JPH0458632B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an image reproduction device using ultrasonic holography, and for example, detects a defect in a metal material using ultrasonic waves and enhances the image of the defect. The present invention relates to an image reproduction device for ultrasonic nondestructive testing that can display images in high resolution in real time.

[Conventional technology]

FIG. 4 is a block diagram illustrating a conventional image reproduction device using ultrasonic holography based on the synthetic aperture method. In the figure, 1 is an ultrasonic transmitter/receiver that sends and receives ultrasound signals at each scan point while scanning on a flat or curved surface, and 2 is an ultrasonic transmitter/receiver 1 that attempts to create images by transmitting and receiving ultrasonic waves. The target object, 3, is a pulser/receiver unit that generates driving electric pulses (or continuous pulses) for transmitting ultrasonic waves from the ultrasonic transmitter/receiver 1 to the target object 2.
4 is a detection unit for supplying a signal to the ultrasonic transceiver 1 and amplifying the ultrasonic reflected signal from the target object 2 received by the ultrasonic transceiver 1 to an appropriate level; Ultrasonic transmitter/receiver 1
5 is an A/D section for performing phase detection between the signal transmitted to the target object 2 and the signal reflected from the target object 2 to obtain a hologram signal;
A hologram memory unit 6 converts the hologram signal output from the detection unit 4 into a digital form to obtain a numerical hologram as a digital quantity, and stores each numerical hologram obtained in the A/D unit 5. 7 for storing corresponding scan points of
8 is a spatial wave propagation function memory section that stores spatial wave propagation functions calculated in advance for waves necessary for image reconstruction calculations, which will be described later; and 8 is a signal processing section that processes each scan signal in the hologram memory section 6. 9 is an image display unit for performing image reconstruction calculation using the numerical hologram corresponding to the point and the spatial wave propagation function in the spatial wave propagation function memory unit 7; A control unit 10 is used to output and display an image of the object 2, and is used to control the operation timing of the entire apparatus, such as the timing of transmitting and receiving ultrasonic waves. Next, image reconstruction calculations in the conventional image reconstruction apparatus using ultrasonic holography shown in FIG. 4 will be explained.

The numerical hologram stored in the hologram memory section 6 in FIG. 4 is made into a function of scan point position coordinates (X, Y), and its image reproduction calculation is performed according to the following equation.

F(X,Y)=∫ ^xX=L/2 _xX=-L/2 ∫ ^yY=L/2 _yY=-L/2 H
(X, Y)・G(x-X,y-Y)dxdy...(1) Here, F is the image distribution function, H is the hologram, and G
is the spatial wave propagation function, and G(x,y) in equation (1)
is a spatial wave propagation function determined by the hologram H formula. Image reconstruction processing for a numerical hologram is performed by calculating the following equation, which is a discretization of equation (1).

F (kx, ky) = _kx-ox=a 〓 ^kx-nx=-a _ky-oy=b 〓 ^ky-ny=-b H (nx, ny)・G (kx−nx, ky−ny) …… (2) Here, kx and ky are the addresses of the reconstructed image pixels,
nx, ny are the addresses of the numerical hologram, and the spatial wave propagation function G is the range of synthetic aperture length determined by the beam spread (-akx-nxa, -bky
-nyb), which is calculated in advance and stored in the spatial wave propagation function memory section 7 shown in FIG. The product-sum operation of the expressions will be performed. Note that this signal processing section 8 is
Currently, there are processors that use microcomputer technology, or general-purpose computers that perform image reconstruction calculations.

[Problem that the invention seeks to solve]

As mentioned above, the image reconstruction device using ultrasonic holography based on the conventional synthetic aperture method uses a so-called microcomputer-level processor as the signal processing unit 8 that executes image reconstruction calculations according to equation (2). Or, because a general-purpose computer is used off-line, it takes a lot of time to obtain a desired reconstructed image. Since the reconstructed image cannot be viewed immediately after the scanning is completed, there has been a problem in that this type of image reconstruction device using ultrasonic holography is difficult to apply to various industries.

