Linear momentum is conserved as well as a kinetic energy. So compton scattering is an example of an elastic collision between two particles and like any elastic collision, the math can get a little bit crazy, but two things are conserved.
COMPTON EFFECT VIDEO FREE
We think that the table above provides a good summary of the contributions of the different physical interactions of X-rays with matter.Compton scattering is a phenomenon that indicates that photons can behave like billiard balls when they interact with free electrons, they simply collide off the electron in an elastic collision. Compton scattering on the other hand is the dominant source of the background radiation in the room. Impact on Staff: Coherent and photoelectric are not significant. So, both Photoelectric and Compton scattering lead to significant contribution there in terms of Patient dose. Impact on Patient Dose: The electrons deposit the energy locally. Impact on Dose: Coherent scattering does not have a significant impact on patient dose. It can lead to different more structured artifacts in a CT image. Compton scattering leads to a background haze in an X-ray image. Photoelectric, is the primary contrast source in your image. Especially with a standard diagnostic energy spectrum. Impact on Image Contrast: Coherent scattering, does not a significant impact on an X-ray image.
That’s why images of bone are exquisite on X-ray imaging because bones have relatively higher Z.Ĭompton scattering, Compton is independent of Z. For photoelectric, it’s dependent on Z^3, so it’s very strongly dependent on Z. Z-Dependence: The Z dependence is directly dependent on Z for coherent scattering. Depending upon what the energy spectrum either photoelectric or Compton will be dominant.If the spectral has a lot of low energy photons, it’s going to be dominated by the Photoelectric effect. So Photoelectric is dominant at lower energies and Compton is dominant at higher energies. So, some energy is going to keep going as the X-ray continues to traverse the matter.Įnergy Summary: Less than 10keV for Coherent scattering and then depending on the material type, around 30keV is the transition between Photoelectric and Compton being dominant. In terms of the Compton scattering, you have some energy deposited locally while the x-ray is changing its direction. So, if we think of that from a dose perspective or from an imaging perspective, this is how contrast is generated on images. Outcome of photoelectric is that, that photon stopped and that energy is deposited locally. Coherent scattering really only plays impact at really low energies. So, for Compton you’ll have some energy going forward and some energy being deposited.ĭominant Interactions: Photoelectric and Compton are the dominant interactions. The electron deposits its energy locally. The X-ray comes in, it’s scattered and an electron is scattered as well. Ĭompton Effect: Compton is somehow in between Coherent Scattering and the photoelectric effect. Those both deposit their energy relatively locally. Photoelectric Effect: The diagnostic X-ray comes in and then that X-ray is stopped locally and an electron and a characteristic lower energy photon are emitted.
Not sign, except for interventions if in beamĬoherent Scattering: In a coherent scattering event you have a diagnostic X-ray come in and then the X-ray goes out with a different angle but the same energy. To conclude this post we provide a summary table so you have a study guide with all of the information just in one place.Įlectrons, characteristic x-rays Deposit Dose This can be achieved by using high Z materials as contrast agents and/or using lower energy x-rays where the photoelectric effect becomes more likely. In general, maximizing the contribution of photoelectric interactions will lead to the highest image contrast. The primary interactions dominating diagnostic x-ray imaging are the photoelectric effect and Compton Scattering. These regions attenuate or absorb the x-rays at a higher rate than other regions. The regions in an x-ray image with the most attenuation are typically shown as bright in an x-ray image.
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