JP2001517782A - Acoustic imaging system - Google Patents

Abstract

An acousto-optic imaging system (18) for forming an image of an object, an acousto-energy source for illuminating the object and an acousto-optic image receiving scattered acoustic energy from the object. A scattered acoustic energy (37) forms an acoustic image in the acousto-optic image forming plate (10), and the scattered acoustic energy (37) is changed by the acousto-optic image forming plate caused by receiving the acoustic energy (37). An optical energy source (22) for generating optical energy whose energy characteristics are changed, and an optical imaging means (32) for forming a non-holographic image of the changed optical energy; ) So that the magnitude of the time integral of the light detected by the optical image is an image having a spatial intensity change, and at a point of the optical image As the degree is related to the distance from the reference position of the corresponding point of the object, the acoustic energy source is driven in pulses.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the field of acoustic image forming systems, and particularly to the field of three-dimensional acoustic image forming systems.

[0002] Acoustic imaging is a very developed technical field and is mainly used in the fields of medical imaging, non-destructive testing and underwater imaging. In general, an acoustic image is formed by transmitting a beam of acoustic energy in the direction of an object to be imaged and receiving it by a directional antenna, such as a phased array of acoustic sensing elements. Thus, in general, scanning a three-dimensional object requires that the beam be scanned in two intersecting dimensions.

[0003] Some systems use a phased array of many elements and a wide range of beam delivery and multi-directional receive antennas. Based on the sum of the acoustic energies received by the individual elements, output from multiple circuits, and because each sum corresponds to a different antenna receive direction, the system can perform multiple outputs from a single transmit beam. Can be obtained. However, in order to form a three-dimensional image, the transmitting beam or the beam receiving direction (generally both) of the antenna must be scanned two-dimensionally or three-dimensionally.

[0004] Strictly speaking, it is not necessary to focus the transmit beam and / or the receive antenna at a specific, generally varying, distance, but to improve image quality and reduce the effects of reflections and off-angle reflections. It may be.

[0005] Furthermore, if a significant number of beams are required, a system that receives multiple beams is very expensive.

[0006] Thus, acoustic three-dimensional imaging systems are generally slow and / or low resolution, whereas there is a need to transmit a large number of sound waves in a relatively short time to form each image. .

[0007] For each image, systems are known that form an acoustic image using a single broad beam of acoustic energy. In the system described in U.S. Pat. No. 4,393,712, the disclosure of which is incorporated herein by reference, an acoustic lens is used to focus acoustic energy on an acousto-optic transducer and observe an optical image. In the background section of this patent, various acousto-optic imaging devices are disclosed and referenced. However, there is no known way to determine depth,
These systems have not been widely implemented.

[0008] US Pat. No. 4,338,821, incorporated herein by reference, produces an optical holographic image using a liquid crystal (LC) imaging plate that converts acoustic energy into an optical image. An acousto-optic imaging system is described.

US Pat. No. 4,379,408, which is incorporated herein by reference, describes a system for optical imaging from acoustic waves using an LC device. Visualization of transmitted and reflected sound waves is described.

[0010] PCT publication, WO 97/011, the disclosure of which is incorporated herein by reference.
11, WO97 / 01112, WO97 / 01113 describe a system that determines the depth of an object in the entire optical image based on reflected light from the object when light irradiation on the object is turned on and off. I have. One of the methods described in these patent applications is a method of determining the depth based on the luminance of an image formed by gating the reflected light.

"Ultrasonic switching of bistable liquid crystal cells" W. Hamidzada and SV Letcher (
Appl. Phys. Lett. 42 (9) May 1983, pp. 785-786) describes a bias for an LC cell that controls the bias and changes the polarization state of the cell by acoustic energy exceeding a threshold. Has been described.

