Patent Publication Number: US-11638562-B2

Title: Brain activity analysis method and apparatus thereof

Description:
This Application is a Divisional Application of patent application Ser. No. 15/642,510, filed 6 Jul. 2017, currently pending. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a brain wave analysis technology, particularly to a brain activity analysis method able to evaluate brain activity and an apparatus thereof. 
     Description of the Related Art 
     The conventional brain wave analysis includes waveform analysis, time-frequency analysis, complexity analysis, etc. The result of time-frequency analysis is an important reference in the related field. However, the evaluation of brain activity based on time-frequency analysis is constrained by the limitations of spectral calculation, such as the mathematic assumption, timescale resolution, information distortion, and harmonics influences. Thus, the applicability of time-frequency analysis is greatly degraded. Further, the current time-frequency analysis technology is less likely to analyze the result of multiplication but can only analyze the result of linear addition. 
     The conventional seizure detection, which based on time-frequency analysis method, adopts frequency measurement (by increasing a 30-40 Hz oscillation component) and amplitude measurement for seizure detection. In general, the changes of a physiological signal, such as brain electrical signal, contain various physiological mechanisms and relevant interferences. The mathematic neural network model consists of addition and multiplication within multiple layer structure. The brain wave signal is resulting from the neural network and is sensed by the electroencephalography. The conventional technology of brain wave analysis is to analyze the “features appearing in neuron operation” or the “brain function states corresponding to brain waves”. However, the existing technology is hard to analyze the signal modulation of multiplication and is limited for relevant applications. 
     The prior art of published related patents respectively have different disadvantages. The U.S. Pat. No. 6,480,743 disclosed a “system and method for adaptive brain stimulation”, which is intended to be used as a treatment of neurological diseases. The patent adopts a half-wave analysis technology to acquire the parameters for setting the waveform of the electric stimulus of treatment. The parameter setting of the prior art is mainly according to the fundamental characteristics of primitive brain wave signal. Thus, the result of identification is mainly affected by the interferences of the primitive brain wave signal. The U.S. Pat. No. 8,131,352 disclosed a “system and method for automatically adjusting detection thresholds in a feedback-controlled neurological event detector”, which adopts the amplitude features of the primitive brain wave with a threshold value for the event detection. However, the amplitude features consists of various physiological information and is much sensitive to the bias of the target signal, which might cause the detection error. The U.S. Pat. No. 6,810,285 disclosed “seizure sensing and detection using an implantable device”, which adopts waveform morphology analysis (including time-domain analysis and feature extraction analysis) to detect neurological events. All the operations thereof are based on the primitive waveform of the brain wave signal. Thus, the detection results are sensitive to the interferences of waveform distortion caused by noises. Further, the accuracy thereof is limited by the fact that a part of regulations of neurological functions are presented in the modulated signals and unlikely to be evaluated and estimated with the features of the primitive waveform. A Taiwan patent No. I487503 disclosed “an automatic sleep staging device, which uses entropy analysis to evaluate the brain activity”. However, the prior art cannot deal with the changes of the time-frequency features of brain wave signal but can only estimate the complexity feature. Besides, the prior art adopts the filtering and smoothing respectively before and after the main waveform processing, which might reduce the key intrinsic characteristics and practically cause detection error. 
     In order to evaluate brain functionality and breakthrough limitations of the conventional technology, the present invention constructs a novel algorithm to implement a brain activity analysis method and an apparatus thereof to analyze the features appearing in neuron operation and the brain function status, named brain activity, corresponding to the brain waves. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide a brain activity analysis method and an apparatus thereof, which decomposes and analyzes frequency modulations and amplitude modulations to construct a multilayer and multidimensional feature space presenting the nonstationary features in brain activities. 
     Another objective of the present invention is to provide a brain activity analysis method and an apparatus thereof, which uses a feature mask to greatly reduce the computation complexity of the conventional decomposition technology and thus obviously reduce computation loading, whereby to improve the feasibility of the brain wave analysis technology. 
     A further objective of the present invention is to provide a brain activity analysis method and an apparatus thereof, which can improve the detection rate of the brain wave analysis. 
     In order to achieve the abovementioned objectives, the present invention proposes a brain activity analysis method, which comprises several steps: sensing at least one brain electrical signal; using a nonstationary decomposition method to acquire a plurality of sub-signals corresponding to intrinsic feature components; demodulating each of the sub-signals to generate modulation signals respectively corresponding to the sub-signals; undertaking recursive iterations, wherein a feature mask is used to determine whether to proceed further decomposition and demodulation of the acquired modulation signals; if yes, perform decomposition and demodulation until the iteration number, which is determined by the feature mask, has been reached; if no, i.e. the decomposition and demodulation is completed, the process directly proceeds to the next step: using the feature mask to select modulation signals of interest from all the modulation signals as feature modulation signals, and undertaking quantitation processes and identification processes of the feature modulation signals to obtain an analysis result corresponding to the brain electrical signal. 
