Comparative accuracy of photon-counting and dual energy CT pulmonary angiography perfusion mapping using V/Q scans as reference standard

To compare the diagnostic performance of photon-counting–detector CT (PCD-CT) and dual-energy CT (DECT) perfusion maps against ventilation–perfusion (V/Q) SPECT/CT as reference standard across diverse clinical indications, and to provide quantitative iodine density reference values. This retrospective study included two independent cohorts who underwent V/Q SPECT/CT and either PCD-CT or DECT. Lobar perfusion was assessed on each modality by two blinded readers with consensus serving as the reference for inter-reader agreement. Diagnostic accuracy, sensitivity, specificity, PPV, and NPV were calculated using V/Q SPECT/CT as the reference standard. Iodine density was measured using standardized regions of interest placed in normally perfused and hypoperfused lobes. Inter-reader agreement was evaluated using Cohen’s κ. Statistical comparisons were performed using paired or unpaired tests as appropriate, with significance set at p < 0.05. PCD-CT demonstrated an accuracy of 0.85, sensitivity of 0.71, specificity of 0.97, and κ of 0.80. DECT demonstrated an accuracy of 0.89, sensitivity of 0.52, specificity of 0.97, and κ of 0.59. Differences in diagnostic performance between PCD-CT and DECT were not statistically significant. Iodine density was significantly higher in normally perfused lung compared with perfusion defects for both PCD-CT (2.10±0.29 vs 0.40±0.18 mg/mL; p < 0.001) and DECT (2.30±0.29 vs 0.49±0.17 mg/mL; p < 0.001). Both PCD-CT and DECT provide high diagnostic accuracy for detecting lobar perfusion defects, with PCD-CT demonstrating higher inter-reader agreement. This study provides the first quantitative iodine reference values for PCD-CT pulmonary perfusion, supporting its potential as a robust functional complement to conventional CTPA.