JP2676014B2 - Transmission method of ultrasonic imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of transmitting waves in an ultrasonic imaging apparatus, and more particularly, to a method of transmitting waves in an ultrasonic imaging apparatus capable of preventing the generation of false images and obtaining highly accurate images. It is about the method.

[0002]

2. Description of the Related Art An underwater television can accurately capture the shape and color of an object, but is limited to a short distance of at most several meters to obtain a clear image even under normal transparency. It On the other hand, since ultrasonic waves are absorbed in water much less than light, ultrasonic waves can reach as far as several hundred meters. Therefore, it is well known that it is possible to obtain a highly practical video device for industrial purposes and various developments are in progress.

In order to obtain an image of a three-dimensionally distributed object, conventionally, a plurality of transmitters and receivers are used, and the phases of the transmitters and receivers are shifted to direct ultrasonic waves toward a symmetrical object. The target point image is obtained by transmitting the reflected wave and the target point image, and the three-dimensional image is obtained by scanning each target point in the target space. In this method, the time from the time of transmission in each scanning direction to the reception (delay time) is obtained, and the image is obtained from the distance to the reflection and the reflection intensity, until the reflection wave is received. There is a problem that it takes time to obtain an image of the entire target space because the next wave cannot be transmitted, and an electronic circuit for analyzing the data becomes complicated.

Therefore, the inventors of the present invention invented an ultrasonic imaging apparatus which obtains image data of the entire target space by one transmission, and is disclosed in Japanese Patent Application No. 63-267176 (JP-A-2-1141).
No. 89). An example of the transmitting / receiving array 1 used in the present invention is shown in FIG. 6, the transmitting / receiving array 1 includes a plurality (16 in FIG. 6) of omnidirectional transmitters 2i (i = 0 to 15, the suffix i is omitted when collectively referred to. As well),
A plurality of (8 in FIG. 6) omnidirectional receivers 4q (q = 0 to
7) were arranged at equal intervals on the concentric circles, and the normal direction passing through the center was arranged toward the target space.

Control of the transmitting / receiving array 1 and signals and image processing are performed by the circuit shown in FIG. In the figure, a microcomputer 6 connects a timing generator 8 for transmission timing and a transient memory 10 for temporarily storing a reception signal with a data bus 12.
The ultrasonic signal transmitted from the transmitter 2 is given from the driver 14 controlled by the timing generator 8. The driver 14 is a power FE (not shown).
It is composed of a transmission amplifier including a switching circuit using T, a phase modulation unit 16 (FIG. 8) and the like.

The reflected wave signal received by the wave receiver 4 is
It is temporarily stored in the transient memory 10 as a series of signals ordered for each of the receivers 4 by a multiplexer 18 having an A / D converter (not shown), and is taken into the microcomputer 6 as data in accordance with a command from the timing generator 8. Be done. The conversion timing pulse of the A / D converter used in the multiplexer 18 is synchronized with the reference clock used to generate the transmission wave. Instead of the multiplexer 18, A / D converters arranged in parallel can be used. The timing generator 8 uses a binary logic signal for both the carrier wave and the phase-modulated wave, and is composed of switches that are alternately turned on and off, and a rectangular wave is used as a drive signal. 2 as a whole
The value signal was used to more easily construct the circuit.

The feature of the invention of the application is that the ultrasonic pulse signals transmitted from the respective wave transmitters 2 are phase-modulated by a modulating wave composed of an orthogonal function such as a Walsh function, and the signals transmitted from the respective wave transmitters 2 are identified. There is a point that made it possible. When the orthogonal function is used in this way, when the correlation with the transmission signal of each reception wave is obtained, a correlation of 1 is obtained for signals of the same phase,
Since the correlation of signals transmitted in different phases is 0, it is possible to identify from which of the transmitters 2 the signal is transmitted. Therefore, it is not necessary to scan the target space with the directional transmission signal, the signals can be transmitted simultaneously in the space, and the time for obtaining one image can be significantly shortened.

