Chapter 8: Problem 29

Why are x rays more strongly absorbed by bones than by muscles and other tissues?

Short Answer

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Answer: Bones absorb X-rays more strongly than muscles and other tissues because they have a higher atomic number and density due to their calcium and phosphate content, which leads to greater X-ray absorption.

Step by step solution

Understanding X-ray absorption

X-rays are a type of electromagnetic radiation that can penetrate through various materials, including the human body. When X-rays pass through a material, they are absorbed at different rates by various substances, depending on their composition and density. The absorption of X-rays by a substance can be explained by two main phenomena: the photoelectric effect and Compton scattering.

The role of atomic number and density

The atomic number (Z) of an element represents the number of protons in the nucleus, and the energy of an X-ray photon is more likely to be transferred to heavier elements compared to lighter ones. Therefore, substances with higher atomic number absorb X-rays more strongly than those with lower atomic numbers. Additionally, materials with higher densities absorb X-rays more efficiently than less dense substances, as the more closely packed atoms lead to more interactions and absorption with the X-rays.

Atomic number and density of bones and muscles

The main component of bones is hydroxyapatite [Ca_10(PO_4)_6(OH)_2], a calcium phosphate mineral, which gives bones their rigidity and strength. Calcium has an atomic number of 20, and phosphate has an atomic number of 15 (phosphorus) and 8 (oxygen). In contrast, muscles and other soft tissues are primarily composed of water, proteins, and lipids, which have atomic numbers of 1 (hydrogen), 6 (carbon), 7 (nitrogen), and 8 (oxygen). Thus, the key elements in bones have higher atomic numbers than those found in soft tissues. Moreover, the mineralized matrix makes bones denser than muscles and other tissues.

Comparing X-ray absorption in bones and muscles

Due to the higher atomic number and density of bones (as a result of the calcium and phosphate content), they absorb X-rays more strongly than muscles and other soft tissues, which contain lighter elements such as hydrogen, carbon, nitrogen, and oxygen. This difference in absorption appears as different shades of gray on an X-ray image, with bones appearing much whiter and more opaque than soft tissues, which appear as varying shades of gray. In conclusion, X-rays are more strongly absorbed by bones than muscles and other tissues because bones have a higher atomic number and density due to their calcium and phosphate content, which leads to greater X-ray absorption.

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Why are x rays more strongly absorbed by bones than by muscles and other tissues?

Short Answer

Step by step solution

Understanding X-ray absorption

The role of atomic number and density

Atomic number and density of bones and muscles

Comparing X-ray absorption in bones and muscles

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