Patent Application
20110082381
A seizure is a sudden loss of consciousness, a change in one's state of consciousness, and/or a loss of control over one's body. An absence seizure is one type of seizure which may occur in certain forms of epilepsy. Absence seizures are sometimes referred to as petit mal seizures. The term “petit mal” was originally coined by physicians and attendants in hospitals of Paris in the early 19th century, and the term “absence seizure” was introduced by Calmeil in 1824 (Da Silva, Electroencephalography: Basic Principles, Clinical Applications and Related Fields, Urban & Schwarzenberg, 1987).
The term petit mal underscores the decrease in convulsions normally associated with grand mal seizures. This contributes to the confusion between complex partial seizures (seizures of focal onset) and typical absence seizures (bihemispheric activity from onset). The two terms, petit mal and absence, can be complimentary; however, the latter may better describe symptoms of the seizures that can manifest as brief episodes of loss of consciousness and responsiveness. Absence seizures are generally short in duration, and it is not uncommon that they can be missed even by experienced witnesses such as parents and teachers. Furthermore, individuals with certain types of epilepsy can experience hundreds of absence seizures each day, resulting in poor performance at school and interfering with quality of life. Anti-epileptic drug (AED) treatments can help inhibit and control the occurrence of absence seizures (Schacther et al., The Comprehensive Evaluation and treatment of Epilepsy: A Practical Guide, Academic Press, 1997).
A common method for evaluating the efficacy of epilepsy treatments is to compare the number of seizures before treatment with the number of seizures after treatment during a finite period of time. To keep track of the number of seizures, the seizures experienced by patients and/or witnessed by observers can be documented by both parties in seizure diaries. However, such diaries have been found to be inaccurate as patients may not remember and observers may not recognize or be attentive to seizures at all times.
Absences seizures are often characterized by sudden loss of consciousness and/or interruption of motor activities for a brief period of time, which can last from a few seconds up to about thirty seconds. Given the short duration typically associated with absence seizures, along with their subtle clinical manifestations, absence seizures can be easily missed by inexperienced observers. In fact, even experienced observers can find it challenging to accurately evaluate and record occurrences of absence seizures.
In existing clinical trials, counting seizure frequency has traditionally been the method used most often in evaluating the efficacy of drug or other interventional therapy in the treatment of seizure disorders. This method tends to be quite tedious and plagued with several sources of measurement errors, including rater accuracy, rater and inter-rater reliability, experience of raters (usually family members or other companions of the patient) and erratic vigilance of observers. Due to the subtlety, high frequency, and short duration commonly associated with absence seizures, these factors are magnified, making the method of counting seizures by layman observers unreliable at best.
An electroencephalogram (EEG) is sometimes used to support the diagnosis of seizures and their types, but not typically for quantifying their occurrence. Manual evaluation of an acquired EEG and scoring of seizures by experienced electroencephalographers can sometimes be used. A typical absence seizure can be characterized by generalized and bilaterally synchronous spike and wave discharges (SWD), from about 5 seconds to about 20 seconds in duration. Like in most generalized epilepsies, SWD in absence seizures is maximal over the fronto-central midline and may start at a rate of about 4/sec, quickly slow down to about 3-3.5/sec, and during the final phase of the absence, slow to about 2.5/sec.
In some clinical studies of absence seizures, manual scoring of EEG recordings has been suggested for evaluating the efficacy of different AED treatments. The manual scoring of absence seizures is typically done by experienced qualified clinicians. However, this process is subject to the expertise and fatigue level of the clinician, as well as the possibility of manual recording errors. Additionally, this process is very time-consuming and tedious, sometimes taking several hours to score a few hours of EEG recordings. Therefore, manual EEG scoring can also be very expensive. Also, failure to spot seizures in an EEG recording can lead to misdiagnosis and even false evaluation of treatment effects.
