RadTech: Physics - Ch.12
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- What are the ways X-rays interact with matter?
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1. Coherent scattering
2. Compton effect
3. Photoelectric effect
4. Pair production
5. Photo disintegration - How are the energy and wavelength of an X-ray related?
- They are inversely proportional.
- Whic X-rays interactions with matter are important to making the X-ray image?
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1. Compton effect
2. Photo electric effect -
Coherent scattering: How are wavelengths and energies related?
What is the amoount of emergy? -
Equal wavelengths and energies of the incident and scattered rays.
Low - Compton effect: What interaction occurs?
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1. X-rays interact with the outer shell electrons.
2. The X-ray is scattered and reduced in energy.
3. An electron is ejected (Compton) and the atom is ionized. - What is the Comton Effect formula?
- Ei = Es + (Eb + Eke)
- Compton effect: How is energy and degree of deflection related?
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1. At 0 deg no energy is transferred.
2.More energy is transferred to the Compton electron up to 180 deg.
3. At 180 deg approx. 2/3 is transferred. - What is back scatter radiation?
- Radiation scattered back in the direction that the incident ray came from.
- What is the relationship between probabability of Compton Effect and X-ray energy.
- They are inversely proportional
- How do scattered X-rays affect the X-ray image?
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1. They have no diagnostic value
2. They reduce image contrast
3. They provide most of the radiation exposure that technologists receive. - What is the interaction with the Photo Electric effect?
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X-rays ionize inner shell electrons.
The x-ray is not scattered and its energy is totally absorbed. - What is the formula for Photo Electric effect?
- Ei = Eb + E ke
- What happens to the electron shells during the Photo Electric effect?
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1. A k shell electron is ejected
2. An electron from another shell, usually the L shell, fills the void.
3. In doing so radiation is emitted - What is Secondary radiation?
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When a k shell electron is ejected an electron from another shell, usually the L shell, fills the void.
In doing so radiation is emitted which is called Secondary Radiation. - Does Secondary radiation have diagnostic value?
- NO
- How is the probability of Photo Electric Effect and X-ray energy related?
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Probability is inversel proportional to the third power of X-ray energy.
P = 1/E cubed - How is the probability of Photo Electric Effect and Atomic Number related?
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Directly proportional to the third power of Atomic Number.
P= Zcubed - What is Pair production?
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The incident X-ray disappears and two electrons are created.
One Positron + and one Electron. - What is the Energy equivalance of an Electron?
- .51 MeV
- Is Pair Production useful for X-ray imaging?
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NO
But is very useful for PET imaging - What is Annihilation radiation?
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A Positron units with a free electron and themass of both is converted to X-radiation.
NB 1.02 MeV is produced - What is Photodisintegration?
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X-rays of sufficient energy avoid interaction with the electron cloud, but are absorbed by the nucleus.
A Nucleon is emitted. - What is Differential Absorption?
- The difference between X-rays that are absorbed photoelecrically and those transmitted to the image receptor.
- What percentage of X-rays incident on a patient reach the image receptor?
- 1Percent
- What percentage of X-rays actually produce the image?
- 0.5 percen
- What type of interaction is more likely to occur at low energies?
- Photo Electric
- What type of interaction is more likely to occur at high energies?
- Compton
- Name two other factors important in making an X-ray image.
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1. The X-ray emission spectrum
2. Mass density of patient tissue - What is low kVp used for?
- To image small differences in soft tissue by getting maximum differential absorbtion.
- What is the relationship between probabiltity of X-ray interaction and tissue.
- Probability is directly proportional to the mass density of the tissue.
- What are Contrast agents?
- Agents with high atomic number used to increase the visibility of organs.
- What is attenuation?
- The ntotal reduction nof the number of X-rays remaining in an X-ray beam after penetration through a given thickness of tissue.
- How are X-rays attenuated?
- Exponentially.
- What is the Half Value Layer?
- The depth ofmaterial that reduces the incident X-ray intensity to half its original value.