JP2013188330A - Photoacoustic apparatus, probe for photoacoustic apparatus and method for obtaining acoustic wave detection signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a probe for a photoacoustic apparatus, which prevents a noise caused by electromagnetic waves from entering the probe and improves irradiation efficiency of a laser beam and further prevents the deterioration of an obtained image.SOLUTION: In a probe for a photoacoustic apparatus for detecting acoustic waves issued from a subject receiving the irradiation of light, a ferromagnetic substance thin film 58 is laminated on a surface of an acoustic lens 57 and a near infrared reflection film 59 for reflecting electromagnetic waves is laminated on the ferromagnetic substance thin film 58. In addition, a protective film 60 composed of an antioxidant material is laminated on the near infrared reflection film 59.

Description

  The present invention relates to a photoacoustic apparatus, that is, an apparatus that performs processing such as irradiating a subject such as a living tissue with light and imaging the subject based on an acoustic wave generated by the light irradiation.

  The present invention also relates to a probe used in such a photoacoustic apparatus and a method for acquiring an acoustic wave detection signal using such a probe.

  Conventionally, a photoacoustic imaging apparatus that images the inside of a living body using a photoacoustic effect is known. In this photoacoustic imaging apparatus, pulsed light such as pulsed laser light is irradiated into the living body. Inside the living body that has been irradiated with the pulsed light, the living tissue that has absorbed the energy of the pulsed light undergoes volume expansion due to heat and generates an acoustic wave (acoustic signal). Therefore, it is possible to detect this acoustic wave with an ultrasonic probe or the like and visualize the inside of the living body based on the detection signal.

  On the other hand, an ultrasonic imaging apparatus using an ultrasonic probe has been conventionally known. This type of ultrasonic probe is provided with an ultrasonic transducer at the tip, and is often composed of a backing material, a piezoelectric body and electrodes sandwiching the piezoelectric material, an acoustic matching layer, an acoustic lens, and the like. In the ultrasonic imaging apparatus, ultrasonic waves are irradiated from a ultrasonic transducer to a subject such as a human body, and reflected ultrasonic waves from the subject are received by the ultrasonic transducer. An ultrasonic image is obtained by electrically processing the reflected ultrasonic detection signal.

  Since the ultrasonic probe as described above can detect an acoustic wave as well as an ultrasonic wave, an apparatus capable of acquiring both a photoacoustic image and an ultrasonic image has been proposed. That is, in such an apparatus, a light irradiation unit that irradiates light toward the subject is added to the ultrasonic probe, and the acoustic wave emitted from the subject that receives the light from the light irradiation unit is superposed on the ultrasonic probe. It is to be detected by a sonic transducer.

  By the way, in the photoacoustic imaging apparatus, the greatest difference from a general ultrasonic diagnostic apparatus is that a laser beam is necessary. The voltage required for a general ultrasonic diagnostic apparatus is about 100 V at maximum, but a voltage of several kV is required to emit laser light having a wavelength in the infrared region, which is used in a photoacoustic imaging apparatus. Therefore, there is a concern about generation of high electromagnetic noise. In order to prevent such electromagnetic noise from entering the ultrasonic probe, as shown in Patent Document 1, a shield film made of metal or the like for shielding electromagnetic waves on the surface of an acoustic lens constituting the ultrasonic probe. There has been proposed a method of providing In order to protect the shield film, a method of laminating a resin film on the shield film has also been proposed (see Patent Document 2).

  On the other hand, when irradiating a living body with laser light in the photoacoustic imaging apparatus, a part of the laser light is reflected on the surface of the living body, so that the laser irradiation efficiency is lowered. For this reason, the method of providing the light reflection member for reflecting the light reflected on the biological surface in an acoustic lens is also proposed (refer patent document 3).

JP 2003-33353 A Japanese Patent Application Laid-Open No. 6-207772 JP2012-040361A

  Since the shield film and the light reflecting member described above are made of a metal material, the reflection performance is deteriorated due to oxidation with time. For this reason, the laser beam reflected on the surface of the living body is absorbed by the oxidized shield film or the light reflecting member, and the shape of the acoustic lens is included in the image as an artifact, so that the image quality of the photoacoustic image is deteriorated. The above Patent Documents 1 to 3 describe a shield film, a light reflecting member, and a protective film, respectively, but no measures are taken against deterioration of image quality due to oxidation of the shield film or the light reflecting member.

  The present invention has been made in view of the above circumstances, and can prevent the intrusion of noise caused by electromagnetic waves into the probe, improve the irradiation efficiency of laser light, and further prevent the deterioration of an acquired image. With the goal.

The probe for a photoacoustic apparatus according to the present invention is a probe for a photoacoustic apparatus that detects an acoustic wave emitted from a subject that has been irradiated with light.
An acoustic lens,
A ferromagnetic thin film provided on the surface of the acoustic lens;
A metal material thin film that reflects electromagnetic waves provided on a ferromagnetic thin film;
And a protective film made of an antioxidant material provided on the metal material thin film.

