JP2016064312A - Acoustic wave detection probe and photoacoustic measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain photoacoustic measurement where high-energy light is transmitted and it is possible to eliminate deviations in the energy levels of light that passes through a plurality of optical fibers.SOLUTION: A photoacoustic wave detection probe 11 comprises: a light-guide part 44 which guides measurement light L so as to irradiate an object M to be examined with measurement light L; and an acoustic wave oscillator 20 which detects a photoacoustic wave U generated within the object M as a result of irradiation with the measurement light L. The light-guide part 44 includes: a homogenizer 40 which generates a flat-top energy profile for the measurement light incident from an upstream side of an optical system; a condensing member 41 which condenses measurement light L that has passed through the homogenizer 40; and a bundle fiber 42 which encompasses a plurality of optical fibers 42a and is positioned in such a manner that the measurement light L having passed through the condensing member 41 is incident from an incident edge E1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a probe and a photoacoustic measurement apparatus that detect an acoustic wave against a measurement target.

  In photoacoustic spectroscopy, a subject is irradiated with pulsed light having a predetermined wavelength (for example, a wavelength band of visible light, near-infrared light, or mid-infrared light), and a specific substance in the subject is irradiated with the pulsed 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 (for example, Patent Document 1). The specific substance in the subject is, for example, glucose or hemoglobin contained in blood. Such 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 (PAT).

  Conventionally, in the measurement (photoacoustic measurement) using the photoacoustic spectroscopy as described above, there are the following problems. The intensity of light applied to the subject is significantly attenuated by absorption and scattering in the process of propagating through the subject. Further, the intensity of the photoacoustic wave generated in the subject based on the irradiated light is also attenuated by absorption and scattering in the process of propagating in the subject. Therefore, in photoacoustic measurement, 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 energy of light irradiated into the subject using high-energy light.

  However, when light of high energy (1 mJ or more) required in photoacoustic measurement is guided by an optical fiber, there is a high possibility that the end face of the optical fiber will be broken, and there is a problem of durability of the optical fiber. Can occur. Normally, when light is incident on the optical fiber, the end face of the optical fiber is disposed at a position near the focal point of the condenser lens so that the beam diameter of the light is within the core diameter of the optical fiber. However, when the light is condensed by the condensing lens, the light is too narrowed and the energy is locally concentrated, and damage to the end face of the optical fiber proceeds from the portion where the energy is concentrated.

  On the other hand, in Patent Document 2, for example, a bundle fiber (fused bundle fiber) in which an incident end portion is fusion-processed is used to efficiently reduce the energy of light incident per unit area. Implementing transmission is disclosed.

JP 2010-12295 A JP 2004-193267 A

  However, even if the method of Patent Document 2 is applied to photoacoustic measurement, there is a problem that the uniformity of the energy profile of the light emitted from the fused bundle fiber cannot be ensured. This is because the method of Patent Document 2 does not ensure the uniformity of the energy profile when light enters the fused bundle fiber. In paragraph 0017 of Patent Document 2, there is a description that light is irradiated with a spot having a diameter substantially the same as the diameter of the fused bundle fiber. In Patent Document 2, light is applied to the incident end of the fused bundle fiber. Is simply condensed with a lens. In this case, it is considered that the energy profile when light enters the fused bundle fiber has a Gaussian distribution, similar to the energy profile of normal light. Then, it is estimated that there is a bias in the amount of energy of light traveling through each optical fiber in the bundle fiber.

  In Patent Document 2, it is only necessary to be able to transmit light, so it is not necessary to ensure the uniformity of the energy profile of the emitted light. However, in photoacoustic measurement, high energy is used from the viewpoint of reconstructing a high-quality photoacoustic signal. In addition to the transmission of light, the uniformity of the energy profile of the light actually irradiated on the subject is also required. For that purpose, it is important to eliminate the bias of the amount of energy of light traveling through each of the optical fibers in the bundle fiber.

  The present invention has been made in response to the above-described demand, and enables transmission of high-energy light in photoacoustic measurement and elimination of a bias in the amount of light energy traveling through each of a plurality of optical fibers. An object of the present invention is to provide an acoustic wave detection probe and a photoacoustic measurement apparatus.

In order to solve the above-described problem, an acoustic wave detection probe according to the present invention includes:
Acoustic wave detection comprising a light guide that guides measurement light so that the measurement light is emitted toward the subject, and an acoustic wave transducer that detects photoacoustic waves generated in the subject by irradiation of the measurement light In the probe for
The light guide is
A homogenizer that flattenes the energy profile of the measurement light incident on the light guide;
A condensing member that condenses the measurement light transmitted through the homogenizer;
A bundle fiber including a plurality of optical fibers, the bundle fiber including a bundle fiber disposed so that the measurement light transmitted through the light collecting member is incident from an incident end of the bundle fiber. .

  In other words, in the present invention, the energy profile is flattened once by passing the measurement light through the homogenizer, and the beam diameter when entering the bundle fiber is controlled by the condensing member.

  In the probe according to the present invention, it is preferable that the homogenizer further diffuses the measurement light. In this case, the condensing member condenses the measurement light so that the minimum beam diameter D of the measurement light defined by the following formula 1 satisfies the following formula 2 in relation to the bundle fiber diameter d. The bundle fiber is preferably arranged so that the measurement light is incident in a state where the beam diameter of the measurement light is 0.8 d or more and 1.2 d or less.

  In this specification, f represents the focal length of the light collecting member, φ represents the divergence angle of the measurement light when entering the homogenizer, and θ represents the diffusion angle of the homogenizer. The “diameter of the bundle fiber” means the maximum distance between the outer circumferences of the cores of the most distant optical fibers among the plurality of optical fibers in the bundle fiber. Further, the “expansion angle” means an angle at which the beam diameter of the laser light expands with propagation. The “diffusion angle” of the homogenizer means a designed diffusion angle, that is, an angle at which the beam diameter of the laser beam incident on and transmitted through the homogenizer as parallel light spreads as it propagates. It should be noted that the “expansion angle” and the “diffusion angle” are expressed as full-plane angles. When measuring these angles, the beam diameter is measured at about 10 points within a range of propagation distance from a certain beam diameter to a beam diameter that is 2.0 times the beam diameter. It is preferable to obtain from the slope of change.

The “beam diameter” is a diameter of a circle including approximately 86.5% of the energy profile of the laser beam and centering on the beam center (usually the maximum position of the beam intensity), so-called 1 / e ² diameter. It can be. In this case, when it is difficult to obtain the center of the beam due to irregular distribution of the beam intensity, a circle having an energy of 86.5% in the vicinity of the position estimated to be the center of the beam is comprehensively created. The diameter of the circle with the smallest value may be used as the beam diameter.

  Further, in the probe according to the present invention, the light guide unit is configured to extend the measurement light to a beam diameter adapted to the opening angle of the plurality of optical fibers immediately before the incident side of the homogenizer. It is preferable to include a beam expander optical system in which an enlargement ratio suitable for the aperture angle is set.

  In the probe according to the present invention, it is preferable that the incident end portion of the bundle fiber is subjected to fusion processing.

  In the probe according to the present invention, it is preferable that the outer circumferences of the plurality of optical fibers at the incident end are covered with a material having high durability against light energy. In this case, the material having high durability against light energy is preferably quartz.

  Further, in the probe according to the present invention, when the measurement light is emitted from the emission end of the entire optical fiber, the emission end of the optical fiber associated with each of the plurality of divided regions divided in the end face arrangement of the incidence end is provided. It is preferable that the energy profile is arranged in accordance with the relative size of each divided region to which the emission end belongs. In this case, the plurality of divided regions are preferably divided according to the distance from the center of the bundle fiber.

  Further, in the probe according to the present invention, the light guide unit has at least a connection surface to which at least a part of the emission end portions of the plurality of optical fibers is connected, and an emission surface from which the measurement light incident from the connection surface is emitted. It is preferable to provide one light guide plate. In this case, it is preferable that a plurality of light guide plates are arranged so as to face each other with the acoustic wave vibrator interposed therebetween.

  In the probe according to the present invention, the homogenizer is preferably a lens diffusion plate in which minute lenses are randomly arranged on one side of the substrate.

  Moreover, it is preferable that the probe according to the present invention includes a holding unit that integrally holds the light collecting member and the bundle fiber. In this case, it is preferable that the holding unit integrally holds the holding unit including the homogenizer.

  Moreover, the probe according to the present invention preferably includes a holding portion that holds the incident end portion so as to cover the incident surface of the bundle fiber and has a window portion at a portion where the measurement light is incident. In this case, the window portion can be composed of an ND filter.

  Further, in the case where the holding portion is provided, the opening member is provided at the incident end of the bundle fiber and has an opening that allows the measurement light incident on the bundle fiber to pass, and the bundle fiber increases toward the incident end. It is preferable to provide an opening member that decreases to a size corresponding to the diameter. Alternatively, the holding portion includes a light guide member including a cap member and a chip formed of a material resistant to light energy and a ring-shaped tip fitted to the cap member inside the holding portion. It is preferable that a light guide member including a diaphragm and a relay lens system is provided inside the holding portion. Moreover, it is preferable that a holding | maintenance part has a connector structure which can be attached or detached with the mounting part of the apparatus housing | casing which includes a light source.

