CN101474079B - Method and device for measuring acoustic impedance of living body based on ultrasound steady state reflection wave - Google Patents

Abstract

The invention relates to a method for measuring the acoustic impedance of an organism based on ultrasound steady state reflected waves, which comprises that (1) multiple frequency continuous baseband signals which are mutually orthometric are structured by using orthogonal frequency division multiplexing modulation mode; (2) an ultrasonic probe sends out the multiple frequency continuous baseband signals; (3) an ultrasound transducer detects reflected state echo signals; and finally the amplitude of reflected waves of a no uniform reflecting interface and phase difference opposite to incident waves are found out by solving equations set. A device realizing the method comprises an ultrasonic probe, a control unit, a transceiving unit, a processing unit and a display element which are respectively connected with the control unit. The ultrasonic probe is connected with the transceiving unit. The processing unit is respectively connected with the transceiving unit and the display element. The method has high calculation accuracy, good anti-interference, good anti-noise capability. Only one probe is needed, thus causing that the cost of development devices is reduced. And the measuring method is simple and can be used in vivo experiment.

Description

Measuring method and device based on the organism acoustic impedance of ultrasound steady state reflection wave

Technical field

The present invention relates to electronic technology and ultrasonic applications technology, specifically be a kind of mutually orthogonal continuous multiple frequency ultrasonic signal of OFDM (OFDM) modulation system structure that utilizes, obtain the measuring method and the device based on the organism acoustic impedance of ultrasound steady state reflection wave of organism different tissues acoustic impedance by the homeostatic reflex echo-signal of measuring this multiple frequency ultrasonic signal.

Background technology

In recent years, ultrasonic technique is particularly being measured human body bone density (bone mineral density) index of correlation, is being determined to be subjected to extensive concern aspect the osteoporosis standard measuring bio-tissue because of low, the no ionizing radiation of expense, easy and simple to handle, advantage such as detection speed carries soon, easily, and has obtained very big progress.Domestic and international existing research and the diasonograph that has gone on the market are all used ultrasonic transmission beam method, utilize ultrasound wave that the feature of material density, structure and material is showed the quality of estimating bone.They with ultrasound wave conduction velocity (SOS) and broadband ultrasonic attenuation (or amplitude fading BUA) as the index of estimating bone state and bone density, and the essential parameter that can't directly obtain reflecting bone mass---acoustic impedance or bone density.

Ultrasound wave conduction velocity (SOS) is one of important parameter of characterising biological tissue acoustic characteristic.In the application of determining osteoporosis, since the anisotropy of spongy bone, the bone trabecular density degree of zones of different, and spacing size, bone density all have very big-difference, thereby can reflect the characteristic of sclerotin with ultrasound transmission velocity (SOS).The research that most of at present relevant ultrasonic transmission beam methods are measured ultrasound wave conduction velocity (SOS) mainly is under isolated condition, and wanting to obtain very high precision in live body (at body) is the comparison difficulty.And the ultrasonic velocity measured value mainly is a structure of measuring bone, can not reflect the content of bone mineral fully.

Ultrasonic when in cancellous bone tissue, propagating, because factors such as the absorption of cancellous bone tissue micro structure, scattering, acoustic beam diffusion, boundary reflection can cause the loss of ultrasonic energy, i.e. ultrasonic attenuation.Different along with spongy bone type and state, the ultrasonic attenuation characteristic there are differences.Broadband ultrasonic attenuation (BUA) is that broad band ultrasonic passes calcaneus with different frequency and measures its net loss value, and because of ultrasonic attenuation almost is the linear function of frequency, its slope is broadband ultrasonic attenuation (BUA).Ultrasonic attenuation is except that having than the substantial connection with supersonic frequency, and it mainly is subjected to the influence of bone density and bone structure.The ultrasonic attenuation of bone is caused by the absorption and the scattering of bone, the bone density height, and ULTRASONIC ABSORPTION is big, and the bone trabecula net distributes closely, thus ultrasonic attenuation (BUA) value is big.When osteoporosis took place, because bone amount and bone density reduce, the bone trabecula net distributed sparse, the cortical bone attenuation, and ULTRASONIC ABSORPTION and scattering reduce, and broadband ultrasonic attenuation (BUA) value then diminishes.

Though the ultrasound wave conduction velocity (SOS) of existing transmission measurement and broadband ultrasonic attenuation (BUA) and bone mineral density have the dependency of height, in this way and device estimate the bone state limitation and deficiency arranged in many aspects:

1) measuring method and the device thereof of existing ultrasound wave conduction velocity (SOS) and broadband ultrasonic attenuation (BUA) have significant limitation.Their measurement must be used two ultrasonic transducers, and this has just brought many shortcomings.Such as, two probes interfaces coupling, two probes are difficult for aiming at fully, and only are applicable to the parallel situation in two surfaces of bone, the angle of the bone of surveying and transducer also can directly have influence on last measurement result.Because when ultrasound wave is propagated in bone, refraction effect can take place if not vertical incidence, the energy ratio that causes entering hyperacoustic energy and incidence wave in the bone at last changes, and influences the accuracy of measured value; So most studies all is to carry out in isolated experiment, in the body experiment, use and be difficult in;

2) in ultrasonic transmission beam method and device thereof, hyperacoustic propagation path is very complicated.Consider the simplest calcaneus measurement situation, a transducers transmit ultrasonic waves signal, after propagating, just arrive the transducer that receives at couplant, muscle, skeleton, muscle, couplant, propagation path therebetween is very complicated, can be subjected to factor affecting such as absorption, scattering, acoustic beam diffusion, boundary reflection, cause the accuracy of measured value to be difficult to be guaranteed.

3) existing ultrasonic transmission measurement must use two ultrasonic transducers (probe), if can then can reduce the cost of diagnostic device with single ultrasonic transducer (probe).

