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Intracranial pressure measurements using an implantable optically based sensing system

The long term goal of this research is the development of an implantable miniature intracranial pressure (ICP) sensor based on a transmissive optical approach. The proposed sensor will be composed of a pressure sensing membrane, an optical transmitter and receiver, and a signal transport mechanism. Two transpoit mechanisms were investigated one using a fiber optic approach and the other a telemetric approach each of which would be used depending on the desired application of intracranial pressure monitoring. Once implanted this sensor could not only be used to continuously monitor ICP but also be used in the development of a new generation of "smart" hydrocephalus shunts to provide feedback from intracranial pressure measurements to control flow through the valve. The current treatment of hydrocephalus relies on implantable shunts which employ passive, pressure operated, mechanical valves. These valves and their associated components must be selected by the surgeon such that the rate of flow through the shunt at the desired maximum pressure is in balance with the given rate of cerebrospinal fluid accumulation. Difficulties with the biomechanics and confounding by the changes in the condition of the patient with time lead to a high rate of complications in hydrocephalus shunting. It is envisioned that in the new design the passive opening of the shunt valve will be replaced by direct pressure detection using the proposed sensor, a control module, and an electronically operated valve. With this design the surgeon could select diverse pressure/flow characteristics to match the individual patient, to tune the device to accommodate changes in the patient, and to monitor the ICP signal externally. The primary focus in this article is to describe the preliminary design of the optically based implantable ICP sensor and present the in vitro results obtained from the optical bench top prototype.