[0012] US Patent Nos. 3,837,423, 3,406,550, 4,652,086, and "New Liquid Crystal Acousto-Optical Display" P, the disclosures of which are incorporated herein by reference.
Greuguss (ACOUSTICA, v. 29, 1972, pp. 52-58) describes various types of LC cells suitable for the conversion of sound waves into optical images and the use of such cells for imaging. Various methodologies have been described. "A New Hypothesis on Ultrasonic Interactions in Nematic Liquid Crystals", JL Dion and AD Jacob (Appl. Phys. Lett. 31 (8), October 15, 1997, pp. 490-493) and "Acoustic-Optical Effects in Nematic Liquid Crystals". S. Nagai, A. P
eters and S. Candau (Revuew de Physique Appliquee, vol 12, 1977, 21
P.) Describes the theory of interaction between the acoustic field and the LC. The disclosures of these articles are also incorporated herein by reference.

It is an object of some aspects of the present invention to reduce scattered acoustic energy from an object by three.
It is to provide a means and a method for converting to a two-dimensional image.

In some preferred embodiments of the present invention, a single pulse of illumination (illuminati
ng) By using an acoustic beam, an image of the surface of the object is formed. Alternatively, higher resolution can be realized by continuously transmitting such a beam.

In some preferred embodiments of the present invention, the internal structure of the object may also be viewed by sequentially viewing “slices” of the object at various distances using multiple illuminating acoustic beams. it can.

In a preferred embodiment of the invention, the object is illuminated with an acoustic beam.
The acoustic energy is reflected from the object and travels to an acousto-optic converter (AOC) such as a bias LC plate described in the section of the prior art. Preferably, the illuminating acoustic beam is pulsed. The tip of the acoustic beam reflected from various parts of the object reaches the transducer at a timing substantially proportional to the total distance traveled by the illuminated and reflected beam. The acousto-optic converter (AOC) is preferably an LC plate, but in the present invention, another type can be used.

The AOC plate is gated on and of controlled in a predetermined relationship with the irradiation pulse and time.
f) is preferred. The AOC board is illuminated (illumina
te) Generate light at the sensor location when receiving sufficient acoustic energy to turn on a portion of the transducer being turned on. Therefore, if AOC is at time t
If the sound beam arrives at part of the transducer at time t2 (between times t0 and t1), gated from 0 to t1, the intensity of the integrated image associated with the part of the transducer is t1- It is proportional to t2. Thus, the brightness of the optical energy detected from the acousto-optic converter is proportional to the gate time, and a reflected wave having sufficient energy to drive the converter reaches the converter. The resulting luminance of a portion of the image thus indicates the distance of the corresponding portion of the object from the reference, imaged in the portion of the transducer associated with the particular portion of the image.

In general, for some embodiments of the present invention, as described above, the state of the transducer is switched when the acoustic energy exceeds the threshold and remains switched while the energy is above the threshold. Embodiments of the present invention will show the outer surface of the object.

In another preferred embodiment of the present invention, slice images of the object are acquired sequentially. In this embodiment of the invention, the illumination energy is short enough so that the length of its reflection falls within a given slice of the object. The cell is gated off around the time when the reflected wave from the wave portion in the slice is expected to arrive. The combination of this gating and the arrival time of the pulse is used to measure the position of the configuration in the slice, as described above.

In one variant of the invention, the images are observed using a CCD camera. Color CC
Using a D camera, a plurality of light sources that are gated at different timings can be used to continuously acquire a plurality of spaced slices of an object by acoustic irradiation with a single pulse. Each of the slices has a different color light source and (with it) C
Acquired using one of the RGB channels of the CD. Generally, the AOC is reset between slices to eliminate the effect of the previous slice on the state of the AOC. This makes it possible to obtain complete three-dimensional information on the object in one third of the time. It also allows images of moving objects, such as the heart, to be formed in real time and at a relatively high frame rate and high resolution.

In another variation, the acoustic threshold changes during multi-pulse irradiation, changing the system sensitivity that suppresses changes in acoustic impedance. This makes it possible to distinguish between acoustically different objects.

