Photoacoustic imager and photoacoustic imaging method

Abstract

To provide a photoacoustic imaging apparatus and a photoacoustic imaging method capable of generating a simple and highly reproducible three dimensional photoacoustic image of a surface layer peripheral blood vessel for the entire foot of a subject.SOLUTION: A light source probe unit is provided so as to be movable along a two dimensional coordinate system in which a longitudinal direction and a vertical direction of an apparatus main body are axes orthogonal to each other in a tank of the apparatus main body, and the light source probe unit is driven and controlled so as to slide along outer surfaces of a sole side and a back side of a foot of a subject in a non-contact manner with reference to a height position of a limb end holding portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a photoacoustic imaging technique for detecting and imaging photoacoustic waves generated from a light absorber within an object by irradiating the object with light. [Background technology]

[0002] In recent years, as photoacoustic imaging technology and photoacoustic tomography technology, a photoacoustic imaging device has been proposed that includes an LED light source unit that irradiates a subject with pulsed light and an ultrasound detector that detects acoustic waves as ultrasound waves generated by an object within the subject (see Reference 1).

[0003] This photoacoustic imaging device irradiates a target object such as a blood vessel with light, and measures the shape of the target object in a non-contact manner with image-level resolution using ultrasonic waves emitted by the excited target object.

[0004] In recent years, there has been a demand for such photoacoustic imaging devices to be used in the diagnosis of peripheral vascular diseases such as diabetic foot disease. For example, a photoacoustic imaging device has been proposed that uses at least one of the extremity tip and the body protrusion of a subject as a test site, irradiates the test site with light, and analyzes the detected signal of the photoacoustic wave obtained to obtain a photoacoustic image that visualizes the sound pressure distribution of the test site or the distribution of information derived from the sound pressure distribution (see Cited Document 2).

[0005] In this photoacoustic imaging device, the sensor unit, which is capable of irradiating pulsed light and receiving photoacoustic waves, has a detection space equipped with an insertion port for inserting the tip of a limb or a protruding part of the body as the test area, and is positioned at an inclination angle so that this insertion port is located on the upper side, allowing images to be displayed in a manner that is convenient for the diagnostician, test subject, etc.

[0006] Also, a photoacoustic device has been proposed that includes a light irradiation unit that irradiates light onto an object, a probe that receives acoustic waves generated from the object as a result of the light irradiation, a first movement mechanism that moves the probe relative to the object, and a second movement mechanism that moves the light irradiation position relative to the object, and that switches between a first control that moves the light irradiation position on the object surface and the probe so as to track each other, and a second control that fixes the light irradiation position on the object surface and moves the probe (see Reference 3).

[0007] In this photoacoustic device, when the area on the subject that can be irradiated with light at a predetermined intensity or higher completely encompasses the area on the subject that corresponds to the imaging area, imaging is performed with the light irradiation position fixed (second control), and otherwise imaging is performed while the light irradiation position and the probe are made to track each other (first control), thereby enabling imaging over a wide area and obtaining stable signals. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-29550 [Patent Document 2] Japanese Patent Application Publication No. 2018-15262 [Patent Document 3] Japanese Patent Application Publication No. 2019-195583 Summary of the Invention [Problem to be solved by the invention]

[0009] Generally, when using a photoacoustic imaging apparatus, an examiner holds the light source-integrated probe in his or her hand and brings it into contact with a target region of a subject to perform a scan.

[0010] Therefore, when using a photoacoustic imaging device to diagnose peripheral vascular diseases such as diabetic foot lesions, the examiner must hold the light source-integrated probe in his or her hand and trace it evenly over the entire foot of the subject, which forces both the examiner and the subject into an awkward posture, and there was a need for practical convenience.

[0011] In fact, in photoacoustic imaging, a high level of technical skill is required for an examiner to use a light source-integrated probe to uniformly scan the underside of the toes, the heel, and the top of the foot of a subject. In particular, it is extremely difficult to manually scan areas that are not flat, such as the fingertips.

