  An experimental setup for consecutive measurement of ion and x-ray absorption
in tissue or other materials is introduced. With this setup using a 3D-printed
sample container, the reference stopping-power ratio (SPR) of materials can be
measured with an uncertainty of below 0.1%. A total of 65 porcine and bovine
tissue samples were prepared for measurement, comprising five samples each of
13 tissue types representing about 80% of the total body mass (three different
muscle and fatty tissues, liver, kidney, brain, heart, blood, lung and bone).
Using a standard stoichiometric calibration for single-energy CT (SECT) as well
as a state-of-the-art dual-energy CT (DECT) approach, SPR was predicted for all
tissues and then compared to the measured reference. With the SECT approach,
the SPRs of all tissues were predicted with a mean error of (-0.84 $\pm$ 0.12)%
and a mean absolute error of (1.27 $\pm$ 0.12)%. In contrast, the DECT-based
SPR predictions were overall consistent with the measured reference with a mean
error of (-0.02 $\pm$ 0.15)% and a mean absolute error of (0.10 $\pm$ 0.15)%.
Thus, in this study, the potential of DECT to decrease range uncertainty could
be confirmed in biological tissue.