Thus, according to a preferred embodiment of the present invention, an acousto-optic imaging system for forming an image of an object comprises: (a) an acoustic energy source for illuminating the object; An acousto-optic imaging plate for receiving scattered acoustic energy from an object, wherein the scattered acoustic energy forms an acoustic image at the acousto-optic imaging plate; and (c) the acousto-optic imaging plate receives the acoustic energy. And (d) an optical imaging means for forming a non-holographic image of the changed optical energy. The magnitude of the time integral of the light detected by the optical imaging means becomes an image having a spatial intensity change, and a point on the optical image As the definitive intensity associated with the distance from the reference position of the corresponding point of the object, the acoustic energy source is output in pulses.

Preferably, the acoustic energy source does not scan the object transversely to the direction of propagation of the illuminating acoustic energy.

In one embodiment of the invention, the optical image is an image of a plurality of points on the surface of the object. Preferably, the optical energy source is pulsed off only after the acoustic energy scattered by the surface reaches the acousto-optic imaging plate.

According to another preferred embodiment of the invention, the image represents a distance from the reference position to a point in the slice of the object. Preferably, the image forming system has a control system for applying a voltage acting to select between a high acoustic threshold state and a low acoustic threshold state of the acousto-optic imaging plate. Preferably, the high acoustic threshold state is selected at a point in time prior to receiving acoustic energy scattered by a portion of the object closest to the acousto-optic imaging plate, wherein the state is the receiving state. Sometimes it is changed to the house sound threshold state, and the time of the change defines the closer distance of the image slice.

Preferably, the optical energy source is pulsed off to define a far distance of the image slice.

In a preferred embodiment of the present invention, the reference position is at a distance corresponding to a scattered wave received when the optical energy is pulsed off. Preferably, the spatially varying intensity is proportional to a distance from the reference position to a point in the acoustic imaging device.

In a preferred embodiment of the present invention, a normalized function is obtained by optically illuminating the acousto-optic plate from a light source for a predetermined time during which the characteristics of the optical energy are changed by the change of the acousto-optic image forming plate. The intensity value is corrected.

In a preferred embodiment of the invention, the light source is linearly polarized, the acousto-optic plate does not affect the optical energy before said change, and the polarization is converted to elliptically polarized after said change. Is done. Also preferably, the imaging device is responsive to a component of the light having a polarization different from the polarization of the light generated by the light source.

In a preferred embodiment of the present invention, the optical imaging device has a CCD camera.

In a preferred embodiment of the invention, the acousto-optic imaging plate is a bistable device.

In a preferred embodiment of the present invention, the image forming plate has a liquid crystal plate.

In a preferred embodiment of the present invention, there is further provided an image forming method for an object. The method comprises: irradiating an object with pulsed acoustic energy; forming an acoustic image of the acoustic energy scattered at a point in a first slice of the object on an acousto-optic imaging plate; An optical imaging device for forming an acoustic image of the acoustic energy scattered at a point in at least another one slice of the object on the image forming plate, and forming a plurality of optical images from the pulsed acoustic energy; And separately detecting said first and another acoustic image, wherein the intensity of the optical image has a spatially varying value related to the distance from the reference position to the position of the corresponding point in each slice.

Preferably, the method comprises sequentially illuminating the acousto-optic imaging plate with pulsed light of different colors to form the plurality of optical images, each representing one of the slices. A step of sequentially detecting light of different colors in pulse form.

In a preferred embodiment of the present invention, the acousto-optic image forming plate has a first state in which the acousto-optic image forming plate has no sensitivity to the scattered energy and a second state in which the acousto-optical image forming plate is changed by the scattered energy. Alternatively, the method comprises the step of switching the acousto-optic imaging plate from the first state to the second state when the scattered energy from each slice reaches the imaging plate for the first time.

Preferably, the method comprises the step of extinguishing the optical energy source when scattered energy from the farthest part of each slice reaches the imaging plate.

In a preferred embodiment of the present invention, the optical imaging device includes a plurality of color channels each having sensitivity to different colors, and the color of the illumination light corresponds to the color of each color channel.

Preferably, the optical image intensity of the formed image corresponds to the time integrated intensity of the light detected by the optical imaging device. In a preferred embodiment of the invention, the scattered acoustic energy is the acoustic energy reflected by the object.

The present invention will be more clearly understood from the following description of preferred and non-limiting embodiments with reference to the drawings.

