The Subject (Patient) and Radiobiology Flashcards
What are the different shades of gray on a film the result of?
differing amounts of photons making it through the patient (differential absorption)
What happens to the photons that don’t make it?
they are attenuated
attenuation = any interaction that removes a photon from the primary beam
What is the term for any interaction that removes a photon from the primary beam?
attenuation
What is transmission the opposite of?
attenuation
What is the term for an x-ray that passes through the patient?
transmission
What impact will an increase kVp have on transmission?
it will increase transmission
What are the two types of Attenuation of our focus?
Compton Scatter
Photoelectric Effect
What is the most common interaction of attenuation?
Compton Scatter
~90%
Where is the photon hitting the atom in Compton Scatter? And what happens?
hits OUTER shell electron –> electron is ejected–> photon deflected–> photon loses energy
Does Compton Scatter or Photoelectric Effect ionize the atom? Is this good or bad?
BOTH ionizes atom
it is BAD
Which type of attenuation deflects (scatters) the photon?
Compton Scatter
scatter = BAD; we want to reduce is as much as possible
What does the angle of deflection occurring during Compton Scatter depend on?
the energy lost to electron
What does a larger angle tell us about the energy lost during Compton Scatter?
larger angle = more energy lost
At what angle does the electron deflect between for Compton Scatter? Greater than what angle is it considered “backscatter”?
0 to 180 degrees
greater than 90 called backscatter
Of the attenuated interactions, what percentage does the Photoelectric Effect make up?
~10%
Where does the photon hit during the Photoelectric Effect? What then happens?
hits INNER shell electron –> electron ejected–> photon disappears–> outer shell electrons fill “hole” –> gives off radiation
What type of Attenuated interaction is the photon absorbed?
Photoelectric Effect
During the Photoelectric Effect, what must the energy be of the photon in order to eject the electron?
greater than the binding energy of the inner shell electron
What other interaction does the Photoelectric Effect should similar to?
Characteristic X-rays w/in the tube–> the only difference is the in the tube it is electron hitting electron
Out of the Photoelectric Effect and the Compton Scatter, which one deflects and which one absorbs?
Photoelectric = absorbs
Compton Scatter = deflects
When we increase the kVp, how is the percent of Photoelectric and Compton interactions change?
increase kVp will:
- decrease percent of Photoelectric interaction
- increase percent of Compton scatter
Which type of Attenuation is it when the photon does not reach the film? What does this give our film?
Photoelectric Effect
CONTRAST
Which type of Attenuation is it when the photon reaches the film? How does this impact contrast?
Compton Scatter
creates fog–> decreases film contrast and adds shades of gray
What effect will more Transmission have on the absorption, shade, and density?
less absorption
darker shade
higher film density
What effect does less Transmission have on absorption, shade, and density?
more absorption
lighter shade
lower film density
What four things does Scatter production depend on?
- density
- kVp
- atomic number of material
- amount of tissue imaged
Out of the four things that produce Scatter, which two can be controlled?
- density
- kVp
- atomic number of material
- amount of tissue imaged
kVp and amount of tissue imaged (collimation)
What are the three ways that we can reduce the amount of tissue imaged to reduce scatter?
- collimate in (increase collimation)
- Recumbent– have the patient lay down –> flattens out tissue due to gravity
- use a grid
What is a grid for x-ray taking? What does it do?
a thin plate in front of Bucky/image receptor
it is innumerable amount of thin strops of lead that STOP scatter from reaching the film
