Radiology Physics Flashcards

Terms Definitions
types of particulate radiation
alpha, beta
Give the reaction that contributes greatest to technologist radiation dose
Define radiographic contrast
Differences in optical density
particulate radiation has ______________________
mass, energy, and velocity
Define radiopaque
Substance that absorbs x-rays (appears white on an x-ray)
which particle is a high speed electron
beta particle
which is more damaging to the tissue
alpha particle
Explain the relationship between kilovoltage, contrast and latitude
Kilovoltage increases contrast decreases and latitude increases (wide) and vice versa
State which of these two is an ionizing event
on what portion of the mouth is exposure time the highest
maxillary posteriors
Use the inverse square law to calculate the change in radiation exposure as distance from the source changes (apply)
I1÷I2 = (D2÷D1)2
Heel effect
absorption of x-rays in the heel of the target resulting in reduced x-ray intensity to the anode side of the central axis. The smaller the anode angle the larger the heel effect
Explain the best way to reduce involuntary motion
Short exposure time
State how much energy is required for a photodisintegration event to occur
10 MeV
Define quantum mottle
Result of random nature of interaction with IR – not enough signal – photon starved
what does the filter do
lessens the number of photons available
Compare terms:High kVp & Low kVp
low contrast & high contrast
Compare photoelectric interaction with a characteristic interaction
Characteristic is because of an electron and a photoelectron is because of a photon
Define radiographic latitude
Range of exposure that will produce a diagnostically acceptable radiograph
State the best way to reduce voluntary motion
Good patient instruction
State the effect Compton scatter has upon radiographic density
Radiographic density increases as Compton scatter increases
State the relationship between image receptor speed and patient dose
As image receptor speed increases patient dose decreases
Compare several characteristic cures and state which curve demonstrates the greatest or least contrast
More vertical – more contrast, more speed – closest to y-axis, less latitudeMore horizontal – less contrast, less speed – farther from y-axis, more latitude
List three ways in which heat is dissipated in an x-ray tube
Radiation, conduction and convection
Define focal spot blur
Softening of the edges of structure on an image caused by the size of the focal spot (blurred region of radiograph)
Actual focal spot size
area on the anode target that is exposed to electrons from the tube current
Explain what happens to the probability of a photoelectric interaction occurring as the subject atomic number of the subject atom increases
As subject atomic number increases photoelectric interaction increases dramatically (X3)
State what happens to field coverage as anode angle increases
As anode angle increases field coverage increases
Give an example of a negative contrast material
Air (increases transmission of x-rays)
Compare the production of heat to the production of x-rays in the x-ray tube
99% heat and 1% x-ray
Describe what happens to the incident photon
Incident photon disappears - is absorbed
Define a compensating filter
Used to give a better image for part thickness (more uniform) EX: trough-chest, “bow-tie”-Computed Tomography, wedge-foot Used to give a better image for part thickness (more uniform) EX: trough-chest, “bow-tie”-Computed Tomography, wedge-foot
Compare the energy and direction of the incident photon and the scattered photon of a coherent scattering interaction
Incident photon and scattered photon have same amount of energy. Direction of the scattered x-ray is different from that of the incident x-ray
Calculate the changes in x-ray intensity when a specific numeric change is made to the mAs of the beam
Double the mAs double the x-ray intensity
List three terms that can be used to refer to the number of photons in the x-ray beam
Quantity, exposure and intensity
Explain how changes in generator power (voltage waveform/ripple) affect x-ray beam quantity and quality
As generator power increases (voltage waveform/ripple decreases), beam quality increases and quantity increases
List the materials used in a tungsten filament
Thoriated tungsten (tungsten with thorium)
Describe what happens during a coherent scattering event
Incident x-ray interacts with a target atom, disappears, causing atom to become excited. The target atom immediately releases this excess energy as a scattered x-ray with a wavelength equal to that of the incident x-ray (almost instantaneously)
when would we want to increase the kV
a heavy person, dense bone, infection
Compare the changes in probability of a photoelectric interaction occurring to the probability of a Compton interaction occurring as x-ray energy increases
Both decrease as energy increases but a HUGE decrease in photoelectric (X3) compared to decrease in Compton
Tell how quantum mottle can be reduced
Increase number of x-rays High mAs, low kVp and slower image receptors will reduce quantum mottle (decrease in mA increases quantum mottle)
Explain what is meant by thermionic emissions
When filament is heated enough, ion production begins the boiling off of electrons (the creation of ions through heat)
State the effect increasing SID will have upon beam quantity (intensity)
Increase in SID will decrease beam intensity (quantity)
Describe what happens during a Compton scattering event
The incident photon interacts with an outer-shell electron and ejects it from the atom, thereby ionizing the atom. The x-ray continues in a different direction with less energy
Large focal spot will have more or less focal spot blur?
Large focal will have more softening (focal spot blur)largere the focal spot creates more focal spot blur
Explain what is meant by quality of the beam
Quality is the penetrability of the beam. (increase quality = increased penetrability)
Read an anode cooling chart or housing cooling chart to determine the exposure capacity of an x-ray tube
Exposure capacity - divide capacity by total exposures made (total exposure capacity and divide by total exposures (HU) made) heat capacity divided by heat units per exposure
State why we wish to reduce the number of low energy photons in the x-ray beam
To decrease patient dose (skin dose)
List two major units used to measure radiation exposure (measure of beam)
mR and Graya (milliroentgens or gray in air
Compare the speeds of a normal rotating anode with a high speed anode
Normal is 3400 rpm and high speed is 10,000 rpm
Compare the actual focal spot size to the effective focal spot size
AFS – area struck by electron beam. EFS – area from IR perspective by angling of the anode (AFS always larger than EFS)
Explain what is meant by extra focal or off-focus radiation
X-rays produced at the anode but not at the focal spot. Electrons bounce off the focal spot and land on other areas of the target
Calculate on object size when given an image size, SID and OID
Object size = image size (SOD ÷ SID) or image size ÷ object size = SID ÷ SOD
Read a tube rating chart and determine whether an exposure is safe
Common sense- if mA + kVp + time is higher than the line it is an unsafe exposure under the line is safe
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