Monochromatic energy images from spectral CT in diagnosing X-ray negative biliary stones

Abstract

Objective To study the role of monochromatic energy images from spectral CT in diagnosing X-ray negative biliary stones. Methods 32 patients who were diagnosed to have X-ray negative biliary stones were retrospectively studied. They were examined by spectral CT scanning and the spectral CT data were loaded into a spectrum analysis software. The optimal contrast-to-noise ratio (CNR) of the monochromatic energy images were exposed and the contrast ratio between the X-ray negative stones and bile on the optimal monochromatic and hybrid energy CT images were compared, respectively. The monochromatic and hybrid energy CT images for diagnosing X-ray negative biliary stones were validated by two senior radio-logists based on postoperative histology. Results The corresponding KeV of optimal CNR for X-ray negative stones were not quite consistent. They were 140KeV in 19 patients, 40KeV in 8 patients, 53KeV, 57KeV, 62KeV, 64KeV and 73KeV in one patient each. The contrast between the negative stones and the adjacent bile were (6.4±5.6) HU on hybrid energy CT images and (50.4±24.4) HU on optimal monochromatic energy CT images. The Eff-Z of negative stones and bile were 6.6±0.6 and 7.9±0.2, respectively. In our study, the diagnostic accuracy of hybrid energy CT images was 34.38% and that of optimal monochromatic energy CT images was 78.13%. Conclusion The optimal monochromatic energy CT images were more va-luable in diagnosing X-ray negative bile duct stones, which were obviously better than the hybrid energy images from traditional CT. Key words: Spectral CT; Biliary X-ray negative stone; Monochromatic energy images; Biliary calculi; Diagnosis