Comparing radiation dose and image quality between spectral CT and conventional multi-slice CT in imaging liver

Objective To evaluate the clinical value of spectral CT mode in imaging liver by comparing the radiation dose and image quality between spectral CT and conventional multi-slice spiral CT (MSCT). Methods Thirty patients (group A) underwent three-phasic enhanced CT scans spectral CT mode in the portal phase (PP) and conventional helical mode in other phases (Discovery CT 750 HD,GE Healthcare).Another 30 patients in group B underwent conventional three-phasic enhanced CT on a 64-slice MSCT (VCT,GE Healthcare) with 120 k Vp and automatic tube current modulation (ATCM) and noise index of 15.The images in PP from the two imaging modes were retrospectively compared.The contrast-noise-ratio (CNR) for the veins was calculated using liver parenchyma as background.For the spectral CT mode,101 sets of monochromatic images were reconstructed from 40 to 140 keV,and the optimal energy level for obtaining the highest CNR was determined using the Gemstone Spectral Imaging (GSI) -viewer software.Image noise (at 70 keV),CNR (at the optimal keV level) for the vein and radiation dose to the patient were obtained for spectral images and statistically compared with those in group B with the conventional MSCT using t test. Results The CTDIw value in PP for spectral CT was 15.64 mGy,30% lower than the (22.44± 5.09) mGy for the conventional MSCT (t=29.56,P 0.05).On the other hand,CNR for the vein at the optimal energy level in spectral CT was 7.17±2.09,which was significantly higher than the 2.76±1.34 for the conventional MSCT (t=7.21,P<0.01). Conclusion Compared with conventional standard-dose liver MSCT,spectral CT imaging provides improved CNR for vessels,comparable image noise for liver parenchyma with 30% dose reduction. Key words: Radiation dosage; Liver neoplasms; Portal vein