51 Questions
What is the main purpose of the f-factor in Method 1 for estimating absorbed dose in tissue?
To estimate dose to tissue from exposure
Which method allows for the creation of coefficients to facilitate estimates of absorbed dose from the air kerma?
Computer simulation (Method 2)
What does absorbed dose in tissue not provide much information about, according to the text?
Biological impact of the radiation
What is an image in the context of this text?
A 2-dimensional representation of an object with location and intensity level
What do both location and intensity carry in an image, according to the text?
Information about the object being represented
What do further dose descriptors, such as equivalent and effective dose, provide according to the text?
More meaningful information about the implications of radiation exposure
What are the interrelated categories mentioned in the text in the context of an image?
IR factors, geometric factors, subject factors
What is the main purpose of Method 2 for estimating absorbed dose in tissue?
To guide estimates of dose using computer simulation
Which interaction involves the incident photon interacting with a single electron, causing it to vibrate or oscillate?
Coherent scattering
In which interaction does the incident photon leave the atom in a slightly different direction and with some reduction in energy?
Compton scattering
Which interaction involves the incident photon interacting with an inner shell electron, causing the atom to be ionized?
Photoelectric effect
At what energy range is coherent scattering most prevalent?
15-30 keV
In which energy range is Compton scattering the predominant interaction of x-rays with soft tissue?
30-60 keV
Which interaction involves the incident photon interacting with the nucleus and can result in the creation of an electron-positron pair?
Pair production
Which interaction causes the excitation of all electrons when the incident photon interacts with the atom?
Coherent scattering
In which interaction does the scattered photon tend to scatter in a more forward direction and has a higher chance of reaching the image receptor?
Compton scattering
At what energy range does the probability of the photoelectric effect interaction decrease?
As incident photon energy increases
Which interaction involves the incident photon interacting with a loosely bound outer shell electron?
Compton scattering
At what energy range is coherent scattering of low probability in diagnostic applications such as mammography?
15-30 keV
Which interaction results in the atom being ionized with an inner shell electron vacancy?
Photoelectric effect
What is the purpose of heavy metal filters in radiation physics?
Maximize absorption in contrast agent and minimize absorption in patient tissues
When do K-edge filters occur?
When photon energy matches binding energy or is just above the binding energy
What do heavy metal filters do to photons?
Transmit photons just below the absorption edge and stop photons just above the absorption edge
What is the purpose of shaped compensating filters in radiation physics?
Provide consistent beam intensity at the image receptor
What is the anode heel effect used for in large radiographs?
To even the density within large radiographs involving progressively thinner anatomical structures
What does photon fluence measure?
The number of photons passing through a unit crossing sectional area
What does photon flux measure?
The rate at which photons pass through a unit area per unit time
What is fluoroscopy used for?
Real-time imaging with low mA and longer time, useful for extended periods of time
What does energy fluence measure?
The amount of energy passing through a unit cross-sectional area
What does KERMA represent in radiation physics?
Kinetic energy transferred to charged particles by indirectly ionizing radiation per unit mass
At what photon energy does equal probability for compton vs photoelectric occur in soft tissues?
30 keV
What is the primary reason for filtration of the beam using filters?
Reducing radiation dose to the patient
What is the purpose of added filtration in beam content?
To selectively remove lower energy photons
What is the effect of beam hardening as the beam passes through matter?
Increase in beam quality
What is the purpose of K-edge filters in optimizing contrast when imaging elements with Z>60?
To balance compton vs photoelectric effects
What is the maximum contrast achieved using K-edge filters for iodine and barium absorption characteristics?
At the K absorption edge of the absorber
What is the effect of heterogeneous beam content?
Results in multiple photon energies within the beam
What is the role of filters in altering the emission spectrum of the beam?
To remove lower energy photons
What is the purpose of effective beam energy in representing a polyenergetic beam?
To represent as a monoenergetic beam
What is the most likely effect of the photoelectric effect when the photon energy is just above the binding energy of the electron?
Increase in photoelectric effect
What components contribute to inherent filtration in a radiation system?
Oil in housing and collimator mirror
What is the purpose of filters in a radiation system?
To remove lower energy photons
What is the proportion of Compton to photoelectric interactions if the energy is doubled?
4:1
What does the linear attenuation coefficient (µ) represent?
Fraction of photons removed from a monoenergetic beam per unit thickness of material
What is the relationship between the half-value layer (HVL) and the linear attenuation coefficient (µ)?
As HVL increases, µ decreases
What does the mean free path (MFP) represent?
Distance a photon travels in matter before interaction
What does the exponential attenuation equation $N=N_0 e^{-\text{µ}x}$ represent?
Number of photons transmitted through a material
What is the primary purpose of the half-value layer (HVL) in radiation physics?
To express beam penetrability
What does the mass attenuation coefficient (MAC) quantify?
Attenuation of materials independent of their physical state
What is the relationship between the linear attenuation coefficient (µ) and the material density (ρ)?
Directly proportional
What is the primary purpose of the mass attenuation coefficient (MAC) in radiation physics?
To quantify the attenuation of materials independent of their physical state
Study Notes
Radiation Physics Lecture Summary
- Exponential attenuation occurs in monoenergetic beams, with the total number of interactions decreasing as photon energy increases.
- In soft tissues, equal probability for compton vs photoelectric occurs at about 30 keV, while for bone, it occurs at about 40 keV.
- Heterogeneous beam content results from multiple photon energies within the beam, and each layer of material selectively removes photons from the beam according to their energies.
- The use of effective beam energy allows for the representation of a polyenergetic beam as a monoenergetic beam with equivalent penetrating behavior.
- Beam hardening refers to the increase in beam quality or average energy as the beam passes through matter, caused by the filtration of lower energy photons from the beam.
- Filters, usually thin sheets of metal, are used to alter the emission spectrum of the beam, with the primary reason for filtration being the elimination of photons that would increase radiation dose to the patient without enhancing the radiographic image.
- Inherent filtration components include the anode disc, tube envelope, oil in housing, and collimator mirror, which exist for another purpose but also have the effect of removing lower energy photons.
- Added filtration, which may be permanent or adjustable, shapes the beam energy and selectively removes lower energy photons.
- The photoelectric effect is most likely to occur when the photon energy is just above the binding energy of the electron it interacts with, and K-edge filters are used to optimize contrast when imaging elements with Z>60.
- Iodine and barium are specifically mentioned for their absorption characteristics, with maximum contrast achieved using K-edge filters when the effective energy of the beam is close to, but slightly above, the K absorption edge of the absorber.
Test your knowledge of radiation physics with this quiz covering topics such as exponential attenuation, photon interactions in soft tissues and bone, heterogeneous beam content, effective beam energy, beam hardening, filtration, inherent and added filtration components, photoelectric effect, and K-edge filters for optimizing contrast in medical imaging.
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