4) existing ultrasonic penetrating apparatus can only be measured ultrasound wave conduction velocity (SOS) and these two parameters of broadband ultrasonic attenuation (BUA), the density degree of sclerotin integral body can only be reflected, and the acoustic impedance parameter or the bone density parameter of spongy bone quality can not be directly reflected comprehensively.And can only measure the parameter of single tissue, so measure when more can not be applied to general organism different tissues acoustic impedance parameter or bone density parameter.

5) existing ultrasonic penetrating apparatus is measured this parameter of ultrasound transmission velocity (SOS), must just can record under the situation of the spread speed of known ultrasound wave in the infantile myasthenia tissue, perhaps in isolated experiment, need known ultrasonic in couplant spread speed and the thickness of sample bone just can record.

6) existing ultrasonic transmission measurement is to adopt continuous emission pulse ultrasonic, because each pulse is a transient wave, the width of each pulse (persistent period) is quite short, causes the detection difficulty that receives transmitted pulse big, omission easily, and be subjected to noise jamming easily.

Summary of the invention

The objective of the invention is at existing method measurement error, limitation is big, can not record essential parameter's (acoustic impedance or density) of reflection bio-tissue density, and each needs a probe transmitting-receiving, defectives such as cost height, a kind of measuring method of the organism acoustic impedance based on ultrasound steady state reflection wave is provided, obtain organism different tissues acoustic impedance by the homeostatic reflex echo-signal of measuring this multiple frequency ultrasonic signal, this method utilizes OFDM (OFDM) modulation system to construct mutually orthogonal continuous multiple frequency ultrasonic signal, obtains the acoustic impedance of organism different tissues by the homeostatic reflex echo-signal of measuring this multiple frequency ultrasonic signal.Computational accuracy height of the present invention, anti-interference is good, and anti-noise ability is strong, and measuring only needs a probe to make the cost of development equipment reduce, and measuring method is simple, is used in the body experiment.

The present invention also aims to provide the measuring device of realizing described method based on the organism acoustic impedance of ultrasound steady state reflection wave.

Organism acoustic impedance measurement method based on ultrasound steady state reflection wave of the present invention comprises the steps:

(1) utilize the mutually orthogonal continuous baseband signal of multifrequency of OFDM (OFDM) modulation system structure, and (carrier frequency is f with ultrasonic carrier _c) the continuous baseband signal of this multifrequency is modulated to multiple frequency ultrasonic transmits continuously;

(2) ultrasound probe transmits this multiple frequency ultrasonic continuously and sends, and is equivalent to send multichannel single-frequency ultrasonic continuous signal, and each road signal all can have reflection through each heterointerface of bio-tissue;

(3) the ultrasonic probe detection of reflected stable-state echo signal of returning, this echo-signal is equivalent to the superposed signal of multipath reflection ripple; This superposed signal obtains the continuous baseband signal of multifrequency that receives after demodulation, the continuous baseband signal of this multifrequency is carried out quadrature decomposes, utilize signal orthogonal each other characteristic in every road to decomposite every road received signal, list about the amplitude of each heterointerface echo with respect to the equation group of the phase contrast of incidence wave; Obtain inhomogeneous reflecting interface reflection wave amplitude by the group of solving an equation at last and with respect to the phase contrast of incidence wave.Obtain the parameters such as acoustic impedance, density, thickness of the every layer tissue of organism successively by the reflection of each heterointerface place, the law of refraction.

The device that is used for said method comprises ultrasound probe, control unit and the Transmit-Receive Unit that is connected with control unit respectively, processing unit and display unit, and ultrasound probe links to each other with Transmit-Receive Unit, and processing unit also is connected with display unit with Transmit-Receive Unit respectively;

Control unit comprises Man Machine Interface, by the operator according to actual needs selection operation control Transmit-Receive Unit, processing unit and display unit;

Transmit-Receive Unit is passed to ultrasound probe and is sent a ultrasound wave by driving signal, and ultrasound probe also sends the echo-signal of receiving to Transmit-Receive Unit;

The ultrasonic carrier that processing unit generation continuous baseband signal of multifrequency quadrature and modulation are used obtains multiple frequency ultrasonic and transmits continuously, and sends to Transmit-Receive Unit after the modulation; Also receive the continuous echo-signal of multiple frequency ultrasonic that Transmit-Receive Unit is beamed back, and demodulation, digital signal is sampled, is quantized into to the continuous baseband signal of the multifrequency that obtains through A/D, doing quadrature then decomposes, list about the amplitude of each interface echo and the equation group of phase place, calculate again ultrasound wave the parameter such as acoustic impedance, density, thickness of the every layer tissue of organism of process;

In the said apparatus, described processing unit comprises digital signal processor, modem, agitator, some frequency dividers and A/D converter, processing unit is finished the work that signal produces and handles: the information that provides according to control unit produces the corresponding continuous baseband signal of multifrequency, and baseband signal becomes ultrasonic signal and passes to Transmit-Receive Unit through modulation; The echo-signal that Transmit-Receive Unit sends is carried out demodulation; With the continuous baseband signal of the multifrequency that demodulates through the A/D sampling, be quantized into digital signal, do quadrature then and decompose, list about the amplitude of each boundary reflection echo with respect to the equation group of the phase contrast of transmitted wave; By the amplitude of each boundary reflection echo of Equation for Calculating with respect to the phase contrast of transmitted wave, obtain the parameters such as acoustic impedance, density, thickness of the every layer tissue of organism more successively by each heterointerface place reflection, the law of refraction.

