[Intl_DxMedPhys] Older Siemens EI question

[Ryan Fisher]

Siemens is weird on this, which makes things messy from our side. They kinda sorta follow the IEC definition and now can report both a “physical EXI” and a “clinical EXI” on their modern systems. I believe the older systems just report what is now the Physical EXI as “EXI”.

Definitions attached, but the physical EXI is the average of the central area of the detector, regardless of what’s there, and with no histogram analysis/pixel rejection. The Clinical EXI considers the pixel values and is expecting some kind of clinical anatomy and does histogram analysis to try to determine the relevant area, and then is reporting the average of only those pixels. For IEC style verification, the physical EXI is what you want, as the clinical one gets weird with flat fields sometimes and can pick a weird clump of pixels somewhere skewing results. Naturally there’s no indication of what pixels are going into the calculation. To make things even more fun, on the modern systems there are calibration factors under the hood to adjust the accuracy of both, but all the Siemens PM procedures require the FSE to set the cal factor for one of them back to 1.

It’s been awhile since I dealt with this, but remember basically just throwing up my hands about it because even if we adjusted the cal factor, the next year you’d come back and it would be set back to 1. Good luck.


Ryan


From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu> On Behalf Of Douglas Pfeiffer via Intl_dxmedphys_wd_osu_list
Sent: Wednesday, October 7, 2026 6:20 PM
To: DxMedPhys List <intl_dxmedphys_wd_osu_list at lists.osu.edu>
Subject: [Intl_DxMedPhys] Older Siemens EI question

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Dear all, I recently tested a 2009 Siemens Axiom Luminos TF and found that the reported EI (or EXI in Siemens parlance) was about 50% of from what it should be. The service engineer replied thusly: In Siemens we calculate the EXI as the arithmetic
Dear all,

I recently tested a 2009 Siemens Axiom Luminos TF and found that the reported EI (or EXI in Siemens parlance) was about 50% of from what it should be. The service engineer replied thusly:
In Siemens we calculate the EXI as the arithmetic mean of gray value of a central area (refer to the example picture below) under consideration of the actual collimation.
EXI value is not calculated for dull detector image.

For the Cannon detector in Luminos TF system, there is no adjustment for the EXI value. The maximum we can do is to calibrate the detector.

The IEC standard [62494-1 (2008)] is very specifically calibrated at RQA5 in a uniform field. Has anyone else been told anything like what this person is saying?

Best regards,
Doug



Douglas Pfeiffer, MS, DABR FACR, FAAPM (he/him)
Medical Physicist, Radiation Safety Officer
Boulder Community Health
xraydoug at me.com<mailto:xraydoug at me.com>
303.415.7515

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The opinions expressed in this message are the product of the gray and white matter loitering in my cranium. I speak for myself and no one else, unless I say otherwise.


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