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Physics Ch 11

Control of Scatter Radiation

QuestionAnswer
X-rays that exit and interact with the IR are called ____ ____ x-rays. image forming
_____ reduces patient radiation dose and improves contrast resolution. Collimation
As scatter increases, the radiographic image loses _____. contrast
As kVp is increased, the number of Compton interactions _____. increases
Low kVp and high maAs result in an ______ pt dose. increased
Approximately ____% of x-rays incident on the patient reach the IR. 1
When kVp is increased, image contrast is ____. reduced
Scatter radiation increases as the x-ray beam field size _____. increases
What are the three primary factors to reduce scatter to the IR? Collimation, patient thickness and kVp
Thinner anatomy will have reduced _____ and increased detail, compared with that of thicker anatomy. scatter
_____ of anatomy improves spatial resolution and contrast resolution and lowers the patient radiation dose. Compression
_____ is the visible difference between the light and dark areas of an image. Contrast
Reduced image ____ results from scattered radiation. contrast
What two devices reduced amount of scatter that reaches the IR? beam restrictors and grids
What are three types of beam restrictors? aperture diaphragm, cones/cylinders and variable aperture collimator
Collimation reduces the patient radiation dose and ____ contrast resolution. improves
Positive beam limiting (PBL) devices were mandated by the US in ___ and removed in ____. 1974, 1994
Total filtration = ____ + _____ Total filtration = Inherent filtration+Added filtration
The added filtration of the collimator assembly is equivalent to approximately __ mm Al. 1
Who demonstrated the technique for reducing the amount of scatter radiation that reaches the IR? Gustave Bucky
Grid ratio = ___/___ Grid ratio=h/D
High grid ratios _____ patient radiation dose. increase
The number of grid strips per centimeter is called the grid _______. frequency
The principal function of a grid is to improve image ______. contrast
What is the contrast improvement factor? k=image contrast with grid/image contrast without grid
Most grids have contrast improvement factors between ___ to ___. 1.5;2.5
The contrast improvement factor is ____ for high ratio grids. higher
The higher the grid ratio, the ____ is the Bucky factor. higher
The Bucky factor increases with increasing ___. kVp
As the Bucky factor increases, radiographic technique and patient radiation dose ____ proportionally. increase
What are the four types of grids? parallel, crossed, focused and moving
The main disadvantage of parallel and crossed grids is ____ _____. grid cutoff
Focused grids coincide with the _______ of the beam. divergence
High ratio grids have less positioning latitude than ___ ratio grids. low
____-____ grid can occur across the image and when the IR sinks into the patients bed during mobile radiography. Off level
An ____-____ grid is more a result of positioning the x-ray tube than the grid. off center
___-___ grid occurs when radiographs are taken at unspecified SID's. Off focus
____ ____ grid occurs when the grid is placed upside down and results in severe grid cutoff. Upside-down
The ___-___ technique will reduce scatter and increase image contrast. air-gap
______ is one disadvantage of the air gap technique. Magnification
At ____ kVp and above, grid ratios greater than 8:1 are used. 90