RU2486501C2 - Laser optical-acoustic tomography method and apparatus for realising said method (versions) - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method involves generating an acoustic pulse using both a distributed optical-acoustic transducer and directly through non-uniformities in the analysed object. Reflected, scattered and transmitted signals are detected using one array of piezoelectric elements which can be placed either between the optical-acoustic transducer and the analysed material, or on the back side of the transducer.

EFFECT: invention enables to obtain laser ultrasonic and optical-acoustic images of non-uniformities in the analysed object in real time with high resolution and high contrast of the obtained images.

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Description

The present invention relates to the field of non-destructive methods for the diagnosis of biological objects and can be used to identify structural heterogeneities in the studied objects and determine their geometric dimensions.

A known method of laser-acoustic control, in which the image of the investigated object is built on the scattered and reflected from inhomogeneities acoustic signals (1). A device that implements the aforementioned method comprises: a pulse-modulated laser connected to an optical fiber, the end of which is directed through an expanding lens to an optical-acoustic transducer, and the piezoelectric receiver is made in the form of a lattice of local piezoelectric elements, each of which is connected through a preamplifier and an analog-to-digital converter with a computer. The disadvantages of this method and device are: low optical contrast of the obtained images of the structure of biological objects, as well as the small depth of the location of heterogeneities inside biological objects, for which it is possible to obtain images. The advantage of this method is the high resolution of images of the structure of the object under study due to the controlled form of the acoustic probe pulse from the optical-acoustic transducer.

A known method for the diagnosis of pathological biological tissue inside a healthy biological tissue using optical acoustic tomography, which consists in irradiating a surface of a healthy biological tissue with a laser pulse, thus generating acoustic signals (pressure waves), recording these acoustic signals using an acoustic receiver, recording the amplitude and the time profile of the pressure wave and analyzing them using computer software (2).

A device for implementing the aforementioned method comprises: a pulsed laser, a laser radiation delivery system, at least one acoustic receiver, an electronic system for recording and processing signals, and a computer with special software that allows you to restore images of biological tissue. In this device, the image of the studied object is constructed from acoustic signals produced by the inhomogeneities of the studied object after they absorb laser radiation. The advantages of the above method (2) are: high optical contrast of the obtained images of the structure of biological objects and a large depth of the location of inhomogeneities inside biological objects, for which it is possible to obtain images. The disadvantage of this device is the low resolution images of the structure of the studied object.

The aim of the present invention is to combine the functionality of the above methods in one device, namely the receipt of laser ultrasonic and optical-acoustic information about the investigated biological object. The combination of such information received at a time in one device has undeniable advantages.

To solve the problem in the method, which consists in generating an optical pulse, converting it into an acoustic signal, emitting this signal into the test medium and receiving a reflected acoustic signal with a piezoelectric element, an acoustic pulse is generated using both a two-way distributed optical-acoustic transducer and directly the inhomogeneities of the studied object, registration of reflected and scattered signals in the first case and transmitted signals in the second case, is carried out more Coy piezoelectric elements, which may be located either between the optical-acoustic transducer and the test material or with the reverse side of the converter, wherein the signals registered lattice piezoelectric elements are processed in real time.

To solve this problem in a known device containing a multi-channel tomographic system, made in the form of a single unit and containing a distributed optical-acoustic generator, as well as a set of piezoelectric elements, each of which is connected through a multi-channel amplifier with a multi-channel analog-to-digital converter and a computer, an acoustic lens, with the help of which focusing is carried out, and a pulse-modulated laser, the laser radiation is supplied to both a multi-channel tomographic system and not mediocre to the investigated object.

For various versions of the device, either two pulse-modulated lasers or one pulse-modulated laser together with a radiation divider can be used.

There are device options in which the array of receivers and the optical-acoustic emitter are made curved with the possibility of focusing radiation and reception in the absence of an acoustic lens.

Possibility of implementation.

The method of laser optical acoustic tomography and a device for its implementation are illustrated in Fig.1-3.

The drawing of Figure 1 shows a multi-channel system for laser ultrasonic and optical acoustic tomography. It contains:

1 - Q-switched laser with a high pulse repetition rate;

2 - a laser radiation delivery system comprising an radiation divider at the output;

3 - combined multifunctional power supply that provides power to the laser, optical-acoustic transducer and analog-to-digital converter;

4 - high-speed multi-channel precision analog-to-digital converter, providing the conversion of the electrical signals of the optical-acoustic converter into digital form, its temporary storage and transmission over the high-speed line to a computer;

5 - a data processing system including a computer connected by a high-speed data line with an analog-to-digital converter and software providing digital data reception, spectral and temporal processing and imaging of an object under investigation on a monitor screen, as well as interactive control of the transmission and processing process data;

6 - a multichannel tomographic system containing an optical-acoustic transducer and a lattice of broadband piezoelectric elements for converting laser pulses into acoustic ones, transmitting them to a test medium, registering reflected and scattered acoustic signals and reconstructing them from an image of a test object in the case of laser ultrasound tomography and for recording acoustic signals from the studied object and restoration of its image from them in the case of optical-acoustic tomography.

