Radiography Essentials Ch11 scatter radiation and its control
Scatter Radiation and Its Control
Scatter radiation that is directed back toward the x-ray tube.
A moving grid.
One of three interactions of radiation with the human body tissues. It occurs at low energy levels with energy transferred to the atom. Only about 5% of exposures is caused by this interaction. Also known as Thompson scatter.
One of three interactions of radiation with the human body tissues. In this effect, the x-ray photon is scattered from the body rather than going directly through to expose the film. This effect is undesirable in radiographic imaging.
A radiography of a very small area of the subject; used when fog compromises the ability to see specific details in a large body part.
A composite of two grids with the lead strips at right angles to each other; also called a crossed grid.
The range of source-image distances (SID) at which the grid will not absorb significant amounts of primary radiation.
Grid for general-purpose use; the lead strips are aligned to the direction of the diverging primary x-ray beam.
A device placed between the patient and the IR to absorb scatter radiation.
A special cassette with a grid built into the front side.
Excessive absorption of useful radiation by the grid.
The number of lead strips per inch.
An image of the grid itself in radiographic images; also called grid striping.
The distance at which the primary x-ray beam is parallel to the focused lead strips of the grid.
The relationship between the height of the lead strips and the width of the spaces between them; determines the effectiveness of the grid.
A grid with strips that are parallel to each other, rather than focused. A
One of three interactions of radiation with the human body tissues. In this effect, the x-ray photon is totally absorbed in the body tissues.
Result of either coherent scattering or the Compton effect.
Radiation produced by the photoelectric effect.
A high-frequency grid that does not move during the exposure.
Produced during photoelectric interactions and is considered secondary radiation.
Scatter radiation creates fog that reduces _______ and reduces the visibility of detail.
Results in more scatter radiation fog.
The patient is the _______ of scatter radiation in radiography.
In the diagnostic range of kVp used (50 to 100) the majority of radiation interactions with the body are ____ interactions.
Unwanted exposure to the film.
The fog produces an overall increase in radiographic ____.
Greater ____ of tissue, the more scatter radiation.
More scatter radiation when the ____ of the subject is increased.
____ radiation is better able to escape the subject and cause fog on the radiograph.
The more ____ the absorbing matter is, the more scatter radiation that is produced because more of the primary beam is absorbed.
factors affecting scatter radiation fog
Tissue thickness, field size, milliampere-seconds, and kilovoltage.
The principal method for reducing scatter radiation fog.
A grid is used when a body part becomes greater than ____ in thickness.
10 to 12 cm.
other strategies for limiting scatter fog
Use of an air gap, limitation of the field size, and reduction of kVp.
____ x-rays not moving in the same direction as the primary x-ray beam are absorbed by the grid.
A ____ has the form of a thin plate and is covered by a protective aluminum coating.
A grid is constructed of tiny, tissue-thin ____ strips, placed on edge separated by radiolucent interspacing material.
Absorb scatter radiation while permitting remnant radiation to pass through.
The effectiveness of a grid is determined by the ____.
The ____ the grid ratio, the less variation is permitted and the greater is the efficiency of the grid.
the range of typical grid ratios
5:1 to 16:1.
grid cassettes/mobile radiography - what ratio?
5:1 and 6:1.
general purpose - what ratio?
general purpose/chest radiography - what ratio?
high-kilovoltage radiography only - what ratio?
Grid frequencies range between ____.
60 and 196 lines/inch.
two methods employed to prevent objectionable grid lines
Using a moving grid or using a grid with very high frequency.
Moving the grid during the exposure ____ the image of the grid lines so that the grid image is not visible on the film.
Bucky grids typically have a ratio of ____.
12:1 to 16:1.
Bucky grids typically have a frequency of ____.
85 to 103 lines/inch.
Upright cassette holders.
Stationary grids typically have a ratio of ____.
8:1 or 12:1.
Stationary grids typically have a frequency of ____.
At least 103 lines/inch.
common grid cassette ratios
5:1, 6:1 or 8:1.
Grid cutoff appears as ____ radiographic density on the side of the image.
No ____ occurs when the x-ray beam is correctly aligned to the grid.
Grid cutoff occurs when the x-ray tube is centered to one side of the grid rather than to the ____.
Focal center line.
causes of cutoff
Lateral decentering, source-image receptor distance outside focal range, lateral angulation or grid level off, and grid reversed.
The higher the grid ratio, the more ____ the alignment must be.
The ____ of a parallel grid is infinity.
A crosshatch grid is desirable because it has an effective ratio ____ than the ratios of two grids combined.
The x-ray tube cannot be ____ when using a crosshatch grid.
Object-image receptor distance.
Increasing OID will ____ the intensity of scatter radiation at the film.
the lateral projection of the cervical spine
One procedure in which the air gap is used by default.
for coned-down images what size IR and square field is used
8 x 10 IR and a 5- or 6-inch square field
"nine-penny test" or collimator tool test
Used to check the collimator.
standard control limit for collimator is that the x-ray light field and the radiation field must be within ____.
± 2% of the SID.
standard control limit for the tube's beam alignment is that the tube must be mounted so that the x-ray beam is within ____.
1 degree of perpendicular.
When kVp is decreased this requires an increase in ____ to compensate.
the direction the majority of photons that are scattered will go