What is the relationship between spatial frequency and MTF?

• A. Direct
• B. No relationship
• C. Inverse
• D. Indirect

Answer: (D)

Spatial frequency tells you how fine the details in an image are, while MTF tells you how much of the image’s contrast is preserved at that level of detail. In radiography, the system can transfer broad, low-frequency features with good contrast, but as you try to reproduce finer, high-frequency details, the contrast transfer diminishes. So the relationship between spatial frequency and MTF is inverse (often described as indirect): higher spatial frequencies come with lower MTF values. This reflects the inevitable drop in the system’s ability to convey very fine details. A lack of relationship would ignore how contrast transfer changes with detail size, and a direct relationship would imply both increase together, which isn’t what happens.