1 Copyright © 2004 by ASME Proceedings of IMECE04 2004 ASME International Mechanical Engineering congress November 13-20, 2004, Anaheim, California USA IMECE2004-62033 CONSTRUCTION AND VALIDATION OF A COMPLAINT MODEL OF THE CEREBROSPINAL FLUID SYSTEM WITH FLUID FILLED SYRINX Bryn A. Martin University of Illinois at Chicago Department of Mechanical and Industrial Engineering Chicago, Illinois Wojciech Kalata University of Illinois at Chicago Department of Mechanical and Industrial Engineering Chicago, Illinois John N. Oshinski Emory University Department of Radiology Atlanta, Georgia Francis Loth, Thomas J. Royston University of Illinois at Chicago Department of Mechanical and Industrial Engineering Chicago, Illinois ABSTRACT A simplified model of the cerebrospinal fluid (CSF) system with compliant fluid filled syrinx has been constructed, tested, and verified to closely mimic the in-vivo flow conditions observed through MRI imaging of the pathological CSF system with syringomyelia. The model is subjected to a MRI derived CSF flow waveform from a patient with Syringomyelia through use of a computer controlled pulsatile pump. Model geometry, flow waveform, and spinal cord compliance are obtained at three axial locations along the system through MRI image processing techniques. MRI testing was conducted with the syrinx open and closed to the external environment. Results indicate that the internal and external flow waveforms were in opposite directions when the syrinx was closed and in unison when the syrinx was open. The observed flow waveform and compliance measurements closely mimicked the in-vivo case when the syrinx is open to the external environment. INTRODUCTION The brain and spinal cord are surrounded by a fluid medium known as cerebrospinal fluid. This fluid moves in a pulsatile manner through the complicated subarachnoid, spinal canal and ventricular spaces of the brain. The pulsatile nature of CSF flow has been associated with changes in blood volume within the cranial cavity due to the cardiac cycle. This blood volume change is a result of the phase difference between blood influx and outflow in the brain. CSF has not been determined to have any bulk motion. Each pulse has equal amounts of fluid motion in both systole and diastole. It is a clear fluid having viscosity nearly that of water and, in a healthy person, is composed of dilute amounts of proteins and monoamines. The fluid is utilized to supply nutrients and remove waste from the brain. The average healthy adult has approximately 125ml of CSF, with the majority residing in the cranial cavity. Various pathological conditions can cause the obstruction of CSF flow. These include Chiari malformation, syringomyelia, and hydrocephalus. Interest has been focused on the examination of hydrodynamic conditions of the CSF in the subarachnoid spaces that result in the pathogenesis of syringomyelia 1 . The goal of the present study is to produce and validate a phantom model of the CSF system that will be used for further pressure and wall surface vibration measurement with an overall goal to better quantify the pressure wave transmission through the CSF system. Figure 1 - Phantom CSF system model cross-sectional view METHODS The syrinx portion of the phantom model was constructed using a mixture of Sylgard 184 poured at a 30:1 ratio (base/hardener) in order to decrease the Young’s modulus of the material which is thought to better mimic the in-vivo case. The 30:1 ratio of Sylgard 184 was tested and determined to have a Young’s modulus of approximately 175kPa. Syrinx geometry was made by casting Sylgard around a copper pipe core with heat shrink tubing as the exterior confinement. Model cross-sectional geometry was nearly constant over the entire length. The tubular model was carefully removed after one week of curing time at room temperature. The spinal cord outer diameter was 1.90cm with an inner syrinx diameter of 1.52cm and total