JP2014124242A - Photoacoustic microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoacoustic microscope which can perform high-speed scanning and whose detection accuracy can be improved over a wide range of scan.SOLUTION: A photoacoustic microscope 10 includes an object lens 13, a photo scanning part 12, a photoacoustic wave detecting part 15, and a synthesis part 20. The object lends 13 makes a sample S to be irradiated with an excitation light L. The photo scanning part 12 deflects the excitation light L and makes it scan the sample S along at least a first scanning direction. The photoacoustic wave detecting part 15 has a plurality of detectors. The plurality of detectors are arranged along a first array direction corresponding to the first scanning direction. The detectors detect a photoacoustic wave generated from the sample S by the irradiation with the excitation light L. The synthesis part 20 synthesizes the photoacoustic waves by matching a phase of the photoacoustic wave detected by each detector.

Description

  The present invention relates to a photoacoustic microscope.

  A photoacoustic wave is a type of elastic wave generated in a thermoelastic process that occurs when a substance is irradiated with light in the absorption wavelength range. Therefore, photoacoustic waves are attracting attention as a technique for imaging absorption characteristics. In addition, photoacoustic waves are a kind of ultrasonic waves and have a characteristic that they are less susceptible to scattering than light, and thus are applied as imaging means inside a living body.

  In photoacoustic microscopes that apply photoacoustic waves to imaging as detection signals, pulsed light that matches the absorption wavelength region of the observation object is used as excitation light, and the excitation light is collected by the objective lens and collected in the specimen. A method is used in which scanning is performed by a spot, and thereby a photoacoustic wave generated at each focused spot position is detected by a transducer or the like. According to such a photoacoustic microscope, when a specimen is scanned with a condensing spot, a photoacoustic wave is generated if an absorbing substance is present at the condensing spot position. Therefore, by detecting the photoacoustic wave, absorption within the specimen Characteristics can be imaged.

  As such a photoacoustic microscope, for example, the one disclosed in Patent Document 1 is known. FIG. 13 shows a photoacoustic microscope disclosed in Patent Document 1. In FIG. In FIG. 13, excitation light L from a laser pulse light source (not shown) includes a condensing lens 101, a pinhole 102, a vibrating mirror 103, an objective lens 104, a correction lens 105, an isosceles prism 106, a silicon oil layer 107, and a rhombus prism 108. And it is condensed inside the sample S through the acoustic lens 109. In addition, the photoacoustic wave U generated from the condensing position in the sample S by the irradiation of the excitation light L is collected by the acoustic lens 109, wavefront converted, reflected in the rhomboid prism 108, and detected by the ultrasonic transducer 110. Is done.

  In FIG. 13, an isosceles prism 106 and a rhombus prism 108 are coupled via a silicon oil layer 107. The acoustic lens 109 has a rhombus prism 108 so that the sound axis corresponding to the optical axis of the optical lens coincides with the optical axis of the objective lens 104 and the focal position of the acoustic lens 109 coincides with the focal position of the objective lens 104. It is joined. The ultrasonic transducer 110 is joined to the rhomboid prism 108 so that the wavefront of the photoacoustic wave U from the focal point of the acoustic lens 109 is converted into a plane wave by the acoustic lens 109 and is perpendicularly incident on the detection surface of the ultrasonic transducer 110. Has been. The specimen S is immersed in the liquid.

Special table 2011-519281 gazette

  In the photoacoustic microscope having the configuration shown in FIG. 13, the excitation mirror L irradiated to the specimen S is deflected by vibrating the oscillating mirror 103, and the specimen S is scanned with a condensing spot of the excitation light L. However, when the excitation light L is deflected by the oscillating mirror 103, the photoacoustic wave U generated by the condensed spot irradiated with a deviation from the focal position of the acoustic lens 109 is subjected to wavefront conversion by the acoustic lens 109, and then an ultrasonic transducer. Incidently with respect to the detection surface 110.

