grid (redirected from movable grid)

grid (grid)

1. a grating; in radiology, a device consisting of a series of narrow lead strips closely spaced on their edges and separated by spacers of low density material; used to reduce the amount of scattered radiation reaching the x-ray film.

2. a chart with horizontal and perpendicular lines for plotting curves.

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baby grid  a direct-reading chart on infant growth.

Potter-Bucky grid  a grid used in radiography; it prevents scattered radiation from reaching the film, thereby securing better contrast and definition, and moves during exposure so that no lines appear in the radiograph.

Wetzel grid  a direct-reading chart for evaluating physical fitness in terms of body build, developmental level, and basal metabolism.

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grid

Etymology: ME, gredire, grate

a device used during a radiographic examination to absorb radiation that is not heading along a straight line from the x-ray source to the film. Such scattered radiation does not contribute useful information and thus constitutes a source of unwanted density. A linear grid consists of alternating parallel strips of radiopaque and radiolucent material. Linear grids may cause variations in image density because of primary-photon attenuation. Density is at a maximum in the center of the film and decreases toward the edges.

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grid,

n a device used to prevent as much scattered radiation as possible from reaching a radiographic film during the making of a radiograph. It consists essentially of a series of narrow lead strips closely spaced on their edges and separated by spacers of low-density material.

grid, crossed,

n an arrangement of two parallel grids rotated in position at right angles to each other. See also grid, parallel.

grid, focused,

n a grid in which the lead foils are placed at an angle so that they all point toward a focus at a specified distance.

grid, moving,

n a grid that is moved continuously or oscillated throughout the making of a radiograph.

grid, parallel,

n a grid in which the lead strips are oriented parallel to each other.

grid, Potter-Bucky,

n.pr a grid using the principle of the moving grid, with an oscillating movement.

grid, stationary,

n a nonoscillating or nonmoving grid; the image of its strips will be visible on the radiograph for which it is used.

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grid

1. a grating; in radiology, a device consisting essentially of a series of narrow lead strips closely spaced on their edges and separated by spacers of low density material; used to reduce the amount of scattered radiation reaching the x-ray film.

2. a chart with horizontal and perpendicular lines for plotting curves.

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grid cassette

a radiographic cassette with a grid permanently installed in it.

grid cutoff

excessive loss of radiation beam because of incorrect angulation between the tube and the lead strips.

grid diaphragm

a grid interposed between the film and the x-ray beam. See also (1) above.

grid factor

because of the filtering out of rays by the lead strips there is a loss of penetrating effect of the beam so that exposure time must be increased.

focused grid

the lead strips in the grid are sloped slightly inwards at the top so that the apertures more closely approximate the angle taken by the rays in a diverging beam.

linear grid

a cassette grid in which the radiopaque strips are parallel to each other.

grid map

a map marked by a grid of numbered intersecting parallel lines making it possible to identify particular locations numerically.

movable grid

one that moves during the exposure of the film to the x-ray beam: a Potter-Bucky grid.

nonfocused grid

see parallel grid (below).

parallel grid

the lead strips in the grid are parallel to each other and vertical to the plane of the film. This has the disadvantage that more diverging rays are absorbed by the grid at the edges of the film than at the center with a lowering of exposure there.

Potter-Bucky grid

a focused grid moved mechanically across the x-ray beam. Suited only to large installations. Called also Bucky and Potter-Bucky diaphragm.

pseudo-focused grid

something of the same effect as a focused grid is obtained by gradually lowering the height of the strips in the grid as they approach the edge of the grid.

grid ratio

the ratio between the height of the strips to the distance separating them. The greater the ratio the more rays will be filtered out.

reciprocating grid

one that moves during the exposure of the subject to the beam of radiation.

rotating grid

one that moves while x-rays are being generated.

stationary grid

one that is stationary while the film is being exposed so that there is a pattern of grid lines on the radiograph.

grid tube

a special tube designed to take cineradiographic x-rays.

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GRID

Gay-related immune deficiency An acronym used early in the AIDS epidemic, as the first cases affected homosexual/gay ♂. See AIDS.