JP3133764B2 - Acoustic image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION This application is filed on May 31, 1991 with the serial number 07 / 708,3.
It is a continuation-in-part application of Serial No. 07 / 891,851, filed on June 1, 1992, which is a continuation-in-part application of No. 54. The present invention relates to an image forming system and method, and more particularly to a system and method for forming an internal image of an object using mathematical methods and acoustic wave data.

In conventional fan-beam transmission tomography, such as used in X-ray computed tomography (X-ray CT),
As the fan beam probes the media along many different trajectories, the attenuation of the X-ray fan beam is measured. The information contained in these attenuated projection images is used to reconstruct a tomographic x-ray image of the medium. The success of X-ray CT (as revealed by the resolution and clarity of the image) is basically due to the incident X-ray beam Related to very short wavelengths. This mathematical reconstruction technique assumes a geometric ray approximation,
It has been greatly simplified.

In ultrasound tomography, the acoustic wavelength Is of the order of magnitude of the size of the non-homogeneous medium in the medium, and the diffraction effects of acoustic waves cannot be ignored. In this case, the attenuation of sound waves is substantially affected by dispersion effects such as diffraction, refraction, reflection and absorption. The simplified mathematical reconstruction algorithm used in conventional X-ray CT is not available in this case.

Ultrasonic diffraction tomography (UDT) technology seeks to mathematically reconstruct a tomographic image of a medium from acoustic wave data with due consideration of the dispersion effects associated with the acoustic wavelengths of interest. This is the full-wave equation,
This is done by considering an even more difficult problem to develop and implement than the geometric wave approximation reconstruction method used in X-ray CT. UDT technology seeks to determine the internal structure of an object through which acoustic waves pass halfway from a set of dispersive wave data detected outside the boundaries of the object.
Born approximation (E.Wols, “Three-dimensional
Structure Determination of Semi-Transparent
Objects from Holographic Data ".Opt.Comm.153-
156 (1969) and the Rytov approximation (AjDevaney,
“Inverse Scattering Within the Rytov approxi
mations ", Opt. Lett, 6, 374 (1981)), several of these mathematical techniques were considered in theory, including a simplified algorithm. Assume that the medium is a weak dispersion of the acoustic wave and that the acoustic wave does not experience a large phase shift in the medium.Computer-lumped full-wave reconstruction algorithms (S. Johnson and M. Tracy, " Inverse
Scattering Solution By a Sinc Basis, Multi
ple Source, Moment Method "Ultrasonic Imaging
5, 361-375 (1983) and references therein) have been proposed for imaging media under conditions that do not fall within the validity of the Bone or Litoff approximations. Prior art patents include Devaney (U.S. Pat. No. 4,598,3).
Nos. 66 and 4,594,662) and Johnson (U.S. Pat.
No. 662,222). Johnson's patent discloses an iterative algorithm that forms an initial estimate of the speed of sound at every point within the object being imaged, calculates a sound speed map (a type of image), and updates this map. . This method is repeated until the remaining error parameters are small enough. Devaney's patent is a technology called filtered back propagation,
An image is formed directly from the data using bone inversion and Litov inversion.

SUMMARY OF THE INVENTION It is an object of the present invention to create an acoustic hologram by applying ultrasonic waves to a medium, to record information about the ultrasonic waves dispersed from the medium, and to quickly and efficiently construct an image of the medium. To provide systems and methods for using that information.

The present invention provides an acoustic image forming apparatus in which a large number of transducers are spaced apart from each other by a distance smaller than half the wavelength of an acoustic wave on a circle surrounding an image forming object. The signal generator generates discrete acoustic frequencies ranging from 100 kHz to 1.5 MHz. The multiplexer systems (1 to 8)
Each transducer is provided so that it can broadcast one signal at a time, the broadcast signal being detected by the other transducers. The electronic device records the detected signal and from this recorded information,
Phase and amplitude data is calculated for each transducer location. A computer programmed with the algorithm uses the phase and amplitude data to form a slice image across the object to be imaged. A single frequency steady state acoustic signal is utilized that allows accurate determination of the phase and amplitude of the acoustic signal at each receiving transducer. Finally, in order to reduce data acquisition time and artifacts, an acoustic signal is used, where each frequency consists of a plurality of discrete identifiable frequencies providing an image of the medium.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram used to illustrate the mathematical reconstruction algorithm.

FIG. 2 is a block diagram of the electrical circuit used in the exact prototype device of the present invention.

FIG. 3 is an illustration of a computer-simulated object used to illustrate some of the features of the present invention.

FIG. 4 shows a real (right) component and an imaginary (left) component of the simulated object single-frequency image.

FIG. 5 shows the sound speed c (r, θ) of the simulated object.
(Left) map and attenuation μ (r, θ) (right) map.

FIG. 6 shows a real (right) component and an imaginary (left) component of the simulated object. These images are the sum of the single frequency images shown in FIG. 5 with the phase shift corrected.

FIG. 7 is a composite image of the simulated object. This combined image is obtained by combining the sound speed map depicted in FIG. 6 and the real components of the image depicted in FIG.

FIG. 8 shows nine images of a female breast generated by a suitable algorithm using the prototype apparatus depicted in FIGS.

FIG. 9 shows 9 pig pig kidneys generated by a suitable algorithm using the prototype device depicted in FIGS.
Shows three images.

FIG. 10 shows images of nine slices of a normal female breast generated with the prototype device depicted in FIGS.

FIG. 11 shows images of nine slices of a female breast with a cyst generated with the prototype device depicted in FIGS.

FIG. 12 shows images of pig kidneys generated with the prototype device depicted in FIGS.

FIG. 13 is an illustration of the invention used in bust formation to show how slices are obtained at various locations.

FIG. 14 is an illustration of the present invention utilized for abdominal imaging.

FIG. 15 is an illustration of an application example of the present invention used for a living tissue inspection needle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a system for applying acoustic waves of discrete frequencies from a plurality of locations to a medium and recording data representing the acoustic waves dispersed from the medium. An algorithm is provided for calculating an image of the medium from the recorded data.

A. Description of the Apparatus A cross-sectional view of a portion of the preferred embodiment and a schematic diagram of the object to be imaged are shown in FIG. In this embodiment, the radius r _o = 10
There are 1024 acoustic transducers 10, ie 10.1,..., 10.1024, arranged at equal intervals on the locus of a 2 mm circle. The transducers 10 can each function as either a transmitter or a receiver for acoustic waves, and have a thinner approximation to a plane referred to herein as the (r, θ) (or (X, Y)) plane. Arranged in slices. z
The direction is perpendicular to this plane. A transducer 10 circumscribes an object 9 supposed to pass half an acoustic wave. In this preferred embodiment, coupling fluid 11 is in a residual volume (shown as a region) inside the circle to effectively couple acoustic waves between transducer 10 and object 9. The object 9 and the coupling fluid 11 in this residual volume
Will hereinafter be referred to as the medium 12. Water is a suitable fluid for imaging human tissue because water and human tissue have approximately equal speeds of sound and densities. For other imaging, the coupling fluid 11 should be selected to have a density ρ _o and a sound velocity c _o approximately equal to the average density and sound velocity of the object 9 to be imaged (salt water is And, sometimes, better than pure water for use with human tissue).

In the preferred embodiment of the present invention, each transducer 10
Has a center frequency of 1 MHz, a bandwidth of 60%, and
Act as an acoustic wave receiver or transmitter at different times. Underwater at 1 MHz frequency, the acoustic wave is λ ₀ =
At 1.5 mm, this wavelength is about the same in human tissue. Mutual spacing of the transducer is a 0.65 mm, in order to carry out proper sampling of the dispersion wavefront (i.e., for avoiding aliasing) lambda somewhat smaller than _0/2. This makes it easy to construct a unique image from the acquired data. In the preferred embodiment, each transducer has a dipole radiation pattern in the (r, θ) plane. The vertical height of the transducer 10 is 12 mm, and each transducer is made substantially parallel in the z-direction over a z-direction distance of about 12 mm to produce a beam propagating from the transducer in the (r, θ) plane. . Thus, one can expect that any image obtained will represent the average of the variance information over the height of the transducer (ie, a slice about 12 mm thick), so that the vertical height of this transducer is approximately Acoustic holograms are created by exposing acoustic waves to an effective thickness across equal media.

