Ultra-high resolution Photon-Counting CTA for follow-up assessment of intracranial aneurysms after flow diverter: Initial experience.

BACKGROUND: Accurate imaging follow-up after flow diverter (FD) treatment is essential, but digital subtraction angiography (DSA) is invasive and conventional CT lacks resolution. Photon-counting CT angiography (PCCTA) offers ultra-high resolution (UHR) and improved artifact reduction. This study compared UHR-PCCTA versus standard resolution (SR)-PCCTA and DSA for comprehensive post-FD assessment. METHODS: This prospective study consecutively enrolled 47 participants treated with FD and subsequently underwent PCCTA with UHR and SR reconstructions between August 2023 and August 2024. Two readers independently analyzed images blindly, including aneurysm size, occlusion status, neck coverage, wall apposition, stent deformation, branch vessel with Likert-scale (1-5). Inter-rater reliability for both UHR and SR-PCCTA was assessed using the intraclass correlation coefficient (ICC) and weighted Cohen's kappa. Diagnostic performance of PCCTA within 1 month after FD was compared with that of immediate post-deployment DSA using confusion matrix. RESULTS: Totally 47 participants with 57 intracranial aneurysms treated with 51 FD stents. UHR-PCCTA exhibited higher diagnostic confidence (median = 5, IQRs = 5-5) compared to SR-PCCTA (median = 4, IQRs = 4-5, P < 0.05). UHR-PCCTA demonstrated a trend toward higher inter-rater agreement (κ: 0.814-1.0; ICC :0.902-0.960) relative to SR-PCCTA (κ: 0.668-1.0; ICC: 0.873-0.966) among both aneurysm and stent morphology. Compared with immediate post-deployment DSA, UHR-PCCTA showed excellent diagnostic accuracy for aneurysm neck coverage (93.3%), wall apposition (100.0%), stent deformation (93.8%), branch vessel inclusion (93.3%), along with very-good accuracy for aneurysm occlusion (88.2%). CONCLUSION: UHR-PCCTA demonstrates high reliability and diagnostic accuracy in the assessment of intracranial aneurysms following FD treatment. Its comprehensive imaging evaluation capability has the potential to inform clinical decision-making.