Grid ratio is defined as:

• A. The ratio of the lead strips to the space between them
• B. The thickness of the lead strips divided by the thickness of the aluminum interspaces
• C. The ratio of the height of the lead strips over the distance between the lead strips
• D. The ratio of the distance between the lead strips over the height of the lead strips

Answer: (C)

Grid ratio describes how tall the lead strips are relative to the width of the spaces between them. It is defined as the height of the lead strips divided by the distance between the strips (h over d, with the interspace typically filled by a material like aluminum). This ratio is a key factor in scatter control and image contrast: increasing the height of the strips or decreasing the space between them improves the grid’s ability to absorb scattered photons, but it also reduces the amount of primary radiation that reaches the image receptor, requiring a higher exposure and increasing sensitivity to misalignment. In practice, grids often have ratios like 5:1, 6:1, 8:1, or 12:1, with higher values offering better scatter cleanup at the cost of dose and alignment sensitivity.