This invention was made to solve the above-mentioned problems, and it is a holographic system based on the synthetic aperture method that can obtain a reconstructed image of a target object at the same time as all scans in a predetermined scan area of an ultrasonic transmitter/receiver are completed. The object of the present invention is to obtain an image reproduction device according to the present invention.

[Means for Solving the Problems] The image reproduction device using ultrasonic holography according to the present invention scans an ultrasonic transmitter/receiver based on the synthetic aperture method, and while transmitting and receiving ultrasonic waves, it detects reflected waves from a target object. In an image reproduction device using ultrasonic holography that reproduces an image using the obtained hologram, the ultrasound wavelength and hologram surface calculated in advance are used for image reproduction processing that is performed sequentially from the hologram obtained for each scan. A spatial wave propagation function memory section that stores a spatial wave propagation function determined by the spatial coordinates of the reproduction surface, an address counter for sequentially accessing the spatial wave propagation function in this spatial wave propagation function memory section, and an address control for this address counter. a multiplier and a first adder that calculate the product sum of the hologram and the spatial wave propagation function based on the address of the address counter and a scan position of the transmitter/receiver; , a second adder for determining an address for reading a corresponding reconstructed image from the reconstructed image memory section in order to accumulate the product-sum result with the reconstructed image, and based on address control of the second adder. and an accumulator for accumulating the product-sum result and the reconstructed image, and performs coherent addition on the reconstructed image coordinates determined from the coordinates of the hologram surface and the spatial wave propagation function.

[Effect]

According to this invention, digitized numerical hologram data is obtained for each scan point of the transmitter/receiver, sequential image reconstruction processing is performed before the next scan operation, and the image reconstruction results are added to the image reconstruction results before a certain predetermined scan. Then, the operation of converting this into an updated image reconstruction result is repeated, and a reconstructed image of the imaging target area is obtained at the same time as all scanning operations are completed.

〔Example〕

Before explaining the embodiment of the apparatus of the present invention, the principle of image reproduction processing applied to the present invention and the calculation processing necessary therefor will be explained with reference to FIG. .

First, with reference to FIG. 3, the principle of image reproduction processing in the present invention will be explained. In this Figure 3, 11 is a numerical hologram H obtained corresponding to each scan point of the ultrasonic transmitter/receiver, 12 is an air wave propagation function G, and 13 is a reconstructed image F.
The product of the numerical hologram data on the numerical hologram H11 obtained at one predetermined scan point and the spatial wave propagation function G is calculated, and the coordinates on the numerical hologram 11, that is, the position coordinates of that scan point and the spatial On a plurality of reconstructed image coordinates on the reconstructed image F13 determined from the coordinates of the wave propagation function G12,
Allocate this result. Then, this result is applied to the reproduced image F13 before the allocation regarding the scan point.
Coherently add the result of the same reproduced image coordinates on the reproduced image F13, which has already been allocated above,
The result of this addition is again used as the value of the reproduced image coordinates. Such processing is started at the same time as the ultrasonic transmitter/receiver receives a reflected wave and detects the phase at the scan start point of a predetermined scan area. After moving the transmitter/receiver and completing both this movement and the above-mentioned image reconstruction processing, the transmitter/receiver is sequentially repeated for the next scan point, thereby reproducing the scan of a predetermined scan area. At the end of the process, the image reproduction process will also be completed.

Next, the method of performing the arithmetic processing necessary for this invention will be explained. According to the image reproduction processing by ultrasonic holography based on the synthetic aperture method used in this invention, by performing phase detection, a complex hologram, which is the numerical hologram H11 shown in FIG.
Hr, Hi are obtained, the spatial wave propagation function G12 used during image reconstruction is also given as a complex number, and Gr, Gi
Therefore, the reconstructed image F13 can be obtained by performing the following calculation.