Detection methods for absence seizures on EEG recording have been proposed in both human and animal models. Some methods utilize band pass filters to identify individual components or other amplitude duration criteria with or without filtering (Quy et al., High-speed Automatic Analysis of EEG Spike and Wave Activity Using an Analogue Detection and Microcomputer Plotting System, Electroencephalography and Clinical Neurophysiology, 49(1-2):187-9, July 1980; Carrie et al., Clinical Evaluation of a Method of Quantification of Generalized Spike-Wave EEG Patterns by Computer During Prolonged Recordings, Computers and Biomedical Research, 10:449-57, 1977; Principe et al., Microcomputer-based System for the Detection and Quantification of petit mal Epilepsy, Computers and Biomedical Research, 12:87-95, 1982; Koffler et al., Automatic Detection of Spike-and-Wave Bursts in Ambulatory EEG Recordings, Electroencephalography and Clinical Neurophysiology, 61(2):165-80, August 1985; Burr et al., Computerized Analysis of Epileptic Activity and Sleep in Mobile Long-Term EEG Monitoring, European Neurology, 25:61-65, 1986). In an animal model, an SWD detector was introduced based on the first derivative of EEG signals, called the steepness of the signals (Westerhuis et al., Automatic Detection of Spike-Wave Discharges in the Cortical EEG of Rats, Measuring Behavior '96, Int. Workshop on Methods and Techniques in Behavioral Research, trecht, The Netherlands, 16-18 Oct. 1996). However, this method sometimes misclassifies eye movement artifacts as absence seizures.
Other detection methods have been proposed, including a method based on the maximum absolute value of the EEG amplitude in the rat model (Fanselow et al., Reduction of Pentylenetetrazole-induced Seizure Activity in Awake Rats by Seizure-triggered Trigeminal Nerve Stimulation, The Journal of Neuroscience, 20:8160-8, 2000). However, this method cannot distinguish between high amplitude artifacts. A spectral-comb based analysis method has been proposed using a time frequency spectrum, produced by Short Time Fourier Transform (STFT), in order to extract some features that enable seizure detection (Van Hese et al., Detection of Spike and Wave Discharges in the Cortical EEG of Genetic Absence Epilepsy Rats from Strasbourg, Physics in Medicine and Biology, 48:1685-700, June 2003). Also, linear models and an artificial neural network has been used for attempting to detect absence seizures in a data set of several absence seizures acquired from patients (Alkan et al., Automatic Seizure Detection in EEG Using Logistic Regression and Artificial Neural Network, Journal of Neuroscience Methods, 148:167-176, 2005; Alkan et al., Comparison of Ar and Welch methods in Epileptic Seizure Detection, Journal of Medical Systems, 30:413-419, 2006). However, the performance of a neural network depends greatly on the training dataset. Thus, none of the existing detection methods is capable of quickly and accurately detecting absences seizures from an EEG recording.
The present invention provides novel methods for quickly and accurately detecting absence seizures.
Embodiments of the present invention provide novel methods for detecting and analyzing absence seizures using EEG recordings from patients.
In an embodiment, a method for detecting absence seizures from an EEG recording can include using wavelet transform. Wavelets can extract an original signal into scales that can be mapped into different pseudofrequencies. Wavelet transform can provide an advantage over Short Time Fourier Transform (STFT) since with wavelets, arbitrary resolution can be achieved in both time and frequency. A variance technique can also be applied to localize an absence seizure. The method can be performed using a processor.
In one embodiment, a method for detecting absence seizures from an EEG recording can include using an algorithm. The algorithm can be based, for example, on the spectral characteristics of the seizure. In a further embodiment, the algorithm can involve using wavelet transform, in which wavelets can extract an original signal into scales that can be mapped into different pseudofrequencies. In yet a further embodiment, the algorithm can include a sliding variance technique (SVT). A processor can be used to execute the algorithm.
When the phrase “a processor can be used to execute the algorithm” or “the algorithm is executed using a processor” is used herein, as a skilled artisan would understand, the meaning is that the steps of the algorithm can be performed using a processor a computer processor) and any calculations performed in the algorithm can be done by the processor.
The present invention provides novel methods for quickly and accurately detecting absence seizures.
Generalized epilepsy (GE), primary or secondary, can often be associated with spike and/or polyspike and wave activity seen on an electroencephalogram (EEG) from onset to offset of seizures. Impairment of consciousness may be the initial manifestation and motor manifestations can be bilateral. Ictal electroencephalographic patterns can reflect neuronal discharge which may be widespread in both hemispheres of a patient's brain.
Ictal EEG characteristics of GE can include: regular, bilateral, and symmetrical spike-and-slow-wave complexes (can have multiple spike-and-slow-wave complexes for typical absence seizures); polyspike and wave, or sometimes spike and wave or sharp and slow waves for myoclonic seizures; and slow waves; fast activity occasional spike-and-wave patterns for clonic seizures; low voltage, fast activity or a fast rhythm of at least about 9 Hz, decreasing in frequency and increasing in amplitude for tonic seizures; fast rhythm of at least about 10 Hz at onset decreasing in frequency and increasing in amplitude during tonic phase, interrupted by slow waves during clonic phase for tonic-clonic seizures; polyspikes and wave or flattening or low-voltage fast activity for atonic seizures; and/or a decremental response for infantile spasms. Fast activity can refer to, for example, at least about 9 Hz.
