JP5469113B2 - Probe unit for photoacoustic analysis and photoacoustic analyzer - Google Patents

Description

  The present invention relates to a photoacoustic analysis probe unit and a photoacoustic analyzer used for examination and diagnosis of a subject using a photoacoustic analysis method.

  Conventionally, as a method for acquiring a tomographic image inside a subject, an ultrasonic image is generated by detecting ultrasonic waves reflected in the subject by irradiating the subject with ultrasonic waves. Ultrasonic imaging for obtaining a morphological tomographic image is known. On the other hand, in the examination of a subject, development of an apparatus that displays not only a morphological tomographic image but also a functional tomographic image has been advanced in recent years. One of such devices is a device using a photoacoustic analysis method. In this photoacoustic analysis method, light having a predetermined wavelength (for example, visible light, near-infrared light, or mid-infrared light) is irradiated to a subject as measurement light, and a specific substance in the subject is irradiated with the measurement light. A photoacoustic wave, which is an elastic wave generated as a result of absorbing energy, is detected, and the concentration of the specific substance is quantitatively measured. The specific substance in the subject is, for example, glucose or hemoglobin contained in blood. A technique for detecting a photoacoustic wave and generating a photoacoustic image based on the detection signal is called photoacoustic imaging (PAI) or photoacoustic tomography.

  Conventionally, there are the following problems in photoacoustic imaging using the photoacoustic effect as described above. The intensity of the measurement light is significantly attenuated by absorption and scattering in the process of propagating through the subject. In addition, the intensity of the photoacoustic wave generated in the subject based on the measurement light is also attenuated by absorption and scattering in the process of propagating in the subject. Therefore, in photoacoustic imaging, it is difficult to obtain information on the deep part of the subject. In order to solve this problem, for example, it is conceivable to increase the generated photoacoustic wave by increasing the amount of measurement light energy in the subject.

  However, when the subject is a living body, the maximum permissible exposure (MPE) per unit area that can be irradiated to the living body is determined in order not to damage the living tissue by the energy of the measurement light. ing. Therefore, even if the amount of light is increased, MPE becomes the upper limit.

  Therefore, as a method for suppressing the amount of light below MPE and detecting a photoacoustic wave having a high S / N, for example, as shown in Patent Document 1, measurement is performed using a bundle fiber including a plurality of optical fibers. A method of irradiating measurement light so that the light intensity distribution is uniform can be mentioned. For example, as shown in Patent Document 1, when a probe unit in which an optical system using a bundle fiber and an ultrasonic detection probe are combined together is used, the cord portion of the probe unit is flexible. Therefore, there is an advantage that the handling performance of the user is improved.

JP 2010-12295 A

  However, when the probe unit as described above is used, the handling performance is improved, but there is a problem that the risk due to the measurement light increases. In photoacoustic imaging, a laser beam is generally used in order to obtain measurement light with sufficient intensity. Therefore, the improvement in the handling performance of the probe unit leads to an increase in the chance of entering a dangerous state in which, for example, laser light enters the human eye. Such a problem can occur not only in photoacoustic imaging but also in examination and diagnosis of a subject using a photoacoustic analysis method.

  The present invention has been made in view of the above problems, and in photoacoustic analysis using a probe unit, it is possible to reduce the risk due to laser light as measurement light and further improve safety. An object of the present invention is to provide a photoacoustic analysis probe unit and a photoacoustic analysis apparatus.