  “Electromagnetic wave” includes light, particularly light in the infrared region.

  In the probe for a photoacoustic apparatus according to the present invention, the total thickness of the ferromagnetic thin film, the metal material thin film, and the protective film is preferably 3 μm or less, and more preferably 1 μm or less.

  In the probe for a photoacoustic apparatus according to the present invention, the ferromagnetic thin film may be made of any one of a ferromagnetic metal, a ferromagnetic alloy, and a ferromagnetic oxide. Specifically, Fe, Ni, Co, Gd or the like is used as the ferromagnetic metal, and an alloy or sintered body such as permalloy, supermalloy, permendur, sendust, SmCo, or NdFeB is used as the ferromagnetic alloy. be able to. Various ferrite materials can be used as long as they are ferromagnetic oxides.

  In the probe for a photoacoustic apparatus according to the present invention, the metal material thin film may be made of a metal material that reflects approximately 80% or more of near infrared rays having a wavelength of approximately 700 nm to 1000 nm. Specifically, a metal material such as Al, Au, Ag, and Rh that reflects near infrared rays having a wavelength of about 700 nm to 1000 nm by about 80% or more can be used.

  In the photoacoustic device probe according to the present invention, the protective film may be made of an organic film or an oxide thin film. Specifically, materials having an antioxidant function such as an organic film such as parylene and various oxide thin films can be used.

  According to the probe for a photoacoustic apparatus of the present invention, a ferromagnetic metal film, a metal material thin film that reflects electromagnetic waves, and a protective film made of an antioxidant material are sequentially formed on the surface of the acoustic lens. Here, the ferromagnetic metal absorbs the magnetic lines of force among the electromagnetic waves, so that the electromagnetic metal, particularly the magnetic lines of force, can be prevented from entering the probe by the ferromagnetic metal film. In addition, the metal material thin film can return laser light having a wavelength in the infrared region reflected inside the living body to the living body, and can reflect radio waves of electromagnetic waves by free electrons. In particular, high-frequency electromagnetic waves can be effectively reflected. As described above, according to the probe for an acoustic device of the present invention, the ferromagnetic metal film and the metal material thin film can prevent a wide range of electromagnetic waves from entering the probe and are outside the ferromagnetic metal film. Infrared light reflected inside the living body by the metal material thin film can be prevented from entering the probe. In addition, since the protective metal film prevents oxidation of the ferromagnetic metal film and the metal material thin film, it is possible to prevent a decrease in light reflectance of the laser beam due to the oxidation of the ferromagnetic metal film and the metal material thin film. As a result, the shape of the acoustic lens can be prevented from being included in the photoacoustic image as an artifact, and as a result, deterioration of the photoacoustic image can be prevented. It is also possible to prevent heat from being easily transmitted to the probe. Further, by preventing oxidation of the ferromagnetic metal film and the metal material thin film, the oxidized ferromagnetic metal film and the metal material thin film generate heat by laser light irradiation, thereby Can also be prevented.

  Therefore, according to the probe for a photoacoustic apparatus of the present invention, the laser irradiation efficiency can be improved to the maximum, and as a result, the sound generation efficiency in the living body can be improved. Thereby, noise due to electromagnetic waves is reduced, and a high-definition photoacoustic image can be acquired.

  In addition, by setting the total thickness of the ferromagnetic thin film, the metal material thin film, and the protective film to 3 μm or less, the acoustic transmittance can be increased to about 90% or more in ultrasonic waves of about 5 MHz, and the total thickness is 1 μm or less. By doing so, the sound transmittance can be about 95% or more.

  Moreover, according to the photoacoustic apparatus according to the present invention, since the probe for the photoacoustic apparatus according to the present invention is provided, noise caused by electromagnetic waves is reduced and a high-definition photoacoustic image can be acquired.

The block diagram which shows schematic structure of the photoacoustic imaging device by one Embodiment of this invention. The perspective view which shows the example of the external shape of the photoacoustic imaging device of this invention 1 is a partially broken perspective view schematically showing a probe according to an embodiment of the present invention. The block diagram which shows the partial structure of the photoacoustic imaging device by other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of a photoacoustic imaging apparatus 10 according to an embodiment of the present invention. The photoacoustic imaging apparatus 10 includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser light source unit 13, and an image display unit 14.

  The laser light source unit 13 emits laser light having a center wavelength of 800 nm, for example. The subject is irradiated with the pulsed laser light emitted from the laser light source unit 13. The laser light is preferably guided to the probe 11 using a light guide unit such as a plurality of optical fibers and irradiated from the probe 11 toward the subject.