The regular, bilateral, and symmetrical spike-and-slow-wave complexes can have a frequency of from about 2 Hz to about 4 Hz. Oftentimes, the frequency is about 3 Hz.
For atypical absence seizures, an EEG can sometimes have more heterogeneous, irregular, and slow spike-and-slow-wave complexes. Abnormalities can be bilateral and sometimes irregular and/or asymmetrical.
In absence seizures, an EEG can be used as a tool to measure and compare the quantity of seizure activity during a finite period of time before and during interventional therapy.
Embodiments of the present invention provide novel methods for detecting and analyzing absence seizures using EEG recordings from patients.
In an embodiment, a method for detecting absence seizures from an EEG recording can include using wavelet transform. Wavelets can extract an original signal into scales that can be mapped into different pseudofrequencies. Wavelet transform can provide an advantage over Short Time Fourier Transform (SIFT) since with wavelets, arbitrary resolution can be achieved in both time and frequency. A variance technique can also be applied to localize an absence seizure. The algorithm can be executed using a processor.
In one embodiment, a method for detecting absence seizures from an EEG recording can include using an algorithm. The algorithm can be based, for example, on the spectral characteristics of the seizure. In a further embodiment, the algorithm can involve using wavelet transform, in which wavelets can extract an original signal into scales that can be mapped into different pseudofrequencies. In yet a further embodiment, the algorithm can include a sliding variance technique (SVT). The algorithm can be executed using a processor.
When the phrase “a processor can be used to execute the algorithm” or “the algorithm is executed using a processor” is used herein, as a skilled artisan would understand, the meaning is that the steps of the algorithm can be performed using a processor (e.g., a computer processor) and any calculations performed in the algorithm can be done by the processor.
An algorithm according to an embodiment of the present invention can include computing the variance profile for each channel by using a moving window of length k samples. For each wavelet-filtered channel that can be seen as a time series of N sample points X=[x1, X1, . . . , xN], the sample variances Vwi=Var(wi) can be computed that correspond to the sets wi={xεX|x≧xi, x<xi+5} where i=1, . . . , N−k. After the variance calculation, the variance profiles for all channels can be added, and thresholding can be performed. Thresholding can be done since time intervals that contain seizure activity may have very high values of variance. Additionally, averaging can amplify characteristics common for all channels and help to cancel out noise. Thus, a series of consecutive ones in the indicator function 1{Vi>P}, where P is some threshold, can suggest the presence of absence seizure activity. The first and the last 1 in such a series can correspond to seizure onset and offset, respectively. To inhibit the detection of artifacts that appear in a certain frequency band of interest, double-thresholding can be performed. That is, thresholding with a high threshold can be performed in order to detect a seizure, and then for each seizure detected local thresholding can be performed (with a lower threshold than the high threshold) in order to determine seizure onset and offset. The high threshold can be set as, for example, the maximum variance value during a seizure. The second threshold can be estimated from, for example, the variance value during the onset and the offset for known examples, if they exist.
In a specific embodiment, a method for detecting absence seizures from an EEG recording can include using an algorithm with the pseudocode given in algorithm (1) below.
Algorithm (1):
The Function CWTA(Xm, αlow, αhigh, β) can be, for example, a function with the pseudocode of Function (1) below.
Function (1):
The Formula (A) used in Function (1) can be a wavelet transform formula. For example, Formula (A) can be the Continuous Wavelet Transform (CWT) formula of Equation (1) below.
C(t,a,b)=∫−∞+∞x(t)ψa,b(τ)dτ (1):
where
is the mother wavelet function. The mother wavelet function can be the Morlet wavelet with an analytic expression given by
Additionally, though line 17 of the pseudocode of Algorithm (1) indicates that spike and wave discharge (SWD) epochs with a distance of less than 1 sec apart should be merged, embodiments of the present invention are not limited to this time value. Any suitable time value can be used for the limit for merging SWD epochs. For example, in an embodiment, SWD epochs that are less than about 0.5 seconds apart can be merged and counted as one SWD epoch. In another embodiment, SWD epochs that are less than about 1.5 seconds apart can be merged and counted as one SWD epoch. In a further embodiment, SWD epochs that are less than about 0.75 seconds apart can be merged and counted as one SWD epoch. In yet a further embodiment, SWD epochs that are less than about 0.25 seconds apart can be merged and counted as one SWD epoch. In yet a further embodiment, SWD epochs that are less than about 2 seconds apart can be merged and counted as one SWD epoch. In yet a further embodiment, SWD epochs that are less than about 2.5 seconds apart can be merged and counted as one SWD epoch. In yet a further embodiment, SWD epochs that are less than about 3 seconds apart can be merged and counted as one SWD epoch. In yet a further embodiment, SWD epochs that are less than about 1.25 seconds apart can be merged and counted as one SWD epoch.
