CN109512389A - Photoacoustic tomography algorithm for reconstructing based on finite size planar transducer - Google Patents
Photoacoustic tomography algorithm for reconstructing based on finite size planar transducer Download PDFInfo
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Abstract
The invention discloses one kind to be based on finite size planar transducer photoacoustic tomography algorithm for reconstructing.In existing photoacoustic tomography algorithm for reconstructing, plane ultrasonic transducer used is usually taken as ideal point energy converter or infinite size planar transducer, but, since the planar dimension of most of ultrasonic transducers in photoacoustic tomography is limited, so off-centered target will obscure in the tangential direction that above two reconstruction model is imaged.A kind of photoacoustic tomography algorithm for reconstructing based on finite size planar transducer proposed by the present invention, relative to existing algorithm, it matches probe size by extending back projection's distance, therefore effectively and rapidly restore the tangential distortion of finite size planar transducer photoacoustic tomography image, improve its tangent resolution, to obtain comprehensive high-resolution photoacoustic tomography result.
Description
Technical field
The present invention relates to photoacoustic tomography technical field, more particularly to a kind of based on finite size planar transducer
Photoacoustic tomography algorithm for reconstructing.
Background technique
Optoacoustic computer assisted tomography technology is that a kind of image contrast for quickly growing in recent years is high, small to human injury
Medical imaging technology.Two-dimensional annular scanning is one of most common implementation in photoacoustic tomography, is widely used to
The visualization of toy cerebrovascular network, the imaging of nude mouse tumor detection and human finger's joint structure.In this scan pattern
Under, (or there are annular arrays to avoid ring for the circular scanning for generalling use plane map sensor to execute around imageable target
Shape mechanical scanning).
Many Considerations of photoacoustic tomography (CSPAT) system design include illumination optical, system compact, cost
Lower, acquisition time is less and geometry constraint conditions of imaging object etc., and picture quality and spatial resolution are still most heavy
The matter of priority wanted；On the one hand, it is risen in the spatial resolution for the image that the distribution of ultrasonic transducer and characteristic obtain in CSPAT
Key effect generallys use macropore in order to ensure energy converter position needed for CSPAT is collected into all supersonic sources in image area
The sensor of diameter or wide receiving angle, having a size of grade.On the other hand, most of algorithm for reconstructing in CSPAT, such as pass
The backprojection algorithm of system, all hypothesis ultrasonic transducers are ideal point or infinite size, in this case, limited in algorithm for reconstructing
Transducer dimensions it is approximate with above two reconstruction model between model mismatch will lead to some rotations of tangential direction in image
Revolving die paste, these spin blurring artefacts are space average of the sound wave in transducer area as caused by limited energy converter aperture
As a result, this causes in the signal detected time of occurrence to trail, this can be converted into space hangover in reconstruction image.Theory point
Analysis shows that, for traditional annular or spherical scanning, the bandwidth of energy converter inherently limits image resolution ratio, and tangentially divides
Resolution with it is directly proportional with a distance from rotation center, and be equal to transducer probe face aperture size.Currently, photoacoustic tomography is ground
Study carefully and developed many advanced algorithms to improve tangent resolution, these algorithms are largely to pass through solution based on model
The geometry of energy converter and other acoustic characteristics are to improve tangent resolution；However, these methods are very complicated, a large amount of numerical value is needed
It is calculated to carry out big matrix.
Summary of the invention
The purpose of the invention is to overcome above-mentioned the shortcomings of the prior art, provide a kind of based on finite size plane
The photoacoustic tomography algorithm for reconstructing of energy converter, should the photoacoustic tomography algorithm for reconstructing phase based on finite size planar transducer
Probe size is matched by extending back projection's distance for existing algorithm, effectively and rapidly restores finite size plane transducing
The tangential distortion of device CSPAT image, improves its tangent resolution, thus obtain comprehensive high-resolution optoacoustic Computerized chromatographic at
As result.
