Why might a radiograph exposed with a 12:1 ratio grid exhibit a loss of receptor exposure at its lateral edges?

A radiograph exposed with a 12:1 ratio grid may exhibit a loss of receptor exposure at its lateral edges primarily due to the grid's design and the positioning of the X-ray beam in relation to it. A grid is used to absorb scatter radiation and improve image contrast, but it is important that the X-ray beam is properly aligned with the grid to ensure even exposure.

In this case, if the source-to-image distance (SID) is too great, the intensity of the X-ray beam diminishes significantly due to the inverse square law, which states that the intensity of radiation is inversely proportional to the square of the distance from the source. As you move farther away from the X-ray tube, the amount of radiation hitting the receptor decreases. With a high ratio grid such as 12:1, which is more efficient at reducing scatter but also more sensitive to misalignment, the effect of the decreased intensity is more pronounced at the edges of the exposure, leading to a noticeable loss of receptor exposure.

In contrast, the other factors like the grid not moving during exposure, the X-ray tube being angled in the direction of the lead strips, or the CR (central ray) being off-center can all contribute to issues with image quality.