A schematic diagram of the experimental system is shown in FIG. The transducer ring 10 consists of 1024 acoustic transducers 10.1, ..., 10.10 arranged in a circle with a radius of 102 mm.
Consists of 24. The transducer ring 10 is divided into eight octants, shown as octants 1 through 8, each octant containing 128 transducers.
Eight multiplexers 70 are coupled to the transducer ring, each multiplexer 70 being a two-channel 64-to-one receive multiplexer 72, and two amplifiers 74 each connected to one channel of the receive multiplexer 72. , 2-channel 64-pin transmission multiplexer 7
6, each comprising two drivers 78 for driving one channel of the two-channel transmission multiplexer and an address recorder unit 79. The data is 16
Collected by eight two-channel analog-to-digital converters 22 with megabytes of Bach memory. System timing is achieved by a programmable timing / control unit 42 and a programmable master clock 28 which drives a phase-locked arbitrary waveform generator 26. The entire system is controlled by a supervisor (management) computer 30, which is associated with a high resolution monitor 32, a keyboard 34, a three gigabyte hide drive 38, and an Ethernet link 31. The timing instruction is sent to the transducer multiplexer 70 via the instruction interpreter 50. The transmitter signal is generated by the arbitrary waveform generator 26 via the transmit bach 52 and sent to the transducer multiplexer 70.

The individual components of the preferred system described herein will now be described in detail.

1) Transducer The transducer 10 used in this system is composed of a composite of a piezoelectric material and a non-piezoelectric material. Each transducer 10 has a center frequency of 1 MHz, a bandwidth of 60%, and operates as an acoustic wave receiver or transmitter at different times. Underwater at 1MHz frequency,
The acoustic wave is λ _O = 1.5 mm, which is approximately this wavelength in human body tissue. The spacing between the centerlines of adjacent transducers should be λ _O / 2 in water for proper sampling of the dispersive wavefront (ie, to avoid aliasing).
Somewhat smaller than. Furthermore, since the width of each transducer is smaller than λ _O / 2,
It has a dipole antenna pattern in the (r, θ) plane. This means that the relative amplitude of the transmitted acoustic energy follows a cosΨ function of the angle に 関 し て measured with respect to a vector perpendicular to the front of the transducer. There are two acoustic impedance matching layers 17 between the transducer 10 and the coupling fluid 11. These layers 17 help couple acoustic energy from the acoustic transducer 10 to the coupling fluid 11. Furthermore, these layers 17
It helps to minimize the amount of acoustic energy reflected back from the front of the transducer 10 into the medium 12. This reflected acoustic energy manifests itself as an imaging artifact in the final image of the medium 12. Some variations in the transducer configuration may be used instead of a composite of piezoelectric and non-piezoelectric materials. These include piezoelectric zirconates such as PZT5
A), transducers made of piezoelectric film (PVDF) or copolymer.

2) Transmitter and receiver multiplexers The transmitter and receiver multiplexers and units are preferably made of off-the-shelf multiplexers commonly used in communication devices. here,
Analog Device Inc.
ADG506 device and Com-Linear CLC522 device are used.

3) Address Decoder This address decoder 79 is a type EP910 programmable logic device provided by Altera Corporation. This unit is programmed to operate the multiplexers 72,76.

4) Instruction interpreter The instruction interpreter 50 has a programmable timing /
Upon receiving a command from the control module 42, the command is transmitted to the address decoder 79 in the multiplexer 70 to operate both the transmitting and receiving transducers. Altera for instruction interpreter 50
Uses a type EP1810 programmable logic device supplied by Corp.

5) Programmable Master Clock The programmable master clock 28 is a computer programmable generator that can accurately generate known clock frequencies for this system. This element 28 generates the main time axis that synchronizes all elements of the system, but is set when the system is initialized for data collection algorithms in use. This programmable master clock 28
Model No.1391 supplied by WaveTek Corporation
VXI module.

6) Programmable timing / control module 42
Formed near the IDT2910 microsequencer from vance Micro Devices Corporation. The programmable timing / control module 42 is made of a programmable bit slice microsequencer and microinstruction RAM clocked and controlled by the programmable master clock 28. This device is designed to generate a unique bit pattern on each successive clock cycle. It is used to initialize the multiplexer, control the instruction interpreter, generate a sample clock to the analog-to-digital converter 22, trigger the arbitrary waveform generator, and enable data acquisition. This programmable timing / control module 42
Are synchronized with the time base generator, so that all of these functions are phase-locked. This module 42 is designed as an interface with the VME bus chassis of the supervisor 30 described below.

7) Arbitrary Waveform Generator The arbitrary waveform generator 26 is a phase-locked computer programmable generator that can generate various arbitrary analog output waveforms required for various data acquisition methods. It is used to synthesize the waveform transmitted to the medium 12 via the transducer 10. It is phase locked to the programmable master clock 28, and
This transmitted waveform is phase locked to the data acquisition sequence as triggered by the programmable timing / control module 42. This arbitrary waveform generator 26
Model number 1395 VX supplied by Wavetek Corporation
It is an I module.

8) Analog-to-digital converter The analog converter 22 is designed by Signal Processing Tec.
Type SPT7922 12-bit, 30MH supplied by hnologies
z Mainly performed by analog-to-digital converters.
Each channel has 8 megabytes of local Bach memory. The analog-to-digital converter 22 is programmed to collect analog data received via the receive multiplexer 72 and temporarily store this data in a digital Bach memory. The preferred system has a 16-channel analog-to-digital converter with a capacity to store 128 megabytes of data.

9) Computer Superviser The entire control of the image forming apparatus is performed by the computer superviser 30. This computer superviser
30 is used to initialize the system, compile and download timing and control algorithms, perform test functions, collect raw data, and execute data editing and reorganization algorithms that generate the final image. The interface to this device is provided by a keyboard 34 and a monitor 32. A three gigabyte hard drive 38 is provided for data storage. The Ethernet link 31 downloads or uploads data and algorithms provided from this device for subsequent offline processing and organizing and editing. Supervisor 30 is a suite of foundation-level products from Radisys Corporation based on the Intel 80486 computer family.
Compiler provided by Zortech Corporation.

10) Significant elements Images obtained with a prototype-like device composed of the inventor and the co-workers are reproduced in FIGS. These images and the particular algorithm used to obtain these images are described in detail in a subsequent part of this patent. Applicants believe that these images
I believe that it is by far the best tomographic image obtained with an acoustic device.

The main principle of the present system that has provided the above improvement over the prior art is the combination of the following hardware elements: 1. A circle surrounding the object is approximately λ / 2 (where λ is A large number of transducers located at a distance that is approximately less than the acoustic wavelength in the medium 12; 2. incident acoustic waves (compared to acoustic wavelengths used in the prior art at frequencies in the range of 3 MHz to 10 MHz); The distortion is greatly reduced for the in-phase wavefront of 100kHz and 1.5M, which allows this acoustic wave to traverse human tissues such as female breasts
Various acoustic frequencies between Hz. The acoustic frequencies in this preferred embodiment are low enough that the reconstruction algorithm can more accurately calculate the final image from the acquired data. However, this acoustic frequency is high enough to provide sufficient spatial resolution in the final image.
Also, the use of acoustic frequencies in the range of 100 kHz to 1.5 MHz minimizes the attenuation of incident acoustic waves, thus enabling the generation of a single large format image of a large portion of tissue.

3. A medium that allows accurate measurement of the phase and amplitude of the acoustic wave at each discrete frequency at each receiver transducer
Creating acoustic holograms by applying acoustic waves in the steady state at 12 discrete frequencies.

4. It is possible to record and store a very large amount of acoustic data quickly in order to develop a data madix that can calculate images.

