A Method and System for Measuring Subharmonic Amplitude Blood Pressure Based on Least Squares Attenuation Compensation

Abstract

This invention discloses a method and system for measuring blood pressure using subharmonic amplitude based on least squares attenuation compensation. The method employs an attenuation estimation algorithm to process radio frequency data in the propagation medium region, obtaining the attenuation characteristics of the propagation medium region for ultrasound signals. The optimal transmitted sound pressure level is updated based on these attenuation characteristics. The subharmonic amplitude of microbubbles in the target blood vessel is obtained at the updated optimal transmitted sound pressure level, and the attenuation characteristics are used to compensate for the subharmonic amplitude. The compensated subharmonic amplitude is then substituted into a model relating blood pressure and subharmonic amplitude to determine the blood pressure value of the target blood vessel. This method uses the same pressure measurement model to perform blood pressure measurements at different sites, enabling non-invasive measurement of blood pressure in the body through subharmonic amplitude-assisted pressure measurement technology. It solves the problem of requiring the establishment of a pressure measurement model before each measurement in traditional subharmonic amplitude-assisted pressure measurement methods, and has high practical and promotional value.

Description

Technical Field

[0001] This invention relates to the field of blood pressure measurement technology, specifically to a method and system for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation. Background Technology

[0002] Among non-communicable diseases, cardiovascular and cerebrovascular diseases remain a leading cause of death globally, and monitoring cardiovascular and cerebrovascular blood pressure is a crucial means of diagnosing and preventing these diseases. Currently, invasive pressure wire measurement remains the "gold standard" for measuring cardiovascular and cerebrovascular blood pressure in clinical practice. This method involves inserting a catheter into the blood vessel at the measurement site via puncture, with the outer end of the catheter directly connected to a pressure sensor. Due to the pressure transmission effect of fluid, the pressure within the blood vessel is transmitted through the fluid inside the catheter and displayed on the external pressure sensor, thus providing real-time changes in intravascular pressure. While this method offers accurate measurements, it may lead to potential complications such as local infections. Studies have shown that the infection risk is 1.3% with peripheral venous catheters, 1.9% with arterial catheters, and 3.3% with central venous catheters, significantly impacting patient prognosis.

[0003] Real-time and accurate measurement of intravascular blood pressure using non-invasive methods has always been a clinical pursuit. Currently, the existing non-invasive blood pressure measurement methods mainly include the following three types: (1) Volume compensation method based on photoplethysmography: Blood pressure is measured based on the change in absorbance caused by the volume of blood vessels. However, it can only measure systolic pressure and cannot achieve dynamic pressure measurement. It is also only applicable to superficial blood vessels, which severely limits its clinical application. (2) Capacitive sensing pressure: Based on a sensitive relative displacement sensor, it captures the slight displacement of the skin surface caused by the cardiac cycle. Combined with a neural network, it converts the pressure waveform. However, it requires model adjustment based on demographic data such as age and weight of the user population, and the training of the network requires a large amount of sample data. (3) Blood pressure monitoring based on ultrasound blood flow detection: Vertical B-ultrasound is used to simultaneously measure the diameter of blood vessels and the blood flow velocity. The blood pressure waveform is estimated based on the ratio between the flow rate change and the cross-sectional area of ​​the blood vessel. However, this method can only measure relative pressure values, and the morphology of the blood vessels and the inhomogeneity of the surrounding tissues will seriously affect the accuracy of the pressure measurement.

[0004] Since its inception in 1999, the microbubble subharmonic amplitude-assisted blood pressure measurement method (SHAPE method) has been extensively studied by teams both domestically and internationally, and is currently being applied to blood pressure measurement in vivo. However, due to the nonlinear characteristics of microbubbles and their high sensitivity to ultrasound fields, a blood pressure measurement model needs to be established before each measurement. This means that when applying this method to in vivo blood pressure measurement, invasive blood pressure measurements are required to establish the measurement model, severely limiting its clinical application. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method and system for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation. Based on the SHAPE method, an attenuation compensation algorithm is introduced to estimate the attenuation coefficient of the medium along the propagation path, thereby correcting the sound pressure of the sound field where the microbubble is located and compensating for the subharmonic amplitude, thus achieving accurate blood pressure measurement.

