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