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26 Cards in this Set
- Front
- Back
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________________ is the reduction of the intensity of the x-ray beam as it passes through the Pt's tissues
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Attenuation
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In what 2 ways does attenuation typically happen?
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absorption
scatter |
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As tissue thickness increases the number of photons that pass all the way through _________________.
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decreases
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The attenuation of an x-ray beam is highly dependent upon the _________________.
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energy of the x-ray photons
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When referring to x-ray beams, what does monochromatic mean?
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all of the photons have the same energy
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Lower energy photons attenuate ________________ than high energy photons.
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more easily
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When an x-ray beam passes through the patient, the _________________ is reduced while the _________________ of the photons is increased
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number of photons
mean energy |
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As lower energy photons get attenuated, the remainder of the beam is said to have become "_________________"
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harder
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What does HU stand for?
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Hounsfield Units
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What is the HU for water?
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0
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What is the hounsfield unit for air?
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-1000
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What is the HU for fat?
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-80
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What is the HU for most soft tissue?
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30-80
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A HU measurement above 100 units generally indicates the presence of _________________.
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calcification
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Hounsfield invented the first clinically useful CT scanner for brain imaging in _________________.
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1967
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On the Hounsfield scale, the higher the number, or more dense the object, typically means the _____________ the shade of gray
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lighter
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The CT number or HU unit is calculated by _________________.
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the filtered back projection
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The _________________ is the tube current. The parameter mAs is the product of _________________ and the rotation time.
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mA
mA |
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_________________ the mAs decreases the appearance of image noise, at the expense of patient dose.
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Increasing
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The mAs does not affect the _________________ or _________________.
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image contrast
spatial resolution |
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The rotation time is the time required for the tube and detectors to rotate _________________.
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360°
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The limit to keeping scan times short is the ______________ associated with high mA and a short scan time.
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ability of the tube to handle the extreme heating
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kV is the ______________.
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Tube Voltage
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The energy of the electrons for the electron beam is determined by the ______________.
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voltage
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Increasing kVp increases the energy of the photons. This increases their ______________ the patient.
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ability to penetrate
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The kVp is the parameter that controls the ______________ in the CT image.
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contrast
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