[0012] Although both of the above-mentioned cited documents 2 and 3 have a configuration in which the light source-integrated probe is movable relative to the device body, they only change the insertion angle of the extremity tip and body protrusion as the test area (cited document 2), or control the movement of the light irradiation unit based on the positional relationship between the imaging area and the light irradiation intensity area (cited document 3), and there was a problem in that this level of movement was far from being enough to evenly scan the entire foot of the subject.

[0013] The present invention has been made in consideration of the above points, and aims to propose a photoacoustic imaging device and a photoacoustic imaging method that are capable of generating simple and highly reproducible three-dimensional photoacoustic images of superficial peripheral blood vessels for the entire foot of a subject. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides a photoacoustic imaging device that detects photoacoustic waves generated from an optical absorber in a subject and images the optical absorber based on the photoacoustic waves, the device comprising: a device main body having a tank-like structure for immersing the extremity of the subject in a liquid; an extremity holder that is provided in the device main body and holds the extremity of the subject in the tank of the device main body; a light source probe unit that is provided to be movable within the tank of the device main body along a two-dimensional coordinate system in which the longitudinal direction and vertical direction of the device main body are axes that are orthogonal to each other, and that integrally includes a light irradiator that irradiates pulsed light of a wavelength that is absorbed inside the subject, and a photoacoustic wave detector that detects the photoacoustic waves generated from the optical absorber; As a standard, the system is provided with a path setting unit that sets scanning paths in a two-dimensional coordinate system on the back and back sides of the subject's extremity, a distance measurement unit that is attached to the light source probe unit and measures the proximity distance from an object facing the detection port of the acoustic wave detection unit, and a unit control unit that controls the light irradiation unit and photoacoustic wave detection unit of the light source probe unit while sliding the light source probe unit non-contactingly along the outer surface of the subject's extremity in accordance with the scanning paths on the back and back sides of the subject's extremity set by the path setting unit so that the proximity distance measured by the distance measurement unit maintains a predetermined distance approximately evenly relative to the outer surface of the subject's extremity.

[0015] As a result, the photoacoustic imaging device eliminates the cumbersome manual process required by conventional methods; the subject simply places the extremity into the tank in the device's main body, and the entire extremity is automatically scanned according to its shape.Since the device is non-contact, pressure on the skin of the extremity is avoided, and highly reproducible 3D photoacoustic images of peripheral blood vessels can be generated in a consistently uniform state.

[0016] In addition, in the present invention, the unit control section controls the orientation of the light source probe unit so that the incident angle of the light irradiation section in the light source probe unit is kept perpendicular to the sliding direction when the light source probe unit is slid.

[0017] As a result, the photoacoustic imaging device can stably generate three-dimensional photoacoustic images of peripheral blood vessels, even for three-dimensional shapes such as the extremity of a subject, by always irradiating light at a perpendicular angle to the extremity of the subject.

[0018] Furthermore, the present invention includes an image generation unit that generates an image based on the photoacoustic wave detected by the photoacoustic wave detection unit, and an image evaluation unit that evaluates the clarity of the image generated by the image generation unit for each scan path, and the unit control unit is configured to slide the light source probe unit again along the corresponding scan path if the clarity of the image evaluated by the image evaluation unit is below a predetermined level.

[0019] In this way, in the photoacoustic imaging device, if slight vibrations such as tremors or convulsions occur in the subject's extremity when the light source probe unit is slid, causing the image of the extremity to become unclear, the device can be automatically scanned again, making it possible to stably generate a three-dimensional photoacoustic image of the peripheral blood vessels, even for a three-dimensional shape such as the extremity.

[0020] Furthermore, in the present invention, the image evaluation unit evaluates the clarity of the shape and state of the peripheral blood vessels inside the skin and body tissue at the extremities of the subject for each scan path from the images generated by the image generation unit.

[0021] As a result, the photoacoustic imaging device evaluates images obtained without contact and without applying pressure to the skin of the subject's extremities, making it possible to generate three-dimensional photoacoustic images of peripheral blood vessels that are always uniform and highly reproducible.

