Coherent demodulation-based acoustoelectric signal decoding method

Abstract

The invention discloses an acoustoelectric signal decoding method based on coherent demodulation. The method comprises the following steps: (1) focusing ultrasonic scanning and ultrasonic excitation signal recording; (2) ultrasonic excitation coded acoustoelectric signal acquisition: focused ultrasound acts on a scanning area, and a target bioelectric current source signal is coded through an ultrasonic excitation signal; at each scanning point, measuring the electric signal under the ultrasonic coding by using a recording electrode to obtain an acoustoelectric signal; (3) coherent demodulation and decoding of the acoustoelectric signal: taking the ultrasonic excitation signal as a coherent carrier wave, realizing coherent demodulation by multiplying a modulated carrier wave and a coherent carrier wave with the same frequency and phase as the modulated carrier wave, mapping a coherent demodulation parameter variable to an acoustoelectric signal decoding process, and multiplying the acoustoelectric signal with the ultrasonic excitation signal to obtain a demodulation signal; and decoding the acoustoelectric signal to obtain an acoustoelectric signal decoding result of the target current source signal.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic focused acoustic and electrical imaging, and in particular relates to an acoustic and electrical signal decoding method for bioelectrical current source detection. Background Art

[0002] The decoding efficiency of acoustic and electrical signals directly affects the spatiotemporal resolution of acoustic and electrical imaging. Existing studies usually use the envelope method based on pulse repetition frequency to decode acoustic and electrical signals. However, existing methods have disadvantages such as relatively low decoding accuracy and susceptibility to noise interference. When the target bioelectrical current source frequency is close to the pulse repetition frequency of the ultrasonic excitation signal, the decoding accuracy will be reduced due to spectral aliasing, and the limitations of the envelope method will be more obvious. To address this problem, applying coherent demodulation to acoustic and electrical signal decoding is expected to improve decoding accuracy and enhance anti-interference capabilities.

[0003] As a type of demodulation method, coherent demodulation has a wide range of applications in the field of communications. Its core is to use known carrier characteristics to remove the carrier component in the modulated signal, thereby completing highly reliable signal recovery. This method is suitable for the demodulation of all linear modulated signals. Its advantage is that it uses known carrier information, has better decoding accuracy and stronger anti-interference ability. It can be seen from the principles of acoustic and electrical imaging and coherent demodulation that acoustic and electrical signal encoding and decoding have similar physical processes as signal modulation and demodulation. It is expected that coherent demodulation can be applied to acoustic and electrical signal decoding to improve its decoding efficiency. Therefore, the present invention proposes an acoustic and electrical signal decoding method based on coherent demodulation, which provides method support for improving acoustic and electrical imaging performance. Summary of the invention

[0004] The present invention provides an acoustic signal decoding method based on coherent demodulation that can improve the acoustic imaging detection capability. According to the response relationship between the modulation signal and the carrier in the coherent demodulation, it is mapped to the acoustic signal and the ultrasonic excitation signal in the acoustic imaging process, and the role of the known focused ultrasonic characteristics in the acoustic signal encoding and decoding is used to achieve acoustic signal decoding. Compared with the existing decoding method, this method makes full use of the known focused ultrasonic characteristics and has the advantages of high precision and high anti-interference ability. The technical solution is as follows:

[0005] A method for decoding acoustic and electrical signals based on coherent demodulation comprises the following steps:

[0006] (1) Focused ultrasound scanning and ultrasound excitation signal recording

[0007] The pulse repetition frequency and pulse width are set to generate a repetitive pulse signal; the repetitive pulse signal is used as an ultrasonic excitation signal and input into an ultrasonic transducer to generate focused ultrasound, so that the ultrasonic transducer scans the target area point by point with a certain step length, collects electrical signals for a period of time at each scanning point, and records the ultrasonic excitation signal at the same time;

[0008] (2) Acquisition of acoustic and electrical signals by ultrasonic excitation coding

[0009] Focused ultrasound acts on the scanning area, and the target bioelectric current source signal is encoded through the ultrasonic excitation signal; at each scanning point, the electrical signal encoded by the ultrasound is measured using a recording electrode to obtain an acoustic-electrical signal;

