![]() ![]() Ideally, a grid should have 100% primary beam transmission while blocking all the scatter radiation. Primary transmission is the percentage of primary radiation transmitted through the grid. Low frequency is 40 to 50 strips per cm, medium frequency is 50 to 60 strips per cm, and greater than 60 strips per cm is high frequency 7. This is typically 30-80 strips (or grid lines) per cm. The strip line density (also known as grid frequency) (number of strips per cm) is 1/(D+d), where d is the thickness of the strip. Higher grid ratios are more effective at reducing scatter, however are more expensive and require a higher dose. mammography), 8:1 is used for 70-90 kVp technique and 12:1 is used for >90 kVp technique. A grid ratio of 5:1 is generally used for 20-40kVp (i.e. The working ability of a grid is described by the grid ratio, which is the ratio of the height of the lead strips (h) to the distance between two strips, i.e. the interspace (D) 7. As scattered radiation is increased in "thicker" patients and at larger field sizes, grids are useful in such scenarios to improve image contrast. The strips can be oriented either linear or crossed in their longitudinal axis. ![]() They are made of parallel strips of high attenuating material such as lead with an interspace filled with low attenuating material such as carbon fiber or organic spacer 7. Grids are placed between the patient and the x-ray film to reduce the scattered radiation reaching the detector (produced mainly by the Compton effect) and thus improve image contrast.
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