Metal Artifacts Reduction Of Hip Prostheses Using Spectral CT With Monochromatic Imaging And Metal Artifacts Reduction Software

Purpose To evaluate the effect of spectral CT for metal artifact reduction in patients with hip prostheses on monochromatic images with or without metal artifacts reduction software(MARs),so as to evaluate the application value of monochromatic images with MARs for reducing artifacts from hip prostheses.Materials and methods This retrospective study included 31 patients who received unilateral hip replacements and spectral CT examination,and 21 patients with monochromatic images reconstructed using the MARs algorithm.The monochromatic images with and without MARs of 1.25 mm slice thickness were sent to GE AW 4.5workstation and receivded state.xls dacuments,then chosed the CT number and SD valueat 80,100,120 and140 ke V monochromatic images with and without MARs.Objective evaluations:(1)on axial image of hip with the most obvious artifacts,three regions of interests(ROIs)were selected on anterior/ posterior/ lateral muscle of hip prostheses and one as background which is the fat far from the artifacts,and two ROIs were drawn at uterus/ prostate and bladder and one background at the fat far from the artifacts,then AIs of five ROIs were computed.(3)The ROIs were selected at the muscle around the hip prostheses and healthy hip,recorded the CT number and SD value of these ROIs.Subjective evaluation:(1)Image quality was evaluated using a 1–4scale scoring method and evaluated by two radiologists independently.(2)Two radiologists evaluated postoperative complications of hip protheses and compared the imaging quality among DR,monochromatic images and MARs images.Statistical analysis: All statistical analysis were performed with SPSS 17.0 software,p<0.05 was statiscally significant.Pared-samples T test was performed for the comparation of AI value,CT number and SD value.The inter-observer agreement between the two residents was calculated by kappa.The intra-observer score was compared by Mc Nemar test.Results:Objective evaluations(1)The AIs were declined with increasing ke V,AIs at140 ke V images were smaller than that of other monochromatic images on anterior,posterior and uterus/ prostate ROIs,and the AIs had significant difference(P<0.05);the AIs of lateral and bladder ROIs at 120 ke V and 140 ke V images were smaller than that at 80 ke V and 100 ke V images,the AIs had significant difference(P<0.05);while the MARs images had the smallest AIs of at 140 ke V image on posterior and pelvic ROIs,and the AIs had significant difference(P<0.05);the AIs of anterior and lateral ROIs at 120 ke V and 140 ke V images were smaller than that at 80 and 100 ke V images,and the AIs had significant difference(P<0.05).(2)AIs at MARs images were smaller than that of monochromatic images with significant difference(P<0.05),while the AIs of pelvic organs had no significant difference(p?0.05).(3)There was significant difference(P<0.05)for the CT numbers of all the ROIs at monochromatic images and lateral ROI at MARs images,and no significant difference for the CT values of anterior and posterior ROIs at MARs images(P?0.05).There was significant difference(P<0.05)for the SD values of all the ROIs at all the images.Subjective evaluation: The inter-observer agreement levels for the image scores were excellent and good for all the images.The monochromatic images at high energy levels had a well effect of removing metal artifacts,and MARs images showed significant reduction of the artifact comparing with the monochromatic images.The subjective score of images at MARs images was higher than that of images at the monochromatic images(p <0.05).Conclusions:1.The monochromatic images with or with MARs can reduce artifacts from hip prostheses.The effect on reducing metal artifacts was equal at monochromatic images for different places,the effect on reducing artifacts images was equal at 120 ke V and140 ke V monochromatic,and also equal at 120 ke V and 140 ke V with MARs images.2.The reduction of artifacts at MARs images was more significant than that at monochromatic images.But MARs images have no obvious advantage for the reduction of artifacts of pelvic organs comparing with monochromatic image.3.The MARs images can reduce artifacts from hip prostheses,the CT values around the hip were more accurate,while the monochromatic images can reduce artifacts to some extent and not eliminate the influence of artifacts in the measurement of CT number.4.Compared to the monochromatic images and DR,the MARs images have more advantages in showing subtle signs of complication.