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93 Cards in this Set
- Front
- Back
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Decay equation |
A(t) = A(0) e^(- lambda x t)
Where, A(t) is the quantity of radioactive material at time t, A(0) is the initial quantity, lambda is the decay constant |
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Half life equation |
t(half) = ln(2) / lambda
Where, lambda is the decay constant |
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Average life equation for radioactive decay |
t(avg) = 1/lambda = 1.44 x t(half) |
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Different types of radioactive decay |
1. Gamma radiation 2. Internal conversion = characteristic radiation or Auger electron 3. Beta+ decay = e- emission 4. Beta- decay = e+ emission 5. Alpha decay = He2+ emission 6. Electron capture |
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Number of e- per inner shell |
2n^2 |
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Direct ionizing agents |
Electrons, protons, positrons, alpha particles |
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Indirect ionizing agents |
Gamma, x-ray, neutrons |
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Auger emission |
Occurs when shell transitioning energy is transferred to another orbital electron (which is then emitted as Auger electron) rather than released as a characteristic x-ray. |
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Specific ionization |
Ion pairs formed from primary and secondary ionizations per unit path length. |
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Specific ionization is proportional to ___ and inversely proportional to ___ |
Proportional to the electrical charge of a particle, inversely proportionate to it's velocity |
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Bragg ionization peak |
A sharp increase in ionization potential near the end of a charged particle's range |
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Bragg peak for diagnostic x-ray occurs at... |
The entrance skin location |
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Linear energy transfer |
The energy deposited per unit path length traveled |
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Is alpha particle more or less damaging than beta or gamma/x-rays? |
More |
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Fraction of Bremsstrahlung interactions is proportional to ... |
Energy of the incoming particle and the atomic number Z of the absorber |
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Positron, electrons loses kinetic energy via |
1. Excitation 2. Ionization 3. Bremsstrahlung |
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Positron annihilation (with an electron) results in ... |
Emission of 2 oppositely directed, 511 keV gamma ray photons, detectable in a PET scanner |
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K shell binding energy of Mo (molybdenum) |
20 keV |
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K shell binding energy of Rh (rhodium) |
23 keV |
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K shell binding energy of Ag |
25 keV |
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K shell binding energy of W |
70 keV |
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K shell binding energy of I |
33 keV |
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K shell binding energy of Ba |
37 keV |
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The primary charged particle interaction occurring at the tungsten anode target used in radiography, fluoroscopy, and CT |
Excitation (>99%), generating heat
Ionization (generating characteristic x-ray) is only 0.01-0.15% of interactions. Bremsstrahlung (generating polyenergetic x-ray) is 0.8-0.9%. |
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Mammography uses Mo and Rh targets, this increases or decreases Bremsstrahlung? |
Decreases. The generated x-ray is primarily characteristic x-ray. |
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Radioactive particle used in thyroid ablation |
Beta emitting radioisotope I-131 |
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Atoms with same Z, different A |
Isotopes |
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Atoms with same A, different Z |
Isobars |
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Atoms with same N, different Z |
Isotones |
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The dose of 250 keV x-rays necessary to produce a specific radiobiological effect, divided by the dose of test radiation required to produce the same radiobiological effect. |
Relative biological effectiveness, which describes the effect of ionization on cells. Increase as LET increases, peaks at LET of 100 keV/micrometer |
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Compton scatter is proportional to ___ and decreases with ___ photon energy |
Proportional to material physical density. Decreases with increasing photon energy |
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The predominant photon interaction in soft tissue above 25-30 keV |
Compton scatter |
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Probability of photoelectric effect depends on |
(Z/E)^3 and material physical density
Z is atomic number of absorbing material. E is energy of incident photon |
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K absorption edge is slightly above or below k shell binding energy? |
Above |
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What is k absorption edge? |
A sharp increase in the probability of photoelectric absorption |
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Which interaction dominates at higher x-ray energy such as chest radiography? |
Compton scatter |
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Which interaction dominates at lower x-ray energy such as mammography? |
Photoelectric absorption |
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Linear attenuation coefficient |
Fraction of x-rays attenuated per unit length, either due to photoelectric effect, Compton scatter, or coherent scatter |
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Decibel |
Db = 10 x log (I2 / I1)
I2 and I1 are sound intensities |
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Types of interaction between an accelerating electron and an atom |
1. Excitation 2. Ionization 3. Bremsstrahlung (braking energy) |
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Percentage of the energy carried by accelerating electrons that produces heat as braking radiation |
Over 99.9% |
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The dose difference between increasing CT scanning length |
No difference.