The photoacoustic measuring device according to the present invention is:
A probe as described above;
Signal processing means for processing the photoacoustic signal of the photoacoustic wave detected by the acoustic wave vibrator.

  In the photoacoustic measurement device according to the present invention, a light source that outputs measurement light, a device housing that has a mounting portion that is optically connected to the light source and holds a homogenizer, a light collecting member, It is preferable that a holding portion that integrally holds the bundle fiber is provided, and the mounting portion and the holding portion have a connector structure that can be attached to and detached from each other. Alternatively, in the photoacoustic measurement device according to the present invention, a light source that outputs measurement light, and a device housing that has a mounting portion that is optically connected to the light source and holds the homogenizer and the light collecting member, A holding structure that holds an incident end so as to cover the incident surface of the bundle fiber, and has a holding part having a window part at a part where measurement light is incident, and a connector structure in which the mounting part and the holding part are detachable from each other It is preferable to have it.

  In the photoacoustic measurement apparatus according to the present invention, the signal processing means preferably includes an acoustic image generation means for generating a photoacoustic image based on the photoacoustic signal. In this case, the acoustic wave transducer detects a reflected acoustic wave with respect to the acoustic wave transmitted to the subject, and the acoustic image generation means generates a reflected acoustic wave image based on the reflected acoustic wave signal. It is preferable to produce it.

  In the acoustic wave detection probe and the photoacoustic measurement device according to the present invention, the light guide unit condenses the homogenizer for flattening the energy profile of the measurement light incident on the light guide unit, and the measurement light transmitted through the homogenizer. And a bundle fiber including a plurality of optical fibers, the bundle fiber being arranged so that the measurement light transmitted through the light collecting member is incident from the incident end. Is. As a result, by dividing the flat-topped measurement light into each optical fiber in the bundle fiber and making it incident, the local energy exceeds the damage threshold energy and the end face of the bundle fiber is damaged in a wide range. Can be prevented. As a result, in the photoacoustic measurement, it is possible to eliminate the uneven energy amount of light that transmits high energy light and travels through each of the plurality of optical fibers.

It is a schematic sectional drawing which shows the structural example of the light guide part of the probe in 1st Embodiment. It is a schematic sectional drawing which shows arrangement | positioning of the acoustic wave vibrator and optical fiber in the probe of 1st Embodiment. It is a schematic sectional drawing which shows the some structural example of a homogenizer. It is a schematic sectional drawing which shows the other structural example of the light guide part of a probe. It is the schematic which shows the end surface arrangement | positioning of the incident end part of the bundle fiber by which the fusion process was carried out. (A) It is a figure which shows the energy profile of the laser beam condensed with the lens, after an energy profile was made into flat top by the homogenizer. (B) It is a figure which shows the energy profile of the laser beam only condensed with the lens, without using a homogenizer. It is a graph which shows the relationship between the optical characteristic of a lens diffusing plate and a condensing member, and the minimum beam diameter. It is a graph which shows the correlation of the diameter of a condensing range, and the minimum beam diameter in case the laser beam with distribution of the angle which the advancing direction and the optical axis of a condensing member have distribution is condensed on the said condensing member. It is the schematic which shows the structure of the light guide part in the case of including a beam expander. It is the schematic which shows the structural example of a light-guide plate. It is a schematic sectional drawing which shows arrangement | positioning of the acoustic wave vibrator in the probe of 2nd Embodiment, an optical fiber, and a light-guide plate. It is the schematic which shows the setting method of the division area | region divided | segmented in the end surface arrangement | positioning of the optical fiber of an incident end part. (A) It is the schematic which shows the design change about the arrangement method of the optical fiber in the probe of 1st Embodiment. (B) It is the schematic which shows the design change about the arrangement method of the optical fiber in the probe of 2nd Embodiment. (A) It is the schematic which shows the structure of the mounting part and holding | maintenance part of an apparatus housing containing a light source. (B) It is the schematic which shows a mode that the holding | maintenance part was mounted | worn with the mounting part of FIG. 14a. (A) It is the schematic which shows the other structure of the mounting part and holding | maintenance part of an apparatus housing containing a light source. (B) It is the schematic which shows a mode that the holding | maintenance part was mounted | worn with the mounting part of FIG. 15a. It is the schematic which shows the other structure of the mounting part and holding | maintenance part of an apparatus housing containing a light source. It is the schematic which shows the structure provided with the opening member in the holding | maintenance part. It is the schematic which shows the structure provided with the cap member (quartz rod) in the incident end part of bundle fiber. It is the schematic which shows the structure provided with the cap member (air gap optical fiber) in the incident end part of bundle fiber. It is the schematic which shows the relationship between the energy profile of an incident beam, and a cap member. It is the schematic which shows the structure provided with the relay lens system in the incident end part of bundle fiber. It is a schematic block diagram which shows 1st Embodiment of the photoacoustic image generation apparatus as a photoacoustic measuring device. It is a schematic block diagram which shows 2nd Embodiment of the photoacoustic image generation apparatus as a photoacoustic measuring device.

  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 Embodiment of Probe for Acoustic Wave Detection”
First, a first embodiment of an acoustic wave detection probe (probe) will be described. FIG. 1 is a schematic cross-sectional view showing a configuration example of a light guide portion of a probe in the present embodiment. FIG. 2 is a schematic cross-sectional view showing the arrangement of the acoustic wave transducer array and the optical fiber in the probe of this embodiment.

  As shown in FIGS. 1 and 2, the probe 11 in the present embodiment includes a light guide unit 44 including a homogenizer 40, a light collecting member 41, and a bundle fiber 42 that has been fused, and an acoustic wave transducer array. 20 and a housing 11 a that holds the emission end E <b> 2 of the bundle fiber 42 and the acoustic wave transducer array 20. In the present embodiment, the probe 11 is used by being optically connected to the laser unit 13 so that the laser light L output from the laser unit 13 enters the homogenizer 40. The laser light L incident on the homogenizer 40 enters the incident end E1 of the bundle fiber 42 via the light collecting member 41. Thereafter, the laser light L guided by the bundle fiber 42 is emitted from the emission end E2 of each optical fiber 42a in the bundle fiber 42, and is irradiated to the subject M as measurement light. Measurement light is not limited to laser light.

<Housing>
The housing 11 a also functions as a holding member for the operator of the probe 11 to hold the probe 11. In the present embodiment, the housing 11a has a handheld shape, but the housing 11a of the present invention is not limited to this.

<Homogenizer>
In this embodiment, the homogenizer 40 is an optical element that flattens the energy profile (energy distribution) of the laser beam L incident from the upstream side of the optical system and diffuses the laser beam L. The flat top laser beam L is guided to the condensing member 41 and enters the incident end E1 in a state having a flat top energy profile. In other words, “to make the energy profile flat” means that the laser light incident on the homogenizer is shaped into an energy profile having a flat top near the center. In this specification, the term “flat top” refers to a case where a concentric circle whose diameter is 80% of the beam diameter in the energy profile of the laser beam emitted from the homogenizer is taken, and a standard deviation is obtained for the energy at each point in the concentric circle. , Which means that the standard deviation is within 25% of the average energy within the concentric circles. Usually, a homogenizer is structurally designed so that light is completely flat top at infinity (that is, the standard deviation is substantially equal to 0). However, in the present invention, the energy profile when the measurement light is incident on the incident end of the bundle fiber is not necessarily in a completely flat top state, and may be in a flat top state within the above range. By making the energy profile of the laser beam L flat-topped, it is prevented that the light intensity is locally increased, and damage to the bundle fiber 42 is also suppressed. Furthermore, variation in light energy incident on each of the optical fibers in the bundle fiber 42 is also suppressed.

  Further, the homogenizer 40 of the present embodiment has a function of diffusing the laser light L output from the laser unit 13 to increase the beam diameter of the laser light L, that is, a function of expanding the distribution of the propagation angle of the light beam included in the laser light L. Fulfill. Thereby, since the light emitting surface of the homogenizer 40 serves as a secondary light source of the laser light L, it is possible to prevent the laser light L from being excessively narrowed when the light condensing member 41 condenses the laser light L. The diffusion angle of the homogenizer 40 is preferably 0.2 to 5.0 °, and more preferably 0.4 to 3.0 °. This is because the transmission efficiency is high. Note that the homogenizer diffusion function is not essential.

  The distance between the homogenizer 40 and the condensing member 41 is appropriately adjusted so that the laser light L transmitted through the homogenizer 40 is efficiently coupled to the condensing member 41. At this time, it is preferable that the homogenizer 40 is disposed on the upstream side of the optical system with respect to the light collecting member 41 and within a range of three times the focal length from the center of the light collecting member 41.

