Rapid magnetoacoustic-electric tomography method without mechanical rotation and scanning measurement

Abstract

The invention provides a rapid magneto-acoustic-electric tomography method without mechanical rotation and scanning. In order to solve the problems of low speed, poor stability, low imaging precision and the like of rotary scanning measurement in the existing magnetoacoustic-electric tomography (MAET), a magnetoacoustic-electric measurement theory suitable for annular sound source excitation and electrode detection is provided on the basis of sound radiation and a magnetoacoustic-electric coupling mechanism. An MAET imaging method based on annular multi-sound-source cyclic excitation and multi-electrode synchronous measurement is developed. The minimum configuration requirement of the MAET system is obtained based on the influence of the annular sound source, the number of electrodes and the positions of the electrodes on the imaging quality, and an optimal configuration scheme of rapid MAET imaging is provided. According to the invention, mechanical scanning without a transducer or phased scanning measurement of an array sound source is utilized, mechanical rotation of an object is not needed, sound source circulation excitation and multi-electrode synchronous measurement are realized through electronic control, and the imaging speed and stability are improved. The device is easy to be fused with a commercial ultrasonic CT system, and cross-scale multi-modal imaging combining ultrasonic and electrical impedance is realized.

Description

Technical Field

[0001] The present invention relates to the fields of medical ultrasound and electrical impedance tomography, and particularly relates to magnetoacousto-electric tomography technology and method based on tissue impedance difference measurement. Technical Background

[0002] Tumor is a disease that seriously threatens human health. Conventional methods such as X-ray, ultrasound, and MRI can detect and characterize the changes in tissue morphological structure and physical parameters, but there are still problems such as ionizing radiation, low spatial resolution, and insufficient real-time performance. Research shows that the relative change in tissue conductivity is significantly greater than that of tissue morphological structure, several times that of acoustic impedance change, and is considered a highly sensitive parameter for early diagnosis of tissue lesions. For the detection of bio-tissue impedance, technologies such as electrical impedance tomography, magnetic induction tomography, and magnetic resonance electrical impedance tomography have been developed, but their practical applications are still limited by large current injection, tissue shielding effect, ill-posedness of image reconstruction, slow imaging speed, and poor spatial resolution. In recent years, based on the coupling characteristics of magnetoacousto-electric and its imaging complementarity, a magnetoacousto-electric tomography technology (MAET) based on the Hall effect has been proposed. It uses the interaction between ultrasonic vibration and magnetic field at the boundary of conductive tissue during sound propagation to generate induced current. The magnetoacousto-electric (MAE) signal detected by the electrode outside the tissue contains the position and conductivity change information of the tissue boundary, and can reconstruct the conductivity distribution of the tissue during sound propagation. MAET does not require current injection, and sound propagation is not affected by tissue insulation. It combines the advantages of high contrast of EIT and high resolution of ultrasound imaging technology, and shows important research value and application potential in the field of biomedical imaging.

[0003] Traditional B-mode MAE imaging uses a planar or focused transducer to linearly scan an object and complete it by receiving MAE signals through vertically placed electrode plates. To improve the axial resolution, imaging depth, and signal-to-noise ratio of imaging, short pulses or coded pulses are used for excitation to detect and image the conductivity boundaries of layered models. Previous studies generally used strongly directional or focused acoustic beams output by large-aperture transducers for scanning measurements, which had good imaging effects on layered tissues perpendicular to the acoustic beam. However, the MAE signal significantly attenuates as the angle between the incident acoustic beam and the tissue boundary increases. Therefore, precise imaging of arbitrarily shaped objects cannot be achieved. Further introducing rotational scanning measurement to compensate for the attenuation of the MAE signal caused by the tissue boundary angle, MAET was realized. Research shows that using plane waves instead of linear scanning can improve the imaging speed. However, since it is difficult for the beam to cover the entire model, a small rotation angle is required to ensure imaging quality, and the plane wave synthesis based on linear array transducer phase control increases the complexity and cost of the system. In the previous research of our laboratory, considering the radiation directivity of the actual transducer and the tilt angle of the tissue conductivity boundary, the general principle of MAET applicable to arbitrarily shaped objects was deduced. Theory and experiments have proved the determining factors of MAE signal attenuation and B-mode image distortion, and it is proved that only small rotation angles and linear scanning steps can improve the MAET image quality, but this will seriously reduce the measurement speed and imaging stability.

[0004] In recent years, significant progress has been made in MAET research, but there are still many areas worthy of improvement in measurement methods and system control. Due to the directivity limitation of conventional planar piston transducers, the beam cannot completely cover the object to be measured, and long-time linear scanning is required to achieve B-mode imaging. The complex mechanical rotation and linear scanning of the MAET system reduce the measurement speed and stability, resulting in a decrease in imaging accuracy; while the plane waves with controllable directions generated by phasing linear array transducers can omit the linear scanning process, but require the support of a complex and expensive phased system; the electrodes for traditional MAE detection are generally placed parallel to the acoustic beam, mainly receiving the MAE signals generated by the perpendicular components of the induced current along the electrode direction, while losing the information in its parallel direction, reducing the information integrity of the MAE signal. Therefore, the imaging contrast of tilted tissue boundaries is poor; traditional MAET systems require two sets of mechanical mechanisms for linear scanning of the transducer and rotation of the object, making it difficult to achieve high-quality imaging efficiently and quickly. Therefore, there is an urgent need to develop a measurement method that does not require mechanical rotation and scanning to achieve high-quality and fast MAET. Summary of the Invention

[0005] In order to improve the measurement speed and imaging quality of MAET, the present invention proposes a fast MAET imaging method without mechanical rotation and scanning measurement, realizing fast imaging based on circular omnidirectional sound source cyclic excitation and multi-electrode synchronous measurement. First, based on the point sound source radiation and magnetoacoustic-electric coupling mechanism, a MAET system model with circular M sound source excitation and N electrode detection is established, and a general MAE theoretical formula applicable to sound source excitation at any position on the circle and measurement by any electrode is derived, and a MAET imaging algorithm based on inverse Radon transform and the sum of MAE signal amplitudes is developed. The results prove that the amplitude of the MAE signal detected by the electrode is determined by the conductivity gradient and direction of the tissue boundary, and the angle between the sound source and the electrode, and the difference in the positions of the circular sound source and the electrode will cause boundary deformation and uneven intensity distribution in the MAET image. Increasing the number of circular sound sources and electrodes can effectively improve the accuracy, integrity and smoothness of the boundary distribution. Then, a measurement method based on circular orthogonal four-electrode synchronous detection is proposed, and the information integrity of the MAE signal is improved through orthogonal component measurement, thereby improving the quality of the MAET image. Further, the radius fluctuation coefficient and intensity relative error of the MAET image boundary are defined for circular boundary imaging quality analysis and measurement system optimization, and it is proved that the minimum configuration of the MAET system is 30 sound sources and orthogonal 4 electrodes, which has good noise resistance and robustness. Further considering the actual application requirements of uniform distribution of circular sound sources and orthogonal placement of electrodes, an optimization scheme for a fast MAET system based on 32 sound sources and orthogonal 4 electrodes is proposed. Finally, a MAET experimental system is constructed using 32 sound sources and 4 orthogonal electrodes, and MAET imaging is performed on an eccentric cylindrical gel tissue model, and a circular smooth boundary image consistent with the model size is accurately reconstructed.

