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13 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What is the advantage of CT over conventional radiography?
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It has extremely good low contrast resolution which enables detection of very small changes in tissue type and gives accurate diagnostic information about the distribution of structures inside the body
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X-rays are ______________ where most are produced from ______________ reactions
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X-rays are polychromatic where most are produced from Bremsstrahlung reactions
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What is the CT scanner actually measuring?
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Linear attenuation coefficient, u, between the detectors
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How is the CT number calculated?
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CT# = u tissue - u water/u water x 1000
What is the CT # for water, air, bone? |
water = 0
air = -1000 bone = 1000 |
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What is helical scanning?
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continuous gantry rotation with table motion
What is the advantage of this?(3) |
no waiting between slices to move table
better Z interpolation scan larger volumes in same time |
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How fast can present day multi-slice scanners do a single slice?
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0.5 Sec
How much faster is this than an older single slice scanner? |
25X
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What is pitch and how is it calculated?
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table movement per width of the collimated scan beam
Pitch = table movement per rotation/(# of slices per rotation)(slice width) What unit are the values in? |
mm
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If the area scanned during 1 rotation of the tube is 10 mm, how much table movement will give you a pitch of 1?
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10mm
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A pt is scanned with the following parameters: 4 slices per rotation, 2 mm scan width, table speed per rotation-10 mm. What is the pitch?
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Pitch = (10mm)/(4mm)(2mm) = 1.25
Why do we want to keep the pitch around 1? |
Lower than 1 increases pt dose while too much above 1 degrades the image
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What is a common cause of a streaking artifact?
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any material harder than bone
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In PET/CT what is used for attenuation correction?
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Linear attenuation correction from CT, faster and noiseless compared to using old method of external sources
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What reconstructive method is used in PET/CT and why?
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Interative as filtered backprojection methods do not work well with PET/CT
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What are the 2 main parameters used to alter the energy and quantity of x-rays?
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mAs and kVp
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