[0010] (3) Coherent demodulation and decoding of acoustic and electrical signals: The ultrasonic excitation signal is used as a coherent carrier. Coherent demodulation is achieved by multiplying the modulated carrier with a coherent carrier with the same frequency and phase as the modulated carrier. The coherent demodulation parameter variables are mapped to the acoustic and electrical signal decoding process. The acoustic and electrical signals are multiplied with the ultrasonic excitation signal to obtain a demodulated signal. The demodulated signal is passed through a low-pass filter to decode the acoustic and electrical signals and obtain the acoustic and electrical signal decoding result of the target current source signal.

[0011] Furthermore, for the electrical signal s O (t) Preprocessing: with pulse repetition frequency f PR Bandpass filtering is performed at the center to obtain the acoustic and electrical signal s AE (t).

[0012] Furthermore, in step (3), the ultrasonic excitation signal is used as a coherent carrier, and the coherent demodulation is realized by multiplying the modulated carrier with the coherent carrier of the same frequency and phase as the modulated carrier, and the coherent demodulation parameter variable is mapped to the acoustic-electric signal decoding process, and the acoustic-electric signal is multiplied with the ultrasonic excitation signal to obtain the demodulated signal. The specific method is: take the acoustic-electric signal s AE (t) is the modulated carrier, which contains the information of the modulated signal; the ultrasonic excitation signal h(t) and the acoustic-electric signal s AE (t) with the same frequency and phase, the ultrasonic excitation signal h(t) is used as a coherent carrier; the acoustic and electrical signal s AE (t) is multiplied by the ultrasonic excitation signal h(t) to obtain the demodulated signal s p (t).

[0013] Furthermore, in step (3), the demodulated signal is passed through a low-pass filter to decode the acoustic and electrical signals, and the acoustic and electrical signal decoding result of the target current source signal is obtained as follows: the spectrum S of the demodulated signal p (ω) is the superposition of the spectrum J(ω) of the target current source signal and several high-frequency components; let the demodulated signal s p (t) through the cut-off frequency f c Satisfy f AE << fc <<f AE +f PR The low-pass filter, f AE The acoustic signal s AE (t) its frequency; take out the low frequency component s AE-dec(t), with the obtained low-frequency component s AE-dec (t) represents the target current source signal J(t), and the low-frequency component s AE-dec(t) As the decoding result of acoustic and electrical signals.

[0014] The present invention designs an acoustic and electrical signal decoding method based on coherent demodulation. By using the coherent demodulation method, the known ultrasonic signal characteristics are fully utilized to achieve high-precision acoustic and electrical signal decoding. Compared with the existing acoustic and electrical signal decoding method, the acoustic and electrical signal decoding method based on coherent demodulation of the present invention has the following advantages:

[0015] (1) It has higher decoding accuracy and better anti-noise ability, which helps to improve the resolution of acoustic and electrical imaging.

[0016] (2) It can solve the problem of spectrum aliasing when the target signal frequency is close to the ultrasonic pulse repetition frequency, thereby enhancing the versatility of the acoustic and electrical imaging method.

[0017] It is expected to provide improved means for electroacoustic imaging and contribute to the further application of electroacoustic imaging technology in bioelectric detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention provides a flowchart of the method for decoding acoustic and electrical signals based on coherent demodulation.

[0019] Figure 2 Decoding results of acoustic and electrical signals using coherent demodulation and envelope methods DETAILED DESCRIPTION

[0020] The present invention is described below in conjunction with the accompanying drawings and embodiments. Figure 1 As shown, the whole process can be divided into the following three steps: ① Focused ultrasound scanning and ultrasonic excitation signal recording: Use a repetitive pulse signal to stimulate the ultrasonic transducer to emit focused ultrasound, use focused ultrasound to scan the target area of ​​the bioelectric source, and record the ultrasonic excitation signal (i.e., repetitive pulse signal) at the same time; ② Acquisition of acoustic and electrical signals encoded by ultrasonic excitation: Collect the electrical signal encoded by ultrasonic excitation while scanning the target area, and obtain the acoustic and electrical signal after preprocessing; ③ Coherent demodulation and decoding of acoustic and electrical signals: Use the ultrasonic excitation signal as a carrier to decode the acoustic and electrical signal to obtain a decoded acoustic and electrical signal. The specific steps are as follows:

