Clinical Application Study Of Dual Energy Virtual Non-contrast Of Dual-source CT In Upper Abdomen

Objective: To investigate the diagnostic value and limitations of dual-energy virtual non-contrast images of dual-source CT in the abdominal lesions. Methods: 226 patients who were suspected with the abdominal lesions were collected between November 1st, 2014 and February 30 th, 2015 from Affiliated Hospital of Zunyi Medical College, 141 male and 85 female, mean age 50.99±14.27 years, range 15–87 years. Conventional and enhanced scans were performed with Siemens Somatom definition flash dual-source CT in all patients. The conventional non-contrast(CNC) was performed with single-energy mode(120k V/350 m As), the arterial phase and portal phase scans were performed with dual-energy mode(100k V/230 m As and Sn140 k V/178 m As). The dual energy(DE) raw data from both detectors were reconstructed by using a soft convolution kernel(D30f), and three different series of images were generated which including 100 k V images, Sn140 k V images, and mixed images with ratio of 0.5(slice thickness =1.5mm, interval=1.0mm.)Images were loaded into a dedicated DE post-processing workstation. DE images from the portal phase were processed by the liver virtual non-contrast(VNC) to generate VNC images. All VNC images were saved and reloaded into three-dimensional software, then axial images(slice thickness= 6mm, interval=6mm) with the same window and level were reconstructed, and then contrastive analysis between reconstructed axial images and the CNC images were performed. A region of interest(ROI) at each anatomical site for CNC and VNC images was delineated in each patient, and the CT value, SD value, SNR and radiation doses were recorded by the same radiologist. Paired-Samples T Test was used to compare CT value, SD, SNR, radiation doses between CNC and VNC. The image quality of two sets of non-enhanced images were evaluated by two experienced radiologists, respectively, and Wilcoxon signed-rank test was used to compare the score results. Based on a standard that conventional non-contrast images combined with enhanced images, the abdominal lesions in this group were divided into benign tumor and tumor-like lesions, malignant tumors, diffuse lesions, infectious lesions, calcifications or stones, vascular lesions, lipiodol deposition and other lesions 8 types. The lesion numbers of various types in two sets of non-enhanced images were recorded, respectively, And chi square test was used to compare the lesion detectability on two sets of non-enhanced images. Results: Image quality of VNC(4.02±0.74) was lower than that of CNC(4.42±0.63) and the difference was significant(P < 0.05). The average CT value on VNC images was lower than that of CNC(all P <0.05), except for liver higher than CNC images(P <0.05),and spleen and fat similar as CNC images(P >0.05). Noise was lower on VNC images than CNC images(all P < 0.05). SNR on VNC images was lower than that of CNC(all P <0.05), except for liver and spleen higher than CNC images(P <0.05),and fat similar as CNC images(P >0.05). Among 226 patients, there were 30(76.9%) hemangiomas,172(83.9%) calcifications or stones in VNC, but the hemangiomas,calcifications or stones in CNC were 39(100%) and 205(100%), respectively. The hemangiomas, calcifications or stones in VNC and CNC were significantly different(P < 0.05). The detection of cyst on VNC images was higher than CNC images(P < 0.05). other types were similar as CNC. The CTDIvol(22.76±1.68), DLP(554.98±87.06) and ED(8.32±1.31) of dual-energy mode were obviously lower than single-energy mode(37.30±3.15,905.62±196.95,13.59±2.20) and the difference was significant(all P < 0.05). The radiation dose reduction achieved by omitting the CNC acquisition was 38%. Conclusion:Although image quality of VNC is lower than that of conventional nonenhanced CT, it can meet the diagosis. The detection of hemangiomas, calcifications or stones on VNC images is lower than CNC images, while there is an advantage for detecting cyst on VNC. Except for calcifications or stones, there is no difference in detecting various types of abdomen lesions by using the method that VNC combined with enhanced images, in addition, radiation dose will be reduced due to adopting VNC.VNC has potential clinical application value.