Purpose:
4D Flow MRI has been used in non-invasive, non-contrast assessment of hemodynamic characteristics throughout treatment in Vein of Galen Aneurysmal Malformation (VGAM) patients [1], [2].  Here we present an advanced application of computational fluid dynamics (CFD) with boundary conditions based on 4D Flow MRI, to characterize pressure drop across the malformation, and compare to intraoperative pressure measurement. 

Materials and Methods:
Images were obtained through an IRB-approved retrospective study. A patient with Vein of Galen aneurysmal malformation (0.64y, M) received 4D Flow MRI (3T Skyra: Siemens, Germany) as part of a clinical protocol. 4D flow measurements were used to obtain geometry of the vasculature (Mimics: Materialise NV, Belgium) and patient-specific boundary conditions. To estimate pressure drop across the malformation transient Navier-Stokes equations were solved numerically (Fluent 19: Ansys, USA). During interventional treatment a pressure probe (arterial: Medtronic Echelon 14 microcatheter; venous: Stryker Excelsior 1018 microcatheter) was used to obtain pressure difference between the proximal arterial feeders and the interior of the aneurysmal malformation (Fig 1A-B). 
Results:
The pressure differential obtained from 4D Flow MRI data and measurement (Fig 1C-D) ranged from 7.86 – 13.17 mmHg over the cardiac cycle, with mean 10.93 mmHg. Direct intraoperative pressure in the proximal right PCA measured 7 mmHg and more distal in the pedicle supplying the malformation measured 6 mmHg. Direct pressure measurement in the recipient venous pouch pre-embolization measured 6 mmHg, decreasing to 5 mm Hg post embolization of the pedicle. This indicates a 1mmHg preoperative pressure differential increasing to 2mmHg postoperatively. 
Conclusion:
As the patient had no evidence of venous hypertension and the measured arterial pressure was unusually low, a possible reason for pressure measurement discrepancy could be the use of a too-large catheter in the arterial intraoperative pressure measurement leading to underestimation of the arterial pressure. 4D Flow MRI can be used as the basis for fluid dynamics calculations in complex VGAM anatomy, and future work will include investigation in additional cases.

Pressure Drop Estimation in Vein of Galen Aneurysmal Malformation: Comparing 4D Flow MRI-Based Computational Fluid Dynamics and Intraoperative Measurement

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