"Apparently it is filled with a water solution and the label just says to keep it frost-free once filled."
A: "It is a “phantom” for a ct/MRI scanner. Used for calibration/QA of the scanner. It is more likely to be an MRI device as it contains Nickel sulfate (NiSO4 H2O6) which is (from looking it up here is used for its magnetic susceptibility quality. Source: radiographer wife!"