In order to solve the above problems, a probe unit for photoacoustic analysis according to the present invention is:
Used for photoacoustic analysis that irradiates a subject with laser light as measurement light, detects a photoacoustic wave generated in the subject, converts the photoacoustic wave into an electrical signal, and performs analysis based on the electrical signal Probe unit
A light irradiation unit for irradiating a laser beam;
An electroacoustic transducer that converts photoacoustic waves into electrical signals;
A container having a bottom made of an acoustically permeable membrane, and an acoustic matching unit having an acoustic matching liquid contained in the container;
The acoustic transmission membrane and the acoustic matching liquid have an acoustic impedance that matches the acoustic impedance of the subject and the acoustic impedance of the electroacoustic transducer,
The electroacoustic transducer is disposed so that the acoustic detection surface of the electroacoustic transducer is in contact with the acoustic matching liquid,
The light irradiation part is arranged so that the laser light is incident on the back surface of the sound transmission film through the acoustic matching liquid at a predetermined angle,
When the predetermined angle is such that the back surface is in contact with air, the laser light satisfies the total reflection condition on the back surface, and when the back surface is in contact with the subject, the laser light is totally reflected on the back surface. The angle is such that the reflection condition is not satisfied.

  In the present specification, the “back surface of the sound transmission film” means the surface of the sound transmission film on the side in contact with the subject.

  In the probe unit according to the present invention, the predetermined angle is determined when the back surface is in contact with the subject, and the laser light is transmitted through the back surface when the laser light deviates from the total reflection condition on the back surface. It is preferable that the angle is such that the transmittance is 90% or more.

  In the probe unit according to the present invention, the refractive index of the sound transmission film and the acoustic matching liquid is preferably 1.3 to 1.4, and the predetermined angle is preferably 42 to 85 °.

  And in the probe unit which concerns on this invention, it is preferable that a container has a light absorption member in the inner wall of a side wall part.

  Furthermore, a photoacoustic analyzer according to the present invention is characterized by including the probe unit described above.

  The probe unit for photoacoustic analysis and the photoacoustic analysis apparatus according to the present invention include, in particular, a container having a bottom made of an acoustic transmission film, and an acoustic matching unit having an acoustic matching liquid contained in the container. The permeable membrane and the acoustic matching liquid have an acoustic impedance that matches the acoustic impedance of the subject and the acoustic impedance of the electroacoustic transducer, and the electroacoustic transducer is acoustically matched to the acoustic detection surface of the electroacoustic transducer. It is arranged so as to contact the liquid, and the light irradiation unit is arranged so that the laser beam is incident at a predetermined angle with respect to the back surface of the acoustic transmission film through the acoustic matching liquid. When the predetermined angle is such that the back surface is in contact with air, the laser light satisfies the total reflection condition on the back surface, and when the back surface is in contact with the subject, the laser light is It is characterized in that the angle does not satisfy the total reflection condition at the surface. Therefore, it is possible to prevent laser light from being accidentally emitted into the air when the probe unit is operated in the air. As a result, in the photoacoustic analysis using the probe unit, it is possible to reduce the risk due to the laser light as the measurement light and further improve the safety.

It is a general | schematic cutting part end view which shows one Embodiment of the probe unit of this invention. It is a general | schematic cutting part end view which shows one Embodiment of the probe unit of this invention. It is the schematic which shows the structure of one Embodiment of the photoacoustic analyzer of this invention. It is a block diagram which shows the structure of the image generation part in FIG.

  Hereinafter, although an embodiment of the present invention is described using a drawing, the present invention is not limited to this. In addition, for easy visual recognition, the scale of each component in the drawings is appropriately changed from the actual one.

  First, the photoacoustic analysis probe unit of the present invention will be described. 1A and 1B are schematic cut end face views showing the configuration of the probe unit 70 of the present embodiment. FIG. 1A shows a state before the probe unit 70 is brought into contact with the subject 7, and FIG. 1B shows a state when the probe unit 70 is brought into contact with the subject 7. FIG. 2 is a schematic diagram illustrating a configuration of a photoacoustic imaging apparatus which is the photoacoustic analysis apparatus of the present embodiment.

