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CT > QC > Flashcards

QC Flashcards

1
Q

What is QC?

A

Quality Control

Testing technical performance of imaging equipment

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2
Q

What is QA?

A

Quality Assurance

Upholds accuracy, consistency, efficiency, and safety of healthcare delivery

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3
Q

Which QC tests are performed daily?

A
  1. Tube warm-up
  2. Air calibration
  3. Visual/environmental inspection
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4
Q

Which QC tests are performed weekly?

A
  1. CT number accuracy of water
  2. Noise
  3. Uniformity
  4. CT number accuracy of materials
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5
Q

Which QC tests are performed monthly?

A
  1. Linearity of CT numbers
  2. Image slice thickness
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6
Q

Which QC tests are performed quarterly?

A
  1. Spatial resolution
  2. Safety light
  3. Interlock
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7
Q

What is QC testing for tube warmup?

A
  1. Lock the scan room door
  2. Follow manufacturer warmup procedure
  3. Repeat if the scanner is left unused for an extended period of time
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8
Q

What is QC testing for air calibration?

A
  1. Lock the scan room door
  2. Ensure nothing is left in the bore of the gantry
  3. Follow manufacturer procedure
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9
Q

What is the linear attenuation coefficient?

A

Measure of the quantity of radiation absorbed per cm of material

Represented by u

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10
Q

What is QC testing for CT number accuracy of water?

A
  1. Scan the water phantom with a standard axial head protocol and a standard axial body protocol
  2. Place a large ROI on the image and record the mean CT number

The number must be 0 (+ or - 4 HU)

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11
Q

What is QC testing for CT image noise?

A
  1. Scan a WATER PHANTOM with a typical axial head protocol and axial body protocol
  2. Place an ROI of 40% of the diameter of the uniform phantom image
  3. Record the CT number standard deviation

Should not deviate more than 10% or 0.2 HU

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12
Q

What is QC testing for CT number uniformity?

A
  1. Scan a WATER PHANTOM with an axial head and body protocol
  2. Place 5 ROI around the image (10% of the diameter)
  3. Calculate the biggest difference between the central ROI and the side

Uniformity should not be greater than 2 HU in difference

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13
Q

What is QC testing for CT number accuracy of materials?

A
  1. Scan the PHANTOM WITH RANDOM MATERIALS with clinically used volatile settings
  2. Place a large ROI over each material and record the mean CT number
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14
Q

What is QC testing for CT number linearity?

A

Compare the CT number against the LAC on a graph

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15
Q

What is QC testing for image slice thickness testing?

A

Use a slice thickness line phantom and record how many lines you can distinguish

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16
Q

What can influence spatial resolution?

A
  1. Scanner design
  2. Image recon
  3. Sampling
  4. Image display capabilities
17
Q

What tools are used for evaluating spatial resolution?

A
  1. Wire test tool
  2. Bar pattern test tool
18
Q

What 3 procedures are done to evaluate spatial resolution?

A
  1. Modulation transfer function
  2. Quantitative method with bar pattern
  3. Visual assessment with bar pattern
19
Q

What are the limits for spatial resolution testing?

A

1 mm or 5 line pairs per cm

20
Q

What is a beam hardening artefact?

A

Dark bands or streaks with a low CT number in the centre (aka cupping artefact)

Causes: attenuation of low energy photons

21
Q

What is a capping artefact?

A

Brighter in middle of image

Cause: Image processing that overcompensates for beam hardening

22
Q

What is the partial volume effect/artefact?

A

Dense object near the edge of a scan FOV

Cause: Small structures that are partially missed as they make up only a bit of the voxel

Correct: overlapping slices

23
Q

What is aliasing?

A

Fine and evenly spaced lines radiating from a dense structure

Cause: pitch is too large

Correct: increase rotation time or reduce pitch

24
Q

What is an edge gradient artefact?

A

Streak artefact or light or dark shading

Cause: funky shaped and highly different density objects next to each other

Correct: thinner slices or lower HU contrast

25
Q

What is motion artefact?

A

Shading or streaks or ghosting

Cause: moving during scan causing changes in attenuation of materials

26
Q

What is a metal artefact?

A

Streaking

Cause: metal objects being too high density

27
Q

What are out of field artefacts?

A

Streaming

Cause: objects outside of the scan that harden the beam which cannot be corrected with algorithms

28
Q

What is a ring artefact?

A

Circles at isocentre

Cause: detector out of calibration

29
Q

What is tube arcing?

A

A mechanical error of the tube within the gantry

Correct: remove gas from tube or install a new one

30
Q

What is a windmill artefact?

A

Streaks or bright and dark near a dense structure that looks like a windmill

Cause: cone shaped beam

Correct: fewer detector rows or fix pitch

31
Q

What is a stair step artefact?

A

Edges of structures that look like stairs

Cause: wide slices used with MPR

correct: use isocentred voxels

CT (7 decks)

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