JPS62153885A - Image reproduction method by ultrasonic wave or electromagnetic wave holography - Google Patents

Abstract

PURPOSE:To speed up image reproduction processing by completing the reproduction of an area which is made into an image the moment all the prescribed scans regarding an object end. CONSTITUTION:When an image is reprduced by ultrasonic holograph based on a synthetic aperture method, a hologram H16A is given as complex holograms Hr and Hi, and a space wave propagation function G17A used for reproducing an image as complexes Gr and Gi. A reproduced image F18A can be obtained according to an equation F=H.G=(Hr.Gr-Hi.Gi)+j(Hr.Gi+ Hi.Gr). Transmitters and receivers are sequentially scanned to reproduce an image according to the equation. The reproduced result is allocated on the reproduced image F18A, coherence- added to the value of a reproduced image F reproduced before said scan is excecuted, and stored. Thus the image reproduction processing and the scan operation of the transmitters and receivers can be co-currently made, and the image of the area which is made into an image can be completed the moment all the prescribed scans end.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an image reproduction method using ultrasonic waves or electromagnetic wave holography. Related to image reproduction methods for ultrasonic non-destructive testing that can display images in high resolution and in real time, or remote sensing that uses electromagnetic waves to visualize the situation on the ground surface from a more remote point in the sky. It is.

[Conventional technology]

First, the principles of an image reproduction method using ultrasound or electromagnetic wave holography based on the one-synthetic volume method will be explained with reference to FIG. 2, taking the case of ultrasound holography as an example. In this Figure 2, (tl is a transmitter/receiver that transmits and receives ultrasonic pulses while scanning two-dimensionally on the It is a point-like object located at the coordinates (ξ0.η0) of Then, it is received again by the transmitter/receiver f/l.Then, the received signal Sr at this time is expressed by the following formula, assuming time '4t.Y is the speed of sound, and ω is the angular frequency of the transmitted ultrasonic wave.This reception The following complex hologram signal is obtained by multiplying the signal K 3in (ωt) by the signal CO3((IJ t) and passing this through a certain predetermined low-pass filter.

Hr (x, y) = t/2cOS(ωtn)
fxlHi (X, Y) = t/2s1n (ω
tn) (,71H(x,y)=Hr(x,y)×JH
t(x, y) = l/2exp(-jωtn) (If the spread width of the ultrasonic beam on the ξη plane containing one point-like object (2) is L as shown in the figure, then its reconstructed image The intensity distribution is obtained by convolution with the spatial wave propagation function G.

+(Y-y') month TldXdyl ts+[S1 equation becomes as follows when integration is performed using Fresnel approximation.

Therefore, the azimuth resolution δ is given by the following equation.

λZ.

δ= -fil By the way, the spread of the ultrasonic beam is usually a rectangular plate of length D, and if the down is 7 dB, the spread angle is approximately λ force, and the spread width is is L:
It is given by λZ o /D. Substituting this L into equation (ri), δ2λZo/(λZo/D)=D (f
fl, and the azimuth resolution is constant regardless of the distance and is approximately equal to the actual aperture of the element.

FIG. 3 is a functional block diagram for explaining an image reproduction method using ultrasonic holography based on the conventional synthetic aperture method. In this Fig. 3, (C) is a transmitter/receiver for transmitting and receiving ultrasonic waves, (3) is a pulser/receiver unit, and (3) is a pulser/receiver unit for transmitting ultrasonic pulses with a certain predetermined spread from the transmitter/receiver C. The transmitter/receiver (C) is driven by the transmitter/receiver (C), and in the same way, the signal reflected from the point-like object (2) shown in Figure 2, which is received by the transmitter/receiver (II), is amplified to a certain level. , the pulsar/receiver section (
3) to continuously generate a signal in phase with the drive signal in synchronization with the drive signal for transmission supplied to the transmitter/receiver (1); (s) is a 9-g phase shifter; There is an oscillator (used to shift the phase of the received signal by 9 degrees), (61, (71 is a phase detection section, which detects the in-phase component of the output signal of the pulser/receiver section f and 71, and the phase detection section, respectively. θ.

It performs product detection with the phase shift component and removes the high frequency component using a low pass filter that uses the frequency component of the transmitted wave as the cutoff wave number, and the phase detection section calculates equations (6) and (3). become. (Te) is an A/D conversion unit, and the real number ring Hr of the complex hologram is the output of the phase detection unit (6), and the imaginary number ring H1 of the complex hologram is the output of the phase detection unit (7), respectively. (lo) and (ll) are hologram signal memory units, respectively, and A/D conversion units (ffl, +91
The transmitting/receiving element (C) that stores the output from the A/
D conversion unit (t), (controls A/D start time, sampling time, etc. for ql, hologram signal memory unit (tO') for real number ring Hr and imaginary number ring Hi of the complex hologram corresponding to each scanning point.

