Improvement in the Image Quality of Bile and Pancreatic Ducts with Dual- Layer Spectral CT

While multiple imaging modalities have been developed for the evaluation of biliary and pancreatic ducts, none is considered ideal. Dual-layer Spectral Computed Tomography (DSCT) offers potential advantages through dual-energy acquisition and spectral imaging, but its application for biliopancreatic ducts remains unclear. The objective of this retrospective observational study was to evaluate image quality and determine the optimal energies of Virtual Monoenergetic Images (VMIs) from DSCT of biliary and pancreatic ducts.

We analyzed contrast-enhanced abdominal DSCT images of 75 patients with normal ductal anatomy. Both conventional Polyenergetic Images (PEIs) and VMIs at energy levels ranging from 40-140 keV (10-keV intervals) were reconstructed. The ductal system was categorized into four groups: intrahepatic bile ducts (Group A), extrahepatic bile ducts (Group B), pancreatic ducts (Group C), and the main pancreatic ducts (Group D). Objective image quality parameters, including CT values, image noise, the Contrast-to-Noise Ratio (CNR), and the Signal-to-Noise Ratio (SNR), were systematically measured and compared across different energy levels.

Compared with the PEIs, the VMIs reconstructed at low keV levels via DSCT demonstrated superior image quality across the four groups. Significant differences in CNR values were observed between VMIs at 40 keV and PEIs in Group A [4.30 (2.79, 6.15) vs. 3.37 (2.52, 4.32), p = 0.013], Group B [10.46 (8.41, 12.43) vs. 5.83 (4.47, 6.94), p < 0.001], Group C [11.50 (9.05, 14.48) vs. 5.34 (4.31, 6.56), p < 0.001], and Group D [9.11 (7.00, 11.86) vs. 5.36 (4.34, 6.95), p < 0.001].

This suggests a clear advantage of low-energy VMIs in depicting subtle ductal anatomy that is poorly visualized on standard CT. The consistent reduction in image quality metrics with increasing energy further supports the use of low-keV settings for soft-tissue duct evaluation. Limitations, including the retrospective design and single-vendor platform, are acknowledged.

Compared with conventional images, VMIs at low keV exhibit superior image quality; thus, VMIs may be incorporated into routine clinical imaging protocols.