In the said apparatus, described processing unit comprises three frequency dividers: one of frequency divider control output multiple-frequency signal frequency is used for producing the continuous baseband signal of multifrequency; The ultrasonic CF signal frequency of two control outputs of frequency divider is used for producing the supersonic frequency carrier signal; Three control output A/D sampled clock signal frequencies of frequency divider.The continuous baseband signal of multifrequency is sent to Transmit-Receive Unit by wired or wireless mode after the modulation of supersonic frequency carrier signal, send to ultrasound probe by Transmit-Receive Unit again.

Work process of the present invention is: the instruction that control unit sends according to the operator is sent control corresponding and is given processing unit, processing unit produces specific continuous baseband signal of multifrequency and modulation supersonic frequency carrier signal to this operation immediately, promptly disposes the control parameter of frequency divider 1 (control output multiple-frequency signal frequency), frequency divider 2 (control output supersonic frequency frequency of carrier signal) and frequency divider 3 (control output A/D sampled clock signal frequency).The continuous baseband signal of multifrequency is sent to Transmit-Receive Unit by wired or wireless mode after the modulation of supersonic frequency carrier signal subsequently, sends to probe by Transmit-Receive Unit again.

Transmit-Receive Unit waits for that control unit sends the order that receives echo then, Transmit-Receive Unit is given processing unit after receiving the echo of stable state, processing unit is to the demodulation of stable state echo elder generation, the continuous baseband signal of the multifrequency that obtains demodulating, sample, be quantized into digital signal through A/D, do quadrature then and decompose, list about the amplitude of each boundary reflection echo with respect to the equation group of the phase contrast of transmitted wave.

Obtain inhomogeneous reflecting interface reflection wave amplitude by the group of solving an equation at last and with respect to the phase contrast of incidence wave.Obtain the parameters such as acoustic impedance, density, thickness of the every layer tissue of organism successively according to the reflection of each heterointerface place, the law of refraction.

Compared with prior art, the present invention has the following advantages:

1, the present invention not only can measure the thickness of organism different tissues, can also measure acoustic impedance, the density reflection of different tissues and organize substitutive characteristics, as the more accurate index reference of evaluation of tissue density.

2, certainty of measurement height of the present invention.Overcome deficiency based on transmission measurement based on the acoustic impedance of reflection method for measuring organism different tissues, the operation easily of single probe does not exist two probes to be difficult for aiming at fully and waits the measurement error of being brought.

3, anti-interference of the present invention is good, utilizes every road mutually orthogonal characteristic of signal to eliminate each other interference.And because noise is uncorrelated with every road signal, so can also eliminate effect of noise.

4, because the reflection echo that the present invention receives is a stable state continuous wave, energy stabilization so detect easily, does not need regularly, thereby the error on not existing regularly.

5,,, make cost reduce so the requirement of transducer is reduced because the present invention adopts single probe.The modern society people more and more pay close attention to healthy, disease, and the reduction of cost makes this device be well suited for family, rural area and community medicine and uses.

6, since certainty of measurement of the present invention to be measured environmental effect little, relevant with A/D sample rate, computational accuracy, so can improve sample rate improves certainty of measurement on the one hand, can or send to large-scale datatron the continuous echo storage of the stable state that records on the one hand in addition and handle calculating by network, by increasing that amount of calculation improves the echo amplitude at each interface and with respect to the estimated accuracy of the phase contrast of transmitted wave, obtain more accurate acoustic impedance value, diagnose out trickle pathology conversion, improve diagnostic level.

7, along with the raising greatly of modern processors (datatron) computing ability, find the solution (formula 13) in the signal processing of the present invention or (formula 14) no longer is a difficult problem, so this technology is feasible, and the suitability is strong.

8, measuring method of the present invention is simple and convenient, can be applied to pop one's head in, the occasion of Transmit-Receive Unit and processing unit wired connection and wireless connections.

9, measuring method of the present invention not only can directly apply to and measure the human body bone density singlely, judges whether to suffer from symptoms such as osteoporosis, can also be applied to measure simultaneously medical treatment or other application scenario of the acoustic impedance of a plurality of different tissues.

10, measuring method of the present invention not only can be used for somatometry, can also be used for the measurement of the acoustic impedance (perhaps density) of other organism different tissues.

Description of drawings

Fig. 1 is the structured flowchart of apparatus of the present invention;

Fig. 2 is the structured flowchart during wired working method for the processing unit of device shown in Figure 1 adopts;

Fig. 3 is the structured flowchart during wireless working method for the processing unit of device shown in Figure 1 adopts;

Fig. 4 is the even sketch map of incidence wave, echo, transmitted wave at the interface of the single tissue odds of organism in the embodiment;

Fig. 5 is at the even sketch map of incidence wave, echo, transmitted wave at the interface of a plurality of tissue odds of organism in the embodiment;

Fig. 6 is the transmission of apparatus of the present invention ofdm signal in embodiment and receives sketch map;

Fig. 7 is the sketch map that concerns between the density, acoustic impedance of the common normal structure of human body in the embodiment;

Wherein Fig. 7-a is the explanation sketch map of the density harmony resistance value of the common normal structure of human body;

Fig. 7-b is the sketch map that becomes linear approximate relationship between the density harmony resistance value of the common normal structure of human body;

Fig. 8 is apparatus of the present invention workflow block diagram;

The workflow block diagram that Fig. 9 finds the solution the amplitude and the phase place of each non-homogeneous interface echo for processing unit among Fig. 8.

The specific embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is described further.

As shown in Figure 1, apparatus of the present invention comprise ultrasound probe, control unit, Transmit-Receive Unit, processing unit and display unit.As shown in Figure 2, processing unit comprises digital signal processor (DSP or monolithic processor ARM etc.), modem, agitator, some frequency dividers and analog-to-digital conversion device (A/D).Agitator uses the 20M crystal oscillator, and frequency divider realizes that with phase-locked loop circuit modulator and demodulator realizes that with mlultiplying circuit analog-to-digital conversion device and digital signal processor select for use the dsp chip TMS 320C2812 of a TI to realize.

