4D Phase Contrast MRI Protocol Optimization using Patient-Specific 3D Printed Replicas for In-Vivo Imaging before and after Flow Diverter Placement

PURPOSE: Hemodynamics in cerebral aneurysms is currently investigated towards its clinical efficacy using non-standardized computational simulation techniques. At the same time, flow patterns and velocities are accessible by 4D phase contrast magnetic resonance imaging (4D pcMRI). Complexity of protocol design and imaging duration has limited the use of this technique in clinical imaging. A new approach is presented to overcome these limitations.

MATERIAL AND METHODS: 3D replicas of two cerebral aneurysms were fabricated by fused deposition prototyping (3D printing) and imaged using 4D pcMRI while connected to an MRI compatible continuous flow loop. Acquisition parameters were optimized with imaging times not to exceed 10 minutes. Six patients harboring cerebral aneurysms with sizes ranging from 4.7 - 13.8mm were imaged with the optimized 4D pcMRI protocol. After treatment with the Pipeline Embolization Device (PED), 4D pcMRI examinations were repeated in three patients.

RESULTS: In all cases, major flow patterns were visualized well; smaller aneurysms posed a challenge due to limited spatial resolution whereas larger aneurysms contained regions of low velocity resulting in limited contrast in the flow-sensitive images. After PED placement, ordered aneurysmal flow was disrupted and intra-aneurysmal velocity was reduced on average by 24.5% (range 12.9 - 31.5%). Exploratory statistical analysis yielded a positive significant correlation (p<0.01) between changes in inflow velocity and post-treatment intra-aneurysmal flow velocity.

CONCLUSION: 4D pcMRI flow imaging in cerebral aneurysms within a time frame suitable for clinical imaging applications is feasible with optimized acquisition parameters thereby enabling quantification of intra-aneurysmal flow changes after FDD treatment.