CN104490365A - Method for rebuilding broad-band photo-acoustic image by using narrow-band sensor - Google Patents

Abstract

The invention discloses a method for rebuilding a broad-band photoacoustic image by using a narrow-band sensor. The method comprises the following steps: repeatedly illuminating a target by pulsed light; producing PA (photoacoustic) signals after the target absorbs the light; and using the narrow-band sensor to receiving multiple groups of PA signals. While the target is a high scattering medium, the PA signals are greatly attenuated before reaching the sensor, so the narrow-band PA signals received by the sensor are weak and the signal-to-noise ratio is very low, multiple groups of narrow-band PA signals need to be pre-processed, and the signal-to-noise ratio of the narrow-band PA signals is improved. Because the PA signal spectrum is distributed in 1-50 MHz, the PA signals in different frequency bands respond the different characteristics of the illuminated target, the actually used sensors are the narrow-band, so the received PA signals are narrow-band. In order to receive the board-band PA signals, multiple narrow-band sensors in the different frequency bands are used necessarily, but the actual operation is inconvenient.

Description

A kind of method using narrow sensor to rebuild broadband light acoustic image

Technical field

The present invention relates to Computer Image Processing field, particularly a kind of method using narrow sensor to rebuild broadband light acoustic image.

Background technology

Photoacoustic imaging is a kind of noninvasive imaging technology, combines the advantage of optical imagery and acoustics imaging, penetrates darker, is therefore medically being widely used, such as, is detecting osteoporosis.General step is: pulsed light is radiated in target, and target absorption light produces PA signal, uses sensor to receive PA (Photoacoustic optoacoustic) photoacoustic signal, measures PA signal reconstruction photoacoustic image.PA signal frequency is distributed in 1-50MHz, the different qualities of the illuminated target of PA signal reaction of different frequency bands, the actual sensor used mostly is narrow sensor, therefore wants to absorb the narrow sensor that whole PA signals will use multiple different-waveband, and inconvenience is also unrealistic.

Summary of the invention

Goal of the invention: technical problem to be solved by this invention is for the deficiencies in the prior art, a kind of method using narrow sensor to rebuild broadband light acoustic image is provided, amplitude-frequency characteristic according to narrow sensor becomes broadband signal to arrowband PA (Photoacoustic) signal restoring that sensor absorbs, obtain more target information amount, with the photoacoustic image that broadband P a-signal reconstructs, resolution is high, and quality is good.

In order to solve the problems of the technologies described above, the invention discloses a kind of method using narrow sensor to rebuild broadband light acoustic image, comprising the following steps:

Step one, pulsed light is radiated in target repeatedly, and target absorption light produces PA (Photoacoustic) signal;

Step 2, uses narrow sensor to receive the PA signal of many group arrowbands;

Step 3, to the many groups arrowband PA Signal Pretreatment received, obtains high-quality arrowband PA signal;

Step 4, according to the amplitude-frequency characteristic of narrow sensor, carries out the restoration disposal of lost part frequency spectrum, thus obtains the PA signal in broadband, obtain more target information to pretreated arrowband PA signal;

Step 5, rebuilds photoacoustic image by time delay summation to the broadband P a-signal that step 4 obtains.

Only use single narrow sensor to carry out data acquisition in the present invention, because the amplitude-frequency characteristic of single narrow sensor is identical, the PA signal collected is narrow band signal, and the target information amount comprised is limited, cannot reconstruct desirable photoacoustic image.

In the present invention, preferably, in step one, target Stimulated Light irradiates generation optoacoustic effect repeatedly, meets equation:

${\▿}^{2}p(r,t)-\frac{1}{c^2}\frac{{\∂}^{2}p(r,t)}{{\∂t}^2}=-\frac{\mathrm{\β}}{C_p}\frac{\∂}{\∂t}H(r,t)---\left(1\right)$

Wherein r is the coordinate vector of target, t is the time, and p (r, t) is acoustic pressure, H (r, t) be the heat source function that incident laser excites at imaging region, H (r, t)=A (r) I (t), A (r) is the light absorption distribution of tissue, I (t) is for irradiating light intensity, and β is thermal coefficient of expansion, C _pfor specific heat capacity, c is the experience velocity of sound, and laser is got to target and sensor and started Received signal strength and be almost and carry out simultaneously.