[0021] (1) Focused ultrasound scanning and ultrasound excitation signal recording

[0022] Set the pulse repetition frequency f PR, pulse width τ, use a function generator to generate a repetitive pulse signal h(t). The repetitive pulse signal h(t) is used as an ultrasonic excitation signal and input into an ultrasonic transducer to generate focused ultrasound. The characteristics of the excitation signal, such as frequency, amplitude, and waveform, directly affect the characteristics of the ultrasonic signal. The ultrasonic excitation signal h(t) is used to approximate focused ultrasound. The ultrasonic transducer is made to scan the target area point by point with a certain step length, collect electrical signals for a period of time at each scanning point, and record the ultrasonic excitation signal at the same time.

[0023] (2) Acquisition of acoustic and electrical signals by ultrasonic excitation coding

[0024] Focused ultrasound acts on the scanning area and encodes the target bioelectric current source signal through the ultrasonic excitation signal. At each scanning point, the electrical signal s encoded by the ultrasound is recorded using a recording electrode. O (t) is measured. Then s O (t) Preprocessing: with pulse repetition frequency f PR Bandpass filtering is performed at the center. The acoustic and electrical signal s is obtained AE (t), whose frequency is f AE .

[0025] According to the acoustoelectric effect formula, the acoustoelectric signal s AE (t) can be expressed as: AE (t) = k·j(t)·(t)#(1)

[0026] Among them, J(t) is the target bioelectric current source signal, k is related to parameters such as tissue resistivity and acoustic-electric effect coefficient and does not change with time t.

[0027] (3) Coherent demodulation and decoding of acoustic and electrical signals

[0028] Coherent demodulation is achieved by multiplying the modulated carrier with a coherent carrier with the same frequency and phase as the modulated carrier. According to formula (1), the coherent demodulation parameter variable is mapped to the acoustic signal decoding process, that is, the acoustic signal s AE (t) is the modulated carrier and contains the information of the modulation signal J(t). The ultrasonic excitation signal h(t) and the acoustic-electric signal s AE (t) with the same frequency and phase, the ultrasonic excitation signal h(t) is used as a coherent carrier. The coherent demodulation method is used to decode the acoustic and electrical signals:

[0029] J(ω) is the frequency domain expression of the current source signal J(t). The ultrasonic excitation signal h(t) is a periodic pulse with a very high oscillation frequency, which can be approximately regarded as a pulse repetition frequency f. PR The frequency domain expression of the periodic square wave H(ω) is:

[0030]

[0031] Where τ is the pulse width of the ultrasonic excitation signal, f PR is the frequency of ultrasonic excitation signal, δ(·) is the Dirac function, and n is the index variable of summation operation.

[0032] Combined with formula (1), we get the acoustic and electrical signal s AE The frequency domain expression S of (t) AE (ω) is:

[0033]

[0034] The acoustic signal s AE (t) is multiplied by the ultrasonic excitation signal h(t) to obtain the demodulated signal s p (t), then the demodulated signal s p The frequency domain expression S of (t) p (ω) is:

[0035]

[0036] Among them, m and n are the indicator variables of the summation operation, J(ω) is the frequency domain expression of the current source signal, H(ω) is the frequency domain expression of the ultrasonic excitation signal, τ is the pulse width of the ultrasonic excitation signal, and f PR is the ultrasonic excitation signal frequency.

[0037] Formula (4) shows that the spectrum S of the demodulated signal p (ω) is the superposition of the spectrum J(ω) of the target current source signal and several high-frequency components. Let the demodulated signal s p (t) through the cut-off frequency f c Satisfy f AE <<f c <<f AE +f PR The low-pass filter removes the high-frequency component and obtains the low-frequency component S AE-dec (t) Approximately satisfies:

[0038] S AE-dec (t)∝J(t)#(5)

[0039] That is, the low-frequency component s AE-dec (t) has a similar waveform and phase to the target current source signal J(t), and the low-frequency component s AE-dec (t) As the decoding result of acoustic and electrical signals.

