Module 5 Exam
If a shoulder examination is done using an 8:1 ratio grid and 12 mAs, how much mAs should be used if the examination must be done tabletop (no grid)?
3 mAs
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.
If 24 mAs and a 6:1 grid results in an excellent radiograph, how much mAs is needed with a 5:1 grid?
16 mAs
The purpose of automatic collimation is
limiting patient exposure
Which of the following grids provides excellent scatter clean-up but requires close to perfect alignment to avoid cutoff?
16:1 ratio grid
Beam-restricting devices are located just above the tube housing.
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
When using automatic collimation, collimating to the anatomy of interest is an unnecessary waste of time; the beam is already collimated.
false
To compensate for the reduction of radiation reaching the IR when a grid is used, ___________ is typically increased. SID
mAs
When imaging the pelvis, changing from 14 x 17 collimation to 8 x 10 collimation requires
mAs must be increased
Anyone in the room during an exposure must wear a lead apron to absorb the scatter radiation produced in the
patient
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
Restriction of the primary beam to the anatomy of interest
reduces 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 unrestricted primary x-ray beam is
round
Focused grids are more effective than parallel grids in absorbing scatter radiation and allowing transmitted radiation to reach the IR.
true
Scatter radiation is of no value in radiographic imaging.
true
To overcome the decrease in sharpness caused by the air gap technique, an increase in SID is required.
true
If a tabletop exposure (no grid) of a humerus requires 2.5 mAs, how much mAs is needed if a 12:1 ratio grid is added?
12.5 mAs
If 22 mAs and a 5:1 grid results in an excellent radiograph, how much mAs is needed with a 12:1 grid?
55 mAs
What is the grid ratio if the grid frequency is 100 lines/inch, and the lead strips are 1.8 mm high and 0.3 mm apart?
6:1
Calculate the new mAs to be used with the grid change. If the original mAs is 24, the original grid was a 5:1, and the new grid is a 16:1, what should the new mAs be to compensate for the change in grid?
72 mAs
Grids are typically only used when the part measures more than ________ cm and ______ kVp is needed for the examination.
10; 60
Grids absorb almost all of the scatter radiation and allow all of the transmitted photons to pass through to the IR.
False
The formula for the grid conversion factor is
GCF = mAs with grid/mAs without grid
Which of the following is the formula used to determine grid ratio?
Grid ratio = height of the lead strips/distance between the lead strips.
If all the convergent points were connected along the length of the grid they would form the
convergent line
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
The beam-restriction device that results in images with the most unsharpness around the edge of the image is the
aperture diaphragm
The simplest type of beam-restricting device is a flat piece of lead with a hole in it called a(n)
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 easily adjusted radiographic beam-restricting device is the
collimator
The most effective and often used radiographic beam-restriction device is the
collimator
For radiographic procedures, scatter radiation is primarily the result of
compton interaction
A flat piece of lead with a hole in it that has a flange directed toward the patient is a(n)
cone or cylinder
The location in space where all the lines extended from the lead strips meet is the
convergent point
Increasing collimation (decreasing the field size) results in
decreased scatter production and higher contrast
_____________________ collimation means _________________ field size.
decreasing; increasing
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 lines per inch or centimeter is the grid
frequency
The type of grid that is permanently mounted but 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
A short-dimension grid
has lead strips running perpendicular to the long axis of the grid
A linear 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?
high kVp and large field size
As compared with lower kVp exposures, when using high kVp will result in a scattered photon that is of ________ energy.
higher
The formula to use when changing from one grid to another is
mAs1/mAs2 = GCF1/GCF2
The air gap technique reduces the amount of scatter radiation reaching the IR because
more scatter misses the IR
A grid with lead strips that run parallel to each other is a
parallel grid or unfocused grid
When the x-ray beam is not lined up with the center of the grid you have _________ cutoff.
off-center
When the SID is above or below the focal range you have _________ cutoff.
off-focus
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
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 or moves slightly from side to side
The field shape produced by a collimator is
rectangular
A significant amount of collimation will have what effect on the amount of radiation reaching the IR
reduced
Grid cutoff results in
reduced exposure to the IR a light film-screen image possible quantum mottle
A focused grid's lead strips are angled to match
the angle of the x-rays in the primary beam
The volume of tissue irradiated is determined by
the area of collimation patient thickness field size
The probability of a Compton interaction occurring is related to
the energy of the xray photon
Linear grids are the most commonly used because
the tube can be angled 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
The Moiré effect can be caused by
using a grid with a frequency similar to the CR laser scanning frequency
The two major factors that affect the amount of scatter radiation produced and exiting the patient are
volume of tissue irradiated and kVp
The type of grid that is usually taped to the front of an IR is the
wafer grid
The Moiré effect is also known as the _________ pattern.
zebra