Diagnostic accuracy of dual-energy CT Rho/Z maps for detecting secondary choledocholithiasis

Background: Because of its ability to identify isoattenuating gallstones, electron density (Rho) and effective atomic number (Z) maps derived from dual-energy computed tomography (CT) hold promise for secondary choledocholithiasis detection in lieu of magnetic resonance cholangiopancreatography (MRCP). The aim of this study was to investigate the diagnostic performance of dual-energy CT Rho/Z maps in detecting secondary choledocholithiasis in patients with gallbladder stones. Materials and methods: This retrospective single-center study included patients who underwent unenhanced abdominal dual-energy CT and MRCP for suspected secondary choledocholithiasis between July 2019 and March 2023. Conventional CT, Rho and Z images were generated. Two radiologists performed blinded consensus choledocholithiasis evaluation in four reading sessions (session 1, conventional CT images; session 2, Rho maps alone; session 3, Z maps alone; session 4, Rho plus Z maps). Diagnostic performance in choledocholithiasis detection was compared between reading sessions using the McNemar and DeLong tests. Results: A total of 89 patients (mean age, 54 years ± 13 [SD]; 45 male) were enrolled, including 41 patients (48.2%) with secondary choledocholithiasis. Diagnostic performance was greater with Rho plus Z maps compared with conventional CT for choledocholithiasis detection, with an area under the receiver operating characteristic curve (AUC) of 0.734 for conventional CT and 0.855 for Rho plus Z maps (P = .007); corresponding sensitivities were 51.2% (22 of 43 patients) for conventional CT and 74.4% (32 of 43 patients) for Rho plus Z maps (P = .004). The corresponding specificities were equal (95.7%, 44 of 46 patients) (P = 1.000). Additionally, Rho plus Z maps achieved comparable diagnostic performance with MRCP for diagnosing choledocholithiasis (AUCs: 0.855 vs 0.875, P = .526). Conclusion: Combined use of Rho and Z maps from unenhanced dual-energy CT improved detection of secondary choledocholithiasis compared with conventional CT and held promise for an alternative to MRCP.