  The probe 11 detects an ultrasonic wave (acoustic wave) generated when the observation object in the subject absorbs the pulse laser beam. For this purpose, the probe 11 has an ultrasonic transducer array (hereinafter referred to as a UT array) composed of a plurality of ultrasonic transducers arranged in parallel in the azimuth direction intersecting with the scanning direction by manual operation described later, for example. Hereinafter, the azimuth direction is referred to as the AZ direction, and the elevation direction perpendicular thereto is referred to as the EL direction. The probe 11 detects an acoustic wave and outputs an acoustic wave detection signal.

  When the above-described light guide unit is coupled to the probe 11, a plurality of ultrasonic vibrations in which the end of the light guide unit, that is, the tips of a plurality of optical fibers are arranged in parallel as described above. It arrange | positions in the state surrounding the circumference | surroundings of a child, and a laser beam is irradiated toward the subject from there. Hereinafter, the case where the light guide unit is coupled to the probe 11 will be described as an example. In addition to the arrangement of the tip of the optical fiber as described above, the optical fiber may be arranged in a cross shape or a lattice shape in a plane where a plurality of ultrasonic transducers are arranged. This is preferable because the optical irradiation uniformity of the laser beam is further improved.

  When acquiring the photoacoustic image of the subject, the probe 11 is moved in the EL direction, whereby the subject is two-dimensionally scanned with the laser light. This scanning may be performed by an inspector manually moving the probe 11 or a more precise two-dimensional scanning may be realized using a scanning mechanism.

  The ultrasonic unit 12 includes a reception circuit 21, an AD conversion unit 22, a reception memory 23, a data separation unit 24, an image reconstruction unit 25, a detection / logarithm conversion unit 26, and an image construction unit 27. The output of the image construction unit 27 is input to the image display unit 14 including, for example, a CRT or a liquid crystal display device. Furthermore, the ultrasonic unit 12 includes a transmission control circuit 30 and a control unit 31 that controls operations of each unit in the ultrasonic unit 12.

  The receiving circuit 21 receives the acoustic wave detection signal output from the probe 11. The AD conversion unit 22 is a sampling unit that samples the acoustic wave detection signal received by the reception circuit 21 and converts it into photoacoustic data that is a digital signal. This sampling is performed at a predetermined sampling period in synchronization with, for example, an externally input AD clock signal.

  The laser light source unit 13 includes a Q switch pulse laser 32 made of a Ti: Sapphire laser, an alexandrite laser, or the like, and a flash lamp 33 that is an excitation light source. The laser light source unit 13 is supplied with a light trigger signal instructing light emission from the control unit 31. When the light trigger signal is received, the flash lamp 33 is turned on and the Q switch pulse laser 32 is turned on. Excited. For example, when the flash lamp 33 sufficiently excites the Q switch pulse laser 32, the control unit 31 outputs a Q switch trigger signal. When receiving the Q switch trigger signal, the Q switch pulse laser 32 turns on the Q switch and emits a pulse laser beam having a wavelength of 800 nm.

  Here, the time required from when the flash lamp 33 is turned on until the Q-switch pulse laser 32 is sufficiently excited can be estimated from the characteristics of the Q-switch pulse laser 32 and the like. Instead of controlling the Q switch from the controller 31 as described above, the Q switch pulse laser 32 may be sufficiently excited in the laser light source unit 13 and then turned on. In that case, a signal indicating that the Q switch is turned on may be notified to the ultrasonic unit 12 side.

  The photoacoustic apparatus of this invention may be comprised so that the ultrasonic image by a reflected ultrasonic wave may be acquired besides a photoacoustic image. Hereinafter, the case of doing so will be described. The control unit 31 inputs an ultrasonic trigger signal that instructs ultrasonic transmission to the transmission control circuit 30. When receiving the ultrasonic trigger signal, the transmission control circuit 30 transmits an ultrasonic wave from the probe 11. The control unit 31 outputs the optical trigger signal first, and then outputs the ultrasonic trigger signal. The light trigger signal is output to irradiate the subject with laser light and the acoustic wave is detected, and then the ultrasonic trigger signal is output to transmit the ultrasonic wave to the subject and the reflected ultrasonic wave. Is detected. Here, in order to transmit an ultrasonic wave from the probe 11, a UT array for acoustic wave detection may be used, or a different one from the UT array may be used.

  The control unit 31 further outputs a sampling trigger signal that instructs the AD conversion unit 22 to start sampling. The sampling trigger signal is output after the optical trigger signal is output and before the ultrasonic trigger signal is output, and more preferably at the timing when the subject is actually irradiated with the laser light. Therefore, the sampling trigger signal is output in synchronization with the timing at which the control unit 31 outputs the Q switch trigger signal, for example. When receiving the sampling trigger signal, the AD conversion unit 22 starts sampling the acoustic wave detection signal output from the probe 11 and received by the receiving circuit 21.