Ultrasound probe is a ultrasonic transducer, by a kind of piezoelectric, i.e. and piezoelectric ceramics such as Barium metatitanate., lead titanates, lead zirconate titanate compositions such as (PZT).Ultrasound probe is used for contacting with measuring object.Ultrasound probe links to each other with Transmit-Receive Unit, and Transmit-Receive Unit will drive signal and pass to ultrasound wave of ultrasound probe transmission, and ultrasound probe also sends the echo-signal of receiving to Transmit-Receive Unit.

Control unit comprises Man Machine Interface, by the operator according to actual needs selection operation control Transmit-Receive Unit, processing unit and display unit.

The processing unit structure comprises digital signal processor (DSP or monolithic processor ARM etc.), modem, agitator, some frequency dividers and analog-to-digital conversion device (A/D) as shown in Figure 2.Processing unit is mainly finished the work that signal produces and handles: 1) information that gives according to control unit produces the corresponding continuous baseband signal of multifrequency, and baseband signal becomes ultrasonic signal through modulation and gives Transmit-Receive Unit; 2) echo-signal that Transmit-Receive Unit is sent is carried out demodulation; 3) with the continuous baseband signal of the multifrequency that demodulates through the A/D sampling, be quantized into digital signal, do quadrature then and decompose, list about the amplitude of each boundary reflection echo with respect to the equation group of the phase contrast of transmitted wave; Calculate the amplitude of each boundary reflection echo and with respect to the phase contrast of transmitted wave; 4) obtain the parameters such as acoustic impedance, density, thickness of the every layer tissue of organism successively by the reflection of each heterointerface place, the law of refraction.

Display unit is the result after to processing unit processes show intuitively according to the display mode that the operator selects, and offers the operator and observes.

Transmit-Receive Unit and control unit, processing unit have two kinds of connected modes: wired connection and wireless connections mode.In wireless connections mode as shown in Figure 3, control unit, processing unit transmit corresponding information by radio-frequency (RF) receiving and transmission module, and Transmit-Receive Unit also should comprise radio-frequency (RF) receiving and transmission module.

The present invention utilizes the OFDM modulation system to construct mutually orthogonal continuous multiple frequency ultrasonic signal, by detecting the echo-signal of stable state, calculate the amplitude of each boundary reflection echo and with respect to the phase contrast of transmitted wave, then according to the acoustic impedance and the density of the magnitude determinations different tissues of echo.Its principle is as follows:

At first analyze the measuring method of single bio-tissue acoustic impedance.As shown in Figure 4, if (interface J is arranged to single bio-tissue ₁With interface J ₂) surface emitting single-frequency ultrasonic continuous signal s (t)=A ₁Cos (2 π f ₀T), A ₁Be the incident wave amplitude, f ₀It is emission signal frequency.At interface J ₁There is transmitted wave A at the place ₂Cos (2 π f ₀T) enter bio-tissue, echo A is arranged simultaneously ₃Cos (2 π f ₀T) reflect a part that becomes the reception echo.At interface J ₂The place produces reflection echo, and this reflection echo is received on the bio-tissue surface, for

So at interface J ₁The echo-signal that the place obtains

It is that incidence wave is at bio-tissue surface (interface J ₁) echo and see through bio-tissue at first non-uniform dielectric interface (the interface J ₂) both stacks of reflection wave signal, its sketch map is seen Fig. 4.A wherein ₃Be bio-tissue surface (interface J ₁) the reflection wave amplitude, A ₄Be that incidence wave sees through bio-tissue, first non-uniform dielectric interface (the interface J in bio-tissue ₂) reflection echo pass interface J ₁After the amplitude of the echo that obtains,

Be with respect at bio-tissue surface (interface J ₁) phase contrast of the incidence wave located.According to digital signal processing theory, can calculate the phase contrast that transmits and receives signal

For:

(formula 1)

＜, be the cross-correlation operation of two sequences.Order

Remove DC component, then can obtain

(formula 2-1)

(formula 2-2)

$T=\frac{n}{f_0}$ N is a positive integer, and then echo amplitude is: $A_4=2\sqrt{a^{\&prime;2}+{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">b</figure-callout>}}^2}.$ By the signal that measures

Calculated

And A ₄, be easy to calculate A ₃According to Huygen's principle and reflection, the law of refraction, the pass between the acoustic impedances of the power of echo, refracted wave and two tissues is:

$\frac{A_1}{{\mathrm{<figure-callout\; id="3"\; label="A"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">A</figure-callout>}}_3}=\frac{Z_2-Z_1}{{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_1}$ (formula 3)

Z wherein ₁Being the acoustic impedance (if probe directly contacts bio-tissue) of probe or the acoustic impedance (if probe is by couplant contact bio-tissue) of couplant, generally is known, Z ₂It is the acoustic impedance of bio-tissue.So can calculate the acoustic impedance of bio-tissue by (formula 3).Spread speed v in bio-tissue is known when ultrasound wave, and then can calculate the material density of bio-tissue $\mathrm{\&rho;}=\frac{Z}{v}.$

This method can also calculate that the ultrasonic emitting end is promptly popped one's head in by (perhaps couplant) and the distance at the bio-tissue first non-uniform dielectric interface is:

(formula 4)

When measuring a plurality of bio-tissue acoustic impedance, suppose has N non-uniform dielectric interface at this moment, as shown in Figure 5.According to hyperacoustic transmission and principle of reflection, establish the echo-signal that each boundary reflection returns and be

The echo-signal that then receives is

(formula 5)

This equation can't solve the phase contrast of N interface correspondence

In order to solve the phase contrast of N interface correspondence

Amplitude A with echo ₁LA _N, need to construct 2N equation at least.We utilize the principle of OFDM modulation system to construct M mutually orthogonal multiple frequency ultrasonic and transmit continuously, construct 2M equation like this.Need only M 〉=N, just can solve the amplitude A of the echo of each interface correspondence ₁LA _N, utilize the power and two of heterointerface place echo, refracted wave to organize the relation of acoustic impedance then, recursion goes out the acoustic impedance of every layer of bio-tissue, and then calculates the material density of the every layer tissue of organism organism.

