The Study Of Monochromatic Imaging In Reducing The Spinal Metal Artifacts On HDCT

Objectives:To investigate the clinical value of Monochramatic imaging inreducing the spinal metal artifacts on HDCT,and find out the optimal monochromaticenergy for reconstruction.Materials and Methods:Thirty five patients with pedicle metal screwes of lumbarvertebrae in our hospital received GSI(gemstone spectral imaging,GSI)examination.The GSI images and140kVp images of5mm slice thickness were sent toGE AW4.5workstation.Eleven groups of monochromatic images from40keV to140keV every interval of10keV and one group140kVp images were obtained by thespectral GSI viewer,respectively.Objective evaluations:(1)one image was selected foreach pair of pedicle screwes,the metal screwes on this image is displaied intactestlybased on the140kVp images.13ROI(region of interest,ROI) were slected,one(asbackground) is the fat far from the screwes,and AI(artifacts index,AI) of the other12ROIes were computed.(2)The images at the pedicle with and without screwes wereselected,the ROI were slected at the greater psoas muscle and vertebral canal,the CTnumbers and SD numbers were obtained.Subjective evaluation:the140kVp imagesand eight groups monochromatic images from70keV to140keV were scored by twoexperienced radiologists independently. statistical analysis：All statistical analysis wereperformed with SPSS software (version19.0;SPSS Inc., Chicago, IL,USA). p <0.05wasaccepted as statistically significant. One-way ANOVA were performed for the AI andthe subject scores. Paired Student’s t-test were performed for the CT numbers、SDnumbers.Results:1. The AI is declined with the increasing keV,the average AIs of monochromaticimages from90keV to140keV monochromatic images are inferior to the140kVpimages.the AIs have no signigicant difference(p>0.05) among the monochromatic images from90keV to140keV for bilateral beside the pedicle,it is from100keV to140keV for the other ROIs.2.There are no significant difference (p>0.05) for the CT values at the greater psoasmuscle between the screw level and no screw level from100keV to120keV and from120keV to140keV at the vertebral canal.There are significant difference(p<0.05) forthe SD number at the greater psoas muscle and the vertebral canal between the screwlevel and no screw level on140kVp images and monochromatic images,but the meansof difference are decline with the keV increasing.3. With the keV increasing,The imaging quality are improved and the artifacts arereduced,the screwes and the bone cortical of pedicle are more clear,but the tissuescontrast aroud the screwes are decreased.There are no signigicant differece for thesubjective scores from120keV to140keV.Conclusions:1.The monochromatic imaging of spectral CT can reduce artifacts of the pediclescrewes.the effect of the higher monochromatic level are better.The AI is declined withthe increasing keV.The effect of monochromatic imaging reducing metal artifacts aresame at different places.100keV is the optic monochromatic level for reconstruction.2.There are no significant difference for the CT values between the screw level andno screw level on the120keV monochromatic images,so the CT values are accuraterelatively on the120keV monochromatic images.The artifacts can be reduced inmonochromatic imaging to some extent,but it can not be diminished completely.3. It is negative correlation between Reducing artifacts and imaging quality.Theimaging quality are improved and the artifacts are reduced with the keV increasing,butthe tissues contrast aroud the screwes are decreased.We should have a balance betweenreducing artifacts and imaging quality when we reconstruct the monochromaticimages.The monochromatic images of140keV is not the best.