  Here, the ultrasonic transducer 110 is set so that the detection sensitivity is highest when a plane wave is incident vertically. Therefore, if the scanning range of the sample S by the vibrating mirror 103 is to be widened, the maximum inclination of the photoacoustic wave U incident on the ultrasonic transducer 110 is increased, and the detection accuracy is lowered. In addition, in place of scanning by the vibrating mirror 103, the excitation light L incident system including the objective lens 104 and the acoustic lens 109 are included so that the photoacoustic wave U from the sample S is always perpendicularly incident on the ultrasonic transducer 110. It is assumed that the photoacoustic wave U detection system and the sample stage on which the sample S is placed are relatively moved. In this case, however, scanning takes time.

  The present invention has been made in view of such a viewpoint, and an object of the present invention is to provide a photoacoustic microscope capable of high-speed scanning and capable of improving detection accuracy over a wide scanning range.

The photoacoustic microscope according to the present invention for achieving the above object is
An objective lens for irradiating the specimen with excitation light;
An optical scanning unit that deflects the excitation light and scans the sample along at least a first scanning direction;
A plurality of detectors for detecting photoacoustic waves generated from the sample by irradiation of the excitation light, wherein the plurality of detectors are arranged along a first arrangement direction corresponding to the first scanning direction; A photoacoustic wave detection unit,
And a synthesizing unit that synthesizes the phases of the photoacoustic waves detected by the respective detectors.

  According to the present invention, it is possible to provide a photoacoustic microscope capable of performing high-speed scanning and improving detection accuracy over a wide scanning range.

It is a schematic diagram which shows schematic structure of the principal part of the photoacoustic microscope which concerns on 1st Embodiment. FIG. 2 is a layout diagram of detectors on a detection surface of the photoacoustic wave detection unit in FIG. 1. It is a functional block diagram which shows roughly the internal structure of the synthetic | combination part of FIG. It is a 1st figure for demonstrating the phase alignment in a synthetic | combination part. It is a 2nd figure for demonstrating the phase alignment in a synthetic | combination part. It is a schematic diagram which shows schematic structure of the principal part of the photoacoustic microscope which concerns on 2nd Embodiment. FIG. 2 is a layout diagram of detectors on a detection surface of the photoacoustic wave detection unit in FIG. 1. It is a figure for demonstrating operation | movement of the drive part of FIG. It is a figure for demonstrating the phase alignment in a synthetic | combination part when detecting a photoacoustic wave as a plane wave. It is a schematic diagram which shows schematic structure of the principal part of the 1st modification of the photoacoustic microscope which concerns on 2nd Embodiment. It is a schematic diagram which shows schematic structure of the principal part of the 2nd modification of the photoacoustic microscope which concerns on 2nd Embodiment. It is a perspective view which shows the shape of the detection surface of the photoacoustic wave detection part in the 3rd modification of the photoacoustic microscope which concerns on 2nd Embodiment. It is a schematic block diagram of the conventional photoacoustic microscope.

  Hereinafter, an embodiment according to an aspect of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram illustrating a configuration of a main part of the photoacoustic microscope according to the first embodiment. The photoacoustic microscope 10 deflects the excitation light L emitted from the pulse light source 11 by the optical scanning unit 12 and irradiates the sample S as a condensed spot through the photoacoustic wave reflection unit 14 by the objective lens 13. The photoacoustic wave U generated from the sample S is reflected by the photoacoustic wave reflection unit 14 in a direction different from the optical path of the excitation light L and detected by the photoacoustic wave detection unit 15.

  For example, when the specimen S is a living body and the blood vessel in the living body is imaged, the pulsed light source 11 emits excitation light L having an absorption wavelength of hemoglobin. Note that the observation target is not limited to blood vessels, and can be applied to imaging of endogenous substances such as melanin. At this time, the excitation light L may be light in the absorption wavelength region of the target substance. It can also be applied to imaging of exogenous substances such as phosphors and metal nanoparticles. In this case, as the excitation light L, light in the absorption wavelength region of the target phosphor in the case of a phosphor is used, and light in the resonance wavelength region of the target metal nanoparticle in the case of a metal nanoparticle. Good. When there are a plurality of absorbers in the sample S, it is desirable to use light having a peak wavelength of the characteristic absorption spectrum of the observation object. In the pulse light source 11, the light emission timing of the pulsed light is controlled by the control unit 21.