[0022] Furthermore, in the present invention, in a photoacoustic imaging method for detecting photoacoustic waves generated from an optical absorber in a subject and imaging the optical absorber based on the photoacoustic waves, an apparatus main body having a tank-like structure for immersing the subject's extremity in a liquid is provided with an extremity holder for holding the extremity of the subject in the tank of the apparatus main body, and a light source probe unit integrally comprising a light irradiator for irradiating pulsed light of a wavelength absorbed inside the subject and a photoacoustic wave detector for detecting photoacoustic waves generated from the optical absorber is provided so as to be movable within a two-dimensional coordinate system in which the longitudinal and vertical directions of the apparatus main body are axes orthogonal to each other within the tank of the apparatus main body, and the extremity of the subject is imaged based on the extremity holder. The method includes a first step of setting scan paths in a two-dimensional coordinate system on the back and back sides of the subject's extremity, a second step of measuring the proximity distance from an object attached to the light source probe unit and facing the detection port of the acoustic wave detection unit, and a third step of controlling the light irradiation unit and photoacoustic wave detection unit of the light source probe unit while sliding the light source probe unit non-contactingly along the outer surface of the subject's extremity so that the proximity distance measured in the second step maintains a predetermined distance approximately uniformly relative to the outer surface of the subject's extremity, according to the scan paths on the back and back sides of the subject's extremity set in the first step.

[0023] As a result, the photoacoustic imaging method eliminates the cumbersome manual process required by the conventional method; the subject simply places the extremity into the tank of the device's main body, and the entire extremity is automatically scanned according to its shape.Since the method is non-contact, pressure on the skin of the extremity is avoided, and highly reproducible 3D photoacoustic images of peripheral blood vessels can be generated in a consistently uniform state. [Effects of the Invention]

[0024] According to the present invention, a photoacoustic imaging device and a photoacoustic imaging method can be realized that can generate simple and highly reproducible three-dimensional photoacoustic images of superficial peripheral blood vessels for the entire foot of a subject. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is an external perspective view showing the configuration of a photoacoustic imager according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a detailed configuration of the 3D automatic scanning device shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the 3D automatic scanning device shown in FIG. 2. [Figure 4] FIG. 1 is a conceptual diagram illustrating the elemental configuration of a 3D automatic scanning device. [Figure 5] FIG. 2 is a conceptual diagram showing a detailed configuration of a light source probe unit. [Figure 6] 1 is a block diagram showing an internal configuration of a signal processing device according to an embodiment of the present invention; [Figure 7] FIG. 1 is a conceptual diagram of a 3D automatic scanning device used to explain scanning the entire foot of a subject. DETAILED DESCRIPTION OF THE INVENTION

[0026] An embodiment of the present invention will be described in detail below with reference to the drawings.

[0027] (1) Configuration of the photoacoustic imager according to this embodiment 1 is a schematic external view of a photoacoustic imager 1 according to this embodiment. This photoacoustic imager 1 has a configuration in which a 3D automatic scanning device 2 that detects photoacoustic waves generated from optical absorbers inside the foot while automatically scanning the entire foot of a subject, and a signal processing device 3 that images the optical absorbers based on the photoacoustic waves detected by the 3D automatic scanning device are connected via a cable (not shown).

[0028] The 3D automatic scanning device 2 has an apparatus main body 10 consisting of a tank-like structure filled with liquid (water, gel, etc.) up to the ankle area of ​​the subject, in which the subject's foot is immersed. The apparatus main body 10 has an extremity holder 11 (Fig. 3) at a predetermined height from the bottom of the tank of the apparatus main body 10, which is adapted to support the subject's foot by abutting against the plantar arch of the subject.

[0029] The 3D automatic scanning device 2 also has a light source probe unit 12 (Figure 5) that is freely movable within the tank of the device main body 10 along a two-dimensional coordinate system in which the longitudinal and vertical directions of the device main body 10 are mutually perpendicular axes.

[0030] In addition, an image display unit 13 such as an LCD monitor for displaying images is connected to the signal processing device 3, and a photoacoustic image generated based on the photoacoustic waves (photoacoustic waves) detected by the light source probe unit 12 can be displayed on the image display unit 13.