  As shown in FIG. 1A, the probe unit 70 includes a light irradiation unit 15 that irradiates the laser light L guided from the light source unit 11, an electroacoustic conversion unit 3 that converts a photoacoustic wave into an electrical signal, A support member 32 that supports the electroacoustic transducer 3, a container 80 whose side wall is composed of a light absorbing member 81 and whose bottom is composed of an acoustic transmission film 82, and an acoustic matching liquid 83 accommodated in the container 80. An acoustic matching unit 8 and a cover 84 that is a handle portion of the probe unit 70 are provided. The acoustic transmission film 82 and the acoustic matching liquid 83 have an acoustic impedance that matches the acoustic impedance of the subject 7 and the acoustic impedance of the electroacoustic transducer 3. The electroacoustic transducer 3 is arranged so that the acoustic detection surface 3 s of the electroacoustic transducer 3 is in contact with the acoustic matching liquid 83. The light irradiation unit 15 is arranged so that the laser light L enters the back surface 82 s of the acoustic transmission film 82 through the acoustic matching liquid 83 at a predetermined angle. In the present invention, the predetermined angle means that when the back surface 82s is in contact with air, the laser light L satisfies the total reflection condition on the back surface 82s (FIG. 1A), and the back surface 82s is in contact with the subject 7. In this case, the angle means that the laser beam L does not satisfy the total reflection condition on the back surface 82s. The condition that the total reflection condition is not satisfied means that when the back surface 82s is in contact with the subject 7, the laser light L is transmitted through the back surface 82s when the laser light L deviates from the total reflection condition on the back surface 82s. The state that can be done. At this time, the transmittance of the laser light L is preferably 50% or more, more preferably 70% or more, and particularly preferably 90% or more.

  On the other hand, the photoacoustic analyzer provided with the probe unit 70 of the present invention is, for example, the photoacoustic imaging apparatus 10 capable of generating a photoacoustic image. Specifically, as shown in FIG. 2, the photoacoustic imaging apparatus 10 of the present embodiment generates a laser beam L including a specific wavelength component and irradiates the subject 7 with the laser beam L, An image generation unit 2 that generates photoacoustic image data of an arbitrary cross section by detecting a photoacoustic wave U generated in the subject 7 by irradiating the subject 7 with the laser light L, an acoustic signal, and an electrical signal The electroacoustic conversion unit 3 that performs the conversion, the display unit 6 that displays the photoacoustic image data, the operation unit 5 for the operator to input patient information and imaging conditions of the apparatus, and these units are integrated. And a system control unit 4 for controlling the system.

  The optical transmission unit 1 includes, for example, a light source unit 11 including a plurality of light sources that output laser beams L having different wavelengths, an optical combining unit 12 that combines the laser beams L having a plurality of wavelengths on the same optical axis, and the laser. A multi-channel waveguide unit 14 that guides the light L to the body surface of the subject 7, an optical scanning unit 13 that performs scanning by switching channels used in the waveguide unit 14, and a laser supplied by the waveguide unit 14 And a light irradiator 15 that emits light L toward the subject 7.

The light source unit 11 includes, for example, one or more light sources that generate light having a predetermined wavelength. As the light source, a light emitting element such as a semiconductor laser (LD), a solid-state laser, or a gas laser that generates a specific wavelength component or monochromatic light including the component can be used. The light source unit 11 preferably outputs pulsed light having a pulse width of 1 to 100 nsec as laser light. The wavelength of the laser light is appropriately determined according to the light absorption characteristics of the substance in the subject to be measured. Although hemoglobin in a living body has different optical absorption characteristics depending on its state (oxygenated hemoglobin, reduced hemoglobin, methemoglobin, carbon dioxide hemoglobin, etc.), it generally absorbs light of 600 nm to 1000 nm. Therefore, for example, when the measurement target is hemoglobin in a living body (that is, when a blood vessel is imaged), it is generally preferable to set the thickness to about 600 to 1000 nm. Furthermore, from the viewpoint of reaching the deep part of the subject 7, the wavelength of the laser light is preferably 700 to 1000 nm. The output of the laser beam is 10 μJ / cm ² to several tens of mJ / cm ² from the viewpoints of propagation loss of laser beam and photoacoustic wave, efficiency of photoacoustic conversion, detection sensitivity of the current detector, and the like. Is preferred. Further, the repetition of the pulsed light output is preferably 10 Hz or more from the viewpoint of the image construction speed. Further, the laser beam may be a pulse train in which a plurality of the above pulsed beams are arranged.

