Comparison of Topogram-based Automated Selection of Tube Potential and Fixed Tube Potential in Imaging Solid Pancreatic Lesions.

Objective To evaluate the image quality and radiation exposure in multidetector computed tomography (MDCT) with automated topogram-based tube potential selection,compared to fixed tube potential,in patients with solid pancreatic lesions. Methods The preoperative pancreatic dual-source CT images of 113 patients who were confirmed as solid pancreatic lesions by postoperative pathology in the Peking Union Medical College Hospital from January 2014 to August 2016 were retrospectively analyzed.Among them,53 patients were examined on fixed tube potential at 120 kV,and tube current was automatically modulated (group 1). Sixty patients underwent topogram-based automatic tube potential selection (Tube voltage step:90,100 kV) and automated mA modulation (group 2). Two experienced radiologists measured the body sizes,assessed subjective and objective image quality of arterial phase and portal phase,and recorded radiation parameters including CT dose index volume (CTDIvol) and dose-length product (DLP). Results Of 60 patients in group 2,45 patients were scaned at 90 kV,15 patients were scaned at 100 kV.The average body diameter [(287±24) mm] in 90 kV group was significantly lower than that [(328±22) mm] in 100 kV group(t=0.731,P=0.0008). The mean CTDIvol [(3.9±1.0) mGy] in group 2 was significantly lower than in group 1 [(9.0±1.9) mGy],reduced by 56.7% (t=17.5,P=0.0003). The average DLP [(109±38) mGy·cm] in group 2 was significantly lower than that in group 1 [(276±83) mGy·cm],reduced by 60.5% (t=14.0,P=0.0007). In group 2,the standard deviations of images background noise in arterial and portal phase were (6.4±0.9) and (6.4±1.0)HU,respectively,which were significantly higher than those in group 1 [(5.6±1.4)HU,t=-3.757,P=0.0003;(5.5±1.4)HU,t=-3.828,P=0.0006]. In group 2,the signal to noise ratios of pancreatic lesions, abdominal aorta in arterial phase and pancreatic lesions, the portal vein in portal phase were 18.8±9.3,76.0±19.3 and 17.4±6.7,33.1±7.2,which were significantly higher than those in group 1 (13.1±8.7,t=-3.379,P=0.001;56.5±22.6,t=-2.268,P=0.025;14.1±8.1,t=-2.283,P=0.024;28.9±8.8,t=-2.613,P=0.009). Conclusion Compared with fixed tube voltage on the second-generation dual-source CT techniques,topogram-based automatic tube potential selection on third-generation dual-source CT can reduce radiation dose without decreasing image quality in imaging solid pancreatic lesions.