  After outputting the optical trigger signal, the control unit 31 outputs the ultrasonic trigger signal at the timing when the detection of the acoustic wave is finished. At this time, the AD conversion unit 22 continues the sampling without interrupting the sampling of the acoustic wave detection signal. In other words, the control unit 31 outputs the ultrasonic trigger signal in a state where the AD conversion unit 22 continues sampling the acoustic wave detection signal. When the probe 11 transmits ultrasonic waves in response to the ultrasonic trigger signal, the detection target of the probe 11 changes from acoustic waves to reflected ultrasonic waves. The AD conversion unit 22 continuously samples the acoustic wave detection signal and the ultrasonic wave detection signal by continuously sampling the detected ultrasonic wave detection signal.

  The AD conversion unit 22 stores photoacoustic data and ultrasonic data obtained by sampling in a common reception memory 23. The sampling data stored in the reception memory 23 is photoacoustic data up to a certain point, and becomes ultrasonic data from a certain point. The data separation unit 24 separates the photoacoustic data and the ultrasonic data stored in the reception memory 23.

  Hereinafter, generation and display of a photoacoustic image or a reflected ultrasonic image will be described. The data separation unit 24 in FIG. 1 receives ultrasonic data read from the reception memory 23 and photoacoustic data obtained by irradiating a subject with pulsed laser light having a wavelength of 800 nm. The data separation unit 24 inputs only photoacoustic data to the subsequent image reconstruction unit 25 when generating the photoacoustic image. The image reconstruction unit 25 reconstructs data indicating a photoacoustic image based on the photoacoustic data.

  The detection / logarithm conversion unit 26 generates an envelope of data indicating the photoacoustic image, and then logarithmically converts the envelope to widen the dynamic range. The detection / logarithm conversion unit 26 inputs the processed data to the image construction unit 27. Based on the input data, the image construction unit 27 constructs a photoacoustic image related to the cross section scanned by the pulse laser beam, and inputs data indicating the photoacoustic image to the image display unit 14. Thereby, the photoacoustic image regarding the said cross section is displayed on the image display part 14. FIG.

  As described above, the probe 11 is moved to scan the subject two-dimensionally with laser light, and a desired part of the subject, such as a blood vessel, is detected based on the image data regarding a plurality of cross sections obtained by the scanning. It is also possible to generate and display a photoacoustic image for three-dimensional display.

  It is also possible to generate and display an ultrasonic image of the subject based on the ultrasonic data separated by the data separation unit 24. The generation and display of the ultrasonic image may be performed by a conventionally known method, and since it is not directly related to the present invention, a detailed description is omitted, but such an ultrasonic image and a photoacoustic image are superimposed. It can also be displayed.

  Next, the probe 11 will be described in detail. Here, as an example, it is assumed that the photoacoustic imaging apparatus is configured as a portable ultrasonic observer as shown in FIG. 2, and the probe 11 used therein will be described. First, the portable ultrasonic observing device shown in FIG. 2 will be described. This portable ultrasonic observation device includes an apparatus main body 112 and a cover 113. On the upper surface of the apparatus main body 112, an operation unit 114 provided with a plurality of buttons, a trackball, and the like for inputting various operation instructions to the portable ultrasonic observation device is disposed. An inner surface of the cover 113 is provided with a monitor 14 (corresponding to the image display unit 14 in FIG. 1) that displays a photoacoustic image, an ultrasonic image, and various operation screens.

  The cover 113 is attached to the apparatus main body 112 via a hinge 116, and the illustrated opening position where the operation section 114 and the monitor 14 are exposed is opposed to the upper surface of the apparatus main body 112 and the inner surface of the cover 113. 114 and a closed position (not shown) that covers and protects the monitor 14. A grip (not shown) is attached to the side surface of the apparatus main body 112, and the portable ultrasonic observation device can be carried with the apparatus main body 112 and the cover 113 closed. On the other side surface of the apparatus main body 112, a probe connection portion 117 and a laser unit connection portion 172 to which the probe 11 is detachably connected are provided.

  On the other hand, for example, a pulse laser unit 170 incorporating a Q-switched solid-state laser is connected to a laser unit connection portion 172 via a power cable 171. When a light emission instruction is given from the operation unit 114 of the portable ultrasonic observing device when acquiring a photoacoustic image, the pulse laser unit 170 receives a predetermined trigger signal and emits a pulse laser beam. The pulsed laser light propagates through the bundle fiber 173 and is irradiated toward the subject from the light irradiation unit 174 formed at the tip of the ultrasonic probe 11. The light irradiation unit 174 may be configured separately from the ultrasonic probe 11.

  Next, the probe 11 will be described. The probe 11 includes a scanning head 118 that is gripped by an operator and applied to a subject, a connector 119 connected to the probe connecting portion 117, and a cable 120 that connects them. The UT array 100 as described above is built in the tip of the scanning head 118.