To achieve the goals above, the present invention provides a kind of photoacoustic tomography weight based on finite size planar transducer
Build algorithm, comprising the following steps:
1) imageable target is fixed in annular ultrasonic transducer array, annular ultrasonic transducer array and imageable target it
Between be full of medium water；
2) laser output laser pulse, makes laser pulse uniform irradiation imageable target, and excitation imageable target generates ultrasound
Pulse signal；
3) each practical ultrasonic transducer in annular ultrasonic transducer array starts simultaneously at the practical ultrasound of record arrival and changes
Can device ultrasonic pulsative signal, and ultrasonic pulsative signal is converted to electric signal, receiver, which occurs, by signal to receive
Electric signal amplifies, and is transferred to data collection system and carries out electrical signal collection；The electric signal of acquisition is handled, is obtained
The reconstruction figure of photoacoustic tomography algorithm for reconstructing based on finite size planar transducer；
4) imaging target image is calculated using backprojection algorithmCorresponding i-th of the practical ultrasound of the pixel at place
The signal value Si (t) of energy converter Pi, then imageable target imageThe image value for locating pixel is equal to ring-shaped ultrasonic transducing
Each practical ultrasonic transducer in device array receivesLocate the superposition of the signal value of pixel, i.e.,
Wherein, practical ultrasonic transducer range Imaging target is R, is t, imaging the time required to the ultrasonic pulsative signal received
Target imageThe pixel at place is R (x, y, Pi), imageable target figure at a distance from i-th of practical ultrasonic transducer Pi
PictureThe signal value Si (R (x, y, Pi)/v) of corresponding i-th of the practical ultrasonic transducer Pi of the pixel at place, v is super
The spread speed of sound in the medium；
5) it is L, image that setting the distance between virtual ultrasound energy converter and practical ultrasonic transducer, which is worth, The picture at place
Distance of the vegetarian refreshments apart from virtual ultrasound energy converter is R '=R+L, thenThe image value for locating pixel is virtual equal to each
Ultrasonic transducer receivesLocate the superposition of the signal value of pixel, i.e.,
Wherein, imageThe distance of i-th of virtual ultrasound energy converter Pi ' of pixel distance at place be R ' (x, y,
Pi '), imageable target imageThe signal value of the corresponding practical ultrasonic transducer Pi of the pixel at place becomes Si [(R '
(x,y,Pi′)-L)/v]；
6) by imagePolar coordinates conversion of the pixel at place at a distance from i-th of virtual ultrasound energy converter Pi '
At rectangular co-ordinate, then formula (2) becomes:
Wherein, R is the diameter of practical ultrasonic transducer scanning track, and N is the quantity of practical ultrasonic transducer, Si(t) it is
By the i-th practical ultrasonic transducer received signal value, θiIt is the angular coordinate of i-th of practical ultrasonic transducers locations, v is ultrasound
Spread speed in the medium, R+L are the diameter of virtual ultrasound transducer scans track；
7) according to vector subtraction and range formula, then the image reconstruction algorithm formula of imageable target is as follows:
Wherein, I is imageImage value after place's reconstruction, n are the scan position number of annular ultrasonic transducer array, Si(t)
For the signal value that i-th of practical ultrasonic transducer receives,For the position of i-th of practical ultrasonic transducer, L changes for virtual ultrasound
Energy the distance between device and practical ultrasonic transducer value, v are the spread speed of ultrasound in the medium.
Preferably, in image reconstruction process, spherical scanning is carried out using annular ultrasonic transducer array, in three-dimensional space
In, spherical scanning is made of m two-dimensional surface scanning process, i.e., each a total of n × m scan position of practical ultrasonic transducer,
Then formula (4) becomes:
Wherein, I is imageImage value after place's reconstruction, Si,j(t) the practical ultrasonic transducer for the position (i, j) receives
Signal,For the position of (i, j) a practical ultrasonic transducer, L is between virtual ultrasound energy converter and practical ultrasonic transducer
Distance value, v is ultrasound spread speed in the medium, and n × m is practical ultrasonic transducer number of scan points.
Preferably, laser described in step 2) is pulse laser, the laser pulse wavelength 532nm.
Preferably, the angle spacing between the adjacent practical ultrasonic transducer is 1 degree, the annular ultrasonic transducer
Array is equipped with 360 practical ultrasonic transducers.
Preferably, the electric signal of described pair of step 3) acquisition is handled, and is in conjunction with the MATLAB software journey in computer
The image reconstruction algorithm of sequence application formula (4) executes signal processing and carries out image reconstruction.
Preferably, the electric signal of described pair of acquisition is handled, and is in conjunction with the MATLAB software program application in computer
The image reconstruction algorithm of formula (5) executes signal processing and carries out image reconstruction.
