Clinical Utility and Limitations of Photon-Counting Detector CTA in the Follow-Up of Flow Diverter Stent.

Objective: Flow diverters (FDs) are widely used to treat intracranial aneurysms, with DSA serving as the gold standard for follow-up evaluation. Although a few studies have reported the use of photon-counting detector CTA (PCD-CTA) for minimally invasive follow-up after standalone FD treatment, PCD-CTA after coil-assisted FD placement has never been documented. Methods: We retrospectively analyzed 11 patients who underwent FD placement between May 2023 and December 2024, all of whom underwent post-procedural evaluation with PCD-CTA. Patients were categorized into 2 groups: standalone FD (n = 6) and coil-assisted FD (n = 5). PCD-CTA was performed on postoperative day 1, at 6 months, and at 12 months. Metal artifact reduction was applied in the coil-assisted group. Results: In the standalone FD group, PCD-CTA enabled reliable assessment of the in-stent lumen, FD apposition to the parent artery, and aneurysm occlusion, with findings consistent with those of DSA. In the coil-assisted FD group, when coils extended near the FD, evaluation of the in-stent lumen, FD-to-parent artery apposition, and aneurysm occlusion was hindered by metal artifacts in slices containing coils. Conversely, when coils were absent near the FD, partial visualization of intra-aneurysmal contrast was possible, although residual aneurysms tended to be underestimated. Conclusion: PCD-CTA demonstrated diagnostic performance comparable to that of DSA for postoperative evaluation following standalone FD placement. However, in coil-assisted FD cases, postoperative assessment remained limited by coil-related metal artifacts.