Room: Exhibit Hall | Forum 8
Purpose: Virtual monoenergetic images (VMI) in dual-energy CT (DECT) require adjusted window/level (W/L) settings for optimal display appearance due to the variation of HU with energy. This study aims to develop a material-of-interest based method for W/L adjustments for VMIs.
Methods: A parameterized fitting of mass attenuation coefficient as a function of atomic number and photon energy was used to derive a short form of HU. The energy dependent part was derived to be integrated as a single factor Q(E). A calibration procedure was designed to determine the Q(E) factor based on measurements of HU(E) on VMIs of the Gammex-467 CT phantom on a DECT scanner (Siemens SOMATOM Definition AS). The energy independent part of HU was found to be specified by electron density and effective atomic number. The ICRU-46 human body tissue composition database was used to develop a material-of-interest model that was hypothesized as universal tissue information in real patients. Given the conventional W/L settings at 120kVp, the corresponding W/L for VMIs can be solved.
Results: The short form of HU was derived to be HU(E) = Ï?'+Q(E)*Z', with (Ï?', Z') as functions of electron density and atomic number. Piecewise linear fitting of Z' as a function of Ï?' was established using the ICRU-46 data. The material-of-interest modeled W/L at 40 to 190keV were obtained for sites including soft tissue, brain, lung, pelvis and spine, based on the conventional W/L settings. Preliminary evaluation on a brain case indicated that improved perceivable information on VMIs with the adjusted W/L could be observed.
Conclusion: The proposed method for W/L settings for VMIs provides an appropriate preset which can help reduce clinic workloads. Further adjustment of the W/L for VMIs may be needed for optimal perception based on image readerâ€™s preferences on image contrast and noise.