     In the method of the present invention, the modulation signals include frequency-modulation parts and amplitude-modulation parts. 
     The present invention also proposes a brain activity analysis apparatus, which comprises at least one sensing unit, a signal processing unit, and a display unit. The sensing unit collects the brain wave signal of a subject to acquire at least one brain electrical signal. The signal processing unit is in communication with the sensing unit to receive the brain electrical signal and uses the abovementioned method to decompose and demodulate the brain electrical signal. According to a feature mask, the signal processing unit determines whether to proceed the recursive iteration of the processing or select modulation signals of interest from all the modulation signals as feature modulation signals. After acquiring the feature modulation signals, the signal processing unit performs quantitation processes and identification processes of all the feature modulation signals to obtain an analysis result corresponding to the brain electrical signal. Then, the signal processing unit presents the analysis result as brain activity on a display unit. 
     In one embodiment, the brain activity analysis apparatus further comprises a storage unit electrically connected with the signal processing unit to store the signals, data, and results, which are processed or generated by the signal processing unit. 
     Below, embodiments are described in detail in conjunction with the accompanying drawings to make easily understood the objectives, technical contents and accomplishments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram schematically showing a brain activity analysis apparatus according to one embodiment of the present invention; 
         FIG.  2    is a flowchart of a brain activity analysis method according to one embodiment of the present invention; 
         FIG.  3 ( a )  is a diagram showing a primitive brain wave signal; 
         FIG.  3 ( b )  is a diagram schematically showing that a brain electrical signal is decomposed into a plurality of sub-signals carrying intrinsic feature components according to one embodiment of the present invention; 
         FIG.  3 ( c )  is a diagram schematically showing that the sub-signals are demodulated into modulation signals each containing a frequency-modulation part and an amplitude-modulation part according to one embodiment of the present invention; 
         FIG.  3 ( d )  is a diagram schematically showing the signals generated after decomposition and demodulation has been proceeded three times according to one embodiment of the present invention; 
         FIG.  3 ( e )  is a diagram schematically showing the signals determined by a feature mask according to one embodiment of the present invention; 
         FIG.  3 ( f )  is a diagram schematically showing that the modulation signals of interest are selected from all the modulation signals according to one embodiment of the present invention; and 
         FIGS.  4 ( a )- 4 ( e )  are diagrams schematically showing the signals generated in sequential cycles of decomposing and demodulating the brain electrical signal measured during normal condition and seizure according to one embodiment of the present invention, wherein the feature mask is M=x(FM[2],AM[1(FM[1,2],AM[1,2]),2]). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The brain activity analysis method and apparatus of the present invention is corresponding to the fundamental operation architecture of a neural network, using a nonlinear waveform decomposition technology to explore features of variations of different modulations and work out multilayer-multidimensional intrinsic variations, whereby to provide a multidimensional and low-distortion analysis technology of neurological function, wherefore the accuracy of using brain waves to diagnose neurological diseases is increased. 
     Refer to  FIG.  1    a block diagram schematically showing a brain activity analysis apparatus according to one embodiment of the present invention. The brain activity analysis apparatus  1  of the present invention comprises a sensing unit  10  detecting the brain wave signal of a subject to acquire a brain electrical signal; a signal processing unit  12  in communication with the sensing unit  10 ; a storage unit  14  electrically connected with the signal processing unit  12 ; and a display unit  16  electrically connected with the signal processing unit  12 . The signal processing unit  12  is an application-specific integrated circuit (ASIC), a microcontroller unit (MCU) or a microprocessor. The signal processing unit  12  receives the brain electrical signal and performs calculations of the intrinsic feature components to obtain an analysis result corresponding to the brain electrical signal, such as the status of brain activity. The models, data, and signals used in processing and analysis and the results are stored in the storage unit  14 , which may be an external or built-in storage device. The display unit  16  presents the information output by the signal processing unit  12  and the results of evaluating the status of brain activity. 
