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58 Cards in this Set
- Front
- Back
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What is Air KERMA?
How can you derive dose from it? |
Measure of machine performance...inferred from absorbed dose (mGy/kg)
Dose = Air KERMA x F factor (F factor for soft tissue is 1, for bone is high (4) |
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What happens to binding energy with increased Z (atomic number)?
...with increased distance from nucleus (M shell vs. K shell)? |
Increases (more protons in nucleus increases ionic attraction)
Decreases (less force from nucleus) |
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What does ionization depend on?
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Overcoming binding energy, which depends on atomic number and density
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What is the number of electrons in the outermost filled shell?
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8 electrons always fills the outermost shell
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What is the does equivalent/quality factor for X rays and gamma rays?
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one, which means mSv = mGy
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What does LET depend on?
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Mass, charge and velocity
The first two are obvious, but the slower the velocity, the higher the LET |
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What are the two currents/voltages of an X ray tube? Which one is associated with the kVp we select as radiology residues?
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Filament voltage (creates the electron cloud)
Tube voltage (potential b/w cathode and anode, this is what we adjust with the kVp...which equals the keV max) |
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What are the three radiosafety values for X ray tube regarding tube leakage, SID of light, aluminum filter)
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100 mR/hr at 1 meter
2% SID difference (relates to the light used to guide the technologists corresponding to actual image) 2.5 mm Al filter thickness (used to filter low energy beams) |
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What are three types of ionizing radiation?
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Cosmic rays
Gamma rays X rays |
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What is the SID for a PA CXR? Typical X ray? Mammo?
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Mind the units
CXR 72 inches Typical XR 40 inches/100 cm Mammo 65 cm |
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What is the effective/average keV?
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1/3 kVp
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There are two types of X rays generated by a Tungsten target, which is polychromatic and which is monochromatic? Which type predominates?
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Bremsstrahlung (polychromatic, hump curve) and Characteristic (monochromatic, tower curve)
For Tungsten, Bremmsstrahlung predominates, but this is different for Molybdenum (which is used for Mammo) |
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What is the highest possible characteristic X ray?
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Whatever the K shell binding energy is (69 keV for Tungsten)
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Lower energy photos provide better contrast resolution (more photoelectric effects), what are the disadvantages though?
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Increased skin dose due to increased number of low energy X rays that don't contribute to imaging
Exposure time is longer to get adequate images, makes this susceptible to patient motion |
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What target do we use for mammo?
What target do we use for thick breasts? What target do we use for medium breasts (not thick but more than normal) |
Moly with Moly filter
Rhodium with Rhod filter Moly with Rhodium filter |
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What is the purpose of filtering Mammo?
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Characteristic X ray is transparent to its own filter, so a Moly filters will filter all but its characteristic X ray of 23 keV, which is perfect for mammo contrast
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How can you decrease the Heel effect?
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Increase SID
Increase angle of target Heel effect is used advantageously in Mammo (I wasn't paying attenuation so I don't know why) |
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What equation explains the probability of photoelectric effect relative to atomic number and energy?
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Z^3/E^3
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What is the K edge of Iodine? What is its significance?
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33 keV; just above this number, there is a huge, brief increase in absorption, so X rays at these energies contrast iodine from surrounding tissues
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What does Compton scatter depend on?
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Not Z dependent
When energies of X rays are way above binding energies, Compton scatter occurs When they are just above BE, then PE occurs |
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What factors in X ray affects Air KERMA/Beam quantitiy/Dose?
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Exposure time
mA mAs kVp (square relationship) Filtration (inverse relationship) |
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What is the relationship of tube angle to image quality?
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Inversely proportional
As tube angle decreases, image quality increases until the Heel effect affects the periphery |
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What focal spot is used for a wrist X ray, small or large?
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Small, heat dissipation is bad for small focal spots, but who cares if you burn a wrist?
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What is the relationship of linear attenuation coefficient (u) with HVL?
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u = 0.693/HVL
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What equation allows you to solve for the intensity of a beam after it penetrates something?
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I = Io (1/2)^#HVLs
Count the HVLs (50%, 25%, 12.5%, 6%, 3%...) 1/2 HVLs are 70% of last HVL (100%, 70%, 50%, 35%, 25%, 17.5%...) Assume u is % loss (e.g. if u = o.01 cm^-1, that is 1% loss/cm) |
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What does adding filtration do to a beam?
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Beam hardening, lower energies are filtered
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What is background radiation exposure to the general public/yr?
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6.2 mGy/year, 1/2 due to medical imaging
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What are the two ALARA action levels?
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10% of ALARA (of 50 mSv or 12.5 mSv/quarter) - letter to physician/tech
30% of ALARA - counsel person |
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What test are pregnant people excluded from?
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Thyroid ablation
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What is the equation denoting the relationship between distance and image intensity?