The stack that the mutually orthogonal multiple frequency ultrasonic in M road transmits continuously is the continuous baseband signal of multifrequency that needs transmission $s(t,f_0)=\underset{i=1}{\overset{M}{\mathrm{\&Sigma;}}}\cos \left(2\mathrm{\&pi;i}{f}_{0}t\right),$ It can be regarded as the transmission of M road signal, and what each road sent is the signal of a single-frequency, and its principle schematic is seen Fig. 5.Every two paths of signals all is mutually orthogonal, as i road signal cos (2 π if ₀T) and j signal cos (2 π if ₀T), i ≠ j, $T=\frac{1}{{\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">f</figure-callout>}}_0},$ At [0, T] interval quadrature, because $\underset{0}{\overset{T}{\&Integral;}}\cos \left(2\mathrm{\&pi;i}{f}_{0}t\right)\cos \left(2\mathrm{\&pi;j}{f}_{0}t\right)\mathrm{dt}=0.$

The continuous baseband signal of multifrequency $s(t,f_0)=\underset{i=1}{\overset{M}{\mathrm{\&Sigma;}}}\cos \left(2\mathrm{\&pi;i}{f}_{0}t\right)$ After the generation, (carrier frequency is f to choose suitable ultrasonic carrier _c) it is modulated.This is equivalent to each road signal on M road is modulated, and the signal after the modulation becomes multiple frequency ultrasonic and transmits continuously, is sent by Transmit-Receive Unit, and its sketch map is seen Fig. 6.

Each road signal all can have reflection through each heterointerface.Suppose that the baseband signal that the i road sends is cos (2 π if ₀T), the ultrasonic propagation meeting runs into N uneven interface, will receive the superposed signal of N echo (after the demodulation) like this:

(formula 6)

Wherein

Be the echo (after the demodulation) of n heterointerface running into after transmitted wave is launched, A _nBe its amplitude,

It is its phase contrast.

The echo that Transmit-Receive Unit receives is the stack of M road echo, obtains the continuous baseband signal d of multifrequency (t) after demodulation.Ultrasound wave can be sneaked into noise n (t) inevitably when sending, transmit, receiving, so the continuous baseband signal of the multifrequency after the demodulation is

$d\left(t\right)=\underset{j=1}{\overset{M}{\mathrm{\&Sigma;}}}{d}_j\left(t\right)+n\left(t\right)$ (formula 7)

D (t) is done quadrature decompose on [0, T], (formula 7) and i road transmitting baseband signal cos (2 π fi ₀T) on [0, T] interval, ask cross-correlation, then can obtain

$g_{i1}\left(t\right)={\&Integral;}_0^{T}d\left(t\right)\cos \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}$

$={\&Integral;}_0^T\underset{j=1}{\overset{M}{\mathrm{\&Sigma;}}}{d}_j\left(t\right)\cos \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}+{\&Integral;}_0^{T}n\left(t\right)\cos \left(2\mathrm{\&pi;}{f}_{0}t\right)\mathrm{dt}$ (formula 8)

$={\&Integral;}_0^T{d}_i\left(t\right)\cos \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}$

(formula 7) and i road transmitting baseband signal cos (2 π if ₀T) orthogonal signalling sin (2 π if ₀T) on [0, T] interval, ask cross-correlation, then can obtain

$g_{i2}\left(t\right)={\&Integral;}_0^{T}d\left(t\right)\sin \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}$

$={\&Integral;}_0^T\underset{j=1}{\overset{M}{\mathrm{\&Sigma;}}}{d}_j\left(t\right)\sin \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}+{\&Integral;}_0^{T}n\left(t\right)\sin \left(2\mathrm{\&pi;}{f}_{0}t\right)\mathrm{dt}$ (formula 9)

$={\&Integral;}_0^T{d}_i\left(t\right)\sin \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}$

Because every road signal is orthogonal each other, so when i ≠ j, ${\&Integral;}_0^T{d}_j\left(t\right)\cos \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}=0,$ ${\&Integral;}_0^T{d}_j\left(t\right)\sin \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}=0.$ Noise and signal are incoherent, therefore ${\&Integral;}_0^{T}n\left(t\right)\cos \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}=0,$ ${\&Integral;}_0^{T}n\left(t\right)\sin \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}=0.$ So (formula 8) and (formula 9) the 3rd equal sign set up.From here as can be seen, the orthogonal signalling anti-interference is good, and can eliminate noise.(formula 6) substitution (formula 8) and (formula 9), can obtain g _I1(t), g _I2(t) expanded expression:

(formula 10)

By (formula 8) as can be known, d (t) cos (2 π if ₀T) obtain a definite value by integration, promptly $g_{i1}\left(t\right)={\&Integral;}_0^{T}d\left(t\right)\cos \left(2\mathrm{\&pi;i}{f}_{0}t\right)\mathrm{dt}=B_i.$ Order $B_i^{\&prime;}=\frac{{2B}_i}{T},$ Can get

(formula 11)

In like manner can get

(formula 12)

Because become narrow band signal, i.e. a f after the continuous baseband signal process of the multifrequency supersonic frequency carrier modulation _c＞＞f ₀, f _c＞＞Mf ₀Though the frequency difference of every road signal all approaches the supersonic frequency carrier frequency, so the hyperacoustic spread speed in every road is identical, identical in the time delay of identical heterointerface place echo, echo amplitude A is also identical.The M road can obtain 2M equation thus:

(formula 13)

According to the number N of heterointerface is whether known finding the solution of (formula 13) be discussed in two kinds of situation below:

1. the number N of heterointerface is known

If the number N of heterointerface is known, that just constructs M=N the mutually orthogonal continuous baseband signal of multifrequency, constructs 2N equation like this.Solve 2N parameter by 2N equation.