F=H・G=(Hr・Gr−Hi・Gi)+j(Hr・Gi+Hi・Gr
)...(3) Now, the number of scans of the ultrasonic transmitter/receiver to reproduce the image of the imaging target area is Nx×N _Y , and the spatial wave propagation function G12 is determined by the synthetic aperture length.
Assuming that corresponds to Mx×M _Y points,
Since the reconstructed image F13, the area is (N _X + M _X ) ×
You only need to prepare (N _Y + M _Y ) points. First, before starting the scan operation, all values at each point in the reconstructed image area are set to "0", and then the ultrasonic transmitter/receiver is sequentially scanned to obtain a complex hologram for each scan operation. Perform the image reconstruction processing shown in equation (3), and use the result of this reconstruction processing as the reconstructed image F.
13 Allocate above. The coordinates of the scan point at this time are (nx, ny) (nx=0, 1, 2, ..., Nx−1.ny
=0, 1, 2,...N _Y -1), and the address coordinates of the spatial wave propagation function G are (mx, my) (mx = 0,
1, 2,…, Mx−1.my=0, 1, 2,…, M _Y
-1), the reproduction processing result is allocated to the image reproduction area, this reproduction processing result is coherently added to the value of the reconstructed image F13 before the relevant scan, and the address where this addition result should be stored is nx +
You can use mx, ny + my. By sequentially performing such operations for each scan operation, the reconstructed image of the entire imaging target area is processed for the complex hologram at the last scan point after the last scan of the predetermined number of scans is completed. By determining the absolute value of the reproduction result of the imaging target area, the reproduction image distribution function given by equation (2) can be obtained. At this time, the area in the reconstructed image where the synthetic aperture length is sufficient is the reconstructed image area (Nx
+Mx, N _Y +M _Y ) respectively Mx, M _Y
This is the part that is inward, and its size is (Nx - Mx, N _Y - M _Y ), and this area is set as the imaging target area.

An embodiment of the present invention will now be described with reference to FIG. FIG. 1 is a block diagram of a signal processing unit for performing image reproduction calculations from complex hologram data. In FIG. 1, 5a and 5b are A/D units that digitize complex hologram signals; is latch, 1
5a, 15b, 15c, 15d are multipliers, 16
a and 16b are spatial wave propagation function memory sections arranged two-dimensionally to store the spatial wave propagation function G, and 17a and 17b are used to set addresses for calling predetermined values of the spatial wave propagation function. 18 is a sign inverter that inverts the sign of data; 19a, 19b, 22a, and 22b are adders; 20a and 20b are reproduced image memory sections that store the reproduced image F; and 21a and 21b are ultrasonic transceivers. Drive unit address indicating scan position, 23a, 23
b is an accumulator. In addition, the latches 14a, 14
b, multipliers 15a to 15d, address counter 1
The arrows attached to the multipliers 7a, 17b and the multipliers 23a, 23b indicate that they are triggered at a certain required timing by a certain predetermined control section (not shown) and perform necessary operations. In this signal processing section, each time a complex hologram Hr, Hi is obtained at each scan point, calculation is performed according to equation (3), and the reconstructed image memory section 20a,
A coherent addition is performed with the data at the designated address of 20b. While performing such calculations, the ultrasonic transmitter/receiver is scanned, and after the scan is completed and the necessary calculations are completed, ultrasonic transmission/reception corresponding to the next successive scan point is performed.