FIG. 1 shows an acousto-optic cell 10 of a type particularly suitable for the present invention. Although there are many different types of similar devices, and many of them can be used in the present invention, preferred embodiments of the present invention provide that the molecules are usually in a horizontal orientation,
That is, a liquid crystal acousto-optic converter oriented in a direction perpendicular to the thickness direction of the cell will be described.

The average alignment of the molecules of the liquid crystal material 12 of the cell 10 is preferably between the glass window 14 on which the antireflection film is formed and the acoustically transparent mirror surface 16,
It can be changed by applying a vertical electric field. For example, Ha referenced above
As described in the article by midzada et al., such cells are bistable. That is, molecules are oriented both vertically and horizontally depending on their energy state. In the preferred embodiment of the present invention, a device having this bistability is used in which the normal orientation is horizontal and the bias orientation is vertical. Sound waves incident on the cell, if they have sufficiently high energy, will move the molecular axes horizontally. The sound wave incident on this cell has higher energy when a vertical electric field is present. The strength of the electric field controls the energy difference between the vertical and horizontal direction of the molecule, and thus controls the amount of acoustic energy required to move the molecule from vertical to horizontal.

FIGS. 2A and 2B illustrate a method for determining the orientation of molecules in a liquid crystal transducer and an acousto-optic transducer 18 useful in the present invention. FIG. 2 (
In A), the above-described electric field is applied to the cell 10 of FIG. 1, and no acoustic energy is given to the cell. Light from an LED or other light source 22 is expanded and collimated by a lens system, shown schematically as lens 24. The collimated light enters the polarization beam splitter 26. Beam splitter 2
Numeral 6 transmits a light beam 28 of a predetermined polarization direction to the cell 10 and reflects light of the orthogonal polarization direction to the absorber 30, and this light is absorbed here. Alternatively or additionally, the light emitted from the LED may be polarized, or the polarizer 21 may be disposed between the light source and the beam splitter 26.

Since there is no acoustic energy, the molecules are oriented in a direction orthogonal to the polarization direction of the light beam 28, and the polarization state of the light is not affected by the presence of the cell, and the mirror surface 16 remains in the polarization state of the light beam 28. Is reflected by This light passes through the beam splitter 26 without being reflected here.

Accordingly, a camera 32, such as a CCD camera, mounted to receive the reflected light from the beam splitter 26 and focused by the lens system shown as the lens 34, does not receive this light. . Note that the light enters the cell in an unexcited state,
Alternatively, a polarizer 36 for blocking stray light having the same polarization direction as the light reflected by the cell can be optionally provided.

FIG. 2B shows acoustic energy 37 incident on the cell 12 from below via the mirror 16.
FIG. Portions of the cell that have been exposed to acoustic energy greater than the transducer threshold have molecules oriented in one of the horizontal directions of the transducer. One of the horizontal directions is generally, preferably, the direction determined by the manufacturing process for manufacturing the transducer. If the light in the beam 28 has a polarization at an angle, preferably 90 degrees, to this horizontal direction, the polarization of this light will be
The light is changed to elliptically polarized light that includes a component having a polarization direction orthogonal to the polarization direction of the light speed 28. This light component is then reflected by the beam splitter 26 and focused by the lens 34 on the camera 32. In the range where the incoming acoustic energy exceeds the threshold for only a portion of the cell, only a portion of the light beam 28 incident on the cell is affected and the pattern is imaged by the camera 32.

FIG. 3 is a schematic diagram of an acousto-optic imaging system 40 useful for imaging an object 42, such as an organ in the body, according to a preferred embodiment of the present invention. Image forming system 4
0 preferably incorporates the acousto-optic transducer 18 described with reference to FIGS. 2A and 2B, including the cell 10, light source 22, lens system 24, polarizer 21, It includes a beam splitter 26, an absorber 30, a camera 32, a lens system 34, and a polarizer 36. The mirror surface 16 of the cell 10 is on the object 42 side and receives acoustic energy therefrom. Preferably, the acoustic energy is focused by one or more acoustic lenses 44, the acoustic lenses having variable acoustic focusing power so that the imaging system 40 can address objects at various distances. Yes,
And / or the interval is also variable. Such focusing systems are described, for example, in previously referenced U.S. Pat. Nos. 4,338,821 and 4,393,712.
Other focusing systems or fixed focus systems can be used. The air gap between the acoustic elements (i.e., the two acoustic lenses, the object under observation, and the cell 10) is preferably filled with a sound transmitting material to adapt the impedance of the various elements to reduce internal acoustic reflection. .

