The experimental quantitative study of spectral CT imaging in reducing the metal artifacts

Abstract

Objective To assess the value of spectral CT in reducing artifacts caused by metallic implants. Methods Porcine lumbar spines were chosen as anthropomorphic phantom. The model was examined before and after implanting the titanic nail into the second and fourth lumbar vertebral body using gemstone spectral CT protocol and standard 120 kVp spectra. Specific pest-processing technique was applied to generate 11 kinds of images of monochromatic energy and Metal Artifacts Reducing system (MARs) with the interval of 10 keV ranging from 40-140 keV. The image quality was compared subjectively between 120 kVp group and GSI group after implantation. Three regions of interest based on distances along the most pronounced artifact were chosen and marked as ROInear, ROImid, ROIfar successively. Artifacts parameters including CT value and SD value were measured. The CT value of different ROIs were compared with LSD and Bonferroni test. Contrast-to-noise ratio and artifacts index were calculated. An optimal range of keV was determined according to artifacts index. Results Image quality of Gemstone spectra images was rated superior to the standard images. An optimized spectrum of keV based on artifacts index was from 80 keV to 100 keV. For ROInear,CT value was ( 80. 25 ± 16. 00) HU and ( 30. 10 ± 10. 45 ) HU respectively in group Mono before implantation and group Mono + MARs after implantation. The differences were significant( Z =2. 978, P ＜ 0. 05 ). For ROImid and ROIfax, CT value was ( 63.21 ± 6. 61 ) HU and ( 54. 84 ± 10. 60 ) HU,(76. 54 ±9.07)HU and (73.20 ±5.39)HU respectively. There was no significant differences (t =0. 530,P ＞ 0. 05; t = 0. 822, P ＞ 0. 05 ). Conclusions Metal artifacts could be reduced effectively at the site 3 cm away from implants using gemstone spectral CT. An accurate CT value of surrounding tissue can be obtained. Key words: Prostheses and implants; Tomography, spiral, computed; Metals