CN105361855A - Method for effectively acquiring event-related magnetic field information in magnetoencephalogram signals - Google Patents
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Abstract
The invention discloses a method for effectively acquiring event-related magnetic field information in magnetoencephalogram signals. The method includes the steps of firstly, collecting and preprocessing magnetoencephalogram data; secondly, building a time-frequency atom database; thirdly, using a single-channel matching pursuit algorithm to build a linear combination; fourthly, forming a multi-channel matching pursuit algorithm; fifthly, determining iteration termination by the total residual energy of all channels so as to obtain atoms after signal decomposition; sixthly, removing the atoms representing artifact noise, and rebuilding the signals. The method has the advantages that the magnetoencephalogram signals are post-processed by the method, stimulation times can be reduced greatly, and test results are prevented from being affected by the fatigue, which is caused by long-time and repeated stimulation, of a scanned person; the training amount of a to-be-tested person is reduced, the requirements of the to-be-tested person are lowered, and the selection range of to-be-tested persons of clinical researches is expanded; data collecting time is reduced, research cost is lowered, and the clinical actual researches and popularization and application of event-related magnetic fields are benefited.
Description
Technical Field
The invention relates to the technical field of image and signal processing, in particular to a method for effectively acquiring event-related magnetic field information in a magnetoencephalogram signal.
Background
An event-related magnetic field (ERF) refers to a weak magnetic field change in the peripheral nervous system and the central nervous system during information transmission caused by the application or removal of stimulation during the action of external or endogenous stimulation on a part of the human sensory system or brain. In the research of brain science, the application of event-related magnetic fields is very wide. Currently, event-related magnetic fields have been applied in fields such as neuroscience research, clinical examination and surgery, anesthesia monitoring, and nerve injury assessment.
The superposition averaging method widely used in practical applications considers that multiple times of stimulation are required to be performed on a subject, and the influence of noise signals on weak magnetic field signals is counteracted through signal averaging. Generally, the average superposition method requires about 50-100 times of stimulation and response signal evaluation to obtain a more ideal ERF signal, which has the direct consequence that the requirement on the scanning endurance of the subject is high, and the long-time repeated stimulation can cause fatigue of the nervous system to influence the test result. Such a data acquisition and post-processing mode is time-consuming, labor-consuming, and has an influence on reliability, and is not favorable for clinical practical research and popularization and application.
Disclosure of Invention
The invention mainly solves the technical problem of providing a method for effectively acquiring event-related magnetic field information in a magnetoencephalogram signal, which can solve the problems existing in the existing data acquisition and post-processing mode.
In order to solve the technical problems, the invention adopts a technical scheme that: a method for effectively acquiring event-related magnetic field information in a magnetoencephalogram signal is provided, which comprises the following steps:
(1) acquiring magnetoencephalogram data and preprocessing the magnetoencephalogram data;
(2) establishing a time-frequency atom library: forming Gabor atoms by a modulated Gaussian window function, and generating a time-frequency atom library by performing stretching, translation and modulation transformation on a single Gabor atom; wherein the Gaussian window function is:
，
in the formula, s, u, v and N are respectively a scale factor, a displacement factor, a frequency factor and a signal length;time-frequency parameters;
(3) converting the single-channel signal f of the magnetoencephalogram into the Hilbert space H from an over-complete library through a single-channel matching tracking algorithmSelecting time-frequency atoms through medium iteration to form a linear combination;
(4) expanding the single-channel algorithm in the step (3) to form a multi-channel matching tracking algorithm, namely, n single-channel magnetoencephalogram signalsLinear decomposition intoA combination of (1);
(5) total energy and new signal for all channels after iteration termination:
after the M step of iteration:
，
when in useWhen so, the iteration terminates;
at this time, the single-channel signal of the magnetoencephalogram is finally decomposed into:
the energy of the channel is:；
(6) atoms representing artifact noise are removed.
In a preferred embodiment of the present invention, in the step (2), the single Gabor atom transformation method is: adjustment constantSo that(ii) a Time-frequency parameterTransform to discretize as follows:，，，，，，phase of。
In a preferred embodiment of the present invention, in the step (3), the single-channel matching pursuit algorithm is:
order toIs composed ofAtoms resolved by the next iteration, the remainder of the 0 th iteration beingOf 1 atThe remainder of the sub-iteration isThen the single channel matching pursuit algorithm is as followsThe following steps:
，
wherein,is composed ofAndthe inner product between.