5. Electronic system for phase synchronization of all aspects of acoustic data generation and collection.

B. Description of Data Acquisition Process The data acquisition process is described for each transducer 10.j (j
= 1,..., N), sequentially operate as a transmitter of a continuous wave single frequency sound (frequency ω ₁ ),
0.k (k = 1,..., N; kNj) means that subsequent reception of the dispersion liquid is performed. Acquisition information is m _jk (ωα) for data acquired at the acoustic hologram creation frequency ωα by applying an acoustic wave (“α” in ωα is a subscript / 4 character; the same applies hereinafter). j, k = 1, ..., N) and is referred to (N-1) in the form of NxN complex matrix with ^two coefficients. (N-1) ² = 1023 ^two coefficients m _jk (ω
α) (j, k = 1, ..., N; jNk) may be collected as described in the following example.

An imaging object 9, such as a female breast, is placed inside the transducer ring 10. The coupling fluid 11 is
And the transducer ring 10.
With operator signals from the keyboard 34, the individual components of the system are initialized by the computer superviser 30. The operator issues commands to the programmable timing and control module 42 to initiate the acquisition sequence. The timing / control module 42 sends a series of instructions to the instruction interpreter 50 to reset the transmitter and receiver multiplexers 60 to their initial state.

Arbitrary waveform generator 26 is then triggered to cause first transmitter 10.1 to broadcast a single frequency (ω ₁ = 687 kHz) sinusoidal acoustic signal to medium 12 via transmit multiplexer 76. This transmitted acoustic wave is dispersed by the inhomogeneity in the medium 12 and hits the other N-1 transducers 10.2, ..., 10.1024, which convert these acoustic signals to a single frequency. To an electrical signal. After a time T = 270 ms, which is twice the propagation time of the acoustic wave across the diameter 2r _O of the device, the acoustic signal of each transducer has reached a steady state. At this time, the electric signals from the respective transducers 10.2 to 10.1024 are sent to the eight 2-channel analog-to-digital converters 22 via the reception multiplexer 72. The exact data acquisition process for each transducer 10 proceeds as follows. Superviser 30 commands programmable timing / control module 42 to provide four quadrature (quadrat) signals from each transducer 10.2 to 10.1024.
ure) Allow the measurement to be performed. These four measurements, denoted A, B, C, and D, are phase synchronized with the signal from the arbitrary waveform generator 26.
5 is a measurement of the voltage output of the transducer in four short, equally spaced intervals during the acoustic period. For example, the input frequency when the 1 MHz (1 cycle is 1x10 ^-6 sec), samples are taken at 0.25X10 ^-6 seconds. The real part of the complex amplitude is determined by subtracting the measured value B from the measured value D, and the imaginary part is determined by subtracting the measured value A from the measured value C. This calculated complex amplitude at each transducer has the phase amplitude information of the acoustic wave at each transducer 10.2 to 10.1024 compared to the input signal from 10.1. This data is temporarily stored in the bat memory unit of the analog-to-digital converter unit 22.

The system has eight two-channel analog-to-digital converters so that signals are recorded in parallel from the transducer 10. 16 transducers 10.2,1
The first signals from 0.66, 10.129, ..., 10.961 are recorded simultaneously. These 16 converters 10.2, 10.66, 10.129, ..., 10.9
After obtaining the data from 61, the receive multiplexer 72
The signals from the 10.3, 10.67, 10.130,..., 10.962 transducers are sent to an analog-to-digital converter 22, which obtains data from these transducers. This acquisition process continues until each analog-to-digital converter 22 has acquired data from 64 transducers 10. This acquisition process requires 270 milliseconds for the signal to reach a steady state, and 512 milliseconds for each analog-to-digital converter 22 to obtain samples from 64 transducers 10. Each receive transducer relative to the transmit transducer 10.1 10.
The digital value representing the phase and amplitude of 2, ..., 10.1024 is N
−1 (ie, 1023) complex coefficients m _jk (ω ₁ ) (j =
1; k = 2,..., 1024) is recorded in the Bach memory of the analog-to-digital converter 22. This data collection process
We now continue by sending an electrical signal of ω ₁ = 687 kHz to the transducer 10.2 acting as a transmitter of acoustic energy. After another time, T = 270 ms, required for the system to reach a steady state, 1023 complex coefficients M
Electrical signals are sequentially measured from the transducers 10.1, 10.3,..., 10.1024 as described above to collect _jk (j = 2; k = 1, 3,..., 1024). This measurement process continues until each transducer 10.1,..., 10.1024 operates as an acoustic wave transmitter. When operating as that transmitter,
A complete set of data representing the complex coefficients m _jk (ω ₁ ) (j, k = 1,..., N; jNk) is recorded for a frequency ω ₁ = 687 kHz. A complete set of data at a single acoustic frequency is obtained in about one second. In a preferred embodiment, the entire previous measurement process consists of a separate m at each of ten discrete frequencies ωα (α = 1, 2,..., 10) separated by 62.5 kHz from 687 kHz to 1.250 MHz. Repeat 10 times to get _jk (ωα).

First, to calibrate the apparatus, a complete set of data is obtained from the medium 12 without the object 9 (only the coupling fluid 11). This data will only be used for transducer calibration as described in Section D.1. Object 9
Is removed and 62.5kHz from 687kHz to 1.250MHz
10 discrete frequencies ωα (α = 1,2, ..., 1
0), in each of the media 12 without the object 9 (only the coupling fluid 11) The entire measurement process described in the previous section is repeated to obtain

C. Calculation of Image from Acquired Data Data m _jk (ωα) (j, k =
1,..., N; α = 1, 2,..., 10) are uniquely determined by the sound velocity c (r, θ) and the attenuation coefficient μ (r, θ) of the medium. The purpose of this set of data m _{jk is} to calculate an image of a 12 mm thick slice of the medium 12 on a digital computer mathematically.
(Ωα). This image shows the media 12
The hydrogen dispersion potential S (α) (r, θ) ｛S (α) at all locations (r, θ) over a 12 mm thick slice “(α)” is a superscript 1/4 square character and I do. same as below. Based on the approximate calculation of｝ (see FIG. 1).

In the preferred embodiment, the acquired data at each frequency ωα
The image of the medium 12 is calculated from m _jk (ωα). S (α)
This image, defined as (r, θ), is a two-dimensional map of the medium 12. The third dimension is averaged over the vertical extent of the transducer 10.

The algorithm for S (α) (r, θ) is obtained from the following well-known acoustic wave equation as Helmholtz equation: ▽ ² f (r, θ) + S ^(α) (r, θ) f (r, θ) = 0
(1) Here, f (r, θ) = ρ (r, θ) / ρ (r, θ)
^1/2 is a single frequency acoustic pressure wave f at frequency ωα
(R, θ) = ρ (r, θ).

ρ (r, θ) is the density distribution in the medium S (r, θ) = k ² (r, θ) −k _O −ρ (r, θ) ^1/2 ▽ ρ
(R, theta) ^-1/2 is the angular frequency of the complex dispersion potential .omega..alpha = acoustic medium _{k O = ωα / c O c} o = velocity of sound in the coupling fluid 11 k (r, θ) = ωα 2 / c 2 (R, θ) -iωN (r, θ)]
^1/2 is a complex waveform vector taking into account the spatially varying sound speed c (r, θ), and the acoustic energy loss term N (taking into account the viscous heating of the medium 12 and the diffraction of acoustic energy from the field of view of the transducer 10 r, θ).

F (r in transducer 10.k (at r _O , θ _k ) by acoustic hologram creation (at ω α) (at acoustic wave) at single frequency of medium 12 by acoustic transducer 10. _j (at r _o , θ _j ) The solution of equation (1) for ( _O , θ _k ) can be expressed in terms of a two-dimensional integral equation including: (i) complex dispersion potential S (α) (r, θ), (ii) transducer (I _O , θ _j ) and (i _O , θ _k ) locations, and (iii) the summarized Hankel (H) function and Bessel (J)
function.