[0006] This invention is achieved through the following technical solution:

[0007] A method for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation includes the following steps:

[0008] The results of the subharmonic amplitude assisted pressure measurement experiment under the optimal emission sound pressure condition were obtained, and the relationship model between blood pressure value and subharmonic amplitude was obtained.

[0009] Under optimal transmission sound pressure conditions, the experimental results of subharmonic amplitude-assisted pressure measurement experiments of real blood vessels were obtained, and the radio frequency data of the propagation medium region were determined based on the experimental results.

[0010] An attenuation estimation algorithm is used to process the radio frequency data in the propagation medium region to obtain the attenuation characteristics of the ultrasonic signal in the propagation medium region.

[0011] Update the optimal emitted sound pressure based on attenuation characteristics;

[0012] The microbubble subharmonic amplitude of the target blood vessel is obtained under the updated optimal emitted sound pressure value. The microbubble subharmonic amplitude is compensated by the attenuation characteristics. The blood pressure value of the target blood vessel is determined by the relationship model between the compensated microbubble subharmonic amplitude and the subharmonic amplitude.

[0013] Preferably, the method for determining the optimal emitted sound pressure is as follows:

[0014] Based on the set acoustic parameters, a harmonic amplitude-assisted pressure measurement experiment was conducted to obtain the subharmonic amplitude corresponding to different pressure values. The relationship curve between the acoustic parameters and the subharmonic amplitude was plotted, and the Logistic equation was fitted to it. The optimal emitted sound pressure was determined according to the type of microbubble.

[0015] Preferably, the relationship model between the blood pressure value and the subharmonic amplitude is expressed as follows:

[0016] Subharmonic(dB)=A*Pressure(mmHg)+B

[0017] Wherein, Subharmonic is the subharmonic amplitude of the vascular region, Pressure is the hydraulic pressure value, A is the slope, and B is the intercept.

[0018] Preferably, the method for determining the attenuation characteristics is as follows:

[0019] Logarithmically transform the RF data spectrum amplitude, and then simplify the transformed RF data spectrum amplitude based on the difference between the RF data spectrum amplitude corresponding to different depths and frequencies and the spectrum measured by the pulse echo reflector.

[0020] The simplified RF data spectrum amplitude model is solved using the least squares method combined with Tikhonov regularization to obtain the attenuation characteristics of the ultrasonic signal in the propagation medium region.

[0021] Preferably, the expression for the RF data spectrum amplitude is as follows:

[0022] |S(f,z)|=|P(f)|D(f,z)A(f,z)B(f)

[0023] Where |S(f,z)| represents the amplitude of the radio frequency data spectrum, f and z represent the frequency and depth, |P(f)| represents the combined effect of electrical excitation and transducer effect, D(f,z) represents the diffraction effect, A(f,z) represents the cumulative attenuation, and B(f) represents the attenuation coefficient of the ultrasonic signal.

[0024] Preferably, the combined effect |P(f)| of the electrical excitation and transducer effect is determined based on the pulse echo reflector measurement spectrum and gain calibration factor;

[0025] The cumulative attenuation A(f,z) of the ultrasonic signal by the medium is determined based on the linear frequency dependence of the ultrasonic signal attenuation and depth information.

[0026] The backscattering coefficient B(f) is a function of the frequency and depth of the ultrasonic signal.

[0027] Preferably, the expression for the amplitude of the RF data spectrum after logarithmic transformation is as follows:

[0028]

[0029] Where, α k Let μ be the attenuation coefficient of the medium corresponding to the k-th layer segment. l The frequency dependence of the backscattering coefficient of the l-th layer segment.

[0030] Preferably, the attenuation characteristics of the propagation medium region are calculated using the following method:

[0031]

[0032] Among them, W i Let I and λ be matrices. i For regularization parameters, A = [A(f1), ..., A(f...] ]N )] T .

[0033] Preferably, the optimal emitted sound pressure value update method is as follows:

[0034] The total attenuation value of the ultrasonic signal is calculated based on the depth information and attenuation characteristics of the propagation medium. The optimal transmitted sound pressure P0 is then updated based on the total attenuation value to obtain the updated optimal transmitted sound pressure P1.

[0035] A system for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation includes,

[0036] The model building module is used to obtain the results of the subharmonic amplitude assisted pressure measurement experiment under the optimal emission sound pressure conditions, and to obtain the relationship model between blood pressure value and subharmonic amplitude.

