Varying tissue thicknesses and densities is referred to as

• A. Receptor contrast
• B. Subject contrast
• C. Image noise
• D. Quantum mottle

Answer: (B)

Subject contrast is the difference in X-ray attenuation produced by the patient’s own tissues. It depends on how thick and how dense the tissues are. When a beam passes through thicker or denser tissue (like bone), more photons are absorbed, so fewer reach the image receptor and that area appears lighter. Conversely, thinner or less dense tissues (like soft tissue or air) allow more photons through and appear darker. The net result is variations in image brightness that reflect the differing attenuation properties within the body. This is distinct from issues related to the imaging system’s response (receptor contrast) or random image noise (quantum mottle).