[Intl_DxMedPhys] CT ACR Phantom lifetime

[Jayse Weaver]

Here's (maybe the only) reference with the HU/temperature relationship calculated for a couple different WE materials

https://urldefense.com/v3/__https://iopscience.iop.org/article/10.1088/0031-9155/47/16/307__;!!KGKeukY!2goHYRMeg6GcZfbNYo6eoYkW7794kVbrYdO2rRoFHhrFl_2_ScJTr-coHTkZOqRcaEXQ5uZy3jGmtuKejAxvLKV6IRs3YPXg8bUKOp5TBu6P4rxm$ 


-----

Jayse M. Weaver, Ph.D. (he/him)

Associate Physicist – Diagnostic Services Medical Physics

Assistant Professor – Diagnostic Radiology and Nuclear Medicine

Rush University Medical Center

[RUSH]

________________________________
From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu> on behalf of Shane McCotter via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu>
Sent: Tuesday, March 31, 2026 8:13 AM
To: Bob Kobistek <bob at rjkmedphys.com>
Cc: intl_dxmedphys_wd_osu_list at lists.osu.edu <intl_dxmedphys_wd_osu_list at lists.osu.edu>
Subject: Re: [Intl_DxMedPhys] CT ACR Phantom lifetime

Rush Email Security

This email originated from outside of RUSH. Do not click links or attachments unless you recognize the sender and know that the content is safe. RUSH will never ask for user ID information via email.

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.

Shane

Sent from my iPhone

> On Mar 31, 2026, at 7:55 AM, Bob Kobistek via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu> wrote:
>
> 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.
>
> 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.
>
>
> Robert J. Kobistek, MS, FACR, DABR, MRSE(MRSC™)
> Medical Physicist
> RJK Medical Physics, Inc.
> 440-463-7879
>
> -----Original Message-----
> From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces+bob=rjkmedphys.com at lists.osu.edu> On Behalf Of Palmer, Matthew R. (BIDMC - Radiology) via Intl_dxmedphys_wd_osu_list
> Sent: Tuesday, March 31, 2026 8:40 AM
> To: intl_dxmedphys_wd_osu_list at lists.osu.edu
> Subject: [Intl_DxMedPhys] CT ACR Phantom lifetime
>
> 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.
>
> 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?
>
> 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.
>
> 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?
>
> Matt  Palmer
> BIDMC
>
>
> ----------------------------------------------------------------------
> PLEASE NOTE: This message is intended for the use of the person to whom it is addressed. It may contain information that is privileged, confidential and exempt from disclosure under applicable law. If you are not the intended recipient, your use of this message for any purpose is strictly prohibited. If you have received this communication in error, please delete the message and notify the sender so that we may correct our records. See our web page at https://urldefense.com/v3/__https://nam10.safelinks.protection.outlook.com/?url=https*3A*2F*2Furldefense.com*2Fv3*2F__http*3A*2F*2Fwww.bilh.org__*3B!!KGKeukY!woIUdJEf54_XpN9yPaTG2HPoL6WxCn6z7zFWZ43f3UGAVUZlySFYuoXevzLV_YlRMmaoQ_RwFJricMckA7yYzkBQgotGLcvGwL3yHB2kGJuLo2A*24&data=05*7C02*7CJayse_M_Weaver*40rush.edu*7C4d731564e3864ee0ce8d08de8f27675c*7C822ee4caeeac4bf4957b97a4bb0b1697*7C0*7C0*7C639105596599199028*7CUnknown*7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ*3D*3D*7C0*7C*7C*7C&sdata=ntIlzfL5gMo8vIPt5P3*2Fi58RcnTcZaid0fmoEJpAn9Q*3D&reserved=0__;JSUlJSUlJSUlJSUlJSUlJSUlJSUlJSUlJSUlJQ!!KGKeukY!2goHYRMeg6GcZfbNYo6eoYkW7794kVbrYdO2rRoFHhrFl_2_ScJTr-coHTkZOqRcaEXQ5uZy3jGmtuKejAxvLKV6IRs3YPXg8bUKOp5TBvqew8WN$ <https://urldefense.com/v3/__http://www.bilh.org__;!!KGKeukY!woIUdJEf54_XpN9yPaTG2HPoL6WxCn6z7zFWZ43f3UGAVUZlySFYuoXevzLV_YlRMmaoQ_RwFJricMckA7yYzkBQgotGLcvGwL3yHB2kGJuLo2A$>  for a full directory of Beth Israel Lahey Health sites, staff, services and career opportunities.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osu.edu/pipermail/intl_dxmedphys_wd_osu_list/attachments/20260331/14b198c3/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Outlook-RUSH.png
Type: image/png
Size: 14397 bytes
Desc: Outlook-RUSH.png
URL: <http://lists.osu.edu/pipermail/intl_dxmedphys_wd_osu_list/attachments/20260331/14b198c3/attachment.png>