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Publication numberWO2000025668 A1
Publication typeApplication
Application numberPCT/US1999/026115
Publication date11 May 2000
Filing date4 Nov 1999
Priority date5 Nov 1998
Publication numberPCT/1999/26115, PCT/US/1999/026115, PCT/US/1999/26115, PCT/US/99/026115, PCT/US/99/26115, PCT/US1999/026115, PCT/US1999/26115, PCT/US1999026115, PCT/US199926115, PCT/US99/026115, PCT/US99/26115, PCT/US99026115, PCT/US9926115, WO 0025668 A1, WO 0025668A1, WO 2000/025668 A1, WO 2000025668 A1, WO 2000025668A1, WO-A1-0025668, WO-A1-2000025668, WO0025668 A1, WO0025668A1, WO2000/025668A1, WO2000025668 A1, WO2000025668A1
InventorsAdel M. Medhkour
ApplicantMedhkour Adel M
Export CitationBiBTeX, EndNote, RefMan
External Links: Patentscope, Espacenet
System and method for long-term recording of neural activity
WO 2000025668 A1
Abstract
The invention provides long term sensing (14), analysis, recording (46), and storage (50) of data from brain wave activity.
Claims  (OCR text may contain errors)
1. Implantable apparatus for recording electrical brain wave activity on a long term basis while enabling a patient to remain ambulatory, said implantable apparatus comprising: a housing; a source of electrical power; means for receiving signals indicative of electrical brain activity from at least one sensor selectively placed relative to the patient to obtain electrical brain wave signals; and a memory for recordation of received electrical brain wave signals from the at least one sensor.
2. The apparatus of claim 1 wherein the received signals have at least one identifiable signal parameter, said apparatus further comprising: means for recordation of data including parameters indicative of patterns of abnormal electrical brain wave activity, said pattern data parameters corresponding to said signal parameters; and means for comparing at least one identifiable signal parameter with the corresponding pattern parameter to determine whether the received signals are electrical brain waves indicative of abnormal brain activity.
3. The apparatus of claim 2 wherein said at least one signal parameter is the amplitude of the received signal or is the frequency of the received signal; and wherein when said at least one signal parameter is the amplitude of the received signal and the pattern parameter amplitude is at least 1 microvolt, said amplitude signal parameter is indicative of abnormal brain wave activity when said amplitude signal parameter exceeds said amplitude pattern parameter; and when said at least one signal parameter is the frequency of the received signal and the pattern parameter amplitude is at least 0.1 Hz, said frequency signal parameter is indicative of abnormal brain wave activity when said frequency signal parameter exceeds said frequency pattern parameter.
4. The apparatus of claim 3 and further including means for recordation of received signals indicative of abnormal brain wave activity.
5. The apparatus of claim 2 wherein said apparatus is operable in at least first and second modes, said first mode comprising operating at a first sampling rate and said second mode comprising operating at a second sampling rate greater than said first sampling rate.
6. The apparatus of claim 5 wherein said apparatus includes means for increasing the sampling rate from the first to the second sampling rate when a received signal is indicative of abnormal brain activity.
7. The apparatus of claim 2 wherein said apparatus includes means for selecting from which sensors signals will be received.
8. The apparatus of claim 7 wherein said apparatus selects sensors receiving signals indicative of abnormal brain wave activity.
9. The apparatus of claim 8 wherein said apparatus includes means for increasing the sampling rate from the first to the second sampling rate when a received signal is indicative of abnormal brain activity.
10. The apparatus of claim 9 wherein said apparatus increases the sampling rate for the selected sensors and reduces the sampling rate for unselected sensors.
11. The apparatus of claim 2 and further comprising means for recordation of said electrical brain waves indicative of abnormal brain activity for later downloading to an external processor.
12. The apparatus of claim 11 and further including a real-time clock and said recordation of said electrical brain wave indicative abnormal brain activity is made in association with the time of the occurrence thereof.
13. The apparatus of claim 1 wherein said apparatus is implanted within the chest of the patient or said apparatus is implanted behind the ear of the patient.
14. The apparatus of claim 1 wherein said apparatus includes means for downloading the stored signals indicative of electrical brain wave activity of interest to an external computer, said means for downloading including either radio frequency telemetry or wireless telephonic communication.
15. A system for providing long-term recordation of the electrical brain wave activity of an ambulatory patient, said system comprising: at least one sensor implanted at pre-selected positions relative to the brain of the patient; and an implantable monitor/recorder comprising: a housing; a source of electrical power; means for receiving signals indicative of electrical brain activity from at least one sensor selectively placed relative to the patient to obtain electrical brain wave signals; and a memory for recordation of received electrical brain wave signals from the at least one sensor.
16. The system of claim 15 wherein said at least one sensor is implanted subcutaneously or intracranially.
17. The system of claim 15 wherein the received signals have at least one identifiable signal parameter, said monitor/recorder further comprising: means for recordation of data indicative of patterns of abnormal electrical brain wave activity, said pattern data parameters corresponding to said signal parameters; and means for comparing at least one identifiable signal parameter with the corresponding pattern parameter to determine whether the received signals are electrical brain waves indicative of abnormal brain activity.
18. The apparatus of claim 17 wherein said at least one signal parameter is the amplitude of the received signal or is the frequency of the received signal; and wherein when said at least one signal parameter is the amplitude of the received signal and the pattern parameter amplitude is at least 1 microvolt, said amplitude signal parameter is indicative of abnormal brain wave activity when said amplitude signal parameter exceeds said amplitude pattern parameter; and when said at least one signal parameter is the frequency of the received signal and the pattern parameter amplitude is at least 0.1 Hz, said frequency signal parameter is indicative of abnormal brain wave activity when said frequency signal parameter exceeds said frequency pattern parameter.
19. The system of claim 18 and further including means for recordation of received signals indicative of abnormal brain wave activity.
20. The system of claim 17 wherein said monitor/recorder is operable in at least first and second modes, said first mode comprising operating at a first sampling rate and said second mode comprising operating at a second sampling rate greater than said first sampling rate and wherein said monitor/recorder includes means for increasing the sampling rate from the first to the second sampling rate when a received signal is indicative of abnormal brain activity.
21. The system of claim 17 wherein said monitor/recorder includes means for selecting from which sensors signals will be received and wherein said monitor/recorder selects sensors receiving signals indicative of abnormal brain wave activity.
22. The system of claim 21 wherein: said monitor/recorder is operable in at least first and second modes, said first mode comprising operating at a first sampling rate and said second mode comprising operating at a second sampling rate greater than said first sampling rate; said monitor/recorder includes means for increasing the sampling rate from the first to the second sampling rate when a received signal is indicative of abnormal brain activity; and said monitor/recorder increases the sampling rate for the selected sensors and reduces the sampling rate for unselected sensors.
23. The system of claim 17 and further comprising means for recordation of said electrical brain waves indicative of abnormal brain activity for later downloading to an external processor.
24. The system of claim 15 wherein said monitor/recorder is implanted within the chest of the patient or behind the ear of the patient.
25. The system of claim 15 wherein said monitor/recorder includes means for downloading the stored signals indicative of electrical brain wave activity of interest to an external computer, said means for downloading including radio frequency telemetry or wireless telephonic communication.
26. The system of claim 15 and further including an external computer for communicating with said monitor/recorder .
27. A method for making a long-term recordation of neural activity, said method comprising: implanting at least one sensor for sensing neural wave activity; implanting a recording apparatus for recording of electrical brain wave activity sensed by the at least one sensor, the apparatus including a means for receiving signals indicative of electrical brain wave activity from the at least one sensor, means for processing the received signals; and means for recordation of the received signals; and downloading said recorded received signals.
28. The method of claim 27 and further comprising: implanting the at least one sensor subcutaneously or intracranially within neural tissue.
29. A method of diagnosing electrical brain wave disorders comprising: implanting at least one sensor subcutaneously or intracranially within neural tissue, said at least one sensor being provided for sensing electrical brain wave activity; implanting a recording apparatus for recording of electrical brain wave activity sensed by the at least one sensor, the apparatus including a means for receiving signals indicative of electrical brain wave activity from the at least one sensor, means for processing the received signals; and means for recordation of the received signals; and recording the received signals in said means for recordation.
30. The method of claim 29 and further comprising: comparing the processed signals with pre-recorded signals indicative of an epileptic episode to determine whether a processed signal is indicative of an epileptic episode; and recordation of processed signals indicative of an epileptic episode in said signal storage means.
31. The method of claim 29 wherein the recording apparatus includes a memory for storing a reference table storing at least one reference pattern indicative of an electrical brain wave of interest, said method further comprising: comparing the received signals indicative of electrical brain wave activity with the at least one reference pattern; and determining whether the signals indicative of electrical brain wave activity match the at least one reference pattern.
32. The method of claim 31 wherein the at least one reference pattern has a code associated therewith, said method further comprising: recording in the means for recordation the code associated with the at least one reference pattern.
33. The method of claim 32 wherein the at least one reference pattern has a code associated therewith, said method further comprising: recording in the means for recordation the code associated with the at least one reference pattern and the time and date of the occurrence of the sensing of the electrical brain wave matching the at least one reference pattern.
34. The method of claim 33 wherein the reference table includes a plurality of reference patterns and each reference pattern has a code associated therewith and the apparatus includes a plurality of sensors, said method further comprising: recording in the means for recordation the code associated with the at matched reference pattern and the time, date of the occurrence of the sensing of the electrical brain wave matching the matched reference pattern, and the sensor or sensors that sensed the electrical brain wave activity.
35. The method of claim 32 wherein the apparatus includes a plurality of sensors, said method further comprising: recording in the means for recordation the code associated with the at matched reference pattern and the time, date of the occurrence of the sensing of the electrical brain wave matching the matched reference pattern, and the sensor or sensors that sensed the electrical brain wave activity.
Description  (OCR text may contain errors)

