QC Flashcards
What is QC?
Quality Control
Testing technical performance of imaging equipment
What is QA?
Quality Assurance
Upholds accuracy, consistency, efficiency, and safety of healthcare delivery
Which QC tests are performed daily?
- Tube warm-up
- Air calibration
- Visual/environmental inspection
Which QC tests are performed weekly?
- CT number accuracy of water
- Noise
- Uniformity
- CT number accuracy of materials
Which QC tests are performed monthly?
- Linearity of CT numbers
- Image slice thickness
Which QC tests are performed quarterly?
- Spatial resolution
- Safety light
- Interlock
What is QC testing for tube warmup?
- Lock the scan room door
- Follow manufacturer warmup procedure
- Repeat if the scanner is left unused for an extended period of time
What is QC testing for air calibration?
- Lock the scan room door
- Ensure nothing is left in the bore of the gantry
- Follow manufacturer procedure
What is the linear attenuation coefficient?
Measure of the quantity of radiation absorbed per cm of material
Represented by u
What is QC testing for CT number accuracy of water?
- Scan the water phantom with a standard axial head protocol and a standard axial body protocol
- Place a large ROI on the image and record the mean CT number
The number must be 0 (+ or - 4 HU)
What is QC testing for CT image noise?
- Scan a WATER PHANTOM with a typical axial head protocol and axial body protocol
- Place an ROI of 40% of the diameter of the uniform phantom image
- Record the CT number standard deviation
Should not deviate more than 10% or 0.2 HU
What is QC testing for CT number uniformity?
- Scan a WATER PHANTOM with an axial head and body protocol
- Place 5 ROI around the image (10% of the diameter)
- Calculate the biggest difference between the central ROI and the side
Uniformity should not be greater than 2 HU in difference
What is QC testing for CT number accuracy of materials?
- Scan the PHANTOM WITH RANDOM MATERIALS with clinically used volatile settings
- Place a large ROI over each material and record the mean CT number
What is QC testing for CT number linearity?
Compare the CT number against the LAC on a graph
What is QC testing for image slice thickness testing?
Use a slice thickness line phantom and record how many lines you can distinguish
What can influence spatial resolution?
- Scanner design
- Image recon
- Sampling
- Image display capabilities
What tools are used for evaluating spatial resolution?
- Wire test tool
- Bar pattern test tool
What 3 procedures are done to evaluate spatial resolution?
- Modulation transfer function
- Quantitative method with bar pattern
- Visual assessment with bar pattern
What are the limits for spatial resolution testing?
1 mm or 5 line pairs per cm
What is a beam hardening artefact?
Dark bands or streaks with a low CT number in the centre (aka cupping artefact)
Causes: attenuation of low energy photons
What is a capping artefact?
Brighter in middle of image
Cause: Image processing that overcompensates for beam hardening
What is the partial volume effect/artefact?
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
What is aliasing?
Fine and evenly spaced lines radiating from a dense structure
Cause: pitch is too large
Correct: increase rotation time or reduce pitch
What is an edge gradient artefact?
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
