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47 terms

Ch 11 - Scatter Radiation

STUDY
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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