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I/Io = (d2/d1)^2
Basically an inverse square law |
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How much transmission does 0.5 mm lead apron allow?
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2%
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What happens to patient does with...
...increased patient thickness? Density? Field size? kVp? Filtration? Beam Ripple? SID? OID? Receptor speed? Grid ratio? |
Patient thickness: increased dose
Density: increased dose Field size: increased dose kVp: nuanced, technically increased, but better quality X rays Filtration: decreased dose Beam ripple: increased dose SID: decreased dose (you're too close man!) OID: increased dose Speed: decreased dose Grid Ratio: increased dose |
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How do you go from CTDIw to CTDIvol?
How do you go from CTDIvol to DLP? |
CTDIvol takes into account Pitch (CTDIw/P)
DLP takes into account length of scan (CTDIvol x length) |
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What is the scatter rule?
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At 1 meter, a scatter beam is 1/1000th of its original intensity
you can combine this with inverse square law of distance to determine a scatter dose |
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What is the MQSA regulation for dose per mammo image (mGy)?
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less than 3 mGy
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What is the L50/60? L100/60?
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5-6 Sv
~12 Sv |
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What is the average latency of leukemia? Solid tumors?
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Solid tumors 20 yrs
Leukemia 2 yrs |
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How does Compton Scatter vary with differing atomic number? Energy?
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Independent of atomic number
inversely proportional to energy - still predominates at higher energies b/c PE effect decreases by E^3 |
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What are the two limitations of PET?
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1. Non collinear detection
2. Finite range of positrons |
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What is the fraction remaining of a substance at its tenth half life or HVL?
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1/1000th or 0.1%
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What is the effect of HVL on a polychromatic beam (Bremsstrahlung)?
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Thickness of HVL increases as you add HVLs
the first HVL hardens the beam, subsequent HVLs must be much thicker because now the beam has higher energy X rays |
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Single largest source of natural radiation?
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Radon 222
alpha emitter, so when inhaled as a dust, causes high LET damage |
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What is the purpose of modulation transfer function?
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Compare different machines and distinguish which components are degrading quality
Ideal is a strain horizontal line, the curve nearest to this is the best functioning machine/component |
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What is the better curve for line spread function?
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Fast decent to zero
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What interaction breaks the bromine barrier to create a latent image?
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Ag ion combines with an electron to form uncharged Ag
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What is the basic set up of a film screen system?
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X rays incident on phosphor, converts to light, AgBr emulsion creates latent image. Double film screen has two emulsion layers and a reflective layer that maximizes utilization of photons
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What is thermophosphorescence?
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Phosphorescence occurring after heat is applied.
We apply a laser to our dosimeter badges to determine our exposure dose. |
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S/N ratio in MR depends on...(what is directly proportional and what is inversely proportional)
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Steep freq encoding gradient, causes increased readout bandwidth - decreases S/N
Voxel size increase (either inc FOV or dec matrix size in phase encoding direction only) - inc S/N Cross talk (overlapping slices, RFs excite same protons) - dec S/N Increasing NEX, inc S/N |
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In what orientation does matrix size determine spatial resolution?
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Frequency encoding direction only
Trick: decreasing matrix size in phase encoding direction preserves spatial resolution, increases S/N |
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What determines scan time?
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TR x NEX x phase encoding steps (matrix size in PE direction) x echo train length
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What is a sentinel event according to the JC?
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1.5 Gy
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What determines what side the X ray tube anode and cathode should be placed?
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The thinnest portion should correspond to the anode side due to decreased energy here (heel effect)
In Mammo we use this, anode side next to nipple, cathode next to chest wall |
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What is the difference between CR and DR?
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Image is collected in each pixel array, as opposed to CR where an analog signal is formed, then subsequently digitized
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What is the advantage of CR over film/screen?
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Ease of radiolography
film screen is cheaper, has higher spatial resolution, lower dose |
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What is the difference between Indirect DR and Direct DR?
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Indirect DR coverts X rays to light via a CsI layer (utilized the K edge of iodine)
Direct DR uses an alpha Selenium layer to collect X rays, skips conversion to light. This reduces light spread. |
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What component of DR creates a pixel?
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Del; TFT switch and photodiode area (InDR) or capacitor
Important to maximize Fill Factor (ratio of TFT switch to light/electron sensitive areas), which represents efficiency of Del |
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What is the effect of TR on S/N in saturation recovery?
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Longer TR, better S/N...but at very long TR there is proton density so don't include this
if you give different tissue longer to separate themselves before second 90 deg RF, they have better diff. of signal |
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Ex. of radionuclide, radiochemical and chemical impurity...
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Radionuclide - moly breakthrough - you are getting the wrong nuclide
Radiochemical - free tech - undesired form of radiopharmaceutical Chemical - Aluminum breakthrough - non radioactive contamination |
