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

Tue Aug 19 16:14:43 EDT 2025

Thanks for those that chimed in, especially Doug Pfeiffer, who provided these before repair (with artifact) and after filter board replacement (good qualitative uniformity) air scan images.

[Filter board artifact0004.jpeg][Filter board artifact0002.jpeg]

I anticipate that other more distinct ring artifacts from defective detectors, even in air, would be of the flavor we normally see in phantoms.

Always appreciate the expertise and resource of everyone on this list!

Cheers,
Enoch

Advance PTO notice: August 29

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>
Address:  3124 South 19th St. #100, Tacoma, WA 98405
Mailing:  PO Box 5299, 19U-C1-RSO, Tacoma, WA 98415

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From: Ding, Lei <lxd906 at med.miami.edu>
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Subject: RE: [EXTERNAL] Re: [Intl_DxMedPhys] CT Artifact Evaluation Absent Large Poly Disk - air scan

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Hi Enoch,

I wish I had saved pictures, but there was a scanner a few months ago that was having some issues. When the engineers arrived, the first thing they did was perform an air scan to check for artifacts. Of course, we saw rings...

IMHO, an air scan is just as valid for detecting artifacts. The only drawback is that you need to manually adjust the window and level to see the artifacts, but it still provides a lot of useful information.

Thank you,

Lei Ding, MS, DABR, DABMP, DABSNM, MRSE
Medical Physicist
University of Miami Miller School of Medicine
1600 N.W. 10th Avenue, RMSB 1081A
Miami, FL 33136
Direct: (305) 243-<tel:%28305%29%20243-5816>6360/ (305) 243-6369
Cell: 813-743-2373

From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu<mailto:intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu>> On Behalf Of Enoch Tung via Intl_dxmedphys_wd_osu_list
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Subject: [EXTERNAL] Re: [Intl_DxMedPhys] CT Artifact Evaluation Absent Large Poly Disk - air scan

Hi list, Re-circulating this to see if anyone has examples of non-uniformities visible through air scans performed. I don't know if the lack of response was due to this being an uncommonly performed approach, visible artifact manifests
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Hi list,

Re-circulating this to see if anyone has examples of non-uniformities visible through air scans performed.

I don't know if the lack of response was due to this being an uncommonly performed approach, visible artifact manifests rarely, or me choosing the wrong time to ask the question just before the AAPM annual meeting.

I appreciate any insight or help anyone may have.

Thanks,
Enoch

From: Enoch Tung
Sent: Friday, July 25, 2025 12:49 PM
To: intl_dxmedphys_wd_osu_list at lists.osu.edu<mailto:intl_dxmedphys_wd_osu_list at lists.osu.edu>
Subject: CT Artifact Evaluation Absent Large Poly Disk - air scan

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!y3qrGEtjkxMvNAoNIaxAF0vUb-Lapm6jbkDMat1WOJ-rvJpzfE29w5FX3pHIrBJwXUgbfjjpKCZRnJe1GXW1Y8mKygnxYK09JRYD_sV6ENr4$ <https://urldefense.com/v3/__https:/accreditationsupport.acr.org/support/solutions/articles/11000056188-quality-control-ct__;!!KGKeukY!1_cZvcWoFXPo6GIt5QbdTx3q5w7z1viB6JqJitALJLFU0p1VxDrNOh7TkddRDIK5omcY84u7R2grKKZsQRMt7g5JDMLeg0utirfBKQH1W52m$>).  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!1_cZvcWoFXPo6GIt5QbdTx3q5w7z1viB6JqJitALJLFU0p1VxDrNOh7TkddRDIK5omcY84u7R2grKKZsQRMt7g5JDMLeg0utirfBKWAMvXQ2$> 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>
Address:  3124 South 19th St. #100, Tacoma, WA 98405
Mailing:  PO Box 5299, 19U-C1-RSO, Tacoma, WA 98415

The information contained in this e-mail message may be privileged, confidential  and protected from disclosure.   If you are not the intended recipient, any dissemination, distribution or copying is strictly prohibited.  If you think you have received this e-mail message in error, please notify the sender via e-mail.

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