Why are aluminum and air preferred as interspace materials for grids?

Aluminum and air are preferred as interspace materials for grids primarily because they provide effective scattering management and structural support. Grids are used in radiography to reduce the amount of scattered radiation that reaches the image receptor, which can degrade image quality. Aluminum, being a lightweight and well-structured material, effectively separates the lead strips in a grid while allowing for the passage of primary radiation. The air space between the lead strips further enhances this effect, as it does not contribute to the scattering of radiation, allowing for clearer images by ensuring that only the direct, useful radiation is captured.

While factors like cost and availability are important considerations in material selection, the technical functionality in managing scatter and supporting the overall structure of the grid is paramount in imaging applications. Other options, such as ensuring complete absorption of radiation, are not accurate in this context since the goal is to allow primary radiation to pass through while minimizing scatter, rather than complete absorption. Similarly, while enhancing image contrast is a result of effective scatter management, it is not the direct role of the materials used in the grid construction.