SYSTEM AND METHOD FOR LONG-TERM RECORDING OF NEURAL ACTIVITY

The present invention relates in general to a system and a method for recording neural activity and in particular to a system and method for monitoring and recording neural activity on a long-term, substantially semi-permanent or permanent basis, to aid in the diagnosis, treatment and follow-up care of persons susceptible to epilepsy.

BACKGROUND OF THE PRESENT INVENTION Animals, including humans, are subject to a variety of diseases related to abnormal brain function, including one commonly known as "epilepsy." "Epilepsy" is broadly defined as an abnormal condition in which subjects suffer from multiple seizure episodes originating in the brain. Though a surprise to many, epilepsy in its various forms currently affects between one and two percent of the population, (Roger Porter "Epilepsy: Prevalence, Classification, Diagnosis, Prognosis" in Neurosurgical Aspects of Epilepsy. American Association of Neurological Surgeons, Chapter 2, 1991 ), with one researcher estimating that as many as 7.5 million of the present

United States population (Hauser WA et al. "Epilepsy: frequency, causes, and consequences" New York, NY: Demos Publications; 1990) will experience an "epileptic" seizure at some point in time during their life. Unfortunately for those who suffer from the disease, epilepsy is a chronic condition. It most often affects the population as children, who then continue to suffer from this infliction throughout their adulthood. If not well controlled or managed, further epileptic episodes may tend to destroy many of the brain cells of the sufferers, leading to disabilities, mental retardation (often severe) and other morbid states such as but not limited to suicide attempts, suicide, and status epilepticus.

Each time a seizure occurs, a certain number of nerve cells become dysfunctional and die. Over time, epileptic patients lose many of their functions due to the death of functional cells. The effects of repeated seizures are staggering to the individual and society, and are just plain heart-rending to see. For example, it is not uncommon to see epileptic patients having a lower IQ (Intellectual Quotient) than the average normal individual of the same age that is not afflicted with the disease. It is estimated that twenty five percent (25%) of all adult epileptic patients are unemployed while the remainder have reduced chances for career advancement, promotion or additional intellectual gain, due to the limitation in their intellectual impairment and disabilities. A large group of epileptic patient do not qualify for a driver license due to the inherent danger of seizure while driving. For children, the negative effects are even more severe, since sixty five percent (65%) with epilepsy experience adverse effects upon their development and their futures as result of their seizures. These patients suffers not only from the physical limitations of a debilitating disorder, but they also suffer from social stigma, psychological stress, and uncertain therapy and prognosis.

As noted, epilepsy finds its origin in the brain, an electro-chemical organ. Within the brain a variety of chemical substances can be found. Some of these, known generally and broadly as neurotransmitters, produce a measurable electrical discharge when activated. The numerous small but distinct electrical discharges produced by these neural cells combine to produce an electrical brain wave (EBW). Electrical brain waves are transmitted from one group of cells to another group of cells or between cells of the same group as part of the routine cellular/neuronal activities that occur in our daily living. EBWs can be characterized by a number of parameters, including amplitude (normal EBWs have an amplitude of about 10 millivolt to about 20 millivolts) and frequency (normal brain waves have a frequency of about 0.5 hertz)

When a subject is in a "normal' functional status of the brain (awake, sleep, movement of parts of the body, sensory, visual, auditory, etc.) a "normal" EBW is produced; similarly, when a subject is in an "abnormal" functional status (epilepsy, movement disorder, stroke, nerve paralysis, etc.), the "normal" EBW changes to an "abnormal" EBW. Therefore, a normal EBW is defined as the natural, normal generation, transmission, conduction of a multiple electrical discharges leading to a normal brain wave, and an abnormal EBW is defined as an abnormal brain wave without regard to the cause thereof. At any time there is an abnormal generation or transmission of the electrical discharges produced in the brain, the normal, orderly communication is disrupted and a seizure results. Epilepsy is manifested by an "abnormal" EBW. The duration of the abnormal chaotic electrical hyperactivity of the brain in an epileptic episode varies with the type of seizure, which is usually a function of the point in the brain where the abnormal EBW originates.

The causes of an epileptic episode are many and varied, ranging from trauma, that is, a direct injury to the head, tumors, or other brain lesions, by way of example only. Often the etiology or origin is unknown or at best uncertain. The diagnosis of epilepsy relies on clinical history, examination, repeated superficial (scalp) electroencephalographic (EEG) recordings, blood and serum laboratory analysis and neurological imaging, including computer tomography (CT) scans and magnetic resonance imaging.

