chunwu zhou, Abstract Co-Author: Nothing to Disclose

Xinming Zhao MD, Abstract Co-Author: Nothing to Disclose

Liming Jiang MD, Abstract Co-Author: Nothing to Disclose

Ning Guo, Abstract Co-Author: Nothing to Disclose

Zheng Zhu, Abstract Co-Author: Nothing to Disclose

Jing Zhao, Presenter: Nothing to Disclose

Use a quantitative phantom to evaluate the ability of beam hardening artifact (BHA) reduction by monochromatic images with CT spectral image by comparison with traditional polychromatic X-ray imaging (TPXI).

A cyclical phantom with diameter of 25cm (Quantitative Standard Pulsating Phantom QSP-1, Fuyo Corporation) was used. Three fresh pig humerus bones and three 10mm-diameter tubes filled with iodine contrast were placed in the center of periphery of the phantom to mimic human’s bones and arteries. The phantom with bones and tubes was immersed in a water tank. Under the condition of helical scan with 120kVp, the CT value of three bones were 1025Hu, 905Hu and 770Hu respectively, the CT value of three tubes were 1200Hu, 1000Hu and 840Hu respectively. Both CT spectral imaging mode (protocol A) and routine CT mode (protocol B) with 120kV and 600mA were used. The other scan parameters were the same for two protocols, including FOV of 25.0cm, slice thickness of 5mm, rotation speed of 0.8s/r and pitch of 0.984. Both the monochromatic images (40-140keV, interval of 10keV) and 120kV TPXI images were reconstructed. Beam hardening artifact index was calculated for each image, according the fomular: BHA index=SQRT(ROIa^2-ROIb^2), where ROIa denotes to the SD value of water in the region adjacent to tubes with obvious BHA, ROIb denotes the SD value of water in the region far away from tubes and bones without obvious BHA. The area of ROIa and ROIb were both about 50mm2. Data was compared with rank sum test.

The BHA index of 120kV TPXI image was 20.45±6.30. The BHA index of each monochromatic image set (ranging from 1.17±0.86 to 9.72±1.32) was lower than that of 120 TPXI image (p<0.001). Monochromatic images at 80keV had the lowest BHA index (1.17±0.86). The variation of BHA index at 90keV to 140 keV(3.13±0.46 to 4.71±1.03) was smaller than that at 40keV to 70keV(9.72±1.32 to 3.28±0.26)(p<0.01).

Monochromatic images have less beam hardening artifact than TPXI images, high keV images(80keV-140keV) are superior to low keV images(40keV-70keV).

CT spectral image provides less beam hardening artifact and more accurate CT attenuation number, which may help clinical diagnosis. 

zhou, c, Zhao, X, Jiang, L, Guo, N, Zhu, Z, Zhao, J, Reducing Beam Hardening Artifact by Monochromatic Images with CT Spectral Image: Comparison with Traditional Polychromatic X-ray Imaging—Quantitative Study in Phantom.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14009935.html