The acoustic energy source 46 illuminates the object with preferably pulsed energy. Acoustic energy is reflected at the interface between the object and its surroundings. Then, a part of the reflected energy is focused on the cell 10 by the lens 44.

When the reflected and focused energy reaches a threshold set by the cell bias, the orientation of the molecules is changed at the irradiated site of the cell and the light source 2
The light from 2 passes through the part and goes to the camera 22. If the acoustic illumination is pulsed, the threshold is first reached from the portion of the object closer to the imaging system and then reflected from the portion of the object further away from the imaging system. Becomes Soon, the light from the light source 22 will be turned off so that no more light reaches the camera 32. The acoustic energy is extinguished after the light is extinguished at a time coincident with the arrival of the last acoustic energy of the pulse from each point of the object to the transducer.

The CCD 32 is a preferred form of CCD camera. The camera 32 integrates the received light such that the brightness of the image captured by the camera is proportional to the interval between the receipt of energy by the cell and the extinction of the light source 22. . Therefore, after correcting the variation in the intensity of the reflected wave, the brightness of the optical image of the closer part of the object generated by the camera becomes higher than that of the farther part. This is shown in FIG. 4, which is a somewhat idealized timing diagram. Here, the top row shows the light from the light source 22 and the second row shows the sound source 46.
, The third row shows the reflected energy received from the portion of the cell 10 near the object at the first position, and the bottom row shows the reflected energy of the object at the second position of the cell 10. It shows the reflected energy received from a distant part. The portion of the lower two stages where the brightness of the image is increased by light is shown by diagonal lines in the figure.

Assuming that the velocity in the medium surrounding the object is ν and the difference between the reception times of the two reflected acoustic waves is Δt, the distance between the two regions of the object is Δt × ν / 2. If the system is correctly calibrated, the image captured by the CCD camera from a single acoustic pulse will determine the distance of all parts of the object visible by the imaging system, since Δt is determined from the difference in brightness. It contains all the information needed to get it.

To calibrate the system, an object is first irradiated with pulsed acoustic energy with the light source 22 turned off. Next, the light source is turned on for a predetermined time t3. For each pixel of the image captured in the above situation, the luminance divided by time t3 corresponds to a calibration factor that converts luminance to time. Note that since the brightness of the image does not depend on the magnitude of the reflection (as long as it exceeds the threshold), the calibration factor is constant or nearly constant over the entire image.

The luminance values of the image pixels (of the image containing the distance information) are divided by a calibration factor for each pixel. The brightness of the image thus obtained is proportional to the distance of the part of the object corresponding to the pixels from the reference plane towards the image forming system.
The reference surface is the surface at which the acoustic energy reflected by this surface reaches the cell 10 just when the light source 22 is turned off.

After capturing the image, a sufficiently strong electric field is applied to the cell so that all molecules are oriented vertically and the cell is reset. Alternatively, if multiple images are taken at long intervals, the second image is a cell in which all molecules are vertical,
It is imaged after reaching a new equilibrium. In the preferred embodiment described above, an electric field is applied to the cell while processing is taking place.

In the preferred embodiment of the invention described above, the optical light generated by the light source is such that only the surface of the object (and its position relative to the reference plane) is imaged. In a second preferred embodiment of the present invention, the internal structure of the object can be determined.

