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Questions and Answers
What effect primarily contributes to image contrast in a radiograph?
What effect primarily contributes to image contrast in a radiograph?
Which of the following describes the primary mechanism of indirect ionization of DNA?
Which of the following describes the primary mechanism of indirect ionization of DNA?
Which interaction occurs when an X-ray ejects an electron from an outer shell electron?
Which interaction occurs when an X-ray ejects an electron from an outer shell electron?
What are deterministic effects of radiation exposure characterized by?
What are deterministic effects of radiation exposure characterized by?
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What happens when a cell's DNA is damaged but not repaired and apoptosis does not occur?
What happens when a cell's DNA is damaged but not repaired and apoptosis does not occur?
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Which statement accurately describes Compton scatter?
Which statement accurately describes Compton scatter?
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What type of radiation effect is considered to have no safe dose?
What type of radiation effect is considered to have no safe dose?
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Which factor influences the likelihood and severity of deterministic effects after radiation exposure?
Which factor influences the likelihood and severity of deterministic effects after radiation exposure?
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Study Notes
X-ray Interactions
- Two types of interactions occur at the atomic level: photoelectric effect and Compton scattering
- Photoelectric effect: Occurs when X-ray interacts with an inner electron shell. The X-ray is fully absorbed, and an electron is ejected. Atoms with more electron shells absorb X-rays better and contribute to contrast in the radiograph. The atom becomes ionized.
- Compton scattering: Occurs when X-ray interacts with an outer electron shell. The electron is ejected but not all the X-ray energy is used; some energy is redirected. This leads to less contrast in the image and more image noise. Atoms are still ionized contributing to dose.
Molecular Level
- X-rays can damage DNA via two mechanisms:
- Direct ionization (rare): Direct interaction between X-rays and DNA molecules, creating ions that can disrupt chemical structure and lead to mutations or DNA strand breaks
- Indirect ionization (majority): Water molecules are ionised, resulting in instability and free radicals. These free radicals then damage DNA.
Cellular Level
- If DNA is damaged:
- Repair: The DNA repair mechanism may fail to fix the damaged DNA, leading to apoptosis(programmed cell death).
- Mutation: If apoptosis doesn't occur, but DNA isn't repaired, mutations can occur.
Tissue Level
- Deterministic Effects: Radiation burns (reddening, hair loss, cataracts) occur 100% above a certain threshold dose. The severity of these effects depends on the dose
- Stochastic Effects: Radiation-induced cancer is a chance effect that can occur with any dose, depending on the probability. The effect's probability is very low at low dose levels. It is not dependent on dose level.
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