imaging ch18

What absorbs scatter radiation before it can reach the IR

Grids

When an X-ray passes through the body one of three things will occur with the primary photons that originated at the target

Pass through the body unaffected

Be absorbed by the body

Interact and change direction (scatter)

Photons that pass through the body unaffected will interact with what

the IR to create the image

Those photons are responsible for creating the __ on the image

Contrast (differences in IR exposures)

Absorption of photons occurs as the result of

Photoelectric interaction

The interaction that provides scatter radiation is known as

Compton interaction

Percentage of Compton interactions increases with__

Increased kVp

The amount of scatter radiation increases with

Patient thickness

Larger field sizes

Decreases in atomic number of the tissue

As a general rule, a grid is used when body part thickness exceeeds __. And when kVp is above

10cm

60 kVp

By removing the grid, the lead strips become __ and we’re no longer visible on the image

Blurred

The radiopaque strips are needed to absorb the scatter radiation and must therefore be made of a __ material with a __ atomic number

Dense

High

___ is defined as the ratio of the height of the lead strips to the distance between the strips

Grid ratio

Higher grid ratios are more effective at removing scatter. True or false

True

What is the name for the number of grid lines per inch or centimeters

Grid frequency

The lead content is greater in a grid that has a __ grid ratio and __ grid frequency

Higher

Lower

As the lead content of a grid ___, the ability of the grid to remove scatter and improve contrast ___

Increases

Increases

Grids with lead strips running in only one direction are called

Linear grids

Linear grids allow the radiographer to angle the tube only along the direction that lines are running. True or false

True

Angulation across the long axis would result in the primary beam being directed into the

Lead strips

If the primary beam is angled into the lead, the lead will __ an undesirable amount of primary radiation, resulting in a problem known as

Absorb

Grid cutoff

For the grid to be properly focused, the X-ray tube must be located along the

Convergence line

The most common use of the grid is for procedures using the

Potter Bucky diaphragm (Bucky)

The Bucky can move the grid during the exposure so that grid lines will be __and therefore not evident on the image.

Blurred

To blur the lead lines, the grid must move at a__ to the direction of the lines.

Right angle

The more efficient a grid is at absorbing scatter, the ___ exposure will be received by the IR.

Less

To increase exposure received by the IR you must

Increase mA

Improper tube positioning results if the CR is directed across the ___ of the radiographic table

Long axis

What is made to be used at a very specific distance identified as the focal range labeled on the front of the grid

Focused grid

What is used as an alternative to the use of a grid

Air gap technique

Air gap technique involves placing the patient at a ___ OID, thus creating an air gap between the pt and IR.

Greater

In digital, image contrast remains unchanged, due to the

LUT’s

Proper alignment with grids and IR is critical for what reasons

Because mAs values are lower, therefore is less exposure latitude in terms of mAs

Any grid cutoff due to misalignment makes its impact more pronounced.

With digital IR, even the smallest amounts of cut-off negatively impacts image quality with the creation of ___

__ ___

Image noise

Artifacts

Inaccurate exposure indicator values

In an effort to lessen the dependence upon grids for good image quality, they have designed grid replacement software that produce images appaearing to have been taken using a ___ when one was not used

Grid

What is designed to remove visible grid lines form an image with a grid

Grid compensation software