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Here's (maybe the only) reference with the HU/temperature relationship calculated for a couple different WE materials https: //iopscience. iop. org/article/10. 1088/0031-9155/47/16/307 ----- Jayse M. Weaver, Ph. D. (he/him) Associate Physicist –</div>
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Here's (maybe the only) reference with the HU/temperature relationship calculated for a couple different WE materials</div>
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<a href="https://urldefense.com/v3/__https://iopscience.iop.org/article/10.1088/0031-9155/47/16/307__;!!KGKeukY!2goHYRMeg6GcZfbNYo6eoYkW7794kVbrYdO2rRoFHhrFl_2_ScJTr-coHTkZOqRcaEXQ5uZy3jGmtuKejAxvLKV6IRs3YPXg8bUKOp5TBu6P4rxm$">https://iopscience.iop.org/article/10.1088/0031-9155/47/16/307</a></div>
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<span style="font-family: Calibri, sans-serif; font-size: 12pt; color: rgb(36, 36, 36);"><b>Jayse M. Weaver, Ph.D.</b></span><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(36, 36, 36);"> (he/him)</span></p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces@lists.osu.edu> on behalf of Shane McCotter via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list@lists.osu.edu><br>
<b>Sent:</b> Tuesday, March 31, 2026 8:13 AM<br>
<b>To:</b> Bob Kobistek <bob@rjkmedphys.com><br>
<b>Cc:</b> intl_dxmedphys_wd_osu_list@lists.osu.edu <intl_dxmedphys_wd_osu_list@lists.osu.edu><br>
<b>Subject:</b> Re: [Intl_DxMedPhys] CT ACR Phantom lifetime</font>
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Temperature definitely affects the phantom. I live in northern Wisconsin and if I don’t bring the phantom in during our cold winters the CT numbers are off like you’re seeing.<br>
<br>
Shane<br>
<br>
Sent from my iPhone<br>
<br>
> On Mar 31, 2026, at 7:55 AM, Bob Kobistek via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list@lists.osu.edu> wrote:<br>
><br>
> My phantom is also >20 y old. I live in northeast Ohio, and it lives in my car almost every day of the year. I also get inaccurate water HU readings compared to actual water, but it's been that way since the phantom was new. I've always blamed the fact that
the red stuff in the phantom isn't really water. For my annual surveys, I just add a remark to my report stating that the scanner passes CT# testing using the manufacturer's water phantom.<br>
><br>
> As for ACR accreditation: CT number failure is a minor failure. You can accumulate as many as 6 minor failures (4 if you're only applying for adult accreditation) and still pass accreditation.<br>
><br>
><br>
> Robert J. Kobistek, MS, FACR, DABR, MRSE(MRSC™)<br>
> Medical Physicist<br>
> RJK Medical Physics, Inc.<br>
> 440-463-7879<br>
><br>
> -----Original Message-----<br>
> From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces+bob=rjkmedphys.com@lists.osu.edu> On Behalf Of Palmer, Matthew R. (BIDMC - Radiology) via Intl_dxmedphys_wd_osu_list<br>
> Sent: Tuesday, March 31, 2026 8:40 AM<br>
> To: intl_dxmedphys_wd_osu_list@lists.osu.edu<br>
> Subject: [Intl_DxMedPhys] CT ACR Phantom lifetime<br>
><br>
> I have a Gammex CT ACR phantom that's probably 20 or more years old. I've noticed recently that it's consistently reporting higher CT numbers for water than the scanner reports for the daily QC measurements on the manufacturer's phantom (actual water). In
the range of 4 - 8 HU on scanners reporting 0 HU on the DQA. This happens on more than one scanner from more than 1 vendor.<br>
><br>
> Is it possible that my phantom has reached its best-before date? Not sure what could be happening to the plastic but can it have become more dense over time?<br>
><br>
> Or, is temperature an issue? We've had a cold winter here in Boston and I transport the phantom in my car and it sometimes stays there overnight.<br>
><br>
> And, is there anything I can do if I'm in a bind - say when the water is above 7 and I need to acquire a series for an ACR submission?<br>
><br>
> Matt Palmer<br>
> BIDMC<br>
><br>
><br>
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