Abstract: Objective To investigate the effect of low concentration of contrast media with energy spectral CT on the image quality of CT portal venography. Methods 50 patients were divided into 5 groups underwent spectral CT examination on a GE Discovery CT 750 HD scanner, the total contrast media were offered at 1 mL/kg to 50 patients, the contrast media concentration of 320 mgI/mL, 288 mgI/mL, 256 mgI/mL, 224 mgI/mL, 192 mgI/mL were offered for the 5 groups patients. During portal phase, 0.625 mm slice thickness polychromatie images and optimal monochromatic images were obtained, and volume rendering and maximum intensity rojection were created to show the portal venography respectively, the CT unit and standard deviation were measured at the port venography and the erector muscle of spine, calculated the signal-noise ratio and the contrast-noise ratio, calculated the singal-noise ratio and contrast-noise ratio with the CT volue of port venography and the erector muscle of spine. The overall imaging quality was evaluated on a five-point scale by 3 radiologists, Comparisons between 5 groups were tested by One-Way ANOVA analysis.Results The monochromatic images at 50-55 keV were found to demonstrate the best CNR for both the portal vein and erector muscle of spine. The SNR with the different concentrations of contrast media was 15.83±3.02, 14.78±2.13, 13.87±1.91, 9.37±2.13, 7.72±2.82 and the CNR was 14.95±3.82, 15.01±3.79, 13.93±3.52, 10.35±4.22, 9.65±3.56. The values by three independent radiologists were 4.50±0.81, 4.45±0.76, 4.41±0.73, 4.38±0.79, 3.5±0.57. The dates of SNR , CNR and values were not statistically significant at the contrast media concentration of 320 mgI/mL, 288 mgI/mL, 256 mgI/mL, 224 mgI/mL(F=36.221, P<0.05). The dates of SNR, CNR and values were statistically significant at the contrast media concentration of 320 mgI/mL, 288 mgI/mL, 256 mgI/mL and 224 mgI/mL, 192 mgI/mL（F=7.221, P>0.05） . In the comparison of image quality, Kappa value was 0.86 with the contrast media concentration of 320 mgI/mL, 288 mgI/mL, 256 mgI/mL and 0.63 with 224 mgI/mL, 192 mgI/mL. Conclusion The best monochromatic images of spectral CT could reduce the contrast media concentration, Recommend concentration of the contrast media was 256 mgI/mL at portal venography by spectral CT imaging. The best monochromatic X-ray keV was 50-55 keV.

Key words: low concentration of contrast media, CT portal venography, image quality, comparative studies