. The size of the vacuum chamber determines how much energy is accumulated in the particles (“Cyclotrons, n. d. ). Medical cyclotrons produce the proton beams that are used to manufacture radioisotopes such as F-FDG. Although PET scans are spectacular diagnostic tools, there are definite limitations associated with their use.
Since positron emission tomography was first approved in 1975, it has had to be continually proved to the Food and Drug Administration, by which the technology is regulated, that it was safe enough for use on humans (Sabbatini, 1997). PET scans are typically outpatient procedures—meaning that after the test is finished, the patient is free to go home and go about their business for the day—demonstrating their relative safety as far as medical procedures go (Krans, 2015).
Even though PET involves radioactive tracers, the exposure to harmful radiation is minimal, as the radiation levels are normally too low to affect normal body processes. Because the test is nuclear by nature, however, the health risks should not be underestimated, either. Gamma rays are a form of high-energy electromagnetic radiation which are produced by the decay of atomic nuclei. They have the potential to be very dangerous to humans, because they can damage animal tissues, in some cases causing cancer or other forms of painful health effects (Gamma Ray, 2015).
Because of exposure to positron emission and gamma rays, when positrons and electrons collide and are annihilated (as shown in the diagram to the left), the electron bonds that hold atoms together in molecules are also destroyed, creating a myriad of health problems (Radiation Exposure, 2015). If the essential molecules upon which living organisms are constructed—such as carbohydrates, lipids, proteins, water, etc. —are broken apart, the organisms are no longer capable of functioning appropriately.
PET scans rely on these forms of radiation to create the images used for diagnostics, so it is clear how they can be perceived as risky. Radiation is hazardous for developing fetuses in particular; for this reason, women are often required to be tested for pregnancy before receiving a scan, and pregnant women and breast-feeding women aren’t permitted to be scanned with the nuclear technology (Krans, 2015). Beyond the hazard of radiation exposure to young children, infants, and fetuses, the impact of PET scans on adults cannot be overlooked.
Some radioactive compounds used for positron emission scanning can persist for a considerable period of time within the body. Only a small volume of the radioactive material is injected into one person at a time, but the long half-lives (the length of time that it takes before half of the sample has decayed) of the compounds can limit the number of times a patient can be scanned, and slightly increase the risk of damage due to the length of exposure (Christenson, 2014).
Positron Emission Tomography has many modern medical applications, and it has the potential for many more uses in the future, as doctors and scientists become more accustomed to the relatively new technology. Though there are health risks associated nuclear technology, and PET scans clearly fall into that category, the health benefits outweigh the negatives, especially as scientific knowledge of illness (such as the ones that PET scans can detect) and nuclear technology increases.
