[Intl_DxMedPhys] CT ACR Phantom lifetime

[Palmer, Matthew R. (BIDMC - Radiology)]

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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


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