Apparatus and Method for Optical Detection of Seizures and Cerebral Edema
Background: Currently seizures are detected from deep brain structures with the use of electroencephalography (EEG). EEG recordings are made through electrodes placed on the scalp, on the brain surface, or inserted deep in the brain. EEG works through amplification of minute voltage potentials generated in brain tissue. As such it has inherently low signal to noise ratio and requires controlled conditions for optimal signal detection. A fiber based optical system has a higher signal to noise ratio and is not effected by electrical interference, patient movement, etc. Technology: We have discovered particular optical parameters which are useful in detection of the seizure and pre-seizure state. Specifically, we have detected optical changes of neural tissue before seizures are detected with electroencephalography (EEG), and before becoming manifested clinically. These changes lends itself to the creation of devices which can predict and record seizures before they occur and trigger interventions to prevent or abort them. Optical devices capable of detecting these changes can also be used to image and map regions of brain tissue undergoing seizure. By coupling a source and a detector to fibers, measurements may be obtained from anywhere the fibers are inserted, including deep brain structures.
Our experimental findings indicate that the detectable changes occur several minutes before clinical or electroencephalographic (EEG) seizure onset. Thus the process of detecting seizure associated changes provides an important tool for detection of the pre-seizure state which provides a therapeutic window for seizure prevention.
Similarly, there is currently no known device capable of directly measuring cerebral edema. The pathologic sequelae of brain swelling are currently assessed through pressure transducers to measure intracranial pressure, and tissue oxygen saturation probes. However, because of brain compliance and blood flow auto-regulatory mechanisms, both increased intracranial pressure and brain hypoxia are late changes that may occur hours after swelling begins.
We have developed a system similar to our seizure detection that, when inserted into the brain, the detect changes in tissue as edema develops. This device is adaptable to a clinically functional implantable probe for direct measurement of cerebral edema in a variety of neurological and neurosurgical conditions. It can provide early warning of pathologic brain swelling well before the currently measurable late sequelae of increased intracranial pressure or hemodynamic changes. Direct detection of cerebral edema allows measurement of one of the primary physiologic events in the cascade of neurologic deterioration from a variety of causes. Earlier detection could allow potentially lifesaving intervention sooner than current monitoring equipment allows. Application: There is currently no method to predict seizure onset using optical techniques. Prediction of seizure onset provides clinical opportunities for therapeutic interventions for prevention or early arrest of clinical seizures. Seizure detection through measurement of optical tissue changes provides a reliable method of seizure prediction which has not hitherto been available. The detection of the pre-seizure state has potential uses for seizure early warning systems, closed-loop seizure termination and prevention devices, improved intra-operative mapping of epileptic foci, and optical recording of seizure activity.
An optical fiber edema probe could be incorporated into a variety of commonly used intracranial monitoring devices, including pressure transducers, ventricular drainage catheters, tissue oxygenation probes, or inserted as a standalone device into an area of interest. The changes would then be analyzed to provide an edema index on a continuous basis to aid physicians in clinical decision making.
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