Podcast
Questions and Answers
Which of the following increases attenuation? (Select all that apply)
Which of the following increases attenuation? (Select all that apply)
- Decreasing the thickness of the material
- Increasing the energy of photons
- Increasing the density of the material (correct)
- Decreasing the atomic number of the material
Lead attenuates less than tissue.
Lead attenuates less than tissue.
False (B)
What are the two coefficients that characterize the attenuation of a material?
What are the two coefficients that characterize the attenuation of a material?
linear attenuation coefficient and mass attenuation coefficient
Attenuation is caused by _____ and scattering.
Attenuation is caused by _____ and scattering.
Match the interaction mechanisms with their relevance to diagnostic imaging:
Match the interaction mechanisms with their relevance to diagnostic imaging:
What is the process called when a high energy photon interacts with a nucleus to create an electron and a positron?
What is the process called when a high energy photon interacts with a nucleus to create an electron and a positron?
Photodisintegration occurs within the diagnostic x-ray range.
Photodisintegration occurs within the diagnostic x-ray range.
What is the primary characteristic of phosphor materials?
What is the primary characteristic of phosphor materials?
In pair production, the energy of the photon is converted into two _______ photons during the annihilation process.
In pair production, the energy of the photon is converted into two _______ photons during the annihilation process.
Match the terms related to radiation with their descriptions:
Match the terms related to radiation with their descriptions:
What occurs during coherent scattering?
What occurs during coherent scattering?
Compton scattering involves the ejection of tightly held electrons from an atom.
Compton scattering involves the ejection of tightly held electrons from an atom.
What is the term for the electron that is ejected during Compton scattering?
What is the term for the electron that is ejected during Compton scattering?
During Compton scattering, energy is divided between the scattered photon, the binding energy of the electron, and the __________ energy of the recoil electron.
During Compton scattering, energy is divided between the scattered photon, the binding energy of the electron, and the __________ energy of the recoil electron.
What effect does scattering have on diagnostic imaging?
What effect does scattering have on diagnostic imaging?
What is the significance of the incident photon's energy in scattering interactions?
What is the significance of the incident photon's energy in scattering interactions?
Match the following types of scattering to their characteristics:
Match the following types of scattering to their characteristics:
The formula for the energy of a photon is represented as E = hf or E = __________.
The formula for the energy of a photon is represented as E = hf or E = __________.
What happens to the energy of the scattered photon when the incident photon has higher energy?
What happens to the energy of the scattered photon when the incident photon has higher energy?
Backscatter radiation describes x-rays scattered in the direction opposite to the incident photon.
Backscatter radiation describes x-rays scattered in the direction opposite to the incident photon.
What is the equation relating the change in wavelength between incident and scattered photons?
What is the equation relating the change in wavelength between incident and scattered photons?
The probability of photon undergoing Compton scattering is _______________ to photon energy.
The probability of photon undergoing Compton scattering is _______________ to photon energy.
Match the following terms with their descriptions:
Match the following terms with their descriptions:
At which angle is energy not transferred to the scattered photon?
At which angle is energy not transferred to the scattered photon?
The probability of photoelectric absorption increases as the atomic number of a material increases.
The probability of photoelectric absorption increases as the atomic number of a material increases.
What must be true for photoelectric absorption to occur?
What must be true for photoelectric absorption to occur?
Most photons scatter in a ___________ direction as photon energy increases.
Most photons scatter in a ___________ direction as photon energy increases.
What defines the maximum energy transfer during scattering?
What defines the maximum energy transfer during scattering?
What are the two main types of x-ray interactions that are important in diagnostic radiography?
What are the two main types of x-ray interactions that are important in diagnostic radiography?
Increasing kVp always results in improved image contrast.
Increasing kVp always results in improved image contrast.
What is the primary purpose of intensifying screens in x-ray imaging?
What is the primary purpose of intensifying screens in x-ray imaging?
The protective coating of the intensifying screens is made of ______.
The protective coating of the intensifying screens is made of ______.
Match the type of luminescence with its description:
Match the type of luminescence with its description:
What happens to image noise when higher kVp and faster screens are used?
What happens to image noise when higher kVp and faster screens are used?
A higher atomic number in phosphors correlates with a lower probability of x-ray absorption.
A higher atomic number in phosphors correlates with a lower probability of x-ray absorption.
What is spatial resolution measured by in x-ray imaging?
What is spatial resolution measured by in x-ray imaging?
As the thickness of the body part imaged increases, the ______ radiation also increases.
As the thickness of the body part imaged increases, the ______ radiation also increases.
What determines the screen speed in x-ray imaging?
