What is the relationship between spatial frequency and the Modulation Transfer Function (MTF)?

The relationship between spatial frequency and the Modulation Transfer Function (MTF) is indeed an indirect one. In digital radiography, spatial frequency refers to the detail present in an image, typically defined as the number of line pairs per millimeter. The MTF measures how effectively a system can reproduce various spatial frequencies in an image.

As the spatial frequency increases, the ability of the imaging system to accurately reproduce those high frequencies often decreases, resulting in reduced contrast for small features. In this sense, while an imaging system may perform well at low spatial frequencies (representing larger structures), its performance at higher spatial frequencies is typically poorer, leading to a decrease in modulation transfer.

Thus, the indirect relationship indicates that as spatial frequency increases, the MTF generally decreases, which reflects the system's limitations in capturing fine detail. Understanding this relationship is crucial for optimizing imaging systems in radiography, ensuring that they retain adequate resolution for the required diagnostic tasks.