BACKGROUND: Ventilation/perfusion single-photon emission computed tomography (V/Q-SPECT) is the standard first-line imaging method for chronic thromboembolic pulmonary hypertension (CTEPH), but it lacks anatomical detail. Photon-counting computed tomography (PCCT) enables high-resolution assessment of perfusion, vasculature, and parenchyma in one scan, potentially improving diagnostic accuracy. OBJECTIVES: To compare quantitative lobar lung perfusion between PCCT and V/Q-SPECT in patients with suspected or confirmed CTEPH. MATERIALS AND METHODS: This retrospective single-centre study included twenty-three patients (ten females, thirteen males; mean age 67.9 ± 10.7 years). The median interval between PCCT and V/Q-SPECT imaging was 3 days (range: 0-11 days). Lung perfusion was analysed on a lobar basis using PCCT-derived perfused blood volume (PBV) maps and V/Q-SPECT perfusion images. Data were normalised using a z-score approach based on the 95% confidence interval. Lobar segmentation was performed with TotalSegmentator. Pearson correlation and Bland-Altman analyses compared lobar and whole-lung perfusion metrics. Perfusion defect volumes were quantified from normalised maps. RESULTS: Whole-lung perfusion correlated strongly between PCCT and V/Q-SPECT (r = 0.72, p < 0.05). Lobar correlations ranged from r = 0.62 to r = 0.85. PCCT yielded slightly higher perfusion values (mean PBV 0.50 ± 0.04) than V/Q-SPECT (0.49 ± 0.09). Bland-Altman analysis showed a bias of +0.015 (limits -0.13 to +0.16). Perfusion defect volumes correlated moderately (whole-lung r = 0.60, lobes r = 0.49-0.77, p < 0.05). CONCLUSION: PCCT-based perfusion imaging shows high concordance with V/Q-SPECT in this cohort, supporting its feasibility as a single-modality tool for functional and anatomical lung evaluation in CTEPH. KEY POINTS: Question PCCT perfusion may address the unmet need for a combined functional and anatomical evaluation of CTEPH in a single examination. Findings PCCT showed strong correlation with V/Q-SPECT for lobar and whole-lung perfusion, with minimal bias and consistent quantitative agreement. Clinical relevance PCCT enables simultaneous high-resolution assessment of perfusion, vasculature, and parenchyma, potentially improving diagnostic confidence and streamlining CTEPH work-up in clinical practice.
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