(formula 13) equation group is a Nonlinear System of Equations, and its method for solving has a lot, existing two kinds of method for solving of brief introduction.

Method for solving one: take exhaustive method to find the solution, this method relatively is applicable to the situation that reflecting interface is few.Because hyperacoustic propagation has decay, the echo amplitude at each interface satisfies-1＜A ₁, A ₂, LA _N＜1, and propagation distance is far away more, and phase contrast is big more, so the reflection echo phase contrast at each interface satisfies 0＜Ω ₁＜Ω ₂＜L＜Ω _N＜π.

For example: (0, π) with the interval five equilibrium of π/100,

L,

(0, π) exhaustive inside interval 100 point values, and satisfy Each takes turns computational process: 1)

L,

(0, π) get the value that meets the demands in interval 100 point values; 2)

L,

Value substitution (formula 13), obtain the overdetermination system of linear equations; 3), judge whether this overdetermination system of linear equations exists mathematical solution to the overdetermination Solving Linear.Remove some relevant equations in the overdetermination system of linear equations earlier, find the solution A then ₁, A ₂, LA _NIf there is not mathematical solution in this overdetermination system of linear equations, then epicycle is calculated and is finished; 4) judge the echo amplitude A at each interface asked ₁, A ₂, LA _NWhether satisfy the physics requirement, promptly whether satisfy-1＜A ₁, A ₂, LA _N＜1, if do not satisfy, then can conclude what this was taken turns

L,

Value is incorrect, reselects the computational process that new value is carried out next round.

The method for solving two of (formula 13) equation group: nonlinear equation is converted to the Chebyshev polynomials system of linear equations.Adopt the method need construct M=2N mutually orthogonal multiple frequency ultrasonic continuous signal, obtain 2N equation by the M road:

(formula 14)

0 Chebyshev polynomials T ₀(x)=1, establish Chebyshev polynomials 1 time Then Know M Chebyshev polynomials by Chebyshev polynomials character Then can be converted into the Chebyshev polynomials system of linear equations to (formula 14)

$\left\{\begin{array}{c}{A}_1{T}_1\left(x_1\right)+A_2{T}_1\left(x_2\right)+L+A_N{T}_1\left(x_N\right)={{\mathrm{<figure-callout\; id="1"\; label="B"\; filenames="H2009100364454E00061.png,H2009100364454E00071.png"\; state="\{\{state\}\}">B</figure-callout>}}_1}^{\&prime;}\\ A_1{T}_2\left(x_1\right)+A_2{T}_2\left(x_2\right)+L+A_N{T}_2\left(x_N\right)={{\mathrm{<figure-callout\; id="2"\; label="B"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">B</figure-callout>}}_2}^{\&prime;}\\ M\\ A_1{T}_M\left(x_1\right)+A_2{T}_M\left(x_2\right)+L+A_N{T}_M\left(x_N\right)={B_M}^{\&prime;}\end{array}\right.$ (formula 15)

Can adopt sophisticated numerical computation methods such as Newton method, Saden that to solve A ₁, A ₂, LA _N, x ₁, x ₂, Lx _N, and then solve

L,

2. the number N of heterointerface is unknown

When the number N of inhomogeneous reflecting interface is unknown, then to come N is composed an initial value L according to the inhomogeneous reflecting interface number of practical situation estimation bio-tissue, this value should promptly be L＞N greater than the N value of reality.

If take exhaustive method to find the solution, then construct M=L the mutually orthogonal continuous baseband signal of multifrequency, construct 2M equation (shape is as (formula 13)).This moment, 2M (equation number)＞2N (unknown number number) found the solution this overdetermined equation group, at first needed to remove some redundant equations, promptly was that relevant equation is removed, thereby obtained the number N and a remaining 2N equation of inhomogeneous reflecting interface.To a remaining 2N equation solution, it is identical to take exhaustive method to find the solution when the method for finding the solution is known with N at last.

If take Chebyshev polynomials linear equation group of methods to find the solution,, construct M equation (shape is as (formula 14)) by M=2L mutually orthogonal continuous baseband signal of multifrequency of structure.This moment, M (equation number)＞2N (unknown number number) found the solution this overdetermined equation group, at first needed to remove some redundant equations, promptly was that relevant equation is removed, thereby obtained the number N and a remaining 2N equation of inhomogeneous reflecting interface.To a remaining 2N equation solution, take Chebyshev polynomials linear equation group of methods to find the solution identical when the method for finding the solution is known with N at last.