The phase modulator 16 of which an example is shown in FIG. 8 will be described. The phase modulator 16 is provided in the driver 14 as described above, and transmits ultrasonic waves output from the carrier wave oscillator 20 to each transmitter by a modulation wave provided from the function generator 22 of the Walsh function and Hadamard matrix. Phase modulation is performed by the phase modulation circuit 24i provided corresponding to 2i. That is,
As the carrier wave, for example, an ultrasonic wave of 50 kHz is used, and this is modulated from the Walsh function generator 22 by a modulation wave previously determined for each wave transmitter 2i. The modulated wave by the Walsh function is a pulse signal obtained by multiplying by 1 or −1 with an integral multiple of one cycle of a sine wave or a rectangular wave as a unit.

The state of this phase modulation will be described with reference to FIG. In the figure, a carrier wave consisting of a sine wave is used as a pulse wave for one transmission, and a pulse wave from the oscillator 20
Output to 16. The illustrated Walsh function waves are 1,1,1,1,1,1,1,1,1, 1,1, -1, -1, -1, -1, -1, in order from the upper center of FIG.
The modulated waves of 1,1, 1, -1,1, -1,1, -1, -1,1, -1 are represented, and the signal waveform phase-modulated by this is shown on the right side of FIG. Since all the row vectors are orthogonal to each other in the matrix in which the signal sequence of each of the transmitters 2 is a row element, the transmitter 2 is obtained by obtaining the correlation function of the received signal and the transmitted signal.
Each signal can be separated. That is, the modulation signal Ui (t) from the i-th transmitter 2 is defined as shown in the following equation (1).

[0010]

However, Δt represents a modulation period (1 clock width), and the modulated wave is defined by the following formula 2 where frequencies f ₀ and n are integers.

[0012]

When the modulated wave is a sine wave,
Depending on when t is 0 ≦ t ≦ Δt and when t> Δt,

[0014]

Takes a value of. This is an object (a set of scattered points)
When the signal of Rk (t) is obtained at the k-th receiver 4 by being scattered by the interference signal Rk (t) and the transmitted signal U,
The correlation function with i (t) is given by

[0016]

Can be obtained by However, τ
Is the transmission signal Ui in the correlation calculation with the interference signal Rk.
Represents the time difference given to. Since Ui (t), which is the reference in the formula of Formula 4, is an orthogonal function as described above, the calculation of Formula 4 has a cross-correlation of 0 for an object in the paraxial region with respect to the array, and Only the correlation function has a constant value. Therefore, when τ is constant for i of the transmission signal, the signal component can be accurately separated and extracted.
Therefore, the ultrasonic imaging apparatus of the present invention can be made simpler and smaller than the ultrasonic imaging apparatus before that, and the time for obtaining the image of the target space can be much shortened. did it.

Next, the outline of the image processing will be described with reference to FIG. The data processed by the microcomputer 6 is given to the minicomputer 26, where it is subjected to image processing. The means can simulate the three-dimensional shape of the pulse wave when the scattered wave passes through each of the wave receivers 4 and the traveling direction of the wave, depending on the time when the scattered wave reaches the wave receivers 4. is there. Therefore, the position of the scattering point can be known by reversing the simulated scattered wave and obtaining the convergence position of the wave. If this is calculated for all received signals, data regarding the shape and position of the object in the target space can be obtained. A three-dimensional image can be displayed by displaying the data on the display device 28, for example, by displaying a distant object (that is, an object that takes a long time to converge) dark and a near object bright.

[0019]

By the way, in the ultrasonic imaging apparatus of the above-mentioned invention, the interference wave observed at the ultrasonic scattering point deviating from the front of the transmitting / receiving array is a path in which the transmission signals transmitted at the same time are different from each other. To propagate in
There is a problem in that transmission signal pulse waves having a large time difference are added to each other, orthogonality is broken, a suspicious image is likely to appear, and it is difficult to obtain correct video information. Hereinafter, this problem will be described with reference to FIG.

In FIG. 10, the coordinates of the transmitters 2 ₄ and 2 ₁₂ arranged in a circle with a radius R are (-R,
0,0) and (R, 0,0), and the coordinates of the scattering point A and the scattering point B are given as (0,0, z ₁ ) and (x _1, y _1, z ₁ ), respectively. To be Therefore, the scattering point A on the Z axis is equidistant from the transmitter 2 ₄ , the transmitter 2 ₁₂ and any other transmitter 2. On the other hand, the scattering point B does not have the same distance from the transmitter 2 ₄ and the transmitter 2 ₁₂ . In this way, the scattering points on the XY plane away from the Z axis are not constant. Therefore, each transmitter 2
The signals simultaneously transmitted from the laser beams arrive at the scattering point A at the same time, but cannot reach the scattering point B off the Z axis at the same time, which causes a difference in the propagation time τi. Therefore, the interference signal Rk (t) b (suffix b is the scattering point B
Is a function of the propagation time difference τi, and the following equation 5

