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Questions and Answers
What percentage of incident radiation is stopped by 2 mm of Aluminium at 60 kV?
What percentage of incident radiation is stopped by 2 mm of Aluminium at 60 kV?
The H½ value for lead in the diagnostic range is greater than 0.1 mm.
The H½ value for lead in the diagnostic range is greater than 0.1 mm.
False
What is the term used for the thickness of a substance that transmits exactly one-half of the incident radiation intensity?
What is the term used for the thickness of a substance that transmits exactly one-half of the incident radiation intensity?
Half value thickness (H½)
At diagnostic energies, the HVT for water is approximately ______ mm.
At diagnostic energies, the HVT for water is approximately ______ mm.
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Match the following materials with their use in radiography:
Match the following materials with their use in radiography:
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What is the primary cause of attenuation in an X-ray beam?
What is the primary cause of attenuation in an X-ray beam?
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Higher atomic number tissues cause less absorption of X-ray photons.
Higher atomic number tissues cause less absorption of X-ray photons.
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What is remnant radiation?
What is remnant radiation?
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The decrease in intensity of an X-ray beam is known as __________.
The decrease in intensity of an X-ray beam is known as __________.
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Which factor does NOT affect the attenuation of an X-ray beam?
Which factor does NOT affect the attenuation of an X-ray beam?
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Match the types of interactions with their definitions:
Match the types of interactions with their definitions:
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Attenuation only occurs via absorption.
Attenuation only occurs via absorption.
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What is one method to adjust the quality of an X-ray beam in diagnostic radiography?
What is one method to adjust the quality of an X-ray beam in diagnostic radiography?
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What happens to the film exposure when bone is present in a radiograph?
What happens to the film exposure when bone is present in a radiograph?
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Air appears white on a radiograph due to its high radiopacity.
Air appears white on a radiograph due to its high radiopacity.
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What significantly affects the radiopacity of tissues?
What significantly affects the radiopacity of tissues?
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The thicker the tissue, the greater the ______ of X-Rays, leading to a whiter image.
The thicker the tissue, the greater the ______ of X-Rays, leading to a whiter image.
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Match the following materials with their appearance on a radiograph:
Match the following materials with their appearance on a radiograph:
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Which of the following is true about the absorption of radiation?
Which of the following is true about the absorption of radiation?
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Specific gravity refers to relative density with respect to air.
Specific gravity refers to relative density with respect to air.
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What is the result of two overlapping tissues in a radiograph?
What is the result of two overlapping tissues in a radiograph?
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______ is emitted as a result of bombardment of a tungsten anode by free electrons.
______ is emitted as a result of bombardment of a tungsten anode by free electrons.
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The attenuation of radiation follows a linear pattern.
The attenuation of radiation follows a linear pattern.
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What does the total linear attenuation coefficient (µ) represent?
What does the total linear attenuation coefficient (µ) represent?
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High atomic number materials have a higher number of electrons, which results in a greater probability of x-ray interaction.
High atomic number materials have a higher number of electrons, which results in a greater probability of x-ray interaction.
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What happens to the transmitted intensity when the thickness of the material increases?
What happens to the transmitted intensity when the thickness of the material increases?
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The relationship between incident and transmitted intensity is __________.
The relationship between incident and transmitted intensity is __________.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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What factors influence the interactions per unit distance of x-ray photons in a medium?
What factors influence the interactions per unit distance of x-ray photons in a medium?
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The linear attenuation coefficient is the same for all materials, regardless of energy.
The linear attenuation coefficient is the same for all materials, regardless of energy.
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What is the transmitted intensity if the incident intensity is 100 units and the total linear attenuation coefficient is 0.2 for a thickness of 5 cm?
What is the transmitted intensity if the incident intensity is 100 units and the total linear attenuation coefficient is 0.2 for a thickness of 5 cm?
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The __________ is characteristic of a particular material and varies depending on radiation energy.
The __________ is characteristic of a particular material and varies depending on radiation energy.