Once a diagnosis of epilepsy is suspected or made, conventional treatment may begin. Current medical therapy for epilepsy may involve the administration of medication or surgical resection of the seizure originating tissue, assuming it can be identified. The latter, while effective, can cure only a select, small, portion of the population. Advances in the knowledge of the origin and mechanisms of the various forms of epilepsy, of which . there about twenty different types recognized by the international medical community, would facilitate their treatment by allowing more rational therapeutic approaches

The diagnosis of epilepsy is confirmed with certainty by recording an abnormal EBW during an EEG procedure. During a traditional EEG, a clinician places electrodes on the surface of the patient's head (scalp) and connects them to an EEG machine to produce a visual image, i.e., a tracing of the electrical brain wave. At the end of the exam, the electrodes are removed, an analysis is made of the tracing, and the patient is discharged if appropriate. Usually EEG machines are located in a hospital, clinic, or physician's office. In case of uncertainty or if the EEG is below acceptable levels of quality, a patient may return to the medical facility and have additional EEGs. In fact, in most cases the traditional scalp EEG will be repeated several times. It is understood that between the two visits there are no recordings made. That is, the brain electrical activity of patients between two EEGs is unknown. While there may be indirect signs in the tracings that are taken that point to epilepsy in an EEG recording, it is very challenging to confirm the true type, location, nature and cause of the disease in a particular individual. In addition, epileptic seizures can occur and the patient may be unaware of their happening between visits. Or if aware of their occurrence, the patient may be unable to accurately recall the particular symptom experienced. The physician is faced with either being uncertain if an epileptic episode has occurred or if it is known that there was an occurrence, the particular symptoms indicative of what particular form of epileptic seizure. This weakness in present diagnostic and treatment programs of epilepsy makes safe, effective, and cost-effective treatment of the patient difficult at best. The overall effectiveness of current treatment programs is difficult to assess, although a large group, about half, of patients will respond to the first drug therapy attempted. A second group, about one fourth of those afflicted with the disease, will respond to a second or third drug. The remainder are considered as having an intractable condition and some may be surgical candidates.

Currently, advances in the knowledge have led to some new techniques for making EEG recordings. Invasive procedures such as sphenoidal, cortical, depth electrode recordings and video/EEG monitoring have become important in the diagnosis of epilepsy. Chronic EEG recording, ambulatory or continuous recording are also indicated in many patients to confirm the diagnosis of epilepsy or its localization in specific brain tissue, thus allowing a better assessment of a potential surgical option of resecting the suspected brain tissue.

At least in part because of the foregoing weakness of the traditional, intermittent scalp EEG, continuous electroencephalograms (CEEGs) are being used more frequently by physicians. Currently, there are two ways in which a CEEG is obtained. First, the patient is fitted with a plurality of superficial (scalp) electrodes. Then a helmet-like device is fitted to their head. The helmet-like device includes external EEG recording apparatus. With this device, the patient can remain ambulatory and leave the hospital. The data produced by this device is often poor, however. To produce quality data the electrodes must remain fixed in the same location. Yet, with this device they are subject to movement. Additionally, they may even become disconnected from the scalp completely, thereby resulting in a return of no data. Poor contact between the electrodes and the skin can also result in poor data. Also, there is no guarantee that the patient will suffer a seizure while wearing the device due to their random nature of occurrence. Finally, because of the nature of the helmet-like device, patients are less likely to engage in their normal day-to-day activities while wearing it. For example, the patient may not go to work and is . likely to engage in subdued activity because of the helmet. As noted above, such normal day-to-day activities may be a trigger for particular seizures. While reasonable in terms of cost ~ approximately $ 1 ,000.00 in today's dollars per day — because of the ability of the patient to leave the hospital, this procedure may not produce any better data than the intermittent EEGs taken using traditional EEG recordings.

The second method of obtaining a CEEG, while producing "better" data, does so at great expense. To obtain the second type of CEEG, a patient is admitted to a hospital for 2 or more days. Patients undergo this method of obtaining CEEGs using scalp electrodes that are connected to an external EEG machine or to a cassette recorder that records and stores the information. During a CEEG recording, the patient is restrained in bed to limit injuries and minimize artifact and noise recording since even minimal displacements of the scalp electrodes significantly affect the quality of the recorded EBW signal, as just noted above with the first type of CEEG. In other words, the patient often finds him or herself lying flat on their back staring at a hospital ceiling while in restraints intended to keep them from moving.

Usually, the second type of CEEGs are obtained simultaneously with video recordings of the patient. This combination video-EEG recording technique is used by the physician to identify and to eliminate particular EEG tracings as epilepsy related since the dual recording enables the physician to identify the psychological conditions that mimic epilepsy. Health care providers benefit from this method by correlating clinical symptoms, if they happen to occur during the recording, to EEG patterns. Since epileptic seizures are unpredictable and have a random occurrence, it is not unusual to see the same patient admitted several times to increase the chances of seizure occurrence and capture by the combined video-EEG recording system. Occasionally, to ensure that a seizure will occur and be recorded, a seizure will be intentionally induced by stressing and traumatizing the patient through such techniques as forced sleep, sleep deprivation, or through the administration of drugs. As expected, CEEG recordings are costly in terms of direct costs, such as hospitalization for extended time periods and physician fees, and indirect costs, including time off work for the patient. It is not unusual for such costs to reach $8,000.00 in today's dollars per week of confinement while the CEEG is being obtained. Currently, repeated admissions of the patient over their life in an often vain attempt to obtain additional information on the efficacy of a particular treatment regimen only add to the costs.

While the present methods of producing CEEG data do provide the physician with some additional information, the data is generally insufficient for one very important reason. In neither method of obtaining CEEG data is the patient able to go about his/her everyday affairs while the recording is occurring. With the first method the patient's activities are constrained by the need to keep the electrodes and helmet in place while in the second method the patient is actually physically restrained. The physician is therefore unable to determine whether certain environmental factors may be at the root of the cause of the seizures, for example, or whether they occur only at specific times of the day, only during the performance of specific activity, in response to specific external stimuli, or some combination thereof.

A more invasive technique of EBW monitoring consists of the intracranial implantation of at least one semi-implantable electrode (SIE). In this procedure, SIEs are implanted in different areas of the brain (usually after surgical exposure of the brain) and are connected to an EEG machine. The procedure is not limited to electrode implantation, however, since of necessity various catheters or wires must also be placed in appropriate locations • within the open brain and then fed outward through a hole in the skull. Since the largest portion of the system — the catheters and the EEG machine ~ are not implanted, the duration of EEG recordings using SIEs is limited to few days (typically 10 to 14 days) to avoid the risk of brain infection, sepsis and death of the patients. Exposing the cerebral cortex following surgical opening of the dura allows easy access of pathogens to the brain, hence the risk of infection. Following the recordation period, patients undergo another surgical operation for the removal of the implanted electrodes.