[0021]

The row vector of the Hadamard matrix, represented by, is shifted with respect to time. Therefore, the cross-correlation term between the interference signal Rk (t) b from the scattering point B and the transmitted signal Ui (t-τ) does not become zero, and the orthogonal relationship becomes incomplete in the calculation of the equation (4). The problem arises. Therefore, when the existence probability of an object in the space is obtained by the correlation calculation, the value of this cross-correlation appears as the existence probability and a suspicion is generated. Therefore, there is a problem in obtaining a highly accurate image.

The present invention has been made by paying attention to the above problem, and transmits transmission signals, which are phase-modulated by a Walsh function and are orthogonal to each other, from a plurality of omnidirectional transmitters simultaneously into a target space. However, in an ultrasonic imaging apparatus that receives the interference wave with a plurality of wave receivers and processes the data, even for an interference signal for each wave transmitter obtained from an object at a position where the distance from each wave transmitter is different, An object of the present invention is to provide a transmission method for an ultrasonic imaging apparatus that can obtain orthogonality.

[0024]

In order to achieve the above object, the structure of the transmission method of the ultrasonic imaging apparatus of the present invention is such that a plurality of omnidirectional transmissions arranged two-dimensionally toward a target space. A pulsed ultrasonic wave signal is simultaneously transmitted from the wave element, and a plurality of omnidirectional wave receivers receive a scattered wave in which the ultrasonic wave signal is scattered in the target space, and the received wave signal is transmitted. In the method of calculating the distribution of the scattering points of the ultrasonic wave in the target space from the elapsed time from the reception to the reception and the intensity, the ultrasonic signal is an ultrasonic carrier wave by a modulated wave composed of an orthogonal function. Phase modulation is performed by changing the combination of the phase-modulated wave and the wave transmitter with a different modulation wave for each wave transmitter and for each wave transmitter, and transmitting the waves multiple times at time intervals that do not interfere with each other. The plurality of transmission signals, and the transmission number and transmission order And are converted into a binary number representation to obtain an exclusive OR for each bit, and a signal having an orthogonal function number matching the sum is transmitted from the transmitter, and a signal having an orthogonal function number matching the sum is transmitted. The distribution of the scattering points is calculated from the received signals of the plurality of times.

The target space means a constant visual field range in water and in the air. In order to calculate the distribution of scattering points once, the number of transmissions of the ultrasonic signal transmitted from each transmitter is
If the number of times is two or more, preferably a multiple of 4, it is possible to obtain data with a more even energy distribution for each point in the target space. The maximum number is not particularly limited, but is usually the number of times equal to the total number of transmitters. It is possible to increase the accuracy of the existence probability as the number of times of transmission increases, while giving the maximum value of the ratio for each of the multiples of 4.

The calculation of the distribution of scattering points by transmitting a plurality of times as described above is performed by calculating the distribution of a scattering point once by transmitting each of a plurality of transmission signals having the same ultrasonic path and no propagation time difference. This can be performed by means for obtaining the sum of the received signals for each and calculating the sum as the received signal. The Hadamard matrix used for the phase modulation is a symmetric matrix, that is, the row number is i,
When the element having the column number j is represented by Wij displayed in binary or binary, Wij = Wji and the row vectors are orthogonal to each other. The Walsh function used for the phase modulation is a function that satisfies this orthogonal condition. Then, the line number i represented by the binary number is made to correspond to the transmitter number,
When the column number j is associated with the signal sequence, the equation 6 representing the orthogonal function is obtained.
And the formula of the Walsh function of Formula 7.
That is,

[0027]

[0028]

However, i and j are represented by binary numbers, XOR represents an exclusive OR, and δij is Kronecker's delta, that is, i.
The symbol is 1 if = j and 0 if i ≠ j. Therefore, the Mδij is a finite value M if i = j, and i ≠ j
Then it will be 0.