[0037] The experimental module is used to obtain the experimental results of the subharmonic amplitude-assisted pressure measurement experiment of real blood vessels under optimal transmitted sound pressure conditions, and to determine the radio frequency data of the propagation medium region based on the experimental results.

[0038] The attenuation characteristic module is used to process the radio frequency data in the propagation medium region using an attenuation estimation algorithm to obtain the attenuation characteristics of the propagation medium region for ultrasonic signals.

[0039] The update module is used to update the optimal emitted sound pressure based on the attenuation characteristics;

[0040] The pressure measurement module is used to obtain the microbubble subharmonic amplitude of the target blood vessel under the updated optimal emitted sound pressure value, and to compensate for the microbubble subharmonic amplitude through attenuation characteristics. The blood pressure value of the target blood vessel is determined by using the relationship model between the compensated microbubble subharmonic amplitude blood pressure value and the subharmonic amplitude.

[0041] Compared with the prior art, the present invention has the following beneficial technical effects:

[0042] This invention provides a subharmonic amplitude blood pressure measurement method based on least squares attenuation compensation. It combines the attenuation characteristics of the ultrasound signal in the propagation medium with subharmonic amplitude-assisted pressure measurement. An attenuation estimation algorithm estimates the attenuation characteristics of the propagation medium, and the emitted sound pressure is corrected based on these attenuation characteristics to place the microbubble in the optimal sound field, achieving optimal measurement accuracy and sensitivity. Under the corrected emitted sound pressure, the subharmonic amplitude of the microbubble is compensated for by the medium's attenuation characteristics to counteract the medium's influence on signal attenuation. This method enables the use of the same pressure measurement model to measure blood pressure at different sites, significantly improving the universality of subharmonic amplitude-assisted pressure measurement. It allows for non-invasive measurement of blood pressure in vivo, solving the problem of requiring pre-measurement model establishment in previous subharmonic amplitude-assisted pressure measurement methods. This improves the universality of the pressure measurement model and promotes the development of subharmonic amplitude-assisted pressure measurement in clinical applications. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the in vitro experimental device based on microbubble subharmonic amplitude-assisted pressure measurement according to the present invention.

[0044] Figure 2 This is a flowchart of the subharmonic amplitude-assisted blood pressure measurement method based on attenuation compensation according to the present invention.

[0045] Figure 3 This is a schematic diagram of the subharmonic amplitude-assisted blood pressure measurement based on attenuation compensation according to the present invention.

[0046] In the diagram: 1-Verasonics Vantage 256 system; 2-Injection pump; 3-Digital pressure gauge; 4-Hydraulic measuring probe; 5-Acrylic water tank; 6-Blood vessel phantom; 7-Ultrasound probe; 8-Peristaltic pump; 9-Magnetic stirrer; 10-Wide-mouth bottle; 11-Blood vessel; 12-Microbubble solution; 13-Soft tissue. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings. These descriptions are intended to explain the invention and not to limit it.

[0048] See Figure 2 A method for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation includes the following steps:

[0049] Step 1: Using water as the propagation medium, change the transmitted sound pressure and pulse length to acquire channel radio frequency data and image data. Determine the vascular phantom region based on the image data. Extract the subharmonic amplitude from the radio frequency data corresponding to the vascular phantom region and evaluate the acoustic parameters in combination with the real hydraulic pressure value. Determine the optimal acoustic parameters for the experiment and record the pressure measurement model corresponding to the optimal acoustic parameters.

[0050] S1.1 Construct a closed-loop subharmonic amplitude auxiliary pressure measurement platform:

[0051] See Figure 1 The subharmonic amplitude-assisted pressure measurement platform includes a Verasonics Vantage 256 system 1, an injection pump 2, a digital pressure gauge 3, a hydraulic measurement probe 4, an acrylic water tank 5, a vascular phantom 6, an ultrasound probe 7, a peristaltic pump 8, a magnetic stirrer 9, and a wide-mouth bottle 10.

