CT能谱成像在消除金属移植物伪影中的应用价值

目的 探讨CT能谱成像(GSI)中单能量图像消除金属移植物硬化伪影的作用.方法 对体内有金属移植物的患者行GSI.其中义齿3例、颈椎钢板植入2例、锁骨钢板植入1例、腰椎金属棒植入1例、人工股骨头3例、髂骨骨折移植物1例、胫骨钢板植入1例.对上述部位行GSI螺旋扫描,管电压采用80 kVp和140 kVp,在0.5 ms内行快速切换扫描.然后重建1.25 mm层厚能谱图像,含40～140 keV共101个单能图像,不同keV单能图像均采用同样的窗宽(1500 HU)、窗位(500HU).测量不同keV单能量图像的伪影指数(AI),分析不同单能量图像伪影消除程度,将AI最小的单能keV图像保存,应用于三维重组.结果 单能图像中AI随keV变化而不同,12例中最大AI为145～225,均在40keV时出现;最小AI为15～190,出现在95～140 keV之间.重组图像时,12例常规的混合能量图像均有明显的金属伪影,用最小AI的单能量图像重建时,可明显肖除或降低金属移植物的硬化伪影.结论 采用CT能谱成像技术,在高keV单能量图像上可以明显降低或消除金属移植物伪影,改善图像质量.

The application of spectral CT imaging in reducing artifacts caused by metallic implants

Objective To assess the capability of monochromatic energy images of Gemstone spectral imaging(GSI) in reducing artifacts caused by metallic implants. Methods Twelve subjects with metallic implants underwent GSI (Discovery CT750 HD, GE Healthcare, Milwaukee ). The metallic orthopedic implants included 3 patients of dentures, 2 patients of cervical spinal vertebraplasty, one clavicle fracture fixation, one lumbar spinal vertehraplasty, 3 patients of artificial femoral head, one iliac fracture fixation and one tibial fracture fixation. GSI was performed by using a single source ultra-fast dual energy X-ray switching (80 kVp and 140 kVp). Following GSI scanning, thin slice images were reconstructed into 1.25 mm slice thickness. The monochromatic energy images were set to the same window width and level (window width 1500 HU,window level 500 HU). The artifact indexes (AI) at different kiloelectronvolts (keV) images were measured and compared. 3D reconstruction was performed using images with minimal AI. Result The artifacts index on monochromatic energy images varied with the change of keV. Of the images from 12 subjects, the maximal AI ranged between 145-225 at 40 keV, and minimal AI ranged between 15-90 at the 95-140 keV. The artifacts are clearly visible on polychromatic energy images and the artifacts are reduced markedly on the monochromatic energy images with minimal AI. Conclusion The artifacts caused by metallic implants can be reduced significantly by GSI with high keV monochromatic energy images.