  The homogenizer 40 may be composed of a single optical element or a combination of a plurality of optical elements. When the homogenizer 40 is composed of a single optical element, for example, a π shaper manufactured by AdlOptica can be used as the homogenizer 40. Further, as the homogenizer 40 having a diffusing function, for example, it is preferable to use a lens diffusing plate 53 in which minute concave lenses or the like are randomly arranged on one side 53S of the substrate (FIG. 4). As such a lens diffusion plate, for example, Engineered Diffusers (model number: EDC-2.0-A, diffusion angle: 2.0 °) manufactured by RPC Photonics can be used. By using such an element, the energy profile and shape of the laser beam L can be changed almost arbitrarily. Thus, when the homogenizer 40 is configured from a single optical element, the light guide 44 can be assembled with a simple configuration.

  On the other hand, when the homogenizer 40 is composed of a plurality of optical elements, for example, the following configuration can be cited. FIG. 3 is a schematic cross-sectional view showing a configuration example of the homogenizer 40. The homogenizer 40 can be configured by arranging, for example, a microlens array A45, a microlens array B46, a plano-convex lens 47, and a variable beam expander 48 as shown in FIG. 3a. The homogenizer 40 can also be configured as shown in FIG. 3b by appropriately combining the holographic diffuser plate 49, the condensing plano-convex lens 50, and the light pipe 51. Further, the homogenizer 40 can also be constituted by a flat top laser beam shaper 52 in which an aspheric lens for correcting a beam energy profile, for example, is incorporated as shown in FIG. 3C.

  The homogenizer 40 may be configured to be held integrally with the light collecting member 41 and the bundle fiber 42 by the holding portion 60a, as shown in FIG. 4a. In this case, it is not necessary to adjust the positional relationship between the homogenizer 40 and the light collecting member 41, and the optical system can be downsized.

<Condensing member>
The condensing member 41 is for guiding the laser light L that has passed through the homogenizer 40 to the incident end of the bundle fiber 42, and can be constituted by a condensing lens, a mirror, or a combination thereof. For example, in this embodiment, the condensing member 41 is a condensing lens system composed of one condensing lens. The focal length of the light collecting member 41 (the distance between the principal point on the bundle fiber 42 side and the focal point) is preferably 10 to 100 mm, and more preferably 15 to 50 mm. This is because the optical system can be miniaturized and the focal length is matched with the numerical aperture NA (about 0.22 at the maximum) of a general optical fiber whose core is made of quartz and whose clad is made of fluorine-doped quartz. Moreover, the condensing member 41 can also be a coupled lens composed of a plurality of lenses. When the condensing member 41 is a coupled lens, the focal length of the condensing member 41 refers to the combined focal length of the coupled lens. The light collecting member 41 may be configured to be held integrally with the homogenizer 40 and the bundle fiber 42 by the holding portion 60a as shown in FIG. 4a, and bundled by the holding portion 60b as shown in FIG. 4b. You may comprise so that only the fiber 42 may be hold | maintained integrally.

<Bundled fiber>
The bundle fiber 42 guides the laser light L collected by the light collecting member 41 (that is, transmitted through the light collecting member 41) to the vicinity of the acoustic wave transducer array 20. Note that another light guide member may be provided between the light collecting member 41 and the bundle fiber 42. For example, as shown in FIG. 5, the bundle fiber 42 includes a plurality of optical fibers 42a composed of a core and a clad, a covering member 42c such as a ferrule and a sheath, an outer periphery of the plurality of optical fibers 42a, and a covering member 42c. It is comprised from the filling member 42b which fills between. The core diameter of the optical fiber 42 a in the bundle fiber 42 is preferably 20 to 300 μm, and more preferably 50 to 200 μm. The optical fiber 42a in the bundle fiber 42 is not particularly limited, but is preferably a quartz fiber.

  Furthermore, in the present embodiment, at least the incident end portion of the bundle fiber 42 is subjected to fusion processing. The fusing process is a bundle processing technique in which, when bundling optical fiber strands, processing is performed with heat and pressure instead of an adhesive. In the bundle fiber that has been fused, the clads are fused together, and the optical fibers are bundled in a hexagonal honeycomb shape, so that an extra gap between the optical fibers is eliminated as compared with the bundle processing using an adhesive. Therefore, there is an advantage that the area occupied by the core per unit area is improved. Further, since a material weak to light energy does not appear at the incident end of the bundle fiber, there is an advantage that durability against light energy is also improved. From the viewpoint of further improving durability against light energy in the bundle fiber 42, the filling member 42b is preferably made of a material having high durability against light energy. An example of such a material is a glass material such as quartz. In such a bundle fiber, for example, a plurality of optical fibers are inserted into a cylindrical member made of quartz, and the optical fiber and the cylindrical member are fused together, and then the surroundings are covered with a covering member. Can be manufactured.

  The position of the bundle fiber 42 is adjusted so that, for example, the incident end E1 is positioned at the focal point of the light collecting member 41. In order to enable fine adjustment of the position of the bundle fiber 42, a bundle fiber position adjusting unit (not shown) that moves the bundle fiber 42 in the optical axis direction may be provided. By doing so, it is possible to adjust the position in the vicinity of the focal position within a range that does not impair the flat top property, and it is also possible to finely adjust the beam diameter when entering the incident end E1. It becomes.

  Further, when the homogenizer 40, the light collecting member 41 and the bundle fiber 42 are integrally held by the holding portion 60a as shown in FIG. 4a, or when the light collecting member 41 and the light collecting member 41 and When the bundle fiber 42 is held integrally, the bundle fiber 42 can be attached and detached with a screw structure or the like so that the incident end E1 of the bundle fiber 42 is easily fixed at the focal position of the light collecting member 41. It is preferable to be fixed to the holding parts 60a and 60b by the structure to be made. In FIG. 4, each of the joining portions 100 a on the condenser lens 41 side of the holding portions 60 a and 60 b and the connection portion 100 b on the bundle fiber 42 side have complementary screw structures, so that the bundle fiber 42 is held by the holding portion. Removably fixed to 60a and 60b. As described above, when the bundle fiber 42 is fixed to the holding portion 60a or 60b by, for example, a screw structure, the bundle fiber position adjusting portion is not necessary, and the optical system can be downsized. In addition, since the bundle fiber 42 can be easily replaced by simply removing the screw from the holding portion 60a or 60b, when the damaged bundle fiber 42 is replaced, the light collecting member 41 and the bundle fiber 42 are aligned again. This eliminates the need for maintenance and improves maintainability. In order to integrate the condensing member 41 and the bundle fiber 42 through a screw portion so that the positional relationship is fixed, for example, an aspheric lens fiber collimator package (model number: F280SMA-A or F280SMA-B manufactured by Thorlabs) is used. , Focal length: 18.4 mm) or the like. In addition, in the series of aspheric lens fiber collimator packages manufactured by Thorlabs, products having focal lengths of about 4 mm to 18.4 mm are available, and can be appropriately selected according to the purpose.

  On the exit side of the bundle fiber 42 in the present embodiment, the exit ends E2 of the plurality of optical fibers 42a are arranged around the acoustic wave transducer array 20 in order to improve the uniformity of the energy profile of the light irradiated to the subject. Are arranged almost evenly.

<Acoustic wave transducer array>
The acoustic wave transducer array 20 is a one-dimensional or two-dimensional array of a plurality of acoustic wave transducers (or acoustic wave detection elements), and converts acoustic wave signals into electrical signals. The acoustic wave vibrator is a piezoelectric element composed of a polymer film such as piezoelectric ceramics, piezoelectric single crystal, or polyvinylidene fluoride (PVDF). In this specification, “acoustic wave” means an ultrasonic wave and a photoacoustic wave. Here, “ultrasonic wave” means an elastic wave and its reflected wave generated in the subject due to vibration of the acoustic wave transducer array, and “photoacoustic wave” means a wave due to a photoacoustic effect caused by irradiation of measurement light. It means the elastic wave generated in the specimen. The acoustic wave transducer array 20 preferably includes acoustic elements such as an acoustic matching layer, an acoustic lens, and a backing material in order to detect an accurate acoustic wave signal.

<Control of beam diameter>
When the homogenizer 40 has a diffusing function, the condensing member 41 has a minimum beam diameter D (that is, a beam diameter at the focal plane) of the laser light L (measurement light) defined by the following formula 3 as the diameter of the bundle fiber 42. The laser beam is condensed so as to satisfy the following formula 4 in relation to d, and the bundle fiber 42 is configured to receive the laser beam in a state where the beam diameter D of the laser beam L is 0.8d to 1.2d. It is preferable that they are arranged so as to be incident.

  The reason why the minimum beam diameter D is set to 0.8 d or more is to suppress damage of the incident end E1 of the bundle fiber 42 (core damage mode) by constricting the beam diameter. Specifically, it is as follows.

  FIG. 6A is a diagram illustrating an energy profile in the focal plane of the laser light L collected by the lens after the energy profile is flattened by the homogenizer 40. FIG. FIG. 6B is a diagram showing an energy profile in the focal plane of the laser light that is only condensed by the lens without using the homogenizer 40. From FIG. 6, it can be seen that the ratio of the full width at half maximum W1 to the minimum beam diameter D1 of the laser beam in FIG. 6a is larger than the ratio of the full width at half maximum W2 to the minimum beam diameter D2 of the laser beam in FIG. . Usually, since the divergence angle φ of the laser light L when output from the laser unit is small (about 0.15 ° at most), the condensed laser light L is narrowed down at the incident end E1 of the bundle fiber 42. It will be. As a result, the energy of the laser beam L is concentrated at the incident end of the bundle fiber 42, and the incident end E1 of the bundle fiber 42 is damaged.