     After the fundamental architecture of the apparatus of the present invention has been described above, the brain activity analysis method of the present invention will be fully described below. Refer to  FIG.  2    a flowchart of a brain activity analysis method according to one embodiment of the present invention, and refer to  FIG.  1    again. The brain activity analysis method of the present invention comprises Steps S 10 -S 24 . In Step S 10 , use the sensing unit  10  to measure the brain wave of at least one subject to acquire at least one brain electrical signal, as shown in  FIG.  3 ( a ) . The brain electrical signal may be an electroencephalography (EEG) signal, an intracranial electroencephalogram (iEEG) signal, or an electrocorticography (ECoG) signal. The brain electrical signal is transmitted to the signal processing unit  12  and processed and analyzed in Steps S 12 -S 24 . 
     In Step S 12 , use a nonstationary decomposition method, such as the empirical mode decomposition (EMD) method, to decompose the brain electrical signal to acquire a plurality of sub-signals carrying intrinsic feature components, as Components 1-7 shown in  FIG.  3 ( b ) . In Step S 14 , demodulate each of the sub-signals, wherein a normalization operation is used to decompose the sub-signals, which respectively carry different intrinsic feature components, to acquire modulation signals respectively corresponding to the sub-signals. The modulation signals include frequency-modulation parts and amplitude-modulation parts. The Layer 1 signal shown in  FIG.  3 ( c )  includes the frequency-modulation parts (W k (t), k=1-7) and the amplitude-modulation parts (A i (t), i=1-7), which are obtained via decomposing every sub-signal. In Step S 16 , perform recursive iteration, wherein a preset feature mask is used to determine whether to perform recursive iteration of the acquired modulation signal (including the frequency-modulation parts and the amplitude-modulation parts), i.e. determine whether to perform a further decomposition-demodulation process of the acquired signals. If no, the process directly proceeds to Step S 20 . If yes, the process proceeds to Step S 18 : continue decomposition and demodulation of the signals. The details of the decomposition and demodulation in Step S 18  are respectively identical to Step S 12  and Step S 14 . After Step S 18  is completed, the process returns to Step S 16  for determining whether to proceed a further decomposition-demodulation process of the signals until the number of decomposition and demodulation has reached the number determined by the feature mask. The number of recursive iteration (the number of decomposition and demodulation of signals) is exactly the number of the layers that the signal is decomposed into. The number of recursive iteration required to analyze the feature is dependent on the characteristics of the signal. In this embodiment, the components of Layer 1 are further decomposed and demodulated for the second time and the third time to generate the Layer 2 modulation signals shown in  FIG.  3 ( c )  and the Layer 3 modulation signals shown in  FIG.  3 ( d ) . 
     The number of recursive iteration and the signal features determine feature components. Therefore, in Step S 20 , set a feature mask M to determine the feature components. As shown in  FIG.  3 ( e )  and  FIG.  3 ( f ) , the feature mask M is used to select modulation signals of interest as feature modulation signals from Layer 1 modulation signals, Layer 2 modulation signals and Layer 3 modulation signals. The feature modulation signals are to be used in the succeeding calculation to obtain the multidimensional variation of the intrinsic features of the brain wave. In Step S 22 , perform quantitation processes of the features of interest, such as calculation of power densities, instantaneous frequencies, or averaged periods of the features of interest. In Step S 24 , use a classification model to perform identification processes. The classification model is constructed according to the personal history and the pre-trained parameters. Thereby, the present invention can obtain the analysis result corresponding to the abovementioned brain electrical signal, i.e. the status of brain activity. After obtaining the status of brain activity, the signal processing unit  12  presents the result on the display unit  16 . 
     Succeeding to full demonstration of the spirit of the present invention, the example shown in  FIG.  4 ( a )  and  FIG.  4 ( b )  is used to illustrate the technical contents of the present invention. The encircled portions are the features selected by the feature mask M=x(FM[2],AM[1(FM[1,2],AM[1,2]),2]), wherein x denotes the brain electrical signal; the Arabic numerals 1, 2 denotes the sub-signals; AM denotes amplitude modulation; FM denotes frequency modulation.  FIG.  4 ( a )  shows the brain electrical signal detected in seizure. The signal in  FIG.  4 ( a )  is decomposed into a plurality of intrinsic feature sub-signals in a nonstationary decomposition method, as shown in  FIG.  4 ( b ) . Each of the sub-signals in  FIG.  4 ( b )  is demodulated into a frequency-modulation part and an amplitude-modulation part, as shown in  FIG.  4 ( c ) . The modulation signals x(FM[2]) and x(AM[1,2]) are selected as the features to be used in the succeeding calculation. The modulation signal x(AM[1]) is further decomposed to develop the intrinsic feature variation of the modulation signal, as shown in  FIG.  4 ( d ) . Each of the signals in  FIG.  4 ( d )  is further demodulated into a frequency-modulation part and an amplitude-modulation part, as shown in  FIG.  4 ( e ) . The modulation signals x(AM[1(FM[1,2])]) and x(AM[1(AM[1,2])]) are selected as the feature modulation signals to be used in the succeeding calculation. Thus, all the feature modulation signals of interest can be obtained according to the feature mask to implement the succeeding calculation. 
