Pay attention to when installing and replacing the grid

The grid is divided into the focal plane and the back focal plane, and the focal plane is the side facing the focal point of the X-ray tube, which is also called the “incident plane”. The X-ray tube is marked or noted on the focal plane, and the centerline of the grid is marked. When using, the focal plane must face the X-ray tube.
At the same time, technical parameters such as the focal length, grid ratio and grid density of the grid must be marked on the upper right corner of the panel to indicate its internal performance.
The following two aspects must be paid attention to when using the grid.
1. Tube voltage compensation
Because the main component material of the grid is lead foil, it not only blocks the scattered rays, but also inevitably blocks a part of the original emission line, which reduces the sensitivity of the film to a certain extent, so the grid is not used in photography. It is necessary to appropriately increase the exposure conditions, that is, increase the tube voltage to increase the penetration ability of X-rays to achieve the purpose of compensation. Specific compensation data should be obtained in conjunction with clinical use.
In general, low-grid-ratio grids are suitable for low-kV tube voltages; high-grid-ratio grids are suitable for high-kV tube voltages.
2. The effect of focus deviation and focal length mismatch
The lead strips of the convergence grid are all aligned to the focus, and the convergence line should be in focus with the X-ray tube during photography.
The points coincide so that the original emission line is parallel to the lead bar and can pass through smoothly, while the scattered line
The direction is random, rarely consistent with the direction of the lead strip, so most of it is absorbed by the lead strip
, The image clarity obtained is better. If the focus of the X-ray tube is deviated from the convergence line of the grid
Or the grid is not placed on the specified focal length, it will inevitably produce the original emission line loss, and its
The percentage of loss is proportional to the amount of deviation and the size of the focal length difference, and at the same time with the filter
The grid ratio of the wire grid has a direct multiple relationship. So the grid should be placed as much as possible
Location. But in actual clinical use, some deviations are inevitable, so the filter
There is a rule for the deviation of the wire grid.

Author：Lillian