  Therefore, in this embodiment, the beam diameter at the lens focal position of the laser light L is controlled by once diffusing the laser light L with the homogenizer 40. FIG. 7 is a graph showing the relationship between the optical characteristics and the minimum beam diameter of the lens diffusers and the condensing member. In the graph, the horizontal axis represents the diffusion angle (deg.) Of the lens diffusion plate, and the vertical axis represents the minimum beam diameter (μm). The round plot in the graph shows data when the focal length of the light collecting member is 100 mm, the square plot shows data when the focal length of the light collecting member is 50 mm, and the triangular plot shows the data when the focal length of the light collecting member is 50 mm. Data when the focal length of the optical member is 25 mm is shown. It can be seen from FIG. 7 that the minimum beam diameter can be adjusted by adjusting the optical characteristics of the homogenizer and the condensing member.

  In such a beam diameter control method, when parallel light traveling in a direction in which the angle formed by the optical axis of the light collecting member is α enters the light collecting member having a focal length f, the parallel light is condensed. This is based on the principle that the position of the condensing point is shifted from the focal point of the condensing member and the distance between the condensing point and the focal point can be approximated by f · tan α.

Therefore, when the angle formed between the traveling direction of the laser beam incident on the light collecting member and the optical axis of the light collecting member has a distribution, the laser light beam is condensed at a position corresponding to each angle. The condensing range (including the skirt) of the entire laser beam obtained by superimposing the condensing points corresponding to the angle becomes larger. For example, when a homogenizer having a diffusing function is disposed upstream of the light collecting member, the angular distribution of the laser beam that was within about φ / 2 before the homogenizer was incident is approximately √ (half angle after transmission through the homogenizer). Since it extends within (φ / 2) ² + (θ / 2) ² ), the condensing range of the entire laser light subsequently collected by the condensing member is further increased correspondingly.

In consideration of the fact that the 1 / e ² diameter of the laser beam in the condensing range is the beam diameter, the diameter of the condensing range is 2f · tan (√ ((φ / 2) ² + (θ / 2) ² ) ) And the minimum beam diameter D are estimated to have a certain correlation with each other.

FIG. 8 shows a case where a laser beam having a distribution of angles formed by the traveling direction and the optical axis of the condensing lens is condensed on the condensing lens. The diameter of the condensing range is 2f · tan (√ ((φ / 2) ² + (θ / 2) ² )) and an experimentally obtained correlation of the actual minimum beam diameter D. More specifically, this graph shows that a homogenizer having a predetermined diffusion angle θ has a wavelength of 532 nm, a pulse width of 3.5 ns, a beam diameter of 3.5 mm when incident on the homogenizer, and a divergence angle φ of 0.13. Result of experiment in which the condensing range when the laser light is condensed by a condensing lens having a predetermined focal length f after the laser beam is incident with a beam profiler (LaserCam-HR manufactured by Coherent) It is. The same beam profiler was used to determine the homogenizer diffusion angle. The five rounded plots in the graph are the results of measurement with an optical system composed of a condensing lens having a focal length f of 100 mm and a homogenizer. The diffusion angle θ of the homogenizer is 0 from the lower left plot. .25, 0.50, 1.02, 2.05 and 3.15 °. In addition, the five-point square plots in the graph are the results of measurement with an optical system composed of a condensing lens with a focal length f of 50 mm and a homogenizer, and the diffusion angle θ of the homogenizer is shown in the lower left plot. 0.25, 0.50, 1.02, 2.05 and 3.15 °. In addition, the triangular plots of five points in the graph are the results of measurement with an optical system comprising a combination of a condensing lens with a focal length f of 25 mm and a homogenizer, and the diffusion angle θ of the homogenizer is from the lower left plot, respectively. 0.25, 0.50, 1.02, 2.05 and 3.15 °.

  It can be seen from FIG. 8 that the minimum beam diameter D has a linear function with respect to the diameter of the focusing range. The slope of the linear function in the graph was about 1.25. Therefore, the minimum beam diameter D is given by Equation 3 above.

  That is, for a predetermined laser beam, not only the focal length and the diffusion angle used in the above-described experiment, but also an arbitrary minimum beam diameter D can be created by appropriately setting the focal length f and the diffusion angle θ. It can be said. The energy density can be lowered as the beam diameter is increased.

  In this embodiment, the damage threshold energy density at the incident end of the bundle fiber 42 is controlled by controlling the minimum beam diameter D of the laser light L using the relationship between the focal length of the light collecting member and the diffusion angle of the homogenizer. The high energy laser beam L can be guided by the bundle fiber 42 so as not to exceed.

  The reason why the minimum beam diameter D is set to 1.2 d or less in relation to the diameter d of the bundle fiber 42 is that the member around the incident end E1 of the bundle fiber 42 is moved to the laser beam L because the minimum beam diameter D increases. This is to prevent the discharge of dust and gases from the damaged part. Such emissions may cause a problem (ambient damage mode) that adheres to the end face of the bundle fiber 42 and induces destruction of the core in the vicinity of the end face and inhibits energy transmission. That is, the minimum beam diameter D is set to 1.2 d or less in order to suppress the occurrence of the surrounding damage mode as described above. The members around the bundle fiber mean, for example, the filling member 42b made of resin and the covering member 42c such as a metal ferrule covering the outer periphery thereof.

  In the range where the minimum beam diameter D exceeds d, since the light intensity on the outer peripheral side of the beam (the side far from the optical axis) is relatively weak, even if the minimum beam diameter D slightly exceeds the bundle fiber diameter. This is because the surrounding damage mode is difficult to occur. A preferable range of the minimum beam diameter D is 0.8 d or more and 1.0 d or less. In addition, the bundle fiber 42 is arranged so that the laser light L is incident in a state where the beam diameter D of the laser light L is not less than 0.8d and not more than 1.2d. This is because the laser beam L is efficiently incident on the incident end E1 of the bundle fiber 42.

  As described above, in the acoustic wave detection probe according to the present embodiment, the laser beam (measurement light) is once passed through the homogenizer to flatten the energy profile, and the beam diameter when entering the bundle fiber is set to the condensing member. Is controlled by. As a result, by dividing the flat-topped laser light into each optical fiber in the bundle fiber and making it incident, the local energy exceeds the damage threshold energy and the end face of the bundle fiber is damaged in a wide range. Can be prevented. The fact that local damage is prevented leads to the fact that more energy can be input as a whole from the viewpoint of energy transmission, and that energy can be appropriately distributed to each optical fiber from the viewpoint of uneven light energy. Represents that As a result, in the photoacoustic measurement, it is possible to eliminate the uneven energy amount of light that transmits high energy light and travels through each of the plurality of optical fibers.

“Second Embodiment of Probe for Acoustic Wave Detection”
Next, an embodiment of the second embodiment of the acoustic wave detection probe will be described. The probe of this embodiment is different from that of the first embodiment in that the light guide unit has a beam expander optical system on the upstream side of the bundle fiber 42. Therefore, detailed description of the same components as those in the first embodiment is omitted unless particularly necessary.

  FIG. 9 is a schematic diagram showing a configuration of the light guide unit including a beam expander.

  The probe 11 in the present embodiment includes a beam expander 55, a homogenizer 40, a light collecting member 41, and a bundle fiber 42 that has been subjected to fusion processing, an acoustic wave transducer array, and a bundle fiber 42. And a housing for holding the emission end portion and the acoustic wave transducer array. In the present embodiment, the probe 11 is used by being optically connected to the laser unit 13 so that the laser light L output from the laser unit 13 enters the beam expander 55. The laser beam L incident on the beam expander 55 enters the incident end E1 of the bundle fiber 42 via the homogenizer 40 and the condensing member 41. Thereafter, the laser light L guided by the bundle fiber 42 is emitted from the emission end portions of the plurality of optical fibers 42a in the bundle fiber 42, and is irradiated on the subject as measurement light.

  The casing, the homogenizer 40, the light collecting member 41, and the acoustic wave transducer array are the same as those in the first embodiment.