The operation of the signal processing section described above will be explained below with reference to FIG. FIG. 2 is an explanatory diagram showing the timing of each section and the movement of data regarding one image reproduction process of the signal processing section in FIG. 1. complex hologram signal
Hr and Hi are digitized by the A/D sections 5a and 5b, and at the end timing of the A/D operation, this data is held by the latches 14a and 14b. At the timing of this latch operation, the address counter 17
a, 17b are set, and the spatial wave propagation function memory sections 16a, 16 store the spatial wave propagation function G.
The two-dimensional address (nx, ny) of b is specified, and the data stored at the specified address
Gr and Gi are accessed. Note that this spatial wave propagation function G data is obtained in advance using an external computer, etc., and after normalizing it to, for example, an 8-bit integer value, it is stored in the spatial wave propagation function memory section 16.
a, 16b. Then, this accessed data is stored in multipliers 15a to 15a.
15d, and becomes stable after a predetermined period of time after the access is made. After this data is stabilized, a multiplication start trigger is applied to the multipliers 15a to 15d to perform necessary multiplication. The outputs of the multipliers 15a to 15d are respectively Hr·
Gr, HiGi, Hr・Gi, HiGr, among which,
The output of the multiplier 15d further passes through the sign inverter 18 and becomes -HiGi. The stabilized data, delayed by the time necessary for this multiplication and sign inversion, is
Next, they are added by adders 19a and 19b, resulting in (HrGr-HiGi) and (HrGi+HiGr). On the other hand, the drive unit addresses 21a and 21b are
The adders 22a and 22b add the values nx, ny and Nx, N _Y of the address counters 17a and 17b, respectively, and calculate the result of the calculation ((Nx, N _{Y )} . Hr・Gr−Hi・
Gi) and (HrGi+HiGr) are to be coherently added to the two-dimensional addresses of the reconstructed image memory sections 20a and 20b. This two-dimensional address (Nx+
The reproduced image data accessed by nx, N _Y +ny) is connected to the output sides of accumulators 23a and 23b, and the calculation results (Hr・Gr−HiGi) and (HrGi+HiGr) are connected to the output sides of accumulators 23a and 23b. stabilizes faster than input. And (HrGr
−HiGi) and (HrGi+HiGr) are in the accumulator 23
After the signal is input to the input terminals a and 23b and stabilized, an accumulation start trigger is applied, and after the accumulation is completed, the accumulation result is written to the addresses (Nx+nx, N _Y +ny) of the reproduced image memory sections 20a and 20b. After this data writing is completed, the address counters 17a, 17
Step b is advanced and the next calculation is performed, and after the necessary calculations are completed for all the data of the spatial wave propagation function G, the next transmission and reception is performed, and the same processing as described above is repeated. Incidentally, according to the apparatus according to the embodiment of the present invention, the time required to perform such a calculation is from the time when the required multiplication is performed in the multipliers 15a to 15d to the time when data is written into the reproduced image memory units 20a and 20b. It is about 1 μs or less. usually,
It is sufficient that the spatial wave propagation function required for synthetic aperture processing is about 100 x 100 points, and in this case, the time to process one piece of complex hologram data is about 10 ms, and the ultrasonic Even including transmission and reception, the scanning operation can be repeated approximately every 20ms, and the desired reconstructed image can be obtained approximately 10ms after the last transmission and reception. This allows playback to be performed in real time. In addition, since image reconstruction processing is performed sequentially, the size of the imaging target surface can be infinitely large by continuously connecting the imaging target surfaces. For example, when the target object 2 is not at the center of the image display section 9, the target object 2 can be displayed at the center of the image display section 9 by changing the imaging target area.

In the above embodiments, the case where the ultrasonic transceivers are mechanically scanned has been explained, but the invention is not limited to this. For example, the ultrasonic transceivers may be assembled into an array and switched by an appropriate electronic switch. Even in the case of electronic scanning, the scanning time described above can be sufficiently followed, and the same effect can be obtained. Further, in the above embodiment, image reproduction processing is performed while sequentially scanning the transmitter/receiver, but the signal processing unit 8 of the conventional device shown in FIG. 4 is replaced with the signal processing device of the above embodiment. Replace and also drive unit address 21
The same effect can be obtained by replacing a and 21b with an address counter and using this address counter to read the hologram H from the hologram memory section 6 shown in FIG. 4 and perform image reproduction processing. play. Furthermore, it is clear that if the spatial wave propagation functions G stored in the spatial wave propagation function memory units 16a and 16b in FIG. It is.