  More specifically, for example, when the hemoglobin concentration of the subject 7 is measured, an Nd: YAG laser (emission wavelength: about 1000 nm) which is a kind of solid-state laser, or a He—Ne gas laser (emission light) which is a kind of gas laser. A laser beam having a pulse width of about 10 nsec is formed using a wavelength of 633 nm. When a small light emitting element such as an LD is used, a material such as InGaAlP (emission wavelength: 550 to 650 nm), GaAlAs (emission wavelength: 650 to 900 nm), InGaAs or InGaAsP (emission wavelength: 900 to 2300 nm) is used. Can be used. Recently, a light-emitting element using InGaN that emits light with a wavelength of 550 nm or less is becoming available. Furthermore, an OPO (Optical Parametrical Oscillators) laser using a nonlinear optical crystal whose wavelength is variable can be used.

  The optical multiplexing unit 12 is for superimposing laser beams L having different wavelengths generated from the light source unit 11 on the same optical axis. Each laser beam is first converted into parallel rays by a collimating lens, and then the optical axis is adjusted by a right-angle prism or a dichroic prism. With such a configuration, a relatively small multiplexing optical system can be obtained, but a commercially available multiple wavelength multiplexer / demultiplexer developed for optical communication may be used. Further, when a light source such as an OPO laser whose wavelength can be continuously changed is used for the light source unit 11, the optical multiplexing unit 12 is not necessarily required.

  The waveguide unit 14 is for guiding the light output from the optical multiplexing unit 12 to the light irradiation unit 15. An optical fiber or a thin film optical waveguide is used for efficient light propagation. In the present embodiment, the waveguide section 14 is composed of a plurality of optical fibers. A predetermined optical fiber is selected from the plurality of optical fibers, and the subject 7 is irradiated with laser light by the selected optical fiber. Although not clearly shown in FIGS. 1A, 1B, and 2, they can be used together with an optical system such as an optical filter or a lens.

  The optical scanning unit 13 supplies light while sequentially selecting a plurality of optical fibers arranged in the waveguide unit 14. Thereby, the subject 7 is scanned with light.

  The light irradiator 15 particularly means the tip of the optical system. In this embodiment, the light irradiation unit 15 is a light guide connected to an optical fiber. A light guide plate or the like can be used as the light guide. When a plate-shaped light guide is used, it is easy to adjust the arrangement of the optical system that defines the incident angle θ of the laser light with respect to the back surface 82s of the sound transmission film 82. For example, the light irradiation unit 15 is arranged along the periphery of the electroacoustic conversion unit 3. The light irradiation unit 15 is arranged so that the laser light L passes through the sound transmission film 82 and enters the back surface 82s at the predetermined angle. In other words, the light irradiation unit 15 is arranged such that the incident angle θ of the laser light with respect to the back surface 82s of the sound transmission film 82 is an angle within a predetermined angle range. The predetermined angle range means that when the back surface 82s of the sound transmission film 82 is in contact with air, the laser light L satisfies the total reflection condition on the back surface 82s, and the back surface 82s is in contact with the subject 7. In this case, it means a set of angles (predetermined angles) at which the laser light L does not satisfy the total reflection condition on the back surface 82s. Although not shown in FIGS. 1A and 1B, strictly speaking, laser light is refracted when passing through the interface between the acoustic transmission film 82 and the acoustic matching liquid 83. Therefore, the arrangement of the light irradiation unit 15 is adjusted so that the incident angle of the laser light L to the back surface 82s becomes the predetermined angle.