Such techniques of SIE may have value in localizing the origin of epileptic episodes in the brain. When an area of the brain is suspected to be the focal zone of epilepsy, the surgeon will implant electrodes inside the suspected area of brain in an attempt, often vain, to try to study the brain tissue that is presumed to cause the disease. Occasionally, after confirmation and correlation of suspicions to EEG findings, the surgeon will determine that the suspected brain tissue is the cause of the epileptic episodes and a surgical resection of the suspected brain tissues will follow. As with CEEG procedures, this surgical procedure is quite costly and may lead to inconclusive results, however. In other words, in some situations, surgically opening a patient's skull to slice away brain tissue may not cure the epilepsy, resulting in the patient continuing to suffer debilitating seizures.

From the foregoing discussion it is apparent that the present day examination for, diagnosis of, and treatment of epileptic disorders suffers from the inability to conduct safe, cost-effective, and qualitatively accurate EEG examinations over a long time period, that is, semi-permanently or permanently. The inability to conduct long term monitoring prevents or inhibits discussion and exchange of ideas and research on the general topic of epilepsy, due in large part to the lack of a consistent terminology to describe the observed symptoms. In addition, the ability to make a proper diagnosis of the patient's condition is hampered by the lack of long term EBW data following the determination that the patient is perhaps subject to epileptic seizures. Furthermore, because of the lack of long term EBW data, the practitioner often finds it difficult to prescribe the correct medication and the proper dosages thereof. Finally, the lack of long term EBW data inhibits the ability of the physician to determine the effectiveness of the prescribed medical regimen.

Stated otherwise, each of the methods used with current or prior diagnostic standards, whether non-invasive or surgical, consist of scheduled EEG recordings that are or can be very costly, are of relatively limited duration (from less than an hour to a limited number of days), and that are not likely to capture an epileptic episode since the recordings occur under artificial conditions and since epileptic seizures are not generally regularly occurring events but are random. In addition, each of the methods used with current or prior diagnostic treatment and follow-up care utilize scheduled EEG tests of limited duration to assess the progression of their disease states and to evaluate the outcome of different treatment methods. While all these prior techniques are effective in obtaining real-time data indicative of a patient's EBW activity between two seizures, these procedures lack the capability of being performed anywhere, at any time, and continuously, that is semi-permanently or permanently. The need for an apparatus for and a method of providing long-term, cost-effective collection of electrical brain wave activity data has been accepted by researchers and physicians for a long time and yet no such apparatus or method has been forthcoming to satisfy this need. Nearly ten years ago Drs. Richard Walsh & George Ojemann, Senior Researchers at University of Washington, Seattle, expressed the need for the ability to monitor patients for months and preferably years in a paper entitled "Anterior temporal lobectomy for epilepsy" Published in Clinical . Neurosurgery. The devices presently available will allow this to occur, but only at very substantial costs and only when confined to a clinical setting. The average charge for a patient in a clinical setting continuously attached to a current technology EEG machine is about $8,000.00 per week. Gathering such information for Vi year or one year would cost over $200,000.00 or $400,000.00, respectively. Such costs are clearly prohibitive, particularly in today's setting of managed care.

Additionally, other researchers such as Jerome Engel from UCLA and Robert Maxwell et al. have derided the current methodologies of obtaining EBW activity recordings over extended time periods because the data that is obtained is less than optimum due to the fact that the patients must be physically restrained to obtain reasonably reliable data and because most of the epileptic events that are monitored are either induced or obtained by stressing the patient until a seizure occurs, as previously noted. Data obtained in such a manner is considered suboptimal and in some cases is inadequate when surgical and therapeutic decisions are being made in consideration of this data and the cost/benefit analysis of such procedures. Because of the great costs involved in obtaining extensive EEG data indicating the type and source of epileptic episodes and because of the inherent unreliability of such data for all of the aforementioned reasons, other methods of obtaining data in a relatively less expensive and less stressful manner for the patient are becoming popular among physicians. Such methods include computed tomography scanning (CT scanning), magnetic resonance imaging (MRI), and fluourodeoxyglucose positron emission tomography scanning (FDG PET scanning), and single photon emission computerized tomography scans (SPECT Scan). (Jerome Engel, "The role of neuroimaging in the surgical treatment of epilepsy" in Dam, Gram, & Schmidt, and in an other publication, Jerome Engel et al. "Presurgical evaluation for partial epilepsy: Relative contribution of chronic depth-electrodes recordings versus FDG-PET and scalp sphenoidal ictal EEG" in Neurology November 1990. Robert Maxwell & al. "Magnetic resonance Imaging in the assessment and surgical management of epilepsy and functional neurological disorders" in Proceedings of the meeting of the American Society for Stereotactic and Functional Neurosurgery, Montreal 1987, Appl. Neurophysiology.50.) Stated otherwise, in spite of the recognition long ago of the desirability of obtaining long term EEG data for the diagnosis and treatment of epilepsy, no such apparatus or method for doing so in a cost-effective manner has been developed and as a result, the medical profession has been turning to imaging techniques to help diagnose and treat this terrible disorder.

In summary, the diagnostic and follow-up (short and long term) analyses of brain electrical activity, such as in patients subject to epileptic seizures, presently involve the use of superficial or semi-implantable electrodes all connected to external EEG machines for relatively short periods of time during which seizures are unlikely to be monitored, unless induced by stressing or traumatizing the patient through drug withdrawal, forced sleep, or sleep deprivation.

It would be desirable to have a system and a method for performing current techniques of diagnosis and follow-up assessment of epilepsy and other neural disorders that did not also have the shortcomings discussed above. SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide a system and a method that is useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders and that is not subject to the aforementioned shortcomings.

It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that enables a diagnostician to make long-term recordings of electrical brain wave activity.

It is still another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that enables a diagnostician to more accurately diagnosis the occurrence and the type of epilepsy suffered by a patient. It is yet another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that enables a diagnostician to more accurately follow-up the initial diagnosis and the occurrence and type of epilepsy suffered by a patient.

It is still yet another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that will facilitate research into the causes and treatment of such abnormal brain functions.

It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that will enable the cost effective, safe, long term recordings of electrical brain wave activity.

It is still another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that is implantable within a body.

It is yet another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that is implantable and contains sufficient data storage capacity for the recordation of electrical brain wave activity for an extended period of time.

It is still another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that enables the sensing and recordation of electrical brain wave activity for an extended period of time apart from a clinical setting.

It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that enables the sensing, analysis and recordation of normal and abnormal electrical brain wave activity on a long term basis.

It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders for communicating the recorded information by use of standard radio frequency telemetry. It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that

It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders for enables the communication of recorded information by use of wireless telephonic means.

It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that analyzes the sensed

EBW using a microprocessor. It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders for operate independently using an energy source or power supply that is also implantable.

It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that enables the recordation of critical or abnormal events along with the normal events while the patient is performing normal day-to-day activities.