[0052] Ultrasound probe 7 is connected to Verasonics Vantage 256 and System 1 via an interface. Verasonics Vantage 256 System 1 allows for setting ultrasound transmission signal parameters. A 6mm inner diameter latex tube serves as a vascular phantom. Ultrasound probe 7 is placed vertically above the vascular phantom 6, ensuring vertical transmission and reception of the ultrasound signal. The vascular phantom 6 is connected to a peristaltic pump 8 and a wide-mouth bottle 10 at its two ends. The peristaltic pump 8 controls the flow rate of the microbubble solution 12 in the closed system by controlling the pump's rotation speed; the flow rate is 200mL / min. A syringe pump 2 is connected between the vascular phantom 6 and the wide-mouth bottle 10 via a three-way switch. The syringe pump 2 injects microbubble solution 12 into the closed space at a rate of 0.035mL / min. The microbubble solution is used to increase the hydraulic pressure value; the connection between the blood vessel phantom 6 and the injection pump 2 is made to the hydraulic measurement probe 4 via a switch tee, and the hydraulic measurement probe 4 is connected to the digital pressure gauge 3 to display the hydraulic pressure value on the screen of the digital pressure gauge 3 in mmHg; the wide-mouth bottle 10 is placed on the magnetic stirrer 9, and the other end is connected to the peristaltic pump 8. The rotation of the magnetic rotor inside the wide-mouth bottle 10 maintains the uniformity of the microbubble solution; physiological saline is filled into the plexiglass water tank 5, and the entire system is connected by latex tubing. The microbubble solution is placed in the wide-mouth bottle 10, and the peristaltic pump 8 makes the microbubble solution flow throughout the closed circulation system.

[0053] S1.2. Conduct a harmonic amplitude-assisted pressure measurement experiment based on a set of acoustic parameters to determine the optimal emitted sound pressure corresponding to the set of acoustic parameters.

[0054] Under certain acoustic parameters, a plane wave sinusoidal signal with a center frequency of 4MHz and a pulse repetition frequency of 500Hz is emitted through an ultrasound probe to obtain channel radio frequency data and image data. The vascular phantom region is located through the image data. The radio frequency data within the vascular phantom region is Fourier transformed to obtain the radio frequency data amplitude. The subharmonic amplitude is obtained by averaging the radio frequency data amplitude within a 0.4MHz bandwidth centered at 2MHz. Finally, the subharmonic amplitude corresponding to all frames is averaged to obtain the subharmonic amplitude corresponding to this set of acoustic parameters.

[0055] By adjusting the injection pump to change the hydraulic pressure in 20 mmHg increments, from 20 mmHg to 160 mmHg, the relationship between each hydraulic pressure value and the subharmonic amplitude was obtained. The acoustic parameters were evaluated through the linear correlation between the subharmonic amplitude and the actual hydraulic pressure value, as well as the decreasing gradient of the subharmonic amplitude as the hydraulic pressure increased. A larger linear correlation and a steeper decreasing gradient corresponded to better parameter values. While ensuring optimal parameters, the shortest possible pulse length was selected. Under a 20 mmHg hydraulic environment, the emitted sound pressure was varied from low to high, and the corresponding microbubble subharmonic amplitudes were recorded. A curve showing the relationship between emitted sound pressure and subharmonic amplitude was plotted, fitted with a Logistic equation, and the optimal emitted sound pressure was selected based on the type of microbubble.

[0056] For example, if the microbubble type used is Sonazoid, the optimal emission sound pressure level corresponds to the point where the second derivative of the curve is 0 (the inflection point). If the microbubble type used is SonoVue, the optimal emission sound pressure level corresponds to the starting point of the flattened segment in the latter half of the curve.

[0057] S1.3 Under optimal sound pressure conditions, conduct subharmonic amplitude-assisted pressure measurement experiments with different hydraulic values ​​to obtain the relationship model between hydraulic value and subharmonic amplitude, and establish the optimal pressure measurement model under optimal acoustic parameters.

[0058] The optimal transmitted sound pressure was used to set the pressurization parameters on the Verasonics Vantage 256 system platform. Signal transmission and reception were performed via an ultrasound probe. The hydraulic pressure was adjusted by an infusion pump according to the values ​​displayed on the hydraulic measurement probe screen, with a step size of 20 mmHg. The hydraulic pressure gradually increased from 20 mmHg to 160 mmHg. Subharmonic amplitude was calculated using the same subharmonic amplitude extraction method as in S1.2, obtaining the correspondence between the actual hydraulic pressure value and the subharmonic amplitude. A first-order linear fit was performed using the least squares method to obtain the conversion model between subharmonic amplitude and blood pressure value, which was then used as the optimal pressure measurement model.