  The UT array 100 is a transducer array designed to receive a relatively high frequency acoustic wave of about 7 to 15 MHz. The transducer array is composed of a plurality of inorganic transducers arranged in parallel in the AZ direction.

  The UT array 100 having the above configuration will be described in detail with reference to FIG. FIG. 3 is a partially broken perspective view schematically showing the configuration of the UT array 100. As shown in FIG. 3, the UT array 100 includes a lower electrode 52 of an inorganic transducer, an inorganic piezoelectric thin film 53, an upper electrode 54 of an inorganic transducer, a first acoustic matching layer on a backing material 51 made of rubber or the like. 55, the second acoustic matching layer 56 and the acoustic lens 57 are laminated in this order, and further, the ferromagnetic thin film 58, the near-infrared reflective film 59, and the protective film 60 are laminated on the acoustic lens 57 in this order. Have

  The lower electrode 52, the inorganic piezoelectric thin film 53, and the upper electrode 54 of the inorganic transducer are divided into a plurality of rows aligned in the AZ direction by dicing in which a plurality of grooves each extending in the EL direction are formed at a predetermined pitch in the AZ direction. Yes. Each of these grooves is filled with an insulating material 61. In this way, the laminated body of the lower electrode 52, the inorganic piezoelectric thin film 53, and the upper electrode 54 divided so as to extend in a line shape in the EL direction between the two insulating materials 61 becomes one inorganic transducer, and these are AZ. A plurality of the transducer arrays are arranged in the direction to constitute an inorganic transducer array.

  As the inorganic piezoelectric thin film 53, for example, a thin film made of a lead zirconate titanate (Pb (Zr, Ti) O3) material such as PZT (registered trademark) can be suitably used. In the inorganic transducer array, the resonance frequency is determined by the thickness and width of the inorganic piezoelectric thin film 53. In this embodiment, the inorganic transducer array is designed to resonate at a relatively high frequency of about 7 to 15 MHz, and the thickness of the inorganic piezoelectric thin film 53 is about 50 to 200 μm. The element pitch of the inorganic transducer is generally about 200 to 500 μm. However, if the width of the element is too wide, the electromechanical conversion coefficient of the inorganic piezoelectric material becomes low. It is desirable to perform dicing and divide within one element. In that case, one width of the plurality of piezoelectric lines in one element is about 50 to 200 μm. Further, the lower electrode 52 and the upper electrode 54 sandwiching the inorganic piezoelectric thin film 53 from above and below are composed of a thin film of platinum, iridium or the like formed by sputtering or the like, for example.

  In each of the inorganic transducers, when the inorganic piezoelectric thin film 53 receives an acoustic wave generated by the subject, the inorganic piezoelectric thin film 53 vibrates to generate a voltage, and this voltage is received via the electrodes 52 and 54. Is output as In the present embodiment, the lower electrode 52 is a signal electrode, and the lower electrode 52 is connected to the amplifier circuit of the receiving circuit 21 shown in FIG.

  The first acoustic matching layer 55 of the transducer is prepared by dispersing fine powder of metal or metal oxide in an organic material such as resin having acoustic impedance suitable for acoustic design, and preparing this between the inorganic piezoelectric material and the resin. It is configured by thinly molding the product. The second acoustic matching layer 56 is formed by thinly molding an organic material such as a resin having an acoustic impedance suitable for acoustic design.

  An acoustic lens 57 is provided on the second acoustic matching layer 56. As a material of the acoustic lens 57, it is desirable to use, for example, epoxy resin or silicon rubber that is closer to the acoustic impedance of the human body than the second acoustic matching layer 56. In FIG. 3, the acoustic lens 57 has a flat plate shape, but a lens having a known shape such as a plano-convex shape or a plano-concave shape can be used.

  Various known materials can be applied as the adhesive used when the layers of the UT array 100 are laminated. In particular, an epoxy resin is preferable because it is excellent in sound permeability and bonding strength and is inexpensive in terms of cost.

  As a material of the ferromagnetic thin film 58 laminated on the acoustic lens 57, any of a ferromagnetic metal, a ferromagnetic alloy or a ferromagnetic sintered body, and a ferromagnetic oxide can be used. As the ferromagnetic metal, Fe, Ni, Co, Gd or the like can be used, and as long as it is a ferromagnetic alloy, an alloy or sintered body such as permalloy, supermalloy, permendur, sendust, SmCo, NdFeB, or the like can be used. Various ferrite materials can be used as long as they are ferromagnetic oxides. By using such a material, the ferromagnetic thin film 58 can absorb the magnetic lines of force in the electromagnetic waves, and therefore can prevent the electromagnetic waves, particularly the magnetic lines of force, from entering the probe 11.

