In vivo and in vitro measurements of cerebral aneurysm hemodynamics

The hemodynamics of cerebral aneurysms is thought to play a critical role in their formation, growth, and potential rupture. Our understanding in this area, however, comes mostly from~in vitro~experiments and numerical simulations, which have limited realism.~In vivo~measurements of the intracranial blood flow can be obtained by Magnetic Resonance Imaging (MRI), but they typically suffer from limited accuracy and inadequate resolution. Here we present a direct comparison between~in vivo~and~in vitro~measurements of the flow inside an internal carotid artery aneurysm. For both, we use 4D (i.e. volumetric and time-resolved) MRI velocimetry performed in a 7 Tesla magnet at sub-millimeter resolution. The~in vitro~measurements are carried out in a 3D printed aneurysm replica scaled up by a factor three, effectively increasing the spatial resolution. The patient-specific inflow waveform and the corresponding Reynolds and Womersley numbers are matched in a flow loop that mimics the impedance of the vascular bed. Direct comparison of the velocity fields allows assessing the robustness of the~in vivo~measurements, while highlighting the insight achievable~in vitro. The data also represents a comprehensive test case for numerical simulations.