FIG. 5 shows an example of such an object 48. The object is located in an enclosure having a first impedance and has an outer shell having a second impedance and an inner core having a third impedance. As illumination waves strike the boundaries of various materials, acoustic energy is reflected back toward the imaging system. However, at the above-mentioned timing, waves reflected on the outer surface of the object rotate the molecules, and thus become insensitive to reflection from the core. One method for solving this obstacle is to change the threshold on the cell 10 and image the target. If the impedance mismatch between the core and the shell is large enough (but not too high), reflection from the shell will not activate the cell, while reflection from the inner surface will activate the cell. This makes it possible to image the interface between the outer shell and the inner core. However, if the difference in impedance is not very large, imaging the material inside is not very effective.

In a further preferred embodiment of the present invention, the system varies the electric field to image the object on a slice basis. At this time, the distance can be obtained within the slice.

FIG. 6 is a timing chart when an image of the slice 50 is formed. 6 corresponds to the vertical electric field applied to the cell 10, the second stage corresponds to pulsed illumination light emitted from the light source 22, the third stage corresponds to acoustic illumination, and the fourth and fourth stages correspond to acoustic illumination.
The fifth and sixth steps correspond to the two reflection components from the positions 52, 56 and 54 of the object 48, respectively. The bottom row shows the orientations of the molecules of the cell 10 corresponding to the images at the positions 52 (the image at the position 54 is the same as the image at the position 52) and 56. In the characteristics, the high level corresponds to the vertical arrangement, The levels correspond to a horizontal arrangement. The top property corresponds to an electric field where the high level sets the threshold to a value high enough that the acoustic energy cannot move the molecules and any horizontal molecules can be quickly rotated vertically. . The lower level corresponds to the level at which the acoustic energy can rotate the molecule from vertical to horizontal.

In FIG. 6, first, a high electric field is applied which switches the polarization by the molecules in the vertical direction and gives a very high acoustic switching threshold. Therefore, the point 52 of the object 48
The acoustic pulse reflected from and reflected from point 58 is not sufficient to switch directions. On the other hand, acoustic pulses arriving late, such as reflections from points 53 and 56, switch molecules and reflect light from light source 22 to camera 32. The relative distance between these points can be known in the same manner as the image obtained by the timing chart of FIG.

Slices, preferably partially overlapping slices, are sequentially captured to generate a three-dimensional image of the object.

Note that the ability to identify an interface in the direction of the acoustic beam is limited by the duration of the acoustic pulse. That is, if two objects are very close compared to the time the pulse travels between them, the two objects cannot be distinguished and the closer interface completely masks the farther one. Resulting in. To reduce the effects of this problem, in a preferred embodiment of the present invention, a series of overlapping slices is obtained. Preferably, the threshold level is set high enough so that the cell is not switched by multiple reflections within the object.

[0061] The above-described image forming configuration includes a single pulse acoustic illumination for photographing the entire surface of the object facing the image forming system, and a single pulse acoustic illumination for photographing a single slice in the object. Is also taken into account. In a further preferred embodiment of the invention, a plurality of spaced apart slices can be acquired in one pulse. In this embodiment of the invention, camera 32 is a color CC.
The light source 22 includes three channels of a CCD camera, for example, a plurality of color light sources corresponding to RGB sensitivities. This method triples the efficiency of the system and reduces the time required to image the entire object by a factor of three.

A first slice is imaged using a red (R) light source and a red CCD channel. The system is reset by raising the electric field to a higher level, and a second slice is imaged using the same acoustic pulse and a green (G) light source and a green CCD channel. The system is reset again and a third slice is imaged using the blue (B) light source and channel as well. Slices are imaged at intervals between slices imaged using the first pulse using a second pulse (and a third pulse, if necessary, followed by a pulse).

As a practical example of the present invention, consider the formation of an image of an object in a human body. The speed of sound in the body is on the order of ν = 1500 m / sec. A typical LC relaxation time, τ, is approximately 10 microseconds. If a 10 cm thick object is sliced and examined using a 5 mm thick slice, 20 slices are required. Note that the resolution of the system is better than the slice thickness.

