Term
| Average energy deposited per ion pair produced in air? in soft tissue? |
|
Definition
air - 34 eV
soft tissue - 22 eV |
|
|
Term
What is specific ionization for a charged particle?
What is is proportional to? |
|
Definition
Number of ion pairs produced per unit length of the charged particles path.
Proportional to the square of the charge, Q2, and inversely proportional to the square of the velocity, V2. |
|
|
Term
| Define path length and range of a particle |
|
Definition
path length - total distance the particle travels
range - depth of penetration of the particle |
|
|
Term
|
Definition
| Linear Energy Transfer - average amount of energy deposited per unit path length of a particle (keV/μm) |
|
|
Term
|
Definition
The square of the charge and inversely proportional to the kinetic energy of the particle.
LET ≈ Q2 / Ek |
|
|
Term
|
Definition
| a scattering event where the total kinetic energy is unchanged |
|
|
Term
|
Definition
| scattering with a loss of kinetic energy |
|
|
Term
| Bremsstrahlung emission per atom is proportional to |
|
Definition
Z2 of the absorber and inversely proportional to the square of the mass of the incident particle
Z2 / m2 |
|
|
Term
| Types of interactions of photons in matter |
|
Definition
| 1) Rayleigh scattering, 2) photoelectric absorption, 3) Compton scattering, 4) pair production |
|
|
Term
| Other terms for Rayleigh scattering |
|
Definition
| Coherent or Classical scattering |
|
|
Term
|
Definition
| The incident photon excites an atom, the atom immediately de-excites, emmitting a scattered photon of the same wavelength and energy. No ionization occurs. |
|
|
Term
| How much of x-ray interactions are Rayleigh scattering? |
|
Definition
| < 5% at 70 keV and about 10% at 30 keV |
|
|
Term
| Compton Scattering dominates in soft tissue at what energy? |
|
Definition
| Above 26 kev to approximately 30 MeV |
|
|
Term
| Compton scattering is most likely to occur between a photon and |
|
Definition
| an outer shell (valence) electron |
|
|
Term
| Compton scattering results in |
|
Definition
| a scattered photon and an ejected (Compton) electron |
|
|
Term
| Energy Conservation in Compton Scattering |
|
Definition
|
|
Term
| The energy of the scattered photon in Compton Scattering is given by |
|
Definition
| Esc = Eo / (1 + (Eo/511) * (1 - Cos(θ))) |
|
|
Term
| At diagnostic energies, the majority of incident photon energy in Compton scattering is transfered to |
|
Definition
|
|
Term
| Compton scattering results in a degradation of ______ and an increase in ________. |
|
Definition
| degradation of image contrast, increase in random noise |
|
|
Term
| Maximal energy transfer to a Compton electron occurs when |
|
Definition
| the scatter photon is at 180 degrees (backscatter) |
|
|
Term
| Maximal energy of a Compton scattered photon at 90 degrees is |
|
Definition
|
|
Term
| Probability of Compton scattering per unit volume is proportional to |
|
Definition
| the density of the material |
|
|
Term
| Compton scattering per unit mass is nearly independent of |
|
Definition
|
|
Term
| The kinetic energy of an ejected photoelectron is |
|
Definition
the incident photon energy minus the binding energy of the orbital electron
Epe = Eo - Eb |
|
|
Term
| The ejection of a photoelectron can be followed by what two processes? |
|
Definition
| Characteristic x-rays or Auger electrons |
|
|
Term
| The probability of photoelectric absorption per unit mass is proportional to |
|
Definition
|
|
Term
| Image contrast decreases with higher energy x-rays because |
|
Definition
| the probability of photoelectric absorption decreases as 1/E3 |
|
|
Term
| Absorption edges occur when |
|
Definition
| the incident photon energy is just above the binding energy of a particular shell |
|
|
Term
| The energy corresponding to an absorption edge increases with the ______ of the element. |
|
Definition
|
|
Term
| When does photoelectric absorption dominate? |
|
Definition
| At lower energies and higher Z materials. |
|
|
Term
| When does Compton scattering dominate? |
|
Definition
| At higher energies and lower atomic numbers (such as tissue and air) |
|
|
Term
| Effective Z for soft tissue. |
|
Definition
|
|
Term
|
Definition
|
|
Term
| Attenuation is the removal of photons caused by |
|
Definition
| absorption and scattering |
|
|
Term
| At what energy is the probability of the photoelectic effect and Compton scattering the same in soft tissue? |
|
Definition
|
|
Term
| Linear attenuation coefficient - definition and units. |
|
Definition
| The fraction of photons removed from a monenergetic beam per unit thickness of material, [cm-1] |
|
|
Term
| The number of photons transmitted through a material is given by |
|
Definition
|
|
Term
| The linear attenuation coefficent is the sum of what? |
|
Definition
The individual linear coefficients from each type of interaction.