[0031] (2) Detailed configuration of the 3D automatic scanning device In the 3D automatic scanning device 2, the device main body 10 is composed of a foot tank section 20, which is a tank-shaped structure consisting of an approximately rectangular parallelepiped structure large enough to allow the subject's foot to be inserted up to the ankle with sufficient room to move, as shown in Figure 2, and a lid-shaped opening frame 21 for holding the extremity holding section 11 (Figure 3) so as to surround the opening of the foot tank section 20.

[0032] In addition, in Figure 3, which shows a cross section of the 3D automatic scanning device 2 shown in Figure 2 taken along arrow A-A', the extremity holding unit 11 is located at a predetermined height from the bottom of the foot bath unit 20 that forms the device main body unit 10, and is configured to abut against the plantar arch of the subject, thereby supporting the subject's foot.

[0033] This extremity holding section 11 is configured to be movable up and down so that it can be fixed in two positions: at a predetermined height position in the foot bath section 20 (hereinafter referred to as the "first position") and at the bottom position of the foot bath section 20 (hereinafter referred to as the "second position"), with the opening position in the foot bath section 20 of the device main body section 10 as the starting position.

[0034] Specifically, this limb holding portion 11 is engaged with two protrusions 21A, 21B that stand up from predetermined positions on the lid-shaped opening frame 21, and is designed to engage with a locking mechanism (not shown) against the direction of gravity in stages at each predetermined position (the above-mentioned starting position, first and second positions).

[0035] An ankle holder 22 is attached to this extremity holder 11 to hold the subject's ankle from the back side, and is configured to be able to move up and down integrally with the extremity holder 11 between a first position and a second position.

[0036] As shown in Figure 4, in the 3D automatic scanning device 2, a pair of slide rails 30A, 30B are built into the lid-shaped opening frame 21 of the device main body 10, along the longitudinal direction of the opening portion of the foot bath section 20.

[0037] The upper ends of support frames 31A, 31B, each having a length from the bottom surface of the foot bath section 20 to the opening, are engaged with the pair of slide rails 30A, 30B so as to be freely slidable along the longitudinal direction of the foot bath section 20.

[0038] A slide driving unit 40 is provided at the upper ends of these support frames 31A, 31B, and causes them to slide along the corresponding slide rails 30A, 30B while maintaining a perpendicular relationship to each of the slide rails 30A, 30B. That is, the slide driving unit 40 has a driving actuator (not shown), and converts the rotational motion of a ball screw (not shown) engaged with the output shaft of the driving actuator into linear motion of the support frames, causing the support frames 31A, 31B to slide along the slide rails 30A, 30B.

[0039] Elevation drive units 41 are provided at both ends of the light source probe unit 12, respectively, to move the light source probe unit 12 up and down relative to the corresponding support frames 31A, 31B along the longitudinal direction of the support frames 31A, 31B. That is, the elevation drive units 41 have a drive actuator (not shown), and move the light source probe unit 12 up and down along the longitudinal direction of the support frames 31A, 31B while converting the rotational motion of a ball screw (not shown) engaged with the output shaft of the drive actuator into linear motion of the light source probe unit 12.

[0040] This light source probe unit 12 has a structure (Figure 5) in which the light irradiation section and the photoacoustic wave detection section, which are generally cylindrical in shape, are integrated, and has an elevation drive section 41 at each end, and a built-in rotation drive section 42 that can rotate the light source probe unit 12 itself via a transmission mechanism (not shown) around a longitudinal axis that includes both ends.

[0041] In this way, the light source probe unit 12 can move freely within the foot bath section 20 of the device main body 10 along a two-dimensional coordinate system in which the longitudinal and vertical directions of the foot bath section 20 are perpendicular to each other.

[0042] When examining the subject's feet using the 3D automatic scanning device 2, the foot tank section 20 of the device main body 10 is filled with liquid (water or gel) up to a height near the subject's ankles.

