Spectral CT monochromatic imaging of hepatocellular carcinoma: effect of image fusion on image quality

Abstract

Objective To assess the effects of image fusion of CT spectral monochromatic imaging on image quality in small hepatocellular carcinoma (HCC). Methods Thirty patients with 40 pathologically proven small HCCs (≤3 cm) underwent upper abdominal plain CT and dual- phase enhanced spectral CT scan were analyzed retrospectively. Conventional 140 kVp polychromatic images (group A) and monochromatic images with energy levels from 40 to 140 keV were reconstructed by using spectral imaging viewer. Monochromatic images with highest CNR(group B) and 70 keV images with lowest noise (group C) were fused to generate fused images (group D) with image fusion software. Objective evaluation of 40 HCCs[contrast-to-noise ratio (CNR) of lesion, image noise in HU] and subjective rating score of 30 patients (image noise score, overall image quality score, and lesion conspicuity score) among the four groups were compared by using One-way ANOVA and Kruskal-Wallis H test. Results CNR (1.3±0.6, 2.1±0.6, 1.5±0.6 and 2.4± 1.3 respectively) and image noise [(20±7), (32±9), (18±3) and (24±6) HU respectively] among group A, B, C and D all had statistical differences(F =5.724 and 13.619, both P values 0.05). Image noise in group D was lower than group B and higher than group C, but showed no difference from group A(all P values >0.05). Image noise scores [(3.5±0.5),(3.3±0.4),(3.6±0.5) and (3.5±0.4) point, respectively] , overall image quality scores [(3.2±0.4),(3.3±0.3), (3.1±0.3)and(3.7±0.4)point respectively] and lesion conspicuity scores [(3.3±0.4),(3.9±0.4), (3.2±0.4)and(3.7±0.4)point, respectively] among the four groups all had statistical differences(Z = 9.581, 37.495 and 43.436, all P values<0.05). Scores of the four groups were all greater than 3 and met the clinical diagnostic level. Group D was higher than group B in image noise score, higher than the other three groups in overall image quality score, higher than group A in lesion conspicuity score (all P values < 0.05). Conclusion Combined use of CT spectral monochromatic imaging and image fusion can improve overall image quality while maintaining or increasing CNR in small HCC. Key words: Liver neoplasms; Tomography, X-ray computed; Comparative study