Unit 2 X-Ray Interaction With Matter Flashcards
Define Attenuation
The reduction in the number of photons as it passes through matter
What are the 3 possible scenarios that can occur when x-rays strike matter?
Absorption: photon is absorbed by the tissue(dose)
Transmission: photon passes through without interaction and hits the IR
Scatter: photon interacts with the body, is deflected, and continues in a new direction
Coherent Scatter Types
-Thomson: one electron excited
-Raleigh’s: all electrons excited
Characteristics of Coherent Scatter interaction
-Low energy primary photon interacts with all of the electrons in the atom(< 10keV)
-Atom becomes excited
-Atom releases a SCATTERED PHOTON with the same energy as the INITIAL PHOTON
Coherent Scatter impact on the body
-Unmodifying: no ionization
-No dose to the patient
Coherent Scatter conditions
-LOW energy x-ray photon
-All tissue types and densities
Coherent Scatter impact on Image
Minimal degradation of image (if any)
X-rays produced in the body are __________ x-rays
Secondary
Photoelectric Absorption characteristics
-Diagnostic energy (25-140 keV)
-Inner shell electron is EJECTED
-Photon is absorbed
-Characteristic cascade occurs
-Weak secondary x-rays
Photoelectric Absorption: Auger Effect
Ejected electron bombards into another electron and ejects it
Photoelectric Effect Impact on the body
-Diagnostic range x-rays are absorbed by tissue
-Photoelectric(PE) = x-ray absorption and ionization = radiation patient dose
-Absorption= structures are visible on an x-ray image
Absorption on image shows up ________, Transmission shows up _________
White; Black
Photoelectric Absorption conditions
-Photon energy must be slightly higher than the binding energy(BE) of the electron
-PE increases with increased atomic #
*Bone: high atomic number (13) = absorbs more x-rays
*Air and Soft tissue: low atomic number (7) = absorbs less x-rays
-Higher atomic density of tissue= increased chance of Photo Electric effect
Photoelectric Effect impact on image
Image formation
Compton Scatter characteristics
-The energy of the incident photon is in the diagnostic range (Diagnostic energy (25-140 keV))
-Photon bombards into OUTER shell electron and ejects it
-Photon continues on in a new direction
-Photon may undergo additional Compton interactions until it is absorbed Photoelectrically
-The higher the angle of deflection, the weaker the photon becomes
-Forward scatter is still highly penetrating
T or F: Photoelectrically is the only way a photon is absorbed
True
Compton scatter: Define Backscatter
Photon directed back towards the tube
Compton scatter impact on the body
-Ionization of atoms: biologic damage
-Increase of patient dose
-Source of occupational exposure(patient is source of exposure, scattered photon from patient can hit radiographer)
-Compton scattered photon will be absorbed photoelectrically
Lead symbol and atomic #? What does it do?
-Pb; 82
-Absorbs Compton scatter Photoelectrically and reduces occupational exposure
High atomic # = high rate of ______
PE(Photoelectric)
Compton Scatter conditions
-Occurs at all photon energy levels
-Occurs at any atomic number
-Increases with increased tissue density and increased tissue volume
More matter means…
More scatter
Compton Scatter impact on Image
Degradation of the image
Describe how kVp impacts the amount of PE vs Compton in a given x-ray exposure
PHOTOELECTRIC:
-Low kVp INCREASES the chance of photoelectric
* LOW energy photon will be ABSORBED in the body
-High kVp DECREASES the chance of photoelectric
*HIGH energy photon will PENETRATE through the body
COMPTON:
-High kVp INCREASES the percentage of photons that undergo Compton
-High energy beams produce high energy scatter photons
Optimum kVp is used to…
Allow maximum penetration while keeping scatter to a minimum
_____ depends on what you’re x-raying, _____ depends on how much you’re x-raying
kVp; mAs
Low kVp
-More absorption
-Less transmission
-Less scatter
(more PE, less Compton + Transmission)
High kVp
-Less absorption
-More transmission
-More scatter
(less PE, more Compton and Transmission)
How does obesity affect the amount of Compton in an exposure?
-Less tissue = less scatter
-More tissue = more scatter, increase mAs
Additive vs Destructive Pathology
-Additive: If a disease causes the affected body tissue to increase in thickness, effective atomic number, and/ or tissue density, there will be a greater attenuation of the x-ray beam. Often requires an increase in technical factors like kVp and mAs
-Destructive: If a disease causes the affected body tissue to decrease in thickness, effective atomic number, and/or tissue density, there will be less attenuation of the x-ray beam. Often requires a decrease in technical factors like mAs and kVp
Define Recoil electron
An outer shell electron that is ejected from its orbit during Compton scatter
Define Angle of deflection? What interaction has this?
-The angle formed by the incident photon trajectory after collision with an outer shell electron (The higher the angle of deflection, the weaker the photon becomes)
-Compton scatter
Secondary radiation happens in which interaction?
Photoelectric
The higher the deflection Angle, the ___________ the photon becomes.
The smaller the deflection Angle, the ___________ the photon becomes.
Weaker; Stronger(more energy)
The chance of a Compton event occuring ______________ as tissue density increases
Increases
The chances of a Compton event occuring __________________ as tissue thickness increases
Increases
Photoelectric effect, Coherent scatter, Compton scatter photons and electrons
Photoelectric: 1 photon in, 1 electron out
Coherent: 1 photon in, 1 Scattered photon out
Compton: 1 photon in, 1 electron and 1 scattered photon out
