A Comparative Study Of Image Quality Of Dual Source Dual Energy CT Pulmonary Angiography With Different Weight Factor

Objective: To study the effects of different weight factors on CT values,noise, SNR and image quality of the CTPAusing the new dual-source CT,and investigate the optimal weight factor of the CTPAusing the newdual-source CT.Materials and Methods:32patients suspected pulmonary embolismunderwent thoracic new dual-source CT scan with and without contrastmedia, and the images of140kV and80kV were obtained and were sent topost processing workstation，then nine sets of140kV and80kV mixingenergy images with different weight factor from0.1to0.9in every patientwere made. First, the CT values and noise of pulmonary arteries includedmain pulmonary artery, left pulmonary artery and left lowerpulmonaryartery of the11sets images were measured, and then the SNR werecalculated. The differences of the11sets images in CT values, noise andSNR were compared using multiple related samples test and LSD-t test.Then, the image quality scores of the pulmonary arteries in the image setswith the maximum CT value, the lowest noise and the highest SNR were ranked by two radiologists using a double blind method. The image qualityscore differences of the image sets were compared using Friedman test formultiple paired samples and Wilcoxon test for paired samples.Results:1.The CT values of the pulmonary arteries at all levels were increasedalong with the increasing of the weight factor. The CT values of the imagesets with80kV(the weight factor of1.0) were maximum and there werestatistically significant differences between the80kV set and the othergroup(P=0.00); the noise of the mixed energy images with weight factor of0.3and0.4were minimum, there was no statistically significant differencebetween the two sets(P>0.05); the SNR of the mixed energy images withweight factor of0.5and0.6were maximum, there was no statisticallysignificant difference between the two sets(P>0.05).2.There were statistically differences in the image quality scoresamong the mixed energy images with weight factor of0.3,0.4,0.5,0.6and1.0(X2=58.32, P=0.00). The scores of the mixed energy images with aweight factor of0.6were maximum, followed by the mixing energy imagewith a weighting factor0.5, but there was no statistically significantdifference between the two sets(Z=-1.00, P=0.31).3.In the patients with BMI <25.0kg/m2, the image quality score with aweight factor of0.6was higher than that with a weight factor of0.5, andthe difference was statistically significant (Z=-2.00, P=0.04). Conclusion: In CTPA using the new dual-source CT, the mixedenergy images with weight factor of0.5and0.6can provide the maximumSNR and the best image quality. However, for the patients with normal size,the mixed energy images with a weight factor of0.6can provide the bestimage quality, thus the weight factor of0.6is recommend in practice.