[0006] The present invention uses the cyclic excitation of a circular omnidirectional sound source and the synchronous measurement of orthogonal electrodes to achieve fast MAET imaging. The single acoustic radiation of the omnidirectional transducer can completely cover the entire measured field, without the need for linear scanning of the transducer or phased scanning of the array sound source. Through electronic control switching, cyclic excitation of the circular sound source and synchronous measurement of the four electrodes can be achieved, and fast measurement can be completed without the mechanical rotation and scanning of traditional MAET, effectively improving the imaging speed and stability, and obtaining high-precision MAET imaging. The present invention simplifies the structure of the MAET system, is easy to integrate with commercial ultrasonic CT technology, realizes multi-modal and cross-scale imaging of human deep tissues, and provides a new fast imaging technology for MAET imaging.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows: a fast magnetoacoustic-electric tomography imaging method without mechanical rotation and scanning measurement, comprising the following steps:

[0008] S1. Establish a MAET measurement system based on a circular omnidirectional sound source array and an electrode array to achieve cyclic excitation of the sound field and synchronous measurement of MAE signals;

[0009] S2. Establish a theoretical model of MAE based on the excitation of sound sources at arbitrary positions on a ring and electrode reception, derive the general theoretical formula of the MAE signal, and obtain the determinants of the amplitude and time of the MAE signal;

[0010] S3. Introduce the cyclic excitation of ring-shaped sound sources and multi-electrode synchronous measurement technology, and propose a high-precision MAET imaging method based on inverse Radon transform and the amplitude sum (sum of squared amplitudes) of MAE signals;

[0011] S4. Establish a cylindrical tissue model, conduct simulations of MAE signals under different numbers of sound sources and electrodes, complete the reconstruction of MAET images, and analyze the influencing factors of imaging quality.

[0012] S5. Based on the analysis of the influence of the number of sound sources and electrodes on the radius fluctuation of the circular boundary of the reconstructed MAET image and the relative error of intensity, propose the minimum configuration requirements of the MAET system, and further obtain the optimization scheme of the fast MAET system.

[0013] Among them, in step S1, specifically as follows:

[0014] M uniformly distributed omnidirectional transducers are set at the boundary of the circular field with radius R0 for circularly emitting sound waves, and N sheet-shaped or needle-shaped electrodes are set for detecting the MAE signals generated by the conductivity boundary of the tissue of the object to be measured. An object to be measured with an arbitrary shape of conductivity distribution is placed in a conductive coupling liquid. The whole field has good acoustic coupling and electrical transmission characteristics. A pair of parallel permanent magnets generate a static magnetic field perpendicular to the measured field. The pulsed sound waves radiated by the transducers propagate as spherical waves, and the sound field covers the entire measured circular field. The vibration of conductive tissue particles caused by sound propagation interacts with the magnetic field to generate induced current, which is received by the electrodes after propagating through the conductive medium, obtaining N MAE signals containing the conductivity gradient and position information of the tissue boundary. Through electronic control of the cyclic excitation of M transducers and the synchronous measurement of N electrodes, the fast measurement of M×N MAE waveforms and the reconstruction of MAET images are realized.

[0015] It is required that the M sound sources used are approximate omnidirectional transducers, and the half-opening angle of their spherical sound radiation should be greater than 60°, and the radiation sound field can completely cover the object to be measured; the surface of the omnidirectional transducer and the coupling liquid should be completely insulated to reduce the interference between the sound field and the electric field; the electrodes need to be placed in the conductive coupling liquid with conductivity to ensure the reliability of current transmission; the boundary and bottom of the circular measured field should be covered with sound-absorbing materials to eliminate the influence of sound reflection and sound scattering; silver or copper sheet-shaped or needle-shaped high-conductivity electrodes should be selected to improve the electric field detection ability, and the electrodes should be placed between two adjacent transducers at the boundary of the circular field to reduce the influence of the circularly distributed electrodes on the radiation sound field.

[0016] Among them, in step S2, specifically as follows:

[0017] The m-th sound source Tm placed circumferentially emits an omnidirectional sound wave, and the sound pressure generated at any position r in the field is where Q = 4πa 2 u0 is the intensity of the spherical sound source, u0 is the vibration velocity on the surface of the sound source, a is the radius of the sound source, k = ω / c is the wave number, ω is the angular frequency, ρ and c are respectively the density and sound velocity of the propagation medium, R Tm = |r - r Tm | is the distance from the sound source position r Tm to r, t = R Tm / c is the propagation time, and the sound pressure generates a particle vibration velocity whose direction is e v , is the gradient operator, and the static magnetic field B and v(r Tm , r) interact to generate an induced current density J(r Tm , r) = σ(r)v(r Tm , r) × B, and its direction is e J , and the n-th electrode En on the circumference detects the current density component generated by the m-th sound source at r as J En (r Tm , r) = J(r Tm , r)cosθ, and its direction is e E , θ is the included angle between e E and e J , θ = π / 2 - χ, χ is the included angle between e E and -e v . Considering the equivalent resistance R En of the electrode En when receiving the induced current at r and the electrode receiving coefficient α, and also considering determined by the included angle γ between e v and the normal direction e n of the conductivity, the MAE voltage generated by the sound source Tm received by the electrode En in the entire field Ω is obtained:

[0018]

[0019] The equivalent resistance R En of the system can be approximately proportional to the propagation distance R En = R s |r En - r|, where R s is the resistance per unit length of the conductive medium, then the MAE voltage signal is obtained as:

[0020]

[0021] where ξ = -2αBa2 u0R s is a constant determined by the system structure and parameters.

[0022] Using the ideal unit impulse signal δ(t) as the excitation sound source, the MAE voltage is corrected as:

[0023]

[0024] where V δ (r En , r Tm , t) is determined by the sound source emission position r Tm and the electrode receiving position r En as well as the conductivity distribution. Considering the convolution of the excitation signal S(t) and the impulse response R(t) of the transducer is the convolution operation symbol, and the general formula for the MAE waveform generated by the m-th sound source received by the n-th electrode in the entire field is obtained as:

[0025]

[0026] The results prove that the radiation sound field can only generate MAE signal pulses at the tissue conductivity boundary, and its position is determined by the propagation time t = |r - r Tm | / c from the sound source to the tissue boundary, and the amplitude is determined by as well as the position information jointly.

[0027] Among them, in step S3, specifically as follows:

[0028] Introduce the circular sound source cyclic excitation and electrode synchronous measurement technology, and propose a MAET imaging method based on the inverse Radon transform and the sum of MAE signal amplitudes (sum of squared amplitudes).

[0029] First, perform the Hilbert transform on the MAE signal waveform W(r En , r Tm , t) received by the m-th sound source excitation and the n-th electrode, and then take the absolute value to obtain the envelope H(r En , r Tm , t) of the MAE signal; Apply the inverse Radon transform based on the diffracted sound source to the envelope of the MAE signal, and back-project the amplitude at all times of H(r En , r Tm , t) into the field on the arc of |r - r Tm | = ct to reconstruct the MAE image g(r En , r Tm , r) = H(r En , r Tm , t)δ(|r - rTm |-ct).

[0030] Then, based on the synchronous measurement of N electrodes, N MAE images g(r En , r Tm , r) under the excitation condition of the sound source Tm are reconstructed. By calculating the sum of the amplitudes and the sum of the squares of the amplitudes of the MAE signals to compensate for the signal attenuation at different electrode positions, the MAE images based on the excitation of the sound source Tm and the synchronous measurement of N electrodes are obtained respectively and

[0031] Finally, the circular M sound source cyclic excitation and N electrode synchronous measurement are introduced. Using the M×N MAE waveforms collected, M MAE images g(r Tm , r) under different sound source excitations are reconstructed. The MAET image is reconstructed through the rotation matrix and image interpolation:

[0032]

[0033] The theoretical results prove that increasing the number M of circular sound sources and the number N of electrodes and increasing their uniform distribution density in the range of 0 - 2π can effectively reduce the influence of the sound source and electrode positions on θ and γ, and improve the accuracy and integrity of the MAET image.

