| Objective To discuss how to utilize the monochromatic energy image and metal artifacts reduction software (MARS) of spectral CT for reducing artifacts generated by biliary 125I seed stent in malignant biliary obstruction.MethodsNineteen patients with biliary 125I seed stent received non-enhanced GSI examination. The polychromatic energy images, monochromatic energy images and MARS images were obtained, while monochromatic images were reconstructed in eleven groups ranging from 40 to 140keV with interval of 10keV. For each group, CT value and SD value of ROI were measured on the heaviest artifacts level, with taking subcutaneous fat as background. And contrast noise ratio (CNR) and the noise index (NI) were calculated and analyzed for finding out the optimal monochromatic energy level. Subjective image quality of three methods was assessed independently by 2 experienced radiologists with a blind method. Kappa test, paired t test or Wilcoxon signed ranks test were done for subjective scores, contrast noise ratio (CNR) and the noise index (NI).Statistical analysis was accomplished with SPSS 18.0 soft.Results1. For each monochromatic energy level, the optimal CNR was obtained at the energy level of 70keV. The monochromatic images are better than the polychromatic images on CNR, NI and subjective rating which have statistical significance. (P<0.001)2. Compared with the optimal monochromatic energy images, artifacts were reduced in the optimal monochromatic energy+MARS images, and the CNR, subjective rating were higher, the NI was lower. There were significant statistical differences between them. (P<0.001)ConclusionSpectral CT can effectively reduce artifacts of biliary 125I seed stent by using monochromatic images and MRAS, and improve the image quality and visibility in the vicinity of 125I seed stent. The optimal monochromatic energy level is 70keV, which can provide both good image quality and the optimal CNR. |
PDF Full Text Request