1. X-ray Interactions with Matter
Stacy Kopso, M.E.d., RT(R)(M)
X-rays travel in straight line

2. Photon Interactions with Matter
Purpose: How X-ray photons interact w/ matter(human tissue)
Reason: To minimize harm to the patient and produce a quality radiographic image
X-rays travel in straight line

3. Compton Interaction
Scattering events that ionize the atom
Incident photon(primary beam) interacts w/ an outer- shell electron of a atom and removes the electron
The energy from the x-ray photon must exceed the energy required to remove the electron from its orbital shell
The remaining energy of the photon undergoes a change in direction and produces a scatter photon
There is partial absorption of the incident photon
Incident photon interacts w/ an outer- shell electron, producing a scatter photon and recoil electron

6. Incident photon interacts w/ an outer-shell electron, producing a scatter photon and recoil electron
Ionize the atom

7. Compton Interaction
Affects on image quality
Decreases image contrast
Results in Image fog
Affects on patient dose
Backscatter- increase pt dose
Sidescatter from patient- occupational exposure
Influenced by
Energy level of the beam (kVp)
Thickness of the tissue irradiated
Incident photon interacts w/ an outer- shell electron, producing a scatter photon and recoil electron

8. Photoelectric Interaction
Incident photon interacts with an inner (K) shell electron of atom and removes the electron
The energy of the incident photon must be equal to or greater than the binding energy of the k shell
Total absorption of the incident photon
An ejected photoelectron exits the atom
The vacancy is filled by an outer shell electron resulting in the emission of characteristic (secondary radiation) photon within the body
An increase in contrast= increase in pt dose

11. Total absorption of the incident photon
The atom is ionized

12. Photoelectric Interaction
Affects on image quality
Directly impacts contrast(white)
Affects on patient dose
Primary source of patient radiation exposure
Influenced by
energy level of the xray beam
Density of the tissue
Atomic number of the tissue
An increase in contrast= increase in pt dose

13. Classical Interactions
AKA: Coherent Scattering or Thomson Scattering
Occurs at very low x-ray photon energy levels
At 70kVp only 3% of the xrays undergo this
Incident x-ray photon interacts with the atom and excites the atom
No electron is removed (no ionizaton)
The incident photon undergoes a change in direction with no energy loss

17. Classical Interactions
Affects on image quality
Degrades image quality
Affects on patient dose
Contribute only to patient skin exposure

18. Photon Interactions with Matter
Pair Production
Does not occur in radiography because the energy levels required exceed the range used in diagnostic x-ray production
Radiation therapy/Nuclear medicine
X-ray photon interacts with the nucleus of the atom
Results in a positron and negatron
Photodisintegration
High energy levels/Does not occur in radiography
Xray photon is absorbed in the nucleus
Nucleus is excited and emits a nuclear fragments

19. Incident photon energy
Compton
Photoelectric
Coherent
Interaction
Middle & outer shells
Inner-shell electrons
Excites the atom
Incident photon energy
Loses 1/3
Loses all energy
No energy loss
Ionization
Must exceed the energy of the orbital electron
Must be equal to or greater than the energy of the orbital electron
No ionization occurs
Pt dose
Backscatter-pt
Side scatter-Occupational
Significant
Skin dose
Image Quality
Fog
Decrease contrast
White/increase in brightness
Minimal effect
Incident photon
Partial absorption
Total absorption
No absorption
Energy
Moderate energy
Higher kVp
Low energy
Lower kVp
Much lower energy
Interaction produces
Scatter photon
Secondary electron
Photoelectron

20. Classwork

21. Differential Absorption
Difference in x-ray interaction by various body tissue
X-ray image is formed by those x-rays that undergo photoelectric absorption (white) and x-rays that are transmitted (black)
bone vs lung
Affected by;
Thickness of body part (mass density)
Type of tissue (atomic number)
Photon energy (kVp)

22. Differential Absorption
Transmission
xray photons that pass through the body and reach the image receptor
Create dark shades of the image
Absorption
photons that are attenuated (weakened of the beam) by the body and do not reach the image receptor
Creates light shade (brightness)
Need both for an image
Radiopaque
absorb xrays
Radiolucent
lower probability of absorption

23. As Tissue thickness increases;
Attenuation
Increases/Decreases
Photoelectric Interaction
Compton Interaction
As atomic # of tissue increases;
X-ray transmission
As photon energy increases;

24. Classwork