Fig 9. Mass HU potency vs. tube voltage for reference materials from the Catphan phantom.

[31] The materials are T (Teflon, or polytetrafluoroethylene C₂F₄, red), D (Delrin, CH₂O, green), A (acrylic, see Fig 8, blue), PS (polystyrene, C₈H₈, brown), and P (both low density polyethylene C₂H₄ magenta, dashed and polymethylpentene C₆H₁₂ cyan, overwritten) The tube voltages have been offset for clarity by -1 kV for and low density polyethylene and acrylic and by +1 kV for polymethylpentene and polystyrene. Conversions from the reported HU values are scaled by the densities 2160, 1415, 1180, 1040, 925, and 833 kg/m³, respectively. The error bars represent the minimum and maximum values as reported by [31] for 8 scanners, scaled by the densities.