[0034] Among them, in step S4, specifically as follows:

[0035] A cylindrical tissue model is established, the MAE signal simulation is carried out under different numbers of sound sources and electrodes, the MAET image reconstruction is completed, and the influencing factors of the imaging quality are analyzed.

[0036] A 16 - sound - source and 16 - electrode MAET system is established. An eccentric cylindrical tissue model is placed inside the measurement field. Through 16 - sound - source cyclic excitation and 16 - electrode synchronous measurement, 16×16 MAE signal waveforms are obtained, and the MAET image is reconstructed. The result shows the reconstructed circular model boundary. However, due to the small number of cyclic excitations of the transducer, the circular boundary has obvious unevenness and discontinuous distribution, and there are also significant artifacts, which proves that the number of sound sources has a significant impact on MAET.

[0037] Among them, in step S5, specifically as follows:

[0038] Based on the analysis of the influence of the number of sound sources and electrodes on the radius fluctuation and intensity relative error of the MAET circular boundary, the minimum configuration requirements of the MAET system are proposed, and further an optimization scheme for the fast MAET system is obtained.

[0039] A circular tissue model was established to simulate the MAE signals synchronously received by 16 electrodes under different M conditions, and the MAET images were reconstructed. The results showed that when the number of sound sources was small, the circular boundary of the MAET image fluctuated significantly, forming a petal distribution of approximate polygons with sharp angles. At the same time, amplitude and shape fluctuations were shown, and obvious circular arc artifacts were accompanied. As M increased, the number of sides of the polygon increased, but the intensity of the petals weakened, the smoothness of the boundary increased, and its contrast and clarity were also correspondingly improved, and the imaging quality was enhanced. Define the radius fluctuation coefficient of the circular boundary where R -3 (i) is the radius at the i-th measurement angle, is the average radius of Q measurements of the circle. The calculation shows that the fluctuation coefficient ε decreases with the increase of M. When M≥30, the radius fluctuation coefficient is less than 0.02 mm. Therefore, taking ε = 0.02 as the acceptable standard for imaging quality, the minimum number of sound sources for the MAET system configuration is M = 30,

[0040] Under the condition of the minimum number of sound sources M = 30, a 64-electrode MAET system was constructed. An eccentric circular tissue model was set up, and N electrodes evenly distributed along the circumference were selected to form different synchronous measurement groups, and different starting electrodes n s and N = 1, 2, 4, 8, 16, 32 and 64 were used to simulate and image the MAE signals. The results proved that when N = 1 and 2, the shape and position of the model boundary could be basically reconstructed, but there were obvious intensity differences in the circular boundary, and its continuity and intensity consistency were greatly affected by the positions of the measurement electrodes. When N = 4, the MAET images measured by the orthogonal four electrodes were almost the same, and the continuity and consistency of its circular boundary were significantly improved. Define the relative error of the circular boundary intensity between the MAET image and the model where Q is the number of circular sampling points, and g p (i) is the intensity of the i-th sampling point on the circular boundary of the MAET image. MAET imaging was carried out under different N and n s conditions to obtain the relationship between the average and N. The results showed that as N increased from 1 to 4, rapidly decreased from 0.19 to 0.027 and tended to be stable after N≥4, proving that when N<4, the quality of the reconstructed MAET image was poor and was greatly affected by the positions of the electrodes; when N≥4, the MAET image could accurately reflect the boundary distribution of the model, and the imaging quality was not affected by the positions of the four orthogonal electrodes. Therefore, taking as the acceptable standard for imaging quality, the minimum number of electrodes for the MAET system is N = 4,

[0041] In summary, the minimum configuration of the MAET system without mechanical rotation and scanning is M≥30 and N≥4. Further, considering the requirements of the annular uniform distribution of transducers and electrodes to ensure that the electrodes do not affect the sound field, the MAET system configuration needs to be set with M and N in accordance with 2 k k (k is an integer greater than 4), so that the sound sources and electrodes are alternately distributed on the circumference, and N is an integer multiple of 4. Under the condition of ensuring the imaging quality, the imaging speed is increased as much as possible. The optimized configuration of the fast MAET system is 32 sound sources and 4 orthogonally distributed electrodes (M = 32 and N = 4).

[0042] As an improvement of the present invention, the method further includes the following steps

[0043] Establish an experimental system with 32 annular sound sources and 4 orthogonal electrodes, perform MAE measurement and MAET imaging on an eccentric cylinder model to prove the correctness of the imaging method and the feasibility of the optimization scheme. The specific implementation process is as follows

[0044] The MAET system includes a computer, a function signal generator, a power amplifier, a 32-channel analog signal switch, a 4-channel analog signal switch, a low-noise preamplifier, a low-pass filter amplifier, an oscilloscope, a cylindrical container, a neodymium iron boron magnet, 32 omnidirectional transducers, and 4 sheet electrodes. The 32 omnidirectional transducers are sequentially connected to the 32-channel analog signal switch, the power amplifier, and the function signal generator. The function signal generator outputs a pulsed sine signal, which is amplified by the power amplifier and drives the transducers to emit sound waves after being switched by the 32-channel analog signal switch; the sound waves propagate in the cylindrical container and generate MAE signals under the action of the magnetic field, which are synchronously detected by the four orthogonally placed electrodes, selected by the 4-channel analog signal switch, amplified by the low-noise preamplifier and the low-pass filter amplifier, and then collected by the oscilloscope and stored in the computer

[0045] Using the measured 32×4 MAE signal waveforms, the annular boundary distribution of the cylindrical model is reconstructed using the above imaging method to prove the feasibility of the fast MAET method. Further, the sound sources and electrodes are selected at intervals, and the number of sound sources and electrodes used for imaging is changed to obtain several experimental conditions below the minimum configuration, such as 16×4, 8×4, 32×2, and 32

[0046] ×1. The MAET images are reconstructed, and the results show that the imaging quality under these conditions has significantly decreased, further proving that the minimum requirements for the MAET system configuration proposed in the present invention are M≥30 and N≥4, and the optimized configuration of the fast MAET system is M = 32 and N = 4

[0047] An electronic device includes a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, it implements the fast magnetoacoustic electrotomography imaging method without mechanical rotation and scanning measurement.

[0048] A computer-readable storage medium stores computer instructions. When the computer instructions are executed by a processor, they implement the fast magnetoacoustic electrotomography imaging method without mechanical rotation and scanning measurement.

[0049] With the above technical solutions, the proposed fast MAET imaging method of the present invention has the following advantages:

[0050] The present invention uses the cyclic excitation of an omnidirectional sound source with a circular distribution and the synchronous measurement of orthogonal electrodes to achieve fast MAET imaging. The single acoustic radiation of the omnidirectional transducer can completely cover the entire field to be measured, eliminating the need for linear scanning of the transducer or phased scanning of an array sound source. By electronically controlled switching, the cyclic excitation of the circular sound source and the synchronous measurement of orthogonal four electrodes can be achieved, and fast measurement can be completed without the mechanical rotation and scanning of traditional MAET, effectively improving the imaging speed and stability and obtaining high-precision MAET images. The present invention simplifies the structure of the MAET system and is easy to integrate with commercial ultrasonic CT technology to achieve ultrasonic and electrical impedance fusion multimodal and cross-scale imaging, providing a new fast imaging technology for MAET imaging. Description of the Drawings

[0051] Figure 1 Schematic diagram of the MAET principle based on an annular omnidirectional transducer array;

[0052] Figure 2 . (a) Schematic diagram of MAET imaging of a circular 16 sound sources and 16 electrodes based on an eccentric cylindrical tissue model, (b) Reconstructed image of cyclic excitation of 16 sound sources and synchronous measurement of 16 electrodes;