In the present invention, preferably, the sensor adopted in step 2 is a series of narrow sensor of the same amplitude-frequency characteristic of linear array, and there are sound wave lens narrow sensor front end;

The arrowband PA signal that sensor absorbs and the pass of former PA signal are:

g(x,y)＝f(x,y)*h(x,y)+η(x,y) (2)

The arrowband PA signal that g (x, y) sensor receives, the original PA signal of f (x, y), the degenrate function that h (x, y) is narrow sensor, η (x, y) noise signal.

Sound wave lens in step 2 make the ultrasound wave produced through optoacoustic effect have certain convergence effect.Due to the amplitude-frequency characteristic of narrow sensor, the signal received is all arrowband PA signal.But in fact target is high scattering material, PA signal is significantly decayed before arrival sensor, and add the noise of system, the arrowband PA signal that final sensor receives is very faint, and signal to noise ratio is very low, therefore will receive many groups, carries out subsequent treatment.

In the present invention, preferably, described pretreatment, be each group of arrowband PA weak output signal and the low problem of signal to noise ratio that receive for sensor, the interval of each group of arrowband PA signal utilizing sensor to receive has small time delay to process.The each group of arrowband PA signal that tiny time postpones to cause cannot align, the cross correlation between each group of arrowband PA signal is utilized to estimate time delay, the starting point of each group of arrowband PA signal is alignd, carries out superposing, interpolation processing, the sample value of the arrowband PA signal after process becomes intensive.Pretreated meaning is, removes noise, improves the quality of arrowband PA signal.

Specifically comprise:

Utilize two the signal p received ₁(t), p ₂t () cross-correlation function comes to postpone t estimated time _s;

If p ₁(t) and p ₂t () is continuous signal, then cross-correlation function is:

$g\left(t\right)=p_1\left(t\right){*p}_1\left(t\right)=\underset{-\∞}{\overset{+\∞}{\∫}}{p}_1^{*}\left(\mathrm{\τ}\right)p_2(t+\mathrm{\τ})\mathrm{d\τ}---\left(3\right)$

p ₁the complex conjugate of (t), for the convolution algorithm of continuous time, the time coordinate corresponding to g (t) peak value is time delay t _s;

If p ₁(t) and p ₂t () is discrete signal, then cross-correlation function is:

${\hat{R}}_{p_1{p}_2}\left(m\right)=\left\{\begin{array}{cc}\frac{1}{L-\left|m\right|}\underset{s=0}{\overset{L-m-1}{\mathrm{\&Sigma;}}}{p}_1(s+m)p_2\left(s\right)& m\&GreaterEqual;0\\ \widehat{R_{p_1{p}_2}}(-m)& m<0\end{array}\right.---\left(4\right)$

L is signal p ₁(t) and signal p ₂the greatest length of (t), m is discrete sampling time point, for the convolution algorithm of discrete time, time coordinate corresponding to peak value is signal p ₁(t) and signal p ₂t () exists time accurate time delay t _s, f _sampleit is the sample frequency of receiving system;

The arrowband PA signal received is alignd, carries out the arrowband PA signal after interpolation processing for:

$\hat{p}(r,L_{\mathrm{int}})=\frac{1}{N_s}\underset{i=1}{\overset{N_s}{\mathrm{\&Sigma;}}}{p}_{i\_\mathrm{shift}}(r,L_{\mathrm{int}})---\left(5\right)$

L _intthe interpolation length of arrowband PA signal, N _sthe sampling frame number of arrowband PA signal, i value 1 ~ N _s, p _{i_shift}(r, L _int) be displacement after arrowband PA signal, finally, N group signal after treatment, the PA signal obtained

$\hat{p}(r,n)=\hat{p}(r,L_{\mathrm{int}}){|}_{L_{\mathrm{int}}=\mathrm{nN}}---\left(6\right)$

N is discrete sampling time point.

In the present invention, preferably, described restoration disposal is the problem that the target information amount contained for arrowband PA signal packet cannot reconstruct desired light acoustic image very little, by the method for liftering, the PA signal recuperation of arrowband is become the PA signal in broadband, obtain more information about target.Process there being the arrowband PA signal of better quality after pretreatment by receiving sensor degenrate function and noise statistics feature two aspects, recover the frequency spectrum of lost part, thus obtain the PA signal in broadband, obtaining more target information amount, preparing for reconstructing satisfied photoacoustic image.