  The optical scanning unit 12 includes, for example, two galvanometer mirrors, and performs two-dimensional scanning in the sample S along the first scanning direction and the second scanning direction by the condensed spot of the excitation light L. Drive control is performed in synchronization with the light emission timing of the pulse light source 11 by the control unit 21.

  The objective lens 13 having a different focal length is appropriately selected and mounted.

  The photoacoustic wave reflection unit 14 includes two right triangular prisms 14a and 14b, and their slopes are coupled by a photoacoustic wave reflection member 14c. The photoacoustic wave reflecting member 14c is transparent to the excitation light L, and is made of a member having different acoustic impedance, such as silicon oil or air, for the right triangular prism 14b on the sample S side. Since the difference between the acoustic impedance of the right triangular prism 14b and the acoustic impedance of the photoacoustic wave reflection member 14c satisfies a predetermined relationship, the photoacoustic wave U is reflected by the photoacoustic wave reflection member 14c.

  The excitation light L that has passed through the objective lens 13 and the photoacoustic wave reflection unit 14 is collected at the focal position of the objective lens 13. The specimen S is arranged so as to overlap with the condensing spot of the excitation light L. The photoacoustic wave U generated from the condensing spot position of the excitation light L of the sample S is incident on the right triangular prism 14b. The photoacoustic wave U is reflected at a boundary surface between the right triangular prism 14b and the photoacoustic wave reflecting member 14c in a direction different from the optical path of the excitation light L, and is emitted from the right triangular prism 14b to the photoacoustic wave detecting unit 15. Is done. Note that at least the space between the objective lens 13 and the sample S and between the right triangular prism 14b and the photoacoustic wave detector 15 is filled with a photoacoustic wave transmission medium such as water through which the photoacoustic wave U easily propagates. It is preferable.

  The photoacoustic wave detection unit 15 includes a plurality of detectors 16 including, for example, ultrasonic transducers. As shown in FIG. 2, the detectors 16 are arranged two-dimensionally along a first arrangement direction corresponding to the first scanning direction and a second arrangement direction corresponding to the second scanning direction. Be placed. Each detector 16 detects the photoacoustic wave U emitted from the right triangular prism 14b.

  As shown in FIG. 3, the synthesizer 20 includes a delay device 20a, an integrator 20b, and a peak detector 20c. The delay device 20a delays each phase so that the phases of the photoacoustic waves U detected by the detectors 16 arranged along the first arrangement direction and the second arrangement direction match. Note that the phase matching of the photoacoustic wave U can be performed not only by a configuration in which each phase is delayed using the delay device 20a but also by a configuration in which a relatively slow phase is advanced. The accumulator 20b integrates, that is, synthesizes the photoacoustic waves U output from the total delay device 20a. The peak detector 20c detects and outputs the peak value of the photoacoustic wave U synthesized by the integrator 20b as an output signal.

  The control unit 21 controls the overall operation of the photoacoustic microscope 10. A storage unit 22 is connected to the control unit 21. In the storage unit 22, the amount of delay in each delay unit 20 a associated with the position of the condensed spot of the excitation light L is stored in a database so that the phase of the photoacoustic wave U detected by each detector 16 is matched. Is done. The relationship of the delay amount associated with the position of the focused spot is calculated and stored in advance for each focal length of the objective lens that can be attached to the photoacoustic microscope. The control unit 21 reads the relationship of the delay amount corresponding to the position of the focused spot corresponding to the focal length of the mounted objective lens 13 from the storage unit 22, and the combining unit 20 is excited by the optical scanning unit 12. Control is performed in synchronization with L scanning. The storage unit 22 stores an operation program or the like by the control unit 21 as necessary. Note that the storage unit 22 may be a built-in memory of the control unit 21.

  A signal processing unit 23 is connected to the control unit 21. The signal processing unit 23 is synchronized with the driving of the optical scanning unit 12 by the control unit 21, that is, the irradiation timing of the excitation light L when the sample S is two-dimensionally scanned in a plane orthogonal to the optical axis O of the objective lens 13. The correspondence relationship between the irradiation position of the excitation light L and the output signal is converted into data based on the output signal obtained from the synthesizing unit 20 in synchronization with the above. For example, the irradiation position of the excitation light L may be associated with the acquired signal intensity, or the irradiation position of the excitation light L may be associated with the acquired output waveform. Further, when the data of the scanning surface of the specimen S is imaged, it is imaged by the signal processing unit 23 and is stored in the image storage unit and displayed on the monitor, for example, although not shown. The signal processing unit 23 may be incorporated in the control unit 21.

