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37 Cards in this Set
- Front
- Back
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What does one eV equal to
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1.6 x 10 e -19 Joules
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What is the charge of an electron?
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1. 6 e -19 C
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What is the unit of electric current?
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Ampere = charge / unit of time = coulomb / sec
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What is power?
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Rate of performing work
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What is the unit of power?
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Watt = joules / sec = volts x ampere = current x voltage
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What's the exposure time for a typical chest x-ray?
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10 mS
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What's the unit of frequency and what does it mean?
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Hertz = cycles per second
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Velocity of photons is equal to ------ x ------
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wavelength x frequency
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What is the usual target in the x-ray tube?
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Tungsten
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What is the usual target in the mammography unit?
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Molybdinium or Rhodium
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What is Brehmsstralung radiation?
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Fraction of the electron kinetic energy is emitted as an x-ray photon, and the electron travels through the target atom, and comes out as an electron of lesser kinetic energy.
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How does Brehnmsstralung radiation vary with increasing target atomic number?
How does Brehmsstralung radiation vary with increasing Voltage |
Brehmsstralung radiation increases with increasing target atomic number and accelerating voltage
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When is characteristic radiation produced?
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When incoming electrons eject atomic electrons, usually occurs as k shell electrons are ejected, incident electron energy has to be greater than the k shell electron energy.
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What three particles are ejected from characteristic radiation?
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K shell electron
Possibly an electron with lower energy - Auger electron x- ray photon |
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What is the characteristic photon energy from tungsten?
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58 - 67 keV
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What is the characteristic energy from Molybdinium?
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17 to 19 keV
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Approximately what percent do the K shell characteristic energy contribute to the x-ray spectrum at 100 KeV?
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10%
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How is x-ray beam intensity related to the exposure time and tube current?
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Directly to ms of exsposure and mA of tube current
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What is the x-ray beam intensity measured in?
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Air kerma
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Does increasing mAs change the energy of x-ray spectrum?
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No, it does not change the energy spectrum
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How is the x-ray beam intensity related to voltage output?
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intensity : kV (squared)
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In radiographic imaging, if KV is increased by 10 - 15% or increased by 10 kV, what effect does it have on air kerma (x-ray intensity) equivalent to?
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Doubling the mAs
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What are x-ray windows in mammography made of and why?
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Berryllium, which absorbs less of lower energy x-rays
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What is line focus principle
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Permits larger heat loading while minimizing the size of the focal spot (due to anode angle, the thickness of the focal spot of the x-rays is less than the thickness of the electrons).
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What is the anode angle and why is it important?
What are the typical anode angle ranges? |
Anode angle is the angle between incident electrons and the anode target. It determines the focal spot size.
7 - 20 degrees |
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Why do focal spots need to be small?
Why do focal spots need to be large? |
Small - to produce sharper images
Large - to permit heat loading, when short exposure time is important |
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What is the nominal focal spot for:
Magnification mammography Mammography Flouroscopy Radiographs |
Mag mammo: 0.1 mm
Mammo: 0.3 mm Fluoroscopy: 0.6 mm Radiographs: 1.2 mm |
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What does an operator choose in automatic exposure mode and what is controlled by the generator circuit?
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Operator chooses the KeV whereas generator circuit controls the tube current and exposure time
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What is the typical tube current for?
Radiographs fluoroscopy |
radiographs: 100 - 1000 mA
Fluorscopy: 1 - 5 mA |
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What is the typical voltage for radiographs and fluoroscopy?
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70 - 90 KV
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What is the typical voltage for abdominal radiograph?
What is the typical voltage for chest radiograph? CT? |
80 kV
140 kV 120 kV |
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What does energy in Joules equal which is deposited on an anode?
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V x I x t Joules = W x t Joules = Power x time = voltage x current x time
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What is tube rating?
What's typical tube rating of x-ray tube with small focal spot? What's typical tube rating of x-ray tube with large focal spot? Tube rating of fluoroscopy? |
Maximum allowable power (kW) at an exposure time of 0.1 sec.
Small focal spot x-ray tube rating: 25 kW Large focal spot x-ray tube rating: 100 kW fluoroscopy tube rating 100 - 500 kW |
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What is the maximum allowable amount for leakage radiation?
What is leakage radiation |
1 mGy / hour at a distance of 1 m from the x-ray tube?
Leakage radiation is the radiation that escapes the x-ray tube housing. |
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What's the typical anode angle for radiography?
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7 - 20 degrees
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What is the binding energy of K shell electrons in tungsten?
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70 kEV , an electron with energy of 65 keV won't be able to knock out any electrons at all.
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What is the typical x-ray tube filament current?
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4 A or 4000 mA (careful with the units)
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