[Intl_DxMedPhys] CT Number Deviations on Siemens Force and Alpha – ACR Phantom Failures

[Imendra Ranatunge]

Hi All,

I’m encountering an issue with a couple of my Siemens CT
scanners—specifically the Force and Alpha models. Several of my CT number
measurements using the ACR phantom are failing for air, water, and bone.
Some units fail all three, while others only one or two.

I tried placing a CTDI phantom adjacent to the ACR phantom, but it showed
no improvement.

I reported the issue to Siemens. They performed a constancy test and stated
that the units were functioning normally. However, my CT number results are
still outside acceptable limits. In my experience, service engineers are
often reluctant to perform time-consuming calibrations unless specifically
requested.

Has anyone experienced this before? If so, do you know which specific
calibration or adjustment Siemens needs to perform to correct these CT
number inaccuracies?

Imendra
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