  According to the photoacoustic microscope according to the first embodiment, each detector 16 detects the photoacoustic wave U from the specimen S, and a different phase is adjusted for each detector 16 and synthesized.

  For example, at the drive position of the optical scanning unit 12 where the condensing spot of the excitation light L is formed on the optical axis O, as shown in FIG. 4, the photoacoustic wave U having a curved wavefront is perpendicular to the detection surface 15a. The light enters the detector 16 from any direction. In the case of the photoacoustic wave U having such a wavefront, the phase of the photoacoustic wave U detected by the detector 16 is delayed toward the end with the center near the apex (see reference sign “A1”). Therefore, the phase of the photoacoustic wave U output from all the delay devices 20a is matched by delaying the phase by a larger delay amount toward the center (see reference numeral “B1”). By integrating the photoacoustic waves U in phase with each other, an output signal having a large peak is generated (see reference sign “C1”).

  Further, at the drive position of the optical scanning unit 12 where the condensing spot of the excitation light L is formed apart from the optical axis O of the objective lens 13, as shown in FIG. 5, a photoacoustic wave having a curved wavefront. U enters the detector 16 from a direction inclined with respect to the direction perpendicular to the detection surface 15a. In the case of a photoacoustic wave having such a wavefront, the phase of the photoacoustic wave U detected by the detector 16 shifts from the center to one end (lower side in FIG. 5) as the vertex, There is a delay (see symbol “A2”). Therefore, the phase of the photoacoustic wave U output from all the delay devices 20a is matched by delaying the phase by a larger delay amount depending on the vertex position (see reference sign “B2”). By integrating the photoacoustic waves U in phase with each other, an output signal having a large peak is generated (see reference sign “C2”).

  Therefore, according to the photoacoustic microscope according to the first embodiment, it is possible to improve the detection accuracy of the photoacoustic wave U from the sample S over a wide scanning range of the sample S. Further, since the sample S is scanned by deflecting the excitation light L by the optical scanning unit 12, high-speed scanning is possible. In addition, since the relationship between the focal spot and the delay amount corresponding to the focal length of the mountable objective lens is stored in the storage unit 22, it is possible to easily cope with the use of objective lenses having various focal lengths. It becomes. Further, it is possible to generate an output signal having a large signal intensity without using an acoustic lens.

(Second Embodiment)
Next, a second embodiment will be described. The second embodiment is different from the first embodiment in that an acoustic lens and a drive unit are provided, the configuration and function of the photoacoustic wave detection unit, and the function of the control unit. The second embodiment will be described below with a focus on differences from the first embodiment. In addition, the same code | symbol is attached | subjected to the site | part which has the same structure as 1st Embodiment.

  As shown in FIG. 6, the photoacoustic microscope 100 of the present embodiment is configured to further include an acoustic lens 170 and a driving unit 180 in the photoacoustic microscope 10 of the first embodiment.

  The acoustic lens 170 is disposed so as to be joined to the exit surface of the excitation light L of the right triangular prism 14b so that the sound axis A corresponding to the optical axis of the optical lens is coaxial with the optical axis O of the objective lens 13. The focal position of the acoustic lens 170 substantially coincides with the focal position of the objective lens 13. Thereby, the photoacoustic wave U generated from the condensing spot position of the excitation light L of the sample S is converted into a plane wave by the acoustic lens 170 and is incident on the right triangular prism 14b.

  The photoacoustic wave detection unit 150 is arranged to be joined to the emission surface of the photoacoustic wave U of the right triangular prism 14b so that the sound axis A of the acoustic lens 170 and the detection surface 150a are orthogonal to each other. In the photoacoustic wave detection unit 150, unlike the first embodiment, as shown in FIG. 7, detectors 160 are arranged so as to be arranged only along the first arrangement direction.