Dose is energy per mass. |
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Equivalent dose change when increasing CT scanning length |
No change. |
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Effective dose change when increasing CT scanning length |
Increase |
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Hounsfeld unit of water |
Zero |
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Hounsfeld unit of air |
-1000 |
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Hounsfeld unit of fat |
-80 to -30 |
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Fundamental SI units |
1. Meter 2. Kilogram 3. Second 4. Kelvin 5. Mole 6. Candela 7. Bacquerel |
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Candela |
Unit of luminous intensity (light output) |
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Illuminance |
The amount of light hitting a surface area, or luminous flux per unit area |
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Compare the maximum energy of an x-ray photon produced by a given x-ray tube voltage, with the value of the voltage across the X-ray tube. |
Numerically the same (kVp and keV) |
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Important properties of anode |
1. Good conductor of heat. 2. Good conductor of electricity. 3. High melting point. 4. High atomic number. |
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Important properties of anode |
1. Good conductor of heat. 2. Good conductor of electricity. 3. High melting point. 4. High atomic number. |
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Why do people not glow after being exposed to radiation |
Human tissue is made of low Z materials and interaction with radiation causes Auger electron emission instead of x-ray production. |
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Auger electron production happens mainly in low or high Z materials? |
Low Z material |
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Does high or low Z material produce more characteristic radiation? |
High Z material |
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Most used target material for X-ray tube target |
Tungsten (90%), rhenium (10%)
High Z, high melting point, good conductor of heat and electricity. Rhenium to help prevent surface cracking of tungsten. |
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The larger the anode angle, the ___ the effective (apparent) focal spot size. |
Larger |
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The change in the x-ray intensity across the x-ray field is called |
Anode heel effect.
Cathode side has greater intensity. |
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kVp controls the quality or quantity of x-ray spectrum produced |
Quality (max energy of electron), also quantity as x-ray production is more efficient at higher energy |
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mA controls the quality or quantity of x-ray spectrum produced |
Quantity, by controlling the thermionic emission at the filament |
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Compare the average x-ray photon energy to the maximum energy of x-ray photon. |
About 1/3 to 1/2 |
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Increase in kVp by 15% results in ___ of the radiation intensity at the detector |
Doubling |
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Effect of increasing the focal spot size on resolution, heat capacity, contrast, and patient dose |
Resolution: decrease Heat capacity: increase Contrast: no change Patient dose: no change |
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How does decreasing the added filter thickness affect patient dose and HVL? |
Increase patient dose, decrease HVL |
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How does decreasing the added filter thickness affect patient dose and HVL? |
Increase patient dose, decrease HVL |
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How does decreasing added filter thickness decrease HVL? |
Decreased filtration -> more low energy photons in x-ray spectrum -> decreased average energy of x-ray -> decreased penetration -> less material is required to reduce the exposure by 1/2 -> decreased HVL |
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How does dose relate to field of view? |
Dose (old) * FOV (old) = dose (new) * FOV (new) |
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How does spatial resolution relate to the pitch in a flat panel detector? |
Resolution in line pair per mm (lpm) = 1 / (2 * pitch) |
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How does dose relate to aperture in image intensifier fluoroscopy? |
Dose(new) / dose(old) = f(new)^2 / f(old)^2
f is the measurement for aperture, the greater the f, the smaller the aperture. |
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Detector quantum efficiency |
Efficiency of converting x-ray to signal |
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How does KAP (Kerma area product) vary with distance of patient from the source? |
KAP does not change with distance |
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How does Air Kerma change with distance? |
AK decreases with square of the distance |
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Definition of signal to noise ratio (SNR) |
SNR = N / sigma
Signal = N = number of photons per area Noise = sigma = standard deviation = square root of N |
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Does noise increase or decrease when SID increases and SOD is constant? |
Increases, due to x-ray spreading out more, and noise is directly proportional to the average number of photons per area. |
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Limiting factor for geometric magnification |
Focal spot size
As magnification increases, geometric blur due to finite focal spot size (i.e. a non-point source) increases. |
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Beer-Lamber law |
I = I(0) * e^(- lambda * x)
I is intensity of x-ray at detector. I(0) is the initial intensity of x-ray. lambda is the attenuation coefficient. x is the thickness of object |
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Concavity of object produces ___ Mach band. Convexity of object produces ___ Mach band. |
Bright. Dark. |
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At what energy does compton effect dominates in soft tissue? |
Above 26 keV |
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At what energy does compton effect dominates over photoelectric effect in soft tissue? |
Above 26 keV |
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At what energy does compton effect dominates over photoelectric effect in bone? |
Above 35 keV |
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Source of scatter in radiography |
Compton and coherent interactions |
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Relationship between scatter and object volume and x-ray energy |
Scatter increases with increase in either object volume and x-ray energy |
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Scatter as a function of s/p |
Scatter = 1 / (1 + s/p)
s/p = ratio of scattered photons to primary photons |
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Grid ratio |
Grid height / interspace width |
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Ways to reduce scatter in radiography |
1. Grid (moving grid = Bucky) 2. Air gap (only in mammography) |
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Why is scatter bad? |
It reduces contrast |
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Does voltage affect both penetration and exposure? |
Yes |
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Does current affect both penetration and exposure? |
No, only exposure |
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How to tell if a CXR has proper penetration |
If vertebral bodies are discernible, it's well penetrated. |
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Moving grid (Bucky) results in greater radiation dose to patient than stationary grid. True or false? |
False. Doses are the same. |
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Double exposure results in image that is too white or too black? |
Too black |
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Artifacts on radiographs |
1. Fogging 2. Incomplete erasure 3. Ghosting 4. Double exposure |
