Test 3 - Chpt 7, 8 Flashcards
Understanding x-ray photon interaction does what (2)
Minimizes harm to the patient
produces better-quality images
X-rays do these 3 things
get absorbed = white
travel straight through = black
scatter or secondary beam = grey
What three interactions are found within the diagnostic range
classical, Compton scattering, photoelectric effect
Coherent scattering AKA
classical or Thomson scattering
What 3 things does the Compton interaction do?
- ionizes the atom = makes it unstable
- Compton electron (ejected electron) goes through interactions of its own in adjacent atoms
- incident photon (Compton scatter photon) is deflected and also causes interactions
In this event, the incident x-ray photon interacts with an orbital electron of a tissue atom and changes direction (no ionization)
coherent/classical / Thomson scattering
Interaction that has a low energy x-ray photon
coherent scattering
What results from coherent scattering? (Contrast)
Slightly lower contrast because it increases the scatter that reaches the IR
coherent scattering is likely to occur when an X-ray photon interacts with what?
the whole atom
What interaction contributes to the highest proportion of scatter in the image?
Compton scattering
What interaction results in image fog?
Compton scatter because the scatter strikes the IR in the wrong place
What is the most prevalent interaction between X-ray photons and the human body in general diagnostic imaging?
Compton scatter
The probability of Compton scatter is related to the?
the energy of the photon
How much energy do Compton scatter photons retain?
about 2/3
The major source of occupational dose is from what interaction?
Compton scatter
During a Compton interaction, what is the electron called that gets knocked out of orbit?
Compton electron
During a Compton interaction, after the electron is knocked out of orbit what does the remaining energy leave the atom as, and what is it called?
leaves the atom as a scattered photon AKA Compton photon
What shell does photoelectric interactions interact with?
inner shell electrons
During a photoelectric interaction, what is the electron called that was knocked out of orbit?
photoelectron
During a photoelectric interaction, what happens after the inner shell electron is knocked out of orbit, and what is created?
inner-shell vacancy creates a cascade effect and creates a characteristic photon
What happens to the characteristic photon that is created from a photoelectric interaction?
gets absorbed by the surrounding tissues
(T/F) The photoelectron has enough energy to undergo interactions of its own
true
What do photoelectric interactions affect?
increases the patient dose and increases image quality
The probability of the photoelectric interaction depends on what three things?
- energy of the incident photons
- atomic number of the tissue atoms
- binding energy of the inner shell
Increasing kVp = # of Compton interactions does what and probability does what?
interactions increase, and probability decreases
decreasing kVp = # of photoelectric interactions does what and probability does what?
interactions increase, probaility compared to Compton increases
Interaction that results in the incident photon having enough energy to not interact with the electrons but interacts with the nucleus instead
pair production
What two things are produced from pair production?
positron and an electron
Pair production is AKA
annihilation reaction
for the positron and electron particles of a pair production interaction to exist they must have what energy?
0.51 MeV each
(the energy equivalent of an electron)
What happens to the electron from a pair production interaction?
goes through many interactions before resting in another atom
What happens to the positron from a pair production interaction?
travels until it strikes an electron and causes an annihilation event
(positron and electron are destroyed, converting their energy into 2 x-ray photons)
How does photodisintegration occur?
when photons with super high energies strike the nucleus of the atom and make it unstable
During photodisintegration, how does the nucleus of the atom become stable?
it ejects a nuclear particle
What is differential absorption?
difference between x-ray photons that are absorbed photo-electrically versus those that penetrate the body
What is it called when X-ray photons pass through the body and reach the IR?
transmission
What is it called when photons are absorbed by the body and don’t reach the IR?
absorption
When an X-ray photon interacts with a macromolecule the energy may manifest as a change to what?
As a change to the structure of the macromolecule
The 3 most common effects of differential absorption
main-chain scission
cross-linking
point lesions
(T/F) the composition of the anatomic tissues affects the x-ray beam interaction
true
What creates an image that structurally represents the anatomic area?
differential absorption
(transmission and absorption)
Do anatomic parts absorb the primary beam to the same degree?
No
What is the reduction in the energy or number of photons in the primary x-ray beam?
attenuation
what occurs as a result of the photon interactions with the atomic structures that compose the tissues?
attenuation
What 2 processes occur in the diagnostic range?
absorption and scattering
total photon absorption depends on what?
the energy of the incoming x-ray photon and the atomic number of anatomic tissue
photoelectric interactions increase with what kVp?
lower kVp
the chance of a photoelectric interaction decreases with what kVp?
increase in kVp
there are more Compton interactions with what kVp?
increase in kVp
there is a decrease in the chance of Compton interactions happening with what kVp?
increase in kVp
Increasing tissue thickness does what to beam attenuation?
increased attenuation
factors that affect beam attenuation (4)
tissue thickness
type of tissue
tissue density
x-ray beam quality
X-rays are attenuated exponentially and reduced about 50% for each _____ cm of tissue thickness
4-5
increase in tissue atomic number does what to beam attenuation?
increases attenuation
What is unwanted exposure on the image caused by scatter?
fog
the invisible image that exists on the exposed IR before it’s processed
latent image
the visible image on IR after processing
manifest image
(T/F) digital images are composed of numeric data that can be easily manipulated by a computer
true
(T/F) quality is improved with a smaller matrix size that includes a greater number of pixels
false
larger matrix
What increases as the matrix increases? (3)
computer processing time
network transmission time
digital storage space
the numeric value assigned to each pixel is determined by the
relative attenuation of X-ray
each pixel has a ________ that controls the exact pixel brightness (gray level) that can be specified
bit depth
Photons that travel through tissue to reach the IR
transmission
Photons exiting the patient to form the image on the IR
Remnant
A tissue with a high what would absorb more photons
Atomic number
What results in a nuclear fragment being emitted
Photodisintegration
Photons formed somewhere other than the target
Off focus
Where patient does is highest
Skin entrance
Emits a positron and an electron having 0.51 MeV
Pair production
There is no ionization with this interaction
Coherent scatter
The reduction in the number of photons as they pass through matter
Attenuation
This results in the whites on the radiographic image
Photoelectric
Refers to how tightly molecules are bonded in an sonic structure
Tissue density
The ______ energy is equal to the difference between the incident photon and the burning energy of the inner-shell electron
Ejected electron
Photoelectric absorption is predominant at what kVp levels and increases image contrast
Lower
Compton scattering becomes the predominate interaction at what kVp levels?
High
Compton only depends on what and not what?
Depends on the energy of the incoming photon
Not the atomic number of the anatomic tissue
photoelectric depends on what two things?
- the energy of the incoming electron
- the atomic number of the tissue
with higher kVp the percentage of photoelectric does what, and Compton interactions?
Photoelectric interactions decreases
Compton interactions Increases
x-rays are attenuated exponentially and generally reduced by how much for each 4-5 cm of tissue thickness?
50%
Higher penetrating X-rays have what wavelength and what frequency?
shorter wavelength
higher frequency
Fluoroscopy can be visualized with what two things?
flat panel detector or image intensifier
How much of the primary beam X-ray beam interacting with the anatomical part reaches the IR
Less than 5%
Classical interactions has an energy of
Less than 10 keV
Compton scattering occurs with what energy photons
Moderate energy X-ray photons
20-40 keV
Photoelectric interactions occur with what diagnostic range
20-120 keV
Photodisintegration occurs with what photon energy
More than 10 MeV
(T/F) the remaining photon from Compton scattering may leave the anatomic part to interact with the IR
true
matter per unit volume or the compactness of the atomic particles composing the anatomic part
tissue density
