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x-ray grids

Why have a grid?. Scatter radiation is inevitably produced when primary radiation passes through subjectWithout a grid radiographic fog is produced on the film which degrades the diagnostic quality. What is a Grid?. Acts as a filter to remove scatter radiation before it hit the film. Grid Structure.

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x-ray grids

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    1. X-ray Grids (Anti-Scatter Grid)

    3. What is a Grid? Acts as a filter to remove scatter radiation before it hit the film

    4. Grid Structure Composed of high x-ray transmitting material and high x-ray absorbing material, each aligned alternately and regularly Transmitting material example is aluminium strips Absorbing material example is lead strips

    5. Grid Ratio Height of lead strips compared to space between strips R = h/D Typically 5:1 to 12:1 Grid ratio is thickness of grid (simple explanation) The thicker the grid the less scatter reaches the film Generally a high x-ray output has higher grid ratio (thickness) Low output = lower ration (thinner) grid

    6. Grid Density Number of lead strips per cm Usually between 34 lines/cm and 100 lines/cm Higher grid density = increased no. of lead strips per cm Higher grid density = better image with less visible grid lines

    7. Focal Range Distance from tube to film (SID) Ideal to match grid to SID Lower ratio grids = wider focal range (typically 8:1 true focal range is 100cm but can be used 86-112cm) Higher ratio grids eg. 12:1, range 92-102cm Short, medium, long terms often used to describe focal range

    8. Focussed Grid Lead strips are tilted progressively as they move away from centre Grid focus where perfect alignment of primary beam with lead strips

    9. Parallel Grid Generally not made with grid ratio > 6.0 Lead strips parallel to each other Strips are never aligned with primary beam since all are vertical (except for strips directly under central ray Cut off on both sides of film whenever used

    10. Cross Grid (cross hatch) 2 grids on top of each other with lead strips of one perpendicular to other

    11. Grid Use Most common is focussed grid Read label to determine focussing distance Establish tube side Use high ratio if used as stationary grid to lessen obvious grid lines Ensure CR is perpendicular to grid to prevent grid cut off Any tube angulation is along lines of grid Increase mAs by 6 steps (4x) when compared to non grid technique

    12. Positioning Latitude

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