One advantage of wavelet transform over SIFT analysis is that frequency resolution can be increased in certain frequency bands while maintaining approximately the same time resolution. For example, wavelet transform can give higher frequency resolution than STFT in the delta band at 3 Hz. This can be especially useful in SWDs of absences seizures because these discharges often occur in a frequency window of from about 2.5 Hz to about 4.5 Hz.
With wavelet transform, scales can be transformed into frequencies using Equation (2).
F
a
=F
c/(αΔ) (2):
where Fα is the frequency that corresponds to the scale α, Fc is the central mother wavelet frequency, and Δ is the EEG sampling period. In a specific embodiment of the present invention using the Morlet mother wavelet function, Fc can be about 0.81 Hz and Δ can be about 1/200 sec.
Additionally, in a certain embodiment, the sampling frequency can be fs=200 Hz, M can be 16 channels, and the scales 36:46 can be used, corresponding to the frequencies 2.5 Hz to 4.5 Hz. In this context, wavelet transform can be used as a band pass filter by keeping scales of interest and rejecting other scales.
A method for detecting absence seizures, comprising:
The method according to embodiment 1, wherein the algorithm comprises a sliding variance technique (SVT).
The method according to any of embodiments 1-2, wherein the algorithm comprises computing a variance profile by using a moving window with a length given by a number of samples.
The method according to any of embodiments 1-3, wherein the algorithm further comprises performing a thresholding process.
The method according to any of embodiments 1-4, wherein the algorithm further comprises performing a double-thresholding process.
The method according to any of embodiments 1-5, wherein the algorithm has a pseudocode of Algorithm (1):
Algorithm (1):
The method according to embodiment 6, wherein T in line 17 of Algorithm (1) is about 1 second.
The method according to any of embodiments 6-7, wherein CWTA(Xm, αlow, αhigh, β) is a function with the pseudocode of Function (1) below.
Function (1):
The method according to embodiment 8, wherein Formula (A) is the Continuous Wavelet Transform (CWT) formula of Equation (1) below.
C(t,a,b)=∫−∞+∞x(t)ωa,b(τ)dτ Equation (1):
where
is the mother wavelet function.
The method according to embodiment 9, wherein the mother wavelet function is the Morlet wavelet function with the analytic expression
A method for detecting absence seizures, comprising performing an algorithm on an EEG recording of a patient, wherein the algorithm has a pseudocode of Algorithm (1):
Algorithm (1):
The method according to embodiment 11, wherein T in line 17 of Algorithm (1) is about 1 second.
The method according to any of embodiments 11-12, wherein CWTA(Xm, αlow, αhigh, β) is a function with the pseudocode of Function (1) below.
Function (1):
The method according to embodiment 13, wherein Formula (A) is the Continuous Wavelet Transform (CWT) formula of Equation (1) below.
C(t,a,b)=∫−∞+∞x(t)ωa,b(τ)dτ Equation (1):
where
is the mother wavelet function.
The method according to embodiment 14, wherein the mother wavelet function is the Morlet wavelet function with the analytic expression
The method according to any of embodiments 1-10, wherein the algorithm is executed using a processor.
The method according to any of embodiments 11-15, wherein the algorithm is executed using a processor.
A study was conducted to measure absence seizures from patients using EEG recordings. Two patients were included in the study; one seizure free and one experiencing over 100 seizures within 4.5 hours. Ambulatory EEG recordings were acquired from two children <13 years of age; one seizure free for 24 hours and one experiencing seizures within 4.5 hours. Subjects were instructed to go about their normal life as usual while EEG recording was ongoing avoiding any type of activity that might result in the loosening or removal of electrodes from the scalp or result in excessive recording artifacts, e.g., gum chewing. The international 10-20 electrode placement system with 19 electrodes was used and the following 16 bipolar channels were chosen: Fp1-F3, F3-C3, C3-P3, P3-01, Fp2-F4, F4-C4, C4-P4, P4-02, Fp1-F7, F7-T3, T3-T5, T5-O1, Fp2-F8, F8-T4, T4-T6, T6-O2. Data points were collected at a sampling rate of 200 Hz for each channel. EEG recordings were scored by a clinically experienced board certified electroencephalographer noting the duration of each SWD from onset to offset to one decimal point of a second. Operationally, two separate epochs of SWD complexes were counted as one event when the inter-epoch duration was less than about 1 second.
