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64 Cards in this Set
- Front
- Back
What is bremsstrahlung radiation
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Bremsstrahlung (braking) x-rays are produced when incident electrons interact with
nuclear electric fields, which slow them down (brake) and change their direction. |
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What does bremsstralung radiation look like
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Schematic of a bremstruhlung radiation
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What does the bremsstrahlung spectrum look like
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How is the energy of an xray determined from the bremsstrahlung radiation
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The closer the electron passes to the nucleus, the greater the interaction of the inci-
dent electron with the nucleus, and the higher the energy of the resulting x-ray. |
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How does the realease of X-rays from characteristic X-ray work
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FIG. 2.3. Characteristic radiation is produced when an incoming electron (1) interacts with an
inner-shell electron (2) and both are ejected (3). When one of the outer-shell electrons moves to fill the inner-shell vacancy, the excess energy is emitted as characteristic radiation (4). Sometimes the excess energy is emitted as an Auger electron (5) rather than as characteristic radiation. |
FIG. 2.3. Characteristic radiation is produced when an incoming electron (1) interacts with an
inner-shell electron (2) and both are ejected (3). When one of the outer-shell electrons moves to fill the inner-shell vacancy, the excess energy is emitted as characteristic radiation (4). Sometimes the excess energy is emitted as an Auger electron (5) rather than as characteristic radiation. |
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What are characteristic X-rays
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What does x-ray intensity refer to
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Intensity refers to the quantity or number of x-ray photons produced.
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Name 3 factors that affect x-ray intensity
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-Intensity is affected by the generator type, beam filtration, and distance from the
beam (inverse square law). |
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What percent of X-ray intensity is from characteristic radiation
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10%
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What is X-ray output proportional to
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X-ray output is directly proportional to the current (mA), and to exposure time (sec-onds).
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What is tube current and exposure time known as
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Th e product of the tube current (mA) and exposure time (seconds) is known as the
mAs, and the x-ray tube output is proportional to the mAs. |
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What are 2 ways of doubling the mAs
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-Doubling the current at constant exposure time has the same effect as doubling the
exposure time at constant tube current. |
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How does doubling the mAs effect the energy spectrum
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Doubling the mAs doubles the number of x-rays emitted but does not change the
energy spectrum |
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What happens to the quantity of x-rays produced when the kVp is increased
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The quantity of x-rays produced can also be increased by increasing the kVp, but this also changes the quality or shape of the x-ray spectrum
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Does increasing kVp increase the quantity
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yes and will increase the energy
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What is intensity synonomous with
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quantity
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What is increased by increasing the kVp
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intensity (quantity) of x-rays
energy (increased quality) |
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What is increased with increasing mAs
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quantity (intensity)
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What are 2 ways to increase the quantity (intensity)
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increase mAs or kVp
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Whe n the mA is increased and the
peak voltage and exposure time are constant, the intensity of the x-rays increases but the en-ergy distribution stays the same |
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Whe n peak voltage is increased and the milliamperes and
exposure time are constant, the intensity, peak, and mean energy of the x-rays increase |
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What is the tube potential proportional to
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Th e quantity (intensity) of x-ray production is approximately proportional to the
square of the tube potential. |
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What is meant by polychromatic X-rays
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X-ray beams in diagnostic radiology are polychromatic and consist of a range of
photon energies |
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What does the term quality X-rays mean
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Quality refers to effective photon energy of the x-rays produced, and relates to their
ability to penetrate the patient. |
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How is the quality of an X-ray beam obtained
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Th e quality of an x-ray beam is obtained from the effective x-ray energy of the x-ray spectrum
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What is the range of effective photon energy
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Th e effective photon energy is taken to be between one third and one half of the
maximum photon energy. |
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What does increasing the kVp do
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Increasing the peak voltage (kVp) increases the x-ray tube output, peak energy,
and mean energy of the beam. |
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What is kVp
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peak voltage
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What does increasing beam quality do to penetrating power
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-Increasing beam quality increases x-ray beam penetrating power because the av-erage photon energy is higher.