[0053] Figure 3 . (a) Electrical impedance distribution of the cross-section of the columnar model, MAET images under the conditions of N = 16 and M = 10, 15, 20, 30, and 40, (c) Circular radius R in the range of 0° - 90° -3 distribution, (d) Relationship between the radius fluctuation coefficient ε and the number of sound sources M;

[0054] Figure 4 . M = 30, N = (a) 1, (b) 2, and (c) 4, three s conditions of MAET reconstructed images based on the sum of MAE amplitudes, (d) Relative intensity error (RE) of the circular boundary and the model boundary of the MAET image under different N conditions as a function of the starting electrode number n sDistribution, (e) average relative error Variation with N, (f) M = 30 and N = 4, three kinds of n s MAET reconstructed images based on the sum of the squares of the magnitudes of the MAE under three conditions;

[0055] Figure 5 . Block diagram of the MAET measurement system;

[0056] Figure 6 . (a) Cross-sectional conductivity distribution of the eccentric cylinder model, measured MAE signal (b) waveform and (c) envelope. MAET images reconstructed under the conditions of M = 32, N = (d1) 1, (d2) 2, and (d3) 4, and MAET images reconstructed under the conditions of N = 4, M = (e1) 16, (e2) 8, and (e3) 4. Detailed implementation manners

[0057] The present invention will be further clarified below in conjunction with the accompanying drawings and specific implementation manners. It should be understood that the following specific implementation manners are only used to illustrate the present invention and not to limit the scope of the present invention.

[0058] Example: Refer to Figures 1-6 , a fast MAET imaging method without mechanical rotation and scanning, the method includes the following steps,

[0059] S1. Establish a MAET measurement system based on a circular omnidirectional sound source array and an electrode array to realize the cyclic excitation of the sound field and the synchronous measurement of the MAE signal;

[0060] S2. Establish a theoretical model of MAE based on the excitation of a sound source at any position in a circle and the reception of an electrode, deduce the general theoretical formula of the MAE signal, and obtain the determining factors of the amplitude and time of the MAE signal;

[0061] S3. Introduce the cyclic excitation of a circular sound source and the multi-electrode synchronous measurement technology, and propose a high-precision MAET imaging method based on the inverse Radon transform and the amplitude of the MAE signal and the sum of the squares of the amplitudes;

[0062] S4. Establish a cylindrical tissue model, conduct simulations of MAE signals under different numbers of sound sources and electrodes, complete the reconstruction of MAET images, and analyze the influencing factors of imaging quality;

[0063] S5. Based on the analysis of the influence of the number of sound sources and electrodes on the radius fluctuation of the circular boundary and the relative intensity error of the reconstructed MAET image, propose the minimum configuration requirements of the MAET system, and further obtain the optimization scheme of the fast MAET system.

[0064] S6. Establish a 32-sound-source and 4-electrode experimental system, conduct MAE measurements and MAET imaging on an eccentric cylinder model to prove the correctness of the imaging method and the feasibility of the optimization scheme.

[0065] The details are as follows:

[0066] First, in step S1, an MAET measurement system based on a circular omnidirectional sound source array and an electrode array is established to achieve cyclic excitation of the sound field and synchronous measurement of the MAE signal. The details are as follows:

[0067] An MAET system is established with the measured field covering the size of the object to be measured. M uniformly distributed omnidirectional transducers are set at the boundary of the circular field to cyclically emit sound waves, and N sheet-shaped or needle-shaped electrodes are set to detect the MAE signals generated by the conductivity boundary of the object tissue to be measured. As Figure 1 shown, a conductive tissue with an arbitrary-shaped conductivity distribution σ(r) is placed in a coupling liquid with a conductivity of σ0. The entire field has good acoustic coupling and electrical transmission characteristics. A pair of parallel permanent magnets generate a static magnetic field B = Be x in the x direction, where e x represents the unit vector in the x direction. M omnidirectional sound sources and N electrodes are uniformly distributed on a circle with a radius of R0. The position coordinates of the mth sound source Tm and the nth electrode En are r Tm and r En , respectively. The surface of the sound source is completely insulated from the coupling liquid to reduce interference between the sound field and the electric field. At the same time, the influence of the electrodes located in the circular distribution on the radiation sound field of the transducer is ignored. The pulsed sound wave radiated by the transducer propagates in a spherical form, and the sound field covers the entire measured circular field. The vibration of the conductive tissue particles caused by the sound propagation interacts with the magnetic field to generate an induced current, which is received by the electrodes placed on the circumference after propagating through the conductive medium, and N MAE signals containing the conductivity gradient and position information of the tissue boundary are obtained. By electronically controlling the cyclic excitation of M transducers and controlling the synchronous measurement of N electrodes, M×N MAE signal waveforms are collected and used to reconstruct the MAE image.

[0068] Then, in step S2, an MAE theoretical model based on the excitation of sound sources at arbitrary positions in a circle and the reception of electrodes is established, the general theoretical formula of the MAE signal is derived, and the determining factors of the amplitude and time of the MAE signal are obtained. The details are as follows:

[0069] As Figure 1 shown, the omnidirectional sound wave radiated by the mth sound source Tm centered at r Tm propagates to an arbitrary position r in the field, and its sound pressure is where Q = 4πa 2 u0 is the intensity of the spherical sound source, u0 is the vibration velocity of the sound source surface, a is the radius of the sound source, k = ω / c is the wave number, ω is the angular frequency, ρ and c are the density and sound velocity of the propagation medium, respectively, and R Tm = |r - r Tm | is the distance from the sound source rTm The distance to r, t = R Tm / c is the propagation time. The sound pressure p(r Tm ,r) generates a particle velocity whose direction is e v =(r - r Tm ) / |r - r Tm |, is the gradient operator. The interaction between the static magnetic field B and the velocity v(r Tm ,r) generates an induced current density J(r Tm ,r)=σ(r)v(r Tm ,r)×B, and its unit vector e J is perpendicular to e v .

[0070] The current density detected by the nth electrode En on the circumference at r En generated by the mth sound source at r is J En (r Tm ,r)=J(r Tm ,r)cosθ, and its unit vector e E =(r En -r) / |r En -r|, where θ is the angle between e E and e J . The amplitude of the MAE signal received by the electrode En is determined by the equivalent resistance R En on the current propagation path and the receiving coefficient α determined by the electrode characteristics. Therefore, the MAE voltage received by the electrode En from the sound source Tm generated in the entire field Ω is

[0071]

[0072] where t = |r - r Tm | / c is the propagation time of sound radiation, θ = π / 2 - χ, and χ is the angle between e E and -e v . Considering that is the conductivity gradient along the sound propagation direction, and its magnitude is determined by the angle γ between e v and the conductivity normal direction e n , the following is obtained:

[0073]

[0074] Since the positions of N electrodes are distributed around the circumference, the propagation distance |r En -r| from r to r En is different, and its equivalent resistance R En ]>can be approximately proportional to the propagation distance R En=R s |r En -r|, where R s is the resistance per unit length of the conductive medium, then the MAE voltage signal is obtained as:

[0075]

[0076] where ξ = -2αBa 2 u0R s is a constant determined by the system structure and parameters. Using the ideal unit impulse signal δ(t) as the excitation sound source to generate the MAE signal, the MAE voltage received by the electrode is corrected as:

[0077]

[0078] V δ (r En ,r Tm ,t) is the spatial transfer function of the system determined by the sound source emission position r Tm and the electrode receiving position r En as well as the conductivity distribution. Driven by the actual excitation signal S(t), the transducer outputs a cluster of pulsed sound waves as where R(t) is the impulse response of the transducer under the excitation of δ(t), is the convolution operation symbol. Therefore, the waveform of the MAE signal generated by the m-th sound source received by the n-th electrode in the entire field is:

[0079]

[0080] The theoretical formula shows that the radiation sound field can only generate MAE signal pulses at the tissue conductivity boundary, and its position is determined by the propagation time t = |r - r Tm | / c, while the amplitude is determined by as well as the position information jointly.

