![]() ![]() The result is higher mAs and higher patient dose. ![]() On the other hand, use of aluminum as interspace material increases the absorption of primary x-rays in the interspace, especially at low kVp. Aluminum also has the advantage of producing less visible grid lines on the radiograph. ![]() What is the grid ratio when the lead strips are 3.2 mm high and separated by 0.2 mm?ġ9 Aluminum has a higher atomic number than plastic and therefore may provide some selective filtration of scattered x-rays not absorbed in the grid strip. The interspace material of most grids consists of aluminum or plastic fiber reports are conflicting as to which is better. The purpose of the interspace material is to maintain a precise separation between the delicate lead strips of the grid. High-ratio grids increase patient radiation dose. This is because the angle of scatter allowed by high-ratio grids is less than that permitted by low-ratio grids. High-ratio grids are more effective in cleaning up scatter radiation than are low-ratio grids. Such a grid is said to exhibit good “cleanup.”ġ6 High-ratio grids increase patient radiation dose. ![]() Laboratory measurements show that high-quality grids can attenuate 80% to 90% of the scatter radiation. If the angle is slight, the scattered x-ray will be transmitted similarly to a primary x-ray. The grid ratio is the height of the grid divided by the interspace widthġ3 If the angle of a scattered x-ray is great enough to cause it to intersect a lead grid strip, it will be absorbed. Scatter radiation is absorbed in the grid material.ġ2 Grid Ratio A grid consists of three important dimensions: the thickness of the grid strip (T), the width of the interspace material (D), and the height of the grid (h). Over the years, Bucky's grid has been improved by more precise manufacturing, but the basic principle has not changed.ĩ The grid is designed to transmit only those x-rays whose direction is on a straight line from the source to the image receptor. The grid is positioned between the patient and the image receptor.ħ This technique for reducing the amount of scatter radiation that reaches the image receptor was first demonstrated in 1913 by Gustave Bucky. An extremely effective device for reducing the level of scatter radiation that reaches the image receptor is the grid, a carefully fabricated series of sections of radiopaque material (grid strips) alternating with sections of radiolucent material (interspace material). C, Moderate contrast results from the use of both transmitted and scattered x-rays.ĥ Two types of devices reduce the amount of scatter radiation that reaches the image receptor: beam restrictors and grids.Ħ Grids Scattered x-rays that reach the image receptor are part of the image-forming process indeed, the x-rays that are scattered forward do contribute to the image. The loss of contrast results from the presence of scattered x-rays.Ĥ A, High contrast would result from the use of only transmitted, unattenuated x-rays.ī, No contrast would result from the use of only scattered x-rays. The radiographic contrast would be very low.ģ In the normal situation, however, x-rays arriving at the image receptor consist of both transmitted and scattered x-rays. If the radiograph were taken with only scatter radiation and no transmitted x-rays reached the image receptor, the image would be dull gray. 1 Radiographic Grids I By Professor StelmarkĢ Even under the most favorable conditions, most remnant x-rays are scattered. ![]()
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