When the thickness of the subject in bone and joint photography exceeds anything, it is necessary to use the grid.

When the thickness of the subject in bone and joint photography exceeds 15cm, the grid is needed.

Data expansion:

Grating is a photographic term, which refers to a filter used to filter out the influence of scattered light on film. It should be placed between the human body and the film, which can filter out most of the scattered rays and only a small part of them will leak.

Convergent grid: each lead is inclined to the focus, that is, the extension lines of the leads are concentrated in the focus; Parallel grid: each lead bar is parallel to each other in the vertical plane; Cross grid: it is composed of two parallel grids, and the direction of lead bars is 90 degrees to each other; Circular grid: it is formed by overlapping from the center to the outside with equal radius and is tile-shaped.

The internal spacers of ordinary grids are made of nonmetallic materials, such as sawdust, paper, plastic and other nonmetallic low-density materials. The internal partition of all-metal grille is made of metal material: aluminum plate. It has high strength and good moisture resistance;

The grid plate is a flat plate with a thickness of 4 ~ 8 mm, and its internal structure is composed of many thin lead bars. The two lead tapes are filled and positioned with X-ray-transparent substances, and are combined together.

The filler can be wood, paper or aluminum sheet. Finally, the upper and lower parts are encapsulated with a thin aluminum plate to form a grid plate. From the cross section, the arrangement direction of the lead bars of the filter plate will converge to one point. Seen from the whole grid, there is a convergence line.

Exposure coefficient B It is generally considered that the exposure coefficient of a grid is one of the criteria for measuring a grid. The exposure coefficient b is the ratio of the exposure amount required to obtain the same density value without using the grid and after using the grid. The value of b is generally between 2 and 6, and the smaller the grid value with the same performance, the better.