Gemstone Spectral Imaging Metal Artifact Removing Technique Using In The Imaging Evaluation Of The Post-Esophageal ¹²⁵I Particle Stent

Objective:To observe the effect of removing the metal artifacts produced by ¹²⁵I particles in esophageal stent, by using Gemstone spectral imaging （GSI） technique and metal-artifacts reduction software（MARS） of GE Discovery CT HD750 machine.Methods:20 patients with esophageal stent implantation underwent spectral CT scan, three sets of data were obtained,140kVp mixing energy image （QC）, the monochromatic imaging （MONO） and the corresponding scanned by metal-artifacts reduction software （MONO+MARS）. In MONO and MONO+MARS images, the 40-140keV images were reconstructed to eleven groups （group spacing 10keV）. Use the volume rendering technique to do the 3D reconstruction of the 3 groups of images.① Subjective ratings:Three experienced radiologists evaluate the image quality of different group independently, the evaluation process is blinding. The evaluation precautions includes the display of ¹²⁵I particles in the esophageal stent, the metal artifacts produced by the ¹²⁵I particles, the effects of removing the metal artifacts, the display of surrounding lesions, the noise of the image, etc. The image quality was rated by using a 0-5 scoring method. ②Objective evaluation:Looking for the single energy value corresponding to the optimal CNR in the Gemstone spectral imaging （MONO） and the corresponding imaging scanned by metal-artifacts reduction software （MONO+MARS）; using the formula to calculate the relative index of the surrounding metal artifacts caused by ¹²⁵I particles, including artifact index（AI）, contrast to noise ratio （CNR）, signal noise （SN） to carry out an objective evaluation. Analyzing the influence of different imaging techniques on image quality through subjective ratings and objective evaluation. Results:1. The subjective ratings of MONO images in 60-70keV were higher than QC images, the subjective ratings of MONO+MARS images in 70-80keV were lower than QC images, and statistical significance was observed between them（P<0.05）.2. In MONO images, the optimal CNR appeared in 66.3±1.94keV level, and in MONO+MARS images, the optimal CNR appeared in 72.85±1.42keV level.3. In MONO image of 60-70keV, comparing to QC image, AI value was higher, and the difference was statistically significant （P <0.05）, CNR and SN value was higher, but there was no statistically significant difference between them （P>0.05）.4. In MONO+MARS image of 70-80keV, comparing to QC image, CNR value was higher, AI value was lower, and the difference was statistically significant （P<0.05）, SN value was higher, but there was no statistically significant difference between them （P>0.05）.5. Comparing to MONO+MARS image, the subjective ratings and AI value of MONO image was higher, the CNR value of MONO image was lower, these index of MONO and MONO+MARS images at different energy levels were statistically significant （P<0.05）, the SN value difference of them was no statistically significant （P>0.05）.Conclusion:In clinical CT scanning of post-esophageal ¹²⁵I particle stent implantation patients, the Gemstone spectral imaging technique （MONO） can remove the metal artifacts produced by 12SI particles in esophageal stent, and improve image quality, the optimal CNR appeared in 60-70keV level. Metal-artifacts reduction software （MARS） over remove the metal artifacts produced by ¹²⁵I particles in esophageal stent, the image quality is poor, it does not fit to apply in clinical CT scanning of post-esophageal I25I particle stent implantation patients.