[0030]

According to the present invention, orthogonality is established for all rows of the Hadamard matrix consisting of the elements 1 and -1. In addition, as a property of the Walsh function, the product of two functions is equal to a function in which the number of the function is displayed in a binary number and the exclusive OR is obtained for each bit. When these are applied to the phase-modulated wave by the Walsh function, it was made paying attention to the time-division transmission in which transmission and reception are sequentially performed from each transmitter. Then, the method of the present invention having the above-mentioned structure is obtained by performing wave transmission a plurality of times, preferably four times or more, more preferably a multiple of four, and usually, the number of wave transmitters is set as the maximum number of repetitions. It has been found that it is possible to prevent the occurrence of false images by calculating the distribution of ultrasonic scattering points from the received signals that are received.

In the following, the operation will be described using mathematical formulas in the case where the number of transmitters is used to transmit using a quadrature signal modulated by the Walsh function. In the equation (6), the p-th transmission signal U _m ^(p) from the m-th transmission element is defined as follows.

[0032]

For the transmitted signal U _m ^(p) and the p-th transmitted signal U _n ^{(p) from the} _n- th transmitter, the correlation φ _mn after P times of transmission is obtained.

[0034] here,

[0035]

And W (m XOR p) i = Wmi · Wpi, W (n
XOR p) j = Wnj · Wpj

[0037]

## EQU4 ## Paying attention to the sum of the number of transmissions p, and setting the upper limit as p = M (number of transmitters), the equation 11 becomes

[0039] The following is derived from the orthogonal relationship of Expression 6.

[0040]

EXAMPLES The wave transmission method of the present invention will be described in detail by way of examples with reference to the accompanying drawings. In the present embodiment, FIG.
1 is used, the phase modulation section 16 of the basic circuit shown in FIG. 7 is changed to the circuit shown in FIG. 1, and the program of the microcomputer 6 is changed according to the method of the present invention. . Therefore, omitting duplicate explanations,
Only different parts will be described. In FIG. 1, the phase modulator 16 includes a carrier oscillator 20 and a Walsh function generator 2
2. The phase modulation circuit 24i and the switching circuit 30. The phase modulator 16 operates according to control signals from the microcomputer 6 (not shown in FIG. 1) and the timing generator 8 (not shown in FIG. 1).

The switching circuit 30 is connected to the Walsh function generator 22 and the phase modulator 24 by 16 lines (the same number as the number of the transmitters 2) 32i and 34j, respectively, and a specified specific The line 32i and the designated specific line 34j are connected according to the control signal of the timing generator 8 (FIG. 7). Below, this switching circuit 30
Will be described with reference to Tables 1 to 3 and FIG. (Margins below this page)

[0042] Table 1 exemplifies the Walsh function when the number of transmitters is 16. The modulated wave of the transmitted signal output from each transmitter 2 is 1 or -1 in the order of the column number for each row.
Is a signal sequence for outputting the binary number of the above with a constant clock width.
The row number in Table 1 of each signal sequence is hereinafter referred to as a modulated wave number. That is, the switching circuit 24 is
The 16 types of modulated waves with the numbers 15 are assigned to the respective wave transmitters 2 on the basis of the control signal given from the microcomputer 6 (FIG. 7). The clock width is Δt in the above formula 1 and is a time width corresponding to two cycles of the carrier wave.

The principle of the assigning operation performed by the switching circuit 30 will be described below with reference to Table 2. Column A of Table 2 is a number i (i = 0 to 1) for identifying the transmitter 2.
5) is displayed in binary. In this embodiment, 16
It was set to perform the calculation for obtaining the distribution of the ultrasonic scattering points once from the transmitted data. Then, in the first transmission, that is, p = 0 (see Eqs. 6 and 8), the modulation numbers 0 to 15 described in Table 1 are replaced by the transmission elements 2i (i =
The switching circuit 24 was controlled so as to transmit waves from 0 to 15).

The column B of Table 2 shows the third transmission (p
= 2), and is obtained as follows according to the present invention. That is, when p = 2 is represented by a binary number, it is displayed as 0010. Also, for example,
The transmitter number 6 is represented by a binary number 0110. When the bitwise exclusive OR (XOR) of these two binary numbers is obtained, 0110 is obtained as shown in Table 3.

