Many illnesses that develop in the human body affect the function of tissues and organs on a cellular level within the body, where they are unfortunately difficult to detect. Cancers, for example can develop almost anywhere in the body and remain invisible externally. How then can a doctor know where the cancer has developed and how to combat it? This issue of the human body being opaque and medical conditions within the body being impossible to see is an issue to which science has been applied to devise a variety of solutions. One such solution is positron emission tomography.
Positron emission tomography is a medical imaging technology. As an imaging technique it is noninvasive, and among imaging techniques it is unique because it measures and monitors the functions of cells and structures in the body (Freudenrich). PET can map blood flow, oxygen use and glucose metabolism, thus enabling the detection of a variety of medical conditions such as aneurysms, tumors, organ malfunctions and brain disorders (Freudenrich). As a research tool, particularly in regards to the brain, and as a diagnostic tool often for cancer, PET is a highly regarded technology with a variety of useful applications.
Positron emission tomography follows the process shown in the flow chart and begins with the synthesis of a radiotracer. One commonly used radiotracer is fluorodeoxyglucose (FDG), a compound that is structurally identical to glucose except for the presence of fluorine-18 instead of a hydroxyl molecule (Sabbatini, “The PET Scan”). Fluorine-18 is a radioisotope of fluorine and decays by β+ decay, which allows it to be used for PET. The fluorine-18 is first synthesized in a particle accelerator, typically a cyclotron, where water rich with oxygen-18 is bombarded with protons (Sabbatini, “The Cyclotron and PET”). The net effect of the subsequent nuclear reaction is that of a neutron in the oxygen-18 nucleus becoming a proton, and because of this, fluorine-18 ions (18F-) are produced. These are collected and attached to deoxyglucose to form FDG. Other radiotracers are produced in the same way. The final radiotracer produced is then placed inside the body of the patient, typically intravenously, and is absorbed by the system as an analog of a material naturally found in the body, where it demonstrates the function and use by the system of the substance to which it is analogous (Vaska).
Radioisotopes used in PET radiotracers all experience β+ decay, and this is the operating principle behind PET. β+ decay is a form of radioactive emission, and occurs when an unstable nucleus attempts to correct an excess of protons. Neutrons and protons both consist of three smaller subatomic particles called quarks, of which there are two types to be found in nucleons: up quarks and down quarks (Duncan 274). A proton consists of two up quarks, each with a positive charge of ⅔ the magnitude of the charge of an electron, and one down quark, which has a negative charge of ⅓ the...