What is the relationship between the fill factor and spatial resolution?

• A. Inversely proportional
• B. Inversely proportional to the square
• C. Directly proportional
• D. Directly proportional to the square

Answer: (D)

Fill factor is the fraction of a detector pixel that is sensitive to x-ray signal. When this fraction is larger, more of the incident energy is collected by the same pixel and there’s less dead space and less spreading of signal between neighboring pixels. That reduces blur between pixels and preserves finer details, so the image can resolve smaller features. In other words, as fill factor increases, spatial resolution tends to improve in a direct, straightforward way—though it can never exceed the limit set by the pixel size and other design factors. It’s not an inverse relationship, and it isn’t tied to the square of the fill factor; the improvement grows with fill factor toward a maximum set by the detector’s pitch and overall construction.