According to the reflection of Huygen's principle and heterointerface place, the law of refraction, by relation between the power of echo, refracted wave and two acoustic impedances of organizing and the corresponding echo amplitude A in each interface that has solved ₁LA _NWith known probe acoustic impedance (perhaps couplant acoustic impedance) Z ₁, just can recursion go out ultrasound wave the acoustic impedance Z of the every layer tissue of organism of process ₂LZ _N-1(see figure 5):

The first interface J ₁Place: incident wave amplitude a ₁, acoustic impedance Z ₁Known, the amplitude A of first interface echo ₁Find the solution out, by $\frac{a_1}{{\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="H2009100364454E00061.png,H2009100364454E00071.png"\; state="\{\{state\}\}">A</figure-callout>}}_1}=\frac{Z_2-Z_1}{{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="H2009100364454E00061.png,H2009100364454E00071.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}$ Can obtain acoustic impedance Z ₂

Incident wave amplitude a ₁, acoustic impedance Z ₁, Z ₂Known, by $\frac{a_2}{a_1}=\frac{\sqrt{Z_1{Z}_2}}{{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="H2009100364454E00061.png,H2009100364454E00071.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}$ Can obtain the first interface J ₁The transmission wave amplitude a at place ₂

Second contact surface J ₂Place: incident wave amplitude a ₂, acoustic impedance Z ₂Known, second contact surface J ₂The amplitude A of echo ₂Find the solution out, by $\frac{a_2}{{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">A</figure-callout>}}_2}=\frac{Z_3-Z_2}{{\mathrm{<figure-callout\; id="3"\; label="Z"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">Z</figure-callout>}}_3+{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2}$ Can obtain acoustic impedance Z ₃

Incident wave amplitude a ₂, acoustic impedance Z ₂, Z ₃Known, by $\frac{a_3}{a_2}=\frac{\sqrt{Z_2{Z}_3}}{{\mathrm{<figure-callout\; id="3"\; label="Z"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">Z</figure-callout>}}_3+{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2}$ Can obtain the transmission wave amplitude a at second contact surface place ₃

By that analogy, can obtain ultrasound wave the acoustic impedance Z of the every layer tissue of organism of process ₄LZ _N-1, and interface J _N-1The transmission wave amplitude a at place _N-1

The acoustic impedance Z of tissue and density p are physical quantitys important in the ultrasound medicine, the intrinsic propesties of all reflecting tissue, and their pass is Z=ρ v.When the ultrasonic tesint frequency was 1MHz, the density, acoustic impedance, the ultrasonic propagation velocity numerical value that record the common normal structure of human body were as shown in table 1, and wherein the relation of density and acoustic impedance is shown in figure Fig. 7-a and 7-b.

The density of the common normal structure of table 1 human body, acoustic impedance, ultrasonic propagation velocity table (R* (Rayleigh)=G/ (CM ²GS))

Medium	Density (G/CM 3)	Ultrasonic longitudinal wave speed (M/S)	Acoustic impedance (10 5R*)	Test frequency (MHZ)
					Blood	1.055	1570	1.656	1
Soft tissue	1.016	1500	1.524	1
					Muscle	1.074	1568	1.684	1
Bone	1.658	3860	5.571	1
					Fat	0.955	1476	1.41	1
Liver	1.05	1570	1.648	1

Acoustic impedance Z and density p have approximate linear as can be seen from Fig. 7-b, and this relation can be come match with a quadratic polynomial.Because acoustic impedance Z and density p have relation one to one, then by the acoustic impedance Z of the every layer tissue of having obtained of organism ₂LZ _N-1Just can obtain the density p of the every layer tissue of organism ₂L ρ _N-1, and by $v=\frac{Z}{\mathrm{\&rho;}}$ Can also obtain the spread speed v of ultrasound wave in the every layer tissue of organism ₂Lv _N-1

And obtain by solving equation

L,

, the thickness that can also calculate the every layer tissue of organism is:

(formula 16)

In wireless connections mode as shown in Figure 3, processing unit comprises with the identical device circuitry of wired connection mode with Transmit-Receive Unit, and comprises the radio-frequency (RF) receiving and transmission module that is operated in 2.4G.

Job step of the present invention is as shown in Figure 8, and is specific as follows:

Step 1 operator provides operation requests.

Applicating example: starting instrument, select ultrasound wave will check what position of organism or what bio-tissue, is superficial tissue, or deep tissue etc.

Step 2 is worked as the operator has operation requests then to be sent to control unit immediately.After control unit receives request signal, send corresponding control information and give processing unit, Transmit-Receive Unit and display unit.

When control unit control Transmit-Receive Unit sends ultrasonic signal, when receives; Which parameter control unit control display unit will show, adopts which type of concrete display mode.It also mainly is to select corresponding information according to operation requests that control unit is given the information of processing unit, selects to check shallow matrix section that then selecting supersonic frequency is tens, tens MHz as operating unit, if select the deep layer position, then selecting supersonic frequency is about 5MHz.Control unit is determined according to these information or the maximum number N at the non-homogeneous interface of this inspection, the frequency of multifrequency digital orthogonal baseband signal and the ultrasonic carrier frequency of modulation tentatively is set.Give processing unit these relevant informations together then.

Step 3 processing unit disposes each frequency divider control parameter, produces the ultrasonic carrier that multifrequency quadrature continuous signal and modulation are used.The frequency of multifrequency quadrature continuous signal is f ₀Integral multiple, ${\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="H2009100364454E00071.png,H2009100364454E00072.png"\; state="\{\{state\}\}">f</figure-callout>}}_0=\frac{1}{T},$ Time span when T is the quadrature decomposition.The present invention can produce 2N frequency flexibly according to different situations and generate the multifrequency digital orthogonal baseband signal, produces carrier wave according to the carrier frequency of determining then, is used for modulation and demodulation.

The continuous baseband signal of step 4 multifrequency quadrature sends to Transmit-Receive Unit by wired or wireless mode after the supersonic frequency carrier modulation, Transmit-Receive Unit is launched by coupled probe again.

Step 5 Transmit-Receive Unit is sent to processing unit after receiving the echo of stable state, and processing unit demodulates the continuous baseband signal of multifrequency, becomes digital signal after A/D sampling, quantification.Deliver to digital signal processor (DSP) computing then, the sample frequency of A/D is controlled by DSP.

Step 6 Digital Signal Processing computational process, mainly find the solution (formula 13) or (formula 14), obtain each non-homogeneous boundary reflection wave amplitude and with respect to the phase contrast of incidence wave, present embodiment adopts exhaustive method to come solving equation group (formula 13), idiographic flow is referring to Fig. 9.