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What is the effect of a less dense medium on x-ray attenuation compared to a denser medium with the same atomic number?
What is the effect of a less dense medium on x-ray attenuation compared to a denser medium with the same atomic number?
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Study Notes
Attenuation of the X-ray Beam
- Attenuation is the decrease in intensity of an X-ray beam as it passes through a material or tissue.
- Attenuation occurs due to interactions between X-ray photons and the atomic structures of the tissue.
- These interactions can cause absorption (photoelectric effect) or scattering (Compton scatter) of the X-ray photons.
- Attenuation is a key factor in diagnostic imaging.
- Penetration is equivalent to transmission.
- The greater the attenuation, the more the beam is weakened.
Objectives
- Understanding the concept of attenuation.
- Identifying factors that affect attenuation.
- Recognizing the importance of attenuation.
Attenuation
- A decrease in X-ray beam intensity as it passes through matter.
- The process is a result of interactions between X-ray photons and the atoms of the medium.
- Interactions may result in scattering (photon deflection) or absorption (photon energy transfer to the atom).
- Attenuation reduces the beam's intensity, causing the beam to become weaker.
Interactions
- X-ray photons can interact with atoms in a medium, causing them to be deflected (scattering) or lose all their energy (absorption).
- Scattered photons may still pass through the material but with altered direction.
- Absorbed photons transfer all their energy to the atom, decreasing the beam intensity.
Attenuation Experiment
- X-ray photons interact with the atoms of the medium, resulting in scattering and absorption.
- Decrease in the intensity of radiation after interaction, with the medium.
- It involves both absorption and scattering.
Attenuation Experiment (Diagram)
- A diagram shows the interaction of photons (A, B, C) with an object.
- Photon A = scattering
- Photon B = absorption
- Photon C = transmission
Attenuation Experiment (Data)
- Measurements of intensity (I₁) and (I₂) are made (I₀=original intensity).
Attenuation
- The attenuated beam that passes through a patient/object is called the remnant radiation.
- Factors such as beam quality/energy, thickness, density and atomic number are associated with the amount of attenuation.
Factors Affecting Attenuation
- Thickness: Increasing thickness increases attenuation.
- Atomic number (Z): Higher Z tissues attenuate more (e.g., bone attenuates more than soft tissue).
- Tissue density: Higher density tissues attenuate more.
- Beam Quality/Energy: Higher energy beams attenuate less.
- In image formation, the reduction of intensities due to absorption and scattering, allows for differentiation of tissues structurally and hence image formation.
Atomic Number, Relative Density, Thickness of Tissue
- Radiopacity depends on atomic number (higher is more radiopaque).
- Air, fluid, and soft tissue have similar atomic numbers, but different specific gravities.
- Thickness also affects attenuation, with thicker tissue attenuating more.
- Radiographs show tissues with different radiopacities.
Linear Attenuation Coefficients
- Explains how X-rays are attenuated in a material.
- Coefficients vary based on material, thickness and energy of the incident radiation.
Exponential Curve
- The relationship between the incident and transmitted intensity is exponential.
- A graph (exponential curve) displays this exponential relationship.
Half-Value Thickness (HVT)
- The HVT is the thickness of a material required to reduce the intensity of a beam of radiation to half its original value.
- HVT is used to measure the absorption of radiation.
- In diagnostic and therapeutic radiology, different materials are used to measure HVT values.
Summary
- Attenuation is the reduction in X-ray intensity due to interactions with the medium.
- The attenuation of X-rays by different substances at a given energy affects the intensity of the transmitted X-rays, which results in an X-ray image.
- The process of attenuation (reduced intensity) and transmission (transmission intensity) form the basis of X-ray image generation.
- Factors affecting attenuation include thickness, atomic number, tissue density, and beam quality.
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Description
Test your understanding of X-ray beam attenuation in diagnostic imaging. This quiz covers key concepts such as how X-ray photons interact with different materials, leading to absorption and scattering. Learn about the factors affecting attenuation and its significance in imaging processes.
