Ch 11 - Scatter Radiation

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Air Gap

The space between the patient and the film.

Backscatter

Radiation that is directed back toward the x-ray tube

Bucky

A moving grid.

Coherent Scattering (AKA: Thompson Scatter)

Takes place at low energy levels. The direction of the coherent scattering is forward, in the same general direction as the incoming x-ray beam.

Compton Effect

The decrease in energy (increase in wavelength) of an X-ray or gamma ray photon, when it interacts with matter

Coned-down image

When a specific area of interest is centered to the field and collimation technique is used. It is said to be

Crosshatch Grid

A composite of two grids with the lead strips at right angles to each other

Focal Range

The range of distances within which the grid will not absorb an undue amount of useful radiation

Focused Grid

The lead strips of the grid are aligned to the direction of the diverging primary x-ray beam

Grid

A device placed between the patient and the IR to absorb scatter radiation while permitting remnant radiation to pass through

Grid Cassette

A special cassette with a grid built into the front side

Grid Cutoff

Excessive absorption of useful radiation by the grid, and appears as decreased density on the side of the image

Grid Frequency

The number of lead strips per inch

Grid Lines

Since the grid absorbs some useful radiation, the radiographic image includes an image of the grid itself called

Grid Radius

The lead strips of a focused grid are precisely aligned to the x-ray beam at a specific SID called the

Grid Ratio

The relationship between the height of the lead strips and the width of the spaces between them, which determines the effectiveness of the grid.

Parallel Grid

A grid with strips that are parallel to each other, rather than focused.

Photoelectric Effect

The incoming photon collides with an inner orbital electron of an atom. The photon is totally absorbed in the process and creates dose in the patient.

Scatter Radiation

The result of either coherent or the Compton effect.

Secondary Radiation

The result of the photoelectric effect.

Stationary Grid

A high-frequency grid that does not move during the exposure

Characteristic Photon

Secondary radiation which is produced by the body due to the photoelectric effect.

Compton Interactions

In the diagnostic range of kVp (50-100kVp) the majority of radiation interactions with the body are

Dr. Gustav Bucky, 1913

Who invented the Bucky and when

Infinity

What is the radius of a parallel grid

Reduces scatter radiation fog on the radiographs

What is the benefit of an Air Gap

Scatter will be decreased

What will happen to scatter when you increase OID

Lateral projection of the cervical spine

Which procedure still uses an air gap technique

Fog; Reduced contrast, Reduced recorded detail

Scattered radiation affects the radiographic image by causing

kVp; Field size

Name two factors that will affect eh quantity of scattered radiation fog on the radiograph

Clean up scattered radiation more effectively

As compared with an 8:1 ratio grid, a 12:1 ratio grid will

Visibility of grid lines

The frequency of a stationary grid affects the

10-12 cm

As a general rule, a grid or Bucky should be used when the part thickness is greater than

Grid cutoff

Lateral angulations, SID out of the focal range, or Position of the x-ray beam off center to one side of the grid will result in

More

Higher kVp results in more/less scattered radiation fog

Grid ratio

The effectiveness of a grid is determined by the

T

(T/F) Increased tissue thickness = Increased scatter

1

The standard control limit for the x-ray tube's beam alignment is that the tube must be within __________ degree of perpendicular

Photoelectric interactions produce characteristic scatter radiation

Which type of radiation interaction produces scattered radiation that is characteristic of the subject irradiated?

Part thickness; field size

List two factors that affect the volume of tissue irradiated

Increased

When kVp is increased, will the quantity of secondary radiation fog be increased or decreased

The patient

What is the principal source of scattered radiation that causes fog in radiography

12:1

State the grid radio that is typical of a table Bucky

103 lines per inch

What is the usual minimum frequency for a stationary grid in an upright grid cabinet

Normal radiographic density in the center and decreased density with lengthwise streaks and apparent grid lineson both sides

What is the typical radiographic appearance of grid cutoff caused by using an SID that is outside the grid's focal range

Increased image quality on the spot film

How might the image of a vertebra on a "spot film" differ from on a 35-43cm radiograph of the spine

Refer to the technique chart, or if the part measures 10-12 cm or more.

How would you determine when to use a grid

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