It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that encodes EBW activity for optimal memory utilization. It is another object of the present invention to provide a system and method useful in the monitoring, diagnosis, treatment, and mapping or localization of epilepsy and other neural disorders that encodes EBW activity for the purpose of generating summary reference data for use by a clinician in the interpretation of the recordings. The foregoing objects of the present invention are provided by a system and method enabling the long term sensing, analysis, recording, and storage of data indicative of EBW. A system recorder in accord with the present invention will embrace an implantable case including a microprocessor for analyzing signals indicative of sensed electrical brain waves and directing the storage of data correlative of the sensed electrical brain waves in a data storage unit. The apparatus may also have a transmitter for downloading and transmission of the stored data to an external computer using radio frequency (rf) telemetry or other known communications systems such as wireless telephonic means. An apparatus in accord with the present invention will enable the long term recording of EBW activity, thereby allowing the patient to leave the hospital and conduct their normal affairs while subsequently providing a health care provider with substantially continuous EBW recording data for later analysis.

This data will enable a physician to better monitor patients, especially since they will be able to review patient brain wave activity accumulated over days, weeks, months and even years and then assess the number of abnormal EBW episodes that do happen randomly. Such an apparatus will allow the treating physician to monitor the electrical progress of patients undergoing different treatment modalities at substantially reduced costs over the prior art devices and techniques.

The present invention also contemplates a system including the foregoing implantable apparatus and at least one implanted sensor such as an electrode for providing signals to the implantable apparatus indicative of electrical brain wave activity. Additionally, a system in accord with the present invention may also include an • external apparatus capable of receiving downloaded information indicative of long term electrical brain wave activity.

In a method in accord with the present invention the implantable unit is surgically implanted into the patient in a preferred location, which may be, by way or example only, behind the ear or in the chest. At least one sensor, and typically a plurality, of electrodes, is then implanted into the patient in a predetermined location. Such a location may be intra-cranial or subcutaneous. Where a subcutaneous implantation of electrodes occurs, the patient's scalp will be prepared and then opened and the electrode(s) will be placed on the patient's skull and then connected to the implantable unit. Preferably, the connection between the electrode(s) and the implantable unit will also be subcutaneous, regardless of the location of the implantable unit. Once the electrodes are securely positioned under the scalp or intracranially, the common wire containing all the leads is funneled under the skin without cutting the skin to be connected to the implantable monitor/recorder. The implantable monitor/recorder is presently contemplated as being implanted in the chest or behind the ear, though continuous development and shrinkage of microprocessors, memory, and batteries may make implantation at nearly any body point possible. After electrically connecting the common wire to the implantable monitor/recorder, the various incisions are all closed and no portion of the implantable system is therefore externalized.

The foregoing objects of the invention will become apparent to those skilled in the art when the following detailed description of the invention is read in conjunction with the accompanying drawings and claims. Throughout the drawings, like numerals refer to similar or identical parts.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a system in accord with the present invention.

Figure 2 illustrates an implantable monitor/recorder unit in accord with the present invention.

Figure 3 depicts a control loop for an apparatus in accord with the present invention.

Figure 4 shows a control loop for operating an apparatus in accord with the present invention upon receipt of a telemetry command.

Figure 5 illustrates a monitor/recording session control loop 160 in accord with the present invention

Figure 6 shows the implantation of the present apparatus in the chest of a person.

Figure 7 shows the implantation of the present invention behind the ear of a person.

Figure 8 illustrates a variety of locations for implantation of electrodes relative to the brain of a patient. Figure 9 illustrates an electrode array useful in accordance with the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The figures disclose an apparatus and method in accord with the present invention for the recordation of electrical brain wave activity on a long-term basis. "Long-term" means, for purposes of this application, continuous or nearly continuous recording for a period from at least one hour up to the entire remaining life of the patient.

Recordings are thus made on continuously or at predefined intervals for extended periods of time.

Referring now to Figure 1, a system 10 in accord with the present invention is shown. System 10 comprises an implantable unit 12 and at least one and preferably a plurality of implantable sensors or electrodes .

14. Sensors 14 are implanted either intracranially or subcutaneously beneath the scalp and on top of the skull. Sensors 14 sense the numerous, minute electrical discharges occurring in the brain that make up electrical brain wave activity and transmit them via connector 16 to unit 12. A body, which could be any kind of animal, is represented schematically by the dotted outline 18 and is provided to show what portions of the present system 10 would be implanted within a body. It is understood that body 18 is not part of the present invention.

At predetermined, scheduled times or as desired, the information relating to EBW activity sensed, analyzed, and recorded by unit 12 will be transmitted to an external processor apparatus 20. Connecting line 22 indicates communication between unit 12 and apparatus 20; such communication can be accomplished with any known means, including, but not limited to, radio frequency (rf) telemetry, cellular or digital telephone technology, or, if the situation should demand, an actual hardwire connection.

Processor apparatus 20 could be a stand-alone computer, including, but not limited to, a personal computer or a work station. Processor apparatus 20 could be programmed to analyze raw data recorded by the unit 12 or it could simply be programmed to display data recorded by the unit 12 that indicative of EBW activity signals that have been sensed and then processed by the unit 12 prior to recordation. It will be understood that processor 20 refers generically to any apparatus that is capable of analyzing, recording, and/or displaying the pre-recorded data provided by unit 12 over communication link 22, regardless of whether such analysis is accomplished purely by hardware, software, or a combination thereof, and that may include it own data storage, display, and printing functions. Referring now to Figure 2, an implantable monitor/recorder 30 in accord with the present invention will be described. Monitor/recorder 30 includes a housing 32, shown in phantom outline. Housing 32 is made of known materials compatible with long term survival and implantation in a body. Housing 32 provides a safe, sealed, environment for the various components held within. Monitor/recorder 30 includes at least one, and preferably a plurality, of sensor/electrode amplifiers 34. The amplifiers 34 receive and process, that is, amplify and filter as is appropriate, signals received from at least one and preferably a plurality of electrodes. As illustrated in the figure, an electrode array 14 comprising a plurality of electrodes 36 is connected to monitor/recorder 30, with each electrode being connected to an amplifier 34 over a line connection or bus 38. Electrodes 36 will sense EBW activity and transmit raw data signals indicative of the EBW activity to the amplifiers 34. It will be understood that the number of electrodes from which signals are being analyzed can be controlled in a manner hereinafter to be described.

After the appropriate amplification and filtering of the raw data signals received from the electrodes 36, the amplifiers will transmit an amplified signal via an appropriate connection 40, which may be a data bus, to an analog to digital converter 42, which is shown as an "A/D Converter" in the figure. A/D converter 42 will convert the amplified signal to a digital signal and provide it via an appropriate connection 44, which may be a data bus, to a microcontroller 46, which will typically include a non-volatile memory and a real-time clock useful in date stamping recorded data. Microcontroller 46, it will be understood, could also be a microprocessor or an application specific integrated circuit or ASIC or any other arithmetic logic unit. Consequently, it will be understood that "microcontroller" refers to any such device or any device equivalent thereto. The microcontroller 46 may conduct further processing of the digital signals as desired and as will be explained in further detail below. Following the • appropriate processing, microcontroller 46 will supply the data via an appropriate connection 48, which may be a data bus, to an internal data storage unit 50 for later downloading.

Microcontroller 46 is also connected to a pair of telemetry drivers 52 and 54 via appropriate connections 56 and 58 respectively. Drivers 52 and 54 are provided for downloading data and receiving programming inputs respectively. Drivers 52 and 54 are each connected to an antenna 60 via connectors 62 and 64, respectively.