[0059] Subharmonic(dB)=A*Pressure(mmHg)+B

[0060] Wherein, Subharmonic is the subharmonic amplitude of the simulated vascular region in dB, Pressure is the hydraulic pressure of the environment in which the microbubbles are located in mmHg, A is the slope of the conversion relationship between subharmonic amplitude and blood pressure, and B is the intercept of the conversion relationship between subharmonic amplitude and blood pressure.

[0061] Step 2, refer to Figure 3 The position of the ultrasound probe is fixed, and the ultrasound signal is emitted based on the optimal emission sound pressure determined in step 1. Radiofrequency data and image data of each channel of the real blood vessel 11 after injection of ultrasound microbubble solution are obtained, and the blood vessel area and the propagation medium area are determined based on the image data.

[0062] S2.1. Place the probe as perpendicular as possible to the blood pressure flow direction in the blood vessel, and keep the probe position unchanged in subsequent experiments. Set the parameters on the Verasonics Vantage 256 system platform, emit an ultrasound signal at the optimal transmission sound pressure, and acquire channel radio frequency data and image data.

[0063] S2.2. Based on the image data, the real blood vessel area and the propagation medium area are calibrated, and the sampling points are converted on the channel radio frequency data according to the sampling rate and sound velocity combined with the calibrated area coordinates to determine the start and end points of the radio frequency data of the propagation medium area, as well as the start and end points of the corresponding radio frequency data of the real blood vessel area.

[0064] Step 3: After beamforming the radio frequency data of each channel, the beamformed radio frequency data matrix is ​​processed by an attenuation estimation algorithm in combination with the propagation medium region selected in Step 2 to obtain the attenuation characteristics of the propagation medium for the ultrasonic signal.

[0065] S3.1 After beamforming the radio frequency data of each channel, extract the radio frequency data within the range of the start and end points of the radio frequency data in the propagation medium region.

[0066] Because the image displayed by the Verasonics Vantage 256 system platform is the result of B-mode imaging of beam-synthesized radio frequency data, there will be no deviation that affects the results.

[0067] Step 3.2: Based on the extracted radio frequency data of the propagation medium region and combined with the following attenuation estimation algorithm, determine the attenuation characteristics of the propagation medium region for the ultrasonic signal.

[0068] After ultrasound waves are emitted by an ultrasonic probe and propagate through a scattering medium, the radio frequency (RF) signal data received by the probe is the result of the combined effects of electrical excitation, transducer effect, diffraction effect, attenuation characteristics of the propagation medium, and scattering characteristics. Therefore, the expression for the RF signal spectral amplitude is determined based on the transducer effect, diffraction effect, attenuation characteristics of the propagation medium, and scattering characteristics.

[0069] |S(f,z)|=|P(f)|D(f,z)A(f,z)B(f)

[0070] Where |S(f,z)| represents the amplitude of the radio frequency signal spectrum, f and z represent the frequency and depth, |P(f)| represents the combined effect of electrical excitation and transducer effect, D(f,z) represents the diffraction effect, A(f,z) represents the cumulative attenuation, and B(f) represents the backscattering coefficient.

[0071] The spectrum measured using a pulse echo reflector is multiplied by an unknown gain calibration factor to replace |P(f)|:

[0072]

[0073] Ultrasonic signals exhibit exponential attenuation during propagation. Since the echo signal received by the probe undergoes two rounds of attenuation by the medium, and in the case of soft tissue (13), the attenuation exhibits a linear frequency dependence, combined with depth information, the attenuation coefficient A(f,z) of the medium for the radio frequency signal can be obtained as e. -2α(z)fz The attenuation coefficient exhibits a spatially varying distribution.

[0074] The backscattering coefficient B(f), as a function of frequency and depth, is expressed as follows:

[0075] B(f)=B′0(z)f μ(z)

[0076] Substitute the cumulative attenuation A(f,z) and backscattering coefficient B(f) into the expression for the RF signal spectral amplitude |S(f,z)| and perform a logarithmic transformation to obtain the transformed RF signal spectral amplitude.