  The drive unit 180 includes, for example, a piezo actuator or a stepping motor. The drive unit 180 integrally displaces the photoacoustic wave reflection unit 14, the photoacoustic wave detection unit 150, and the acoustic lens 170 along the second scanning direction based on a control amount acquired from the control unit 210. .

  The control unit 210 controls the overall operation of the photoacoustic microscope 100. The storage unit 22 is connected to the control unit 210. In the storage unit 22, the control amount of the driving unit 180 synchronized with the scanning of the excitation light L by the optical scanning unit 12, that is, the photoacoustic wave reflection unit, corresponding to the focal length of the objective lens that can be attached to the photoacoustic microscope 100. 14, the displacement amounts of the photoacoustic wave detection unit 150 and the acoustic lens 170 are stored in a database. Then, the control unit 210 reads a control amount (displacement amount) corresponding to the focal length of the mounted objective lens 13 from the storage unit 22, and synchronizes the driving unit 180 with the scanning of the excitation light L by the optical scanning unit 12. Control.

  According to the photoacoustic microscope according to the second embodiment, as in the first embodiment, each detector 160 detects the photoacoustic wave U from the sample S, and the detection is arranged along the first arrangement direction. Different phases are adjusted for each unit 160 and synthesized. In the second embodiment, since the acoustic lens 170 is provided, the photoacoustic wave U is incident on the photoacoustic wave detection unit 150 as a plane wave, but the plane wave is also the same as in the first embodiment. The phase of the photoacoustic wave is adjusted.

  In addition, according to the photoacoustic microscope according to the second embodiment, the plane wave viewed from the first scanning direction of the photoacoustic wave U from the sample S is synchronized with the scanning of the excitation light L by the optical scanning unit 12. The photoacoustic wave reflection unit 14, the photoacoustic wave detection unit 150, and the acoustic lens 170 are moved along the second scanning direction by the driving unit 180 so as to be perpendicularly incident on the detection surface 150 a of the photoacoustic wave detection unit 150. Moved together. That is, at the driving position of the optical scanning unit 12 where the condensing spot of the excitation light L is formed on the optical axis O of the objective lens 13, the focal position of the acoustic lens 170 is excited as shown in FIG. It is controlled so as to coincide with the condensing spot position of the light L. Further, at the driving position of the optical scanning unit 12 where the condensing spot of the excitation light L is formed away from the optical axis O of the objective lens 13, the focal position of the acoustic lens 170 is as shown in FIG. Control is performed so as to coincide with the condensing spot position of the excitation light L separated from the optical axis O. That is, in the second embodiment, the acoustic lens 170 is synchronized with the scanning position of the excitation light L by the optical scanning unit 12 so that the focal position of the acoustic lens 170 coincides with the condensed spot position of the excitation light L. Are moved in the second scanning direction by the drive unit 180 together with the photoacoustic wave reflection unit 14 and the photoacoustic wave detection unit 150.

  Therefore, also in the photoacoustic microscope according to the present embodiment, the same effect as the photoacoustic microscope according to the first embodiment can be obtained.

  Although the present invention has been described based on the drawings and embodiments, it should be noted that those skilled in the art can easily make various changes and modifications based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention.

  For example, in the first embodiment, the acoustic lens 170 may be provided as in the second embodiment. By providing the acoustic lens 170, the curved photoacoustic wave U can be converted into a plane wave and detected by the detector 16. By converting to a plane wave, as shown in FIG. 9, the delay amount is linearized and reduced, so that the detection accuracy of the photoacoustic wave detection unit 15 can be improved.

  In the second embodiment, the configuration in which the plane wave viewed from the first scanning direction of the photoacoustic wave U from the sample S is incident on the detection surface 150a of the photoacoustic wave detection unit 150 perpendicularly is based on the driving unit 180. The displacement of the photoacoustic wave reflection unit 14, the photoacoustic wave detection unit 150, and the acoustic lens 170 is not limited.

  For example, as illustrated in FIG. 10, the driving unit 181 drives the photoacoustic wave detection unit 150, and the photoacoustic wave U is sent to the photoacoustic wave detection unit 150 in synchronization with the scanning of the excitation light L by the optical scanning unit 12. May be controlled based on the control amount from the control unit 21 so that the inclination of the detection surface 150a of the photoacoustic wave detection unit 150 with respect to the sound axis A of the acoustic lens 170 is controlled.