(ll), and controls the execution of image reproduction processing using data groups in the hologram signal memory units (tO) and (lt');
13) is a spatial wave propagation function memory section, which uses data groups of complex holograms corresponding to each scanning point stored in the hologram signal memory sections (10) and (ll) to
(lψ) is a signal processing unit that can perform image reconstruction calculations according to Equation 1, a hologram signal memory unit (tO),
(s) using the complex hologram value H (X, Y) and the spatial wave propagation function value G (X-x, Y-y) stored in the spatial wave propagation function memory section (13). (ts) is an image display unit that outputs and displays the reproduced image obtained by the signal processing unit (c0).

The image reproduction process in the signal processing unit (tu) is started after the transmitter/receiver element (c) has completed all scanning of a predetermined scan area.This image reproduction process is performed according to equation (5). , and convolution with the spatial wave propagation function G stored in the spatial wave propagation function memory section (13) is performed.By the way, when performing this convolution integral discretely, the wavelength λ of the ultrasonic wave and Playback surface distance Zo.

xY direction scan pitch △X, ΔY1 scan number Nx
, NyO, fast Fourier transform (FFT) cannot be used, and the sum-of-products calculation must be repeated the required number of times according to equation (s). Here, a method of image reconstruction calculation in image reconstruction by ultrasonic holography based on the conventional synthetic aperture method shown in FIG. 3 will be explained with reference to FIG. 9. In this first figure, (16) is
The hologram H1 (17) obtained on the Y plane (scan plane or hologram plane) has a spatial wave propagation function G, (lf
f) is the reconstructed image F on the xy plane (reproduction plane) in FIG. 2, and the hologram H (/A), the spatial wave propagation function G (/N, /g') is shown focusing on the case of reproducing one reproduced image pixel.As shown in the figure, in order to obtain one reproduced image pixel on the reproduced image TP(tg'), To do this, it is necessary to multiply the data group for all holograms H(16) within the synthetic aperture length by the spatial wave propagation function a(te), and then sequentially add the products.

[Problem that the invention seeks to solve]

In the past, since the calculations had to be done as described above, image reproduction processing could not be performed until the entire scan of the transmitter/receiver (c) in Fig. 3 was completed.
Therefore, there is a problem in that the time required for the transmitter/receiver (,l) to scan the entire scan area poses a major problem in speeding up the image reproduction process. [Means for Solving the Problems] Ultrasonic waves or electromagnetic waves according to the present invention The image reconstruction method using holography is based on the synthetic aperture method, and phase-detects the reflected wave signal from the target object obtained by transmitting and receiving signals for each scan from an ultrasonic or electromagnetic wave transmitter/receiver.
The complex hologram obtained at each position of the transmitter/receiver is digitized, the product with the spatial wave propagation function calculated in advance is calculated, and coherent addition is performed on the reproduced image coordinates determined from the hologram coordinates and the spatial wave propagation function coordinates. The image reproduction process is performed sequentially.

[For production]

According to this invention, a complex hologram is obtained every time a transmitter/receiver is scanned, the necessary image reconstruction processing is performed before the next scan, this result is added to the image reconstruction results before the relevant scan, and the relevant scan is performed again. By repeating the operation of updating the image reproduction result at a certain point in time as many times as necessary, the image reproduction of the imaging target area is completed when all predetermined scans are completed.

〔Example〕

Before explaining the embodiment method of the present invention, the characteristic points of the method of the present invention will be explained with reference to FIG. In this Fig. 9, (16A) is the hologram H1 (/7A) obtained on the XY plane (scan plane or hologram plane) in Fig. 2 is the spatial wave propagation function G, (ltA)
Similarly, is the reproduced image F on the xy plane (reproduction plane) in FIG. The method according to the embodiment of the present invention differs from the conventional method shown in FIG. and the spatial wave propagation function G(/?A)
The result is allocated to a plurality of reconstructed image coordinates on the reconstructed image F (/ffA) determined from the coordinates of . During this allocation operation, coherent addition is performed with the result at the corresponding reconstructed image coordinates on the reconstructed image F(tg) of the allocation before that scan point, and this is used as the updated value at the reconstructed image coordinates. . Such processing starts at the same time as the transmitter/receiver receives a reflected wave at the scan start point of a certain predetermined scan area and detects the phase of the reflected wave. The operation of moving the transceiver and transmitting/receiving to the next scanning point is repeated after both the movement and the above-described image reproduction processing are completed. Thus, image reconstruction is also completed at the end of scanning a certain predetermined scan area.

Next, an example method of the present invention will be explained in detail. When image reconstruction is performed by ultrasonic holography based on the synthetic aperture method, the hologram H(/AA) shown in FIG. 9 can be obtained by performing a predetermined phase detection. . Also, the spatial wave propagation function G(/?A) in Fig. 9 used during image reproduction
is also given as a complex number and set as Or r 01. Therefore, the reconstructed image F(tgA'') in Fig. ψ can be obtained by performing the following calculation.