Monitor/recorder 30 further includes a power source 66 including a battery 68. Battery 68 supplies electric power via a line 70 to a forward emission transistor or FET 72, which functions as a voltage regulator and switch, which in turn supplies power to the microcontroller 46 via a connection 74. Power is also supplied to the rest of components of monitor/recorder 30 as indicated by 76 "System Power". Such components include the electrode amplifiers 34, the telemetry drivers 52 and 54, the analog to digital converter 42, and the memory or data storage 50.

It will be understood that the microcontroller 46 is connected by an appropriate connector 78 to the electrode amplifiers 34 to allow for selective amplification and combination of the sensed EBW signals provided by the electrodes 36. That is, the sensed EBW signals can be combined in a variety of ways as will be explained below to provide different forms of data to the microcontroller 46. For example, after implantation it may be decided that it is not necessary to record the signals from certain areas of the brain. Microcontroller 46 will thus provide an appropriate signal to the appropriate amplifier to discontinue amplifying the signal received from its associated electrode. Additionally, it may be desired to combine the data from one or more electrodes and provide a combined signal to the microcontroller 46. Appropriate signals will be supplied from the microcontroller 46 to the amplifiers 34 to combine the desired electrode signals under such circumstances.

In addition, microcontroller 46 may be connected via a line 80 to the A/D converter 42. When so connected, microcontroller 46 may supply the appropriate signals to converter 42 to adjust the sampling rate and the range of the converted signals. Referring now to Figure 3, a control loop 100 useful in accord with the present invention and employed by monitor/recorder 30 will be described. Following initialization of the monitor/recorder 30 at 102, the monitor/recorder 30 will first inquire as indicated at 104 whether a telemetry command has been received as indicated at 106. If a telemetry command has been received, as indicated by the flow line 108 marked "Yes," then the received telemetry command will be handled appropriately as indicated at 110. Such commands may include commands to download stored data or may include new programming instructions for the monitor/recorder 30.

If no telemetry command has been received as indicated at 112, then the microcontroller 46 will inquire as to whether there is currently a monitoring session underway as at 114. If no session is currently underway as indicated at 116, then the microcontroller 46 will again inquire at a predetermined time as to whether any telemetry command has been received as indicated at 118. If a monitoring session is currently underway as indicated at 120, then the monitoring session will be continued as at 122, with periodic inquiries being made as to whether a telemetry command has been received as at 118.

Figure 4 illustrates a control loop 120 for operation of monitor/recorder 30 following receipt of a telemetry command 122. Following receipt and identification of a telemetry command, monitor/recorder 30 will first inquire as to whether the command includes a new parameter regarding the monitoring operation as at 124. Such parameters may include, but are not limited to, which electrodes from which data will be recorded, the length of a monitoring session, etc. If a new parameter is included as at 126, the new parameter will be set as at 128 in the monitoring loop to be described with respect to Figure 5. If no new parameter is included as at 130, then the telemetry command will be checked to see if it commands the beginning of a new monitoring session as at 132. If a new monitoring session is ordered as at 134, then the memory may be cleared and the acquisition of data will begin anew as at 136. The new monitoring session may be pre-programmed or programmable, i.e., operator dependent. Where a new monitoring session is not part of the telemetry command, as at 138, then the command will be next checked to see if it is a command to upload stored data from the memory 50 of the monitor/recorder 30 as at 140. Where such a command is included, as at 142, then the stored data will be uploaded to a processor

20, which may be a personal computer, as at 144. If the telemetry command is not a command to upload data, as at 146, then the telemetry command will be examined to see if it is a command to operate and upload data in real-time operation as at 148. If the telemetry command is to perform a real time operation as at 150, then monitor/recorder 30 will begin outputting the desired data in real-time as indicated at 152. Finally, if the command is not to initiate a real-time operation and uploading of data, as at 154, then the command is presumably an unknown command or error as 156 and the operation will return to the main control loop described in Figure 4. Upon completion of any of the other telemetry commands, i.e., 124, 130, 140, or 148, control will also return to the main loop shown in Figure 4.

It should be understood that a telemetry command will generally comprise one or more of several possibilities, either of which may occur in various orders. For example, a telemetry command may require data to be uploaded for analysis, following which a physician may send a telemetry command to begin a real-time operation and then change a parameter. Thus, the loop described in Figure 4 could occur in several different orders and the particular order of checking what the actual telemetry command is not critical or essential to present invention. In addition, there may be several variations of each command. For example, a new monitoring session could come in two forms, one that clears the memory 50 or one that saves the data in the memory 50.

Referring now to Figure 5, a monitor/recording session control loop 160 in accord with the present invention will be described. Thus, the beginning of a recording session after the specification of the appropriate recording parameters by the physician is shown at 162. The various waveforms indicative of EBW activity will be sensed as at 164 and next, as indicated at 166, may be compared to patterns held in memory 50 of monitor/recorder 30 as at 168. Next, as indicated at 170, the sensed waveforms will determine whether there is a match with a stored pattern as at 172. If there is not pattern match as at 174, then the signal will either be discarded or will be stored to memory when the operation is in a continuous recording mode 176. For example, it may be determined for a particular patient that storing of EBW activity occurring during sleep is not required for particular patients. In such an instance, where a waveform is recognized is occurring during sleep, such waveforms will not be recorded for that patient. In other patients, continuous recording may be desired and as such even the sleeping waveforms will be recorded. After recording a waveform, then the monitor/recorder 30 will return to sampling of the waveforms as at 178.

Where a sampled waveform matches a pattern, as at 180, the monitor/recorder 30 will determine whether the pattern is a trigger for some action as at 182 typically recording but also for upgrading of sampling parameters. . If the pattern is a trigger as indicated at 184, the sampled waveform will be date stamped and recorded to memory as at 176. The sampling parameters will then be upgraded and continuous recording will begin. If the pattern is not a trigger as at 186, then the pattern and the time and date associated therewith are recorded to memory as at 188. Following storage of the time and date stamped pattern at 188, the monitor/recorder will continue sampling as at 190.

As indicated previously, one mode of operation of the present invention contemplates storage of waveforms indicative of an epileptic episode in a reference table held in memory 50 of the monitor/recorder 30.

The sensed EBW waveforms, which are held within a temporary memory in microcontroller 46, are then compared to the waveforms held within the reference table. After the comparison, the sensed waveform is categorized and then time and date stamped and permanently recorded in memory 50.

In further detail, as the digitized signals reach the microcontroller 46, the microcontroller 46 will determine whether the a differential signal, that is, a signal resulting from the combination of two or more electrodes is being received, or whether the signal is a reference signal. It will also determine from which channels, that is, which electrodes, the microcontroller is receiving signals. The digitized signals will then be analyzed and then recorded or stored in memory 50.

In still further detail, once an EBW has been compared to a stored pattern, there are three possible outcomes of the comparison. These are that the EBW is an epileptic or other known abnormal brain wave form, that the EBW is a normal brain wave form, and that it is not an epileptic or other known abnormal electrical brain wave form but rather is an unknown electrical brain wave form.