Through the above technical solutions, beneficial effects of the present invention:
(1) most of to use ideal point energy converter or unlimited ruler in the existing photoacoustic tomography based on circular scanning
The model of very little planar transducer is imaged, and easily causes off-centered imageable target image blur in tangential direction.This
Invention successfully overcomes this problem, so that its tangent resolution has obtained greatly by extending virtual transducer distance
It improves；
It (2) is that a kind of model is simple the present invention is based on delay stack algorithm, freedom degree is big, and algorithm stability is very high, and
Calculate simple algorithm；
(3) present invention haves no need to change the structure of existing optoacoustic chromatography probe, is adapted to all ultrasonic transducers
Size.
Detailed description of the invention
Fig. 1 a is schematic diagram of the photoacoustic tomography using the backprojection algorithm of ideal point transducer models；
Fig. 1 b is schematic diagram of the photoacoustic tomography using the backprojection algorithm of infinite size transducer models；
Fig. 1 c is schematic diagram of the photoacoustic tomography using the backprojection algorithm of finite size transducer models；
Fig. 1 d is the imaging process schematic diagram that photoacoustic tomography uses finite size transducer models；
Fig. 2 a is the image that photoacoustic tomography uses ideal point transducer models algorithm for reconstructing to obtain；
Fig. 2 b is the image that photoacoustic tomography uses infinite size transducer models algorithm for reconstructing to obtain；
Fig. 2 c is the image that photoacoustic tomography uses finite size transducer models algorithm for reconstructing to obtain；
Fig. 3 a is three kinds of Model Reconstruction algorithms of photoacoustic tomography lateral contour datagram at away from imageable target center 2mm
Table；
Fig. 3 b is three kinds of Model Reconstruction algorithms of photoacoustic tomography lateral contour datagram at away from imageable target center 4mm
Table；
Fig. 3 c is three kinds of Model Reconstruction algorithms of photoacoustic tomography lateral contour datagram at away from imageable target center 6mm
Table；
Fig. 4 is photoacoustic tomography system schematic.
Description of symbols
1 ideal point energy converter, 2 infinite size energy converter, 3 finite size energy converter
4 virtual ultrasound energy converter, 5 projection line, 6 imageable target
61 point targets
Specific embodiment
Technical solution of the present invention is described in further detail in the following with reference to the drawings and specific embodiments, it is described specific
Embodiment is only explained the present invention, is not intended to limit the invention.
A kind of photoacoustic tomography algorithm for reconstructing based on finite size planar transducer, comprising the following steps:
Imageable target is fixed in annular ultrasonic transducer array, between annular ultrasonic transducer array and imageable target
Full of medium water；
Laser output laser beam simultaneously issues ultrasonic trigger signal；
After laser pulse uniform irradiation imageable target, imageable target absorbs the rapid expanded by heating of light and then shrinks to produce
Raw ultrasonic pulsative signal, ultrasonic pulsative signal start in medium water to fix velocity of sound v and propagate around；
Laser pulse issue moment simultaneously, each practical ultrasonic transducer in annular ultrasonic transducer array is simultaneously
Start recording reaches the ultrasonic pulsative signal of practical ultrasonic transducer；The ultrasonic pulsative signal being collected into is by practical ultrasonic transducer
After being converted to electric signal, receiver is occurred by signal and amplifies the ultrasonic electric signal received, and is transferred to data and adopts
Collecting system carries out ultrasonic signal acquisition；
It (is used in conjunction with the software program in computerExecute signal processing) using backprojection algorithm into
Row image reconstruction sets ultrasonic transducer range Imaging target as R, is t the time required to the ultrasonic pulsative signal that receives, according to when
Between relationship t=R/ ν, ν=1.495mm/ μ s application the backprojection algorithm of t and distance R calculate target image be imagedPlace
Corresponding i-th of the practical ultrasonic transducer Pi of pixel signal value Si (t), imageable target imageThe pixel at place
Point is R (x, y, Pi), imageable target image at a distance from i-th of practical ultrasonic transducer PiThe pixel at place is corresponding
I-th of practical ultrasonic transducer Pi signal value Si (R (x, y, Pi)/v), then imageable target imageLocate pixel
The each practical ultrasonic transducer that is equal in annular ultrasonic transducer array of image value receiving Locate the letter of pixel
Number value superposition, i.e.,
It is L that the distance between virtual ultrasound energy converter and practical ultrasonic transducer, which is arranged, to be worth, then image The picture at place
Distance of the vegetarian refreshments apart from virtual ultrasound energy converter is R '=R+L, imageI-th of pixel distance of place is virtual super
The distance of sonic transducer Pi ' is R ' (x, y, Pi ')；Imageable target imageThe corresponding practical ultrasound of the pixel at place is changed