This logical operation is performed by the microcomputer 6
To run. The result of performing the above calculation for each of the transmitters 2 is shown in column B of Table 2. The result of this binary operation is 10
The values converted to decimal numbers are shown in the decimal column of Table 2. The switching circuit 30 transmits each modulated wave of each modulation number based on the calculation result of the column B from the transmitter 2 of the corresponding number so as to transmit the signal of the modulation number at the left end of Table 2 to each line 32i.
Is controlled by the microcomputer 6 so as to connect to each line 34j. Table 3 shows the results. Table 3 shows
Each of the transmitters indicates which modulation number of the signal was transmitted during the p-th transmission.

[0046] FIG. 2 illustrates the relationship between the modulated wave and the phase-modulated transmission waveform in the case of Δt = 2 / f ₀ . The carrier wave used in this case had a sine waveform. Also,
The transmitting / receiving array 1 used has the same shape as that shown in FIG. 2, and 16 transmitting / receiving elements 2 are arranged at equal intervals on the circumference of a radius of 612 mm, on a concentric circle of radius 819 mm, etc. Eight wave receivers 4 were arranged at intervals.

In Example 1, one rod-shaped object was placed in the center of the field of view, and the phase modulating section 16 of FIG. 1 was used. (A in FIG. 3) was determined. On the other hand, from the same transmitting / receiving array 1,
The method of the invention of the prior application (comparative example 1: C in FIG. 3) in which signals are phase-modulated by the Walsh function at the same time from all the transmitters 2 and the comparative example for each transmitter 2i (i = 0 to 15) Comparative Example 2 (B in FIG. 3) was performed in which each signal of No. 1 was transmitted once so as not to interfere with each other and this was repeated four times. In Comparative Example 2, the sum of the number of the transmitter 2 and the number of transmissions indicating the number of transmissions and the number of transmissions modulo the number of transmitters corresponds to the row vector of the conversion code string, and theoretically,
There is no defect in the appearance of the suspicion of the invention of the prior application.

In Example 2, three rod-shaped objects were set upright at equal intervals and the central object was placed in the center of the visual field.
An image (A in FIG. 4) was obtained from the results of 16 transmissions under each transmission condition up to. Comparative Example 3 is an image (C in FIG. 4) of the result of performing the symmetrical object of Example 3 by the method of the prior invention, and Comparative Example 4 compares Comparative Example 3 with Comparative Example 2, It is an image (FIG. 4-B) obtained by repeating the transmission 16 times, so that the transmission signals from the respective transmission elements 2i (i = 0 to 15) do not interfere with each other.

FIG. 3 shows the transmission / reception array 1 from the front center 1
The conditions were set dimensionally with ultrasonic scattering points arranged. The results are that in Comparative Example 1, the suspicious image is significantly suppressed in comparison with Comparative Example 1, but the results of Example 1 are shown. Is further improved. Also, FIG.
The ultrasonic wave scattering array 1 is two-dimensionally arranged from the front center thereof under the condition that ultrasonic scattering points are arranged, and the result is as follows.
As the condition becomes stricter than in the case of FIG. 3, more suspicious images are generated. However, with respect to the result of Comparative Example 3 in which transmission is performed once,
In Comparative Example 4 in which this was transmitted in 16 times and repeated 4 times, the occurrence of false images was significantly suppressed, and in Example 1,
Furthermore, it was confirmed that the generation of false images could be suppressed.

In the third embodiment, the phase modulator 16 of FIG. 1 is used, and the distribution calculation of the scattering points is performed a plurality of times (including one time) from one time (prior invention) to 16 times of transmission. ) Is obtained, and the ratio (minimum value / maximum value) of the minimum value and the maximum value of the received energy is calculated. The energy was calculated by the sum of squares of Rk (t) b shown in the equation (5). As shown in FIG. 4, the results of Example 3 show that the energy uniformity is rapidly improved from 1 to 4 times, and the number of transmitted waves is 4, 8, 12 and 16 times. ,Respectively,
The energy distribution becomes more uniform as a whole while increasing the maximum value as the number of transmitted waves increases to 0.980, 0.991, 0.990, and 0.993. The horizontal axis of FIG. 4 represents the number of times of wave transmission when one distribution calculation of scattering points is performed, and the vertical axis represents the energy ratio.