What determines the screen speed in x-ray imaging?
Compton scattered x-rays provide useful information for image formation.
Compton scattered x-rays provide useful information for image formation.
What is the formula for calculating the Intensification Factor (IF)?
What is the formula for calculating the Intensification Factor (IF)?
The reflective layer of the intensifying screen is made from ______.
The reflective layer of the intensifying screen is made from ______.
Match the following factors affecting scatter radiation to their descriptions:
Match the following factors affecting scatter radiation to their descriptions:
Study Notes
Attenuation
- Attenuation refers to the reduction in intensity of photons due to absorption and scattering.
- Factors increasing attenuation include:
- Increased material thickness.
- Higher material density, e.g., lead attenuates more than tissue.
- Elevated atomic number, leading to higher density.
- Lower photon energy, as higher energy photons can pass without interaction.
- Characterized by linear attenuation coefficient (μ) and mass attenuation coefficient (μ/ρ).
Basic Interaction Mechanisms
- Coherent scattering occurs for low-energy photons (<10 keV) with no energy loss; irrelevant for diagnostic imaging.
- Compton scattering involves an x-ray photon interacting with outer-shell electrons, leading to ionization and energy loss.
- Photoelectric absorption occurs when an x-ray photon fully transfers energy to an inner-shell electron, ejecting it and ionizing the atom.
- Pair production creates an electron-positron pair from high-energy photons (≥1022 keV); not applicable in the diagnostic range.
- Photodisintegration strikes nuclei with high-energy photons (>10 MeV) to emit nuclear fragments; irrelevant for x-ray diagnostics.
Compton Scattering
- Involves an x-ray photon ejecting a loosely held outer-shell electron, forming a Compton or recoil electron.
- The scattered photon has lower energy and longer wavelength; energy distribution: E(in) = E(scat) + E(b) + E(KE).
- Recoil electrons are absorbed within 1-2 mm of soft tissue and can contribute significantly to patient dose and film fog.
Energy Transfer and Scatter Angle
- Energy conservation principle applies during scattering; energy of incident photon equals energy of the scattered photon plus binding and kinetic energies.
- Scattering angle affects energy change; maximum energy transfer occurs at 180 degrees, while no energy transfer occurs at 0 degrees.
Backscatter Radiation
- Refers to x-rays scattered in the original direction of the incident photon; most photons scatter forward, especially at higher energies.
Probability of Scattering
- Probability of Compton scattering is higher with loose electron density and inversely proportional to photon energy, decreasing as energy increases.
Photoelectric Absorption
- Occurs when an x-ray photon interacts with an inner-shell electron, where the photon transfers all its energy.
- Photoelectric absorption requires incident photon energy to be equal to or greater than the binding energy, e.g., K-shell binding energy for oxygen is 0.53 keV.
- High atomic number materials increase absorption probability, whereas higher photon energy decreases it.
Differential Absorption
- Diagnostic images rely on the difference between x-rays absorbed (photoelectric) and transmitted.
- Compton scattering leads to film fog and reduced image contrast, more significant at lower x-ray energies.
Intensifying Screens
- Devices converting x-rays into visible light to reduce patient dose; consists of various layers:
- Base: polyester for strength and flexibility.
- Reflective layer: enhances light direction towards the film.
- Phosphor layer: absorbs x-rays and emits visible light.
- Protective coating: prevents damage and allows light passage.
Luminescence
- The phenomenon of light emission due to electron excitation; two types are fluorescence (instant) and phosphorescence (delayed).
Phosphors Characteristics
- Essential characteristics include high atomic number, conversion efficiency, appropriate spectral emission, and minimal afterglow.
Screen Speed and Image Quality
- Screen speed ranges from 100 (slow, detailed) to 1200 (very fast), influencing fluoroscopic efficiency and patient dose.
- Higher screen speed tends to generate image noise and reduced spatial resolution.
Beam Restricting Devices
- Factors affecting scattered radiation intensity:
- kVp: Higher energy decreases the likelihood of photoelectric interactions, leading to increased scatter.
- X-ray field size: Larger fields increase scatter due to more potential interactions.
- Tissue thickness: Thicker tissues lead to more scatter.
Overall Concepts
- A balance of kVp is necessary to maintain adequate contrast while minimizing patient dose.
- Effective imaging practices require understanding relationships between absorption interactions, screen dynamics, and radiation safety.
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Description
This quiz covers the fundamentals of photon attenuation, focusing on how absorption and scattering contribute to the process. It explores factors such as material thickness, density, atomic number, and photon energy in relation to attenuation. Test your understanding of these concepts and their implications in different materials.
