Evaluation of Brain Extracranial-to-Intracranial (EC-IC) Bypass Treatments by Using Computational Hemodynamic Technology

Computational fluid dynamics(CFD) techniques were used to investigate the hemodynamic effect on EC-IC brain bypass. Local hemodynamic factors at the vascular anastomosis sites have long been thought to play an important role in the platelet activation, growth of intimal hyperplasia and thrombosis of brain bypass anastomosis and hence, affecting graft longevity. In this study, the medical imaging data computed tomography (CT) angiography were collected in DICOM format and processed by using commercial visualization and mesh generation software, which allowed extraction of the luminal surface of the vascular anastomosis in brain bypass surgery. 3-D geometries were reconstructed for the purpose of numerical analysis. With the real-time velocities derived from doppler ultrasound measurements as boundary conditions, the results of blood flow pattern across the patient-specific brain bypass was evaluated. On the computational simulation, we observed there was almost a constant blood flow rate in the graft and internal carotid artery (ICA), and energy loss between proximal and distal also appeared constantly up to 60 % ICA stenosis. Beyond this point with further narrowing of the ICA, the blood flow shunting started to occur. There was also a significant energy loss and pressure gradient different at the bypass segment. We found there was no significant wall shear stress (WSS) different at the border-zone of middle cerebral artery (MCA) against the different angle of distal bypass anastomosis. The results indicated that hemodynamic characteristics were not sensitive to the anastomosis angle. Image-based patient-specific computational models can be used in an efficient manner that allows clinical studies of brain bypass hemodynamics. This modeling not only help us to quantify the WSS, velocity and pressure gradient in brain bypass surgery, it may also help guide future therapeutic strategies to reduce graft failure and preserve the perfusion at the border-zone area. Keywords—Cerebral revascularization, Extracranial-toIntracranial (EC-IC) bypass, Computational fluid dynamic, Brain bypass surgery, Hemodynamics.