<Beam expander optics>
For example, as shown in FIG. 9, the beam expander optical system 55 has a beam diameter adapted to the aperture angles of the plurality of optical fibers 42a in the bundle fiber 42, and further to an optimum beam diameter for the aperture angles. It expands the measurement light. “The beam diameter suitable for the aperture angle of the optical fiber” means that when the light is condensed at the incident end of the bundle fiber through the homogenizer and the condensing member, the light converging angle is the aperture angle of the optical fiber. "The optimum beam diameter with respect to the aperture angle of the optical fiber" means the beam diameter at which the light collection angle is almost the aperture angle of the optical fiber at that time. . Further, the beam expander optical system 55 is disposed on the upstream side (that is, the light source side) of the light collecting member 41. The magnification of the beam expander optical system 55 is such that the laser light L can be incident on the incident end E1 of the bundle fiber 42 with a wider divergence angle within a range not exceeding the numerical aperture of the optical fiber 42a. To match the opening angle of the optical fiber 42a. For example, a quartz fiber having a general core / cladding structure has a numerical aperture of 0.20 to 22, and an opening angle of 11.4 to 12.7 °. By setting in this way, the divergence angle of the light after exiting the optical fiber 42a can be increased as much as possible, and the illumination can be made uniform at a shorter distance from the exit end face of the optical fiber 42a. The beam expander optical system 55 may be disposed between the homogenizer 40 and the light collecting member 41. However, as shown in FIG. It is preferable to arrange at the position of

  The beam expander optical system 55 as described above can be made by appropriately combining, for example, a concave lens and a convex lens according to the numerical aperture of the optical fiber 42a.

  As described above, also in the acoustic wave detection probe according to the present embodiment, the laser beam (measurement light) is once passed through the homogenizer to flatten the energy profile and collect the beam diameter when entering the bundle fiber. It is controlled by the member. Thereby, there exists an effect similar to 1st Embodiment.

  Furthermore, in this embodiment, the beam expander optical system 55 is used to expand the measurement light to an optimum beam diameter with respect to the aperture angles of the plurality of optical fibers 42a in the bundle fiber 42, so that the uniformity of illumination is improved. This can be further improved.

“Third embodiment of probe for acoustic wave detection”
Next, an embodiment of the third embodiment of the acoustic wave detection probe will be described. The probe of this embodiment is different from that of the first embodiment in that the measurement light guided by the bundle fiber 42 through the light guide plate is irradiated. Therefore, detailed description of the same components as those in the first embodiment is omitted unless particularly necessary.

  FIG. 10 is a schematic diagram illustrating a configuration example of the light guide plate. FIG. 11 is a schematic cross-sectional view showing the arrangement of the acoustic wave vibrator, the optical fiber, and the light guide plate in the probe of this embodiment.

  The probe 11 according to the present embodiment includes a homogenizer, a light collecting member, a light guide unit composed of a fused bundle fiber 42 and a light guide plate 43, an acoustic wave transducer array 20, and an output end of the bundle fiber 42. E2 and a housing 11a for holding the acoustic wave transducer array 20. Also in this embodiment, the probe 11 is used by being optically connected to the laser unit so that the laser light L output from the laser unit is incident on the homogenizer. The laser beam L incident on the homogenizer is incident on the incident end of the bundle fiber 42 via the condensing member. Thereafter, the laser light L guided by the bundle fiber 42 is directly incident on the connection surface S1 of the light guide plate 43 from the emission ends E2 of the plurality of optical fibers 42a in the bundle fiber 42, and is guided by the light guide plate 43. The laser beam L thus emitted is emitted from the emission surface S2 of the light guide plate 43 and is irradiated on the subject M as measurement light.

  The housing, the homogenizer, the light collecting member, and the acoustic wave transducer array 20 are the same as those in the first embodiment.

<Light guide plate>
The light guide plate 43 is a plate that performs special processing on the surface of, for example, an acrylic plate or a quartz plate, and uniformly emits light from one end surface (connection surface S1) from the other end surface (output surface S2). is there. For example, as shown in FIG. 10, the light guide plate 43 can be manufactured by forming a resin film 43b having a low refractive index on a pair of opposing side surfaces of the quartz plate 43a. In this case, the laser light incident from the connection surface S1 propagates while being subjected to multiple reflection at the interface S3 between the quartz plate 43a and the resin thin film 43b, and is emitted from the emission surface S2. The emission end E2 of the optical fiber 42a is arranged substantially evenly on the connection surface S1 of the light guide plate 43 and is optically connected. When the light guide plate 43 has a tapered shape that spreads from the connection surface S1 toward the emission surface S2 as shown in FIG. 10a, it is possible to irradiate the laser light L uniformly over a wider range. The light guide plate 43 may have a rectangular parallelepiped shape as shown in FIG. 10c. As shown in FIG. 11, in this embodiment, the two light guide plates 43 are arranged to face each other with the acoustic wave transducer array 20 interposed therebetween, and the optical fiber 42 a is connected to the connection surface S <b> 1 of each light guide plate 43. Has been. The light guide plate 43 has a mechanism for diffusing light at the tip thereof (diffusion plate, resin containing scattering particles, etc.) or a traveling direction of the light acoustic wave so that a wider range of the subject M can be irradiated with the laser light L. A mechanism (such as a notch for refracting light) directed toward the transducer array 20 may be provided.

  As described above, also in the acoustic wave detection probe according to the present embodiment, the laser beam (measurement light) is once passed through the homogenizer to flatten the energy profile and collect the beam diameter when entering the bundle fiber. It is controlled by the member. Thereby, there exists an effect similar to 1st Embodiment.

  Furthermore, in the present embodiment, since the measurement light is irradiated through the light guide plate, it is possible to further improve the uniformity of the energy profile of the light irradiated to the subject.

<Change in probe design>
In the present invention, the energy profile is flattened by passing the measurement light once through a homogenizer. However, even if a homogenizer is used, it may be difficult to make the energy profile completely uniform. Therefore, in the present invention, it is preferable to consider the position of the optical fiber in the bundle fiber when arranging the emission end of the optical fiber.

  For example, the energy profile of normal laser light has a Gaussian distribution centered on the optical axis. In this case, even when a homogenizer is used, a local intensity bias depending on the distance from the optical axis may occur. Specifically, for example, in the energy profile of FIG. 6a, there is a region where the strength gradually decreases from the flat top region to the outer edge. Thus, for example, as shown in FIG. 12, in the arrangement of the end face of the incident end, a plurality of optical fibers are divided into a divided region (center side region 62) near the center of the bundle fiber 42 and a divided region (outer side region 64) near the outer periphery. To divide. And the optical fiber 62a which belongs to the center side area | region 62, and the optical fiber 64a which belongs to the outer peripheral side area | region 64 are arrange | positioned uniformly according to the relative magnitude | size for every these division area. Here, “arrange” means that the emission ends of the optical fibers 62a and 64a are arranged at equal intervals around the acoustic wave transducer array 20 as shown in FIG. 13A, and that, for example, as shown in FIG. 13B. In other words, the light emitting ends of the optical fibers 62a and 64a are arranged on the connection surface of the light guide plate 43 at equal intervals. In addition, the term “uniformly according to the relative size of each divided region” to which the output end belongs here does not necessarily mean that the ratio of the number of optical fibers belonging to each divided region is 1: 1. According to the ratio of the number of optical fibers belonging to each divided region, it means that the emission end portions of the optical fibers belonging to the respective divided regions are mixed and arranged as a whole. By doing so, it is possible to reduce the influence of the local intensity deviation and further improve the uniformity of the energy profile of the measurement light actually irradiated on the subject.

  The region dividing method is not limited to the above-described method. For example, the region can be divided into three regions according to the distance from the center of the bundle fiber, or can be divided into six equal angles about the center.

  Furthermore, when the holding unit integrally holds the components of the light guide unit, the holding unit preferably has a connector structure that can be attached to and detached from the mounting unit of the apparatus housing that contains the light source. For example, FIG. 14a is a schematic diagram illustrating the configuration of the mounting portion 69 and the holding portion 65a of the apparatus housing 68 including the laser unit 13 (light source). The apparatus housing 68 incorporates the laser unit 13, and the laser unit 13 and the lens diffusion plate 53 (homogenizer) are optically connected by mounting the holding unit 65 a on the mounting unit 69.

  For example, the connector structure of the holding portion 65a is basically the same as that of the holding portion 60a of FIG. 4a, but differs in that it has a protrusion 66 that can be moved in the vertical direction on the paper surface by an elastic member 67 such as a spring. The protrusion 66 is pushed down into the groove of the holding portion 65a when an external force is applied from above, and then returns to the original state by the restoring force of the elastic member 67 when the external force stops working. Note that the surface of the protruding portion of the protruding portion 66 forms a curved surface so that the protruding portion 66 is pushed down into the groove of the holding portion 65a even when an external force in the horizontal direction of the paper surface acts. On the other hand, as shown in FIG. 14 a, the mounting portion 69 is provided with an engaging portion 69 a made up of a groove having a shape complementary to the protruding portion 66, for example. When the insertion of the holding portion 65a into the mounting portion 69 is started, the projecting portion 66 is pushed down by the inner wall of the mounting portion 69, and when the projecting portion 66 reaches the engaging portion 69a, the projecting portion 66 returns to its original position. The protrusion 66 and the engaging portion 69a are engaged. The outputted laser light L is guided to the lens diffusion plate 53 by the optical system 70 and then propagates through the probe of the present invention.

  Alternatively, as an example in which the holding portion has a connector structure that can be attached to and detached from the mounting portion, a mode as shown in FIG.

