Development and external validation of a dual-energy CT-biochemical score for the detection of radiolucent common bile duct stones

The purpose of this study was to evaluate the diagnostic performance of dual-energy computed tomography (DECT) effective atomic number (Z_eff) mapping for detecting radiolucent common bile duct (CBD) stones and to develop and externally validate a simple, combined imaging-biochemical score.

This retrospective multicenter study included consecutive adults who underwent magnetic resonance cholangiopancreatography (MRCP) due to suspected choledocholithiasis after a negative conventional abdominal dual-layer DECT performed within 21 days. In the derivation cohort, Z_eff and electron-density maps were independently reviewed by two radiologists, with consensus adjudication for interreader disagreements, using MRCP as the reference standard for CBD stones. Variables associated with MRCP-confirmed stones were entered into a multivariable logistic regression to derive a simplified score (i.e., ZBG score) based on Z_eff map positivity, conjugated bilirubin or gamma-glutamyl transferase serum levels, which was then validated in an external validation cohort.

The derivation cohort included 100 patients (mean age, 65.8 ± 19.3 [standard deviation] years; 54 men), of whom 19 had radiolucent CBD stones. The validation cohort included 101 patients (mean age, 60.2 ± 19.4 [standard deviation] years; 49 men), of whom 17 had radiolucent CBD stones. Consensus Z_eff mapping yielded 63% sensitivity (95% confidence interval [CI]: 38-84), 86% specificity (95% CI: 77-93), and 82% (95% CI: 73-89) accuracy for the diagnosis of radiolucent CBD stones. Z_eff map positivity (odds ratio [OR], 18.69; 95% CI: 4.22-82.68; P < 0.001) and conjugated bilirubin ≥ 50 µmol/L and/or γ-glutamyl transferase > 500 IU/L (OR, 20.67; 95% CI: 3.39-126.09; P = 0.001) were two variables that were independently associated with CBD stones. These two variables were combined into the ZBG score, with 1 point assigned to each item. The resulting ZBG score (range: 0-2) showed an area under the curve of 0.870 (95% CI: 0.801-0.939) in the derivation cohort and 0.877 (95% CI: 0.791-0.963) in the validation cohort for the diagnosis of radiolucent CBD stones.

For patients with suspected CBD stones and negative conventional CT results, a simple score combining DECT Z_eff mapping and routine cholestatic biomarkers provides accurate risk stratification for radiolucent CBD stones.