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165 Cards in this Set

  • Front
  • Back
Scatter radiation is primarily the result of the _________ _______.
Compton interaction
The Compton interaction is what?
An incoming x-ray photon loses energy and changes direction.
What are the two major factors that affect the amount of scatter radiation exiting the patient?
kVp and the volume of tissue irradiated
Exams using _______ kVp produce a greater propertion of scattered x-rays as compared to ______ kVp exams
high; low
As the x-ray beam field size increases, the _______ amount of scatter radiation is produced.
greater
As part thickness decreases, the _______ amount of scatter radiation is produced.
less
What are two purposes for beam restriction?
limiting patient exposure and reducing the amount of scatter radiation produced within the patient
The unrestricted primary beam is ________ shaped and projects a _______ field on the patient and IR.
cone; round
T or F. Beam restriction and collimation are used interchangeably.
True
As collimation increases , field size ________. As collimation decreases, field size ________ and patient dose _________.
decreases; increases; increases
Beam restriction devices reduce the amount of scatter radiation that is produced within the patient, reducing the amount of scatter, thereby increasing what?
Radiographic contrast
As collimation increases, the field size _______ and the quantity of scatter radiation _______.
decreases; decreases
T or F. As collimation decreases, the field size increases and the quantity of scatter increases.
True
What happens to radiographic contrast if you increase collimation?
Contrast increases
What happens to radiographic contrast if you decrease collimation?
Contrast decreases
As collimation increases, radiographic density ________. As collimation ________, radiographic density increases.
decreases; decreases
When you want to change density which part of your technique do you change?
mAs
For significant collimation it is recommended that an increase of ____ to ____% of the mAs is needed to compensate for the loss of density.
30; 50
What kind of beam restricting device is a flat piece of lead with a hole in it?
aperature diaphragm
Cones and cylinders are better at limiting what compared to aperature diaphragms?
unsharpness
Which are more useful, cones or cylinders? Why?
Cylinders; if the angle of the flange of the cone is greater than the angle of divergance of the primary beam, the base plate of the cone is the only metal actually restricting.
What is the most useful, and accepted type of beam-restricting device?
collimator
A collimator has _____ or _____ sets of lead shutters.
two or three
Why is the collimator considered a more useful beam restricting device?
It has the ability to produce projected field sizes of varying sizes because it is adjustable.
What is another term used for automatic collimators?
positive beam-limiting devices
T or F. Automatic collimators automatically limits the size and shape of the primary beam to the size and shape of the image receptor.
True
When was the radiographic grid invented? By whom?
1913; Gustave Bucky
How thick is a radiographic grid?
Approximately 1/4-inch thick
A _______ is a device that has very thin lead strips with radiolucent interspaces.
grid
A grid is intended to absorb scatter radiation emitted from the patient, and improve what?
contrast
A grid should be used when the anatomic part being radiographed is larger than what size?
10 cm.
A grid should be used when the anatomic part being radiographed requires a kVp of _____ or more.
60 kVp
True or False. Scatter radiation decreases radiographic contrast.
True
Scatter radiation adds unwanted _______ to the radiograph and _______ image quality.
density; decreases
What seperates the lead lines on a grid?
radiolucent interspace material
What is the interspace material made of?
aluminum
What is grid frequency?
It expresses the number of lead lines per unit length.
What is the range of grid frequencies?
25 to 45 lines/cm
What is grid ratio?
Defined as the ratio of the height of the lead strips to the distance between them.
How is grid ratio mathematically expressed?
Grid ratio=height/distance
Grid ratios range from _____ to _____.
4:1; 16:1
As grid ratio increases, scatter cleanup improves and radiographic contrast ______.
increases
As grid ratio _______, scatter cleanup is less effective and radiographic contrast decreases.
decreases
Grid pattern refers to what?
the linear pattern of the lead lines of a grid
What are the two types of grid patterns?
linear and crossed or crossed hatched
A _______ grid has lead lines that run in only one direction.
linear
A _______ grid has lead lines that run at a right angle to one another.
crossed or crossed hatched
Which grid type is the most popular? Why?
linear ;because they allow angulation of the x-ray tube along the length of the lead lines
What is grid focus?
the orientation of the lead lines to one another.
What are the two types of grid focus?
parallel and focused
A ______ grid has lead lines that are primarily in flouroscopy and mobile imaging.
parallel or non-focused
What is the advantage of focused grids?
They allow more transmitted photons to reach the image receptor.
If imaginary lines were drawn from each of the lead lines in a linear focused grid, these lines would meet to form what?
Convergent point
If points were connected along the length of the grid they would form an imaginary line, this would form what?
Convergent line
The _______ _______ is the distance between the grid and the convergent line or point.
focal distance
The ______ ______ is the recommended range of SIDs that can be used with a focused grid.
focal range
T or F. Because the lead lines in a parallel grid are not angled, they have a focal range extending from a minimum SID to infinity.
True
The gird conversion factor can be expressed mathematically as what?
