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CT & MRI > CT Principle 3 > Flashcards

CT Principle 3 Flashcards

1
Q

CT based artifact types

A
  1. patient
  2. physics principles
  3. hardware
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2
Q

Examples of patient based artifacts

A
  1. metallic implants
  2. motion
  3. MPR
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3
Q

Examples of hardware based artifacts

A
  1. ring artifact
  2. cone beam artifact
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4
Q

Examples of physic principle based artifacts

A
  1. beam hardening
  2. partial volume
  3. photon starvation
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5
Q

what artifacts come from beam hardening

A

streak & cupping artifacts

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6
Q

beam hardening effect

A

when lower energy photons are absorbed faster than higher energy photons, resulting in a high mean energy and harder beam

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7
Q

how does cupping artifact occur

A

beam hardens more than expected causing the attenuation profile to differ from ideal profile

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8
Q

how to fix cupping artifact

A
  1. higher kVp
  2. reconstruction algorithm
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9
Q

how does streaking artifacts occur

A

dark streaks appear between 1/2 very dense objects

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10
Q

how to fix streaking artifact

A
  1. metal artifact algorithm
  2. higher kVp
  3. remove artifact
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11
Q

what causes metal streak artifacts

A
  1. photon starvation
  2. beam hardening
  3. scatter
  4. poison / white noise
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12
Q

how do metal streak artifacts appear

A

starburst artifact where bright streaks originate from 1 point into nearby structures

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13
Q

how does Poisson noise occur

A

statistical error of low photon count; random thin streaks along direction of greatest attenuation

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14
Q

how to fix metal artifact from dense dental filling

A

metal algorithm reconstruction

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15
Q

how do contrast density artifacts occur

A

non-uniform distribution of contrast agents leading to streaks in tissue enhancement

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16
Q

how to fix contrast density artifact

A

optimize contrast injection protocol for even distribution with saline flushes to clear contrast from vessels

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17
Q

how do beam hardening artifacts occur

A

x-ray hardens from lower energy x-rays absorbed by dense tissues

18
Q

how to fix beam hardening artifact

A
  1. advanced reconstruction algorithms
  2. adjust energy settings
  3. avoid high density objects in scanning area
19
Q

how do metal implant artifacts occur

A

metal implant/object absorbed x-rays leading to streaks and shades

20
Q

how to fix metal implant artifact

A
  1. adjust scan parameters
  2. metal artifact reduction algorithms
  3. alternative modalities
21
Q

partial volume artifact AKA ___

A

streak-like artifacts

22
Q

where does partial volume effect occur most frequently at

A

bony structures at skull base & petrous bone region

23
Q

how does partial volume artifact occur

A

when very dense structures are partially included in the slice leading to high contrast errors

24
Q

how does photon starvation occur

A

more than expected x-ray beams are absorbed in 1 projection leading to less signal for detectors

25
Q

how do photon starvation artifacts appear

A

streak artifacts in widest part of object scanned

26
Q

what causes photon starvation artifacts

A
  1. poor scan technique
  2. reconstruction algorithm
27
Q

how to fix photon starvation artifacts

A
  1. IR
  2. patient positioning
  3. hands up
  4. increased dose
  5. thicker slices
28
Q

how does patient motion artifact occur

A

voluntary / involuntary movement which disrupts spatial alignment of acquired data

29
Q

how to fix patient motion artifact

A
  1. remain still
  2. sedation / gating technique
  3. faster scan technique
30
Q

what causes ring artifacts

A
  1. rotate-rotate type
  2. mis-calibrated DELs
31
Q

how to fix ring artifacts

A

recalibrate / replace DELs

32
Q

what causes cone beam artifact

A
  1. larger cone angles
  2. thinner slices
  3. object seen at diff detectors at diff angles
33
Q

when are cone beam artifacts the most prominent

A
  1. larger cone beam angle
  2. thinner slices
  3. 16+ slice scanner
34
Q

how to fix cone beam artifact

A
  1. manufacturer reconstruction algorithm
  2. position ROI in isocenter
35
Q

how are cone beam artifacts similar to partial volume effect

A

objects are off-center and more pronounced at image edges

36
Q

LCD

A

low contrast detectability

37
Q

what influences LCD performance

A

mAs, kVp, slice thickness, pitch, beam collimation, processing & visualization

38
Q

what does QC involve

A

monitoring, evaluation, maintenance

39
Q

what is HU

A

Hounsfield Units; standardized units to represent tissue radiodensity

40
Q

what is the HU value for air calibration

41
Q

what does weekly QC CT phantom testing involve

A
  1. CT number accuracy
  2. low contrast resolution
  3. distance accuracy
  4. high contrast resolution

CT & MRI (12 decks)

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