[Intl_DxMedPhys] Help with Hologic Dimensions artifact

[Travis Greene]

All,

I'm hoping you can help me identify the source of an artifact in a bus with a Hologic Dimensions installed.  I went to perform a major repair evaluation following the replacement of the x-ray tube, filter assembly, and collimator.  The x-ray tube cracked and leaked oil all over the tube assembly.  First time I've ever heard of that happening on a mammo unit, but I digress.  During my evaluation I came across the attached artifact.  Initially, the artifact was visible only in 2D contact images.  It's towards the chest wall about halfway from center to the left edge.  It was not visible in 3D or 2D mag images.  The artifact is in a single row of the detector going from chest to anterior direction.  I believe this is the gate direction for this detector.

The FSE was still on site so I asked her to take a look and see if they could map out the bad pixels.  The remote tech support guy pulled up the raw images and the artifact could not be found in the for-processing image.  Subsequent testing had the artifact appear intermittently, but usually in the same location.  Several repetitions of flat field shots yielded 3D projection images that had the artifact intermittently and in multiple location in some instances.  The presentation of the artifact was always the same regardless of where it appeared.  Bright towards the chest wall edge and black towards the anterior edge.  Always in a single row of the image.  We looked at another 2D image where the artifact was present in the image and again, it could not be found in the raw image.  If the artifact is not visible in the raw image (what the detector sees) then the artifact has to be added by the bad pixel correction, the gain correction, or the final image processing; right?

The plan is to replace the detector today.  However, I don't think this will resolve the problem.  Do you think replacing the detector is the right intervention or do you think the problem is caused by some other component?  My thought is that this is a processing error not a readout error.  I wonder if the old Nvidia1650 graphics card in the system is having issues after being rattled around on the highway for several years.

Lastly, for the first time ever, I failed a Hologic Dimensions for AEC reproducibility for the 3D images.  Oddly, the kVp was switching between 29 and 30 when using the ACR phantom exam card.  I had thought when using this exam card, the kVp was fixed by the software to be 29kVp and could not be changed.  Any idea why the exposure settings might have been changing?  Is this a problem with the software?  In over a decade of evaluating these systems, I have never seen this behavior.  Typically, the 3D AEC phantom exposures are nearly identical for all four of them.

I would appreciate any advice you might have on this situation.

Thank you,

Travis

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