Spatial resolution in radiography depends on how accurately the imaging system preserves the spatial location of detected X-ray photons. Several physical factors influence this.

One important factor is the detector pixel size. Digital radiography images are composed of a grid of pixels, and each pixel records the signal from photons detected in a small area of the detector. Smaller pixels allow finer sampling of the image and therefore improve spatial resolution.

Another important factor is the focal spot size of the X-ray tube. X-rays originate from a small region on the anode called the focal spot. If the focal spot is large, photons originate from slightly different positions, producing geometric blur at the detector. Smaller focal spots therefore improve spatial resolution.

Spatial resolution can also be affected by processes within the detector itself. In indirect detectors, visible light produced in the scintillator may spread laterally before reaching the photodiodes, slightly blurring the signal. Structured scintillators such as cesium iodide help reduce this effect by guiding light toward the detector elements.

Motion of the patient or anatomical structures during the exposure can also reduce spatial resolution by producing motion blur.

The ability of an imaging system to reproduce different spatial frequencies is often described by the modulation transfer function (MTF), which quantifies how well image contrast is preserved at different levels of detail.