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Ch18 The Grid

Principles of Radiographic Imagine- Carlton

The Grid Absorbs scatter, improves contrast
X-Ray Beam - as it passes through the body three things happen: Pass through unaffected or un-attenuated, Absorbed by the body photoelectric effect, interact and change direction (Comptons) - produces scatter (patient is source of scatter)
Effect of scatter on image contrast overall graying/fog, undercuts true image, DOES NOT produce image details, densities added in a negative sense
Scatter Contribution to patient dose and poor image quality major contributor, once produced, how can it be reduced to not degrade image quality? -GRIDS
Function of the grid IMPROVE CONTRAST
Function of the grid Higher kVp - grid efficiency goes DOWN
How does the grid work? Grid removes scatter by absorption (lead strips) improve contrast image, ideal all exit or remnant beam should pass through grid...
Exit X-Ray Beam Scattered photons- of no diagnostic value, add to overall density-graying effect (fog), decreases contrast = low contrast poor contrast resolution, the % of comptons increases
The amount of scatter radiation INCREASES when: Increase in patient thickness, Increase in field size, decrease in the atomic number of the tissue, such as soft tissue (electrons are most loosely bound)
Grid Use Thicker, larger body parts, procedures that require high kVp techniques, absorbs scatter radiation (cleans up image)
Grid Rules Thickness exceeds 10 cm, kVp exceeds 60 kvp
1913 Gustav Peter Bucky Original idea, crude design, thin lead strips
1920 Hollis Potter Lead strips running in one direction, thinner lead strips
Potter-Bucky Diaphragm Grid moves during exposure
Created by: lorperkins