RADS 3033 - Principles of Radiographic Imaging Ch 11
Grids are typically only used when the part measures more than __________ cm and ___________ kVp is needed for the examination
10; 60
For radiographic procedures, scatter radiation is primarily the result of
Compton scatter
The air gap technique is a frequently used method for reducing the amount of scatter radiation reaching the IR
False
When using automatic collimation, collimating to the anatomy of interest is an unnecessary waste of time; the beam is already collimated
False
The formula for the grid conversion factor is
GCF = mAs with grid / mAs without grid
The air gap technique is based on creating a gap by increasing the ________
OID
To compensate for some of the loss of recorded detail due to the large OID used with the air gap technique, the _______ should be increased as well
SID
Scatter radiation is of no value in radiographic imagiing
True
Grid cutoff results in -reduced exposure to the IR -a light film-screen image -possible quantum mottle
all of the above
The volume of tissue irradiated is determined by -the area of collimation -patient size -field size
all of the above
Which of the following factors need to be considered when determining the grid to be used for a specific examination -patient exposure -level of contrast improvement needed -focal range
all of the above
When imaging the pelvis, changing from 14x17 collimation to 8x10 requires
an increase in mAs
The beam-restricting device that results in images with the most unsharpness around the edges of the image is the
aperture diaphragm
The flat piece of lead with a hole in it is the
aperture diaphragm
The automatic collimator
automatically collimates to the IR size
The higher the grid ratio, the __________ the scatter clean up and the __________ the radiographic contrast
better, higher
The grid is located
between the patient and IR
The reason the grid in the bucky reciprocates is to
blur out the grid lines
The grid is part of a device located just below the tabletop that also includes a tray to hold the IR. This device is the
bucky
The beam-restriction device that includes a visible light projecting the x-ray field size onto the patient is the
collimator
The most effective and often used radiographic beam-restriction device is the
collimator
a flat piece of lead with a hole in it that has a flange directed toward the patient is a
cone or cylinder
If all the convergent points were connected along the length of the grid they would form the
convergent line
The location in space where all the lines extended from the lead strips meet is the
convergent point
Beam restriction serves which two main purposes
decrease patient dose and decrease scatter
__________ collimation means __________ field size
decreasing; increasing
Beam-restricting devices are located just above the tube housing
false
Grids absorb almost all of the scatter radiation and allow all of the transmitted photons to pass through to the IR
false
It is safe to assume that the x-ray beam field size and the light field size are exactly the same
false
The grid limits the amount of scatter radiation produced in the patient
false
The grid used for the air gap technique should be high frequency
false
The distance between the grid and the convergent line is the
focal distance
The recommended SIDs that can be used with a focused grid is the
focal range
The number of lead liner per inch or centimeter is the grid
frequency
The type of grid that includes a channel for the IR to slide into is the
grid cap
An IR that has a grid permanently attached to its front surface is a
grid cassette
To determine the amount of mAs to be increased when making grid changes, it is necessary to use the GCF, also known as the
grid conversion factor
Absorption of transmitted photons by a grid caused by misalignment is
grid cutoff
Which of the following is the formula used to determine grid ratio
grid ratio = height of the lead strips / distance between the lead strips
A short-dimension grid
has lead strips running perpendicular to the long axis of the grid
A linear grid -has lead strips that cross each other -has lead strips that travel in one direction -is the most common type of radiographic grid
has lead strips that travel in one direction; is the most common type of radiographic grid
Which of the following produces the greatest amount of scatter radiation exiting the patient -low kVp and small field size -low kVp and large field size -high kVp and small field size -high kVp and large field size
high kVp and large field size
the purpose of automatic collimation is
limiting patient exposure
To compensate for the reduction of radiation reaching the IR when a grid is used____________ is typically increased
mAs
The air gap technique reduced the amount of scatter radiation reaching the IR because
more scatter misses the IR
When the x-ray beam is not lined up with the center of the grid you have _____________ cutoff
off-center
The only grid cutoff error that can occur with a parallel grid is
off-level
When the x-ray beam is angled across the lead strips you have ___________ cutoff
off-level
a grid with lead strips that run parallel to each other is a -parallel grid -focused grid -nonfocused grid
parallel grid; nonfocused grid
0.Anyone in the room during an exposure must wear a lead apron to absorb the scatter radiation
patient
The material between the lead strips of a grid must be
radiolucent
The relationship between the height of the lead strips and the distance between them is the grid
ratio
During the exposure, the grid in the bucky -reciprocates -moves slightly from side to side -moves slightly from top to bottom
reciprocates; moves slightly from side to side
When there is significant collimation, the amount of radiation reaching the IR is
reduced
Restriction of the primary beam to the anatomy of interest -reduces patient exposure -is a major cause of repeated images -reduces the amount of scatter produced
reduced patient exposure; reduces the amount of scatter produced
For a lateral lumbar spine, placing a lead shield on the table behind the area of exposure
reduces the scatter reaching the IR
The exam room in our lab that offers automatic collimation is
room 3
The unrestricted primary x-ray beam is
round
A focused grid's lead strips are angled to match
the angle of the x-rays in the primary beam
The probability of a Compton interaction occurring is related to
the energy of the x-ray photon
Linear grids are the most commonly used because
the tube can be angles in the direction of the lead lines
Grids absorb scatter radiation because the scattered photons
travel at an angle to the transmitted photons
Adding a grid or increasing grid ratio results in an increase in patient dose
true
Focused grids are more effective than parallel grids in absorbing scatter radiation and allowing transmitted radiation to reach the IR
true
The cutoff that appears as a strip of appropriate density in the middle of the image and a significant loss of density on both sides is
upside-down focused
The Moire effect can be caused by -using a grid with a frequency similar to the CR laser scanning frequency -using a focused grid upside down in the bucky -using a grid cassette in the bucky
using a grid with a frequency similar to the CR laser scanning frequency; using a grid cassette in the bucky
The two major factors that affect the amount of scatter radiation produces and exiting the patient are
volume of tissue irradiated and kVp
The type of grid that is usually to the front of an IR is the
wafer grid
The Moire effect is also known as the __________ pattern
zebra