In the present invention, preferably, described method for reconstructing is time delay summation algorithm.In optoacoustic is rebuild, time delay summation algorithm and Inverse Projection are applied more, and backprojection reconstruction algorithm is weighted summation to the time inverse of photoacoustic signal, and time delay summation algorithm is directly sued for peace to photoacoustic signal.Compared to backprojection reconstruction algorithm, time delay summation algorithm has weighted sum to low frequency and high-frequency signal, and contain enough low-frequency information, the image of reconstruction is comparatively smooth.

In the present invention, preferably, after being reconstituted in pretreatment and restoration disposal described in.Pretreated high-quality arrowband PA signal, much noise is removed, the broadband P a-signal after restoration disposal, and the target information amount comprised significantly promotes, and the photoacoustic image reconstructed all is increased significantly in resolution He in picture quality.

Specifically, the inverse process that the process of reconstruction of image is optoacoustic effect described in formula (1), sound pressure signal detected on an array of sensors is:

$p(r_0,t)={\mathrm{\&eta;}\&Integral;\&Integral;\&Integral;d}^3\mathrm{rA}\left(r\right)\frac{{\mathrm{\&delta;}}^{\&prime;}(t-\frac{|r_0-r|}{c})}{4\mathrm{\&pi;}|r_0-r|}---\left(7\right)$

Wherein η=β/C _p, r ₀the coordinate vector of sensor, | r ₀-r| is the distance that reconstruction regions arrives sensor, and δ ' is the derived function of the delta-function that laser pulse produces, and namely the inverse process of said process is process of reconstruction, and method for reconstructing calculates according to formula (8):

for the effective aperture of sensor, when linear sensor, the approximate time delay summation algorithm by formula (9) of this absorption distribution is obtained:

$A\left(r\right)=\frac{{\mathrm{\&Sigma;}}_{k}w(k,r)p_k(r,t+T(k,r))}{{\mathrm{\&Sigma;}}_{k}w(k,r)}---\left(9\right)$

Wherein k represents sensor, and w (k, r) represents weight, and T (k, r) is the time from position r to sensor k, p _kultrasonic signal sequence received by sensor k;

Postpone summation to low frequency and high-frequency signal all weighted sums, the image smoothing obtained.

The present invention carries out the restoration disposal of lost part frequency spectrum to pretreated arrowband PA signal, recovers the PA signal in broadband.Broadband light acoustic image is rebuild subsequently based on this broadband P a-signal.A kind of method using narrow sensor to rebuild broadband light acoustic image disclosed by the invention, a kind of method using narrow sensor to rebuild broadband light acoustic image disclosed by the invention, not only can improve imaging resolution, and effectively can improve image quality, widen the range of application of photoacoustic imaging.

Accompanying drawing explanation

To do the present invention below in conjunction with the drawings and specific embodiments and further illustrate, the advantage of above and other aspect of the present invention will become apparent.

Fig. 1 is the schematic diagram that sensor receives many group arrowbands PA signal.

Fig. 2 is present system schematic diagram.

Fig. 3 is flow chart of the present invention.

Detailed description of the invention

As shown in Figure 3, the invention discloses a kind of method using narrow sensor to rebuild broadband light acoustic image, comprise the following steps:

Step one, pulsed light is radiated in target repeatedly, and target absorption light produces PA (Photoacoustic) signal;

Step 2, uses narrow sensor to receive the PA signal of many group arrowbands;

Step 3, to the many groups arrowband PA Signal Pretreatment received, obtains high-quality arrowband PA signal;

Step 4, according to the amplitude-frequency characteristic of narrow sensor, carries out the restoration disposal of lost part frequency spectrum, thus obtains the PA signal in broadband, obtain more target information to pretreated arrowband PA signal;

Step 5, rebuilds photoacoustic image by time delay summation to the broadband P a-signal that step 4 obtains.

As shown in Figure 2, functional generator sends the Laser output system output pulsed light that laser trigger signal controls fixed wave length on the one hand, and sending signal informs gallery job initiation on the one hand.By fiber-optic illuminated on sample, there is optoacoustic effect in pulsed light, produces sound pressure signal.Sonac receives sound pressure signal, and pass to gallery, gallery is programmed, for computer work.

