Glossary of RadTech: Physics - Ch.12

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What are the ways X-rays interact with matter?
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?
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.

Compton effect: What interaction occurs?
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?
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?
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?
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?
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?
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?
How is the probability of Photo Electric Effect and X-ray energy related?
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?
Directly proportional to the third power of Atomic Number.

P= Zcubed
What is Pair production?
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?

But is very useful for PET imaging
What is Annihilation radiation?
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?
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?
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?
Name two other factors important in making an X-ray image.
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?
What is the Half Value Layer?
The depth ofmaterial that reduces the incident X-ray intensity to half its original value.

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