[0051]

As described above, since the transmitting method of the ultrasonic imaging apparatus of the present invention is configured, the ultrasonic scattering points (objects) are different from each other in comparison with the case where the prior invention is performed by transmitting once. When the distance from the transmitter is at different positions, the orthogonality between the received signals obtained from each transmitter is lost.By calculating the distribution of scattering points from the data transmitted multiple times,
Since the generation of false images is prevented and the existence probability distribution of scattering points is sharpened to obtain a clear image, it is possible to improve the image resolution and simultaneously transmit data from the transmitter array for data processing. It has become possible to make more effective use of the ultrasonic imaging device.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an outline of a phase modulator according to an embodiment of the present invention.

FIG. 2 shows the first four columns of the waveform of a transmission signal that is phase-modulated based on Table 1, where A is the waveform in the 0th row, B is the waveform in the first row, and C is the waveform in the second row. , D shows the waveform of the third row, respectively.

FIG. 3A is a graph of an image according to Example 1, and B is a graph.
Is a graph of an image according to Comparative Example 2, and C is Comparative Example 1.
It is a graph figure of the image by.

FIG. 4A is a graph of an image according to the second embodiment, and B is a graph.
6 is a graph of an image according to Comparative Example 4, and C is Comparative Example 3.
It is a graph figure of the image by.

FIG. 5 is a graph showing the result of Example 3 in which the ratio of the minimum value and the maximum value of the energy distribution is calculated with respect to the number of transmissions.

FIG. 6 is a front view of a transmission / reception array of the ultrasonic imaging apparatus according to the prior invention.

FIG. 7 is a control circuit diagram according to a block diagram of an ultrasonic imaging apparatus according to the prior invention.

FIG. 8 is a block diagram illustrating an outline of the phase modulator of FIG.

9 is a partial waveform chart showing an example of a waveform of a modulated wave obtained by the phase modulator of FIG.

FIG. 10 is a perspective view of a target space for explaining the problem of the prior invention described in FIG. 7.

[Explanation of symbols]

1 Transmit / Receive Array 2 Transmitter 6 Microcomputer 8 Timing Generator 10 Transient Memory 14 Driver 16 Phase Modulator 18 Multiplexer 20 Carrier Oscillator 22 Walsh Function Generator 24 Phase Modulator 26 Switching Circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hajime Yuasa Hajime 5-6-4 Tsukiji, Chuo-ku, Tokyo Mitsui Engineering & Shipbuilding Co., Ltd. (72) Shuzo Hisamoto 5-6-4 Tsukiji, Chuo-ku, Tokyo Mitsui Engineering & Shipbuilding (72) Inventor Norio Ishii 5-6-4 Tsukiji, Chuo-ku, Tokyo Mitsui Shipbuilding Co., Ltd. (72) Inventor Takashi Aoki 5-6-4 Tsukiji, Chuo-ku, Tokyo Mitsui Shipbuilding Co., Ltd. ( 72) Inventor Yukinobu Sanada 5-6-4 Tsukiji, Chuo-ku, Tokyo Mitsui Engineering & Shipbuilding Co., Ltd.

Claims (2)

(57) [Claims] 1. A plurality of omnidirectional transmitters arranged two-dimensionally toward a target space to simultaneously transmit pulsed ultrasonic signals, and the ultrasonic signals are scattered in the target space. The scattered wave is received by a plurality of omnidirectional receivers, and the received signal is a distribution of ultrasonic scattering points in the target space from the elapsed time from the time the signal is transmitted to the time it is received. In the method of calculating, the ultrasonic signal, the ultrasonic carrier, performs phase modulation by a modulation wave consisting of an orthogonal function, the phase modulation by a different modulation wave for each transmitter, moreover, for each transmitter, By changing the combination of the phase-modulated wave and the wave transmitter, it is transmitted a plurality of times at time intervals that do not interfere with each other,
For the plurality of transmission signals, the transmission element number and the transmission order are converted into binary notation to obtain an exclusive OR for each bit, and a signal having an orthogonal function number that matches the sum is transmitted from the transmission element. Then
A transmission method for an ultrasonic imaging apparatus, wherein the distribution of the scattering points is calculated from the received signals of a plurality of times. 2. A single calculation of the distribution of scattering points is performed to obtain a sum of received signals for each transmission obtained from a plurality of transmission signals having the same ultrasonic path and no propagation time difference, and the sum is calculated. The method according to claim 1, wherein the ultrasonic signal is calculated as a received signal.