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Selection of anti-scatter grids in radiodiagnostics

There are many options for anti-scatter x ray grids in radiology diagnostics. Let us follow the editor to find out what kinds of grids there are.
Wire grid: used to filter out the scattered rays produced by the human body during photography.
The appearance is a thin plate with a thickness of 3~5mm. Generally, a lead bar with a thickness of 0.05-0.1mm is used, which is sandwiched between aluminum or paper with a thickness of 0.15-0.35mm. The filler can be wood, paper, aluminum sheet, etc. The height of the lead strip is the thickness of the grid plate. Finally, the upper and lower sides are packaged with thin aluminum plates. Its specifications are:
(1) Focal length (f): The extension of each lead strip will converge to a point. The vertical distance from this point to the grid is the focal length (radius) of the grid. A straight line is drawn in the center to indicate the direction of the lead, which is the focal plane.
(2) (Grid density N): The number of lead bars contained in the grid plate per centimeter defines its grid density. The grid density generally used is 40~65 lines/cm.
(3) Grid ratio (R): refers to the ratio of the height of the lead bars of the grid to the gap between the grid bars. The higher the ratio, the stronger its ability to filter out scattered rays. The commonly used grids have a grid ratio between 8:1 and 14:1.
According to the structural characteristics of the grid, it is classified: focus type, parallel type, and cross type.
There are four situations in which the gate cutting effect occurs:
The focus grid is reversed: the photo shows a high density in the center line and a gradual decrease in the density on both sides.
Tendency to tilt: ① The center line is perpendicular to the grid plate, but deviates from the center line of the grid plate to one side; ② The center line is not perpendicular to the grid plane, and the density on both sides of the photo is inconsistent.
The top and bottom deviate from the focal length of the grid: the density of the center line is high, and the density on both sides gradually eases and decreases.
Double Bias: The photo density is high on one side and low on the other.
Precautions for the use of wire grids:
①No inversion
② The center line is aligned with the center of the grid, and the left and right deviation does not exceed 3cm;
③ The inclined X-ray tube is parallel to the arrangement direction of the lead bars;
④Use within the permitted range.
Selection of filter grid: When the use requirement is high to eliminate scattered rays, select a grid with a large grid ratio; when X-rays are oblique, cross-type grids cannot be used.

X-ray grid

1. The commonly used grid ratio for high kV photography is 12:1.
2. When taking grid photography, it is necessary to appropriately increase the exposure conditions.
3. The filter grid should be placed between the human body and the film box, with the focusing surface facing the X-ray incident direction.
4. In the principle of use, the thickness of the subject should be more than 15cm and more than 60kv.
5. The vertical chest radiograph requires a grid focal length of 180cm and a grid ratio of 12:1 or 14:1.
6. The change of the focal length f of the grid during photography should not be greater than or less than 25% of the focal length.
7. For movable grids, the movement time of the grid should be at least 1/5 of the exposure time.
8. The photographing condition is 80kV, and the grid ratio is 8:1. (100kV is 10:1; 120kV is 12:1)
9. Mammography grids are commonly used 80LP/cm ultra-dense grids or high-pass porous grids (honeycombs).
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Author:X Ray Grids Maker

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