To form an image of a slice of this thickness, the acoustic pulse width must be the thickness divided by the speed, ie, 3.3 microseconds in length. Using the above-described RGB imaging procedure, three slices can be imaged per acoustic pulse. Due to the finite relaxation time of the LC plate, the slices must be separated by at least ντ, ie a distance of 15 mm. That is, it is possible to form an image of every five slices using the same acoustic pulse. However, in general, it is desirable that the pulses have a relatively large interval, that is, for example, that an image of every eight slices is formed. Therefore, the first, eighth, and fifteenth slice images are formed by the first acoustic pulse, and the second, ninth, and sixteenth slices are formed by the second acoustic pulse. Therefore, the seventh acoustic pulse (and seven triple slice imaging (triple
slice acquisitions) are required to form an image of the entire object. Assuming a distance of 10 cm between the image and the object, the last reflection from the acoustic pulse travels 30 cm before being received by the imaging device. Thus, the pulses are at least 3 / ν seconds, or 2 msec apart. Another constraint is the time between fields or frames of the CCD camera. For a regular camera, the time between fields is 16.6 m
sec, the maximum acoustic pulse rate using such a system is 60 pulses per second. This is done by imaging the object in 117 msec (8.
5 objects). However, if a high-speed CCD camera is used, a higher frame rate is used, and the imaging time of the entire object is basically 14 ms.
c, and the object imaging rate is about 70 objects / sec. Slow rates are used to reduce the effects of double reflections and reflections from other parts of the body. However, even at slow rates, real-time imaging of moving parts of the body, such as the heart, can be performed at high resolution.

The present invention has been described using an annular acoustic energy source for illuminating an object to be imaged. This is desirable because the plane of the object being imaged is parallel to the imaging system. However, the sound source may be located beside the imaging system and the axis may be parallel or at a small angle to the imaging system. Further, while the preferred embodiment of the present invention employs bistable AOC (LC), continuous acoustic energy, such as analog LC, is used to keep the orientation of the molecule rotated. You may use the system you need. Although the system is described as having a CCD for imaging, the system may use other imaging devices, such as film or CID devices, as in another preferred embodiment of the present invention. .

The configurations and methods described herein can be combined in various ways based on various preferred embodiments. Further, some features of the preferred embodiment of the present invention may be omitted in accordance with another preferred embodiment. Various other modifications of the preferred embodiments of the invention, which fall within the scope of the claims, will occur to those skilled in the art. It is to be understood that the preferred embodiments of the present invention are illustrative only and are not intended to limit the scope of the invention as defined in the claims.

[Brief description of the drawings]

FIG. 1 schematically illustrates the operation of a liquid crystal acousto-optic converter useful in a preferred embodiment of the present invention.

FIGS. 2A and 2B are diagrams illustrating the influence of sound waves on light reflected by a liquid crystal acousto-optic transducer according to a preferred embodiment of the present invention.

FIG. 3 is a schematic diagram of an acousto-optic imaging system according to a preferred embodiment of the present invention.

FIG. 4 is a timing diagram of an acousto-optic imaging system according to a first preferred embodiment of the present invention.

FIG. 5 is a diagram showing an object in which an image is formed using some of the preferred embodiments of the present invention.

FIG. 6 is a timing diagram of an acousto-optic imaging system for forming an image of two slices as shown in FIG. 5, according to another preferred embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 acousto-optic cell 14 glass window 16 mirror surface 18 acousto-optic converter 21 polarizer 22 light source 24 lens 26 polarizing beam splitter 30 absorber 32 camera 34 lens 36 polarizer

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] March 23, 2000 (2000.3.23)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Claims (25)