[0077]

[0078] Considering plane wave propagation, the diffraction effect D(f,z) can be ignored, i.e., D(f,z) is approximately equal to 1. The propagation medium region whose attenuation characteristics are to be estimated is divided into L segments, each with a thickness of z. The RF signal of the l-th segment is affected by the attenuation characteristics of the media corresponding to the previous l segments and the scattering characteristics corresponding to the l-th segment. The expression for the amplitude of the converted RF signal spectrum is as follows:

[0079]

[0080] In the above formula, α k Let μ be the attenuation coefficient of the medium corresponding to the k-th layer segment, where k ranges from 1 to l. l The frequency dependence of the backscattering coefficient of the l-th layer segment.

[0081] The expression for the converted RF signal spectrum amplitude is simplified based on the difference Q(f, z) between the RF signal spectrum amplitude corresponding to different depths and frequencies and the spectrum measured by the pulse echo reflector.

[0082] make (B0) l =G(B′0) l Substituting these values ​​simplifies the model to:

[0083] Q(f,z)=ln|(B0) l |-2α1fz-2α2fz-…-2α l-1 fz-2α1f(z l -(l-1)z)+μ l lnf

[0084] By changing the depth and frequency values, an expression as shown above can be obtained at different depths z and frequency values ​​f. By superimposing the equations corresponding to L slices and N frequency points, and extracting the parameters, the above expression can be rearranged into the matrix calculation formula shown below:

[0085] q=Aθ

[0086] Where θ = [ln|(B0)1|, ..., |(B0)] L |,α1…α L μ1, ..., μ L ] T

[0087] q=[Q(f1,z1)…Q(f1,z L ), Q(f2, z1)…Q(f2, z L ), ..., Q(f N ,z1)…Q(f N , z L )] T

[0088] A = [A(f1), ..., A(f2)] N )] T

[0089]

[0090] Where q and A are known parameters, and θ is the parameter to be determined, which includes the attenuation coefficient α of the medium.

[0091] The amplitude of the simplified radio frequency signal spectrum is solved by using the least squares method combined with Tikhonov regularization to obtain the attenuation characteristics of the ultrasonic signal in the propagation medium region.

[0092] The simplified RF signal spectral amplitude is solved by minimizing the least squares error using the least squares method. Assuming the dielectric attenuation coefficient exhibits a smooth spatial variation, a suitable Tikhonov regularization term enforces this continuity. The resulting optimization problem is shown below, with the parameter θ that minimizes the following equation being the estimated parameter.

[0093]

[0094] Where, λ i The regularization parameter must be a positive value, i.e., λ. i >0. W i Let I be the identity matrix, a square matrix with all elements equal to 1 on its diagonal from the top left to the bottom right. Γ1 = [Δ0 0], Γ1 = [0Δ0], Γ1 = [0 0Δ], where Δ is shown below:

[0095]

[0096] By simplifying the formula, the above optimization problem has a closed-form optimal solution, which is the expression for the attenuation characteristics of the ultrasonic signal in the propagation medium region:

[0097]

[0098] Step 4: Calculate and update the optimal transmitted sound pressure value (P1) based on the attenuation characteristics and the optimal transmitted sound pressure value (P0) determined in Step 1.

[0099] The local attenuation coefficient values ​​can be determined based on the attenuation characteristic θ obtained in step 3.2: α1,…α L The total attenuation α of the ultrasound signal is obtained by combining the depth information of the propagation medium in the image data. tol ;

[0100]

[0101] Combining the optimal emitted sound pressure P0 and total attenuation α determined in step 1 tol The optimal transmitted sound pressure level is updated, and the updated optimal transmitted sound pressure level P1 is as follows:

[0102] P1 = P0 / α tol

[0103] Step 5: Based on the updated optimal transmitted sound pressure value (P1), conduct a subharmonic amplitude-assisted pressure measurement experiment to obtain channel radio frequency data.

[0104] Step 6: Perform beamforming on the channel RF data and calculate the microbubble subharmonic amplitude of the simulated blood vessel region.

[0105] Step 7: Compensate the microbubble subharmonic amplitude calculated in Step 6 according to the attenuation characteristics to obtain the compensated microbubble subharmonic amplitude.

[0106] A1=A0 / α tol

[0107] Where A1 is the compensated microbubble subharmonic amplitude, and A0 is the microbubble subharmonic amplitude obtained in step 6.