[0081] Furthermore, in step S3, the annular sound source cyclic excitation and electrode synchronous measurement technologies are introduced, and a MAET imaging method based on inverse Radon transform and the sum of MAE signal amplitudes (sum of squared amplitudes) is proposed, specifically as follows:

[0082] First, perform the Hilbert transform on the waveform of the MAE signal excited by the m-th sound source and received by the n-th electrode and then take the absolute value to obtain the MAE signal amplitude envelope H(r En ,r Tm ,t) = ABS(Hilbert[W(r En ,r Tm ,t)]), which satisfies |r - r Tm| = ct. Then, the inverse Radon transform based on the diffractive sound source is introduced, and the amplitude at all times of H(r En , r Tm , t) is back-projected into the field region |r - r Tm | = ct on the circular arc, and the MAE image g(r En , r Tm , r) = H(r En , r Tm , t)δ(|r - r Tm | - ct) based on the radiation of the sound source Tm and the reception of the electrode En is reconstructed. Further, the amplitude and (sum of squared amplitudes) of the MAE signals measured synchronously by the N electrodes are used to compensate for the signal attenuation at different angles, and the MAE image based on the excitation of the sound source Tm and the synchronous measurement of the N electrodes is obtained:

[0083] Or

[0084] Finally, the circular M sound source cyclic excitation and the N electrode synchronous measurement are introduced, M×N MAE waveforms are collected, and M MAE images under different sound source excitations are reconstructed. Considering the included angle between the sound sources The MAET image is reconstructed through the rotation matrix and image interpolation:

[0085]

[0086] Theoretical proof shows that increasing the number M of circular sound sources and the number N of electrodes and increasing their uniform distribution density in the range of 0 - 2π can reduce the influence of the positions of the sound sources and electrodes on θ and γ, and improve the accuracy and integrity of the MAET image.

[0087] Further, in step S4, a cylindrical tissue model is established, the MAE signal simulation is carried out under different conditions of the number of sound sources and electrodes, the MAET image reconstruction is completed, and the influencing factors of the imaging quality are analyzed as follows:

[0088] An MAET system with M = 16 and N = 16 and an excitation signal frequency f = 2 MHz is established, and its yz cross-sectional distribution is as Figure 2As shown in Fig. (a), the center of the circular field is located at the origin of coordinates. Sixteen omnidirectional transducers and sixteen plate electrodes are alternately placed, ignoring the edge reflection of sound waves and the influence of the electrodes on the radiation sound field. An eccentric cylindrical tissue model with a radius of 10 mm is placed inside the measurement field, and its center is located at (10, 10) mm. The conductivities of the model and the surrounding medium are set to 1 and 0.03 S / m respectively, and the sound speed is set to 1540 m / s. The sixteen transducers are cyclically excited, and the sixteen electrodes are synchronously measured to collect the 16×16 received MAE signal waveforms. Through the cyclic excitation of 16 sound sources and the synchronous measurement of 16 electrodes, 16×16 MAE signal waveforms are obtained, and the rotation matrix is introduced for reconstruction to obtain the MAET image as shown in Figure 2 Fig. (b). The reconstruction results show a clear circular model boundary. However, due to the small number of cyclic excitations of the transducers, the circular boundary has an uneven and discontinuous distribution, and obvious artifacts also exist.

[0089] Based on the analysis of the influence of the sound source and the electrode on the radius fluctuation and intensity relative error of the MAET annular boundary, the minimum configuration requirements of the MAET system are proposed, and further an optimization scheme for the fast MAET system is obtained as follows:

[0090] To determine the influence of the number of sound sources N on the MAET imaging quality, a circular tissue model with a radius of 10 mm as shown in Figure 3 Fig. (a) is established. Its conductivity is set to σ = 1 S / m, the center is located at (0, 0) mm, and it is placed in a conductive liquid with σ0 = 0.03 S / m. The MAE signals synchronously received by 16 electrodes are simulated under different conditions of M = 10, 15, 20, 30, and 40 to obtain the MAET images as shown in Figure 3 Figs. (b1)-3(b5). The results show that the annular distribution of the tissue model can be reconstructed by MAET under several M conditions, and the peak sound pressure is located on the ring with a radius of 10 mm. When M = 10, the boundary fluctuation is obvious, forming a petal distribution similar to a 10-sided polygon with sharp corners. At the same time, amplitude and shape fluctuations are shown, accompanied by obvious circular arc artifacts. However, as M increases, the number of sides of the polygon increases, but the intensity of the petals weakens, the smoothness of the boundary increases, and its contrast and clarity also increase accordingly. When M = 30, the model boundary as shown in Figure 3 Fig. (b4) forms an approximately standard annular distribution, and the imaging quality is basically acceptable, but the outward petal-shaped radiation at 30° is still visible. When M is increased to 40, the shape and size of the annular boundary basically remain unchanged, but the intensity of the 40-petal distribution is significantly reduced, the intensity of the annular distribution of the model boundary increases, the contrast is enhanced, and the imaging quality is significantly improved.

[0091] Extract Figure 3 the outer radius (R at the -3 dB attenuation of the peak intensity on the annular boundary in Figs. (b1)-3(b5)-3 ) Distribution to obtain the annular intensity distribution within the range of 0° - 90° as shown in Figure 2 (c). The results show radius fluctuations, and the fluctuation range decreases as M increases. To quantitatively evaluate the coherence and smoothness of the model boundary in the MAET image, the radius fluctuation coefficient is defined as:

[0092]

[0093] where R -3 (i) is the radius at the i-th measurement angle, and is the average radius of Q measurements of the annulus at this time. Figure 3 (d) shows the relationship between the radius fluctuation coefficient ε and M. When M is increased from 10 to 40, the fluctuation coefficient decreases from 0.64 to 0.019 mm, proving that the fluctuation coefficient ε decreases as M increases. Therefore, with ε = 0.02 mm as the standard, the number of sound sources of the MAET system under acceptable imaging quality conditions must be M ≥ 30.

[0094] A MAET system with 64 electrodes is constructed using at least 30 sound sources. The sound sources and electrodes are evenly placed in a circular pattern on the field boundary. An eccentric circular tissue model with a center at (10, 10) mm, a radius of 10 mm, and a conductivity σ = 1 S / m is placed in a conductive liquid with σ0 = 0.03 S / m. A uniformly distributed N electrodes are selected along the circumference to form different synchronous measurement groups, with the number of electrodes in the measurement group being N = 1, 2, 4, 8, 16, 32, and 64, and the starting electrode number being n s . Under the conditions of N = 1, 2, and 4, different electrode combinations of n s are selected to perform MAE signal simulation and MAET image reconstruction on the eccentric circle model, and the results are as shown in Figure 4 (a) - 4(c). Figure 4 (a) shows that a single - electrode measurement can basically reconstruct the shape and position of the model boundary, but there are obvious intensity differences in the annular boundary, proving that the continuity and intensity consistency of the MAET - reconstructed model boundary are greatly affected by the position of the measurement electrode. When it is increased to N = 2, Figure 4 (b) shows that the two - electrode measurement with circumferential symmetric distribution can compensate for the signal attenuation to a certain extent, improve the continuity of the annular boundary, and reduce the intensity difference, but there are still intensity differences in the annular boundary distribution, and its position changes with the electrode position. When N = 4, Figure 4 (c) shows that the results of the orthogonal four - electrode measurement are almost the same, and the continuity and consistency of its annular boundary are significantly improved, proving that the orthogonal placement of four - electrode measurement can effectively improve the information integrity of the measured MAE signal, improve the accuracy of the MAET model boundary, and the imaging results are not affected by the position of the orthogonal electrodes, with good performance stability.

