Thursday, December 14, 2023
NRC dose limit for members of the public mnemonic
Wednesday, December 13, 2023
Tuesday, December 12, 2023
Monday, December 11, 2023
Sunday, December 10, 2023
PET crystals
https://youtube.com/shorts/KrYSxeF0CqA?si=LdTNJd2aJc4FK0mc
LSO/LYSO has small decay time
Allows for improved coincidence timing
Friday, December 8, 2023
Deterministic vs Stochastic effects
Deterministic effects (or tissue reactions) of ionizing radiation are related directly to the absorbed radiation dose and the severity of the effect increases as the dose increases.
Example: Cataracts
Mnemonic: DDD Deterministic severity Determined by Dose
Stochastic effects of ionizing radiation are chance events, with the probability of the effect increasing with dose, but the severity of the effect is independent of the dose received. Stochastic effects are assumed to have no threshold.
Example: Cancer
Mnemonic:
Stochastic Severity No
Probability So
Photolectric effect and Compton scatter
In the Compton effect, a photon interacts with an outer shell electron, resulting in the ejection of the electron and a scattered photon with reduced energy.
Compton scatter is a significant contributor to image noise. It can result in scattered photons reaching the detector and degrading image contrast.
Compton scatter is more likely to occur with higher-energy photons, such as those around 140 keV.
The photoelectric effect is more pronounced at lower energies and is characterized by the complete absorption of a photon by an inner-shell electron, leading to the ejection of the electron.
The Photoelectric Effect is particularly important in medical imaging applications using low-energy X-rays, where it contributes to contrast in radiographic images.
Mnemonic: Compton is with COmpletely More energy PhoTONs (Compton scatter is more likely to occur with higher-energy photon)
photoeLEctric absorbs aLL Lower Energies