The mean HU and standard deviation (SD) were measured in the liver, the hypervascular portion of the VX2 tumor which represented hypervascular tumors, and the central necrotic area of the VX2 tumor which represented hypovascular tumors in 140kVp images with I 300 as a reference standard and in monoenergetic images (between 40keV and 140keV) with I 150 and I 75 .
Source: wiktionary