[0108] Step 8: Substitute the microbubble subharmonic amplitude A1 after compensation in Step 7 into the conversion relationship model between subharmonic amplitude and blood pressure value in Step 1 to calculate the corresponding pressure value.

[0109] When measuring the target human body, in step 5, the RF data within the patient's blood vessels is extracted for subharmonics. The compensated microbubble subharmonic amplitude is calculated using the compensation formula in step 7. The compensated subharmonic amplitude is then substituted into the optimal pressure measurement model in step 1 for conversion to obtain the estimated blood pressure value.

[0110] This invention proposes a subharmonic amplitude blood pressure measurement method based on least squares attenuation compensation. On the basis of the SHAPE method, an attenuation compensation algorithm is introduced to calculate the attenuation characteristics of the ultrasonic signal through the propagation medium path. Based on the attenuation characteristics, the optimal emitted sound pressure of the sound field where the microbubble is located is corrected and the subharmonic amplitude is compensated. By combining the relationship model between blood pressure value and subharmonic amplitude, accurate blood pressure measurement can be achieved.

[0111] This invention also provides a system for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation, comprising:

[0112] The model building module is used to obtain the results of the subharmonic amplitude-assisted pressure measurement experiment under the optimal emission sound pressure conditions using water as a medium, and to obtain the relationship model between blood pressure value and subharmonic amplitude.

[0113] The experimental module is used to obtain the results of subharmonic amplitude-assisted pressure measurement experiments under optimal emission sound pressure conditions using ultrasonic microbubble solution as a medium, and to obtain radio frequency data of the propagation medium region and the simulated blood vessel region.

[0114] The attenuation characteristic module is used to process the radio frequency data in the propagation medium region using an attenuation estimation algorithm to obtain the attenuation characteristics of the propagation medium region for ultrasonic signals.

[0115] The update module is used to update the optimal emitted sound pressure value based on the attenuation characteristics;

[0116] The pressure measurement module acquires the microbubble subharmonic amplitude of the target blood vessel under the updated optimal emitted sound pressure value, and compensates for the microbubble subharmonic amplitude through attenuation characteristics. The compensated microbubble subharmonic amplitude is then substituted into the relationship model between blood pressure value and subharmonic amplitude to determine the blood pressure value of the target blood vessel.

[0117] This invention provides a subharmonic amplitude blood pressure measurement method based on least squares attenuation compensation. First, optimal acoustic parameters are determined and the corresponding pressure measurement model is recorded and stored in a phantom experiment. The optimal transmitted sound pressure is obtained by estimating and compensating for the sound pressure using the estimated medium attenuation coefficient. The transmitted sound pressure is adjusted, and the received radio frequency data is combined with the region of interest to extract the subharmonic amplitude of microbubbles. Then, the subharmonic amplitude is compensated using the attenuation coefficient. The compensated subharmonic amplitude is then used in the pressure measurement model to calculate the blood pressure value. This method eliminates the need to rebuild the pressure measurement model before each measurement, improving the method's universality and promoting its clinical development.

[0118] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for sub-harmonic amplitude blood pressure measurement based on least square attenuation compensation, characterized in that, Includes the following steps: Under optimal sound pressure conditions, the results of subharmonic amplitude-assisted pressure measurement experiments with water as the propagation medium at different pressure values ​​were obtained, and a model relating blood pressure to subharmonic amplitude was derived. Under optimal transmission sound pressure conditions, the experimental results of the subharmonic amplitude-assisted pressure measurement experiment of real blood vessels were obtained, and the radio frequency data of the propagation medium region were determined based on the experimental results. An attenuation estimation algorithm is used to process the radio frequency data in the propagation medium region to obtain the attenuation characteristics of the ultrasonic signal in the propagation medium region. The method for determining the attenuation characteristics is as follows: Logarithmically transform the RF data spectrum amplitude, and then simplify the transformed RF data spectrum amplitude based on the difference between the RF data spectrum amplitude corresponding to different depths and frequencies and the spectrum measured by the pulse echo reflector. The simplified radio frequency data spectrum amplitude model is solved by using the least squares method combined with Tikhonov regularization to obtain the attenuation characteristics of the ultrasonic signal in the propagation medium region. Update the optimal emitted sound pressure based on attenuation characteristics; The subharmonic amplitude of microbubbles in the target blood vessel is obtained under the updated optimal emitted sound pressure value. The subharmonic amplitude of microbubbles is compensated by the attenuation characteristics. The compensated subharmonic amplitude of microbubbles is substituted into the relationship model between blood pressure value and subharmonic amplitude to determine the blood pressure value of the target blood vessel.

