[Intl_DxMedPhys] CT Artifact Evaluation Absent Large Poly Disk - air scan

[Enoch Tung]

Hi list,

Does anyone have examples of artifacts that can be observed in performing air scans for the comprehensive SFOV in the absence of a large uniformity phantom?

I'm referencing the alternative method as suggested by the ACR CT QC Manual (https://urldefense.com/v3/__https://accreditationsupport.acr.org/support/solutions/articles/11000056188-quality-control-ct__;!!KGKeukY!3KbO6gInQC3SR7tG9SEKK3iZXBiuu923FIglEsIqZhheg0E4CNfDAvmUPFcfa0EZrqhrGaSxCsmvRxndI7EXmrBEzhLY1BVtjgPGB6gfjbtB$ ).  The exact instruction are:
Artifact Evaluation Absent Large Poly Disk
Should your facility not have a large poly disk available to perform artifact evaluation on the scan field of view (SFOV) as required, this approach provides a method to qualitatively evaluate the level of non-uniformities in the SFOV outside of the phantom FOV.

  1.  Taking care to center the phantom to the SFOV, perform the usual daily QC phantom scan using the smallest T allowed by the maximum NxT
  2.  Perform artifact evaluation using ACR CT QC manual<https://urldefense.com/v3/__https://www.acr.org/Clinical-Resources/Clinical-Tools-and-Reference/Specialties/Medical-Physics-Resources__;!!KGKeukY!3KbO6gInQC3SR7tG9SEKK3iZXBiuu923FIglEsIqZhheg0E4CNfDAvmUPFcfa0EZrqhrGaSxCsmvRxndI7EXmrBEzhLY1BVtjgPGBznCHjL2$ > method to determine if there are potentially clinically significant artifacts over the phantom FOV (if artifacts are seen, use clinical image significance evaluation method below)
  3.  After verifying the absence of such artifacts over the phantom FOV, at least monthly perform an air scan using a modified version of the daily QC protocol that uses the largest clinical SFOV available
  4.  To evaluate the L SFOV images for potentially clinically significant artifacts outside of the phantom FOV, set a window width of approximately 100 HU and a window level of approximately -1000 HU
  5.  Draw a 20 cm diameter ROI in the center of the image
  6.  Review all images qualitatively comparing the level of visualized non-uniformities outside the ROI to that inside the ROI
  7.  Consider a similar level of non-uniformities to be acceptable
  8.  If there is an increased level of non-uniformities seen outside the ROI, review clinical scans to determine if artifacts are clinically significant
  9.  Clinical scans reviewed should be of the large scan field of view using all typical reconstruction window and level settings

I'm interested how non-uniformities will show as neither myself nor our technologist have been able to observe such.

Thanks,
Enoch


Enoch Tung | Medical Physicist (Diagnostic and Health), Radiation Safety Officer, Laser Safety Officer
Imaging Services | MultiCare
Office: 253.301.5027 | Cell: 617.543.5488 | Fax: 253.301.5010 | Email: enoch.tung at multicare.org<mailto:etung at multicare.org>
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