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Pressure drop reconstruction in the aqueduct of sylvius from MRI acquisitions

From measurement of the oscillating flux of the cerebrospinal liquid (CSL) in the aqueduct of Sylvius, we elaborate a patient-based methodology for pressure evaluation. Highresolution anatomical MRI first permits a precise threedimensional anatomical digitalyzed reconstruction of the Sylvius’s aqueduct shape. Cine phase-contrast MRI is now an invaluable tool for pathologies investigations (Tain and Alperin 2009) for the evaluation of blood flow in then brain vessels as well as inside the CSL flow inside the brain cavities. It permits the evaluation of the CSL pulsatile flux inside the aqueduct. Produced mainly in the lateral and third ventricules, CSL flows along the aqueduct of Sylvius to reach the fourth ventricle, then passes into the SubArachnoid Spaces (SAS) and is absorbedmainly into sagittal sinus blood. Under normal circumstances CSL oscillates in and out ventricular cavities with a net outward flow QS equals to the CSL physiological production rate. The aqueduct, is a slighly curved pipe with a variable elliptic section. It is the smallest cavity between Lateral Ventricules and SAS. This is where most of the viscous dissipation and thuswheremost of the pressure drop occurs (Sweetman et al. 2011). The aqueduct influence on the pressure distribution inside the brain’s cavities thus deserves special attention, especially in the context of stenotic conditions (Fin and Grebe 2003). We show that a slighly curved, low Dyne number and small reduced Reynolds approximation for the CSL oscillation inside the aqueduct of Sylvius is a fair description. It permits to develop a very fast estimate of the pressure drop, shear and hydraulic admittance.