  For example, the connector structure of the holding portion 65b is basically the same as that of the holding portion 60b in FIG. 4B, but differs in that it has a protrusion 66 that can move in the vertical direction on the paper surface by an elastic member 67 such as a spring. The protrusion 66 is the same as described above. On the other hand, as shown in FIG. 15 a, the mounting portion 69 is provided with an engaging portion 69 a made up of a groove having a shape complementary to the protruding portion 66 and the lens diffusing plate 53. When the insertion of the holding portion 65b into the mounting portion 69 is started, the protruding portion 66 is pushed down by the inner wall of the mounting portion 69, and then when the protruding portion 66 reaches the engaging portion 69a, the protruding portion 66 returns to its original position. The protrusion 66 and the engaging portion 69a are engaged. At the same time, the arrangement of the lens diffusing plate 53 and the condensing member 41 is fixed and can be optically connected. The output laser light L is guided to the lens diffusion plate 53 by the optical system 70 and then propagates through the light guide unit in the present invention. This aspect is preferable because only the measurement light diffused from the apparatus is output even when the probe is not attached.

  Alternatively, as an example in which the holding portion has a connector structure that can be attached to and detached from the mounting portion, a mode as shown in FIG.

  For example, the holding portion 65c is a holding portion that holds the incident end so as to cover the incident surface of the bundle fiber 42, and includes a projection 66 similar to the above and a window portion 74 at a portion where the laser light L is incident. It is a holding part which has. The window portion 74 is made of a light transmissive material (for example, quartz), and is provided on the optical path of the laser light L so as to close the groove where the incident surface of the bundle fiber 42 is exposed. Thereby, for example, the incident surface of the bundle fiber 42 exists in the space sealed by the holding portion 65c. The surface of the window 74 on the light source side preferably has an antireflection coating (AR coating) such as a MgF2 film, a Ta2O5 film, or a SiO2 multilayer film. On the other hand, as shown in FIG. 16, the mounting portion 69 is provided with a beam expander 73, a homogenizer 40, and a condensing member 41, in addition to an engaging portion 69a having a groove complementary to the protruding portion 66, for example. ing. For example, the beam expander 73 includes a plano-concave lens 71 and a convex lens 72. The mounting procedure between the holding portion 65c and the mounting portion 69 is the same as described above. When the holding portion 65 c is attached to the attachment portion 69, the laser light L that has passed through the beam expander 73, the homogenizer 40, and the condensing member 41 passes through the window portion 74 and enters the incident surface of the bundle fiber 42. In this aspect, since dust or the like is attached to the light source side surface of the window portion 74 having a lower energy density than the incident surface of the bundle fiber 42, there is an advantage that end face damage is less likely to occur. 14 or 15, the same effect can be obtained by providing a window portion. Moreover, since the condensing member 41 is installed on the light source system side, when attaching and detaching the holding portion 65c and the mounting portion 69, the requirement of the angle accuracy of the holding portion 65c is alleviated, and the positional accuracy is emphasized. There is also an advantage that it should be considered.

  In FIG. 16, an ND filter can be used as the window unit 74. The ND filter is, for example, a quartz substrate coated with an oxide multilayer film. In such a case, the intensity of the laser beam L can be reduced on the probe side, and a laser beam intensity adjusting mechanism is not required on the light source system side.

  For example, as shown in FIG. 17, it is preferable that the holding portion has an opening member that allows measurement light incident on the bundle fiber to pass therethrough and an opening member having a tapered structure at the incident end of the bundle fiber 42. The diameter of the opening is formed so as to decrease to a size corresponding to the diameter of the bundle fiber toward the incident end. For example, in FIG. 17, the diameter of the opening on the bundle fiber side of the opening member 75 matches the diameter of the bundle fiber. The taper angle of the taper structure is preferably larger than the light collection angle when entering the bundle fiber 42 and smaller than the NA of the optical fiber. The opening inner surface of the opening member 75 is configured to reflect, scatter, or absorb light. Therefore, when the inner surface of the aperture reflects or scatters light, light having an angle component deviating from the incident angle that can be received by the optical fiber can be incident on the optical fiber via reflection or scattering. The light transmission efficiency is further improved. On the other hand, when the inner surface of the aperture absorbs light, light with an angle component deviating from the incident angle that can be received by the optical fiber is absorbed in a wide range away from the optical fiber, so that it is absorbed near the optical fiber. Damage to the optical fiber is suppressed more than when

In order to have a configuration in which the inner surface of the opening reflects light, for example, the inner surface of the opening may be subjected to a smoothing process such as mirror finishing or a film having a high reflectance such as a gold thin film may be formed. In order to make the inner surface of the opening scatter light, for example, the opening member is made of a ceramic thick powder or sintered body such as Al ₂ O ₃ , TiO ₂ , ZrO _2, or Teflon (registered). Trademark) or unpolished glass. Further, in order to make the inner surface of the opening absorb light, for example, the opening member may be made of metal such as aluminum, brass or copper.

  Further, when there is a possibility that the surrounding damage mode may occur due to the influence of the bottom portion of the energy profile, for example, damage to the surrounding member (ferrule or the like) of the bundle fiber as shown in FIG. 18A, FIG. 18B or FIG. 20 is prevented. It is preferable to provide a light guide member for this purpose at the incident end of the bundle fiber. For example, the light guide member of FIGS. 18A and 18B is formed of a material that is resistant to light energy of the cap member (for example, sapphire having excellent light absorption in the wavelength band of measurement light to be used). The tip 77 is composed of a ring-shaped tip 77 fitted to the cap member. As the cap member, for example, a quartz rod 76a (FIG. 18A) or an air gap optical fiber 76b (FIG. 18B) can be used. The tip 77 is fitted to the incident end of the cap member. In particular, when the air gap optical fiber 76b is used as a cap member, it is preferable that the chip 77 is embedded in the connector of the air gap optical fiber 76b. For example, the air gap optical fiber 76b of FIG. 18B is provided with a connector 65d on the bundle fiber 42 side, an detachable output side connector 65e, and an incident side connector 65f, and a chip 77 is embedded in at least the incident side connector 65f. . When such a light guide member is used, the light at the base is absorbed or reflected by, for example, the chip 77 and blocked (FIG. 19). Accordingly, the light at the base portion is prevented from reaching the peripheral member of the bundle fiber, and the occurrence of the peripheral damage mode is prevented.

  On the other hand, for example, the light guide member in FIG. 20 includes a first diaphragm 78 (for blocking the bottom portion), a second diaphragm 79 (for adjusting the light amount), a relay lens system 80, and a third diaphragm 81 (for blocking the bottom portion). Consists of For example, the first diaphragm 78 is disposed in the vicinity of the focal point of the condensing member 41, the second diaphragm 79 is disposed in the vicinity of the relay lens system 80, and the third diaphragm 81 is disposed in the vicinity of the incident end of the bundle fiber. When such a light guide member is used, the beam diameter can be enlarged or reduced before and after the relay lens system 80, and the relay lens system 80 is adjusted when the bundle fiber diameter differs depending on the probe used. Thus, the beam diameter can be set to a desired size. The light skirt portion is blocked by the first diaphragm 78 and the third diaphragm 81, and the second diaphragm 79 provided immediately before the relay lens system 80 is used for adjusting the amount of light.

  Further, for example, the light guide member (FIG. 18A) composed of the quartz rod 76a and the chip 77 and the light guide member (FIG. 20) composed of the apertures 78, 79, 81 and the relay lens system 80 are shown in FIGS. It can also be provided inside the holding part as shown in FIG.

  As described above, the convenience as a probe is improved by providing the holding portion with a connector structure that is detachable from the mounting portion. The connector structure is not limited to the above structure, and the holding part is preferably compact.

“First Embodiment of Photoacoustic Measuring Device”
Next, a first embodiment of the photoacoustic measurement device will be described. In the present embodiment, the case where the photoacoustic measurement device is a photoacoustic image generation device that generates a photoacoustic image based on a photoacoustic signal will be specifically described. FIG. 21 is a block diagram showing a configuration of the photoacoustic image generation apparatus 10 of the present embodiment.

  The photoacoustic image generation apparatus 10 of the present embodiment includes a probe 11, an ultrasonic unit 12, a laser unit 13, an image display unit 14, and an input unit 16 according to the present invention.

<Laser unit>
The laser unit 13 corresponds to a light source in the present invention, and outputs, for example, laser light L as measurement light that irradiates the subject M. The laser unit 13 is configured to output a laser beam L in response to a trigger signal from the control unit 29, for example. The laser light L output from the laser unit 13 is guided to the probe 11 using light guide means such as an optical fiber, and is irradiated from the probe 11 to the subject M. The laser unit 13 preferably outputs pulsed light having a pulse width of 1 to 100 nsec as laser light.

Further, the pulse width t _P (ns) of the laser light L preferably satisfies the following formula 5. Here, A is the pulse energy (J) when the laser light used is incident on the bundle fiber, λ is the wavelength (nm) of the laser light used, and G is the damage threshold energy density (J / Mm ² ), λG and tG are the wavelength and pulse width of the laser light for which the damage threshold energy density was obtained, respectively, and d is the diameter (mm) of the bundle fiber. This is because the following formula 6 is preferably satisfied in order to prevent end face damage of the bundle fiber.

