What is the method for measuring primary transmission with a grid?

The primary transmission of a grid is assessed by comparing the exposure values recorded with and without the grid in place. The correct approach involves taking the exposure with the grid and dividing it by the exposure without the grid. This calculation enables the evaluation of how much radiation actually passes through the grid relative to the total amount of radiation initially directed towards the grid.

This method emphasizes the grid's effectiveness in reducing scattered radiation, which often degrades image quality in fluoroscopic procedures. By defining transmission in this way, one can quantify how well the grid allows useful primary radiation to contribute to the image while minimizing the effect of scatter.

In contrast, using the other formulations would not correctly represent the relationship between grid effectiveness and exposure values, as they inaccurately position the exposure data in the equation or change the focus of the measurement from the intended primary transmission concept. Thus, understanding the relationship and proper calculation ensures accurate assessment of the grid's performance in fluoroscopic applications.