Where the captured EBW is an epileptic or other known abnormal wave form, the dynamic sampling rate, that is, the rate at which monitor/recorder 30 samples brain wave activity, will automatically readjust itself according to predetermined parameters to a higher sampling rate. In addition, the montage selection, that is, whether the recording is referential (from a single electrode) or differential (from multiple electrodes) may be changed. At the same time, the microcontroller/processor may open up, that is, turn on, several leads, or it may shut down, that is, turn off, several leads, thus optimizing the recording of the desired EBW activity of interest. The microcontroler/processor will upgrade the time intervals and recording mode from normal to continuous mode as described further below. The input waveform is time stamped, labeled, coded and recorded sequentially.

If the compared sensed EBW is not an epileptic wave form but is instead a normal electrical wave, the monitor/recorder operates in the normal mode and the dynamic sampling rate remains at baseline operating rate.

Only a code identifying the EBW and the date and time of its occurrence will be recorded.

Where the sensed EBW is an unknown brain electrical wave form, the microcontroller/processor 46 will first identify the phase of the circadian cycle to optimize the reference table search capabilities, upgrade the dynamic sampling rate, close (i.e., turn on) all channels, and upgrade the time interval. At the end of the episode, the microcontroller/processor 46 will code only the segment of anomaly and code it as new. The distinctive characteristics of the newly acquired wave form will be calculated and added to the reference table. Upon uploading the stored information, the physician will have the option of reprogramming the reference table based on clinical assessment of the anomalous EBW and any newly acquired parameters.

Figures 6 and 7 illustrate the implantation of a monitor/recorder 30 according to the present invention. ■ Thus, Figure 6 illustrates a person 200 with a monitor/recorder 30 implanted in the chest (more specifically, between the major and minor pectoralis muscles of the chest wall) of person 200. Monitor/recorder 30 is electrically connected via a line 202, which will extend under the skin, to at least one sensor and typically an electrode array 204 implanted within the head 206 of the person 200. Figure 7 shows a person 200 with a monitor/recorder 30 implanted behind the ear 208 of the person. Once again, monitor/recorder 30 is electrically connected via a line 202 to at least one sensor and typically an electrode array 204 implanted within the head 206 of the person 200.

It will be understood that the location of the implantation of the monitor/recorder 30 within the patient is not critical to the present invention. Presently, the implantation location of the monitor/recorder 30 is limited by its size. As electronic components and their power supplies continue to shrink in size in the future, the number of available locations for implant will increase.

Referring now to Figure 8, the various locations for an electrode array implantation will be described. Figure 8 illustrates a transverse section through a human head 210. Head 210 includes a scalp 212 with the appropriate follicular covering 214 overlying a skull 216. Skull 216 protects a brain 218 including, in part, of course, a temporal lobe 220 and ventricles 222 Several differing electrode arrangements can be used with the present invention. First, an electrode array can be placed subcutaneously, that is, between the scalp 212 and the skull 216 as shown by 224. Another location for an electrode array is epidurally as at 226. Third, an electrode array can be placed subtemporally as at 228. Fourth, depth electrodes 230 can be inserted into the brain as shown. Finally, an electrode array can be placed subdurally directly against the cortex of the brain as at 232. It will be understood that each electrode arrangement 224-232 will be connected via the appropriate connector 234 to monitor/recorder 30. As shown in Figure 9, the electrode arrays discussed here include a pad 236 holding a plurality of exposed electrodes 238 with a single connecting lead 240 comprising multiple wires extending outwardly therefrom to the monitor/recorder 30. Pad 236 will take on various configurations depending upon its intended implantation location, as will the distribution of the electrodes thereon.

The present invention is capable of operation in several different modes, for example, a normal mode, a continuous mode, and a real-time mode. Each of these modes will be explained hereafter.

Normal mode

In a normal mode of operation, the monitor recorder 30 will sample particular, specified electrodes at a specified rate and in a specified mode, that is, either differential or referential. The sampling rate can be continuous or for specific time periods followed by specific time intervals. For example, sampling could occur for, say, one minute, followed by an interval of no sampling of, by way of example only, ten minutes. With the present invention, the electrodes to be sampled can be determined at the time of implant or at a later time with a telemetry command. Furthermore, the sampling period and interval can be determined by the physician at implant or at a later time. The sampling will provide to the microcontroller 46 a waveform indicative of EBW activity. As noted, this sampled waveform will be compared to the patterns stored in the reference table of memory 50 for identity or near-identity based upon such waveform attributes as amplitude, frequency, peak-to-peak time intervals, and slopes.

Each of the patterns may be associated with a particular, pre-determined code indicative of that pattern. If an input - waveform matches a stored pattern, then the input waveform will be stored in memory 50 as data representing the particular pattern matched, that is, the code for that pattern, the electrode from which the pattern originated, the length of time that the wave form lasted, and the time and date at which the wave form occurred. xample, stored information representative of the sensed EBW might look like the following:

ElecElecElectrode 1 trode 2 trode 3 (etc.)

PATLENGTH DATE PATLENGTH DATE

TERN (minutes) BEGAN TERN BEGAN

1 57 1998:030:08:20:00 3 20 1998:030:12:50:00 5

2 1 1998:030:09:17:00 1 30 1998:030:13:10:00 4

1 23 1998:030:09:18:00 2 14 1998:030:13:40:00 2

It will be appreciated that the foregoing is but one example of the manner in which data may be stored with regard to the present invention. In the foregoing example, the date is expressed in the format of yeaπday of the yeaπhour of the day using 24 hour format:minute of the houπsecond of the hour. Other formats could also be used. Furthermore, the foregoing is provided by way of illustration, it being clearly recognized that more than two electrodes may be used and that the number to be used is limited only to the discretion of the health care professional and the storage capacity and memory of the monitor/recorder 30.

To illustrate a method of analysis in greater detail, it will be understood that when the present invention is used specifically for monitoring and recording epileptic episodes, the monitor/recorder 30 will first analyze sensed EBW for amplitude spikes. That is, with one exception, each epilepsy type is characterized by an increase in amplitude. The one exception is a form of epilepsy known as myoclonic jerks, wherein the EBW may take a flat waveform pattern with an amplitude spike of normal amplitude level and slow in its frequency . Individual types of epilepsy are characterized by differing frequencies. In operation, then, monitor/recorder will examine the sensed EBW for an amplitude spike above a predetermined level, say 10-20 or 25 microvolts. When such a voltage spike is found, the apparatus will examine the sensed EBW to determine the frequency. When the frequency is determined, for example, to lie between 2.5 and 3.5 hertz, then the reference table in microcontroller 46 will be queried to determine which pattern is matched by those EBW characteristics. The reference table will also include the upgraded operating parameters for monitor/recorder 30 for use during the epileptic episode.

Upgraded Mode

If an EBW is sensed that does not match one of the predetermined patterns stored in memory, then the continuous mode of operation will begin. Where no pattern match is obtained, then the monitor/recorder 30 may be upgraded to sample at the maximum rate with the maximum number of electrodes and each sample will be recorded and time and date stamped.

