Surgery – Diagnostic testing – Detecting brain electric signal
Reexamination Certificate
2000-03-02
2002-10-29
Shaver, Kevin (Department: 3736)
Surgery
Diagnostic testing
Detecting brain electric signal
Reexamination Certificate
active
06473639
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to information processing techniques used in the treatment of epilepsy and to devices for using these techniques.
BACKGROUND OF THE INVENTION
The current state-of-the-art in workstations for processing EEG signals allow for the viewing of either monopole or bipolar montages of electrode inputs. A bipolar EEG signal represents the voltage difference between two spatially separated electrodes. Existing workstations generally do not have the capability to process and display signals produced by summing two or more monopole or bipolar EEG signals. Epileptiform activity detection software, such as that by Gotman, processes individual electroencephalogram (hereinafter “EEG”) channels rather than a pre-processed aggregation of selected EEG channels. In U.S. Pat. No. 6,016,449, Fischell et. al. describe an implantable system for the processing of EEG signals. Fischell et al. further describe the use of a physician's workstation for programming a separate implantable device. Physician's Workstations may also be used independently for patient diagnosis, treatment evaluation, and pre-implantation patient testing. Although an implantable device for detecting and stopping a neurological event, such as those described in the Fischell et al. patent, may be the final patient treatment, it is highly desirable first to determine the appropriate modality of treatment and to evaluate its potential for working with an external system. It is also highly desirable that the epileptiform activity algorithms created during patient testing and evaluation then be programmable into the implantable electrical stimulation therapy device itself.
In U.S. Pat. No. 5,311,876, Olsen et al. describe detection of seizures in a patient-independent manner by use of standardization techniques. Olsen et al. do not disclose patient-specific detection customization as part of a treatment based on electrical stimulation. Systems such as those described by Olsen et al. typically are used by neurologists to accelerate the analysis of patient EEGs by identifying spikes and other abnormal EEG waveforms.
SUMMARY OF THE INVENTION
This invention is a processed display channel based system for epileptiform activity detection which is applicable both to an implantable electrical stimulation therapy device (a neuropacemaker) and to a Physician's Workstation System (PWS) used for pre-implant patient testing. The PWS, often based on a Windows PC, provides a neurologist with diagnostic tools for collecting and processing EEG signals and evaluating detection algorithms including patient specific parameters for detecting and stopping neurological events such as epileptic seizures, Parkinson's tremors, and migraines. The PWS may also be used to program a neuropacemaker with the patient specific parameters for detecting and stopping neurological events identified with the PWS.
It is understood that “EEG” is used throughout the following discussions to encompass not only electroencephlagram data from scalp (surface) electrodes, but also electrocortigram data from intracranial electrodes. The phrase “brain electrodes” is used throughout the following discussions to mean any electrodes within or near the brain including scalp (surface) electrodes and intracranial electrodes. The phrase “epileptiform activity” refers to activity within the brain of a person with epilepsy which is indicative of the disease. Epileptiform activity is present during a clinical epileptic seizure but may also sometimes occur without clinical symptoms.
In J. Clin. Neurophysiol, Vol 16, No. 2, p. 131, 1999; Gotman defines behavioral and electrographic seizures:
“A behavioral seizure is defined as the behavioral manifestations of an epileptic seizure as perceived by the patient, seen by an observer, or recorded on videotape.”
An electrographic seizure (or EEG seizure) is defined as “an abnormal paroxysmal EEG pattern.”
For the purposes of this application, clinical seizures include behavioral seizures as defined by Gotman as well as electrographic seizures having functional or cognitive deficits that may be identified through patient testing.
The term “onset” means the point in time at which a seizure (electrographic, behavioral or clinical) begins.
For the purposes of this application, the phrase “precursor to a seizure” and term “precursor” are defined as any one or more of the following:
1. A segment of EEG or of processed EEG signal prior to the onset (start) of an electrographic seizure,
2. A segment of EEG of processed EEG signal occurring at the start of an electrographic seizure,
3. A segment of EEG or processed EEG signal prior to the onset (start) of a clinical seizure.
For the purposes of this application, the use of the term “seizure” pertains primarily to electrographic seizures, as the processed display channel (hereinafter “PDC”) based neurological event detection described herein is performed on EEG or processed EEG signals.
A “template” is defined to be any one of the following:
1. A set of algorithm detection parameters which have been programmed into a PWS or neuropacemaker.
2. The set of patient specific detection system selections used for epileptiform activity detection including PDC selection, choice of detection algorithm(s) to be used on the PDC(s), and the specific set of algorithm detection parameters which have been programmed into a PWS or neuropacemaker.
Included in this invention is the simultaneous detection by two or more detection algorithms on a single PDC signal or by two or more different detection algorithms on two or more PDC's. For example, a DC shift algorithm may be used to process a first PDC, the first PDC being created by the addition of the two or three EEG channels which best show a DC shift prior to the onset of a clinical seizure. A waveform detector may simultaneously monitor a second PDC for a 10 to 14 Hz repetitive spikey waveform. The PDC may be created by subtracting one EEG channel from another and using bandpass filtering the difference between 5 and 20 Hz.
Preferably, the PDC based seizure detector uses two PDC's (or one PDC with multiple parameter sets): a first PDC being optimized to depict or detect a precursor to a patients' seizure, and a second PDC being optimized to depict or detect epileptiform activity several seconds into to seizure. Different detection algorithms, or a single algorithm with two different sets of parameters, may be programmed to detect the precursor from the first PDC and the in-seizure epileptiform activity several seconds into the seizure from the second PDC of the first PDC. This two-PDC technique has several advantages for a responsive electrical stimulation therapy device, such as:
1. If a precursor is missed, the in-seizure epileptiform activity is still detected and stimulation applied to stop the seizure.
2. If the precursor is detected and the applied stimulation is ineffective in stopping the seizure, the in-seizure epileptiform activity would be detected and a second stimulation with the same (or, perhaps, an increased) current can be applied.
3. If there is a “false positive” precursor detection where a stimulation is applied and the stimulation induces epileptiform activity, the second PDC and its in-seizure detector would detect the induced epileptiform activity and cause stimulation to be applied to stop the induced epileptiform activity.
4. In patients with very few seizures, a neuropacemaker may be implanted with only the in-seizure PDC implemented. When seizures occur and are detected, the EEG data for a period of time before the detection would be stored by the neuropacemaker. The recorded data would be used to improve the seizure detection program through identification of the seizure precursor allowing selection of first of the two PDC's. Such data recording is disclosed by Fischell in U.S. Pat. No. 6,016,449.
5. Another option for patients with very few seizures is to have epileptiform activity induced by stimulation during pre-implant testing using the PWS. During su
Fischell David R.
Harwood Jonathan
Pless Benjamin D.
Morrison & Foerster / LLP
Natnithithadha Navin
Neuropace, Inc.
Shaver Kevin
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