μ = μrayleigh + μPE + μCompton + μpair production |
|
|
Term
| What is the "problem" with linear attenuation coefficient? |
|
Definition
| It is dependent on the density of the material. |
|
|
Term
| Mass attenuation coefficient |
|
Definition
| Linear attenuation coefficient normalized to the unit density. |
|
|
Term
| Mass attenuation coefficient is ________ of density. |
|
Definition
|
|
Term
| The units of mass attenuation coefficient are |
|
Definition
|
|
Term
| The symbol for mass attenuation coefficient is |
|
Definition
|
|
Term
| Using the mass attenuation coefficient, the number of photons transmitted through a material is given by |
|
Definition
|
|
Term
| The product ρx is called the |
|
Definition
| mass thickness or areal thickness |
|
|
Term
|
Definition
| excludes scatter radiation from reaching the detector |
|
|
Term
|
Definition
| scatter photons remain in the beam and reach the detector |
|
|
Term
|
Definition
| HVL - thickness of material required to reduce the intensity (air kerma) of a beam to 1/2 it's initial value. |
|
|
Term
| In terms of linear attenuation coeffient, the halve value layer is given by |
|
Definition
|
|
Term
|
Definition
| 1) photon energy, 2) geometry, 3) attenuating material |
|
|
Term
| Effective energy of a polyenergetic beam is |
|
Definition
| expressed as the energy of a monoenergetic beam with the same "effective" penetrability. |
|
|
Term
| The effective energy from a diagnostic x-ray tube is typically _____ to _____ the maximal energy of the beam. |
|
Definition
|
|
Term
| Mean Free path - definition and formula |
|
Definition
average distance a photon travels before an interaction.
MFP = 1/μ |
|
|
Term
| The shift of the x-ray spectrum to higher energies as the beam passes through material is called |
|
Definition
|
|
Term
|
Definition
| ratio of the first HVL to the second HVL |
|
|
Term
| A monoenergetic source has a homogeneity coefficient of |
|
Definition
|
|
Term
|
Definition
the number of photons that pass through a unit cross sectional area
Φ = N / area [cm-2] |
|
|
Term
|
Definition
| The fluence rate - fluence per unit time [cm-2 s-1] |
|
|
Term
|
Definition
The amount of energy passing through a cross-sectional area.
Ψ = Φ (photons/area) * E (energy/photon) [J/m2] |
|
|
Term
|
Definition
| Energy Fluence per unit time |
|
|
Term
| Two step process for indirectly ionizing radiation to deposit energy. |
|
Definition
1. Energy from the photon is transferred into kinetic energy of charged particles (electrons)
2. The charged particles deposit their energy through excitation and ionization. |
|
|
Term
|
Definition
| Kinetic energy released in matter - kinetic energy transferred to charged particles by indirectly ionizing radiation per unit mass |
|
|
Term
|
Definition
|
|
Term
| mass energy transfer coefficient |
|
Definition
mass attenuation coefficient mulitplied by the fraction of the energy of the interacting photons that is transfered to charged particles as kinetic energy.
μtr / ρo |
|
|
Term
| Why does the mass energy transfer coefficient go down as energy of the incident photon increases. |
|
Definition
| As energy increases, Compton scattering increases, so less energy is transfered to charged particles |
|
|
Term
| How do you calculate kerma for a monoenergetic beam? |
|
Definition
K = ψ * (μtr/ρo)E
energy fluence * mass energy transfer coefficient |
|
|
Term
|
Definition
energy absorbed per unit mass of material
D = E / m [J/kg or Gy] |
|
|
Term
| mass energy absorption coefficient |
|
Definition
mass attenuation coefficient times the fraction of energy of the interacting photons that is absorbed in the mass
(μen / ρo) |
|
|
Term
| Why is the mass energy absorption coefficient not the same as the mass energy transfer coefficient. |
|
Definition
| Energetic electrons can produce bremsstrahlung radiation that can escape the volume of interest. In soft tissue, there is practically no bremsstrahlung production, so the absorption coefficient and the transfer coefficient are nearly identical. |
|
|
Term
| In terms of energy fluence, dose can be calculated as |
|
Definition
D = Ψ * (μen / ρo)E
Dose equals energy fluence * mass energy absorption coefficient |
|
|
Term
| What is the difference between dose to air and kerma? |
|
Definition
| Dose to air is based on mass energy absorption coeffient and kerma is based on mass energy transfer coefficient. Dose will be slightly less than kerma. |
|
|
Term
|
Definition
Amount of electrical charge produced by ionizing radiation per unit mass of air.
X = Q / m [C/kg] |
|
|
Term
| Units of exposure and how are they related? |
|
Definition
| 1 R (roentgen) = 2.58x10-4 C/kg |
|
|
Term
| Average energy deposited per ion pair in air. |
|
Definition
|
|
Term
| 1 R of exposure results in what air kerma? |
|
Definition
|
|
Term
|
Definition
The total amount of energy deposited into a mass.
ε = dose (J/kg) * mass (kg) = [J] |
|
|
Term
|
Definition
| Product of the absorbed dose and the radiation weighting factor. It accounts for the increased probability of stochastic effects from high LET radiations. |
|
|
Term
|
Definition
rem or sievert (Sv)
1 Sv = 100 rem |
|
|
Term
| Radiation weighting factors for x-rays, protons, neutrons, and alpha particles. |
|
Definition
| x-rays - 1, protons - 2, neutrons - 2.5-20 (energy dependent), alpha particles - 20 |
|
|
Term
|
Definition
Determines the detriment from stochastic effects from a partial body irradiation compared to a whole body irradiation by using tissue weighting factors.
Effective dose = Σ Equivalent dose * HT |
|
|
Term
|
Definition
sievert (Sv) or rem
1 Sv = 100 rem |
|
|
Term
| The tissues with the largest tissue weighting factors are |
|
Definition
| the breast, bone marrow, colon, lung, and stomach. Each has wT = 0.12. |
|
|
Term
| What is the formula for beam intensity transmitted through a material when using broad-beam geometry. Give the definition for the new term. |
|
Definition
I = B I0e-μx
B is the buildup factor - ratio of scattered and primary to primary beam alone
|
|
|
