Evaluation of HOP-MRA for Post-Coil Embolization Assessment of Cerebral Aneurysms: A Comparative Study with 3D-TOF MRA

Purpose: Hybrid of opposite contrast magnetic resonance angiography (HOP-MRA) is a technique that enhances the visualization of slow-flow vessels by subtracting the low-signal component of flow-sensitive black blood (FSBB) imaging from the high-signal component of 3D time-of-flight (TOF) MRA. This study evaluates the utility of HOP-MRA in assessing residual lumen and parent artery structure following cerebral aneurysm coil embolization, focusing on its relevance in neurovascular imaging. Methods: A comparative analysis was conducted using both in vitro phantom models and in vivo patient data. A phantom model containing a coiled aneurysm was assessed with HOP-MRA and 3D-TOF MRA to evaluate susceptibility artifacts. Additionally, 12 patients with 13 coiled aneurysms underwent both imaging modalities. Aneurysm remnant and parent artery visualization were graded using a three-grade scale, and interobserver agreement was analyzed. Results: Phantom experiments revealed increased susceptibility artifacts with HOP-MRA, particularly in the parent artery region. However, in vivo imaging demonstrated no significant difference in parent artery and aneurysm remnant visualization between HOP-MRA and 3D-TOF MRA (interobserver agreement: 96%). HOP-MRA provided more anatomically accurate depictions in select cases compared with digital subtraction angiography, particularly in small residual aneurysm remnants. Conclusion: Despite susceptibility artifacts observed in vitro, HOP-MRA demonstrated comparable performance to 3D-TOF MRA in assessing post-embolization aneurysm remnants and adjacent vasculature. This suggests that HOP-MRA can be utilized as an alternative imaging technique, particularly in cases where slow-flow remnants are suspected, when appropriate parameters are applied.