The signal value of energy device Pi becomes Si [(R ' (x, y, Pi ')-L)/v]；ThenThe image value for locating pixel is equal to each void
Quasi- ultrasonic transducer receivesLocate the superposition of the signal value of pixel, i.e.,
By imagePolar coordinates of the pixel at place at a distance from i-th of virtual ultrasound energy converter Pi ' are converted into
Rectangular co-ordinate, then formula (2) becomes:
Wherein, R is the diameter of practical ultrasonic transducer scanning track, and N is the quantity of practical ultrasonic transducer, Si(t) it is
By the i-th practical ultrasonic transducer received signal value, θiIt is the angular coordinate of i-th of practical ultrasonic transducers locations, v is ultrasound
Spread speed in the medium, R+L are the diameter of virtual ultrasound transducer scans track；
According to vector subtraction and range formula, then the image reconstruction algorithm formula of imageable target is as follows:
Wherein, I is imageImage value after place's reconstruction, n are the scan position number of annular ultrasonic transducer array, Si(t)
For the signal value that i-th of practical ultrasonic transducer receives,For the position of i-th of practical ultrasonic transducer, L changes for virtual ultrasound
Energy the distance between device and practical ultrasonic transducer value, v are the spread speed of ultrasound in the medium.
Wherein it is possible to simple transformation be carried out to experimentation, even if individually practical ultrasonic transducer drives in stepper motor
Under do 360 degree rotation mode replace annular ultrasonic transducer array, (feelings when N=1 are only represented in figure shown in d referring to Fig.1
Shape), when practical ultrasonic transducer is at the position P1, at the t1 moment, because of point and practical ultrasonic transducer on this curve of X1
Distance it is all equal, so the signal that practical ultrasonic transducer receives at this time is the ultrasonic pulses letter that all points on X1 generate
Superposition number at practical ultrasonic transducers locations P1；Similarly t2 moment, the signal that practical ultrasonic transducer receives are X2 curve
The superposition for the ultrasonic pulsative signal that upper all points generate；Practical ultrasound is reached according to the ultrasonic pulsative signal of difference in this way to change
The time of energy device is different, as soon as practical ultrasonic transducer has collected the signal of a time series after laser pulse；
Then practical ultrasonic transducer rotates the next position specified to requirement of experiment by stepper motor, i.e. P2 in figure continues to adopt
Collect ultrasonic signal, repeat the above process until rotating a circle, it will be able to the same function of realizing annular ultrasonic transducer array.
In the situation of the entire circular scanning of application annular ultrasonic transducer array, two neighboring practical ultrasonic transducer
Between angle φ it is identical, and practical ultrasonic transducer total number be N.
In reconstruction process, the photoacoustic tomography technology based on spherical scanning can also be used, in three dimensions, by
M two-dimentional acquisition plane process is constituted, i.e., constantly moves a certain distance repetition along axial direction using annular ultrasonic transducer array and adopt
Collect ultrasonic pulsative signal, until completing axial scan, i.e., practical a total of n × m scan position of ultrasonic transducer, then formula
(4) become:
Wherein, I is imageImage value after place's reconstruction, Si,j(t) the practical ultrasonic transducer for the position (i, j) receives
Signal,For the position of (i, j) a practical ultrasonic transducer, L is between virtual ultrasound energy converter and practical ultrasonic transducer
Distance value, v is ultrasound spread speed in the medium, and n × m is practical ultrasonic transducer number of scan points.
The imaging capability of photoacoustic tomography algorithm for reconstructing based on finite size planar transducer of the invention, mainly with
Ideal point transducer models algorithm for reconstructing and infinite size transducer models algorithm for reconstructing compare；6 sample of imageable target is adopted
Body Model is imitated made of agar powder, wherein first 2g agar powder is added in 100mL water, pours into corresponding mould after heating dissolution
It is stood in tool, is cooled into cylindrical agar block gel；Again using lead for retractable pencil as point target 61, be inserted into respectively away from imitative body center 0mm,
The position of 2mm, 4mm and 6mm obtain 6 sample of imageable target.6 peripheral diameter of imageable target be 40mm, on the lateral direction x away from
Position from 6 center 0mm to 6mm of imageable target is uniform-distribution with 4 point targets 61；Laser is using Nimma-600 model
Q-switched Nd:YAG. nanosecond laser, Output of laser wavelength 532nm, pulsewidth 8ns, repetition rate 10Hz；Used in acquisition
Planar transducer diameter be 5mm, centre frequency 5MHz, bandwidth 71%；6 center of imageable target and planar transducer it
Between distance R be 22mm；Annular ultrasonic transducer array has 360 planar transducers, the angle interval between planar transducer
It is 1 degree, imageable target 6 is located at the rotation center of circular scanning；It can laterally be indicated with the direction x, tangentially the available direction y indicates.