[0095] To quantitatively evaluate the image quality of reconstructed MAET, the relative error (RE) of the annular boundary intensity distribution between the MAET image and the model is defined as:

[0096]

[0097] where Q is the number of annular sampling points, and g p (i) is the intensity of the i-th sampling point on the annular boundary of the MAET image, and its corresponding measurement angle is 360°i / Q. Under the conditions of N = 1, 2, 4, 8, 16, and 32, by changing n s = 1, 2, 3, …, 63, and 64 to adjust the positions of the electrodes in each synchronous measurement group, simulate the MAE signal and complete the MAET image reconstruction, and obtain the distribution of the relative error of the annular intensity distribution of the model boundary as shown in Figure 4 (d) with respect to n s . It can be seen that RE shows an N-periodic fluctuating distribution, and its amplitude decreases with the increase of N. When N = 1 and 2, the quality of the reconstructed MAET image is poor, the RE value of the annular boundary intensity distribution is large, and the fluctuation range is large, indicating that the position of the measurement electrodes has a greater impact on the image quality; when N ≥ 4, the RE value rapidly decreases to 0.027 with minimal fluctuations, indicating that a uniformly distributed 4-electrode ring can obtain complete MAE information, effectively improving the quality of the MAET image, and the electrode position has less impact on the image quality. For the RE distribution under the same N and different n Figure 5 in s (d), the arithmetic mean calculation is performed to obtain the relationship between and N as shown in Figure 3 (e). The results show that as N increases from 1 to 4, rapidly decreases from 0.19 to 0.027 and stabilizes after N ≥ 4, indicating that when N < 4, due to fewer electrodes being unable to obtain the component information of the MAE signal in all directions, the quality of the reconstructed MAET image is poor and is greatly affected by the electrode position; while when N ≥ 4, the MAET image can accurately reflect the boundary distribution of the model, and the imaging quality is not affected by the positions of the four orthogonal electrodes. Therefore, taking as the acceptable standard for imaging quality, the minimum number of electrodes for the MAET system is N = 4. When N = 4, different electrode combinations of n

[0098] are selected to simulate the MAE signal of the eccentric circle model, and the MAET image is reconstructed using the MAE amplitude squared sum algorithm, as shown in s . Figure 4(f1)-4(f3) The results show that the amplitude squared sum algorithm for detecting MAE based on orthogonal four electrodes can accurately reconstruct the circular boundary of the model, and their circular peak intensities are almost exactly the same. Further, changing n s The relative error RE of reconstructing the circular boundary by orthogonal four electrodes is calculated to be 0.027, and it hardly fluctuates with the change of n s The results prove that the amplitude squared sum algorithm based on MAE signal has a clearer physical meaning and is an MAET imaging algorithm with better image reconstruction effect.

[0099] In summary, the minimum configuration of the proposed MAET system without mechanical rotation and scanning is M≥30 and N≥4. Further, considering the requirements of the circular uniform distribution of transducers and electrodes to ensure that the electrodes do not affect the sound field, the optimized configuration of the MAET system needs to set M and N with 2 k (k is an integer greater than 4) so that the sound source and the electrodes are alternately distributed on the circumference, and N is an integer multiple of 4. Therefore, under the condition of ensuring the imaging quality, the optimized configuration of the MAET system that can improve the imaging speed as much as possible and meet the actual application requirements is 32 sound sources and orthogonally distributed four electrodes (M = 32 and N = 4).

[0100] Finally, in step S6, a 32 - sound - source and 4 - electrode experimental system is established to measure MAE and perform MAET imaging on an eccentric cylinder model to prove the correctness of the imaging method and the feasibility of the optimization scheme, as follows:

[0101] As Figure 5 shown, the MAET system includes computer A, function signal generator B, power amplifier C, 32 - channel analog signal switch D, 4 - channel analog signal switch E, low - noise pre - amplifier F, low - pass filter amplifier G, oscilloscope H, cylindrical container, neodymium iron boron magnet, 32 omnidirectional transducers, and 4 plate - shaped electrodes. The 32 transducers are sequentially connected to the 32 - channel analog signal switch, power amplifier, and function signal generator. The function signal generator outputs a pulsed sine signal, which is amplified by the power amplifier and drives the transducers to emit sound waves after being switched by the 32 - channel analog signal switch; the sound waves propagate in the cylindrical container and generate MAE signals under the action of the magnetic field, which are detected by the orthogonally placed four electrodes. After being selected by the 4 - channel analog signal switch, they are amplified by the low - noise pre - amplifier and low - pass filter amplifier and then collected by the oscilloscope and stored in the computer.

[0102] Using the measured 32×4 MAE signal waveform, the annular boundary distribution of the cylindrical model is reconstructed by the imaging method proposed above to prove the feasibility of the fast MAET method. Further, the sound source and electrodes are selected at intervals, and the number of sound sources and electrodes used for imaging is changed to obtain several experimental conditions below the optimized minimum configuration, such as 16×4, 8×4, 32×2, and 32×1. The quality of the reconstructed MAET images all decreases significantly, proving that the minimum requirements for the MAET system configuration proposed in the present invention are M≥30 and N≥4. At the same time, it also proves that the optimized configuration of the fast MAET system is M = 32 and N = 4.

[0103] Example 2:

[0104] Based on the above theory and simulation research conclusions, this example uses 32 transducers with an annular uniform distribution and 4 electrodes placed orthogonally to build an experimental system as shown in Figure 5 to conduct MAET imaging experiments, with the following:

[0105] (1) The radius a of the planar piston transducer is 3.5 mm, and the frequency f is 2 MHz. A hemispherical convex lens with a radius of a is designed and fabricated using acrylic resin material, and it is coaxially installed on the transducer surface to construct an omnidirectional transducer, modulating the acoustic wave output by the planar transducer to form an approximately omnidirectional radiation sound field.

[0106] (2) Thirty-two omnidirectional transducers are evenly installed in the central plane of the boundary of a cylindrical container with a diameter of 120 mm and a height of 60 mm. The acoustic axes of the radiated acoustic waves propagate along the radial direction. Absorbing materials are arranged on the inner side and bottom of the cylinder to reduce acoustic reflection. The entire system is placed in the central region of a pair of neodymium iron boron magnets (100 mm * 100 mm * 50 mm), which generate an approximately uniformly distributed magnetic field of about 0.3 T, completely covering the gel model to be measured. A cylindrical gel model with a diameter of 30 mm and a conductivity of 1 S / m is eccentrically placed inside the container, and the outside is filled with a liquid with a conductivity of 0.3 S / m to ensure acoustic wave propagation and current propagation. The surfaces of the transducers and the lens are completely insulated from the conductive liquid to reduce interference in the sound field and electric field.

[0107] (3) Under the control of a computer, a function signal generator (33220A, Agilent Technologies, USA) outputs a single-cycle sine pulse signal (V pp= 1 V, f = 2 MHz, PRF = 100 Hz), amplified by a power amplifier (53 dB, E&I 2200L, Electronics and Innovation Ltd, USA), is switched and output by a 32-way switch, and can drive 32 transducers individually or cyclically to generate an omnidirectional pulsed sound field. Four electrodes are orthogonally placed inside the cylindrical sound-absorbing material to receive the MAE signals generated by the gel model. After being amplified by a low-noise preamplifier (46 dB, NF SA-230F5, NF Corporation, Japan) and a self-made band-pass amplifier (45 dB, cut-off frequency 1.5 - 2.5 MHz), they are collected by a digital oscilloscope (DSO9064A, Agilent Technologies, USA) after being switched by a 4-way switch and stored in a computer for later signal processing and MAET image reconstruction.