[0043] (3) Detailed explanation of the light source probe unit 5, the light source probe unit 12 is provided with an integrated light irradiator 50 that irradiates pulsed light of a wavelength that is absorbed inside the subject, and a photoacoustic wave detector 51 that detects photoacoustic waves generated from a light absorber. In this embodiment, the light source probe unit 12 is configured so that the pair of light irradiators 50 sandwich the photoacoustic wave detector 51, and is capable of performing inspection in either the forward or reverse scan direction.

[0044] As described above, the lifting / lowering drive unit 41 and the rotation drive unit 42 are provided at both ends of the light source probe unit 12 via transmission mechanisms (not shown).

[0045] As described above, this light source probe unit 12 is rotatable around the axis connecting both ends, and the irradiation port of the light irradiation unit 50 and the detection port of the photoacoustic wave detection unit 51 are formed along the longitudinal direction (axial direction) with a length approximately the width of a human foot.

[0046] The light irradiation unit 50 has a plurality of light-emitting diode elements (not shown) connected in series and arranged in the longitudinal direction (axial direction). The light irradiation unit 50 emits pulsed light having a wavelength in the infrared range (for example, a wavelength of about 850 [nm]) from the plurality of light-emitting diode elements in response to a current supplied from a light source driving unit 52 (FIG. 6), and irradiates the subject with each pulsed light.

[0047] Furthermore, by setting the wavelength of the pulsed light in advance depending on the type of object in the subject (light absorbers such as hemoglobin, blood vessels, nerve tissue, tumors, etc.), it is possible to image only the desired object.

[0048] The pulsed light irradiated onto the subject from the light irradiator 50 of the light source probe unit 12 is absorbed by an object (light absorber) within the subject. The object expands and contracts (returns from the expanded size to its original size) according to the irradiation intensity (absorption amount) of the pulsed light, generating a photoacoustic wave from the object.

[0049] In this way, in the light source probe unit 12, when the light irradiating unit 50 irradiates a target object (blood vessels, nerve tissue, tumor, etc.) of the subject with light, specific molecules in the body are excited by the light absorption by the target, and heat is generated when the excited state returns to a steady state. The photoacoustic wave detecting unit 51 detects photoacoustic waves (photoacoustic waves) of molecules generated by the temperature difference (thermal expansion) in the surrounding area.

[0050] (4) Internal configuration of the signal processing device 6 shows the internal configuration of the signal processing device 3 in the photoacoustic imager 1. The signal processing device 3 has a unit control unit 60 that controls the entire photoacoustic imager 1, a storage unit 61 that reads and writes various data under the control of the unit control unit 60, an image generation unit 62 that generates a photoacoustic image based on the photoacoustic ultrasound (photoacoustic wave) detected by the light source probe unit 12, and an image evaluation unit 63 that evaluates the clarity of the image generated by the image generation unit for each scan path. The unit control unit 60 is mainly configured using a microcomputer consisting of an MCM (Multi-Chip Module) equipped with a CPU (Central Processing Unit), memory, etc.

[0051] The unit control section 60 is configured to drive and control the light irradiation by sending a trigger signal to the light source driving section 52. The light source driving section 52 generates a direct current from power supplied from an external power source (not shown), and switches on or off a switch, for example, made of a field effect transistor (FET), based on a pulsed trigger signal from the unit control section 60, thereby causing each of the plurality of light emitting diode elements to emit pulsed light of a predetermined width and frequency.

[0052] In addition, the unit control unit 60 sends a sampling trigger signal to the image generation unit 62 to generate an image (a tomographic image based on acoustic waves) of a resolution corresponding to the object in real time, and displays the image on the image display unit 13, which consists of a liquid crystal panel or the like connected to the signal processing device 3.

[0053] Furthermore, the unit control unit 60 functions as a path setting unit that sets scan paths in a two-dimensional coordinate system on the back and back sides of the extremity of the subject, with the extremity holder 11 as the reference.

[0054] That is, the unit control unit 60 (path setting unit) sets scanning paths for the light source probe unit 12 to slide non-contact, using the height position (the first and second positions described above) of the extremity holding unit 11 as a reference, while maintaining a predetermined proximity distance from the outer surface of the sole and back of the subject's foot, and while taking that proximity distance into consideration, so as to cover almost evenly along the outer surface of the sole and back of the foot.

