Surgical resection of epileptogenic foci is a commonly practiced and often beneficial treatment for patients suffering debilitating seizures arising from otherwise intractable epilepsy. The success of this procedure depends on the ability of the medical team to precisely locate the epileptogenic zones in the patient's brain and to identify important cortical regions that must be avoided during resection. The accepted best method for locating the epileptogenic zones is to record seizure activity with intracranial, subdural electrode arrays implanted chronically for several days. The electrode arrays are connected by cables to external recording equipment for the duration of the monitoring period. This invasive procedure has disadvantages: 1) a lengthy and costly hospital stay is required;2) a family member or sitter must be with the patient at all times, 3) the patient is tethered to the wall by cables making it difficult for some patients to cope;4) the long duration implantation increases the likelihood of serious infection;5) there is a risk of intracerebral hemorrhage if the cables are accidentally pulled and the grids move;and 6) ten to twenty percent of patients have too few seizures during the hospitalization to identify the epileptic zone with certainty. We propose to develop wireless intracranial, subdural electrode arrays that will avoid these disadvantages. The wireless subdural arrays will allow complete closure of the craniotomy used for surgical placement and will avoid the use of the transcranial multiwire cables that connect the recording electrodes to data processing and storage hardware. The ability to completely close the dura and skull, avoiding wired conduits to the brain, will reduce the risk of morbidity due to infection and reduce cost by allowing the patient to leave the hospital for the majority of the monitoring phase. A potentially significant benefit of wireless outpatient monitoring is the ability to provide longer monitoring periods, which allows the recording of habitual seizure activity while the patient is on his full regimen of anti-seizure medication. Localization based on habitual seizure activity is expected to improve outcomes of the resective surgery. The wireless electrode arrays will reduce patient distress and discomfort by avoiding the use of a head mounted umbilical for hardwired recording and by improving patient mobility. The stability of the arrays in body fluids is obtained through the use of amorphous SiC (a-SiC) and silicone encapsulation, made possible through advances at EIC Laboratories in thin film processing and encapsulation strategies for neural recording and stimulation electrodes on polymer substrates. The Phase I objective is to complete the design, fabrication and in vitro testing of a 64-channel subdural grid array with an integrated circuit controller (an ASIC). The testing would demonstrate the functional stability of the array, in vitro, in anticipation of animal safety studies to be performed in a Phase II effort. The Phase I Aims are as follows:
Aim 1. To design an ASIC for 64-channel recording and wireless transmission of ECoG waveforms with the additional capability of providing a wireless means of bipolar stimulation for cortical mapping;
Aim 2. To fabricate 64-channel wireless recording arrays with integrated ASIC and RF coils, a-SiC/silicone encapsulation, and low-impedance sputtered iridium oxide (SIROF) recording and stimulation sites;
Aim 3. To evaluate the 64-channel arrays with electrically active ASICs and coils by in vitro functional testing under normal and accelerated conditions. The program is a collaboration between EIC Laboratories Inc. (Norwood, MA) and Sigenics Inc. (Chicago, Ill). In Phase I, EIC will conduct the array fabrication and testing while Sigenics will design the integrated circuit and telemetry system.
The development of wireless subdural electrode arrays for recording seizure activity in the localization of epileptogenic foci prior to epilepsy surgery is being proposed. The wireless arrays will reduce the cost of the procedure, decrease the risk to the patient, and improve the outcome of the epilepsy surgery. The wireless arrays will benefit patients with intractable epilepsy whose seizures are not well-controlled by medication.