[0108] (4) In the experiment, 32 sound sources were cyclically excited and 4 orthogonal electrodes were synchronously measured, and 32×4 measured MAE signal waveforms were acquired. The conductivity distribution of the cross-section of the experimental model is as Figure 6 (a) shown, and the sound speed in the measured circular field is uniformly approximated as 1550 m / s. Figure 6 (b) and (c) show the MAE signal waveforms and their envelopes measured by a certain electrode. Figure 6 (b) Two obvious MAE voltage wave clusters A and B correspond to Figure 6 (c) Two envelope peaks A and B, which respectively correspond to the two boundaries of the gel model. Their measurement times are approximately 25.2 and 43.7 μs respectively, and the length corresponding to the time interval of 18.5 μs exactly matches the diameter of the cylinder of 30 mm. Since when sound waves propagate in the cylindrical model and the surrounding liquid, acoustic reflections between the model boundaries will generate MAE voltages with relatively small amplitudes, many wave clusters with relatively small amplitudes are formed between wave clusters A and B.

[0109] (5) Using the 32×4 MAE signals collected, under the condition of M = 32, system configurations with N = 1, 2, and 4 were respectively adopted to reconstruct the MAET images normalized by their respective intensity maximum values as shown in Figure 6 (d1)-6(d3), showing that when M = 32, the three N-reconstructed MAET images can accurately reconstruct the shape and position of the model boundary. When N = 1, Figure 6 (d1) The continuity and consistency of the circular boundary of the MAET image are poor, obvious edge burrs appear, and artifacts with different intensities are shown; when N = 2, Figure 6 (d2) The continuity and consistency of the circular boundary are improved, and the intensity of the central artifact is weakened; when N = 4, Figure 6(d3) shows a clear eccentric circular ring with good continuity and uniformity at its boundary, while the internal artifacts are significantly suppressed, forming an approximately uniform distribution.

[0110] (6) Fix the number of electrodes N = 4. Select different excitation transducers at intervals from the measured 32×4 MAE signal waveforms to form system configurations with M = 16, 8, and 4, and obtain the MAET images shown in Figure 6 (e1)-6(e3). The results show that the MAET image with M = 32 has the best boundary reconstruction effect. As M decreases, the continuity of the circular boundary decreases, forming an M-sided distribution with obvious sharp angles; when M decreases to 8 and 4, the boundary shows an 8-sided and 4-sided shape and cannot form a circular distribution, so the reconstruction of the model conductivity boundary cannot be achieved. The results prove that the number of transducers M determines the shape of the boundary. The larger M is, the higher the integrity and accuracy of the reconstructed model boundary shape; while the number of electrodes N determines the consistency and continuity of the boundary strength. The larger N is, the higher the continuity and consistency of the strength distribution of the reconstructed model boundary, and the smaller the artifacts.

[0111] (7) The experimental results prove the feasibility of the proposed fast MAET imaging method without mechanical rotation and scanning measurement, and also prove that the minimum configuration of the MAET system is M≥30 and N≥4, while the optimized scheme for the fast MAET system is 32 sound sources and orthogonal 4 electrodes.

[0112] Although the preferred embodiments of the present application have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present application.

[0113] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. A fast magnetoacoustic electrical tomography method without mechanical rotation and scanning measurement, characterized in that, Including the following steps: S1. Establish an MAET measurement system based on a circular omnidirectional sound source array and an electrode array to achieve cyclic excitation of the sound field and synchronous measurement of MAE signals; S2. Establish an MAE theoretical model based on the excitation of a sound source at any position in a circle and electrode reception, derive the general theoretical formula for MAE signals, and obtain the determinants of the amplitude and time of MAE signals; S3. Introduce the cyclic excitation of a circular sound source and the synchronous measurement technology of multiple electrodes, and propose a high-precision MAET imaging method based on the inverse Radon transform and the amplitude sum (sum of squared amplitudes) of MAE signals; S4. Establish a cylindrical tissue model, conduct simulations of MAE signals under different numbers of sound sources and electrodes, complete MAET image reconstruction, and analyze the influencing factors of imaging quality; S5. Based on the analysis of the influence of the number of sound sources and electrodes on the radius fluctuation of the circular boundary and the relative intensity error of the reconstructed MAET image, propose the minimum configuration requirements for the MAET system, and further obtain an optimized scheme for a fast MAET system.

2. A fast magnetoacoustic electrical tomography imaging method without mechanical rotation and scanning measurement according to claim 1, characterized in that In step S1, to establish an MAET measurement system based on a circular omnidirectional sound source array and an electrode array to achieve cyclic excitation of the sound field and synchronous measurement of MAE signals, the specific steps are as follows: Set M uniformly distributed omnidirectional transducers on the boundary of a circular field with a radius of R0 to cyclically emit sound waves, and set N sheet-like or needle-like electrodes to detect the MAE signals generated by the conductivity boundary of the tissue of the object to be measured. An object to be measured with an arbitrary shape of conductivity distribution is placed in a conductive coupling liquid. The entire field has sound coupling and electrical transmission characteristics. A pair of parallel permanent magnets generate a static magnetic field that vertically penetrates the measured field. The pulsed sound waves radiated by the transducers propagate as spherical waves. The sound field covers the entire measured circular field. The vibration of conductive tissue particles caused by sound propagation interacts with the magnetic field to generate an induced current, which is received by the electrodes after propagation through the conductive medium, obtaining N MAE signals containing the conductivity gradient and position information of the tissue boundary. Through electronic control of the cyclic excitation of M transducers and the synchronous measurement of N electrodes, rapid measurement of M×N MAE waveforms and MAET image reconstruction are realized. It is required that the M sound sources used are approximate omnidirectional transducers, and the half-opening angle of their spherical sound radiation should be greater than 60°, and the radiation sound field can completely cover the object to be measured; the surface of the omnidirectional transducer and the coupling liquid should be completely insulated to reduce the interference between the sound field and the electric field; the electrodes need to be placed in the conductive coupling liquid with conductivity to ensure the reliability of current transmission; The boundary and bottom of the circular measured field should be covered with sound-absorbing materials to eliminate the influence of sound reflection and sound scattering; Silver or copper sheet-like or needle-like high-conductivity electrodes should be selected to improve the electric field detection ability. The electrodes should be placed between two adjacent transducers on the boundary of the circular field to reduce the influence of the circularly distributed electrodes on the radiation sound field.

3. A fast magnetoacoustic electrical tomography imaging method without mechanical rotation and scanning measurement according to claim 1, characterized in that In step S2, to establish an MAE theoretical model based on the excitation of a sound source at any position in a circle and electrode reception, derive the general theoretical formula for MAE signals, and obtain the determinants of the amplitude and time of MAE signals, the specific steps are as follows: The m-th sound source Tm placed circumferentially emits an omnidirectional sound wave, and the sound pressure generated at any position r in the field is where Q = 4πa 2 u0 is the intensity of the spherical sound source, u0 is the vibration velocity on the sound source surface, a is the radius of the sound source, k = ω / c is the wave number, ω is the angular frequency, ρ and c are the density and sound velocity of the propagation medium respectively, R Tm = |r - r Tm | is the distance from the sound source position r Tm to r, t = R Tm / c is the propagation time, and the sound pressure generates a particle vibration velocity whose direction is e v , is the gradient operator, and the interaction between the static magnetic field B and v(r Tm , r) generates an induced current density J(r Tm , r) = σ(r)v(r Tm , r) × B, and its direction is e J ; The current density component J generated by the m-th sound source at r is detected by the n-th electrode En on the circumference En (r Tm ,r) = J(r Tm ,r)cosθ, and its direction is e E , where θ is the angle between e E and e J , θ = π / 2 - χ, and χ is the angle between e E and -e v . Considering the equivalent resistance R En during the propagation of the induced current generated at r received by the electrode En and the electrode reception coefficient α, and also considering determined by the angle γ between e v and the normal direction e n of the conductivity, the MAE voltage generated by the sound source Tm received by the electrode En in the entire field domain Ω is obtained: The equivalent resistance R of the system En is proportional to the propagation distance R En = R s |r En - r|, where R s is the resistance per unit length of the conductive medium, then the MAE voltage signal is obtained as follows: where ξ = -2αBa 2 u0R s is a constant determined by the system structure and parameters; Using the ideal unit impulse signal δ(t) as the excitation sound source, the MAE voltage is corrected as: where V δ (r En , r Tm , t) is determined by the sound source emission position r Tm and the electrode receiving position r En as well as the conductivity distribution. Considering the convolution of the excitation signal S(t) and the impulse response R(t) of the transducer is the convolution operation symbol, the general formula for the MAE waveform generated by the m-th sound source received by the n-th electrode in the entire field is obtained as follows: The derived theoretical formula proves that the radiation sound field can only generate MAE signal pulses at the tissue conductivity boundary, and its position is determined by the propagation time t = |r - r Tm | / c from the sound source to the tissue boundary, while the amplitude is determined by and the position information jointly.