  The electroacoustic conversion unit 3 is composed of a plurality of minute conversion elements arranged in a one-dimensional or two-dimensional manner, for example. The conversion element is, for example, a piezoelectric element made of a polymer film such as piezoelectric ceramics or polyvinylidene fluoride (PVDF). The electroacoustic conversion unit 3 receives a photoacoustic wave U generated in the subject 7 by the irradiation of the laser light L from the light irradiation unit 15. This conversion element has a function of converting the photoacoustic wave U into an electric signal at the time of reception. The electroacoustic conversion unit 3 is configured to be small and light, and is connected to a receiving unit 22 described later by a multi-channel cable. The electroacoustic conversion unit 3 is selected according to the diagnostic region from among sector scanning, linear scanning, convex scanning, and the like. The support member 32 is mounted with a cable, a drive circuit, and the like that connect the electroacoustic conversion unit 3 and the image generation unit 2 and the like.

  The acoustic matching unit 8 includes a container 80 and an acoustic matching liquid 83 accommodated in the container. In the present invention, the acoustic matching unit 8 performs an acoustic matching function for matching the acoustic impedance of the subject 7 and the acoustic impedance of the electroacoustic conversion unit 3. The acoustic matching function is a function for achieving acoustic matching between the subject 7 and the electroacoustic transducer 3. Thereby, a photoacoustic wave can be detected efficiently. In general, the acoustic impedance of the piezoelectric element material and the living body are greatly different. Therefore, when the piezoelectric element material and the living body are in direct contact with each other, reflection at the interface is increased and the photoacoustic wave U cannot be efficiently transmitted. For this reason, the photoacoustic wave U can be efficiently transmitted by arrange | positioning the acoustic matching liquid 83 comprised with the liquid substance which has an intermediate acoustic impedance between piezoelectric element material and a biological body.

  The container 80 holds the acoustic matching liquid 83. As a material of the container 80, for example, ABS resin can be used. In the present embodiment, the bottom of the container 80 is in direct contact with the subject 7. Accordingly, at least a portion of the container 80 that comes into contact with the subject 7 includes the acoustic transmission film 82 having a transmittance of the photoacoustic wave U of 70% or more so that the photoacoustic wave U can be efficiently transmitted. When the transmittance of the photoacoustic wave is less than 70%, the absolute amount of the photoacoustic wave U reaching the electroacoustic conversion unit 3 is excessively decreased, and it becomes difficult to obtain a photoacoustic wave U having sufficient intensity.

  The material of the sound transmission film 82 seems to have the predetermined angle from the relationship between the refractive index of air (n = 1) and the refractive index of the skin of the subject 7 (n = 1.3 to 1.4). Selected from materials having a high refractive index. Examples of the material of the sound transmission film 82 include PTFE (polytetrafluoroethylene) resin (n = 1.35), FEP (tetrafluoroethylene / hexafluoropropylene copolymer) resin (n = 1.34), and Polyethylene (n = 1.50) or the like can be used. Moreover, it is preferable that the container 80 is equipped with the light absorption member 81 on the inner wall of the side wall part. Most of the laser light L reflected by the back surface 82s of the sound transmission film 82 is repeatedly reflected a plurality of times and finally absorbed by the light absorbing member 81. This facilitates handling of the laser light L reflected by the back surface 82s of the sound transmission film 82. Examples of the material of the light absorbing member 81 include a carbon sheet.

  The acoustic matching liquid 83 is a part mainly responsible for the acoustic matching function of the acoustic matching unit 8. Examples of the material of the acoustic matching liquid 83 include various oils such as water (n = 1.33) and soybean oil (n = 1.48). The photoacoustic wave U generated in the subject 7 is detected by the electroacoustic conversion unit 3 through the acoustic matching liquid 83.

