What is the grid factor?

• A. The number by which mAs must be multiplied if a grid is used (depends on grid ratio and lines/cm)
• B. The exposure time required for grid use
• C. The physical weight of the grid
• D. The color of lead in the grid

Answer: (A)

The grid factor is the multiplier used to compensate for the attenuation of the primary x-ray beam by a radiographic grid. When a grid is used, lead strips absorb part of the beam, so you must increase the exposure to keep the same image receptor exposure. The grid factor is defined as the exposure required with the grid divided by the exposure required without the grid, and it depends on grid ratio and how densely the lines per centimeter are spaced. A higher grid ratio or more lines per centimeter means more attenuation and a larger grid factor. For example, if you needed 8 mAs without a grid and 32 mAs with the grid for the same receptor exposure, the grid factor would be 4. The other options describe things that don’t define grid factor—exposure time alone, weight, or color of the grid.