The solution is “(Α)” in the term f (α) (r _O , θ _k ) ｛f (α)
Is a superscript 1/4 character. same as below. ｝ Is the transducer 1 expressed in terms of amplitude and phase relative to the pressure wave occurring at the location of the transducer 10.j.
Represents a pressure wave (frequency ωα) at the position of 0.k. This is exactly equivalent to the acquired data m _jk (ωα) described in Chapter B. _{^{Therefore, f (α) (r o}} , θ k) ≡m jk (ω α). (3) Therefore, equation (2) can be written as: Here, S (α) (r, θ) is a complex image of the medium 12 determined from the data obtained at the frequency ωα. It is (r,
is a two-dimensional matrix representing the acoustic dispersion potential at (1024) ² (r, θ) points in a 12 mm thick slice through the medium 12 in the (θ) plane. S (α) (r, θ)
Each of the (1024) ^two complex values have real and imaginary components.

H ′ _m (K _O r _O ) is the first derivative of the Hankel function representing the antenna pattern of the transmitter transducer 10.j,
5 is a correct mathematical expression for the dipole transducer used in the preferred embodiment. The Hankel function is
For example, “The Poketbook by Abramowitz and Stegun
of Mathematical Functions ", Chapter 9, Verla
g Harri Deutach 1984, summarized. The antenna pattern of any given transducer can be modeled as the sum of the antenna pattern weights, such as monopole, dipole, quadrupole, etc. These antenna patterns are, for example, “Classical Electrody
namics ", JDJackson, Chatter 16, I. Wiley and Son
s, New York, 1962.

H ′ _n (k _O r _O ) is the first derivative of the Hankel function representing the antenna pattern of the receiver transducer 10.k.
For the dipole transducer used in this preferred embodiment, its function is the same as for the transmitter transducer.

The J _m (k _O r) and J _n (k _O r), a Bessel function determined for all values r in based on summarized Bessl function values (r, theta) plane.

Represents the Fourier transform of the displayed function given by: Represents the inverse Fourier transform of the displayed function given by: Equation (4) can be transformed by the appropriate mathematical operation into the following shape giving S (α), (r, θ) for the measured acoustic data m _jk (ωα): D. Image Formation The entire process of generating an S (α) (r, θ) image in this example is described herein with respect to equation (7).

Step (1). The first step is to calibrate the transducer. This is because the medium 12 is
Object 9 is removed so that only 10 discrete frequencies ω
A set of data as described in Chapter B for each of α (α = 1, 2, ..., 10) Is done by first obtaining (The frequency is 68
It is discrete at intervals of 62.5 kHz between 7 kHz and 1,250 kHz. ) The calibration factor is determined by requiring the computer to create a weighting factor to produce a uniform grayscale image when the bath-only data is processed as given by steps 2 to 9 in this section. Is done. The additional calibration factors are determined to eliminate the frequency dependence of the transducer and to scale each complex grayscale image of the water bath to provide the same image at each discrete frequency ωα. These calibration factors have ten discrete frequencies ωα (α = 1,
2, ..., 10) is stored as a separate 1024x1024 calibration matrix. These calibration matrices are stored in the memory of the computer 72.

Step (2). The data representing the m _jk (ωα) of the medium 12 is equally spaced between 687 kHz and 1,250 kHz.
For each of these frequencies, as described in Chapter B. For each frequency ωα, m _jk (ωα) is a 1024 × 1024 complex matrix consisting of phase and amplitude data.

Step (3). For each discrete frequency ωα, computer 72 multiplies m _jk (ωα) by the calibration matrix determined in step (1) of this section to provide calibrated m _jk (ωα) data.

Step (4). Using the calibrated m _jk (ωα) data, the computer 72 calculates the following quantity for each frequency ωα.

This operation is performed by calibrating the complex matrix m _jk (ωα)
Construct a fast fast Fourier transform of As a result of this Fourier transform, calibration m _jk (ωα) for each frequency ωα
Is in the form of a 1024x1024 matrix in an azimuth mode space that depends on the azimuth mode values specified by the azimuth mode numbers p and q.

Step (5). Next, the antenna patterns H ′ _p (k _O r _O ) and H ′ _q (k _O r _O ) are calculated for each transducer 10. This includes the azimuth mode numbers p, q = −512 to 51
A summary of the first derivative derivative of the Hankel function for 2 is involved. These values are stored in the memory of the computer 72.

Step (6). In this step, the product of the antenna patterns calculated in step (5) for each transmitter-receiver combination at frequency ωα and for each mode combination (p, q) to calculate the next quantity is Simply divide the quantity determined in step (4): Step (7). Next, a weighting function J _p (k _O r) J _q (k _O r) at each point r and θ which is a 1024 × 1024 matrix
^Calculate e− ^{iθ (p + q)} . J _p and J _q are determined from a Bessel function table stored in the memory of the computer 72.

Step (8). Next, the weighting function calculated in step (7) is multiplied by the quantity calculated in step (6) and added over the azimuthal modes p and q to obtain the following quantity: This step is performed at each point (r, θ) of the medium 12. The result of this step is S (α) _conv (r, θ). This is an image of S (α) (r, θ), which is
It is synthesized with [J _O (k _O r)] ² representing a smooth image of (α) (r, θ). To obtain a more accurate image, S (α) _conv
It is necessary to separate the quantity [J _O (k _O r)] ² from (r, θ).

Step (9). Convolution method and separation (d
ecomvolution) method is a standard mathematical calculation, for example, “Descrete-Time Signal Processing”, pg.
by Oppenheim and Schafer, Prentice-Hall (1989)
It is described in. The composition and separation of the two spatial functions is
It can be calculated in the spatial domain or the Fourier wave vector domain. This preferred embodiment is able to calculate the synthesis and separation in the Fourier wave vector domain. However, those skilled in the art will recognize that these syntheses and separations can be easily performed in the spatial domain. Fourier transform of _{[J O (k O r)} ] 2 is, 1 / π · 1 / k · 1 / (4k O -k) is ^1/2.

Therefore, the image S (alpha) as follows (r, theta) for computing the _{S (α) conv (r,} θ) from _{[J O (k O r)} ] 2 is separated: Using equation (11), an image S (α) (r, θ) at each frequency ωα of the medium 12 can be generated. To display the image on the monitor of the digital computer, the computer 72 converts the polar coordinates (r, θ) to the Cartesian coordinates (x, y).
To generate S (α) (x, y). Each of S (α) (x, y) is a matrix of values. Each value of the matrix includes two numbers, a first number representing the real part of the value and a second number representing the imaginary part of the value.

The magnitude of these numbers can be represented as a gray scale on a computer monitor at grid pixels (x, y). (As this number increases, the pixels become whiter and vice versa.) When this is done, two separate images for each frequency, one from the real part of the value of S and one of S One comes from the imaginary part.

E. Combination of single frequency images The value of S (α) (r, θ) at the discrete frequency ωα
Produces a good image. The speed of sound and the damping coefficient of the medium 12 are almost independent of frequency, for example 687 kHz to 1.25 MHz
An image of S (α) (r, θ) acquired at different frequencies ωα over a specific frequency range, such as, ideally, provides the same image of medium 12 independent of frequency ωα It should be. However, this image can be complicated by frequency-dependent artifacts that occur in reflections of acoustic energy from the front of the receiver transducer 10.k and from multiple dispersal events in the medium 12. Combining the reconstructed (α) (r, θ) images at different frequencies ωα reduces image artifacts and improves image quality. The following description will focus on seven preferred methods of combining single frequency images S (α) (r, θ) composed of different frequencies ωα.

Images S (α) (r,
To combine θ), the next calculated term (α)
Defining (r, θ) has proven useful: In equation (12), (α) (r, θ) is first expressed as S (α)
Calculate the FFT of (r, θ), then divide by k, and
It is calculated by calculating the inverse FFT of the result.