  The image generation unit 2 of the photoacoustic imaging device 10 selectively drives a plurality of conversion elements constituting the electroacoustic conversion unit 3 and gives a predetermined delay time to the electric signal from the electroacoustic conversion unit 3 to adjust the phase. A receiving unit 22 that generates a reception signal by performing addition, a scanning control unit 24 that controls the selection drive of the conversion element and the delay time of the receiving unit 22, and various processes on the reception signal obtained from the receiving unit 22 And a signal processing unit 25 for performing

  As illustrated in FIG. 3, the reception unit 22 includes an electronic switch 53, a preamplifier 55, a reception delay circuit 56, and an adder 57.

  When receiving the photoacoustic wave in the photoacoustic scanning, the electronic switch 53 selects a predetermined number of adjacent conversion elements 54. For example, when the electroacoustic conversion unit 3 is composed of 192 conversion elements CH1 to CH192 of the array type, such an array conversion element is converted into an area 0 (area of conversion elements from CH1 to CH64) by the electronic switch 53. ), Area 1 (region of the conversion element from CH65 to CH128) and area 2 (region of the conversion element from CH129 to CH192) are handled by being divided. When an array type conversion element composed of N conversion elements in this way is handled as a group (area) of n (n <N) adjacent transducers, and an imaging operation is performed for each area, It is not necessary to connect preamplifiers or A / D conversion boards to the conversion elements of all channels, the structure of the probe unit 70 can be simplified, and an increase in cost can be prevented. In addition, when a plurality of optical fibers are arranged so that each area can be individually irradiated with light, the light output per time does not need to be increased, so an expensive light source with a large output is used. There is also an advantage that it is not necessary. Each electric signal obtained by the conversion element 54 is supplied to the preamplifier 55.

  The preamplifier 55 amplifies a minute electric signal received by the conversion element 54 selected as described above, and ensures a sufficient S / N.

  The reception delay circuit 56 forms a converged reception beam by matching the phase of the photoacoustic wave U from a predetermined direction with the electrical signal of the photoacoustic wave U obtained from the conversion element 54 selected by the electronic switch 53. Give a delay time to do.

  The adder 57 adds together the electrical signals of a plurality of channels delayed by the reception delay circuit 56 to combine them into one reception signal. By this addition, phasing addition of acoustic signals from a predetermined depth is performed, and a reception convergence point is set.

  The scanning control unit 24 includes a beam focusing control circuit 67 and a conversion element selection control circuit 68. The conversion element selection control circuit 68 supplies position information of a predetermined number of conversion elements 54 at the time of reception selected by the electronic switch 53 to the electronic switch 53. On the other hand, the beam focusing control circuit 67 supplies delay time information for forming reception convergence points formed by a predetermined number of conversion elements 54 to the reception delay circuit 56.

  The signal processing unit 25 includes a filter 66, a signal processor 59, an A / D converter 60, and an image data memory 62. The electrical signal output from the adder 57 of the receiving unit 22 removes unnecessary noise in the filter 66 of the signal processing unit 25, and thereafter, the signal processor 59 performs logarithmic conversion of the amplitude of the received signal to make the weak signal relative. Stress. In general, the received signal from the subject 7 has an amplitude with a wide dynamic range of 80 dB or more, and a weak signal is emphasized in order to display it on a normal monitor having a dynamic range of about 23 dB. Amplitude compression is required. The filter 66 has a band pass characteristic, and has a mode for extracting a fundamental wave in a received signal and a mode for extracting a harmonic component. The signal processor 59 performs envelope detection on the logarithmically converted received signal. The A / D converter 60 A / D converts the output signal of the signal processor 59 to form photoacoustic image data for one line. The photoacoustic image data for one line is stored in the image data memory 62.

  The image data memory 62 is a storage circuit that sequentially stores the photoacoustic image data for one line generated as described above. The system control unit 4 reads out data for one line of a certain section stored in the image data memory 62 and necessary for generating a one-frame photoacoustic image. The system control unit 4 combines the data for one line while spatially interpolating to generate photoacoustic image data for one frame of the cross section. Then, the system control unit 4 stores the photoacoustic image data for one frame in the image data memory 62.