In the present invention, step one, when sharp target illuminated, produces optoacoustic effect.Target absorption light makes therein temperature change thus causes some regional structure and change in volume, and when using laser pulse repeatedly to irradiate target, the lifting of target inside temperature can cause the harmomegathus of target volume, thus to external radiation PA signal.

In the present invention, step 2, narrow sensor is placed on the position parallel with target, receives PA signal, because target is the medium of high scattering, significantly decayed before PA signal arrives sensor, add the noise of system, the PA signal that sensor is received is very faint, and signal to noise ratio is low, thus to receive several groups, for follow-up pretreatment is prepared more.Due to the spectral characteristic of narrow sensor self, can only receive narrow-band PA signal, other frequency ranges are filtered, and be therefore narrow band signal, quantity of information is limited.The arrowband PA signal that sensor absorbs and the relation of former PA signal are from (1)

g(x,y)＝f(x,y)*h(x,y)+η(x,y) (1)

The arrowband PA signal that g (x, y) sensor receives, the original PA signal of f (x, y), the degenrate function that h (x, y) is narrow sensor, η (x, y) noise signal.Can be found out by formula (1), due to the amplitude-frequency characteristic of narrow sensor, the signal received is arrowband PA signal.

In the present invention, the uncertainty due to system can be found out by the reception of Fig. 1, result in the existence that tiny time postpones.The interval very accurately (max{|T of laser pulse ₁-T ₂| <1ns), life period postpones hardly, but the time delay (max{|T in the time of reception interval of sensor ₃-T ₄| >0.1 μ s) can not ignore.Therefore the many groups arrowband PA signal received cannot align.Utilize the cross correlation of each group of arrowband PA signal, can time delay be estimated, utilize the time delay obtained by each group of signal alignment, and carry out superposing, interpolation operation, obviously make the sample value of arrowband PA signal become intensive, this operation, effectively can remove noise, improve signal quality.The basic thought of correlation estimation delay algorithm utilizes two the signal p received ₁(t), p ₂t () cross-correlation function comes to postpone estimated time.For continuous signal p ₁(t) and p ₂(t), cross-correlation function is:

$g\left(t\right)=p_1\left(t\right){*p}_1\left(t\right)=\underset{-\&infin;}{\overset{+\&infin;}{\&Integral;}}{p}_1^{*}\left(\mathrm{\&tau;}\right)p_2(t+\mathrm{\&tau;})\mathrm{d\&tau;}---\left(2\right)$

p ₁the complex conjugate of (t), t is the time, for the convolution algorithm of continuous time.According to cross-correlation function, the time coordinate corresponding to g (t) peak value is time delay t _s.For discrete signal p ₁(t) and p ₂(t), cross-correlation function is:

${\hat{R}}_{p_1{p}_2}\left(m\right)=\left\{\begin{array}{cc}\frac{1}{L-\left|m\right|}\underset{s=0}{\overset{L-m-1}{\mathrm{\&Sigma;}}}{p}_1(s+m)p_2\left(s\right)& m\&GreaterEqual;0\\ \widehat{R_{p_1{p}_2}}(-m)& m<0\end{array}\right.---\left(3\right)$

L is signal p ₁(t) and signal p ₂the greatest length of (t), m is discrete sampling time point, for the convolution algorithm of discrete time, but signal p can only be obtained by formula (3) ₁(t) and signal p ₂t () exists be receiving system sample frequency) time accurate time delay t _snamely time coordinate corresponding to peak value.

The arrowband PA signal alignment utilizing time delay to make to receive, carries out superposing, interpolation, and the arrowband PA signal after process is:

$\hat{p}(r,L_{\mathrm{int}})=\frac{1}{N_s}\underset{i=1}{\overset{N_s}{\mathrm{\&Sigma;}}}{p}_{i\_\mathrm{shift}}(r,L_{\mathrm{int}})---\left(4\right)$

L _intbe the interpolation length of arrowband PA signal, r is the coordinate vector of target, N _sthe sampling frame number of arrowband PA signal, i value 1 ~ N _s, p _{i_shift}(r, L _int) be displacement after arrowband PA signal.Finally, N group signal after treatment, the PA signal obtained

$\hat{p}(r,n)=\hat{p}(r,L_{\mathrm{int}}){|}_{L_{\mathrm{int}}=\mathrm{nN}}---\left(5\right)$

N is discrete sampling time point.

