Which of the following factors is NOT related to grid efficiency?

Grid efficiency refers to how well a grid can absorb scatter radiation while allowing primary radiation to pass through. This concept is vital in radiography, where maximizing image quality is dependent on reducing scatter and improving contrast.

Grid ratio, which is the height of the lead strips to the distance between them, is a significant factor because a higher grid ratio typically leads to enhanced absorption of scatter radiation, thus improving the grid's efficiency. The number of lead strips per inch also contributes to grid efficiency; a greater number of lead strips can enhance the grid's ability to filter out scatter by providing more barriers to it.

The amount of scatter transmitted through the grid is core to understanding grid efficiency, as this directly impacts the quality of the image. Less scatter transmitted means better contrast and image clarity, which shows the effectiveness of the grid.

In contrast, focal spot size does not have a direct relationship with grid efficiency. While focal spot size affects spatial resolution and the sharpness of the image, it is not a factor that influences how well a grid can manage scatter radiation. Therefore, it stands apart from considerations specifically related to the efficiency of grids.