Radiographic Grids Overview

Radiographic Grid

• Radiographic grids are designed to transmit only x-rays traveling in a straight line from the source to the image receptor.
• The grid is positioned between the patient and the image receptor.
• The grid is placed between the patient (behind the table or upright bucky) and the cassette.
• Improper placement, such as placing the grid backwards, can cause grid errors.
• Grids consist of a series of radiopaque material (interspace material).
• The use of grids helps reduce scatter radiation reaching the image receptor.
• This technique was first demonstrated in 1913 by Gustave Bucky.
• Grid ratio, a fundamental concept in understanding grid technology, is the height of the grid divided by the interspace width.
• For example, a 12:1 grid has a lead strip height of 12 inches and an interspace width of 1 inch.
• High ratio grids are more effective in reducing scatter radiation than low ratio grids, but increase patient dose.
• Contrast Improvement Factor is the ratio of radiographic contrast with a grid to that without a grid. It measures the improvement in image quality when grids are used.
• Bucky Factor is the ratio of patient dose with and without a grid. It measures the increase in exposure necessary to compensate for the use of a grid.

When to Use a Grid

• Use a grid when the kVp is above 60.
• Use a grid when the body part exceeds 10cm and the tissue density is primarily soft tissue and bone.

Grid Classifications

• Grids can be stationary or moving.

Grid Types

• Grids can be linear, parallel, focused, or crossed.

Parallel Grid

• Used in portable and OR radiography.
• Cleans up scatter radiation in only one direction.
• Has a "grid-cut off."

Focused Grid

• Designed to minimize grid cut-off.
• Used in moving grids.
• More superior than parallel grids.

Crossed Grid

• Consists of two linear grids superimposed, one above the other.
• Used in special procedures.
• More efficient in cleaning up scatter radiation.
• Has more grid cut-off.
• Not commonly used.

Moving Grid

• An obvious, annoying shortcoming of moving grids is that they can produce grid lines on the image.
• Moving grids were introduced in 1920 by Hollis E. Potter, by moving the grid while the x-ray exposure is being made.
• Moving grids are either reciprocating (back-and-forth) or oscillating (circular).

Grid Problems

• Off-level grid
• Off-center grid
• Off-focused grid
• Upside-down grid
• Combined off-center/off-focused

Air Gap Technique

• The image receptor (IR) is moved 10–15 cm away from the patient to reduce scatter radiation. A portion of scatter x-rays generated in the patient would be scattered away from the IR and not recorded.

This quiz covers the essential concepts of radiographic grids, including their design, function, and placement. Learn about the impact of grid ratio on image quality and scatter radiation. Test your understanding of grid technology and its historical development.