The present invention finds the compact form of backprojection algorithm while using finite size planar transducer 3, thus greatly
Improve image tangent resolution.
As shown in figure 4, receiver, which occurs, for signal uses Olympus Olympus ultrasonic pulse generation/receiver (model
5072PR, 5073PR), the signal that data collection system uses Beijing Di Yang Centrix Technology Ltd. to produce is LDI400VSE
Data collection system；Laser emits laser pulse to imageable target 6, and imageable target 6 is heated to generate ultrasonic pulsative signal, surpasses
Ping receives and is converted to electric signal by each ultrasonic transducer in annular ultrasonic transducer array, using signal
It is acquired after the amplification of receiver occurs by data collection system；It is if being scanned using individual ultrasonic transducer, then ultrasonic
Energy converter, which needs to be pivoted under stepper motor effect, realizes circular scanning, if carrying out spherical scanning, then ring-shaped ultrasonic
Transducer array, which is listed in, to be axially displaced to realize spherical scanning under stepper motor effect, can also use individual ultrasonic transducer
It is first pivoted, is axially displaced to realize spherical scanning again, wherein driver drives stepper motor work under the control of the computer
Make；Image weight is carried out to signal data collected in conjunction with the MATLAB software program application backprojection algorithm in computer
It builds, finally obtains the image of imageable target.
As illustrated in figure 1 c, in the present invention, the virtual ultrasound far from practical ultrasonic transducers locations is created first to change
Energy device 4, it is L that setting the distance between virtual ultrasound energy converter 4 and practical ultrasonic transducer, which are worth, then practical ultrasonic transducer receives
Signal can be approximated to be by 4 received signal of virtual ultrasound energy converter, only have time delay L/v；It willRectangular co-ordinate is substituted into, then the weight at picture point (x, y) that the present invention obtains
Built-in value is determined by the signal of position and the sweep radius of virtual ultrasound energy converter of practical ultrasonic transducer:
Wherein, R is the diameter of practical ultrasonic transducer scanning track, and N is the quantity of practical ultrasonic transducer, Si(t) it is
By the i-th practical ultrasonic transducer received signal, θiIt is the angular coordinate of i-th of practical ultrasonic transducers locations, v is that ultrasound exists
Spread speed in medium, R+L are the diameter of virtual ultrasound transducer scans track.
For common backprojection algorithm schematic diagram as shown in Fig. 1 a, 1b, backprojection algorithm measures pixel and each ultrasound first
Then time delay between energy converter obtains final pixel value by the sum of ultrasonic transducer signal of corresponding time delay.
Fig. 1 a shows image reconstruction schematic diagram when energy converter is considered as ideal point energy converter 1, this is also current most
The principle of number CSPAT algorithm for reconstructing, in this CSPAT algorithm for reconstructing based on ideal point, projection line 5 is (equal in other words
Time delay line) it is that one group of concentric curve centered on practical ultrasonic transducers locations is located on image in this algorithm
Numerical value is rebuild by the signal deciding of transducer position at (x, y):
Wherein, R is the diameter of ultrasonic transducer scanning track, and N is the quantity of total ultrasonic transducer, SiIt (t) is by i-th
Ultrasonic transducer received signal, θiIt is the angular coordinate of i-th of ultrasonic transducer, v is the spread speed of ultrasound in the medium；It should
Equation can provide uniform resolution ratio for ideal point energy converter 1, but for the planar transducer with finite size, when a mesh
When mark 61 is far from 6 center of imageable target, image tangent resolution will deteriorate.
