Thermal measurement of cerebrospinal fluid flow rate in hydrocephalus shunt

This paper presents a novel mechanism for convenient in vitro measurement of cerebrospinal fluid flow rate in hydrocephalus shunts. Thermal time of flight method has been employed in the measurements conducted on a modified shunt system covered with artificial skin. The shunt tube is proposed to include bio-compatible materials such as titanium for better thermal responses. To facilitate clinical measurements by neurosurgeons, a dry, semiconductor thermoelectric cooling device has been designed to initiate the thermal transfer while maintaining a safe operating temperature and clean thermal excitation. Velocity thus flow rate of the cerebrospinal fluid has been derived by decoupling the thermal transfer in the measured differential time at two measurement spots of the titanium elements. Device design was based on comprehensive system simulation using finite element analyses on the fluidic and thermal behaviors of the shunt system. Microcontroller and proper control schemes have been used for desired thermal excitation and temperature registrations. The mechanism has been validated in measurements conducted on a laboratory setup consisting of the modified shunt, covered by commercial synthetic human skins in an environment similar to human physiology. The measurement results have demonstrated good agreements with the simulation results in the clinically practical flow rates ranging from 0.5 mm/sec to 1.0 mm/sec.