Finals | Five X-ray Interaction with Matter Flashcards
This refers to the x-ray beam before any interaction with the patient, grid, table, or image intensifier.
Primary Beam
The beam that interacts with the detector and will have been significantly attenuated.
Exit Beam
This is a direct result of the Compton effect in the patient and contributes the most to staff radiation dose.
Scattered Radiation
This is leakage from the x-ray tube housing. It doesn’t contribute significantly to staff dose.
Leakage Radiation
Emission of x-ray photons that originate outside of the anode focal spot.
Off-focus radiation
It interacts with whole atom
LOW-ENERGY X-RAY
It interacts with electrons (outer or inner shell)
MODERATE-ENERGY X-RAY
It interacts with nuclear field or nucleus
HIGH-ENERGY X-RAY
FIVE WAYS OF X-RAY INTERACTION WITH MATTER
- Coherent
- Compton
- Photoelectric Effect
- Pair Production
- Photodisintegration
First described Coherent Scattering
J.J. Thomson
Other names for coherent scattering
Classical
Unmodified
Rayleigh
Thomson Scattering
Coherent scattering occur at —
below 10 kEv x-rays
During coherent scattering, the (1) interacts with the (2), causing it to become (3)
- incident x-ray
- whole atom
- excited
Results in a change in x-ray direction without a change in its energy
Coherent scattering
Scattered x-ray and incident x-ray relation in coherent scattering
Scattered X-ray λ = Incident X-ray λ
Is of little importance to diagnostic radiology
Coherent scattering
The incident x-ray interacts with the outer-shell electron and ejects it from the atom
Compton Effect/ Scattering
Ejected electron of compton effect/ scattering
Compton/ Secondary/ Recoil Electron
Results in a change in x-ray direction & reduction of its energy
Compoton effect/ Scattering
Scattered x-ray and incident x-ray relation in compton effect/ scattering
Scattered X-ray λ > Incident X-ray λ
Energy formula for compton effect/ scattering
Ei = Es (Eb + EKE)
Compton effect occurs at —
30 keV and above
Ei
incident x-ray
Es
scattered x-ray energy
Eb
electron binding energy
E(KE)
electron kinetic energy
The probability of the Compton Effect is (1) to x-ray energy (1/E) & independent of (2)
- inversely proportional
- atomic number
The incident x-ray interacts with the
inner-shell electron
Photoeelectric effect
Ejected electron of photoelectric effect
Photoelectron
Results in a total x-ray energy that is totally absorbed
Photoelectric effect
Energy formula for photoelectric effect
Ei = Eb + EKE
Phototelectric occurs at —
10-150 keV
Characteristic x-rays are produced
Photoelectric effect
Three products of photoelectric effect
- Characteristic x-rays
- Photoelectron (ejected electron)
- Positive atom (deficient of one electron)
Good effects of photoelectric effect
- No scattered radiation
- Produce good quality radiographic image
Bad effecct of photoelectric effect
- Increase radiation exposure to patient
Total x-ray absorption
Photoelectric effect
The probability of the photoelectric effect is directly proportional to the (1) of the (2)
- third power
- atomic number (Z^3)
The probability of the photoelectric effect is inversely proportional to the (1) of the (2)
- third power
- x-ray energy (1/E^3)
The incident x-ray interacts with the nuclear force field
Pair production
Results: x-ray disappears & two electrons with opposite charge appear (positron & electron)
Pair production
Pair production occur at —
> 1.02 MeV x-rays
Where is pair production useful in?
PET NucMed
Does not occur during x-ray imaging
Pair production
A process wherein the mass of positron & electron is converted to energy
ANNIHILATION RADIATION
The incident x-ray interacts directly into the nucleus
Photodisintegration
Results: x-ray is absorbed by the nucleus and nucleon/ nuclear fragment is emitted
Photodisintegration
Photodisintegration occur at —
> 10 MeV x-rays
Does not occur in diagnostic radiology
Photodisintegration
Energy level of the five x-ray interaction with matter
Coherent: Low
Compton: Moderate
Photoelectric: Moderate
Pair production: High
Photodisintegration: High
Results of coherent
- Change in x-ray direction represented by scattered x-ray
- No change in x-ray energy
Results of compton
- Change in x-ray represernted by scattered x-ray
- Reduced in x-ray energy
- Compton electron emitted
Results of phototelectric
- X-ray disappear
- Photoelectron, characteristic positive atom are produced
Results of pair production
- X-ray disappear
- Two electrons with opposite charge appear, annihilation radiation is produced
Results of photodisintegration
- X-ray absorbed in the nucleus
- Nuclear fragment emitted
Different degrees of absorption in different tissues
Differential absorption
Results of differential absorption
image contrast & formation of the x-ray image
Differential absorption occurs because of —
- Compton scattering
- Photoelectric effect
- X-rays transmitted through the patient
Differential absorption and kVp relation
Differential absorption increases as the kVp is reduced (↓kVp, ↑DA)
To image small differences in soft tissue, one must use (1) to get maximum (2)
- low kVp
- differential absorption
THREE TYPES OF X-RAY IMPORTANT IN MAKING A RADIOGRAPH
- scattered by Coherent and Compton interaction
- absorbed photoelectrically
- transmitted by the patient without interaction
THREE TYPES OF X-RAY IMPORTANT IN MAKING A RADIOGRAPH
Those scattered by Coherent and Compton interaction
◦ Doesn’t provide diagnostic information
◦ Result: image noise
THREE TYPES OF X-RAY IMPORTANT IN MAKING A RADIOGRAPH
Those absorbed photoelectrically
◦ Provides diagnostic information
◦ Appearance: radiopaque
THREE TYPES OF X-RAY IMPORTANT IN MAKING A RADIOGRAPH
Those transmitted by the patient without interaction
◦ Provides diagnostic information
◦ Appearance: radiolucent