In a preferred embodiment of the present invention, in the step (4), the multi-channel matching pursuit algorithm is: let the residual of the 0 th iteration of channel l beOf 1 atThe remainder of the sub-iteration isThen the multi-channel matching pursuit algorithm is:
。
in a preferred embodiment of the present invention, in the step (6), the artifact noise atom includes:
firstly, before stimulation, the scale factor of the displacement factor is less than 1.5 times of the oscillation modulation period, and the duration of the displacement factor is less than 100 ms;
② the scale factor is larger than 5 times of oscillation modulation period, and the atom lasts for the whole time period.
The invention has the beneficial effects that: the invention discloses a method for effectively acquiring event-related magnetic field information in a magnetoencephalogram signal, which has the following advantages:
(1) by carrying out post-processing on the magnetoencephalogram signals, the invention can greatly reduce the stimulation times and avoid the influence on the test result caused by the fatigue of a tested person due to long-time repeated stimulation;
(2) the training amount of the subject is reduced, the requirement on the subject is reduced, and the selection range of clinical research on the subject is expanded;
(3) the data acquisition time is shortened, the research cost is reduced, and the clinical practical research and the popularization and the application of the event-related magnetic field information are facilitated.
Drawings
FIG. 1 is a flow chart of a method of the present invention for efficiently obtaining event-related magnetic field information in magnetoencephalogram signals;
FIG. 2 is a graph comparing the results of the process of the present invention and the conventional average superposition method.
Detailed Description
The following detailed description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings, will make the advantages and features of the invention easier to understand by those skilled in the art, and thus will clearly and clearly define the scope of the invention.
Referring to fig. 1 and 2, an embodiment of the present invention includes:
the invention discloses a method for effectively acquiring event-related magnetic field information in a magnetoencephalogram signal, which comprises the steps of establishing a time-frequency atom library, carrying out multichannel matching tracking algorithm calculation on data after magnetoencephalogram data scanning and standard processing, removing artifact atoms, reserving meaningful atoms, carrying out signal recombination, and obtaining a final signal. As shown in fig. 1, the specific steps are as follows:
(1) acquiring magnetoencephalogram data and preprocessing the magnetoencephalogram data;
(2) establishing a time-frequency atom library: forming Gabor atoms by a modulated Gaussian window function, and generating a time-frequency atom library by performing stretching, translation and modulation transformation on a single Gabor atom; wherein the Gaussian window function is:
，
in the formula, s, u, v and N are respectively a scale factor, a displacement factor, a frequency factor and a signal length. By adjusting constantsSo that Time-frequency parameters; time-frequency parameterTransform to discretize as follows:，，，，，，phase of. According to the discrete mode, the time-frequency atom library is generated，As time-frequency parametersA set of (a);
(3) converting the single-channel signal f of the magnetoencephalogram into the Hilbert space H from an over-complete library through a single-channel matching tracking algorithmSelecting time-frequency atoms through medium iteration to form a linear combination;
order toIs composed ofAtoms resolved by the next iteration, the remainder of the 0 th iteration beingOf 1 atThe remainder of the sub-iteration isThen, the single-channel matching pursuit algorithm is expressed as follows:
，
wherein,is composed ofAndthe inner product between;
(4) expanding the single-channel algorithm in the step (3), namely a multi-channel matching tracking algorithm, and converting n single-channel magnetoencephalogram signalsLinear decomposition intoA combination of (1);
let the residual of the 0 th iteration of channel l beOf 1 atThe remainder of the sub-iteration isThen the multi-channel matching pursuit algorithm is:
；
(5) total energy and new signal for all channels after iteration termination:
after the M step of iteration:
，
when in useWhen so, the iteration terminates;
at this time, the single-channel signal of the magnetoencephalogram is finally decomposed into:
the energy of the channel is:；
(6) removing atoms representing artifact noise, the artifact noise atoms comprising:
firstly, before stimulation, the scale factor of the displacement factor is less than 1.5 times of the oscillation modulation period, and the duration of the displacement factor is less than 100 ms;
② the scale factor is larger than 5 times of oscillation modulation period, and the atom lasts for the whole time period.