     In the present invention, the main application of the feature mask is to determine the number of decomposition and demodulation of signals and the positions of the selected feature modulation signals. The example described above uses a word string M=x(FM[2],AM[1(FM[1,2],AM[1,2]),2]) to express the feature mask. However, the feature mask can also be expressed by a sequence matrix, wherein the odd-numbered matrix dimensions are the sequences of the post-decomposition sub-signals, and the even-numbered matrix dimensions are the sequences of the post-demodulation modulation signals, and wherein the number denotes the feature modulation signal selected by the matrix dimension. In the even-numbered matrix dimension, FM is arranged in the front, and AM is arranged in the rear. Thus, x(AM[1(FM[1,2])]) and x(AM[1(AM[1,2])]) can be denoted by ([2], [([1, 2] [1, 2]), 2]). 
     In the present invention, the feature mask can also be expressed by a multidimensional matrix, such as a multidimensional Boolean matrix (abbreviated as T/F). The details thereof are stated below: 
     The first decomposition outputs three sub-signals of 1-dimensional sequences in form of [( )( )( )]. 
     The demodulation converts the sub-signals into 2-dimensional sequences having two modulation parts in form of [([ ],[ ]) ([ ],[ ]) ([ ],[ ])] with FM arranged before and AM arranged behind, wherein 
     x(FM[2]) is expressed by [([F],[F]) ([T],[F]) ([F],[F])]; 
     x(AM[1,2]) is expressed by [([F],[T]) ([F],[T]) ([F],[F])]; 
     x(FM[2], AM[1,2]) is expressed by [([F],[T]) ([T],[T]) ([F],[F])]. 
     The modulation component is decomposed into three sub-signals of 3-dimensional sequences in form of [([( ) ( ) ( )],[( ) ( ) ( )], ([( ) ( ) ( )],[( ) ( ) ( )])([( ) ( ) ( )], [( ) ( ) ( )])]. 
     Then, the iterative demodulation converts the sub-signals into 4-dimensional sequences having two modulation components in form of [([([ ],[ ]) ([ ],[ ]) ([ ],[ ])],[([ ],[ ]) ([ ],[ ]) ([ ],[ ])]) ([([ ],[ ]) ([ ],[ ]) ([ ],[ ])],[([ ],[ ]) ([ ],[ ]) ([ ],[ ])]) ([([ ],[ ]) ([ ],[ ]) ([ ],[ ])],[([ ],[ ]) ([ ],[ ]) ([ ],[ ])])] with FM arranged before and AM arranged behind. 
     A portion of the selected feature mask can be expressed as follows: 
     x(AM[1(FM[1,2])]) is denoted by [([F],[([T],[F]) ([T],[F]) ([F],[F])]) ([F],[F]) ([F],[F])]; 
     x(AM[1(AM[1,2])]) is denoted by [([F],[([F],[T]) ([F],[T]) ([F],[F])]) ([F],[F]) ([F],[F])]. 
     In summary, x(FM[2], AM[1(FM[1,2], AM[1,2]), 2]) in the abovementioned example can be expressed by a multidimensional matrix denoted by [([F],[([T],[T]) ([T],[T]) ([F],[F])]) ([T],[T]) ([F],[F])]. 
     In addition to involving the estimation of waveforms and frequency spectral analysis of the conventional technology, the present invention further provides calculations of intrinsic features, which are particularly useful for the multilayer neural network where many intrinsic features are not obvious in the primitive wave and the primitive frequency spectrum. The present invention not only presents variations of brain wave to enhance accuracy of the identification but also performs decomposition and analyzation with respect to different frequency modulations and amplitude modulations to form a multilayer and multidimensional feature space, which is sufficient to reveal nonstationary features of brain activity. Further, the feature mask used by the present invention can significantly reduce the complexity the conventional technology suffers in decomposing signals and effectively reduce the load in computation. Therefore, the present invention can greatly promote the practicability of brain wave-based diagnosis in neurological diseases. 
     The embodiments have been described above to demonstrate the technical contents and characteristics of the present invention and enable the persons skilled in the art to understand, make, and use the present invention. However, these embodiments are only to exemplify the present invention but not to limit the scope of the present invention. Any equivalent modification or variation according to the spirit of the present invention is to be included within the scope of the present invention.