[Claims] 1. An acousto-energy source for illuminating an object, and (b) an acousto-optic image forming plate for receiving scattered acoustic energy from the object, wherein the scattered acoustic energy is an acousto-optic image. (C) an optical energy source for producing an acoustic image on the forming plate, the optical energy source producing an optical energy whose energy characteristics are changed by a change of the acousto-optical image forming plate caused by receiving the acoustic energy; Optical imaging means for forming a non-holographic image of the optical energy, wherein the magnitude of the time integral of the light detected by the optical imaging means is an image having a spatial intensity change, and The acoustic energy source is pulsed such that the intensity at a point in the optical image is related to the distance of the corresponding point of the object from the reference position Acousto-optic imaging system for forming an image of driven, object. 2. The system according to claim 1, wherein the acoustic energy source does not scan the object transversely to the direction of propagation of the illuminating acoustic energy. 3. The system according to claim 1, wherein the optical image is an image of a point on the surface of the object. 4. The system of claim 3, wherein the optical energy source is pulsed off only after the acoustic energy scattered by the surface being imaged reaches the acousto-optic imaging plate. 5. The system according to claim 1, wherein the image is an image representing a distance of a point in a slice of the object from a reference position. 6. The system according to claim 5, further comprising a control system for applying a voltage acting to select between a high acoustic threshold state and a low acoustic threshold state of the acousto-optic imaging plate. 7. The high acoustic threshold state is selected at a point in time prior to receipt of acoustic energy scattered by a portion of the object closest to the acousto-optic imaging plate, the state being: 7. The system of claim 5 or 6, wherein upon receipt, the low acoustic threshold state is changed and the time of the change defines a closer distance of an image slice. 8. The system of claim 5, wherein the optical energy source is pulsed off to define a far distance of the image slice. 9. The system according to claim 4, wherein the reference position is at a distance corresponding to a scattered wave received when the optical energy is pulsed off. 10. A system according to any of the preceding claims, wherein the spatially varying intensity is proportional to the distance from the reference position to a point in the acoustic imaging device. 11. A light source for optically illuminating an acousto-optic plate from a light source for a predetermined time during which a characteristic of optical energy is changed by a change of an acousto-optic image forming plate, thereby correcting an intensity value by a normalization function. A system according to any of the preceding claims. 12. The light source of claim 1, wherein the light source is linearly polarized, the acousto-optic plate does not affect the optical energy before the change, and the polarization is converted to elliptically polarized light after the change. A system according to any of the preceding claims. 13. The system of claim 12, wherein the imaging device is responsive to a component of the light having a polarization different from a polarization of the light generated by the light source. 14. The system according to any of the preceding claims, wherein the optical imaging device comprises a CCD camera. 15. The system according to any of the preceding claims, wherein the acousto-optic imaging plate is a bistable device. 16. A system according to any of the preceding claims, wherein the imaging plate comprises a liquid crystal plate. 17. The system according to any of the preceding claims, wherein the scattered acoustic energy corresponds to energy reflected from a plurality of points on the object. 18. Irradiating an object with pulsed acoustic energy to form an acoustic image of the acoustic energy scattered at points in a first slice of the object on an acousto-optic image forming plate; Forming an acoustic image of the acoustic energy scattered at a point in at least another one slice of the object on the optical imaging plate; and forming a plurality of optical images from the pulsed acoustic energy by optical imaging An apparatus for separately detecting the first and another acoustic image, wherein an intensity of the optical image has a spatially varying value related to a distance from a reference position to a position of a corresponding point in each slice. And a method of forming an image of an object. 19. The acousto-optic imaging plate is sequentially illuminated with pulsed light of different colors to form the plurality of optical images, each representing one of the slices, to produce the plurality of optical images. The method according to claim 18, wherein the light is sequentially detected. 20. The acousto-optic image forming plate is configured to switch between a first state insensitive to the scattered energy and a second state changed by the scattered energy. 20. The method of claim 19, wherein the acousto-optic imaging plate is switched from the first state to the second state when the scattered energy from the first reaches the imaging plate. 21. The method according to claim 19, wherein the optical energy source is extinguished when scattered energy from the farthest part of each slice reaches the imaging plate. 22. The optical imaging device according to claim 19, wherein the optical imaging device includes a plurality of color channels each having sensitivity to a different color, and the color of the illumination light corresponds to the color of each color channel. The described method. 23. The method according to claim 18, wherein the optical image intensity of the formed image corresponds to the time integrated intensity of the light detected by the optical imaging device. 24. The method according to claim 18, wherein the scattered acoustic energy is acoustic energy reflected by the object. 25. The property of electrical energy that is altered is polarization.
25. The method of claim 24, wherein