Feasibility of using virtual non-contrast images derived from spectral CT instead of the true non-contrast images for thyroid nodules evaluation

HU Lei; LUO Dehong; LI Lin; LIN Meng; ZHAO Yanfeng; GUO Wei; ZHAO Xinming; ZHOU Chunwu

doi:10.19300/j.2017.L4603

Abstract：Objective The study aimed to determine whether virtual non-contrast (VNC) images derived from spectral CT can replace true non-contrast (TNC) images for thyroid nodules evaluation. Methods Retrospectively analyzed images of 72 patients with thyroid diseases who had undergone traditional plain CT scan and enhanced spectral CT scan in our hospital during Feb.-Oct. 2014. The CT values of different tissues, subjective image quality, objective image quality, diagnostic ability of calcifications, and radiation dose were compared between TNC and VNC images with paired t test and Wilcoxon signed rank test. Results 1. Significant differences were observed in CT values of thyroid nodules and other tissues except fat (P<0.05) between TNC and VNC images. Except of normal thyroid tissues, all the CT value differences were less than 4 HU. There was no significant difference in fat CT values between TNC and VNC images (P>0.05). The noise of VNC images was higher than that of TNC, and the SNR, CNR of VNC images were lower than those of TNC (P<0.05). 2. The median scores of objective image quality of TNC and VNC images both were 4.0, and the score of VNC images was lower than that of TNC, but the difference was not significant (P>0.05). 3.TNC images presented calcification in 24 cases, whereas VNC images in 22 cases. No significant difference was found in calcification number between TNC and VNC images (P>0.05), however the long-axis diameters of the largest calcifications were smaller on VNC images than that on TNC images (P<0.05). 4. The values of dose length product and effective dose of the enhanced spectral CT were much lower than those of TNC plus enhanced CT scan, and the differences were significant(P<0.05). Compared with conventional non-contrast and contrast mode scan, spectrum mode enhanced scan reduced effective dose by 48.76%. Conclusion VNC images could be a potential sub-stitution for TNC images for thyroid nodules evaluation.