The method of the present invention and the conventional average superposition method are used for testing the testee and processing the result, as shown in figure 2,
(a) performing 100 repeated stimulations of the same type on a subject, and superposing and averaging acquired magnetoencephalogram signals to obtain a brain energy topological graph;
(b) performing repeated stimulation of the same type on a subject for 4 times, and superposing and averaging acquired magnetoencephalogram signals to obtain a brain energy topological graph;
(c) and 4 times of repeated stimulation of the same type is carried out on the testee, and a brain energy topological graph is obtained after the treatment of a multichannel matching tracking algorithm.
From the graph, it can be found that the brain energy topological graph presented after the superposition and average of the magnetoencephalogram signals under 4 times of stimulation has obvious abnormality (graph b); after the treatment by the method of the invention, the energy topological result (graph c) is basically consistent with the brain energy topological graph obtained by typical 100 times of stimulation and superposition averaging. Through the comparison, the method can effectively extract meaningful event-related magnetic field information closely related to stimulation under the condition of limited stimulation.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (5)
1. A method for efficiently acquiring event-related magnetic field information in a magnetoencephalogram signal, comprising the steps of:
(1) acquiring magnetoencephalogram data and preprocessing the magnetoencephalogram data;
(2) establishing a time-frequency atom library: forming Gabor atoms by a modulated Gaussian window function, and generating a time-frequency atom library by performing stretching, translation and modulation transformation on a single Gabor atom; wherein the Gaussian window function is:
，
in the formula, s, u, v and N are respectively a scale factor, a displacement factor, a frequency factor and a signal length;time-frequency parameters;
(3) converting the single-channel signal f of the magnetoencephalogram into the Hilbert space H from an over-complete library through a single-channel matching tracking algorithmSelecting time-frequency atoms through medium iteration to form a linear combination;
(4) expanding the single-channel algorithm in the step (3) to form a multi-channel matching tracking algorithm, namely, n single-channel magnetoencephalogram signalsLinear decomposition intoA combination of (1);
(5) total energy and new signal for all channels after iteration termination:
after the M step of iteration:
，
when in useWhen so, the iteration terminates;
at this time, the single-channel signal of the magnetoencephalogram is finally decomposed into:
the energy of the channel is:；
(6) atoms representing artifact noise are removed.
2. The method for effectively acquiring event-related magnetic field information in a magnetoencephalogram signal according to claim 1, wherein in the step (2), the single Gabor atom transformation method is as follows: adjustment constantSo that(ii) a Time-frequency parameterTransform to discretize as follows:，，，，，，phase of。
3. The method for effectively acquiring event-related magnetic field information in a magnetoencephalogram signal according to claim 1, wherein in the step (3), the single-channel matching pursuit algorithm is:
order toIs composed ofAtoms resolved by the next iteration, the remainder of the 0 th iteration beingOf 1 atThe remainder of the sub-iteration isThen, the single-channel matching pursuit algorithm is expressed as follows:
，
wherein,is composed ofAndthe inner product between.
4. The method for effectively acquiring event-related magnetic field information in a magnetoencephalogram signal according to claim 1, wherein in the step (4), the multi-channel matching pursuit algorithm is: let the residual of the 0 th iteration of channel l beOf 1 atThe remainder of the sub-iteration isThen the multi-channel matching pursuit algorithm is:
。
5. the method for effectively acquiring event-related magnetic field information in magnetoencephalogram signals according to claim 1, wherein in the step (6), the artifact noise atoms comprise:
firstly, before stimulation, the scale factor of the displacement factor is less than 1.5 times of the oscillation modulation period, and the duration of the displacement factor is less than 100 ms;
② the scale factor is larger than 5 times of oscillation modulation period, and the atom lasts for the whole time period.
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Cited By (3)
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| CN106798557A (en) * | 2017-02-27 | 2017-06-06 | 上海理工大学 | Brain magnetic information determination method based on atomic magnetic force sensing |
| CN110464310A (en) * | 2019-08-29 | 2019-11-19 | 山东百多安医疗器械有限公司 | A kind of pole weak magnetic measuring method and therapeutic effect of acupuncture measurement device judging therapeutic effect of acupuncture |
| CN114676266A (en) * | 2022-03-29 | 2022-06-28 | 建信金融科技有限责任公司 | Conflict identification method, device, equipment and medium based on multilayer relation graph |
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Cited By (6)
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