  Alternatively, as shown in FIG. 11, the acoustic lens 170 is movably joined to the exit surface of the photoacoustic wave U of the right triangular prism 14b, and is driven in the exit surface, that is, in a plane orthogonal to the sound axis A. The movement may be performed by the unit 182 based on the control amount from the control unit 21.

  In the second embodiment, the optical scanning unit includes, for example, one galvanometer mirror, and the main scanning of the condensed spot along the first scanning direction is performed by the galvanometer mirror. May be configured to be performed by moving the sample stage on which is mounted. In this case, the drive unit can omit the displacement control corresponding to the sub-scanning direction. In such a configuration, the acoustic lens 170 may be omitted. However, when the acoustic lens 170 is omitted, in order to detect the curved photoacoustic wave U with high accuracy in the second arrangement direction, the detector 160 is arranged along the curve as viewed from the first arrangement direction, The surface on which the detector 160 is disposed is preferably a curved surface (see FIG. 12).

  In the second embodiment, the photoacoustic wave detection unit 150 is similarly disposed away from the photoacoustic wave reflection unit 14, and the photoacoustic wave reflection unit 14 and the acoustic lens 170 are moved together by the driving unit 180. The structure to be made may be sufficient.

  In the first and second embodiments, the relationship between the position of the focused spot and the delay amount and the control amount of the drive unit 180 are not necessarily stored in the storage unit 22 as a database. Alternatively, the synthesizing unit 20 and the driving unit 180 can be controlled based on the output of a software function generation circuit or the like. Therefore, in the present invention, the storage unit is not necessarily an essential configuration.

DESCRIPTION OF SYMBOLS 10,100 Photoacoustic microscope 11 Pulse light source 12 Optical scanning part 13 Objective lens 14 Photoacoustic wave reflection part 14a, 14b Right-angled triangular prism 14c Photoacoustic wave reflection member 15,150 Photoacoustic wave detection part 15a, 150a Detection surface 16,160 Detector 170 Acoustic lens 180, 181, 182 Drive unit 20 Combining unit 20a Delay unit 20b Accumulator 20c Peak detector 21, 210 Control unit 22 Storage unit 23 Signal processing unit A Sound axis L Excitation light O Optical axis U Photoacoustic wave S specimen

Claims (6)

An objective lens for irradiating the specimen with excitation light;
An optical scanning unit that deflects the excitation light and scans the sample along at least a first scanning direction;
A plurality of detectors for detecting photoacoustic waves generated from the sample by irradiation of the excitation light, wherein the plurality of detectors are arranged along a first arrangement direction corresponding to the first scanning direction; A photoacoustic wave detection unit,
A photoacoustic microscope comprising: a synthesizing unit that synthesizes the phase of photoacoustic waves detected by each of the detectors.   The photoacoustic microscope according to claim 1, wherein a surface of the photoacoustic wave detection unit on which the detector is disposed has a curved surface. The photoacoustic microscope according to claim 1 or 2,
The objective lens can be mounted with different focal lengths,
The synthesizing unit adjusts the phase of the photoacoustic wave based on the focal length. The photoacoustic microscope according to any one of claims 1 to 3,
An acoustic lens that converts a wavefront of a photoacoustic wave generated from the sample by irradiation of the excitation light, further comprising:
The detector detects a photoacoustic wave whose wavefront has been converted by the acoustic lens. The photoacoustic microscope according to claim 4,
A drive unit that displaces at least one of the acoustic lens and the photoacoustic wave detection unit;
The photoacoustic wave detection is performed in synchronization with scanning of the excitation light along the second scanning direction by the optical scanning unit that deflects the excitation light in a second scanning direction different from the first scanning direction. The photoacoustic microscope further comprising: a control unit that controls the driving unit so that the photoacoustic wave is vertically incident on the unit. The photoacoustic microscope according to any one of claims 1 to 4,
The optical scanning unit deflects the excitation light so as to scan in a second scanning direction different from the first scanning direction;
A plurality of the detectors are arranged in the photoacoustic wave detection unit along a second arrangement direction corresponding to the second scanning direction.

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