  As the near-infrared reflective film 59 laminated on the ferromagnetic thin film 58, a metal material having a relatively high light reflectance in the infrared region can be used. Specifically, a metal material such as Al, Au, Ag, or Rh that has a relatively high conductivity and reflects near infrared rays having a wavelength of about 700 nm to 1000 nm at about 80% or more can be used. Further, by using such a metal material, radio waves of electromagnetic waves can be reflected by free electrons. In particular, high frequency electromagnetic waves can be effectively reflected. The near-infrared reflective film 59 is not only a 1D probe using an inorganic piezoelectric material, but also a 2D probe using an inorganic piezoelectric material, a 1D or 2D probe using an organic piezoelectric material, or an inorganic piezoelectric material and an organic piezoelectric material. Can be used for any ultrasonic probe using an acoustic lens such as a MUT.

  Here, in many living tissues, the light absorption characteristics change according to the wavelength of light. For example, the molecular absorption coefficient at a wavelength of 750 nm of oxygenated hemoglobin (hemoglobin combined with oxygen: oxy-Hb) contained in a large amount in human arteries is higher than the molecular absorption coefficient at a wavelength of 800 nm. On the other hand, the molecular absorption coefficient at a wavelength of 750 nm of deoxygenated hemoglobin (hemoglobin deoxy-Hb not bound to oxygen) contained in a large amount in veins is lower than the molecular absorption coefficient at a wavelength of 800 nm. Utilizing this property, for example, by examining whether the photoacoustic signal obtained at a wavelength of 748 to 770 nm is relatively large or small with respect to the photoacoustic signal obtained at a wavelength of 793 to 802 nm, the light from the artery The acoustic signal and the photoacoustic signal from the vein can be discriminated. For this reason, in the present embodiment, laser light having a wavelength in the near infrared region is used.

  For the protective film 60 laminated on the near-infrared reflective film 59, a material having an antioxidant function such as an organic film such as parylene and various oxide thin films can be used. By using such a material, it is possible to prevent the ferromagnetic thin film 58 and the near-infrared reflective film 59 from being oxidized and prevent heat from being easily transmitted to the probe 11.

  The total thickness of the ferromagnetic thin film 58, the near-infrared reflective film 59, and the protective film 60 is preferably 3 μm or less so that the sound transmittance is about 90% or more in an ultrasonic wave of about 5 MHz from the viewpoint of sound transmittance. . In particular, 1 μm or less at which the sound transmittance is about 95% or more is more preferable.

  Hereinafter, an embodiment in which an inorganic transducer array is formed on a rubber backing material will be described with reference to FIG.

  DC sputtering is performed so that each thickness of Au, Pt / Ti = 300/150/30 nm in this order is Ti, Pt, and Au on both surfaces of the lead zirconate titanate piezoelectric body polished to a thickness of 130 μm. Thus, the lower electrode 52 and the upper electrode 54 were formed. The lead zirconate titanate piezoelectric element formed in this manner was bonded to the rubber backing material 51 with a thermosetting epoxy resin so as to sandwich an FPC (flexible printed circuit board).

  Next, dicing is performed using a dicer so that the portion between the two dicing grooves extends in the EL direction as one line having a width of 250 μm with respect to the lead zirconate titanate piezoelectric element bonded on the backing material 51. Went.

Next, the insulating material 61 was formed by filling a dicing groove by pouring a thermosetting epoxy resin. At the same time, the first acoustic matching layer 55 is manufactured by polishing a metal oxide fine particle dispersed resin whose acoustic impedance is adjusted to about 9 Mrayl (however, rayl = N · s / m ³ ) to a thickness of about 80 μm. Then, this was bonded on the lead zirconate titanate piezoelectric element with a thermosetting epoxy resin. Further, an organic piezoelectric sheet having a thickness of 80 μm for forming the second acoustic matching layer 56 was formed. An epoxy resin having an acoustic impedance of 3.0 Mrayl (however, rayl = N · s / m ³ ) was used for this organic piezoelectric sheet. The second acoustic matching layer 56 was bonded onto the first acoustic matching layer 55 with a thermosetting epoxy resin.

Next, an acoustic lens 57 made of silicone rubber was prepared, and magnetite (Fe ₂ O ₃ ), which is a type of ferrite that is a ferromagnetic material, was formed on the surface thereof to a thickness of 500 nm using RF sputtering. Furthermore, Au was formed into a film with a thickness of 100 nm by DC sputtering. Further thereon, a parylene thin film was formed to a thickness of 100 nm by vapor deposition. The total thickness of the magnetite, Au and parylene thin films was 700 nm.

  Then, the acoustic lens 57 was bonded on the second acoustic matching layer 56. This adhesion was performed by applying a thermosetting epoxy resin to the surface of the second acoustic matching layer 56 and thermocompression bonding.

