Program Information
Development of a Strategy to Correct for HU Drifting as a Result of Beam Hardening Caused by Soft Tissues
H Ai1*, R Wendt1 , (1) The University of Texas MD Anderson Cancer Center, Houston, TX
Presentations
TH-CD-601-3 (Thursday, August 3, 2017) 10:00 AM - 12:00 PM Room: 601
Purpose: We have previously reported the dependence of the CT Hounsfield Unit on the Total In-Slice Attenuation (TISA), which arises from the beam hardening by soft tissue. We have refined our measurements and propose a correction strategy for this effect.
Methods: A CIRS electron density phantom (model 62) with eight tissue-equivalent inserts was scanned on the CT component of a Siemens mCT Flow PET/CT scanner. Superflab strips (thickness = 1cm) were wrapped around the phantom to simulate adult bodies from normal to obese patients. HU was measured using ROIs placed within the tissue equivalent inserts for each scenario and plotted against TISA, which is defined as the summation of pixel HU value × pixel area over all active pixels of the CT image (HU was shifted by 1000 so that HUair=0).Linear regression analysis was performed between TISA and measured HU for each tissue type, according to the model HU=A1×TISA+A0. A0 is the expected HU value in the absence of attenuation, while A1 is the rate of HU variation as TISA changes. Both coefficients were estimated for the eight tissue types directly from the measured HU and TISA. Additional linear regression analysis was performed between the coefficients and the HU value of the underlying tissue, HU0.
Results: Linear correlation was observed for all tissue types in the electron density phantom. Correlations were negative for tissues with HU>0, and positive for tissues with HU<0. In addition, we observed a linear relationship between A0 and HU0, and a bilinear relationship between A1 and HU0 with the transition point occurring at approximately HU=0.
Conclusion: A1 and A0, are also linearly correlated with the HU of the underlying tissue. The measured HU of a tissue can thus be combined with the measured TISA in a slice to determine the HU of the underlying tissue.
Contact Email: