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

[Shane McCotter]

Not sure if this will help, but try using the Quantative recon method (if I remember right). Had this issue with a Siemens before and apps recommended that recon.

Shane


Sent from my iPhone

On Jul 24, 2025, at 8:37 AM, Imendra Ranatunge via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu> wrote:


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

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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