What is the equation for calculating the S-value?

The S-value is a representation of the "Dose Area Product" (DAP) or the exposure delivered to a certain area during a fluoroscopic procedure. In this context, it is used to evaluate patient exposure to radiation based on the amount of radiation measured in milliroentgens (mR). The correct formulation for calculating the S-value is to take a constant (200) and divide it by the measured radiation exposure (mR). This equation helps in determining the efficiency of the fluoroscopic system in terms of radiation output relative to the exposure received.

This formula indicates that as the measured radiation in milliroentgens increases, the S-value decreases, suggesting better radiation efficiency and possibly lesser exposure risk for the patient. By employing this equation, radiologic professionals can ensure they are optimizing their techniques to minimize patient exposure while still achieving the necessary diagnostic results.