Wanqin Wang, Presenter: Nothing to Disclose

Bin Liu MD, Abstract Co-Author: Nothing to Disclose

Yong Zhou MD, Abstract Co-Author: Nothing to Disclose

Xingwang Wu, Abstract Co-Author: Nothing to Disclose

Xiaohu Li, Abstract Co-Author: Nothing to Disclose

Shuai Zhang, Abstract Co-Author: Nothing to Disclose

Yun Shen PhD, Abstract Co-Author: Employee, General Electric Company Researcher, General Electric Company

The purpose of this study was to select the optimal monochromatic level for gemstone spectral imaging (GSI) to minimize both the image noise and the beam-hardening artifacts (BHAs) caused by high concentration of iodine contrast agent.

A cylindrical plastic phantom with nine hard plastic tubes filled with different concentrations (100.0,50.0,30.0,20.0,10.0,5.0,2.0,0.7,0.4, mg I/ cc) of iodine solution, the tube with highest concentration in center and other eight tubes arranged clockwise with concentration in outer circle, underwent HDCT (Discovery CT750 HD) scans with conventional 120kV(p) mode and GSI mode, respectively. All data were transferred to Workstation (AW4.4, GE Healthcare) to obtain one set of polychromatic images (120 kilovolt (peak) (kV[p]) and twenty-one sets of monochromatic images (40-140keV, interval of 5keV). The background noise of the most significant affected region (area between the 100.0 mg I/cc and 50.0 mg I/cc hard plastic tubes) was measured and compared between the polychromatic and monochromatic images. Beam-hardening artifact is defined as square root of the difference between the square number of noise of region of interest and noise of background.

The background noise with the monochromatic sets reduced by -160% (40keV), -99% (45keV), -53% (50keV), -16% (55keV), 13% (60keV) , 37% (65keV) , 56% (70keV) , 70% (75keV) , 80% (80keV) , 82% (85keV) , 82% (90keV) , 79% (95keV) , 76% (100keV) , 73% (105keV) , 69% (110keV) , 67% (115keV) , 64% (120keV) , 62% (125keV) , 60% (130keV) , 58% (135keV) and 57% (140keV), respectively, compared to the polychromatic image. For BHA, the reductions were -159%, -98%, -52%, -16%, 13%, 37%, 57%, 73%, 86%, 96% (85keV), 96%(90keV), 88%, 83%, 78%, 74%, 71%, 68%, 65%, 63%, 61% and 59%. Both the 85 and 90keV sets had significant background noise and BHA reduction (p=0.000 and p=0.000, respectively, for noise and BHA), but there was no significant difference between the two of them (p=0.232 for noise and p=0.817 for BHA).

Compared to conventional 120kVp mode, High-definition CT gemstone spectral imaging can considerably reduce image noise and BHAs of iodine contrast agent. The optimal monochromatic levels are 85keV and 90keV.

The BHAs caused by high concentration of iodine contrast agent can often blur structures surrounding it and restrict assessment. Reducing BHAs can improve diagnostic accuracy.

Wang, W, Liu, B, Zhou, Y, Wu, X, Li, X, Zhang, S, Shen, Y, High Definition CT Gemstone Spectral Imaging of the Phantom: Initial Results of Selecting Optimal Monochromatic Images for Beam-hardening Artifacts and Image Noise Reduction.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034324.html