Selecting optimal monochromatic level with spectral CT imaging for improving imaging quality in hepatic venography

Objective To investigate the effect of spectral CT monochromatic images for improving imaging quality in hepatic venography. Methods Thirty patients underwent spectral CT examination on a GE Discovery CT 750 HD scanner.During portal phase,1.25 mm slice thickness polychromatic images and optimal monochromatic images were obtained,and volume rendering and maximum intensity projection were created to show the hepatic veins respectively.The overall imaging quality was evaluated on a five-point scale by two radiologists.Inter-observer agreement in subjective image quality grading was assessed byKappastatistics.Paired-sample t test were used to compare hepatic vein attenuation,hepatic parenchyma attenuation,CT value difference between the hepatic vein and the liver parenchyma,image noise,vein-to-liver contrast-to-noise ratio (CNR),the image quality score of hepatic venography between the two image data sets. Results The monochromatic images at 50 ke V were found to demonstrate the best CNR for hepatic vein.The hepatic vein attenuation[ (329±47) HU],hepatic parenchyma attenuation[ (178±33) HU],CT value difference between the hepatic vein and the liver parenchyma[ (151±33) HU],image noise (17.33±4.18),CNR (9.13±2.65),the image quality score (4.2±0.6) of optimal monochromatic images were significantly higher than those of polychromatic images[ (149±18) HU],[ (107±14) HU],[ (43±11) HU],12.55±3.02,3.53±1.03,3.1±0.8 (t values were 24.79,13.95,18.85,9.07,13.25 and 12.04,respectively,P<0.01).In the comparison of image quality,Kappa value was 0.81 with optimal monochromatic images and 0.69 with polychromatic images. Conclusion Monochromatic images of spectral CT could improve CNR for displaying hepatic vein and improve the image quality compared to the conventional polychromatic images. Key words: Hepatic vein; Tomography,X-ray computed; Comparative study