1) Sum of complex images S (α) (r, θ) From the acquired data n _jk (ωα), as given in steps (1) to (9) of chapter D, each frequency ωα
Reconstruct separate images of S (α) (r, θ) at (α = 1,2, ..., 10). Then, add these complex images to produce: Next, the image is converted into Cartesian coordinates (z, y), and the image S _total (r, θ) having less image artifacts and higher clarity than the image S (α) (r, θ) of each single frequency. θ).

2) Sum of S (α) (r, θ) image size From the acquired data m _jk (ωα), as given in steps (1) to (9) of chapter D, each frequency ωα
Reconstruct separate images of S (α) (r, θ) at (α = 1,2, ..., 10). Let the size of these complex images be S
(Α) (r, θ) = [S (α) (r, θ) S (α) ^* (r,
θ)] ^1/2 (S (α) ^* (r, θ) is S (α) (r, θ)
Is the conjugate complex number of Next, the sizes of these images are added to produce: Further, each image S (α) is converted into Cartesian coordinates.
Image S with fewer artifacts and higher clarity than (r, θ)
Generate _total (r, θ).

3) Sound velocity map and attenuation map calculated from the S (α) (r, θ) image The sound velocity map and attenuation map of the medium 12 are as follows:
(Α) can be calculated from (r, θ): Step (1). From the acquired data m _jk (ωα),
S (α) at each frequency ωα (α = 1,2, ..., 10) as given in steps (1) to (9) of chapter D
Reconstruct separate images at (r, θ). Next, the map (α) (r, θ) is calculated at each frequency ωα, as given in equation (12).

Step (2). Computer 72 calculates the following function: For each point (r, θ) on the medium 12, P (r, θ, τ) is
θ) represents the synthesized acoustic pulse P (τ) converged to θ).

Step (3). For each point (r, θ) of the medium 12, P
(Tau) has the maximum value P _max of the value of tau referred to as tau _max. The computer 72 calculates P _max (r, θ) for each point (r, θ).
θ) and determine the value of τ _max (r, θ).

Step (4). Computer 72 creates a sound velocity map c (r, θ) of medium 12 by the following calculation: Step (5). Computer 72 then produces an attenuation map N (r, θ) of medium 12 by the following calculation: In Equation (16), r _O is the radius of the transducer ring, and c _O is the sound velocity of the coupling fluid 11 (17) In Equation (17), μ _O is the damping coefficient of the coupling fluid 11. The values of c (r, θ) and N (r, θ) are r and θ
Is a 1024x1024 matrix. These are converted to Cartesian coordinates (x, y) and displayed on a computer screen with c and N values drawn as grayscale values.

4) Refined sound velocity map and attenuation map calculated from S (α) (r, θ) Sound velocity c (r, θ) map and attenuation N (r, θ) calculated by equations (15) to (17) The map represents a suitable image of the medium 12. This section describes the single frequency images S (α) (r, θ) to c (r, θ) and N (r,
The purification calculation of θ) is described.

Step (1). From the acquired data m _jk (ωα),
S (α) at each frequency ωα (α = 1,2, ..., 10) as given in steps (1) to (9) of chapter D
Reconstruct separate images at (r, θ). Next, as given in the map (α) (r, θ) in equation (12), each frequency ω
Calculate with α.

Step (2). Next, each frequency ωα (α =
Map ▲ S ^(α) _{△ p, △ q} ▼ (r,
Calculate θ): This map ＳS ^(α) _{pp, △ q,} (r, θ) represents the coupling of acoustic energy from the azimuth modes p and q to the modes p + △ p and q +! Q.

Step (3). Computer 72 then calculates the following equation (19): ! p = -6 to +6,! q = 0;! p = 0,! q = -6 to +6;
Excellent results were obtained with the sum of! P = -6 to +6 and! Q = -6 to +6. Other combinations of! p and! q could be used.

For each point (r, θ) of the medium 12, P _corr (r, θ, τ)
Is the synthesized acoustic pulse P converged to the point (r, θ)
_Corr (τ). P _corr (r, θ, τ) is a refined expression of the function P (r, θ, τ) given by equation (15).

Step (4). For each point (r, θ) of the medium 12, P
_corr (tau), the maximum value Pmax in value of tau referred to as tau _max
Having. The computer 72 calculates P _max for each point (r, θ).
(R, θ), and instead of P (r, θ, τ), P _corr (r,
It is programmed to determine the value of τ _max (r, θ) as done in step (3) of section E.3 except that it uses (θ, τ).

Step (5). Using the refined values of τ _max (r, θ) and P _max (r, θ), the sound velocity c (r, θ) and damping N (r , θ).

5) Complex image S (α) (r, θ) reconstructed as given in steps (1) to (9) of chapter F of S (α) (r, θ) image with phase shift corrected Represents a suitable image of the medium 12. The complex phase of these images may be distorted at each point (r, θ) due to the limitations of the reconstruction algorithm as given in steps (1) to (9) of chapter D. This section describes how to correct the phase shift in the images S (α) (r, θ) and the combination of these images to reduce the visual artifacts.

Step (1). From the acquired data m _jk (ωα),
S (α) at each frequency ωα (α = 1,2, ..., 10) as given in steps (1) to (9) of chapter D
Reconstruct separate images at (r, θ). As given in equation (12), a map (α) (r, θ) is calculated at each frequency ωα.

Step (2). Then calculate the map τ _max (r, θ) as described by the method given in section E.3 or E.4.

Step (3). Computer 72 map _total
Calculate (r, θ) as follows: Step (4). The final image S _total (r, θ) is determined by the following calculation: This image shows only the high spatial frequency components (ie, fine details) of the medium 12. These fine details can be found in Medium 12
It also includes sharp edges or discontinuities at the speed of sound within and small objects of a size comparable to the acoustic wavelength.

6) Composite Image The image S _total (r, θ) calculated in Section E.5 is combined with the map τ _max (r, θ) to provide a more accurate representation of the medium 12, the composite map S _comp (r, θ). , θ). The S _comp (r, θ) image contains both high and low spatial frequency components of the medium 12.

Step (1). Computer 72 may be installed in Chapter E.3 or E.4
Τ _max (r, θ) described by the method given in, and _total (r, θ) given by equation (20).

Step (2). Computer 72 then calculates the following equation: In equation (22), In represents the natural logarithm and △ ω is the gap between frequencies ωα (（ω = 62.5 kHz in the preferred embodiment).

Step (3). Computer 72 then calculates S _comp as follows: Next, the computer 72 converts S _comp (r, θ) into Cartesian coordinates (x, y) and displays it on a computer monitor.

7) Further refined sound velocity map calculated from S (α) (r, θ) This chapter describes the sound velocity map c (r, θ) calculated in E.3 and E.4
A method for further improving the accuracy of the method is described. In Chapters E.3 and E.4, the pulse P (τ) at each point (r, θ) has a maximum value P _max
Τ _max (r, θ) is calculated as a value τ having
Then, a sound speed map is obtained from this information. In this chapter,
The moving time τ _av (r, θ) as the average arrival time of the power included in the pulse P (τ) is calculated. This map τ _av (r,
θ) is then used to calculate a refinement map of the sound velocity c (r, θ) of the medium 12.

Step (1). Computer 72 calculates the following quantities: Here, ＳS ^(α) _{pp, △ q} ▼ (r, θ) is calculated as in equation (18), and * indicates a conjugate complex number. The preferred embodiment is: 1)! P = -6 to +6;! Q =
0; 2)! P = 0,! Q = -6 + 6; or 3)! P = -6 + 6,! Q =
It has a sum of -6 to +6. Other combinations of Δp and Δq could be used.