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What are the relative effects on film density between kVp and mAs
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A rule of thumb is that increasing the peak voltage by 15% has the same effect on
film density as that of doubling the mAs. |
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What does reducing the voltage waveform ripple do to the average photon energy
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Reducing the voltage waveform ripple increases average photon energy and thus x-ray beam quality
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What is ripple
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A constant high voltage is desired across the x-ray tube for x-ray production, but in
practice, there is some variation in the voltage, which is called ripple. |
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What does voltage ripple look like
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What does a X-ray tube look like
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What is this image demonstrating
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The magnified view of the target illustrates the line focus principle, whereby
the focal spot size (F) is smaller than the electron beam (L) because of the anode angle. |
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What is the electron source of the x-ray tube
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X-ray tubes contain a negatively charged cathode containing the filament that
serves as an electron source. |
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Where are the X-rays produced in the X-ray tube
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Th e anode is positively charged and includes the target where x-rays are produced.
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Why is the x-ray tube in an evacuated envelope
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Th e anode and cathode are contained in an evacuated envelope to prevent the elec-trons from colliding with gas molecules.
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What is the function of the X-ray tube housing
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Th e envelope is contained in a tube housing that protects and insulates the tube and
provides shielding to prevent leakage radiation. |
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What part of the tube housing helps in cooling
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Th e housing contains an oil bath to provide electrical insulation and help cool the
tube. |
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What are anodes made of
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tungsten
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Do some anodes have 2 focal spot sizes
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yes
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What is a focusing cap
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A focusing cup or cathode block surrounds the filament and helps direct the elec-trons toward the target.
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What does a focusing cap look like
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What does expulsion of electrons from the cathode look like
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What causes electrons to be released by the cathode filament
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Electrons that flow through electrical circuits cannot generally escape from the conductor material and move into free space. They can, however, if they are given sufficient energy. In a process known as thermionic emission, thermal energy (or heat) is used to expel the electrons from the cathode. The filament of the cathode is heated in the same way as a light bulb filament by passing a current through it. This heating current is not the same as the current flowing through the x-ray tube (the MA) that produces the x-radiation. During tube operation, the cathode is heated to a glowing temperature, and the heat energy expels some of the electrons from the cathode.
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What causes the temperature to increase in the cathode
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Th e high resistance in the filament causes temperature to rise (>2200°C), resulting
in the thermionic emission of electrons. |
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What is the negative cloud surrounding the cathode called
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Electrons emitted from a heated filament form a negative cloud around the filament
called a space charge, which prevents further emission of electrons. |
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What is the tube current
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Electrons emitted from a heated filament form a negative cloud around the filament
called a space charge, which prevents further emission of electrons. |
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What is the range of tube current
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Tub e current is in the range of 1 to 1,000 mA.
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What occurs to the cathode at low peak voltage
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A t low peak voltage, the potential is insufficient to cause all the electrons to be pulled
away from the filament, and a residual space charge remains (space charge limited operation). |
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What occurs a saturation voltage
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A t the saturation voltage, all electrons are immediately pulled away from the fil-ament, and the tube current is maximized.
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What is the high voltage created by the generator used for
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to accelarate the electrons as they move from the cathode to the anode
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What is the typical voltage across the cathode filament itself (different then previous)
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Typical voltages across the x-ray tube filament are 10 V, and currents through
the cathode filament are 4 A. |
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How much power is dissipated by the cathode filament
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Th e power dissipated from the filament (I x V) is typically 40 W
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What does the x-ray tube and generator working in tandem look like
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What do characteristic lines look like on an X-ray spectra
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If the kVp is low do we see characteristic lines
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no
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If the kVp is low do we see characteristic lines
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no
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What is the voltage waveform chart
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How is peak voltage demonstrated
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not that more x-rays are produced at peak voltage
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In an X-ray tube how is Voltage and kVp and keV related
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In the x-ray tube, electrons are generated at the filament end of the x-ray tube by thermionic emission (boiling of electrons from the filament). They are then given kinetic energy by applying a high voltage between the filament and the target. If a voltage of 100,000 volts (100 kVp) is applied to the x-ray tube, the electrons will strike the target producing x-rays with energies from 0 to 100 keV. Note: kVp is the voltage applied to the x-ray tube and keV is the energy of the x-ray. The low energy x-rays can not get out of the x-ray tube so the actual spectrum of x-rays range from about 10 keV to 100 keV. The higher the x-ray energy, the higher its ability to penetrate tissue. As the kVp increase so does the intensity of the x-ray beam, i.e. more x-rays of all energies are generated. (ignore picture)
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