In the present invention, step 4, if with arrowband PA signal reconstruction photoacoustic image, what obtain is fuzzy and the many image of noise, can not be satisfactory.Fuzzy is because frequency component information is not enough, especially high fdrequency component is lost, the frequency information that narrow sensor filters out by the method for available liftering recovers, liftering is the deconvolution carrying out based on sensor pulse response to signal, can close to primary signal, in the method, signal after liftering is the broadband signal close to original PA signal, but directly liftering is when there being noise jamming, recovery effect is undesirable, and known noise in the entire system cannot be ignored.

Therefore this example adopts the method for Wiener filtering, and Wiener filtering considers degenrate function on the one hand, and consider noise factor on the one hand, compare direct liftering, can recover the broadband P a-signal of better quality, liftering is the special case of Wiener filtering.The broadband P a-signal that Wiener filtering recovers, signal to noise ratio significantly improves, and the quantity of information comprised is closer to the PA signal before sensor filtering, and the PA signal recovered with this carries out photoacoustic image reconstruction, can obtain high-resolution, high-quality image.The target of Wiener filtering is that the signal that makes to recover and original signal mean square error are minimum.The Fourier transformation of the signal recovered obtained is provided by following formula (6):

$\hat{F}(u,v)=\left[\frac{1}{H(u,v)}\frac{{\left|H(u,v)\right|}^2}{{\left|H(u,v)\right|}^2+K}\right]G(u,v)---\left(6\right)$

The conversion that H (u, v) is transfer function, H ^*(u, v) is the complex conjugate of H (u, v);

G (u, v) is the conversion of the image that step 3 obtains;

it is the conversion recovering signal;

|H(u,v)| ²＝H ^*(u,v)H(u,v)；

K is a constant;

In this example, Wiener filtering is the deconvolution carrying out based on sensor amplitude-frequency characteristic to signal, and therefore the transfer function of Wiener filter is exactly the transfer function of narrow sensor, and K gets 10dB.Noise factor is white noise, and white noise is the noise that power is equal in each frequency range, because the bandwidth of narrow band signal that the bandwidth of noise receives much larger than narrow sensor, so by system noise as white noise process.With these two parameters, the broadband signal that the signal of Wiener filtering after Wiener filtering process significantly reduce for noise is carried out to signal, it is abundanter that the target information amount that broadband signal comprises compares signal before treatment, can reconstruct gratifying high-resolution, high-quality photoacoustic image based on this.

In the present invention, step 5, the signal reconstruction photoacoustic image recovered by step Wiener filtering.This example have employed and postpones summation reconstruction photoacoustic image.The process of reconstruction of image is the inverse process of optoacoustic effect, and sound pressure signal detected on an array of sensors is

$p(r_0,t)={\mathrm{\&eta;}\&Integral;\&Integral;\&Integral;d}^3\mathrm{rA}\left(r\right)\frac{{\mathrm{\&delta;}}^{\&prime;}(t-\frac{|r_0-r|}{c})}{4\mathrm{\&pi;}|r_0-r|}---\left(7\right)$

Wherein η=β/C _p, β is thermal coefficient of expansion, C _pbe specific heat capacity, A (r) is reconstruction regions light absorption distribution, r ₀the coordinate vector of sensor, | r ₀-r| is the distance that reconstruction regions arrives sensor, and δ ' is the derived function of the delta-function that laser pulse produces.Namely the inverse process of said process is process of reconstruction, and method for reconstructing is provided by formula below

for the effective aperture of sensor, c is the experience velocity of sound being generally used for rebuilding, value 1.48mm/ μ s in laboratory.When linear sensor, this absorption distribution can be similar to be obtained by time delay summation algorithm

$A\left(r\right)=\frac{{\mathrm{\&Sigma;}}_{k}w(k,r)p_k(r,t+T(k,r))}{{\mathrm{\&Sigma;}}_{k}w(k,r)}---\left(9\right)$

Wherein k represents sensor, and w (k, r) represents weight, and T (k, r) is the time from position r to sensor k, p _kultrasonic signal sequence received by sensor k.

Postpone summation to low frequency and high-frequency signal all weighted sums, the image smoothing obtained, can disclose the internal structure of image.