Step (2). Computer 72 calculates an average travel time τ _av (r, θ) image of medium 12 by the following calculation: Step (3). Computer 72 then calculates a sound velocity image c (r, θ) of medium 12 by the following calculation: Step (4). Computer 72 then creates an attenuated image μ (r, θ) of medium 12 by the following calculation: F. Computer simulation A computer simulation was created to check the algorithm. The following hardware other than the computer was not used for these reconstructions. FIGS. 4 to 7 show images reconstructed from data simulated at 1 MHz using the same transducer configuration as the working prototype system. FIG.
The simulated object shown in Figure 1 is a 3 inch diameter cylinder of a homogeneous material having a sound velocity 5% greater than the surrounding coupling fluid. The two 1 cm diameter cavities in the object have the same sound speed as the coupling fluid 3 surrounding this object. The damping coefficient of the object and coupling fluid is equal to zero (ie, no damping). The image was created by the following method. That is, FIG. 4 shows the real (right) component and the imaginary (left) component of the single-frequency reconstruction, as described in Section D. FIG. 5 shows a sound velocity image and an attenuation image as described in section E.4. Figure 6 shows that, as described in Chapter E.5,
The real (right) and imaginary (left) components of the 10 single-frequency reconstructions corrected for phase shift and added are shown. FIG. 6 shows the composite image described in section E.6.

G. Real Images FIGS. 8-12 show real images obtained using the prototype apparatus described in Chapters A through D. FIG. FIG. 8 shows nine images of a 1.2 cm slice of a female breast. The acquired data is the same for all nine images,
The reconstruction method differs for each image. Starting from the top left corner and going from left to right, the image consists of (1) the real component of the single frequency image (Chapter D), 2) the imaginary component of the single frequency image (Chapter D), 3) 5) Single-frequency image size corrected for phase shift (chapter E.1), 4) Real component of single-fraction image corrected for phase shift (Chapter E.5), 5) Single-phase image corrected for phase shift Imaginary part of one frequency image (chapter E.5), 6) magnitude of five single frequency images each corrected for phase shift (chapter E.5), 7) sound velocity image (chapter E.7) , 8) the attenuated image (Chapter E.7) and 9) the square root of the sum of the squares of the sound velocity image and the attenuated image (Chapter E.7). FIG. 9 shows nine images of a resected porcine kidney obtained using the prototype device described in Chapters AB and reconstructed in the manner described for FIG.

FIG. 10 shows nine images of a female breast obtained with the prototype device described in Chapters A and B with respect to FIG. The woman has her left breast lying face down on a table in a water bath containing the transducer assembly 80 through an 8-inch hole. The nine images were obtained by sequentially moving the transducer assembly 80 from the area of the breast 86 close to the woman's chest wall in steps of 1 cm from the upper left corner of FIG. 10 to the breast nipple. . This image is the magnitude of the sum of five single frequency images, each corrected for phase shift as described in Section E.5. FIG.
7 shows a similar image of another female breast with a large fluid-filled cyst.

FIG. 12 shows an image of a resected porcine kidney that was reconstructed using the prototype device described in Sections AB and reconstructed according to the method described in Section E.1.

H. Guide of Biopsy Needle The present invention can be used for monitoring of a biopsy needle when inserted into a volume of tissue of the human body, for example, the breast of a woman. FIG. 15 shows an example of the present invention for this purpose. Coupling of acoustic energy from the transducer ring 91 to the breast 90 may be achieved with the use of a fluid-filled sac according to the breast. Tomographic images of several slices of the breast are made as in FIG. 10 to locate this biopsy. A certain amount of the breast to be biopsied is determined from these tomographic images. The computer analyzes the image of the tomographic image to determine where the tip of the biopsy needle 93 should be placed. The computer then guides the biopsy needle 93 to a predetermined location. Another set of tomographic images can be obtained with this biopsy needle in place to confirm the position of the tip of the biopsy needle.

I. Image of Temperature Distribution The present invention provides an apparatus and a method for measuring a temperature change of the medium 12. This is achieved by the fact that a change in the temperature of the body tissue results in a change in the speed of sound of this tissue. The speed of sound of a locally heated human body tissue can be expressed as: c (r, θ) ｛heated｝ = c (r, θ) + △ T (r, θ) [d / dTc (r, θ)] (26) where ΔT (r, θ) is the temperature distribution resulting from local heating of the tissue, and c (r, θ) is the human body tissue at the surrounding human body temperature. , And d / dTc (r, θ)
Is the differential change in sound speed with respect to temperature. For example, 37 ° C
C (r, θ) = 1596m / sec
Where d / dTc (r, θ) = 0.96 m / (sec− ° C.). laser,
Alternatively, a temperature change of {T = 5 ° C. due to local heating of the liver due to microwave heating is [c (r, θ) ⁻¹ ]} T (r,
θ)] [d / dTc (r, θ)] = 0.3%.

As specified in the methods in Sections A through F, the present invention provides a method of locally heating a volume of tissue and then combining the sound velocity and temperature image by directly imaging the sound velocity of this tissue. Can be used to generate
Alternatively, a sound velocity image of the tissue can be made before and after subtraction or division of the two images to create an image of a certain amount of local heating of the tissue and the next temperature distribution.

J. Other Embodiments This embodiment involves the use of a periodic broadband generated ultrasound signal in which a periodic time-varying signal is sequentially transmitted from each transducer into the medium. This signal has a center frequency of 1 MHz, a frequency bandwidth of 600 kHz, and 16
Repeated every millisecond. The Fourier transform of this signal consists of a combination of ten discrete frequencies equally spaced at 62.5 kHz from 687 kHz to 1.25 MHz. The relative acoustic signal strength of the discrete frequency components is substantially uniform over this frequency range. The relative phase of the discrete frequency components is randomized to provide a substantially flat time response of the periodic time varying signal. After approximately 270 milliseconds, twice the acoustic transit time across the diameter of the transducer ring, the broadband signal reaches a steady state. After this time, each receiver encounters a time-varying signal that repeats every 16 microseconds. Data is acquired from each receiver and stored for 16 ms at a 4 MHz data rate. This acquisition method is repeated for each transducer acting as a sound transmitter. The Fourier transform of this time-varying receiver signal is
Gives 2.5kHz (1 / (16ms)) frequency resolution. This data set is comparable to the data obtained by the acquisition method described in Chapters C and D, where ten separate data sets are acquired at 10 discrete frequencies from 650 kHz to 1.25 MHz at 62.5 kHz intervals. I do. However, the overall acquisition time is reduced to 3 seconds with the wideband acquisition method.

Other embodiments of the present invention also include a transducer array geometry. These other examples include, for example, abdomen, female breast, cranial cavity, neck,
It would be appropriate to facilitate coupling of acoustic waves to various parts of the human body, including the arms and thighs, or other non-human subjects. An embodiment designed to produce an image of the abdominal region of a human patient is shown in FIG. An apparatus for performing a mammography examination is shown in FIG. In this embodiment, a ring of 1024 transducers 80
It is vertically movable in an oil tank 82 surrounding an aquarium 84 so that a complete scan of the female breast 86 is obtained. These images can be viewed separately, as shown in FIG. 10, or they can be combined in a computer to display a three-dimensional image of the breast. Other embodiments have similar devices for imaging arteries and veins in the arms and legs. Other embodiments include rings of acoustic transducers that do not lie on the trajectory of a circle, rings of transducers that do not completely surround the media to be imaged, and various lengths that partially circumscribe the media. And a set of transducers arranged in parallel rows on opposite sides of the medium to be imaged. Also, in other embodiments,
It relates to the use of a rubber fluid-filled bag to couple acoustic waves from the transducer to the medium shown in FIG. Various numbers of transducers can be used, but the number should be at least eight, and as described above, the transducers should be separated by no more than half a wavelength of the transmitted acoustic wave. Is preferred. For non-circular arrays, the algorithm obtained above would have to be recalculated to take into account the appropriate boundary conditions.

Another embodiment is a method for probing media with electromagnetic waves having an energy spectrum ranging from 1 MHz to x-ray energy, including radio, microwave, infrared, visible, and ultraviolet imaging devices. It is related to the application of.

The prototype was tested at frequencies ranging from 500 kHz to 1.25 MHz with good results, but these ranges were
It is believed that this technology can extend from 0kHz to 1.5MHz.

Although the preferred embodiment described above used the same transducer for broadcasting and receiving, separate means for broadcasting and receiving were used for broadcasting and around the medium to simulate the ring of the broadcast transducer. Separate means for receiving can also be rotated. A similar arrangement could be provided to rotate the receiver to simulate the ring of a receiving transducer.

