In the context of X-ray imaging, what does tissue density refer to?

Tissue density in X-ray imaging primarily refers to the difference in absorption of X-rays by various types of tissues within the body. This concept is crucial because different tissues interact differently with X-rays based on their composition and density. For instance, denser tissues, such as bone, absorb more X-rays and appear whiter on the X-ray images compared to less dense tissues, such as muscles or fat, which allow more X-rays to pass through and consequently appear darker.

This differential absorption is what enables radiologists to distinguish between various structures and to identify abnormalities. The ability to visualize these differences is fundamentally what makes X-ray imaging a valuable diagnostic tool in medicine. In this context, the material's atomic number, thickness, and types of tissues can influence absorption; however, the term "tissue density" specifically emphasizes the varying degrees of absorption which directly contribute to the contrast on X-ray images.