Grid filter

Lattice screening (synonym: hood, Bucky, blend Potter - Bucky tray is currently not used)-a device designed to enhance the contrast x-ray image by absorbing scattered body x-ray radiation.
Screening grille consists of a body mounted on the inside of him, screen transfer mechanism raster, control systems and alarm systems (Fig. 1). A raster is a set of thin (0.02 to 0.3 mm) narrow lead plates separated by layers of wood or cardboard, and currently, plastic or aluminium.


Fig. 1. Flat mobile screening grill: 1-the call; 2 - the platoon commander handle; 3 - kasutatavatele.

Fig. 2. Radiography with screening bars: 1 - x-ray film; 2 - raster grid; 3 - researched object.

In directed raster plate-oriented focus x-ray tube; therefore the main part of the direct x-ray radiation passes between the plates. A large part of the scattered radiation is not the same as in the direction of the direct beam and is absorbed lead plates of the image (Fig. 2)If this decreases the veil due to the scattered radiation and increases contrast images. Rasters in which the plates are parallel, called flat, but it is most common screening lattice with directional rasters for certain focal lengths (from 90 to 150 cm). If the raster is not on the passport distance, there has been a sharp decrease in the intensity at the edges of the field. The most important characteristic of screening lattice is its ratio (the ratio of the width of the gap between the plates to their height). With the decrease of the ratio decreases the intensity transmitted through screening lattice total (primary and secondary) radiation that can be compensated by increasing the shutter speed or voltage generation.
At voltage up to 100 kV is used to screen lattice with a ratio of 1:6, which is slightly absorbs the primary radiation and keeps out 70-80% secondary, at high voltages are applied to the screening lattice with a ratio of 1:12 and smaller. There are stationary screening lattice (lattice Lysholm) and mobile. Screening grille Lysholm has a flat raster with very thin (0,02-0,03 mm) lead plates and narrow (0.2-0.3 mm) in between. Such screening grating is placed on cassette (or tape) and allows you to study at any position of the patient. It leaves on the radiograph subtle touches that do not interfere with the perception of the x-ray image. Its weaknesses include the lack of orientation, strong primary radiation absorption and permeability of thin plates for the scattered radiation. In the photo with a mobile screening lattice image lead plates eroded and does not interfere with x-rays. A raster is driven by means of a spring or motor. To avoid stripped shadows from the plates, the movement raster should be a little more exposure. However, short exposures shadow arise in uniform motion raster due to the so-called stroboscopic effect. To fight it used uneven, decelerating by a law movement raster or apply vibratory screening lattice. For a very short extracts use of screening lattice with a large number of plates per centimeter length of the raster. Minimum shutter speed for raster indicated in the passport (for domestic screening gratings - 0,04 seconds). Modern screening grilles are supplied with several removable rasters designed for specific voltage and shutter speed.