Motion affects MTF curves in digital radiography. Which statement best describes its effect and detection method?

• A. Motion improves high-frequency MTF, reducing blur
• B. Motion has no effect on MTF
• C. Motion degrades low-frequency MTF, not high frequency
• D. Motion degrades high-frequency MTF, leading to image blur

Answer: (D)

Motion causes the image to blur by smearing the signal along the direction of movement. In digital radiography, the MTF describes how well the system preserves contrast at different spatial frequencies, and it is tied to the point spread function. When motion broadens the PSF, the high-frequency components—those that carry fine detail—are damped more than the low-frequency ones, so the MTF drops more steeply at higher spatial frequencies. The result is blur and a loss of sharpness, especially in fine structures.

To detect this effect, measure the MTF using a sharp-edge or line-pair phantom. Motion broadens the edge spread function and the line-spread function, and the resulting MTF curve shows a reduced high-frequency response. In short, motion degrades high-frequency MTF, leading to image blur, and you confirm it through MTF analysis or by observing reduced ability to resolve fine details.