GCF = mAs with the grid/ mAs without the grid
As grid ratio _______, radiographic density _______.
increases; decreases
As grid ratio decreases, density _______.
increases
What is the mathematical equation for removing a grid?
GCF= mAs with the grid/
mAs without the grid
What is the mathematical equation for changing between grids with different grid ratios?
mAs(1)/=GCF(1)/
mAs(2) GCF(2)
As grid ratio increases, patient dose does what?
increases
____________ is defined as a decrease in the number of transmitted photons that reach the image receptor because of some misalignment of the grid.
Grid Cutoff
What are the four types of grid cutoff?
Upside-down focused, Off-level, Off-cneter, Off-focus
What kind of cutoff occurs when a focused grid is placed upside-down on the image receptor, resulting in the grid lines going opposite the angle of divergence of the x-ray beam.
Upside down focused
What does the upside-down cutoff do to the image?
It causes the lateral edges of the film to be very light.
What type of cutoff occurs when the x-ray beam is angled across the lead strips?
Off-level
What does off-level cutoff do to the image?
It produces an overall decrease in density on the image
What kind of cutoff occurs when the central ray of the x-ray beam is not aligned from side to side with the centerof a focused grid?
Off-center
What type of grid cutoff occurs when using an SID outside of the recommended focal range?
Off-focus cutoff
What does off-focus cutoff do to the image?
It creates a loss of density at the periphery of the radiograph.
What is the most common type of grid cutoff?
off-level
If you increase grid ratio, patient dose, contrast, and the likelihood of grid cutoff _______.
increase
The typical grid is _______ , focused, mid-ratio (between _____ and _____), and has a focal range that includes and SID of _____ or _____ inches.
linear; 8:1, 12:1; 40, 72
The air gap technique uses what to reduce scatter?
increased OID
The air gap technique decreases image quality. To make up for unsharpness and increase recorded detail, you must increase what?
SID
The purpose of a grid is to what?
increase contrast
With which of the following grids would a convergent line be formed if imaginary lines from its grid lines were drawn in space above it?
Linear focused
The type of motion most used for moving grids today is what?
reciprocating
Grid cutoff, regardless of the cause, is most recognizable as reduced ______.
density
The study of the relationship between the intensity of radiation exposure to the film and the amount of blackness produced after processing is what?
Sensitometry
The _______ __ _______ ______ is the measurement of the quantity of radiation reaching an area of the film.
intensity of radiation exposure
_________ provides a method of evaluating the characteristics of film and film screen combinations used in radiography.
Sensitometry
What is also a method of evaluating the performance of automatic processors?
Sensitometry
What is the device that is constructed of uniform absorbers of increasing thickness, such as aluminum or tissue equivalent plastic?
Penetrometer
A penetrometer produces a series of uniform densities that resemble what?
Step-wedge densities
What does a sensitometer do?
It is designed to produce consistent step-wedge densities by eliminating the variability of the x-ray unit.
After a film from a sensitometer has been processed, a density step-wedge image, or __________ _______, is produced.
sensitometric strip
What is a device that is used to menerically determine the amount of blackness on the film after processing?
Densitometer
What term is defined as a measurement of the amount of light transmitted through the film?
Optical density
What is the diagnostic range of optical densities?
.50 to 2.0
An optical density of 1.0 indicates that ______ of light was transmitted.
10%
A _______ change in optical density results from a change in the percentage of light transmittance by a factor of 2.
.3
Because the range of radiographic densities is large, the calculation of radiographic densities is compressed into what?
logarithmic scale
A film that allows 100% of the original incident light to be transmitted has a logarithmic value of _____.
0
A film that allows 100% of the original incident light to be transmitted is light or dark?
Light
Film A allows 0.32% of light to be transmitted, while Film B allows 12.5% of light to be transmitted. Which of these two films will be lighter?
Film B
What is the light transmittance formula?
I(t)/I(o) x 100
Film A has an optical density of 1.3, Film B has an optical density of 3.3. Which of these films is darker?
Film B
What is the optical density formula?
Optical density=Log(10) I(o)/ I(t)
What is the range of optical densities?
0.0 to 4.0
What is the lowest range amount of optical density?
.10 to .20
What is the minimum amount of density on the film termed?
base plus fog (B+F)
The useful range of optical densities is what?
.25 to 2.5
What is the diagnostic range of optical densities for general radiography?
.5 to 2.0
When optical density measurements from a sensitometric strip are graphed on paper, the result is a ________ ________.
sensitometric curve
The sensitomtric curve demonstrates the relationship between the instensity of radiation exposure (x axis) and the resultant _______ _______ (y axis)
optical densities
What are four other names for the sensitometric curve?
Characteristic curve, D log E curve, H & D curve, or Hurter & Driffield curve
Along the x-axis, for every 0.3 change in _____ _______ ______, the intensity of radiation exposure changes by a factor of 2.
log relative exposure
An increase of 0.3 log relative exposure results in a _______ of the amount of radiation exposure.
doubling
What are the three distinct regions of a sensitometric curve?
toe, straight-line, shoulder
T or F. The toe region of the curve represents the area of high density.
