IMAR技术在去除腰椎内固定金属伪影中的应用价值

Value of IMAR Iterative Algorithm in Removing Metal Artifacts of Lumbar Internal Fixation

目的探讨双源CT中,IMAR技术对腰椎内固定术后金属伪影的应用价值。方法对32例腰椎内固定术后拟行腰椎CT检查的患者,行西门子Force双源CT 256容积扫描后重建获得图像。行腰椎CT检查后,采用滤波反投影算法(FBP)和滤波反投影算法加迭代去金属算法(FBP+IMAR)分别对扫描后数据重建。对比两组CT图像的CT值、伪影指数和平均梯度评价IMAR技术对金属伪影的抑制效果。最后,由3名高年资放射医师根据螺钉周围软组织、竖脊肌、螺钉植入和椎体的显示情况评价FBP+IMAR组和FBP组重建得CT图像。结果FBP+IMAR组重建得到CT图像在软组织和竖脊肌处CT值、平均梯度大于FBP组(P<0.05),而伪影指数小于FBP组(P<0.05)。FBP+IMAR组重建得到CT图像在金属与骨质处CT值和伪影指数小于FBP组(P<0.05),而平均梯度大于FBP组(P<0.05)。远离金属螺钉的软组织处,FBP+IMAR组重建得图像的CT值、平均梯度和伪影指数与FBP组无明显区别,差异无统计学意义(P>0.05)。在软组织、竖脊肌及金属与骨质界面的显示,FBP组重建CT图像评分低于FBP+IMAR组(P<0.05)。结论IMAR技术能有效减少腰椎内固定术后金属伪影,提高CT图像质量,有助于准确观察椎弓根、螺钉的位置和提高解剖结构清晰度,为评价腰椎内固定术后的治疗效果提供科学、准确的参考数据。

Objective To explore the application value of IMAR technology in dual source CT for metal artifacts after lumbar internal fixation.Methods The image of 32 patients who were scheduled to undergo lumbar CT examination after lumbar internal fixation were reconstructed by Siemens Force dual-source CT 256 volume scan.Concretely,after lumbar CT examination,the scanned data were reconstructed by filtered back projection algorithm(FBP)and filtered back projection algorithm plus iterative metal artifact removal algorithm(FBP+IMAR)respectively.Then,the CT value,artifact index and average gradient of CT images in two groups were compared to evaluate the suppression effect of IMAR technology on metal artifacts.Finally,three senior radiologists evaluated the reconstructed CT images of the FBP+IMAR group and the FBP group according to the displays of the soft tissue surrounding the screw,psoas major muscle,screw implantation,and vertebral body.Results The CT value and average gradient of the reconstructed CT images in soft tissue and erector spinal in FBP+IMAR group were higher than those in FBP group(P<0.05),while the artifact index was lower than that in FBP group(P<0.05).The CT value and artifact index of the reconstructed CT images at the interface between metal and bone in FBP+IMAR group were lower than those in FBP group(P<0.05),and the average gradient was higher than that in FBP group(P<0.05).There was no significant difference in CT value,average gradient and artifact index between the FBP+IMAR group and the FBP group in the soft tissue far from the metal screw(P>0.05).The results of soft tissue,erector spinal and vertebral pedicle presented the reconstructed CT image score in FBP group was lower than that in FBP+IMAR group(P<0.05).Conclusion IMAR technology can effectively reduce metal artifacts after lumbar internal fixation,improve CT image quality,facilitate the accurate observation of the position of pedicle and screw and enhance the clarity of anatomical structure,which provide scientific and accurate reference data for evaluating the treatment effect after lumbar internal fixation.