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54 Cards in this Set
- Front
- Back
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Detector type used in fluoroscopy |
1. Newer: Flat panel detectors (FPD), including direct and indirect. 2. Older: Image intensifiers + amplifier + lens + CCD |
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Automatic exposure control in fluoroscopy is called... |
Automatic brightness control (ABC)0 |
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Projection in fluoroscopy is named based on ... |
The side of the patient closest to the detector (opposite to the projection radiography) |
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Ideal technique for digital subtraction angiography (DSA), and why |
70 kVp. Average photon energy = 0.5 x kVp, is slightly greater than the k-edge of iodine, 33 keV. |
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Ideal technique for barium studies, and why |
90-110 kVp. K-edge of barium is 37 keV. Extra voltage to get better mucosal relief pattern. |
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3 determinants of resolution |
1. Detector 2. Motion artifact 3. Effective focal spot size |
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Does collimation improve resolution? |
No |
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How to increase contrast in fluoroscopy |
Collimate
Pros: decrease KAP Cons: smaller FOV |
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How to decrease scatter in fluoroscopy |
Collimate
Pros: decrease KAP Cons: smaller FOV |
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How increase geometric magnification in fluoroscopy |
Increase SID by pullling detector away from patient
Pros: decrease scatter Cons: 1. decrease resolution by increasing effective focal spot size 2. increase operator dose 3. increase patient dose |
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Dose quantity in fluoroscopy |
Air Kerma (AK) |
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Best way to minimize dose to operator and patient in fluoroscopy |
Minimize the time that the X-ray tube is on |
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0.5 mm of lead decreases operator exposure by... |
99% |
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What happens to KAP and AK with narrower collimation |
Decrease KAP. In II, increase AK. In FPD, AK is unchanged. |
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Why avoid lateral and oblique views when possible |
To minimize dose.
The shortest path through the patient results in the least patient-related attenuation which lets AED keep mA low. |
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Ways to minimize dose in fluoroscopy |
1. Shorter time 2. Increase distance, between staff and source, between patient and source 3. Thicker shielding 4. Narrower collimation 5. Avoid lateral and oblique views when possible 6. Avoid magnification in II 7. Use pulse mode |
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ALARA stands for... |
As Low As Reasonably Achievable |
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Upper limit of leakage radiation from the X-ray tube housing ... |
1 mGy/h at a distance of 1 meter |
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A Joint Commission (JC) sentinel event is declared if unintended cumulative dose is ... |
15 Gy to a single field |
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Maximum entrance air kerma rate in nondiagnostic fluoroscopy allowed by FDA is ... |
100 mGy/min |
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Maximum entrance air kerma rate in DSA allowed by FDA is ... |
No limit |
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Air Kerma |
Amount of energy per mass of air (gray = J/kg) |
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At 1 m from the patient, dose to an unshielded operator is ... |
1/1000 of dose to the patient |
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Fluoroscopy dose reporting required by FDA |
Air Kerma Rate (mGy/min) Cumulative Air Kerma (CAK) |
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Ways to minimize dose in fluoroscopy |
1. Shorter time 2. Increase distance, between staff and source, between patient and source 3. Thicker shielding 4. Narrower collimation 5. Avoid lateral and oblique views when possible 6. Avoid magnification in II 7. Use pulse mode 8. Fluoroscopy positioning (minimize distance between patient and detector, between source and operator) |
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AK calculated exactly at the skin surface |
Entrance skin kerma (ESK) |
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X-ray energy dissipated per kg of flesh |
Entrance skin dose (ESD) |
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Maximum entrance skin dose (ESK) |
Peak skin dose (PSD) |
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The deterministic effects like epilation and desquamation are related to what dose unit in fluoroscopy |
Air Kerma (Gy) |
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Stochastic risk (cancer) is estimated by which dose unit in fluoroscopy |
Kerma Area Product (KAP) (Gy-cm^2) |
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What is KAP |
Kerma Area Product, or Dose Area Product = AK (Gy) x Area of exposed field (cm^2) |
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DCC x KAP = ? Where DCC is a dose conversion coefficient related to the tissue irradiated |
Effective dose
Relates to cancer risk |
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Artifact, in which image intensifier curvature causes decreased brightness at image periphery |
Vignetting artifact |
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Artifact, in which image intensifier curvature warps the image as if it's wrapped around a pincushion |
Pincushion artifact |
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Artifact, in which external magnetic field warps the fluoroscopy image, only in image intensifier |
S distortion artifact |
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Artifact, in which light emitted by the output phosphor in a TV display is reflected by the glass window, decreasing image contrast especially in the patient's tissue near borders with air, only in image intensifier |
Veiling glare (or flare) artifact |
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In direct and indirect FPD, photosensitive components (photodiode in indirect, electrode contact in direct) + thin film transistor = ? |
Detector element |
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In indirect and direct FPD, % of area in detector element that is the photosensitive component is called ... |
Fill factor |
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Binning of detector elements causes ... |
Higher signal-to-noise ratio but lower spatial resolution |
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Components of indirect FDP |
CsI scintillators, converts x-ray to light -> detector element (photodiodes converts light to current + thin film transistors) |
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Components of direct FDP |
Amorphous selenium -> thin film transistors |
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Components of image intensifier |
Input screen (CsI phosphor converts x-ray to light + photocathode converts light to electrons) -> electron vacuum tube -> output screen (phosphor converts electron to light) -> glass window -> aperture -> lens + CCD camera
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Image intensifier increases signal by |
1. Flux gain (via electron acceleration) 2. Magnification gain (via focusing electron beam)
Brightness gain = flux gain x magnification gain |
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Detector quantum efficiency (DQE) |
The efficiency of converting x-ray to output signal |
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DQE of FPD compared to screen film |
DQE of FPD >> DQE of screen film |
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What is the dose change with electronic magnification using FPD and II? |
FPD: KAP decreases due to decreased area, dose unchanged II: dose increases due to ABC |
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What is the dose change with geometric magnification using FPD and II? |
For both, dose increases due to ABC |
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Spatial resolution is limited in II by |
TV display |
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Spatial resolution is limited in FPD by |
Detector |
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The number of detector elements needed for 1 line pair |
2 |
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Resolution in line pairs = |
1/(2 x pitch) |
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Technique change needed to decrease quantum mottle |
Increase kVp (which decreases contrast), increase mA |
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To trick ABC to increase dose in II, need to change ___ |
Decrease aperture.
(New dose)/(old dose) = (new f)^2/(old f)^2, where f quantifies the aperture
Bigger f = smaller aperture |
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Is RAO or LAO preferred for femoral run? |
RAO |