The second model of common backprojection algorithm is to be considered as the transducing of infinite size based on large scale line energy converter
The schematic diagram of device 2, such case is as shown in Figure 1 b, and projection line 5 is parallel with 2 plane of infinite size energy converter；In this algorithm,
The reconstruction numerical value being located at (x, y) on image are as follows:
Wherein, R is the diameter of ultrasonic transducer scanning track, and N is the quantity of total ultrasonic transducer, SiIt (t) is by i-th
Ultrasonic transducer received signal, θiIt is the angular coordinate of i-th of ultrasonic transducer, v is the spread speed of ultrasound in the medium；So
And for lesser ultrasonic transducer, when point target 61 is far from 6 center of imageable target, image tangent resolution will be disliked
Change.
Fig. 2 a is using 1 model imaging algorithm of ideal point energy converter, i.e., the image that obtains of formula (6), Fig. 2 b use nothing
The image that limit 2 model imaging algorithm of size transducer, i.e. formula (7) obtain.Where it can be seen that 6 center of range Imaging target
Two point targets 61 of 4mm and 6mm, the lateral wheel compared with two point targets 61 at range Imaging target 6 center 0mm and 2mm
Wide significant extension, 6 center of range Imaging target is remoter, and the tangential direction the y distortion of target is more obvious, the tangential direction y point of system
Resolution is deteriorated.
Fig. 2 c is the i.e. obtained image of formula (3) using 3 model imaging algorithm of finite size energy converter of the invention, root
According to vector subtraction and range formula, formula (3) can be converted into formula (4), in the case where carrying out spherical scanning, formula (4)
Formula (5) can be converted into.The distance between the virtual ultrasound energy converter 4 and practical ultrasonic transducer 3 that wherein select value for
27mm.Comparison diagram 2a and Fig. 2 b can be seen that using the tangent resolution and figure for removing 0mm, 2mm Place object in inventive algorithm
Basic almost outer in 2a and Fig. 2 b, the tangent resolution of remaining target has all obtained improving significantly in figure, tangential Fuzzy Pseudo
Shadow has obtained effective recovery.
Fig. 3 a, 3b and Fig. 3 c are Fig. 2 a, Fig. 2 b and Fig. 2 c point at range Imaging target 6 center 2mm, 4mm, 6mm respectively
The lateral data profile that target 61 is extracted.
Wherein solid line is with the lateral contour that algorithm is rebuild in the present invention, the ideal point model algorithm reconstruction of asterism line
Lateral contour, line of dots are the lateral contours rebuild with unlimited model algorithm.
Ordinate be Fig. 2 a/2b/2c abscissa 2/4/6mm locate pixel gray value normalization data value, 0 be it is black, 1 is
It is white；Abscissa is the ordinate of pixel in Fig. 2 a/2b/2c；
By the gray value of pixel at abscissa 2mm respectively divided by the maximum value of pixel gray value at the abscissa, i.e.,
Obtain normalization data value；
The image value for repeating to substitute into pixel at abscissa 4mm, 6mm obtains corresponding normalization data value；It will normalization
Data value is as ordinate, and using the y-axis coordinate of pixel in corresponding diagram 2a/2b/2c as available Fig. 3 a of abscissa, 3b
With outline data chart shown in Fig. 3 c.
Comparison is as can be seen that use the photoacoustic tomography algorithm for reconstructing of finite size planar transducer of the invention
The tangential blurring artefact of CSPAT figure is effectively restored.
The above embodiment is a preferred embodiment of the present invention, but embodiments of the present invention are not limited to above-mentioned implementation
The limitation of example, above-mentioned specific embodiment are other any without departing from spirit of the invention for explaining to the present invention
The change made under essence and principle, such as data pre-processing and post-processing etc., are regarded as equivalent substitute mode, belong to
Protection scope of the present invention.
