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: X-rays are more strongly absorbed by bones than by muscles and other tissues because bones have a higher density and higher effective atomic number (due to the presence of calcium and phosphorus) than soft tissues. This leads to a higher probability of photoelectric absorption in bones, resulting in the distinctive contrast between bones and soft tissues seen in x-ray imaging.

Step by step solution

Understand the properties of x-rays

X-rays are a form of electromagnetic radiation with a wavelength range of 0.01 to 10 nanometers, which corresponds to a high-energy photon. They can penetrate various materials and be absorbed or scattered by them, depending on their atomic structure and density.

Understand the composition and properties of bones

Bones are primarily made up of a mineral called hydroxyapatite (Ca10(PO4)6(OH)2), which contains elements such as calcium, phosphorus, and oxygen. Additionally, bones also contain carbon, nitrogen, and hydrogen from proteins (collagen) that provide structural support. The high concentration of calcium and phosphorus in bones leads to their relatively high density.

Understand the composition and properties of muscles and other tissues

Muscles and other soft tissues, such as fat and skin, primarily consist of water, proteins, lipids, and carbohydrates. These tissues contain mainly lighter elements, such as hydrogen, carbon, nitrogen, and oxygen, and have a lower density compared to bones.

Explain the interaction between x-rays and matter

When x-rays pass through matter, they can undergo three types of interactions: photoelectric absorption, Compton scattering, and coherent scattering. The probability of photoelectric absorption, which results in the complete absorption of the x-ray photon, is highly dependent on the atomic number (Z) of the absorbing material. The higher the atomic number, the higher the probability of photoelectric absorption. Soft tissues have a lower probability of photoelectric absorption than bones due to their lower effective atomic numbers.

Compare the absorption of x-rays by bones and soft tissues

As bones have a higher density and higher effective atomic number (due to the presence of calcium and phosphorus) than soft tissues, they are more likely to absorb x-ray photons through the photoelectric effect. This causes x-rays to be more strongly absorbed by bones than by muscles and other tissues, resulting in the distinctive contrast between bones and soft tissues seen in x-ray imaging.

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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

Understand the properties of x-rays

Understand the composition and properties of bones

Understand the composition and properties of muscles and other tissues

Explain the interaction between x-rays and matter

Compare the absorption of x-rays by bones and soft tissues

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