In the present invention, whole flow process, comprises the steps:

Step one, pulsed light is radiated in target repeatedly, and target absorption light produces PA (Photoacoustic) signal;

Step 2, uses narrow sensor to receive the PA signal of many group arrowbands;

Step 3, to the many groups arrowband PA Signal Pretreatment received, obtains high-quality arrowband PA signal;

Step 4, according to the amplitude-frequency characteristic of narrow sensor, carries out the restoration disposal of lost part frequency spectrum, thus obtains the PA signal in broadband, obtain more target information to pretreated arrowband PA signal;

Step 5, rebuilds photoacoustic image by time delay summation to the broadband P a-signal that step 4 obtains.

In whole flow process, step one, pulsed light irradiates target repeatedly, and the gradient of temperature of target can cause the harmomegathus of volume, gives off PA signal, and PA signal contains abundant target internal information, and frequency spectrum is at 1-50MHz.

In whole flow process, step 2, due to the amplitude-frequency characteristic of narrow sensor, can to PA signal filtering, can only absorption portion frequency range, system noise can not be ignored, see formula (1), independent one group of weak output signal and poor signal to noise, receiving many groups for process afterwards prepares.

In whole flow process, step 3, carries out pretreatment to many groups PA signal that sensor absorbs, utilizes sensor to have time delay, according to the cross correlation of each group of signal, sees formula (3), estimates concrete time delay t _s, then the starting point of each group of signal alignd, carry out superposing, interpolation, the sample value of signal becomes intensive, sees formula (4), (5) eliminate noise like this, improve signal quality.

In whole flow process, step 4, restores pretreated signal Wiener filtering, utilizes formula (6), recovers broadband signal, makes the signal recovered closer to primary signal, comprises the target information of more horn of plenty.

In whole flow process, step 5, rebuilds photoacoustic image to the signal time delay summation after restoring, can obtain smooth image, and can disclose the internal structure of image.Because step 4 has recovered broadband signal, the image after reconstruction and original image are more close, are the high quality graphics of a panel height resolution, high-contrast.

The invention provides a kind of method using narrow sensor to rebuild broadband light acoustic image; the method and access of this technical scheme of specific implementation is a lot; the above is only the preferred embodiment of the present invention; should be understood that; for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.The all available prior art of each ingredient not clear and definite in the present embodiment is realized.

Claims (6)

1. use narrow sensor to rebuild a method for broadband light acoustic image, it is characterized in that, comprise the following steps:

Step one, pulsed light is radiated in target repeatedly, and target absorption light produces PA signal;

Step 2, the PA signal of the N group arrowband using narrow sensor receiving target to produce;

Step 3, to the many groups arrowband PA Signal Pretreatment received, obtains high-quality arrowband PA signal;

Step 4, according to the amplitude-frequency characteristic of narrow sensor, carries out the restoration disposal of lost part frequency spectrum, thus obtains the PA signal in broadband, get more target information to pretreated arrowband PA signal;

Step 5, rebuilds photoacoustic image by time delay summation to the broadband P a-signal that step 4 obtains.

2. a kind of method using narrow sensor to rebuild broadband light acoustic image according to claim 1, it is characterized in that, in step one, target absorption light produces PA signal and produces optoacoustic effect, meets equation:

${\&dtri;}^{2}p(r,t)-\frac{1}{c^2}\frac{{\&PartialD;}^{2}p(r,t)}{\&PartialD;t^2}=-\frac{\mathrm{\&beta;}}{C_p}\frac{\&PartialD;}{\&PartialD;t}H(r,t)---\left(1\right)$

Wherein r is the coordinate vector of target, t is the time, and p (r, t) is acoustic pressure, H (r, t) be the heat source function that incident laser excites at imaging region, H (r, t)=A (r) I (t), A (r) is the light absorption distribution of tissue, I (t) is for irradiating light intensity, and β is thermal coefficient of expansion, C _pfor specific heat capacity, c is the experience velocity of sound.

3. a kind of method using narrow sensor to rebuild broadband light acoustic image according to claim 1, it is characterized in that, the sensor adopted in step 2 is a series of narrow sensor of the same amplitude-frequency characteristic of linear array, and there are sound wave lens narrow sensor front end;

The arrowband PA signal that sensor absorbs and the pass of former PA signal are:

g(x,y)＝f(x,y)*h(x,y)+η(x,y) (2)

The arrowband PA signal that g (x, y) sensor receives, the original PA signal of f (x, y), the degenrate function that h (x, y) is narrow sensor, η (x, y) noise signal.

