Chapter 12

Which of the following grids provides excellent scatter clean-up but requires close to perfect alignment to avoid cutoff?

16:1 ratio grid

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

A radiographic image was created using a 12:1 grid and 70 kVp at 10 mAs. What exposure technique change would maintain a similar exposure to the image receptor when converting to a 6:1 ratio grid?

70 kVp at 6 mAs

What is the grid ratio if the lead strips are 2.4 mm high, 0.02 mm wide, and 0.3 mm apart?

8:1

To determine the amount of mAs to be increased when making grid changes, it is necessary to use the GCF, also known as the

GCF = mAs with grid/mAs without grid.

Which of the following produces the greatest amount of scatter radiation exiting the patient?

High kVp and large field size.

For the air gap technique to be effective in reducing scatter radiation reaching the image receptor, what must be increased?

OID

The air gap technique is based on creating a gap by increasing the ______.

OID

When imaging the pelvis, changing from 14 x 17 collimation to 8 x 10 collimation requires

an increase in mAs

The automatic collimator

automatically collimates to the IR size.

The grid is located

between the patient and the 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 most effective and often used radiographic beam-restriction device is the

collimator

what type of beam-restricting device provides the most flexibility in adjusting the x-ray field size?

collimator

For radiographic procedures, scatter radiation is primarily the result of

compton interaction

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.

Which of the following will decrease the amount of scatter radiation produced?

decreasing the x-ray field

As collimation increases, the quantity of scatter radiation increases. Increasing collimation means decreasing the field of view (FOV).

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 lines per inch or centimeter is the grid

frequency

Absorption of transmitted photons by a grid caused by misalignment is

grid cutoff

Angling the x-ray tube along the long axis of a crossed grid would result in:

grid cutoff

The undesirable reduction in density on one or both sides of a radiograph due to misalignment of the x-ray beam to a grid is called:

grid cutoff

The number of grid strips or grid lines per inch or centimeter is called:

grid frequency

What describes the number of lead lines per unit length?

grid frequency

Which of the following is the formula used to determine grid ratio?

grid ratio = height of lead strips/distance between the lead strips

The grid rationis the ratio of the:

height of the lead strips to the distance between the lead strips

As compared with lower kVp exposures, when using high kVp will result in a scattered photon that is of ___________ energy

higher

Increasing the field size (FOV), will _________ the amount of scatter

increase

Increasing the x-ray beam energy will ____________ the amount of scatter

increase

Using a higher the grid ratio will 1. increase spatial resolution 2. increase scatter clean up 3. increase radiographic contrast

increase scatter clean up and increase radiographic contrast only.

With exposure technique compensation, _____ the grid ratio will _____ patient radiation exposure.

increasing, increase

Which of the following is not a type of beam restrictor?

lead shield

The most common field size limitation device in use is the:

light-localizing variable aperture collimator

The purpose of automatic collimation is

limiting patient exposure

What type of grid has lead strips running parallel to the long axis of the grid?

long dimension

To compensate for the reduction of radiation reaching the IR when a grid is used, ___________ is typically increased.

mAs

The formula to use when changing from one grid to another is

mAs1/mAs2 = GCF1/GCF2

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

Grids are typically used when: 1. Part measures more than 10 cm 2. At least 60 kVp needed for the exam 3. Part transmits little scatter radiation

part measures more than 10 cm and at least 60 kVp needed for the exam only.

Which items are decreased with an increase in collimation?

patient dose scatter radiation

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 and moves slightly from side to side.

The field shape produced by a stationary x-ray collimator is

rectangular

A significant amount of collimation will have what effect on the amount of radiation reaching the IR

reduced

Restriction of the primary beam to the anatomy of interest

reduces patient exposure and 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

Which of the following will cause an increase in image contrast?

smaller field sizes

A focused grid's lead strips are angled to match

the angle of the x-rays in the primary beam. (convergence)

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 x-ray 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.

As the grid ratio increase, contrast increase, and patient dose increase

true

The two major factors that affect the amount of scatter radiation produces and exiting the patient are

volume of tissue irradiate and kVp

Under which circumstances would a technologist want to use a grid?

when radiographing a large or dense body part when using a high kVp

The Moiré effect is also known as the _________ pattern.

zebra