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