False, area of low density
The _______ ______ _______ is where the diagnostic or most useful range of densities is produced.
straight-line region
The shoulder region of the curve represents the area of ______ density.
high
What is the point on the curve where maximum density has been produced called?
D max
If you reach maximum optical density and continue to increase exposure you will begin to reverse the amount of optical density, what is this process called?
solarization
Define speed of a film.
A film's sensitivity to radiation exposure
As film speed increases, the optical density produced ______.
increases
Changes in exposure have little effect on density in which regions of the sensitometric curve?
toe and shoulder
When the exposure technique used produces densities outside the straight-line portion of a sensitometric curve, how is contrast affected?
It is decreased
The sensitometric curve ______ ______ _______indicates the intensity of exposure needed to produce a density of 1.0 + base + fog.
speed exposure point
The speed of a film typically is determined by locating the ______ ______ on the curve that corresponds to the optical density of 1.0 + base+ fog.
speed point
T or F. The lower the speed exposure point, the slower the film speed.
False, the faster the speed
The _______ the speed exposure point, the slower the film speed.
higher
T or F. Sensitometric curves of faster speed film are positioned to the left of slower speed film.
True
What is the film speed formula?
Antilog (log RE(2) - log RE(1))
Radiographic contrast is the result of two types of contrast, what are they?
subject contrast and film contrast
The ability of a radiographic film to provide a level of contrast can be evaluated by the _______ of the curve.
slope
What is the mathematical equation for the slope of a line?
Slope = Y (rise)/ X (run),
y2-y1/x2-x1
The steeper the slope of the straight-line region, the _______ the film contrast.
higher
Determining the slope along any portion of the sensitometric curve provides information about contrast produced at that point. What is this point called?
Gradient point
When comparing film, the RT typically determines contrast by calculating the sensitometric's ________ ______ of the slope of the straight-line region.
Average gradient
What is the mathematical application for calculating average gradient?
Average gradient= D(2) -D(1)/
logRE(2)-logRE(1)
The greater the average gradient, the ______ the film contrast; The lower the average gradient, the _______ the film contrast.
higher; lower
What is another gradient point that is calculated from points surrounding the optical density of 1.0 found within the straight-line region on the curve?
Gamma
________ ________refers to the range of exposures that produce optical densities within the straight line region of the curve.
Exposure latitude
T or F. Exposure latitude and film contrast have an inverse relationship.
True
High-contrast film has a _______ latitude, and low-contrast film has ______ latitude.
narrow, wide
Film B has an exposure speed point of 1.5, and Film A has an exposure speed point of 1.2. What is the difference in speed?
Film A is twice as fast as Film B.
Changes in radiation exposure have the greatest effect on optical densities in which sensitometric region?
Straight-line
The more sensitive the film the _______ (faster or slower) the film?
faster
If film speed increases the optical density (increase or decrease)
increase (therefore would decrease technique)
What does the speed point correspond to?
Optical density of 1.0 plus B+F
what does speed exposure point indicate
intensity exposure needed to produce a density of 1.0 plus B+F
Compare the sinsitometric curve of 2 different types of film
P 242 - figure 9-10
the more sensitive film is the (more or less) mAs and (more or less) exposure
Less mAs and less exposure
How do we evaluate contrast of particular film?
by the slope of the straight line region - the steeper the slope the higher the contrast film
what is gradient point?
determined by calculating the slope of the line. It can be calculated for any region on the sensitometric curve (toe, middle, or shoulder)
What is average gradient?
calculaion used to determine the film contrast. usual average gradient between 2.5 and 3.5
the higher the average gradient the (higher or lower) the film contrast
higher
What is Gamma?
calculated from points surrounding the optical density of 1.0 found within the straight line region of the sensitometric curve
What is exposure latitude?
a film characteristic that is the range of exposures that produc optical densities within the straight line region of the sensitometric curve
the higher the contrast on film the (wider or narrower) the latitude?
narrower
Low contrast film has a wide or narrow latitude?
wide
Is digital imaging or film screen more responsive to a wider range of x-ray photons?
digital imaging
Is sensitometry used w/ digital imaging or film?
film
what is sensitometry?
a method to evaluate film & machines by comparing the intensity of the radiaion exposure to the amount of density on the film after processing.
what is the penetrometer used to test?
the tube itself.
what does the penetrometer consist of?
made of aluminum and is in stp wedge shape to simulate various thickness of body parts.
what does a sensitometer test?
the processor
what does the densitometer test?
it measures how much light is able to get to the film. Numerically determines the amount of blackness on the film after processing.
what is the range for optical density?
0-4; but really can't be 0.50 - would be considered base + fog. usually runs 0.10 or 0.20
for every 0.3 change in optical density the % of light transmitted has changed by a factor of what?
factor of 2 or doubled
the % of light transmitted and optical density are (inversly or directly) related.
inversly - as one goes up the other goes down.