Digital signal after digital signal processing unit (DSP) transforms A/D is done quadrature and is decomposed, and lists 2N equation.The idiographic flow of finding the solution 2N equation as shown in Figure 9.If not evenly the number N at interface is known, is the equation group of 2N with exhaustive method solving equation number then, obtain the individual non-homogeneous boundary reflection wave amplitude of N and with respect to the phase contrast of incidence wave.If not evenly the number N at interface is unknown, then need earlier the equation group of linear correlation to be removed, obtain the number M and a remaining 2M equation at non-homogeneous interface, make N=M then, the solving equation number is the equation group of 2N, obtains N non-homogeneous boundary reflection wave amplitude and with respect to the phase contrast of incidence wave.In the time of exhaustive according to each non-homogeneous boundary reflection wave amplitude with respect to the qualifications-1＜A of the phase contrast of incidence wave ₁, A ₂, LA _N＜1 and Ω ₁＜Ω ₂＜L＜Ω _NShorten exhaustive computation time.

By calculating each the non-homogeneous boundary reflection wave amplitude obtained and, obtain the parameters such as acoustic impedance, density, thickness of the every layer tissue of organism successively according to each heterointerface place reflection, the law of refraction with respect to the phase contrast of incidence wave.

The result that step 7 pair processing unit obtains: the number at non-homogeneous interface, each non-homogeneous boundary reflection wave amplitude and show at display unit with form intuitively with respect to parameters such as the acoustic impedance of the phase contrast of incidence wave, the every layer tissue of organism, density, thickness, convenient and user alternately.

Claims (4)

1. the organism acoustic impedance measurement method based on ultrasound steady state reflection wave is characterized in that comprising the steps:

(1) utilizes the mutually orthogonal continuous baseband signal of multifrequency of OFDM modulation system structure, and with ultrasonic carrier the continuous baseband signal of this multifrequency is modulated to multiple frequency ultrasonic and transmits continuously;

(2) ultrasound probe transmits this multiple frequency ultrasonic continuously and sends, and is equivalent to send multichannel single-frequency ultrasonic continuous signal, and each road signal all can have reflection through each heterointerface of bio-tissue;

(3) the ultrasound probe detection of reflected stable-state echo signal of returning, this echo-signal is equivalent to the superposed signal of multipath reflection ripple; This superposed signal obtains the continuous baseband signal of multifrequency that receives after demodulation, the continuous baseband signal of this multifrequency is carried out quadrature decomposes, utilize that orthogonal each other characteristic decomposites every road received signal between the signal of every road, list about the amplitude of each heterointerface echo with respect to the equation group of the phase contrast of incidence wave; Obtain the amplitude of heterointerface echo by the group of solving an equation at last and with respect to the phase contrast of incidence wave; Obtain acoustic impedance, density and the thickness parameter of the every layer tissue of organism successively by each heterointerface place reflection, the law of refraction.

2. organism acoustic impedance measurement device of realizing the described method of claim 1 based on ultrasound steady state reflection wave, it is characterized in that comprising ultrasound probe, control unit and the Transmit-Receive Unit that is connected with control unit respectively, processing unit and display unit, ultrasound probe links to each other with Transmit-Receive Unit, and processing unit is connected with display unit with Transmit-Receive Unit respectively;

Control unit comprises Man Machine Interface, by the operator according to actual needs selection operation control Transmit-Receive Unit, processing unit and display unit;

Transmit-Receive Unit is passed to ultrasound probe and is sent a ultrasound wave by driving signal, and ultrasound probe also sends the echo-signal of receiving to Transmit-Receive Unit;

The ultrasonic carrier that continuous baseband signal of multifrequency that the processing unit generation is mutually orthogonal and modulation are used obtains multiple frequency ultrasonic and transmits continuously, and sends to Transmit-Receive Unit after the modulation; Also receive the continuous echo-signal of multiple frequency ultrasonic that Transmit-Receive Unit is beamed back, and demodulation, digital signal is sampled, is quantized into to the continuous baseband signal of the multifrequency that obtains through A/D, doing quadrature then decomposes, list about the amplitude of each interface echo and the equation group of phase place, calculate again ultrasound wave acoustic impedance, density and the thickness parameter of the every layer tissue of organism of process.

3. device according to claim 2, it is characterized in that described processing unit comprises digital signal processor, modem, agitator, some frequency dividers and A/D converter, processing unit is finished the work that signal produces and handles: the information that provides according to control unit produces the corresponding continuous baseband signal of multifrequency, and baseband signal becomes ultrasonic signal and passes to Transmit-Receive Unit through modulation; The echo-signal that Transmit-Receive Unit sends is carried out demodulation; With the continuous baseband signal of the multifrequency that demodulates through the A/D sampling, be quantized into digital signal, do quadrature then and decompose, list about the amplitude of each interface echo with respect to the equation group of the phase contrast of incidence wave; By the amplitude of each interface echo of Equation for Calculating with respect to the phase contrast of incidence wave, obtain acoustic impedance, density and the thickness parameter of the every layer tissue of organism more successively by each heterointerface place reflection, the law of refraction.

4. device according to claim 3 is characterized in that described processing unit comprises three frequency dividers: one of frequency divider control output multiple-frequency signal frequency is used for producing the continuous baseband signal of multifrequency; Two control output ultrasonic carrier signal frequencies of frequency divider, and be used for producing the ultrasonic carrier signal; Three control output A/D sampled clock signal frequencies of frequency divider; The continuous baseband signal of multifrequency is sent to Transmit-Receive Unit by wired or wireless mode after the modulation of ultrasonic carrier signal, send to ultrasound probe by Transmit-Receive Unit again.

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