4. a kind of method using narrow sensor to rebuild broadband light acoustic image according to claim 3, it is characterized in that, the pretreatment in step 3 comprises:

Utilize two the signal p received ₁(t), p ₂t () cross-correlation function comes to postpone t estimated time _s;

If p ₁(t) and p ₂t () is continuous signal, then cross-correlation function is:

$g\left(t\right)=p_1\left(t\right)*p_1\left(t\right)=\underset{-\&infin;}{\overset{+\&infin;}{\&Integral;}}{p}_1^{*}\left(\mathrm{\&tau;}\right)p_2(t+\mathrm{\&tau;})\mathrm{d\&tau;}---\left(3\right)$

p ₁the complex conjugate of (t), for the convolution algorithm of continuous time, the time coordinate corresponding to g (t) peak value is time delay t _s;

If p ₁(t) and p ₂t () is discrete signal, then cross-correlation function is:

${\hat{R}}_{p_1{p}_2}\left(m\right)=\left\{\begin{array}{cc}\frac{1}{L-\left|m\right|}\underset{s=0}{\overset{L-m-1}{\mathrm{\&Sigma;}}}{p}_1(s+m)p_2\left(s\right)& m\&GreaterEqual;0\\ R_{p_1{p}_2}^{^}(-m)& m<0\end{array}\right.---\left(4\right)$

L is signal p ₁(t) and signal p ₂the greatest length of (t), m is discrete sampling time point, for the convolution algorithm of discrete time, time coordinate corresponding to peak value is signal p ₁(t) and signal p ₂t () exists time accurate time delay t _s, f _sampleit is the sample frequency of receiving system;

The arrowband PA signal received is alignd, carries out the arrowband PA signal after interpolation processing for:

$\hat{p}(r,L_{\mathrm{int}})=\frac{1}{N_s}\underset{i=1}{\overset{N_s}{\mathrm{\&Sigma;}}}{p}_{i\_\mathrm{shift}}(r,L_{\mathrm{int}})---\left(5\right)$

L _intthe interpolation length of arrowband PA signal, N _sthe sampling frame number of arrowband PA signal, i value 1 ~ N _s, p _{i_shift}(r, L _int) be displacement after arrowband PA signal, finally, N group signal after treatment, the PA signal obtained

$\hat{p}(r,n)=\hat{p}(r,L_{\mathrm{int}}){|}_{L_{\mathrm{int}}=\mathrm{nN}}---\left(6\right)$ N is discrete sampling time point.

5. a kind of method using narrow sensor to rebuild broadband light acoustic image according to claim 4, is characterized in that, in step 4, adopts the method for Wiener filtering to carry out image restoration, make the signal that recovers and original signal mean square error minimum.

6. a kind of method using narrow sensor to rebuild broadband light acoustic image according to claim 5, it is characterized in that, the method for reconstructing that step 5 adopts is time delay summation algorithm, the inverse process that the process of reconstruction of image is optoacoustic effect described in formula (1), sound pressure signal p (r detected on an array of sensors ₀, t) be:

$p(r_0,t)=\mathrm{\&eta;}\&Integral;\&Integral;\&Integral;d^3\mathrm{rA}\left(r\right)\frac{{\mathrm{\&delta;}}^{\&prime;}(t-\frac{|r_0-r|}{c})}{4\mathrm{\&pi;}|r_0-r|}---\left(7\right)$

Wherein η=β/C _p, r ₀the coordinate vector of sensor, | r ₀-r| is the distance that reconstruction regions arrives sensor, and δ ' is the derived function of the delta-function that laser pulse produces, and namely the inverse process of said process is process of reconstruction, and method for reconstructing calculates according to formula (8):

for the effective aperture of sensor, when linear sensor, the approximate time delay summation algorithm by formula (9) of this absorption distribution is obtained:

$A\left(r\right)=\frac{{\mathrm{\&Sigma;}}_{k}w(k,r)p_k(r,t+T(k,r))}{{\mathrm{\&Sigma;}}_{k}w(k,r)}---\left(9\right)$

Wherein k represents sensor, and w (k, r) represents weight, and T (k, r) is the time from position r to sensor k, p _kultrasonic signal sequence received by sensor k;

Postpone summation to low frequency and high-frequency signal all weighted sums, the image smoothing obtained.