Spectral CT-derived peripheral iodine concentration in acute pulmonary embolism: association with subsegmental emboli and pulmonary infarction

OBJECTIVE: Pulmonary infarction (PI) is a recognised complication of acute pulmonary embolism (PE). While computed tomography pulmonary angiography (CTPA) provides high-resolution morphological imaging, it does not permit direct functional assessment of regional lung perfusion. Spectral CT pulmonary angiography (SCTPA) enables quantitative perfusion analysis using iodine maps. However, the relationship between peripheral perfusion impairment, subsegmental emboli (SSE), and PI remains incompletely understood. This study investigated their association using SCTPA. MATERIALS AND METHODS: This retrospective single-centre study included 62 patients: 31 with SCTPA-confirmed acute PE and at least one PI, and 31 controls without PE or PI. Peripheral iodine concentration (pIC) was quantified in standardised subpleural regions of interest in each lung segment. Embolic burden was assessed using the Mastora score. SSE were identified on SCTPA and analysed on a segmental basis. RESULTS: A total of 440 embolic occlusions were identified. In this selected cohort, PI occurred exclusively in segments affected by SSE and was not observed in segments without SSE. In mixed-effects modelling, SSE were independently associated with reduced pIC (β = -0.706, p < 0.001), while segmental emboli were also independently associated with lower pIC (β = -0.137, p < 0.001); lobar and central emboli showed no significant independent associations. The Mastora score showed a moderate correlation with the number of manifest PI (ρ = 0.566, p = 0.011). CONCLUSION: In this cohort, SSE were closely associated with PI and reduced peripheral iodine concentration. Quantitative pIC reflects regional hypoperfusion and provides functional information on lung perfusion in acute PE. KEY POINTS: Question: Can spectral CT-derived peripheral iodine concentration characterise regional perfusion impairment associated with subsegmental emboli and pulmonary infarction in acute pulmonary embolism? FINDINGS: In this selected cohort, pulmonary infarction occurred only in segments with subsegmental emboli, which showed reduced peripheral iodine concentration (pIC) on spectral CT iodine maps. RELEVANCE STATEMENT: Spectral CT-derived peripheral iodine concentration may provide functional information on regional hypoperfusion in acute pulmonary embolism and improve understanding of infarction-related perfusion impairment.