  The UT array 100 formed as described above was connected to an FPC (flexible printed circuit board) constituting the receiving circuit 21 of FIG. A probe connecting portion 117 shown in FIG. 2 is connected to the FPC, and the probe 11 is completed by connecting the cable 120 to the FPC via the connector 119.

  Using this probe 11, a living body was irradiated with pulsed laser light having a wavelength of 800 nm, and a photoacoustic signal was received. Signals in a relatively high frequency range from 7 MHz to 15 MHz were strongly observed with an inorganic transducer array designed with a center frequency of 10 MHz.

  In photoacoustic imaging, a large voltage of several kV is required for laser oscillation, and a high level of electromagnetic noise is generated. However, no electromagnetic noise was detected in a signal received by this probe. This is considered to be an effect of the ferromagnetic thin film 58 and the near-infrared reflective film 59 provided on the probe surface. In addition, this probe received a signal with higher brightness than normal photoacoustic imaging. This is considered to be because the near-infrared laser beam reflected from the living body is reflected by the probe surface and efficiently returned to the living body by the near-infrared reflecting film 59 provided on the probe surface. Further, it is considered that the protective film 60 prevents a decrease in reflectance of near infrared laser light due to oxidation of the ferromagnetic thin film 58 and the near infrared reflection film 59.

  In the above description, a so-called linear electronic scanning type probe has been exemplified. However, as a probe for a photoacoustic apparatus of the present invention, a radial electronic scanning type or one transducer is mechanically rotated, rocked, or slid. A mechanical scan scanning type ultrasonic probe may be used. Furthermore, the probe for a photoacoustic apparatus according to the present invention can be applied to an in-vivo probe inserted into a forceps channel of an electronic endoscope or a photoacoustic apparatus integrated with an electronic endoscope.

  As the laser light source constituting the pulse laser unit, in addition to the solid-state laser used in the above embodiment, an AlGaAs semiconductor laser having an oscillation wavelength of up to about 800 nm, an InGaAs semiconductor laser having an oscillation wavelength of up to about 900 nm, etc. Applicable. Further, a combination of an optical amplification type laser light source that uses a semiconductor laser as a seed light source and an optical wavelength conversion element, more specifically, a semiconductor laser that emits laser light having a wavelength of about 1560 nm, and the laser light is amplified. A fiber amplifier composed of a polarization-preserving Er (erbium) -doped optical fiber and an SHG (second harmonic generation) element that converts the laser light amplified there into a second harmonic having a wavelength of about 780 nm, etc. Is also applicable.

  In addition, the photoacoustic apparatus and method of the present invention are not limited to the above embodiment, and various modifications and changes made from the configuration of the above embodiment are also included in the scope of the present invention.

  For example, the photoacoustic apparatus of the above-described embodiment is configured to be able to acquire and display an ultrasonic image by reflected ultrasonic waves, but the photoacoustic apparatus of the present invention does not have such a function. It may be configured as.

  The present invention can also be applied to a photoacoustic apparatus that performs a deconvolution process. FIG. 4 is a block diagram showing a part of the photoacoustic apparatus configured to perform the deconvolution processing. 4 is inserted, for example, between the image reconstruction unit 25 and the detection / logarithmic conversion unit 26 shown in FIG. 1, and is connected to the optical differential waveform deconvolution unit 40 and its subsequent stage. And a correction unit 46. The optical differential waveform deconvolution unit 40 includes Fourier transform units 41 and 42, an inverse filter operation unit 43, a filter application unit 44, and a Fourier inverse transform unit 45.

  The optical differential waveform deconvolution unit 40 deconstructs an optical pulse differential waveform obtained by differentiating the time waveform of the light intensity of the pulsed laser light irradiated to the subject from the data indicating the photoacoustic image output from the image reconstruction unit 25. Volute. By this deconvolution, photoacoustic image data showing an absorption distribution is obtained.

  Hereinafter, this deconvolution will be described in detail. The Fourier transform unit (first Fourier transform unit) 41 of the optical differential waveform deconvolution unit 40 transforms the reconstructed photoacoustic image data from a signal in the time domain to a signal in the frequency domain by discrete Fourier transform. . The Fourier transform unit (second Fourier transform unit) 42 converts a signal obtained by sampling the optical pulse differential waveform at a predetermined sampling rate from a time domain signal to a frequency domain signal by discrete Fourier transform. For example, FFT can be used as the Fourier transform algorithm.

  In the present embodiment, it is assumed that the sampling rate of the acoustic wave detection signal in the AD converter 22 is equal to the sampling rate of the optical pulse differential waveform. For example, the acoustic wave detection signal is sampled in synchronization with a sampling clock of Fs = 40 MHz, and the optical differential pulse is also sampled at a sampling rate of Fs_h = 40 MHz. The Fourier transform unit 41 performs Fourier transform on the photoacoustic image data output from the image reconstruction unit 25 obtained as a result of sampling at 40 MHz by, for example, 1024 points of Fourier transform. In addition, the Fourier transform unit 42 performs Fourier transform on the optical pulse differential waveform sampled at 40 MHz by 1024 points of Fourier transform.