The reader should interpret the above embodiments of the invention as examples and the scope of the invention should be determined by the appended claims and their legal equivalents.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Martin, Peter, J. United States, California 92024 Encinatas, Avenida Mimosa 1819 (72) Inventor Palmer, Douglas, A. United States, California 92107, San Diego, Tree Esta Drive 1224 (72) Inventor Otto, Gregory United States, California 92129, San Diego, Azaga # E-202 9919 (72) Inventor Clam, Robert, M. United States, California 92065, Lomona, Black Canyon 2348 (56 References JP-A-52-152679 (JP, A) JP-A-6-183 (JP, A) JP-A-6-43242 (JP, A) JP-A-1-221149 (JP, A) A) Patent flat 3-258251 (JP, A)

Claims (54)

(57) [Claims] 1. An acoustic imaging apparatus for producing tomographic images along image slices over a medium defining an average sound speed: A) a number of acoustic transducers arranged on a circle, a number of which are N Each of the multiple transducers, greater than = 2πD / λ, where D is the diameter of the circle, λ is the wavelength, and N is the number of transducers placed in the circle. When excited with a periodic signal in the range of 100 kHz to 1.5 MHz, sends an acoustic signal into the interior of the medium, and produces an electrical signal when excited with the acoustic signal transmitted through the medium. B) at least one in the frequency range 100 kHz to 1.5 MHz;
Electronic signal generating means for generating a periodic electronic signal at two discrete frequencies, wherein the electronic signal is continuous for at least a time interval of D / c (c is the average sound velocity of the medium). C) applying a plurality of said acoustic transducers, one at a time, into said medium and to each of said plurality of acoustic transducers for broadcasting acoustic energy into said medium at a discrete frequency in the frequency range of 100 kHz to 1.5 MHz. First multiplex means for applying said periodic electronic signal is provided; D) by means of an electrical transducer signal generated by said plurality of said plurality of transducers excited by means of acoustic energy transmitted over said medium. Recording means for recording the information to be transmitted; and E) pre-recording said information transmitted by said electronic transducer signal. A second multiplexing means for connecting the plurality of transducers to the recording means so that the recording means can record, F) using the information recorded by the recording means to slice the image; Computer apparatus having an algorithm for calculating an image of a tomographic image of said medium along said medium. 2. The acoustic image forming apparatus according to claim 1, wherein said at least one identifiable discrete frequency is a plurality of identifiable discrete frequencies. 3. The acoustic image forming apparatus according to claim 1, wherein said transducers are equally spaced on said circle. 4. The acoustic image forming apparatus according to claim 1, wherein the number is at least 256. 5. The acoustic image forming apparatus according to claim 1, wherein said acoustic recording means includes a plurality of analog / digital exchangers each having a buffer memory unit for temporarily storing digital acoustic information. 6. The buffer memory unit of claim 5, wherein each of said buffer memory units has a storage capacity of at least one million bytes.
The acoustic image forming apparatus as described in the above. 7. An acoustic imaging apparatus for providing an image of at least a portion of a medium, comprising: A) transmitting an acoustic signal into the medium from at least seven broadcast locations on a circle at least partially surrounding the medium. One at a time
Sound broadcasting means for broadcasting from two locations, said sound means being at least one discrete frequency and continuous for a time at least equal to the travel time of said sound signal across said medium; B) Audio signal detection means for detecting an audio signal broadcast by the broadcast means at a plurality of detection locations on the circle at least partially surrounding a medium; C) the audio broadcast from the at least seven locations A set of data representing the phase and amplitude of the acoustic signal received at the plurality of locations with respect to the phase and amplitude of the signal is received for the acoustic signal broadcast to provide for each of the plurality of locations. Data acquisition and comparison means for comparing signals; and (D) at least one image of at least a portion of the medium utilizing the phase and amplitude data. Has mathematical means for: 1) transforming the phase and amplitude data into a set of data defining azimuth data set in azimuthal mode space (the The set of data represents the azimuth mode at the location of the broadcast means and the detection means.) 2) The azimuth data to take into account the transducer antenna pattern to generate an antenna independent azimuth data set. And 3) multiplying the set of azimuth data independent of the antenna by a weighting function calculated at a number of locations on the medium, and generating a composite image of the medium. Sum over azimuthal mode; and 4) sound programmed to accomplish the steps of separating the composite image of the medium to generate the image of the medium. Image forming apparatus. 8. The method according to claim 1, wherein said calculating means is programmed to perform another step of sequentially accomplishing said A) through D) at a plurality of discrete frequencies to form a plurality of single frequency complex images. Item 7. The acoustic image forming apparatus according to Item 7. 9. The acoustic image of claim 8, wherein said calculating means is programmed to perform another step of adding said plurality of single frequency complex images to produce a complex image to be combined. Forming equipment. 10. The method of claim 8 wherein said calculating means is programmed to perform another step of adding the amplitudes of said plurality of single frequency complex images to produce a combined image. Acoustic image forming device. 11. An acoustic image forming apparatus according to claim 8, wherein said calculating means is programmed to perform the following other steps: A) synthetic sound sequentially focused on said plurality of locations in said medium. Utilizing the plurality of single frequency complex images to construct a set of time data representing a pulse; and B) calculating an image of the medium using the set of time data. 12. The set of means for determining arrival time data of the synthesized acoustic pulse from the broadcast location to the multiple locations in the medium and further to the detection location. 12. The acoustic image forming apparatus according to claim 11, wherein the apparatus is programmed to use the time data of (1), and the arrival time data forms an arrival time image. 13. The computer means of claim 12, wherein said computer means is programmed to perform another step of separating a function of said time of arrival image to produce a sound velocity image.
The acoustic image forming apparatus as described in the above. 14. The acoustic image forming apparatus according to claim 13, wherein said function is a diameter of said circle divided by said arrival time image. 15. The computing means determines maximum pulse power data of the combined acoustic pulse from the broadcast location to the multiple locations in the medium and further to the detection location around the medium. 12. The acoustic image forming apparatus of claim 11, wherein the set of time data is programmed to utilize the set of time data, and the maximum pulse power data forms a peak pulse power image. 16. The acoustic image forming apparatus according to claim 11, wherein said calculating means is programmed to perform another step of the function of said maximum pulse power image to generate an attenuation image. 17. The acoustic image forming apparatus according to claim 16, wherein the function is a logarithm of a power image of the maximum pulse divided by a diameter of the circle. 18. The acoustic image forming apparatus according to claim 8, wherein said calculating means is programmed to perform the following other steps: A) Synthetic sound which sequentially focuses on said plurality of locations in said medium. Utilizing the plurality of single frequency complex images to construct a set of temporal data representing a pulse; and B) affecting the synthesized acoustic pulse from the azimuth mode numerically close to the azimuth mode data set. And C) calculating a set of time data generated from said set of time data, and C) calculating an image using said generated set of time data. 19. The computing means for determining accurate arrival time data of the synthesized acoustic pulse from the broadcast location to the multiple locations in the medium and further to the detection location. 19. The acoustic image forming apparatus according to claim 18, wherein the apparatus is programmed to use the corrected set of time data, and the generated arrival time data forms a generated arrival time image. 20. The apparatus of claim 19, wherein said calculating means is programmed to perform another step of separating a function of said refined arrival time image to produce a refined acoustic image. Acoustic image forming apparatus. 21. The acoustic imaging apparatus of claim 20, wherein said function is a diameter of said circle divided by said refined arrival time image. 22. The calculation means for determining the maximum pulse power data of the synthesized acoustic pulse from the broadcast location to the multiple locations in the medium and further to the detection location. 20. The acoustic imaging apparatus of claim 18, wherein the apparatus is programmed to utilize a set of time data, and wherein the refined maximum pulse power data forms a refined peak pulse power image. 23. The sound of claim 22, wherein said calculating means is programmed to perform another step of separating a function of said growing maximum pulse power image to produce an accurate attenuation image. Image forming device. 24. The function of claim 17, wherein the function is a logarithm of the refined maximum pulse power image divided by a diameter of the circle.
