Which term describes the signal differences in the remnant beam?

• A. Differential attenuation
• B. Quantization
• C. Contrast resolution
• D. Bit depth

Answer: (A)

Signal differences in the remnant beam come from differential attenuation: as X-rays pass through the body, tissues absorb photons to varying extents based on density, thickness, and atomic number. Denser or thicker areas absorb more photons, so fewer reach the detector and those regions appear darker; less dense areas transmit more photons and appear lighter. This variation in transmitted intensity creates image contrast and is what the term describes. Quantization and bit depth relate to how that signal is digitally recorded and displayed, affecting gray levels and noise but not the fundamental physical process that generates the remnant-beam differences. Contrast resolution is about how well small gray differences can be distinguished, which depends on noise and bit depth, not the basic attenuation differences themselves.