4. A rapid magnetoacoustic electrical tomography imaging method without mechanical rotation and scanning measurement according to claim 1, characterized in that In step S3, the techniques of circular sound source cyclic excitation and electrode synchronous measurement are introduced, and a high-precision MAET imaging method based on inverse Radon transform and the sum (sum of squared amplitudes) of MAE signal amplitudes is proposed as follows: First, perform the Hilbert transform on the waveforms W(r En ,r Tm ,t) of the m-th sound source excitation and the MAE signals received by the n-th electrode, and then take the absolute value to obtain the envelope H(r En ,r Tm ,t) of the MAE signals; apply the inverse Radon transform based on the diffracted sound source to the envelope of the MAE signals, and backproject the amplitudes at all times of H(r En ,r Tm ,t) onto the arc of |r - r Tm | = ct in the field of view to reconstruct the MAE image g(r En ,r Tm ,r) = H(r En ,r Tm ,t)δ(|r - r Tm | - ct), Based on the synchronous measurement of N electrodes, reconstruct N MAE images g(r En , r Tm , r) under the excitation condition of the sound source Tm. Compensate for the signal attenuation caused by the measurement angles at different electrode positions through the calculation of the sum of the amplitudes and the sum of the squares of the amplitudes of the MAE signals, and obtain the MAE images based on the excitation of the sound source Tm and the synchronous measurement of N electrodes respectively and Finally, introduce the circular M sound source cyclic excitation and N electrode synchronous measurement, and use the M×N MAE waveforms collected to reconstruct M MAE images g(r Tm ,r) under different sound source excitations, and reconstruct the MAET image through the rotation matrix:

5. A rapid magnetoacoustic electrical tomography imaging method without mechanical rotation and scanning measurement according to claim 1, characterized in that In step S4, a cylindrical tissue model is established, MAE signal simulations are carried out under different conditions of the number of sound sources and electrodes, MAET image reconstruction is completed, and the influencing factors of imaging quality are analyzed as follows: A 16 sound source and 16 electrode MAET system is established. An eccentric cylindrical tissue model is placed inside the measurement field. 16 transducers are used for cyclic excitation, and 16 electrodes are used for synchronous measurement to obtain a 16×16 MAE waveform, and the MAET image is reconstructed. The results show the reconstructed circular model boundary, proving that the number of sound sources has a significant impact on MAET.

6. A rapid magnetoacoustic electrical tomography imaging method without mechanical rotation and scanning measurement according to claim 1, characterized in that, In step S5, based on the analysis of the influence of the number of sound sources M and the number of electrodes N on the radius fluctuation of the circular boundary of the MAET image and the relative intensity error, the minimum configuration requirements of the MAET system are proposed, and further an optimization scheme for the fast MAET system is obtained as follows: A circular tissue model was established to simulate the MAE signals synchronously received by 16 electrodes under different numbers of sound sources, reconstruct MAET images, and define the radius fluctuation coefficient of the circular boundary. where R -3 (i) is the radius at the i-th measurement angle, is the average radius of the circular ring measured Q times. The calculation shows that the fluctuation coefficient decreases with the increase in the number of sound sources. When M ≥ 30, the radius fluctuation coefficient is less than 0.02 mm. Therefore, with ε = 0.02 as the acceptable standard for imaging quality, the minimum number of sound sources for the MAET system configuration is M = 30. Under the condition that the minimum number of sound sources M = 30, a 64-electrode MAET system is constructed. An eccentric circular tissue model is set up, and N electrodes evenly distributed along the circumference are selected to form different synchronous measurement groups, and different starting electrodes n are carried out s MAE signal simulation and imaging under the conditions of N = 1, 2, 4, 8, 16, 32, and 64 are carried out, and the relative error between the MAET image and the annular boundary intensity of the model is defined where Q is the number of annular sampling points, and g p (i) is the intensity of the i-th sampling point on the annular boundary of the MAET image. MAET imaging is carried out under different N and n s conditions to obtain the average relationship between and N, and it is proved that as N increases from 1 to 4, rapidly decreases from 0.19 to 0.027, and tends to be stable after N ≥ 4. When N < 4, the quality of the reconstructed MAET image is poor and is greatly affected by the electrode positions; when N ≥ 4, the MAET image can accurately reflect the boundary distribution of the model, and the imaging quality is not affected by the positions of the four orthogonally distributed electrodes. Therefore, with = 0.027 as the acceptable standard for imaging quality, the minimum number of electrodes of the MAET system is N = 4, and they need to be placed orthogonally In summary, the minimum configuration of the proposed MAET system without mechanical rotation and scanning is M≥30 and N≥4. Further considering the actual requirements of uniform distribution of transducers on the circumference and orthogonal distribution of electrodes, the optimized configuration of the MAET system is M = 32 and N = 4.

7. A rapid magnetoacoustic electrical tomography imaging method without mechanical rotation and scanning measurement according to claim 1, characterized in that, A circular 32 sound source and orthogonal 4 electrode experimental system is established to perform MAE measurement and MAET imaging on the eccentric cylindrical model, proving the correctness of the imaging method and the feasibility of the optimization scheme. Among them, the MAET system includes a computer, a function signal generator, a power amplifier, a 32-channel analog signal switch, a 4-channel analog signal switch, a low-noise preamplifier, a low-pass filter amplifier, an oscilloscope, a cylindrical container, a neodymium iron boron magnet, 32 omnidirectional transducers, and 4 sheet electrodes. The 32 omnidirectional transducers are sequentially connected to the 32-channel analog signal switch, the power amplifier, and the function signal generator. The function signal generator outputs a pulsed sine signal, which is amplified by the power amplifier and drives the transducers to emit sound waves after being switched by the 32-channel analog signal; the sound waves propagate in the cylindrical container and generate MAE signals under the action of the magnetic field, which are synchronously detected by the four orthogonally placed electrodes. After being selected by the 4-channel analog signal switch, they are amplified by the low-noise preamplifier and the low-pass filter amplifier and then collected by the oscilloscope and stored in the computer. Using the measured 32×4 MAE signal waveform, the circular boundary distribution of the cylindrical model is reconstructed by using the above imaging method, proving the feasibility of the fast MAET method.

8. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, it implements a fast magnetoacoustic electro-tomography imaging method without mechanical rotation and scanning measurement as described in any one of claims 1 to 7 above.

9. A computer-readable storage medium having computer instructions stored thereon, characterized in that, When the computer instruction is executed by the processor, it implements a fast magnetoacoustic electro-tomography imaging method without mechanical rotation and scanning measurement as described in any one of claims 1-7.

Images