The control and operation of the system is carried out from computer 5, and the laser operation is synchronized by special signals generated in the block of the analog-to-digital converter 4. The signal is started-read by the photodiode pulse matched with the laser pulse.

A diagram of a multi-channel tomographic system 6 is shown in FIG. 2. It contains: an optical system - 8, a sound pipe - 9, an optical-acoustic transducer - 10, a piezoelectric array - 11, an acoustic lens - 12, an object under investigation - 13, an amplifier - 14. Figure 3 shows a diagram of a multi-channel tomographic system 6 for the case curved piezoelectric receivers and an optical-acoustic transducer. It contains the same elements, only the positions of the object under study - 13, amplifier - 14 and optical radiation - 15 change by 12.13 and 14, respectively.

The tomography system operates as follows.

In the case of laser ultrasound tomography, the pulses of optical radiation 7 from the laser are transmitted through the optical system 8, which forms the required beam size, and the sound duct 9, transparent for optical radiation 7, to the optical-acoustic transducer 10, where the formation of a broadband acoustic pulse occurs due to unsteady thermal expansion . When a multichannel tomographic system is operating, acoustic signals are recorded from the studied object in focus. In order for the shape of the recorded acoustic signal from the object under study not to be distorted, it is necessary to provide a time window for the delay between the arrival of the acoustic signal from the object under study and the arrival of acoustic signals reflected from the boundaries of the elements of the multichannel tomographic system. For these purposes, a multi-channel tomographic system contains a sound pipe 9, which provides a proper time window for delaying the arrival of subsequent reflected acoustic pulses from the boundaries of the elements of the tomographic system. The optical-acoustic transducer 10 is a plane-parallel plate made of a material that absorbs laser radiation well, has a high thermal expansion coefficient and is matched by acoustic impedance with the material of the sound duct 9. The acoustic signal from the optical-acoustic transducer 10 propagates to the array of the piezoelectric receivers 11 and is recorded system as a reference. Acoustic pulses from each piezoelectric receiver are propagated through the acoustic focusing lens 12, which is matched in acoustic impedance with the material of the piezoelectric receivers and with the medium in which the object under study is located to the object being studied 13. Acoustic pulses passing through the structure of the object under study are reflected and scattered from the desired inhomogeneities and, passing back through the acoustic focusing lens 12, are recorded by the array of piezoelectric receivers 11. Electrical signals from the piezoelectric receivers, passing the amplification Tel 14, fall to the analog-to-digital converter 4 (1). To build images using a computer that runs in real time.

In the case of optical acoustic tomography, the pulses of optical radiation 15 go directly to the studied object 13. As a result of the absorption of laser radiation, heating and inhomogeneous expansion of the studied object occurs, which leads to the formation of acoustic pulses. Acoustic pulses passing through the acoustic focusing lens 12 are detected by the array of piezoelectric receivers 11. Sound pipe 9 provides a proper time window for delaying the arrival of subsequent reflected acoustic pulses from the boundaries of the elements of the tomographic system. The electric signals from the piezoelectric receivers, passing the amplifier 14, fall on the analog-to-digital Converter 4. For the construction of images is also used a computer operating in real time.

An example of a signal from a point source registered by one of the piezoelectric receivers is shown in FIG. 4.

To obtain images of the object under study using both methods, it is possible, for example, to send pulses of optical radiation from a laser and register the received signals alternately with a piezoelectric detector array.

Sources of information used in the preparation of the application.

1. Patent of Russia No. 2232983

2. US Patent No. 5840023

Claims (4)

1. The method of laser, optical-acoustic tomography, which consists in generating an optical pulse, converting it into an acoustic signal, emitting this signal into the test medium and receiving the reflected acoustic signal with a piezoelectric element on the one hand, and irradiating the test object with laser radiation, generating an acoustic signal from this object due to the optical-acoustic effect, and receiving an acoustic signal from the other side of the piezoelectric element, characterized in that the acoustic pulse is generated as using a predetermined optical-acoustic transducer, as well as directly by the inhomogeneities of the object under study, and registration of reflected, scattered and transmitted signals is carried out by a single array of piezoelectric elements. 2. Device for laser optical acoustic tomography, containing a multi-channel tomographic system, made in the form of a single unit and containing an optical system, an optical-acoustic transducer, as well as a piezoelectric array, each of which is connected through a multi-channel amplifier with a multi-channel analog-to-digital converter and a computer , an acoustic lens and a pulse-modulated laser, characterized in that a laser radiation divider is introduced into the device, the first output of which is connected to second object, and the second with the optical system. 3. The device according to claim 2, characterized in that the piezoelectric array and the optical-acoustic transducer are made curved. 4. Device for laser optical acoustic tomography, containing a multi-channel tomographic system, made in the form of a single unit and containing an optical system, an optical-acoustic transducer, as well as a piezoelectric array, each of which is connected through a multi-channel amplifier with a multi-channel analog-to-digital converter and a computer , an acoustic lens and a pulse-modulated laser, characterized in that it contains a second laser.

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