  For example, in this embodiment, the laser unit 13 is a Q switch (Qsw) alexandrite laser. In this case, the pulse width of the laser light L is controlled by, for example, Qsw. The wavelength of the laser light is appropriately determined according to the light absorption characteristics of the substance in the subject to be measured. For example, when the measurement target is hemoglobin in a living body (that is, when a blood vessel is imaged), generally, the wavelength is preferably a wavelength belonging to the near-infrared wavelength region. The near-infrared wavelength region means a wavelength region of about 700 to 850 nm. The laser beam L may be a single wavelength or may include a plurality of wavelengths (for example, 750 nm and 800 nm). Furthermore, when the laser light L includes a plurality of wavelengths, the light of these wavelengths may be irradiated to the subject M at the same time, or may be irradiated while being switched alternately.

<Probe>
The probe 11 is a probe according to the present invention that detects a photoacoustic wave U generated in the subject M, and in the present embodiment, is a probe according to the third embodiment.

<Ultrasonic unit>
The ultrasonic unit 12 includes a reception circuit 21, an AD conversion unit 22, a reception memory 23, a photoacoustic image reconstruction unit 24, a detection / logarithm conversion unit 27, a photoacoustic image construction unit 28, a control unit 29, an image synthesis unit 38, and Observation method selection means 39 is provided. For example, the receiving circuit 21, the AD converting means 22, the receiving memory 23, the photoacoustic image reconstruction means 24, the detection / logarithmic conversion means 27, and the photoacoustic image construction means 28 are integrated into a photoacoustic as a signal processing means in the present invention. It corresponds to image generation means.

  The control unit 29 controls each unit of the photoacoustic image generation apparatus 10 and includes a trigger control circuit 30 in the present embodiment. The trigger control circuit 30 sends a light trigger signal to the laser unit 13 when the photoacoustic image generation apparatus is activated, for example. As a result, the flash lamp is turned on in the laser unit 13 and the excitation of the laser rod is started. And the excitation state of a laser rod is maintained and the laser unit 13 will be in the state which can output a pulse laser beam.

  The control unit 29 then transmits a Qsw trigger signal from the trigger control circuit 30 to the laser unit 13. That is, the control means 29 controls the output timing of the pulsed laser light from the laser unit 13 by this Qsw trigger signal. In the present embodiment, the control unit 29 transmits the sampling trigger signal to the AD conversion unit 22 simultaneously with the transmission of the Qsw trigger signal. The sampling trigger signal serves as a cue for the start timing of the photoacoustic signal sampling in the AD conversion means 22. As described above, by using the sampling trigger signal, it is possible to sample the photoacoustic signal in synchronization with the output of the laser beam.

  The receiving circuit 21 receives the photoacoustic signal detected by the probe 11. The photoacoustic signal received by the receiving circuit 21 is transmitted to the AD conversion means 22.

  The AD conversion means 22 is a sampling means, which samples the photoacoustic signal received by the receiving circuit 21 and converts it into a digital signal. For example, the AD conversion unit 22 includes a sampling control unit and an AD converter. The reception signal received by the reception circuit 21 is converted into a sampling signal digitized by an AD converter. The AD converter is controlled by the sampling control unit, and is configured to start sampling when the sampling control unit receives a sampling trigger signal. The AD converter 22 samples the received signal at a predetermined sampling period based on, for example, an AD clock signal having a predetermined frequency input from the outside.

  The reception memory 23 stores the photoacoustic signal sampled by the AD conversion means 22 (that is, the sampling signal). Then, the reception memory 23 outputs the photoacoustic signal detected by the probe 11 to the photoacoustic image reconstruction unit 24.

  The photoacoustic image reconstruction unit 24 reads out the photoacoustic signal from the reception memory 23 and generates data of each line of the photoacoustic image based on the photoacoustic signal detected by the acoustic wave transducer array 20 of the probe 11. . The photoacoustic image reconstruction unit 24 adds data from, for example, 64 acoustic wave transducers of the probe 11 with a delay time corresponding to the position of the acoustic wave transducer, and generates data for one line (delay). Addition method). The photoacoustic image reconstruction means 24 may perform reconstruction by the CBP method (Circular Back Projection) instead of the delay addition method. Alternatively, the photoacoustic image reconstruction unit 24 may perform reconstruction using the Hough transform method or the Fourier transform method.

  The detection / logarithm conversion means 27 obtains an envelope of the data of each line, and logarithmically converts the obtained envelope.

  The photoacoustic image construction means 28 constructs a photoacoustic image for one frame based on the data of each line subjected to logarithmic transformation. The photoacoustic image construction means 28 constructs a photoacoustic image by converting, for example, a position in the time axis direction of the photoacoustic signal (peak portion) into a position in the depth direction in the photoacoustic image.

  The observation method selection means 39 is for selecting a display mode of the photoacoustic image. Examples of the volume data display mode for the photoacoustic signal include a mode as a three-dimensional image, a mode as a cross-sectional image, and a mode as a graph on a predetermined axis. The display mode is selected according to the initial setting or the input from the input unit 16 by the user.

  The image synthesizing unit 38 generates volume data using sequentially acquired photoacoustic signals. The volume data is generated by assigning the signal value of each photoacoustic signal to the virtual space according to the coordinates associated with each frame of the photoacoustic image and the pixel coordinates in the photoacoustic image. For example, the coordinates when the Qsw trigger signal is transmitted, the coordinates when light is actually output, the coordinates when sampling of the photoacoustic signal is started, and the like are associated for each frame of the photoacoustic image. When assigning signal values, if the locations to be assigned overlap, for example, the average value of the signal values or the maximum value among them is adopted as the signal value of the overlapping location. Further, if there is no signal value to be assigned, it is preferable to interpolate using the peripheral signal values as necessary. Interpolation is performed, for example, by assigning weighted average values of four adjacent points in order from the closest point to the interpolation location. As a result, more natural volume data can be generated. Further, the image composition unit 38 performs necessary processing (for example, scale correction and coloring according to the voxel value) on the generated volume data.

  In addition, the image composition unit 38 generates a photoacoustic image according to the observation method selected by the observation method selection unit 39. The photoacoustic image generated according to the selected observation method becomes the final image (display image) to be displayed on the image display means 14. In the above-described photoacoustic image generation method, after the photoacoustic image is once generated, the user can naturally rotate or move the image as necessary. In other words, when a three-dimensional image is displayed, the user sequentially designates or moves the viewpoint direction using the input means 16 to recalculate the photoacoustic image and rotate the three-dimensional image. Will do. It is also possible for the user to change the observation method as appropriate using the input means 16.

  The image display means 14 displays the display image generated by the image composition means 38.

  As described above, also in the photoacoustic measurement apparatus according to the present embodiment, the energy profile is flattened by passing laser light (measurement light) once through a homogenizer, and the beam diameter when entering the bundle fiber is set as the condensing member. Is controlled by. As a result, in the photoacoustic measurement, it is possible to eliminate the uneven energy amount of light that transmits high energy light and travels through each of the plurality of optical fibers.

  As a result, since a stronger and more uniform photoacoustic signal can be obtained, a high-quality photoacoustic image can be generated. Further, the laser light transmission cable can be reduced in size and weight, and the operability of the photoacoustic measurement apparatus is improved.

“Second Embodiment of Photoacoustic Measuring Device”
Next, a second embodiment of the photoacoustic measurement apparatus will be described. Also in this embodiment, the case where a photoacoustic measuring device is a photoacoustic image generation apparatus is demonstrated concretely. FIG. 22 is a block diagram illustrating a configuration of the photoacoustic image generation apparatus 10 of the present embodiment. This embodiment is different from the first embodiment in that an ultrasonic image is generated in addition to the photoacoustic image. Therefore, a detailed description of the same components as those in the first embodiment will be omitted unless particularly necessary.

  Similar to the first embodiment, the photoacoustic image generation apparatus 10 of the present embodiment includes a probe 11, an ultrasonic unit 12, a laser unit 13, an image display unit 14, and an input unit 16 according to the present invention.

<Ultrasonic unit>
In addition to the configuration of the photoacoustic image generation apparatus shown in FIG. 21, the ultrasonic unit 12 of the present embodiment includes a transmission control circuit 33, a data separation unit 34, an ultrasonic image reconstruction unit 35, a detection / logarithmic conversion unit 36, And an ultrasonic image constructing means 37. In the present embodiment, the reception circuit 21, AD conversion means 22, reception memory 23, data separation means 34, photoacoustic image reconstruction means 24, detection / logarithmic conversion means 27, photoacoustic image construction means 28, ultrasonic image reconstruction. The means 35, the detection / logarithmic conversion means 36, and the ultrasonic image construction means 37 are integrated and correspond to an acoustic image generation means as a signal processing means in the present invention.

