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Quality Control

Quality Control. Bushong Chapter 10. QC. The CT number of water should be 0 Scan a water phantom, select a large enough region of interest (ROI), the average CT number should be within +/- 3

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Quality Control

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  1. Quality Control Bushong Chapter 10

  2. QC • The CT number of water should be 0 • Scan a water phantom, select a large enough region of interest (ROI), the average CT number should be within +/- 3 • Scan an empty gantry aperture, select a large ROI, the average CT number for air should be within -1000 +/- 5

  3. QC • CT noise is evaluated by scanning a water bath. The standard deviation should not exceed +/- 10 • Spatial resolution is evaluated by scanning any number of phantoms-hole patters, or line pair patterns • Spatial resolution should be at least equal to the manufacturers specifications

  4. QC • Most CT imagers can image .5mm (10 lp/cm), some as good as .2mm (20 lp/cm) in a high resolution mode • Contrast resolution is evaluated with either a phantom, thick or thin, various hole sizes filled with water, or various hole sizes of various depth for partial volume effects • Contrast resolution should be at least 5mm at 5% contrast

  5. QC • Distance measurement accuracy is evaluated by imaging the American Association of Physicists in Medicine (AAPM) test object that has pins separated by 10mm • The electronic distance calipers must be accurate to within +/- 5%

  6. QC • The video monitor should be evaluated for distortion by pressing a clear plastic rules against the screen image of the 10mm pin test object to ensure the same 5% accuracy • Scan plane localization, usually a laser light localizer, should be accurate to within 1mm. A number of test devices are available

  7. QC • Patient couch indexing can be checked with cardboard wrapped film or marks on the couch and rail. The limit of error is 1% • Slice width is usually evaluated with a ramp test object and should be within 50% for nominal widths of 5mm and above and 100% for thinner slices

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