An algorithm having the pseudocode of Algorithm (1) was used and detected only one false positive finding in the first patient and detected 120 out of 150 continuous uninterrupted 3 Hz spike SWD epochs in the second patient. Of the 30 SWD epochs missed in the second patient, 27 were less than 2.1 seconds in duration. The remaining epochs were 3.1 seconds, 3.3 seconds, and 4.1 seconds of interrupted 3 Hz SWDs. The algorithm used provided an efficient., automatic detection scheme for diagnostic and therapeutic evaluation in patients with absence seizures.
Additionally, an electroencephalographer labeled and scored all SWD epochs separately and independently from the algorithm. The onset and offset of each epoch of continuous 3 Hz SWD were recorded to the nearest first decimal utilizing digital time stamped by the EEG acquisition machine. Any typical 3 Hz SWD interrupted by less than a one second interval was defined as one epoch of 3 Hz SWD. Onset was subtracted from offset times to obtain duration of each epoch in seconds. Durations of all epochs obtained by manual scoring were compared to durations of matching epochs detected by the algorithm.
A false positive was defined as an artifact or EEG misclassified as a seizure, a false negative was defined as an SWD epoch that was not detected by the algorithm. Occurrences of false positives, total time of false negatives, and precision in detecting seizure onset and offset time were considered.
For patient 1 with 24 hours of seizure free EEG recordings, the algorithm produced only one false positive detection. This false positive is shown in
Of 150 manually scored 3 Hz SWD epochs in patient 2, the algorithm detected 120. The distribution of missed and detected 3 Hz SWD epochs by duration is shown in
The sliding window length chosen helps determine how well the algorithm detects short epochs. Smaller windows can be very sensitive to small changes in frequency and amplitude but can also be contaminated by artifacts of similar changes. On the other hand, if the variance window becomes too long (in samples), it can be easy to miss epochs shorter than the window length. A 1 second window was chosen due to the fact that SWD epochs 3 sec long are not generally clinically important. The algorithm detected successfully 120 3 Hz SWD epochs. In total, the percentage of error in terms of number of 3 Hz SWD epochs was 20% ( 30/150), as calculated by Equation (3).
% Error=(#missed/# manually scored)×100% (3):
The percentage error in terms of cumulative time of missed 3 Hz SWD time was 5.61% (48.82 sec/870.60 sec), as calculated by Equation (4).
% Error=(cumulative time missed/cumulative manually scored time)×100% (4):
The fact that the second error percentage was very low means that the majority of missed epochs were of short length. Table 1 and
In Table 1, the percentage error based on # missed is calculated from Equation (3) considering only the epochs longer than x seconds in each column (where x=1 in the first column, 1.5 in the second column, etc.). The percentage error based on duration missed is calculated from Equation (4) considering only the epochs longer than x seconds in each column (where x=1 in the first column, 1.5 in the second column, etc.).
For the successfully detected events the error was computed both in terms of number of samples and duration (seconds) for the onset, and offset of SWD. The results are shown in Table 2. Also, Table 3 shows the error for the total detected duration.
False positives detected in patient 2 are shown in
Despite the difficulty in detecting absence seizure, the algorithm detected clinically significant 3 Hz SWD epochs with high sensitivity and precision. Only one false positive epoch in patient 1 was detected and 97.25% of all 3 Hz SWD about 3 sec long were detected in patient 2.
The sensitivity of the proposed algorithm is influenced by the length of the sliding window. Smaller window length can lead to higher sensitivity and higher chance for false positive detection while larger window length can result in lower resolution and lower chance for false positive detection. The window length in this example was chosen to yield high sensitivity and specificity for the 3 Hz SWD.
A study was conducted using the algorithms of the subject invention on animal models. Eight-hour recordings were acquired from a total of four 4-month old Fischer 344 (F344) rats. In total, six screw electrodes were implanted in the skull of each animal: 2 frontal (F3, F4), 2 central (C3, C4), and 2 parietal (P3, P4). The electrode configuration is shown in
Long term video-EEG recordings were visually scanned to detect and score SWD occurrence; identified SWDs were confirmed by an electroencephalographer. The exact number of epochs and their cumulative time during the 8 hours of recordings can be seen in the Table 4.
