[Intl_DxMedPhys] rotation time artifact

[Chong, Sang hoon (LHMC - Radiology)]

Dear Idris,

0.33s is pretty close to the minimum rotation time of the CT scanner (0.27 s), and your artifact might have been caused by not enough sampling. Is this the first time seeing such an artifact from the particular protocol?

I’d suggest increasing mAs, decreasing pitch, or using a different reconstruction algorithm, and see if that improves the artifact. Or to test, maybe try using a smaller phantom and see if the problem persists. I hope someone else can also chime in to confirm.


Best,

Sang Hoon

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Sang Hoon (Bryan) Chong, Ph.D.

Diagnostic/Nuclear Medicine Medical Physicist

Department of Radiology

41 Mall Road P.O. Box 541 Burlington, MA 01805

T: 781-744-8177 | C: 267-218-5887

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From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces+sanghoon.chong=lahey.org at lists.osu.edu> on behalf of Cuddy-Walsh, Sarah (HC/SC) via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu>
Date: Friday, January 2, 2026 at 10:11 AM
To: Idris Elbakri <idris at canqap.co>, intl_dxmedphys_wd_osu_list at lists.osu.edu <intl_dxmedphys_wd_osu_list at lists.osu.edu>
Subject: [External] Re: [Intl_DxMedPhys] rotation time artifact


Unclassified / Non classifié

I haven’t seen this before but am intrigued. Is the DAP the same for all protocols (i.e. does the dose rate increase as the rotation time decreases?). Have you tried checking the position of the detector/x-ray source in the header for each projection? What is the extent of the rotation (ex. 210 degrees)?

Happy New Year!
Sarah Cuddy-Walsh, Ph.D.

From: Idris Elbakri <idris at canqap.co>
Sent: 2025-12-31 7:27 AM
To: intl_dxmedphys_wd_osu_list at lists.osu.edu
Subject: [Intl_DxMedPhys] rotation time artifact

Dear colleagues, I am curious to see if anyone has encountered a CT artifact that appears when certain rotation times are used. This artifact started appearing a few weeks ago on our head protocol on a Philips Spectral 7500. I investigated a

Dear colleagues,

I am curious to see if anyone has encountered a CT artifact that appears when certain rotation times are used. This artifact started appearing a few weeks ago on our head protocol on a Philips Spectral 7500. I investigated a bit and found that the artifact appears when the rotation times are short (0.33 and 0.4 seconds) and disappears at 0.5 sec or higher. Is the fast rotation inducing some sort of vibration? Nothing in the protocol has changed from a few weeks ago when there was no artifact.

Upon further ingestigation I also think the artifact appears in other protocols, but is not as obvious, and its dependence on rotation time is not evident. I still suspect some sort of mechanical effect.

I suspect the vendor will push back and say that there is nothing wrong with the scanner as they have just completed a PM. I appreciate any insight you can provide if you have seen something like this and how you might have resolved it.

Cheers,

Idris Elbakri, PhD, MCCPM
PS. Figure from left to right: 0.33, 0.4, 0.5 and 0.75 sec rotation times.

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