Conclusions and Future Directions

1. Conductance values of Cerebrospinal fluid (CSF) and brain matter (gray and white matter) in animal and human brain tissues. Measured vs published data. B Conductance (mS) Biological Tissue Sensor Measured values of Conductance Published values of Conductance A Gel Gel B C 1 Conductivity of gray and white matter (brain tissue) 0.172 ± 0.078 mS 0.06-0.3 mS D E Artificial Artificial CSF CSF D D C C A A B B 2 Conductivity of Cerebrospinal fluid 2.01 ± 0.10 mS 1.81-2.0 mS A E E A A Hydrocephalus Hydrocephalus Normal Normal Solution Approach Conductance Ratio Tissue Tissue Artificial Artificial BACD BACD E E Conductance (mS) CSF CSF Catheter Schematic used to measure Conductance of CSF and dog brain tissue In a volume under static conditions, the net current flow is zero: Current emitting electrode Measurement electrodes Ground V V AC AC With the following constitutive relationship: Electrical Conductivity for CSF Sample(CSF, Dog Brain Tissue) • Equation to calculate conductivity: We get Laplace’s equation: And since the gradient of the scalar potential is the electric field vector: Which can be solved using Finite Element Analysis Provided that the electric field remains constant, an expansion of the ventricle will lead to a change in the electric field distribution. The impedance-volume relationship can be correlated by: Brain Surrogate Model Hydrocephalus Case Study Conductivity ratio (σ) Human Brain Dog Brain aCSF 0.9 % Saline / 0.02 % NaCl 0.9 % Saline / 0.1 % NaCl 0.9 % Saline / 0.9 % NaCl 0.9 % Saline / 0.3 % NaCl 0.9 % Saline / 0.6 % NaCl E D Power RF Transmitter 2 2 C Microcontroller Hydrocephalus B 1 1 3 3 Conductance (mS) Pump Pump A Normal 20 40 60 80 100 120 140 160 180 200 220 240 Volume (cc) An Impedance Sensor to Monitor Cerebral Ventricular VolumeSukhraaj Basati, Madhu Smitha Harihara Iyer, Brian Sweetman and Andreas LinningerLaboratory for Product and Process Design, Dept. of Bioengineering University of Illinois at ChicagoMidwest Biomedical Engineering Conference, Chicago, IL. April 04, 2008 Motivation An abnormal accumulation of CSF leads to a condition known as Hydrocephalus. Over 150,000 people are diagnosed with this disease in the U.S. each year. CSF-Filled Lateral Ventricle Normal Patient Hydrocephalus Patient • The current treatment method for all types of Hydrocephalus incorporates an intracranial pressure based shunt. Frequent problems encountered with long-term intracranial pressure based shunts include: • Under-drainage or Over-drainage possibly leading to fatality. • Multiple shunt revisions which require surgery • (The average lifespan of a shunt is five years). • For children: Failure rate = 50%. • For adults: Complication rate = 35 %. • To improve treatment options for patients suffering from Hydrocephalus we propose to: • Measure volume changes regardless of pressure changes. • Improve lifespan of treatment method. • Verify the theoretical pressure-volume correlation to better understand Hydrocephalus dynamics Agarose Gel Formulation Agarose gel (Sigma-Aldrich) was used as a brain surrogate for our experiments. Conclusions and Future Directions Promising experimental and simulation results show that the conductance-volume relationship for Hydrocephalus patients can be used as a treatment option. • Future Directions include: • Implementation of a microcontroller and • shunt for control of ventricular volume. • Microfabrication of sensor along with wireless • data transmission. • Dynamic system to measure sensor stability • over time. • Position of electrode placement and • optimization of conductance-volume relationship. • Animal Experiments. • A possible treatment method including: • Conductance-Volume Sensor • Controller • Pump Acknowledgments • Financial support provided for part of this research under NIH grant 5R21EB4956-2 is gratefully acknowledged. The work was also supported by a grant from the STARS kid foundation. • We would also like to thank: • Dr. Richard Penn, University of Chicago • Dr. Michalis Xenos • Dr. Mahadevabharath R. Somayaji • Dr. Patrick Rousche • COMSOL Multiphysics 3.2 (evaluation version)