  The display unit 6 includes a display image memory 63, a photoacoustic image data converter 64, and a monitor 65. The display image memory 63 is a buffer memory that reads photoacoustic image data for one frame to be displayed on the monitor 65 from the image data memory 62 and temporarily stores it. The photoacoustic image data converter 64 performs D / A conversion and television format conversion on the photoacoustic image data for one frame stored in the display image memory 63, and the output is displayed on the monitor 65.

  The operation unit 5 includes a keyboard, a trackball, a mouse, and the like on the operation panel, and is used by an apparatus operator to input necessary information such as patient information, imaging conditions of the apparatus, and a display section.

  The system control unit 4 includes a CPU (not shown) and a storage circuit (not shown), and controls each unit such as the optical transmission unit 1, the image generation unit 2, and the display unit 6 and controls the entire system according to a command signal from the operation unit 5. Supervised. In particular, the input command signal of the operator sent via the operation unit 5 is stored in the internal CPU.

  Next, the operation of the present invention will be described.

  The photoacoustic analysis probe unit 70 and the photoacoustic imaging apparatus 10 according to the present invention are arranged such that the light irradiating portion passes through the acoustic matching liquid and the laser light is incident on the back surface of the acoustic transmission film at a predetermined angle. When the back surface 82s is in contact with air, the laser beam L satisfies the total reflection condition on the back surface 82s, and the back surface 82s is in contact with the subject 7. In this case, the laser beam has an angle that does not satisfy the total reflection condition on the back surface.

  The total reflection condition on the back surface 82 s of the laser light L incident on the back surface 82 s of the sound transmission film 82 differs depending on whether or not the back surface 82 s is in contact with the subject 7. This is because the refractive index of air (n = 1) and the refractive index of the skin of the subject 7 (n = 1.3 to 1.4) are different.

  For example, when the acoustic matching liquid 83 is water (n = 1.33), the acoustic transmission film 82 is FEP resin (n = 1.34), and the refractive index of the skin of the subject 7 is n = 1.37, the back surface When 82s is in contact with air, the total reflection critical angle is approximately 49 °. On the other hand the same conditions, the incident laser beam L from any angle for better refractive index of the skin of the subject is greater than the refractive index of the acoustically transparent film 82 in the case of back surface 82s is in contact with the object 7 Even in theory, total reflection does not occur. Therefore, in the case of the above conditions, the predetermined angle range that is a set of the predetermined angles is 49 ° or more. However, considering the incident efficiency of the laser beam L on the subject 7, the incident angle of the laser beam L is preferably set to 85 ° or less.

  And when actually arrange | positioning an optical system, the angle which the back surface 82s of the sound transmission film 82 and the optical axis of the light irradiation part 15 in the said back surface 82s comprise is a preferable said predetermined angle range 49-85, for example. Set to be included in °. Here, the optical axis of the light irradiation unit 15 on the back surface 82s means the optical axis of the light irradiation unit 15 in consideration of refraction at the interface between the acoustic transmission film 82 and the acoustic matching liquid 83.

  The laser light is incident on the optical fiber as the waveguide section 14 with a divergence angle, or the laser light propagates through a light guide or the like as the light irradiation section 15, whereby the laser light L is emitted from the light irradiation section 15. There may be a divergence angle when exiting. In such a case, the angle formed by the back surface 82s and the optical axis of the back surface 82s is preferably set in consideration of the divergence angle during emission. That is, for example, when the divergence angle at the time of emission can be regarded as about ± 5 °, the angle formed by the back surface 82s and the optical axis of the back surface 82s is set to be in the range of 54 to 80 °. It is preferable.

