Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are commonly utilized to look at the inside of the brain. PET and SPECT tests can be done for a wide number of reasons, from diagnoses to psychological studies. Epilepsy, cancer and neurodegenerative diseases, among others, can be detected using this technology.
A positron is a subatomic particle also known as an anti-electron. It essentially has the same properties as an electron, but is positively charged. A photon is a discrete packet of electromagnetic radiation. The definitions and properties of these particles are important to understanding how PET and SPECT tests work.
PET utilizes a radiotracer that emits a positron, which collides with two electrons and produces gamma rays. The machine ‘reads’ these gamma rays and forms a picture. SPECT, on the other hand, uses a radioisotope with a short half-life that emits gamma rays to achieve a similar goal. SPECT is more common and less expensive, but PET is being more widely adopted because it is better than SPECT, magnetic resonance imaging (MRI) and x-ray computer tomography (CT). The images produced are often of higher quality.
Radiotracers are typically administered intravenously. This is a fancy way of saying they are injected into the patient’s veins. Due to the risks of such a procedure, the quantities of radioactive material used are incredibly small!
Copper, gallium and zirconium are the most commonly used metals in PET radiotracers. Zirconium is one of the most common because it sticks around a long time. (It takes 78.4 hours for half of the zirconium to decay.) In SPECT, technetium and indium are preferred. Technetium is easy to make in a lab, while indium is used due to its long half-life. Indium is used for specific purposes, such as conjugating to biomolecules with slower-moving pharmacokinetics.
In a world where medical technology is constantly changing, it’s important to understand the complexity of radiology. Many students have received these procedures, or will in the future as they become more effective and accessible. A brief understanding of how they work is important to understanding how they can help us and what the results mean.