Room: Exhibit Hall | Forum 2
Purpose: Two new tools available in Radiation Oncology clinics are Dual-energy CT (DECT) and Siemens'DirectDensityTM (DD) reconstruction algorithm, which allows scans of any kV setting to use thesame calibration. This study demonstrates why DD scans should not be used incombination with DECT post-processing and quantifies the magnitude of potential errors inimage quality and dose.
Methods: A CatPhan 504 phantom was scanned with a dual-pass DECT and reconstructed with many differentkernels, including several DD kernels. The HU values of various inserts were measured. TheRANDOÂ® man phantom was also scanned. Bone was contoured and then histograms of the boneHU values were analyzed for Filtered-Backprojection (FBP) and DD reconstructions of the 80 and140kV scans, as well as several virtual, mono-energetic reconstructions generated from FBP andDD reconstructions. "Standard" dose distributions were calculated on several reconstructions of bothphantoms for comparison.
Results: The DD kernel over-corrected the high-Z material inserts relative to bone, giving an excessively lowrelative electron density (RED). A unique artifact was observed in the high density inserts of theCatPhan in the mono-energetic scans when utilizing a DD kernel, due to the overcorrection in theDD scan of the material, especially at lower kV.
Conclusion: While DD and DECT perform as expected when used independently, errors from their combineduse were demonstrated. Dose errors from misuse of the DD kernel with DECT post-processing wereas large as 2.5%. The DECT post-processing was without value because the HU differences betweenlow and high energy were removed by the DD kernel. When using DD and DECT, we recommendthe use of a DD reconstruction of the high energy scan for the dose calculation, and use of a FBPfilter for the low and high energy scans for the DECT post-processing.