MRI-Based Validation of Aortic Blood Flow Simulations in a Rabbit Model of Extracorporeal Circulation

Background: The impact of different extracorporeal circulation (ECC) scenarios on arterial blood flow profiles remains yet unclear. Presently, computational fluid dynamics (CFD) allow for the simulation of blood flow profiles, local flow velocities, emergence of turbulences, and wall shear stress (WSS). However, the underlying simulation algorithms require validation by in vivo measurements. Therefore, we used our previously published miniaturized MRI-compatible rabbit ECC model to demonstrate blood flow profiles, wall shear stress and turbulences in dependency on different ECC scenarios in an MRI scanner, aiming at the validation and optimization of numerical blood flow simulation algorithms.

Method: Eight New Zealand White rabbits underwent antegrade (n = 4; via ascending aorta) or retrograde (n = 4; via abdominal aorta) ECC. MRI data were acquired in a 9.4-Tesla MR scanner with an inner gradient diameter of 30 cm. 3D flow data were acquired by phase contrast velocity mapping using Bruker FLOWMAP sequences. Image-based CFD models of rabbit aortas were established and compared with the MRI measurements. Then, the effect of antegrade versus retrograde perfusion on wall shear stresses was investigated with the in silico model.

Results: The MRI measurements as well as the simulations precisely showed the jet stream through the ECC cannula toward the aortic arch, as well as the vortices in the aortic root during antegrade perfusion. Velocity at the centerline showed an excellent correlation between CFD and MRI with R ² = 0.92 (p < 0.01). Blood flow volumes for the inflow as well as for the outflows through the aortic branches were concordant in MRI and simulations, with minor deviations such as 157 versus 160 mL/min descending aortic flow. In contrast to the MR measurements, the simulations allowed for the visualization of complex three-dimensional flow structures such as vortices at the brachiocephalic trunk. Comparison of antegrade versus retrograde perfusion yielded much lower wall shear stress (25 Pa vs. 2.5 Pa) at the brachiocephalic trunk.

Conclusion: MRI-based real-time blood flow measurements in a rabbit model of ECC were established and conducted to validate numerical blood flow simulation algorithms. Results uncover complex flow structures during ECC and a drastic effect of the cannulation on the WSS. Further improvement of the boundary conditions will optimize the accuracy of the computer simulations, particularly concerning the flow in smaller arterial branches.

Publication History

Article published online:
28 January 2023