〔Effect of the invention〕

As explained above, the image reproduction device using ultrasonic holography according to the present invention scans an ultrasonic transmitter/receiver based on the synthetic aperture method and generates a hologram obtained from reflected waves from a target object while transmitting and receiving ultrasonic waves. In an image reconstruction device using ultrasonic holography, the wavelength of the ultrasonic waves calculated in advance and the distance between the hologram surface and the reproduction surface are a spatial wave propagation function memory section that stores a spatial wave propagation function determined by spatial coordinates; an address counter for sequentially accessing the spatial wave propagation functions in this spatial wave propagation function memory section; a multiplier and a first adder for calculating the sum of products of the hologram and the spatial wave propagation function; a reconstructed image memory section that stores a reconstructed image; a second adder for determining an address for reading a corresponding reconstructed image from the reconstructed image memory section in order to accumulate the sum result with the reconstructed image; According to the present invention, the present invention includes an accumulator that accumulates the product-sum result and the reconstructed image, and performs coherent addition on the reconstructed image coordinates determined from the coordinates of the hologram surface and the spatial wave propagation function.
Digitalized numerical hologram data is obtained for each scan point of the transmitter/receiver, sequential image reconstruction processing is performed before the next scan operation, and the result is added to the image reconstruction results before a certain predetermined scan, and this is updated. The operation of obtaining the image reconstruction result is repeated, and a reconstructed image of the imaging target area is obtained at the same time as all scanning operations are completed. Therefore, it is possible to obtain a desired reproduced image in a short time, and this type of apparatus can be effectively applied to various industries. In addition, since image reconstruction processing is performed sequentially, the size of the imaging target surface can be infinitely large by continuously connecting the imaging target surfaces.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a signal processing device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation timing and data movement of the signal processing device described above, and FIG. 3 is an image of the signal processing device according to the present invention. FIG. 4, which is a diagram explaining the principle of the reproduction process, is a block diagram of a conventional image reproduction apparatus using ultrasonic holography. 1...Ultrasonic transmitter/receiver, 2...Target object, 3...
...Pulser/receiver section, 4...Detection section, 5, 5
a, 5b... A/D section, 6... Hologram memory section, 7, 16a, 16b... Spatial wave propagation function memory section, 8... Signal processing section, 9... Image display section,
10... Control unit, 11... Numerical hologram H, 12... Spatial wave propagation function G, 13... Reconstructed image F, 14a, 14b... Latch, 15a, 15
b, 15c, 15d...multiplier, 17a, 17b
... Address counter, 18 ... Sign inverter, 1
9a, 19b, 22a, 22b...Adder, 20
a, 20b...Reproduced image memory section, 21a, 21b
...Drive unit address, 23a, 23b...Accumulator. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Image reproduction by ultrasonic holography, which performs image reconstruction using a hologram obtained from reflected waves from a target object while transmitting and receiving ultrasonic waves by scanning an ultrasonic transmitter/receiver based on the synthetic aperture method. In the device, a spatial wave propagation function that stores a spatial wave propagation function determined by the wavelength of the ultrasonic wave calculated in advance and the spatial coordinates of the hologram surface and the reproduction surface is used for image reconstruction processing that is performed sequentially from the hologram obtained for each scan. a propagation function memory unit, an address counter for sequentially accessing the spatial wave propagation function in the spatial wave propagation function memory unit, and calculating the sum of products of the hologram and the spatial wave propagation function based on address control of the address counter. a multiplier and a first addition section; a reconstructed image memory section for storing a reconstructed image; a second adder that obtains an address for reading a corresponding reconstructed image from an image memory section; and an accumulator that accumulates the product-sum result and the reconstructed image based on address control of the second adder. An image reproduction device using ultrasonic holography, comprising: performing coherent addition on reconstructed image coordinates determined from the coordinates of the hologram surface and the spatial wave propagation function.