PET Scans Flashcards
What does PET stand for?
Positron Emission Tomography
What type of particle is crucial to PET scans, indicated by the first part of its name?
Positron (the anti-particle of an electron, also known as a beta plus particle)
What does the term ‘emission’ refer to in the context of PET scans?
The emission of positrons from a radioactive tracer within the body
What does ‘tomography’ signify in PET scans, similar to CT scans?
That many images are combined to create a 3D rendering of the body’s internal structures
What is the fundamental goal of medical physics scanning techniques like PET, according to the source?
To look inside the human body without the need for surgery
Define a ‘radioactive tracer’ as used in PET scans.
A substance that consists of radioactive material attached to a natural chemical
Name a common radioactive tracer used in PET scans, as highlighted in the notes.
Fluoro-deoxyglucose (FDG)
Explain why FDG is an effective radioactive tracer for PET scans.
The body treats it like glucose and absorbs it, especially in metabolically active tissues like cancer cells and the brain, while the attached fluorine-18 is radioactive
How is the radioactive tracer typically introduced into a patient’s body for a PET scan?
Usually by injection, but it can also be swallowed or inhaled depending on the area being examined
Which types of cells tend to take up FDG at a higher rate?
Rapidly growing cancer cells and brain cells
What are two key reasons for using fluorine-18 in the FDG tracer?
It decays into a stable product and has a short half-life (around two hours)
What type of particle is produced during the radioactive decay of fluorine-18?
A positron (beta plus particle)
What type of electromagnetic radiation is produced as a result of positron-electron annihilation?
Two gamma photons
Describe what happens when a positron emitted by the tracer encounters an electron within the patient’s body.
They undergo annihilation, a process where their mass is converted into energy
In what direction do the two gamma photons travel after the annihilation event, and why?
In opposite directions, in order to conserve momentum
What does a region of high activity, appearing as ‘glowing’ in a PET scan image, typically indicate?
A higher concentration of the radioactive tracer and therefore more frequent annihilation events, suggesting areas of increased metabolic activity such as rapidly growing cancer cells
What is the role of the ring of detectors surrounding the patient in a PET scanner?
To detect the gamma photons that are emitted from the annihilation events within the body
What is a ‘line of response’ in PET imaging?
An imaginary straight line drawn between two detectors that have simultaneously detected gamma photons, indicating a possible path of the annihilation event
Define ‘coincidence detection’ in the context of PET scanning.
The simultaneous or near-simultaneous detection of two gamma photons by detectors positioned opposite each other in the ring
How is the precise location of a tumour or other area of interest determined using PET scanning?
By the intersection of multiple lines of response generated from numerous annihilation events detected from different angles
Why are gamma photons suitable for detection outside the body in PET scans?
They have high penetrating power and can exit the body easily