The continuous mode will also be entered when a particular pattern is matched and that particular pattern has been designated as a trigger by the physician or by the reference table. Typically, such wave forms would be indicative of an epileptic episode. Nevertheless, the present invention is not limited to monitoring of epileptic conditions, but can be used to monitor and record EBW activity generally. Thus, the physician could specify other wave forms as triggers.

Once a trigger waveform is recognized, the monitor/recorder will reconfigure its monitoring parameters to record continuously rather than intermittently like in the normal mode. This reconfiguration could take several different forms. By way of example, the electrodes whose use is not relevant to recording the trigger waveform could be opened. That is, if the trigger EBW occurred in one hemisphere, those electrodes in the other hemisphere could be shut off. Alternatively, if an epileptic episode were detected while only one or two electrodes were being monitored, then additional electrodes could be turned on or all could be.

Additional changes that could occur in the recording parameters would be to change the sampling rate. • Usually, this would involve an increase in the sampling rate since where there is no EBW activity of interest, the sampling rate and thus the resolution of the EBW can be low. In addition, where such a change would prove to be of benefit the input could change from differential to referential and vice-versa. When in continuous mode, the monitor/recorder 30 will preferably no longer use pattern matching but will instead store all of the sensed data to memory 50. The length of time that the monitor/recorder 30 is in continuous mode could be pre-determined in association with a particular trigger pattern or could be set by the physician. Thus, the duration may last for a few minutes, five minutes, ten minutes or whatever the predetermined time period is. Such a sampling might look like the following.

Electrode Electrode Elec1 2 trode 3 (etc.)

PATTERN LENGTH DATE PATTERN LENGTH DATE (minutes) BEGAN BEGAN

1 57 1998:030:08:20:00 3 20 1998:030:12:50:00 5

2 1 1998:030:09:17:00 1 30 1998:030:13:10:00 4

1 23 1998:030:09:18:00 2 14 1998:030:13:40:00 2

*Epilepsy Pattern Detected, Continuous Recording Began 1998:030:09:40:22 sample 1; sample 2; sample 3: .... sample 500; sample 501

*EpiIepsy Pattern Ended, Continuous Recording Ended 1998:030:09:50:22

Electrode Electrode Electrode

1 2 3 (etc.)

PATTERN LENGTH DATE PATTERN LENGTH DATE (minutes) BEGAN BEGAN

3 23 1998:030:09:50:22 3 20 1998:030: 1

At the end of the predetermined period of continuous recording, monitor/recorder 30 will once again check the EBW for amplitude and frequency variations above normal.

If the EBW is still abnormal, monitor/recorder 30 will continue upgraded recordation of the EBW activity for a longer predetermined period of time. At the end of the second period of continuous recording, the EBW will again be checked and if still abnormal, the continuous recording will continue for yet a third period of time longer than the second. This cycle of recording, checking and recording will continue until the EBW no longer shows any abnormality as determined by the comparison made to the reference table. Once the EBW has returned to normal, normal or baseline mode of operation will be resumed.

Yet a third mode of operation of the present invention is a real-time operation. In such an operating mode the monitor/recorder 30 will simultaneously record and transmit the record data to an external display. Or the monitor/recorder 30 could transmit data directly to processor 20, which could perform the analysis previously described in terms of comparing the sensed EBW activity and comparing it with patterns of EBW stored in processor 20. The processor 20 could assign codes to the EBWs also.

Other advantages of the present invention include the ability to schedule particular times for making recordings. For example, if epileptic episodes appear to be associated with particular events in a patient's life or particular times of day, then the monitor/recorder 30 can be programmed to sense and record at those times only. Or if it is known that a particular patient is not subject to seizures during sleep, the monitor/recorder 30 can be programmed to recognize typical sleep EBW activity and discontinue analysis and recordation during that time period.

The present invention may also be used to map or localize the source of an epileptic episode or other abnormal brain wave within the brain. To do this, an abnormal EBW will first be recognized by the above or another form of analysis. The apparatus will upgrade its monitoring status to upgraded mode. In one embodiment of the present invention, all channels, that is, all of the electrodes, closest to the source of the abnormal EBW will be closed, that is, turned on, while the other electrodes will be opened. The relative strengths of the electric fields produced by the abnormal discharges of the brain cells can be measured at the various electrodes. Since it is known that the strength of an electric field varies as the inverse of the distance squared from the source of the field, simple measurements of the electric field strength at each electrode will indicate which electrode is the closest to the discharge. The relative distances of each electrode from the discharge can be similarly determined. Assuming that the electrode positions relative to each other are known (through such techniques as computed tomography, magnetic resonance imaging, or x-rays), the location of the abnormal discharge can be determined using known methods. Yet another way of mapping the location of the discharge is with the previously disclosed infratemporal electrode. With this electrode placement, the focus of the discharge can be located by rotating among the various electrodes the selection of which ones are closed, thus allowing the monitor/recorder to determine which electrodes are closest to the discharge. Thus, the present invention will enable the physician to verify the suspected location of the diseased tissue causing the abnormal brain wave discharges. The patient can then be assessed for the possible surgical resection of the tissue. The present invention allows the physician to recall stored data in many ways. Some of those many ways include, but are not limited to the following:

a. a histogram of patterns matched during a recording session (10 events of pattern 1 ; 5 events of pattern

2; 3 events of pattern 4 ... 4 events of unknown waveforms) b. recall data per event (recall all data associated with event 3, for example) c. recall the event data from a particular electrode (recall the data from electrode 1 for event 3, for example) d. recall data and reprocess data from a newly programmed differential electrode selection

The present invention contemplates that the physician will be able to downloaded recorded EBW, in both encoded and raw format, as desired. That is, the physician will query the monitor/recorder 30 with the appropriate command and request that all data relating to pattern 1, for example, be downloaded. The physician could thus focus initially on the actual incidents of abnormal brain wave activity. Additionally information could be downloaded as desired.

By allowing the change from normal to continuous mode, the monitor/recorder's power and memory can be optimized. Thus, where there exists no reason to sense and record at a high sampling rate, battery power and memory can be saved by using a low sampling rate. The present invention having thus been described, other modifications, alterations, or substitutions may now suggest themselves to those skilled in the art, all of which are within the spirit and scope of the present invention. It is therefore intended that the present invention be limited only by the scope of the attached claims below.

What is claimed is:

Patent Citations
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US4566464 *27 Jul 198128 Jan 1986Piccone Vincent AImplantable epilepsy monitor apparatus
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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
WO2003077985A1 *19 Feb 200325 Sep 2003Forschungszentrum Jülich GmbHDevice for treating patients by means of brain stimulation
EP2051626B1 *2 Aug 200717 Dec 2014Imperial Innovations LimitedApparatus and method for obtaining eeg data
US88557582 Aug 20077 Oct 2014Imperial Innovations LimitedApparatus and method for obtaining EEG data
US895886818 May 200917 Feb 2015Georgia Tech Research CorporationSystems and methods for multichannel wireless implantable neural recording
Classifications
International ClassificationA61B5/00
Cooperative ClassificationA61B5/412, A61B5/4094, A61B5/0006
European ClassificationA61B5/41D, A61B5/00B3B
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