F = HOG = (Hr-Or-HisGi)+j
(Hr-Gi+J4i・Gr) f91 Now, the number of times the transceiver is scanned to reproduce the image of the imaging target area is Nx X NY, and the ninth
The spatial wave propagation function G(/?A) shown in the figure is Mx
Assuming that there are only X MY points, the reproduced image F(tgA
) Nodame area is (Nx+Mx)×(NY+MY
) points only.

First, before starting scanning, all values at each point in the reconstructed image area are set to "O". Next, the transmitter/receiver is sequentially scanned, the required complex hologram is obtained each time the scan is performed, and image reconstruction processing as shown in equation %(9) is performed. (t
tA) Spread on top. The coordinates of the scan point at this time are (nx, ny) (n) (=' * ' + 2
+ ”'”'NX-' lny == (7I/
r, ...---NY-/), and the address coordinates of the spatial wave propagation function G are (mx, my)(r
nx=0. t, ko + “”” + MX ' *my
=Q + i + 2 + ・””・+ My i
), the reproduction result corresponding to each point in the image reproduction area is assigned, and the reproduction result is coherently added to the value of the reproduced image F (/ffA) shown in Fig. ψ before the relevant scan. , this update result address (nx+m)(
+ny+my).

By performing these operations sequentially for each scan,
The reconstructed image for the entire imaging target area is obtained by processing the complex hologram corresponding to each scan point after the last scan of the required number of scans is completed, and then By determining the value, a reconstructed image intensity distribution IF(X, Y)l given by the equation Is1 can be obtained. At this time, the area in the reconstructed image that has a sufficient synthetic aperture length is the area that is inside by Mx and MY from both ends of the reconstructed image area (Nx+Mx, Ny+My'), and its size is ( Nx-Mx.

NY-MY), and this area becomes the imaging target area.

According to this embodiment method, 1J? ! The reproduction process and the scanning operation of the transmitter/receiver can be performed in parallel. After the completion of the scan, a reconstructed image can be obtained within the time required for one scan.

In addition, as the method of the above embodiment, the case where image reconstruction is performed using a complex hologram has been explained, but even if the hologram has only a real part, when using the synthetic aperture method, it is determined by the scan coordinate and the synthetic aperture length. Once the coordinates of the spatial wave propagation function are determined, the coordinates of the reconstructed image area where the reconstructed calculation results are coherently added can be determined, and since image reconstruction processing can be performed for each scan, it is possible to obtain a reconstructed image immediately after the scan is completed. In this respect, the same effects as the present invention can be obtained.

〔Effect of the invention〕

As explained above, the image reproduction method using ultrasonic or electromagnetic wave holography according to the present invention is based on the synthetic aperture method, and is obtained by transmitting and receiving signals for each scan from an ultrasonic or electromagnetic wave transmitter/receiver or a transmitter/receiver array. The reflected wave signal from the target object is phase-detected, and the complex hologram obtained at each position of the transmitter/receiver is digitized. Since the image reconstruction processing is sequential in that coherent addition is performed on the reconstructed image coordinates determined from the wave propagation function coordinates, the imaging target area is The reproduction of the image is also completed, and the effect that the required image reproduction can be achieved in an extremely short period of time is achieved.

Brief explanation of tA V plane 9.1 is an explanatory diagram of the image reproduction process in the embodiment method of this invention, and Figure 2 is a principle explanatory diagram of the image reproduction method by ultrasonic holography based on the one-synthetic frontage method. FIG. 3 is a functional block diagram for explaining a conventional image reproduction method, and FIG. 9 is an explanatory diagram of image reproduction processing in the conventional method.

(c. - Ultrasonic transducer, (=)... point-like object, (3).
・Pulser/receiver section, (cap/φ oscillator, (5)...9
(g) phase shifter, (4+, (ri)-fist phase detector, (g
), Iql... A/D conversion section, (lO), (/l)...
φ hologram signal memory section, (t2')...control section, (13)...-spatial wave propagation function memory section, (
/q)...Signal processing section, (ts)...Image display section, (t
6), (tt, A)...Hologram data H, (tt)
, (tqA)...Spatial wave propagation function G, (tt'), (
tgA')φ・Reconstructed image F.

Claims (1)

[Claims] In an image reconstruction method using ultrasound or electromagnetic wave holography based on the synthetic aperture method, reflected wave signals from a target object obtained by transmitting and receiving ultrasound or electromagnetic wave signals for each scan from an ultrasound or electromagnetic wave transmitter/receiver or a transmitter/receiver array are used. The complex hologram obtained at each position of the transmitter/receiver by phase detection is digitized, and the product of the previously calculated ultrasonic or electromagnetic wave wavelength and the spatial wave propagation function determined by the spatial coordinates of the hologram surface and the reproduction surface is calculated. An image reconstruction method using ultrasonic waves or electromagnetic wave holography, characterized in that an image reconstruction process is performed in which the image is coherently added on reconstructed image coordinates determined from hologram coordinates and spatial wave propagation function coordinates.