  In the present embodiment, in addition to detecting a photoacoustic signal, the probe 11 performs output (transmission) of ultrasonic waves to the subject and detection (reception) of reflected ultrasonic waves from the subject with respect to the transmitted ultrasonic waves. As the acoustic wave transducer for transmitting and receiving ultrasonic waves, the acoustic wave transducer array 20 described above may be used, or a new acoustic wave transducer array separately provided in the probe 11 for transmitting and receiving ultrasonic waves. May be used. In addition, transmission and reception of ultrasonic waves may be separated. For example, ultrasonic waves may be transmitted from a position different from the probe 11, and reflected ultrasonic waves with respect to the transmitted ultrasonic waves may be received by the probe 11.

  When generating an ultrasonic image, the trigger control circuit 30 sends an ultrasonic transmission trigger signal to the transmission control circuit 33 to instruct ultrasonic transmission. Upon receiving this trigger signal, the transmission control circuit 33 transmits an ultrasonic wave from the probe 11. The probe 11 detects the reflected ultrasonic wave from the subject after transmitting the ultrasonic wave.

  The reflected ultrasonic wave detected by the probe 11 is input to the AD conversion means 22 via the receiving circuit 21. The trigger control circuit 30 sends a sampling trigger signal to the AD conversion means 22 in synchronization with the timing of ultrasonic transmission, and starts sampling of reflected ultrasonic waves. Here, the reflected ultrasonic waves reciprocate between the probe 11 and the ultrasonic reflection position, whereas the photoacoustic signal is one way from the generation position to the probe 11. Since the detection of the reflected ultrasonic wave takes twice as long as the detection of the photoacoustic signal generated at the same depth position, the sampling clock of the AD conversion means 22 is half the time when the photoacoustic signal is sampled, for example, It may be 20 MHz. The AD conversion means 22 stores the reflected ultrasonic sampling signal in the reception memory 23. Either sampling of the photoacoustic signal or sampling of the reflected ultrasonic wave may be performed first.

  The data separator 34 separates the photoacoustic signal sampling signal and the reflected ultrasonic sampling signal stored in the reception memory 23. The data separation unit 34 inputs a sampling signal of the separated photoacoustic signal to the photoacoustic image reconstruction unit 24. The generation of the photoacoustic image is the same as that in the first embodiment. On the other hand, the data separation unit 34 inputs the separated reflected ultrasound sampling signal to the ultrasound image reconstruction unit 35.

  The ultrasonic image reconstruction unit 35 generates data of each line of the ultrasonic image based on the reflected ultrasonic wave (its sampling signal) detected by the plurality of acoustic wave transducers of the probe 11. For the generation of the data of each line, a delay addition method or the like can be used as in the generation of the data of each line in the photoacoustic image reconstruction means 24. The detection / logarithm conversion means 36 obtains the envelope of the data of each line output from the ultrasonic image reconstruction means 35 and logarithmically transforms the obtained envelope.

  The ultrasonic image construction unit 37 generates an ultrasonic image based on the data of each line subjected to logarithmic transformation.

  The image synthesizing unit 38 synthesizes the photoacoustic image and the ultrasonic image. The image composition unit 38 performs image composition by superimposing a photoacoustic image and an ultrasonic image, for example. The synthesized image is displayed on the image display means 14. It is also possible to display the photoacoustic image and the ultrasonic image side by side on the image display means 14 without performing image synthesis, or to switch between the photoacoustic image and the ultrasonic image.

  As described above, also in the photoacoustic measurement apparatus according to the present embodiment, the energy profile is flattened by passing laser light (measurement light) once through a homogenizer, and the beam diameter when entering the bundle fiber is set as the condensing member. Is controlled by. Thereby, there exists an effect similar to 1st Embodiment.

  Furthermore, the photoacoustic measuring device of this embodiment generates an ultrasonic image in addition to the photoacoustic image. Therefore, by referring to the ultrasonic image, a portion that cannot be imaged in the photoacoustic image can be observed.

  In addition, although the case where a photoacoustic measuring device produced | generated a photoacoustic image and an ultrasonographic image was demonstrated above, such image generation is not necessarily required. For example, the photoacoustic measurement device can be configured to measure the presence / absence of a measurement target and a physical quantity based on the magnitude of the photoacoustic signal.

DESCRIPTION OF SYMBOLS 10 Photoacoustic image generation apparatus 11 Acoustic wave detection probe 12 Ultrasonic unit 13 Laser unit 14 Image display means 16 Input means 20 Acoustic wave transducer array 21 Reception circuit 24 Photoacoustic image reconstruction means 28 Photoacoustic image construction means 30 Trigger Control circuit 33 Transmission control circuit 34 Data separation means 35 Ultrasound image reconstruction means 37 Ultrasound image construction means 38 Image composition means 39 Observation method selection means 40 Homogenizer 41 Condensing member 42 Bundle fiber 42a Optical fiber 43 Light guide plate 44 Light guide Unit 53 lens diffusing plate 55 beam expander optical system 60a, 60b holding unit 62 center side region 64 outer side region 65a, 65b, 65c holding unit D having connector structure minimum beam diameter E1 incident end E2 emitting end L Laser beam M Subject U Photoacoustic wave

Claims (15)

A light guide unit that has an incident end and an exit end, guides measurement light from the entrance end to the exit end, and emits the measurement light toward the subject; and within the subject by irradiation of the measurement light A photoacoustic measurement device comprising an acoustic wave detection probe comprising an acoustic wave transducer for detecting a generated photoacoustic wave, and a device housing to which a proximal end of the probe is attached,
The probe has a holding part that holds an incident end of the light guide part,
The device housing has a mounting portion that is detachably connected to the holding portion,
The mounting portion includes a homogenizer that flattenes the energy profile of the measurement light incident on the light guide portion, and a condensing member that condenses the measurement light transmitted through the homogenizer.
The light guide unit held by the holding unit includes a bundle fiber including a plurality of optical fibers through which the measurement light transmitted through the light collecting member is incident from an incident end.
The homogenizer is a lens diffuser plate in which minute lenses are randomly arranged on one side of a substrate, and further diffuses the measurement light,
The condensing member condenses the measurement light so that the minimum beam diameter D of the measurement light defined by the following expression 1 satisfies the following expression 2 in relation to the diameter d of the bundle fiber:
The photoacoustic measurement device, wherein the bundle fiber is arranged so that the measurement light is incident in a state where a beam diameter of the measurement light is 0.8 d or more and 1.2 d or less.
(In Expression 1, f represents the focal length of the light collecting member, φ represents the divergence angle of the measurement light when entering the homogenizer, and θ represents the diffusion angle of the homogenizer.)   In the mounting portion, just before the incident side of the homogenizer, an enlargement factor adapted to the aperture angles of the plurality of optical fibers so as to expand the measurement light to a beam diameter adapted to the aperture angles of the plurality of optical fibers. The photoacoustic measuring device according to claim 1, wherein a beam expander optical system in which is set is attached.   The holding part which hold | maintains the said incident end part so that the incident surface of the said bundle fiber may be covered, Comprising: The holding | maintenance part which has a window part in the part into which the said measurement light injects is provided. Photoacoustic measuring device.   The photoacoustic measuring device according to claim 3, wherein the window portion is configured by an ND filter.   An opening member having an opening for allowing the measurement light incident on the bundle fiber to pass therethrough and provided at an incident end of the bundle fiber, the diameter of the opening corresponding to the diameter of the bundle fiber toward the incident end The photoacoustic measuring device according to any one of claims 1 to 4, further comprising an opening member that decreases to a size.   The holding unit includes a light guide member including a cap member and a ring-shaped chip that is a chip formed of a material resistant to light energy and is fitted in the cap member. The photoacoustic measuring device according to claim 1, wherein:   5. The photoacoustic measurement apparatus according to claim 1, wherein the holding unit includes a light guide member including an aperture and a relay lens system inside the holding unit.   The photoacoustic measuring device according to any one of claims 1 to 7, wherein a fusion processing is applied to an incident end portion of the bundle fiber.   9. The photoacoustic measurement according to claim 1, wherein outer circumferences of the plurality of optical fibers at the incident end are covered with a material having high durability against light energy. apparatus.   The photoacoustic measuring device according to claim 8, wherein the material having high durability against the light energy is quartz.   The light guide unit includes at least one light guide plate having a connection surface to which at least a part of the emission end portions of the plurality of optical fibers are connected, and an emission surface from which the measurement light incident from the connection surface is emitted. The photoacoustic measuring device according to claim 1, wherein the photoacoustic measuring device is provided.   The photoacoustic measuring device according to claim 10, wherein a plurality of the light guide plates are arranged so as to face each other with the acoustic wave vibrator interposed therebetween.   The photoacoustic measuring device according to any one of claims 1 to 12, further comprising: a signal processing unit that processes a photoacoustic signal of a photoacoustic wave detected by the acoustic wave vibrator.   The photoacoustic measurement device according to claim 13, wherein the signal processing means includes acoustic image generation means for generating a photoacoustic image based on the photoacoustic signal. The acoustic wave transducer detects a reflected acoustic wave with respect to an acoustic wave transmitted to the subject,
15. The photoacoustic measurement apparatus according to claim 14, wherein the acoustic image generation unit generates a reflected acoustic wave image based on the reflected acoustic wave signal.