[0040] The decoding results of the acoustic and electrical signals using the coherent demodulation method (black thick solid line) and the envelope method (black thin solid line) are shown in Figure 2. Figure 2 The result after coherent demodulation decoding is consistent with the frequency and phase of the source signal, and has better decoding accuracy than envelope decoding.

[0041] The acoustic and electrical signal decoding method based on coherent demodulation designed by the present invention can be used in the fields of clinical medical diagnosis, neuroscience and engineering research, and further research can promote the application of acoustic and electrical imaging technology as a new type of bioelectric detection technology, which is expected to obtain considerable social and economic benefits.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for decoding acoustic and electrical signals based on coherent demodulation, comprising the following steps: (1) Focused ultrasound scanning and ultrasound excitation signal recording The pulse repetition frequency and pulse width are set to generate a repetitive pulse signal; the repetitive pulse signal is used as an ultrasonic excitation signal and input into an ultrasonic transducer to generate focused ultrasound, so that the ultrasonic transducer scans the target area point by point with a certain step length, collects electrical signals for a period of time at each scanning point, and records the ultrasonic excitation signal at the same time; (2) Acquisition of acoustic and electrical signals by ultrasonic excitation coding Focused ultrasound acts on the scanning area, and the target bioelectric current source signal is encoded through the ultrasonic excitation signal; at each scanning point, the electrical signal encoded by the ultrasound is measured using a recording electrode to obtain an acoustic-electrical signal; (3) Coherent demodulation and decoding of acoustic and electrical signals: The ultrasonic excitation signal is used as a coherent carrier. Coherent demodulation is achieved by multiplying the modulated carrier with a coherent carrier with the same frequency and phase as the modulated carrier. The coherent demodulation parameter variables are mapped to the acoustic and electrical signal decoding process. The acoustic and electrical signals are multiplied with the ultrasonic excitation signal to obtain a demodulated signal. The demodulated signal is passed through a low-pass filter to decode the acoustic and electrical signals and obtain the acoustic and electrical signal decoding result of the target current source signal.

2. The method for decoding acoustic and electrical signals according to claim 1, characterized in that: For electrical signals O (t) Preprocessing: with pulse repetition frequency f PR Perform bandpass filtering at the center to obtain the acoustic and electrical signal s AE (t).

3. The method for decoding acoustic and electrical signals according to claim 1, characterized in that: In step (3), the ultrasonic excitation signal is used as a coherent carrier, and the coherent demodulation is realized by multiplying the modulated carrier with the coherent carrier of the same frequency and phase as the modulated carrier, and the coherent demodulation parameter variable is mapped to the acoustic-electric signal decoding process, and the acoustic-electric signal is multiplied with the ultrasonic excitation signal to obtain the demodulated signal. The specific method is: take the acoustic-electric signal s AE (t) is the modulated carrier, which contains the information of the modulated signal; the ultrasonic excitation signal h(t) and the acoustic-electric signal s AE (t) with the same frequency and phase, the ultrasonic excitation signal h(t) is used as a coherent carrier; the acoustic and electrical signal s AE (t) is multiplied by the ultrasonic excitation signal h(t) to obtain the demodulated signal s p (t).

4. The method for decoding acoustic and electrical signals according to claim 3, characterized in that: In step (3), the demodulated signal is passed through a low-pass filter to decode the acoustic and electrical signals, and the method for obtaining the acoustic and electrical signal decoding result of the target current source signal is: the spectrum S of the demodulated signal p (ω) is the superposition of the spectrum J(ω) of the target current source signal and several high-frequency components; let the demodulated signal s p (t) through the cut-off frequency f c Satisfy f AE <<f c <<f AE +f PR The low-pass filter, f AE The acoustic signal s AE (t) its frequency; take out the low frequency component s AE-dec (t), with the obtained low-frequency component s AE-dec (t) represents the target current source signal J(t), and the low-frequency component s AE-dec (t) is the decoding result of acoustic and electrical signals.

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