Chronological Changes in Intra-aneurysmal Signal Intensity on T1-weighted Black Blood Images after Endovascular Treatment for Unruptured Intracranial Aneurysms

Intra-aneurysmal thrombus formation is crucial for the healing of endovascularly treated aneurysms. This study evaluated whether T1-weighted black blood imaging can monitor thrombus formation by examining the relationship between chronological signal intensity changes and aneurysm occlusion status after flow diverter stenting and coil embolization. We retrospectively analyzed 78 patients with 83 aneurysms (flow diverter stenting: 28, coil embolization: 55) who underwent T1-weighted black blood imaging at 1 week, 3 months, and 6 months post-treatment. Relative signal intensity was calculated as the signal intensity of the aneurysmal sac divided by the signal intensity of the genu of the corpus callosum. Satisfactory occlusion (O'Kelly-Marotta grades C or D) at 6 months was the primary endpoint for flow diverter stenting, while residual intra-aneurysmal blood flow during the follow-up was defined as recurrence after coil embolization. In flow diverter stenting cases, relative signal intensity was elevated at 3 months and remained stable. Relative signal intensity 3 months after flow diverter stenting was significantly higher in the satisfactory occlusion group than the non-satisfactory occlusion group (0.99 ± 0.55 vs. 0.51 ± 0.34, p = 0.03) and independently associated with satisfactory occlusion (adjusted odds ratio per 0.1 increase = 1.35, p = 0.01). In coil embolization cases, relative signal intensity was highest at 1 week and decreased linearly. Higher relative signal intensity 1 week after coil embolization was associated with lower recurrence rates (0.60 ± 0.22 vs. 0.41 ± 0.12, p = 0.002) and independently linked to aneurysm recurrence (adjusted odds ratio per 0.1 increase = 0.55, p = 0.004). Relative signal intensity changes on T1-weighted black blood imaging differ between flow diverter stenting and coil embolization. High relative signal intensity 3 months after flow diverter stenting and relative signal intensity 1 week after coil embolization were significantly correlated with favorable outcomes.