The inverse filter calculation unit 43 obtains the inverse of the Fourier-transformed optical pulse differential waveform as an inverse filter. For example, the inverse filter calculation unit 43 obtains conj (fft_h) / abs (fft_h) ² as an inverse filter, where fft_h is a signal obtained by Fourier transforming the optical pulse differential waveform h. The filter application unit 44 applies the inverse filter obtained by the inverse filter calculation unit 43 to the photoacoustic image data Fourier-transformed by the Fourier transform unit 41. For example, the filter application unit 44 multiplies the Fourier coefficient of the photoacoustic image data by the Fourier coefficient of the inverse filter for each element. By applying the inverse filter, the optical pulse differential waveform is deconvolved in the frequency domain signal. The Fourier inverse transform unit 45 transforms the photoacoustic image data to which the inverse filter is applied from a frequency domain signal to a time domain signal by Fourier inverse transform. An absorption distribution signal in the time domain is obtained by inverse Fourier transform.

  By performing the processing described above, the optical differential term can be removed from the acoustic wave detection signal in which the optical differential term is convoluted, and the absorption distribution can be obtained from the acoustic wave detection signal. When such an absorption distribution is imaged, a photoacoustic image showing the absorption distribution image is obtained.

  The correction unit 46 corrects the data obtained by deconvoluting the optical pulse differential waveform, and removes the influence of the reception angle dependent characteristics of the ultrasonic transducer in the probe 11 from the data obtained by deconvoluting the optical pulse differential waveform. . Further, the correction unit 46 removes the influence of the incident light distribution of the light on the subject from the data obtained by deconvolution of the optical pulse differential waveform in addition to or instead of the reception angle dependent characteristics. Note that a photoacoustic image may be generated without performing such correction.

DESCRIPTION OF SYMBOLS 10 Photoacoustic imaging apparatus 11 Probe 12 Ultrasonic unit 13 Laser light source unit 14 Image display part 21 Reception circuit 22 AD conversion part 23 Reception memory 24 Data separation part 25 Image reconstruction part 26 Detection and logarithmic conversion part 27 Image construction part 30 Transmission control circuit 31 Control unit 32 Q switch pulse laser 33 Flash lamp 41, 42 Fourier transform unit 43 Inverse filter operation unit 44 Filter application unit 45 Fourier inverse transform unit 51 Backing material 52 Lower electrode of inorganic transducer 53 Inorganic piezoelectric thin film 54 Upper electrode of inorganic transducer 55 First acoustic matching layer 56 Second acoustic matching layer 57 Acoustic lens 58 Ferromagnetic thin film 59 Near-infrared reflective film 60 Protective film 100 UT array 170 Pulse laser unit

Claims (8)

In a probe for a photoacoustic apparatus for detecting an acoustic wave emitted from a subject irradiated with light,
An acoustic lens,
A ferromagnetic thin film provided on the surface of the acoustic lens;
A metal material thin film that reflects electromagnetic waves provided on the ferromagnetic thin film;
A probe for a photoacoustic apparatus, comprising: a protective film made of an antioxidant material provided on the metal material thin film.   2. The probe for a photoacoustic apparatus according to claim 1, wherein a total thickness of the ferromagnetic thin film, the metal material thin film, and the protective film is 3 [mu] m or less.   2. The probe for a photoacoustic apparatus according to claim 1, wherein a total thickness of the ferromagnetic thin film, the metal material thin film, and the protective film is 1 [mu] m or less.   The probe for a photoacoustic apparatus according to any one of claims 1 to 3, wherein the ferromagnetic thin film is made of any one of a ferromagnetic metal, a ferromagnetic alloy, and a ferromagnetic oxide.   5. The probe for a photoacoustic apparatus according to claim 1, wherein the metal material thin film is made of a metal material that reflects approximately 80% or more of near infrared light having a wavelength of approximately 700 nm to 1000 nm.   The probe for a photoacoustic apparatus according to any one of claims 1 to 5, wherein the protective film is made of an organic film or an oxide thin film.   A photoacoustic apparatus comprising the probe for a photoacoustic apparatus according to claim 1. In the photoacoustic apparatus, the acoustic wave detection signal is obtained by the photoacoustic apparatus probe according to any one of claims 1 to 6,
An acoustic wave in a predetermined first frequency region is detected by the transducer to obtain an acoustic wave detection signal,
An acoustic wave detection signal acquiring method, wherein an acoustic wave detection signal is acquired by detecting an acoustic wave in a second frequency region including a region on a lower frequency side than the first frequency region by the transducer.

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