Claims (6)
1. a kind of photoacoustic tomography algorithm for reconstructing based on finite size planar transducer, which is characterized in that including following step
It is rapid:
1) imageable target is fixed in annular ultrasonic transducer array, is filled between annular ultrasonic transducer array and imageable target
Full medium water；
2) laser output laser pulse, makes laser pulse uniform irradiation imageable target, and excitation imageable target generates ultrasonic pulse
Signal；
3) each practical ultrasonic transducer in annular ultrasonic transducer array starts simultaneously at record and reaches practical ultrasonic transducer
Ultrasonic pulsative signal, and ultrasonic pulsative signal is converted to electric signal, the telecommunications that receiver will receive is occurred by signal
It number amplifies, and is transferred to data collection system and carries out electrical signal collection；The electric signal of acquisition is handled, obtains and is based on
The reconstruction figure of the photoacoustic tomography algorithm for reconstructing of finite size planar transducer；
4) imaging target image is calculated using backprojection algorithmCorresponding i-th of the practical ultrasonic transduction of the pixel at place
The signal value Si (t) of device Pi, then imageable target imageThe image value for locating pixel is equal to annular ultrasonic transducer battle array
Each practical ultrasonic transducer in column receivesLocate the superposition of the signal value of pixel, i.e.,
Wherein, practical ultrasonic transducer range Imaging target is R, is t, imageable target the time required to the ultrasonic pulsative signal received
ImageThe pixel at place is R (x, y, Pi), imageable target image at a distance from i-th of practical ultrasonic transducer PiThe signal value Si (R (x, y, Pi)/v) of corresponding i-th of the practical ultrasonic transducer Pi of the pixel at place, v are ultrasound
Spread speed in the medium；
5) it is L, image that setting the distance between virtual ultrasound energy converter and practical ultrasonic transducer, which is worth, The pixel at place
Distance apart from virtual ultrasound energy converter is R '=R+L, thenThe image value for locating pixel is equal to each virtual ultrasound
Energy converter receivesLocate the superposition of the signal value of pixel, i.e.,
Wherein, imageThe distance of i-th of virtual ultrasound energy converter Pi ' of pixel distance at place is R ' (x, y, Pi '),
Imageable target imageThe signal value of the corresponding practical ultrasonic transducer Pi of the pixel at place become Si [(R ' (x, y,
Pi′)-L)/v]；
6) by imagePolar coordinates of the pixel at place at a distance from i-th of virtual ultrasound energy converter Pi ' are converted into directly
Angular coordinate, then formula (2) becomes:
Wherein, R is the diameter of practical ultrasonic transducer scanning track, and N is the quantity of practical ultrasonic transducer, SiIt (t) is by i-th
Locate practical ultrasonic transducer received signal value, θiIt is the angular coordinate of i-th of practical ultrasonic transducers locations, v is that ultrasound is being situated between
Spread speed in matter, R+L are the diameter of virtual ultrasound transducer scans track；
7) according to vector subtraction and range formula, then the image reconstruction algorithm formula of imageable target is as follows:
Wherein, I is imageImage value after place's reconstruction, n are the scan position number of annular ultrasonic transducer array, SiIt (t) is the
The signal value that i practical ultrasonic transducer receives,For the position of i-th of practical ultrasonic transducer, L is virtual ultrasound energy converter
The distance between practical ultrasonic transducer value, v are the spread speed of ultrasound in the medium.
2. the photoacoustic tomography algorithm for reconstructing according to claim 1 based on finite size planar transducer, feature
It is, in image reconstruction process, carries out spherical scanning using annular ultrasonic transducer array, in three dimensions, spherical shape is swept
It retouches and is made of m two-dimensional surface scanning process, i.e., each a total of n × m scan position of practical ultrasonic transducer, then formula (4)
Become:
Wherein, I is imageImage value after place's reconstruction, Si,j(t) letter received for the practical ultrasonic transducer of the position (i, j)
Number,For the position of (i, j) a practical ultrasonic transducer, L is between virtual ultrasound energy converter and practical ultrasonic transducer
Distance value, v are the spread speed of ultrasound in the medium, and n × m is practical ultrasonic transducer number of scan points.
3. the photoacoustic tomography algorithm for reconstructing according to claim 1 or 2 based on finite size planar transducer, special
Sign is that laser described in step 2) is pulse laser, the laser pulse wavelength 532nm.
4. the photoacoustic tomography algorithm for reconstructing according to claim 1 or 2 based on finite size planar transducer, special
Sign is that the angle spacing between the adjacent practical ultrasonic transducer is 1 degree, the annular ultrasonic transducer array installation
There are 360 practical ultrasonic transducers.
5. the photoacoustic tomography algorithm for reconstructing according to claim 1 based on finite size planar transducer, feature
It is, the electric signal of described pair of step 3) acquisition is handled, and is in conjunction with the MATLAB software program application formula in computer
(4) image reconstruction algorithm executes signal processing and carries out image reconstruction.
6. the photoacoustic tomography algorithm for reconstructing according to claim 2 based on finite size planar transducer, feature
It is, the electric signal of described pair of acquisition is handled, and is the figure in conjunction with the MATLAB software program application formula (5) in computer
Image reconstruction is carried out as algorithm for reconstructing executes signal processing.
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