What imaging metric is determined principally by pixel size?

• A. Spatial resolution
• B. Contrast resolution
• C. Detective Quantum Efficiency
• D. Attenuation

Answer: (A)

Pixel size sets how finely the image is sampled. Spatial resolution is about how small details can be distinguished, and it is determined mainly by how large each pixel is—the smaller the pixels, the more tightly the image is sampled and the sharper the detail you can resolve. When pixels are large, every patch of the image is averaged over a bigger area, which blurs fine features and lowers resolution. Using smaller pixels increases the sampling frequency and pushes the system closer to the limit dictated by the detector and optics, such as focal spot size and geometry.

Contrast resolution, by contrast, concerns the ability to differentiate different gray levels, which depends on dynamic range, noise, and bit depth, not pixel size. Detective Quantum Efficiency refers to how effectively the detector converts incoming photons into a usable signal, a property of the detector tech rather than how finely the image is sampled. Attenuation is the physical reduction of beam intensity by tissues, again not a sampling metric.