What factors influence spatial resolution in DR, and how is pixel pitch related to the Nyquist frequency?

• A. Spatial resolution is fixed; Nyquist frequency irrelevant.
• B. Only detector material affects spatial resolution; Nyquist frequency equals sampling rate.
• C. Pixel pitch has no relation to Nyquist frequency.
• D. Spatial resolution influenced by detector sampling (pixel pitch) and system optics; Nyquist frequency is half the sampling rate; smaller pixel pitch enables higher potential resolution.

Answer: (D)

Spatial resolution in digital radiography comes from two main influences: how finely the image is sampled by the detector and how sharp the whole imaging chain is optically. The detector samples the scene with pixels spaced by the pixel pitch, so a smaller pitch means a higher sampling rate. The Nyquist frequency is half of that sampling rate, and it marks the highest spatial frequency you can faithfully represent without aliasing. So, reducing pixel pitch raises the Nyquist limit and, in principle, allows finer detail to be recorded, assuming the optics and detector can preserve those frequencies.

But resolution isn’t governed by sampling alone. Geometric unsharpness from the focal spot size and other optical factors in the imaging chain blur high-frequency details, reducing the actual achievable resolution even if the pixel pitch is small. That’s why both detector sampling and system optics shape the final image sharpness.

In short, spatial resolution is determined by detector sampling (pixel pitch) and system optics; the Nyquist frequency is half the sampling rate and sets the maximum resolvable frequency, with smaller pixel pitch enabling a higher potential resolution, provided the optics and detector performance support it.