23. The acoustic image forming apparatus according to 23. 25. The computing means comprising: A) combining each single frequency complex image to generate a plurality of combined single frequency complex images; and B) combining a plurality of phase shift corrections. Multiplying each of said composite single frequency complex images by an exponential function of said arrival time image to generate a single frequency complex image; and C) applying said plurality of phase shift corrections to generate a composite complex image of phase shift correction. 13. The programmed single-frequency complex image is added to accomplish the steps of: and D) separating the phase-corrected complex image to produce a phase-corrected complex image. Acoustic image forming apparatus. 26. The method according to claim 25, wherein said calculating means is programmed to perform another step of calculating a magnitude of said complex image of phase shift correction to generate an image of phase shift correction. Acoustic image forming device. 27. The acoustic image forming apparatus according to claim 19, wherein said calculating means is programmed to perform the following other steps: A) for generating a plurality of synthesized single-frequency complex images. B) combining the exponential functions of the generated arrival time images with each of the composite units to generate a plurality of composite phase-corrected corrected single-frequency images. Multiplying the one-frequency complex image; C) adding the plurality of generated phase-shift-corrected composite single-frequency complex images together to generate an accurate phase-shift-corrected composite complex image; and D). Separating the refined phase shift correction composite complex image to generate a refined phase shift correction complex image. 28. The calculation means is programmed to perform another step of calculating the magnitude of the generated phase shift correction complex image to generate an accurate phase shift correction image. 28. The acoustic image forming apparatus according to claim 27, wherein: 29. An acoustic imaging apparatus according to claim 25, wherein said calculating means is programmed to perform the following other steps: A) The arrival time image to generate a synthesized complex image. And B) separating the combined complex image to generate a complex image. 30. The acoustic image forming apparatus according to claim 27, wherein said calculating means is programmed to perform the following other steps: A) generating the corrected composite complex image; Adding the refined arrival time image and the logarithmic function of the refined composite phase shift correction complex image; and B) adding the refined composite complex to produce a refined complex image. Separate images. 31. The acoustic imaging apparatus according to claim 7, wherein said at least discrete frequencies are a plurality of discrete frequencies. 32. The method according to claim 31, wherein said calculating means is programmed to achieve said 1) to 4) with respect to a plurality of identifiable discrete frequencies to form a plurality of single frequency complex images. apparatus. 33. The acoustic image of claim 32, wherein said calculating means is programmed to perform another step of adding said plurality of single frequency complex images to generate a plurality of images to be combined. Forming equipment. 34. The method according to claim 32, wherein said calculating means is programmed to perform another step of adding the amplitudes of said plurality of single-frequency complex images to produce a combined image. Acoustic image forming device. 35. A sound forming apparatus according to claim 32, wherein said calculating means is programmed to perform the following other steps: A) Synthetic sound pulses sequentially converging at said multiple locations in said medium. Utilizing the plurality of single frequency complex images to construct a set of time data representing: and B) calculating an image utilizing the set of time data. 36. The set of means for determining arrival time data of the synthesized acoustic pulse from the broadcast location to the multiple locations in the medium and further to the detection location. 36. The acoustic image forming apparatus according to claim 35, wherein the apparatus is programmed to use the time data, and the arrival time data forms an arrival time image. 37. The computer means is programmed to perform another step of separating a function of the time of arrival image to generate a sound velocity image.
The acoustic image forming apparatus as described in the above. 38. The acoustic image forming apparatus according to claim 37, wherein said function is a diameter of said circle divided by said arrival time image. 39. The computing means determines maximum pulse power data of the combined acoustic pulse from the broadcast location to the multiple locations in the medium and further to the detection location around the medium. 36. The acoustic image forming apparatus of claim 35, wherein the apparatus is programmed to utilize the set of time data to generate the peak pulse power image. 40. An acoustic imaging apparatus according to claim 39, wherein said calculating means is programmed to achieve another step in the function of said maximum pulse power image to generate an attenuated image. 41. The acoustic image forming apparatus according to claim 40, wherein the function is a logarithm of a power image of the maximum pulse divided by a diameter of the circle. 42. An acoustic image forming apparatus according to claim 32, wherein said calculating means is programmed to perform the following other steps: A) Synthetic sound focusing sequentially on said plurality of locations in said medium. Utilizing the plurality of single frequency complex images to construct a set of temporal data representing a pulse; and B) a contribution to the synthetic acoustic pulse from the azimuth mode in numerical proximity to the azimuth mode data set. And C) calculating an accurate set of time data from the set of time data by adding C., and C) calculating an image using the corrected set of time data. 43. The calculating means for determining the accurate arrival data of the synthesized acoustic pulse from the broadcast location to the multiple locations in the medium and further to the detection location. 43. The acoustic image forming apparatus of claim 42, wherein the apparatus is programmed to utilize the refined set of time data, and wherein the refined arrival time data forms a refined arrival time image. 44. The apparatus according to claim 43, wherein said calculating means is programmed to perform another step of separating a function of said refined arrival time image to produce a refined sound velocity image. Acoustic image forming apparatus. 45. The acoustic imaging apparatus of claim 44, wherein said function is a diameter of said circle divided by said refined arrival time image. 46. The computing means for determining an accurate maximum pulse power data of the combined acoustic pulse from the broadcast location to the multiple locations in the medium and further to the detection location. 43. The acoustic image forming apparatus of claim 42, wherein the apparatus is programmed to utilize the set of time data, and wherein the refined maximum pulse power data forms a refined peak pulse power image. 47. The method of claim 46, wherein said calculating means is programmed to perform another step of separating a function of said refined maximum pulse power image to produce a refined attenuation image. Acoustic image forming device. 48. The acoustic image forming apparatus according to claim 47, wherein said function is a logarithm of said maximum pulse power image divided by a diameter of said circle. 49. An acoustic imaging apparatus according to claim 42, wherein said calculating means is programmed to perform the following other steps: A) for generating a plurality of synthesized single frequency complex images. B) combining the exponential function of the time-of-arrival image with each of the synthesized single-frequency complex images to generate a single-frequency complex image that results in the synthesis of a plurality of phase shift corrections. C) summing the plurality of phase shift correction composite single frequency complex images to generate a phase shift correction composite complex image; and D) generating the phase shift correction complex image. Separate the composite complex image for phase shift correction. 50. The method of claim 49, wherein said calculating means is programmed to perform another step of calculating a magnitude of said phase shift corrected complex image to generate a phase shift corrected image. Acoustic image forming device. 51. An acoustic imaging apparatus according to claim 50, wherein said calculating means is programmed to perform the following other steps: A) for generating a plurality of synthesized single frequency complex images. B) synthesizing each of the single-frequency complex images into a plurality of the corrected phase-shift corrections; exponential function of the corrected time-of-arrival images to generate a single-frequency complex image; Multiplying a single-frequency complex image; C) adding the plurality of generated phase-shift-corrected composite single-frequency complex images together to generate an accurate phase-shift-corrected composite complex image; and D. ) Separating the complex phase-corrected corrected complex image to generate a complex phase-corrected phase-corrected image. 52. The calculating means is programmed to perform another step of calculating a magnitude of the generated phase shift correction complex image to generate an accurate phase shift correction image. 50. The acoustic image forming apparatus according to claim 49, wherein: 53. The acoustic image forming apparatus according to claim 49, wherein: A) a logarithmic function of the arrival time image and the synthesized phase-shift-corrected complex image to generate a synthesized complex image. B) separating the combined complex image to generate a complex image. 54. The acoustic image forming apparatus according to claim 51, wherein said calculating means is programmed to perform the following other steps: A) The acoustic image forming apparatus for generating an accurate composite complex image. Adding the generated arrival time image and the logarithmic function of the refined composite phase shift correction complex image; and B) the refined composite complex image to produce a refined complex image. Is separated.