Feasibility Of Replacing Conventional Unenhanced Scan With Virtual Non-contrasted Imaging Of Revolution CT In Abdominal Examination

Purpose:to compare the difference between revolution ct abdominal virtual non-contrast(VNC)and conventional non-contrast(CNC),and to explore the feasibility of revolution ct abdominal virtual plain scan instead of conventional plain scan.Methods:a total of 105 patients with suspected abdominal lesions underwent plain and three-phase(arterial,portal and delayed)dynamic contrastenhanced CT scans in our hospital from January 2018 to June 2018 were selected with the approval of the Ethics Committee.Three groups of VNC images were reconstructed by software.The image quality of three groups of VNC images was evaluated by two experienced diagnostic doctors with double blind method.The objective indexes of image quality include the average CT value of region of interest(ROI),image noise,signal-to-noise ratio(SNR),contrast-to-noise ratio(CNR)and lesion detection rate.Results:(1)Subjective image quality score:the average subjective image quality score of two observers on three groups of VNC was lower than that of CNC,and there was significant difference between them(P<0.01).(2)Objective evaluation of image quality:there was no significant difference in the mean CT value of liver ROI between the three groups of VNC images and CNC(P>0.05).There was no significant difference in the mean CT value of erector spine muscle between portal phase VNC images and CNC(P=0.317),but there was significant difference between arterial phase VNC,delayed phase VNC and CNC(P<0.05).The mean CT value of abdominal aorta ROI in arterial VNC images was significantly different from that in CNC images(P<0.01),but there was no significant difference between portal VNC and delayed VNC images(P>0.05).There was no significant difference between VNC in pulse phase and CNC in delayed phase(P>0.05),and there was no significant difference in mean CT value of spleen ROI between the three groups(P>0.05).There were statistically significant differences between CNC and CNC in three groups of VNC images(P<0.05),SNR in three groups of VNC images(P<0.01),CNC and portal phase in three groups of VNC images(P=0.041),VNC in arterial phase,VNC in delayed phase and CNC in delayed phase.The difference was not statistically significant(P>0.05).(3)The detection rate of lesions: 154,152,151 and 149 were detected by Revolution CT and three groups of VNC respectively.The detection rates of CNC and VNC in tumor-like changes,vascular lesions,calculi or calcification were not consistent between the three groups,and the overall differences were statistically significant(P<0.05).Among the three groups,the detection rate of VNC for microcyst(diameter<5mm)was higher than that of CNC,and the detection rate of VNC for microangioma in arterial phase was the same as that of CNC.VNC in delayed phase was the lowest,followed by VNC in portal phase.VNC is easy to miss the diagnosis of small calculi or calcified lesions(diameter<2mm).Although intrahepatic calcified lesions with diameter>2 mm or intrahepatic bile duct stones or cholecystolithiasis can be detected,the range of lesions is thinner than that of CNC,and the range of lesions is narrower.(4)Radiation dose assessment:Revolution CT abdominal examination omitted routine plain scan steps,routine plain scan combined three groups of VNC imaging and single three-phase enhancement for statistical analysis can effectively reduce the radiation dose of nearly 1/4.Conclusion:the image quality of revolution ct virtual plain scan can meet the need of imaging diagnosis and reduce the radiation dose effectively,making it possible to replace conventional plain scan.