For detecting SWD discharges in a rat model, the proposed detection scheme is based in time frequency decomposition of the EEG employing the wavelet transform. Wavelet transform has profound advantages over the classical STFT because one can increase the scale (or frequency) resolution while keeping the same time resolution. Subsequently, the variance profile of the EEG is computed and seizures are detected by a double thresholding process. The algorithm was found to have high sensitivity and a minimal false positive detection rate for SWDs localized in the frequency band of about 3 Hz. For the detection of SWDs, an algorithm was used for detection including wavelet decomposition, variance profile computation, and thresholding.
Every differential channel of the raw EEG recordings, which can be represented as a time series X(t), was decomposed into a time-scale domain using the wavelet transform: C(t, a, b)=Σ−∞∞x(t)ψa,b(τ)dτ, where
is the mother wavelet function. ψ(τ)=cos(5τ) was used, which is a form of the Morlet mother wavelet. The Morlet mother wavelet has a low time-bandwidth product, infinite differentiation, and explicit expression, which are useful in EEG analysis. A time scale plot of a recorded absence seizure is shown in
Scales were converted into frequencies using
where fc is the central frequency of the mother wavelet, in this case, 0.81 Hz, and Δ= 1/200 sec is the sampling period. Among all the scales that can decompose the EEG signal, most important are those that correspond to the frequency band in which SWD activity appears (for example, about 7 Hz). Thus, only the scales 19-25 were kept and summed for every channel.
Based on the observation that the high SWD activity produces wavelet profiles of high variance, the variance profile was computed for each channel using a sliding window of width k=200 samples (i.e., corresponding to 1 sec of recording). All variance profiles for all channels were summed to reject noise and artifacts that are not generalized (i.e., not appearing in all channels). A variance profile of the seizure can be seen in
For accurate localization of the onset and offset times of a seizure based on the variance profile of the EEG recordings, a double thresholding technique was used. The two thresholds can be seen as the flat lines in
For the sample points of the variance profile curve that “hit” the high threshold, a local search was performed to specify the exact onset and offset sample points of the seizure. That is, referring to
The detection sensitivity and false positive rate can be highly dependent on the parameters of the algorithm (e.g., thresholds). The algorithm was applied using 10 different thresholds, and sensitivity and specificity were computed. Sensitivity was defined as the number of epochs detected over the total number of scored epochs, and false positive rate was defined as the number of false positives over the corresponding recording time.
A receiver operating characteristic (ROC) curve can be used as a plot of sensitivity versus specificity. The ROC can be very useful in visualizing how the sensitivity percentage changes as a function of missed seizure rate and help an end user to decide the optimal point (corresponding threshold) that fits a specific application.
With this definition of sensitivity and false positive rate, all epochs are treated in the same manner without taking into consideration the epoch length. That is, one SWD epoch of 10 sec in length will contribute the same as an epoch of 1 sec. Given this consideration, sensitivity and specificity can be defined based on the cumulative SWD time or “cumulative epileptiform burden.” In this case, sensitivity is defined as the cumulative detected time (in see) over the total time, whereas the false positive rate is defined as the cumulative missed seizure time over the corresponding time of the recordings.
The proposed algorithm is robust with respect to the input parameters, which means that the output (detected epochs) cannot differ significantly when small changes are made to the threshold parameters. In addition, the ROC analysis showed that high sensitivity rates (greater than about 90%) can be achieved along with a low false positive rate (about 2 to about 4 false positive epochs per hour). When considering the cumulative time of the SWD epochs instead of the absolute number of the epochs, the algorithm demonstrated, on average, over 90% accuracy while the total missed SWD time did not exceed about 8.5 seconds per hour. The sensitivity percentages and the false positive rates can increase dramatically when epochs longer than some predefined duration are considered.
All patents, patent applications, provisional applications, and publications referred to or cited herein, supra or infra, are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.
This application claims the benefit of U.S. provisional application Ser. No. 61/075,601, filed Jun. 25, 2008, which is incorporated herein by reference in its entirety.
The subject matter of this application has been supported by a research grant from the National Institute of Neurological Disorders and Stroke under grant number NINDS R01 NS046015 (KMK). Accordingly, the government has certain rights in this invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US09/48488 | 6/24/2009 | WO | 00 | 11/11/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 61075601 | Jun 2008 | US |