  Further, for example, when the acoustic matching liquid 83 is soybean oil (n = 1.48) and the acoustic transmission film 82 is polyethylene (n = 1.50), the total reflection critical angle is when the back surface 82s is in contact with air. It is approximately 42 °. On the other hand, when the back surface 82s is in contact with the subject 7 under the same conditions, the total reflection critical angle is approximately 66 °. That is, if the incident angle of the laser beam L is 65 ° or less, the laser beam L can enter the skin. Therefore, in the case of the above conditions, the predetermined angle range that is a set of the predetermined angles is 42 to 65 °.

  Also in this case, when the optical system is actually arranged, for example, the angle formed by the back surface 82s and the optical axis of the back surface 82s is included in the predetermined angle range of 42 to 65 °. Set to Similarly, for example, when the divergence angle at the time of emission can be regarded as about ± 5 °, the angle formed by the back surface 82s and the optical axis of the back surface 82s is set to be in the range of 47 to 60 °. It is preferred that

  As described above, according to the present invention, it is possible to prevent laser light from being accidentally emitted into the air when the probe unit is operated in the air. As a result, in the photoacoustic analysis using the probe unit, it is possible to reduce the risk due to the laser light as the measurement light and further improve the safety.

  The present invention is not limited to photoacoustic imaging but can be similarly applied to examination and diagnosis of a subject using a photoacoustic analysis method.

DESCRIPTION OF SYMBOLS 1 Light transmission part 2 Image generation part 3 Electroacoustic conversion part 3s Sound detection surface 4 System control part 5 Operation part 6 Display part 7 Subject 8 Acoustic matching part 10 Photoacoustic imaging device 11 Light source part 12 Optical multiplexing part 13 Optical scanning part DESCRIPTION OF SYMBOLS 14 Waveguide part 15 Light irradiation part 22 Reception part 24 Scan control part 25 Signal processing part 32 Electroacoustic conversion part support member 80 Container 81 Light absorption member 82 Acoustic transmission film 82s Acoustic transmission film back surface 83 Acoustic matching liquid 84 Cover L Laser beam U Photoacoustic wave θ Incident angle of laser beam to back surface of acoustic transmission film

Claims (5)

For photoacoustic analysis in which a subject is irradiated with laser light as measurement light, photoacoustic waves generated in the subject are detected, the photoacoustic waves are converted into electrical signals, and analysis is performed based on the electrical signals. In the probe unit used,
A light irradiation unit for irradiating the laser beam;
An electroacoustic transducer that converts the photoacoustic wave into an electrical signal;
A container having a bottom made of an acoustically permeable membrane, and an acoustic matching unit having an acoustic matching liquid contained in the container;
The acoustic permeable membrane and the acoustic matching liquid have an acoustic impedance that matches the acoustic impedance of the subject and the acoustic impedance of the electroacoustic transducer,
The electroacoustic transducer is arranged so that the acoustic detection surface of the electroacoustic transducer is in contact with the acoustic matching liquid,
The light irradiating part is arranged so that the laser light enters at a predetermined angle with respect to the back surface of the acoustic transmission film through the acoustic matching liquid,
When the back surface is in contact with air, the predetermined angle satisfies the total reflection condition on the back surface, and when the back surface is in contact with the subject, the laser light is A probe unit having an angle that does not satisfy the total reflection condition on the back surface.   When the predetermined angle is such that the back surface is in contact with the subject, the laser light has a transmittance of 90% or more when transmitted through the back surface because the laser light deviates from the total reflection condition on the back surface. The probe unit according to claim 1, wherein the probe unit has an angle such that   The probe unit according to claim 1 or 2, wherein a refractive index of the acoustic transmission film and the acoustic matching liquid is 1.3 to 1.4, and the predetermined angle is 42 to 85 °.   The probe unit according to claim 1, wherein the container has a light absorbing member on an inner wall of the side wall portion.   A photoacoustic analyzer comprising the probe unit according to claim 1.

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