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The Grid

Principles of Radiographic Imaging 5th Edition Chapter 18

QuestionAnswer
Two Linear grids placed on top of one another so that the lead strips form a criss-cross pattern Criss-Cross Grid
Two linear grids placed on top of one another so that the lead strips form a criss-cross pattern Cross-Hatched Grid
A grid created with the central grid strips parallel with the strips and becoming more inclined as they move away from the central axis; the lines would intersect along a point in space called the line of convergence Focused Grid
A device used to improve contrast of the radiographic image Grid
The result of the primary beam being angled into the lead strips Grid Cutoff
The number of grid lines per inch or centimeter Grid Frequency
The ratio of the height of the lead strips to the distance between the strips Grid Ratio
A grid with lead strips running in only one direction Linear Grid
A grid created with the lead and interspace strips running parallel to one another; the lines will never intersect Parellel Grid
Why does a grid improve contrast? Grids absorb scattered radiation before it can reach the image receptor
As a general rule, when should a grid be used? Body part thickness exceeds 10 cm, and kVp is above 60
How is a grid constructed? Selection of materials, grid ratio, and grid frequency
Define Grid Ratio: The ratio of the height of the lead strips to the distance between the strips
What type of grid pattern has lead strips running in only one direction? Linear Grid
How is a focused grid designed? The central grid strips are parallel and as the strips move away from the central axis they become more and more inclinded
As the ability of a grid to clean up scatter increases, what is the effect on patient dose and image receptor exposure? The more efficient a grid is at absorbing scatter, the less image receptor exposure. To compensate for the loss of exposure there is an increase in mAs, which increases patient dose.
How is the contrast improvement of a grid measured? The contrast improvement factor. K=radiographic contrast with the grid, over radiographi. The higher the K factor, the greater the contrast.
How does an off-level grid error occur? When the tube is angled across the long axis of the grid strips
How does the air-gap technique improve contrast? The technique involves placing the patient at a greater object IR eistance, that creating an air grap between the patient and IR
Created by: Dallas1856