2. The method for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation according to claim 1, characterized in that, The method for determining the optimal transmitted sound pressure is as follows: Based on the set acoustic parameters, a harmonic amplitude-assisted pressure measurement experiment was conducted to obtain the subharmonic amplitude corresponding to different pressure values. The relationship curve between the acoustic parameters and the subharmonic amplitude was plotted, and the Logistic equation was fitted to it. The optimal emitted sound pressure was determined according to the type of microbubble.

3. The method for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation according to claim 1, characterized in that, The relationship model between blood pressure value and subharmonic amplitude is expressed as follows: in, The subharmonic amplitude of the vascular region. This is the hydraulic value. Let B be the slope and B be the intercept.

4. The method for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation according to claim 1, characterized in that, The expression for the amplitude of the radio frequency data spectrum is as follows: in, Indicates the amplitude of the radio frequency data spectrum. and Indicates frequency and depth, This represents the combined effect of electrical excitation and transducer effect. Indicates diffraction effect, Indicates cumulative decay. This represents the attenuation coefficient of the ultrasonic signal.

5. The method for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation according to claim 4, characterized in that, The combined effect of electrical excitation and transducer effect It is determined based on the measured spectrum of the pulse echo reflector and the gain calibration factor; Cumulative attenuation of ultrasonic signals by the medium The determination is based on the linear frequency dependence of ultrasonic signal attenuation and depth information; Backscattering coefficient It is a function of the frequency and depth of the ultrasound signal.

6. The method for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation according to claim 1, characterized in that, The expression for the amplitude of the RF data spectrum after logarithmic transformation is as follows: in, Let be the attenuation coefficient of the medium corresponding to the k-th layer segment. For the first Frequency dependence of backscattering coefficients of layer segments.

7. The method for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation according to claim 6, characterized in that, The calculation method for the attenuation characteristics of the propagation medium region is as follows: in, For matrix , For regularization parameters, .

8. The method for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation according to claim 1, characterized in that, The optimal emitted sound pressure value update method is as follows: The total attenuation of the ultrasonic signal is calculated based on the depth information and attenuation characteristics of the propagation medium. The optimal transmitted sound pressure is then determined based on this total attenuation value. Update to obtain the updated optimal transmitted sound pressure level. .

9. A system for measuring subharmonic amplitude blood pressure based on least squares attenuation compensation, characterized in that, include, The model building module is used to obtain the results of subharmonic amplitude-assisted pressure measurement experiments with water as the propagation medium under optimal sound pressure conditions, and to obtain a model of the relationship between blood pressure and subharmonic amplitude. The experimental module is used to obtain the experimental results of the subharmonic amplitude-assisted pressure measurement experiment of real blood vessels under optimal transmitted sound pressure conditions, and to determine the radio frequency data of the propagation medium region based on the experimental results. The attenuation characteristic module is used to process the radio frequency data in the propagation medium region using an attenuation estimation algorithm to obtain the attenuation characteristics of the propagation medium region for ultrasonic signals. The method for determining the attenuation characteristics is as follows: Logarithmically transform the RF data spectrum amplitude, and then simplify the transformed RF data spectrum amplitude based on the difference between the RF data spectrum amplitude corresponding to different depths and frequencies and the spectrum measured by the pulse echo reflector. The simplified radio frequency data spectrum amplitude model is solved by using the least squares method combined with Tikhonov regularization to obtain the attenuation characteristics of the ultrasonic signal in the propagation medium region. The update module is used to update the optimal emitted sound pressure based on the attenuation characteristics; The pressure measurement module is used to obtain the microbubble subharmonic amplitude of the target blood vessel under the updated optimal emitted sound pressure value, and to compensate for the microbubble subharmonic amplitude through attenuation characteristics. The compensated microbubble subharmonic amplitude is then substituted into the relationship model between blood pressure value and subharmonic amplitude to determine the blood pressure value of the target blood vessel.

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