[0055] This scanning path is set as a path in a two-dimensional coordinate system within the foot bath section 20 of the device main body section 10 in the 3D automatic scanning device 2, with the longitudinal and vertical directions of the foot bath section 20 as mutually perpendicular axes.

[0056] Here, the light source probe unit 12 is provided with a distance measurement unit 70 that measures the proximity distance from an object facing the irradiation port of the light irradiation unit 50 and the detection port of the photoacoustic wave detection unit 51. This distance measurement unit 70 is made up of, for example, a TOF (Time of Flight) sensor. The TOF sensor utilizes the principle that the round-trip distance between the sensor and the object can be determined by multiplying the time it takes for pulsed projected laser light to be reflected on the surface of the object and received (i.e., the delay time between the projected pulse and the received pulse) by the speed of light (approximately 300,000 km / sec).

[0057] The unit control unit 60 then adjusts the height position of the light source probe unit 12 so that the proximity distance measured by the distance measurement unit 70 maintains a predetermined distance approximately evenly relative to the outer surface of the subject's foot according to the set scanning path on the back and back sides of the subject's foot, and at the same time controls the drive of the light source probe unit 12 so that it slides non-contact along the outer surface of the subject's foot.

[0058] Specifically, the unit control unit 60 drives and controls the slide drive unit 40 to slide the pair of support frames 31A, 31B along the corresponding slide rails 30A, 30B in the longitudinal direction of the foot bath section 20, and drives and controls the lift drive unit 41 to lift and lower the light source probe unit 12 vertically relative to the pair of support frames 31A, 31B.

[0059] In this way, the light source probe unit 12 can be freely moved within the foot tank section 20 of the device main body section 10 in the 3D automatic scanning device 2 along a two-dimensional coordinate system in which the longitudinal and vertical directions of the foot tank section 20 are mutually perpendicular axes, in accordance with the control of the unit control section 60 in the signal processing device 3.

[0060] As a result, in the photoacoustic imaging device 1, when the light source probe unit 12 slides non-contact over the entire foot of the subject, the deviation between the scan path and the actual sliding movement is compensated for by the measurement results from the distance measurement unit 70, according to the scan paths set on the back and back sides of the foot of the subject. This allows for consistent non-contact scanning even of three-dimensional shapes such as the foot, and enables stable generation of three-dimensional photoacoustic images of peripheral blood vessels.

[0061] In addition, the unit control unit 60 drives and controls the rotation drive unit 42 to rotate the light source probe unit 12 around a longitudinal axis including both ends of the light source probe unit 12 as the center of rotation, thereby orienting the irradiation port of the light irradiation unit 50 and the detection port of the photoacoustic wave detection unit 51 in the desired direction.

[0062] That is, the unit control section 60 controls the orientation of the light source probe unit 12 during sliding movement of the light source probe unit 12 so that the incident angle of the light irradiation section 50 in the light source probe unit 12 remains perpendicular to the sliding direction.

[0063] As a result, the photoacoustic imaging device 1 can stably generate three-dimensional photoacoustic images of peripheral blood vessels even for three-dimensional shapes such as the foot by always irradiating light onto the subject's foot at a perpendicular angle.

[0064] (5) Operation and effects of the photoacoustic imaging device In the above configuration, in the photoacoustic imaging device 1, the foot tank section 20 of the device main body section 10 of the 3D automatic scanning device 2 is filled with liquid (water) up to the height of the subject's ankle, and the extremity holding section 11 is positioned at the start position of the foot tank section 20 of the device main body section 10 (Figure 7(A)).

[0065] In this case, the light source probe unit 12 is placed at the front bottom of the foot bath section 20 of the device main body section 10 as its default position, and its rotational position is adjusted so that the irradiation port of the light irradiation section 50 is facing vertically upward.

[0066] Next, when the subject places his / her foot on the extremity holder 11 and the extremity holder 11 is positioned at a first position in the foot bath 20, the signal processing device 3 (unit control unit 60) follows the scan path set on the underside of the subject's foot, sliding the light source probe unit 12 along the longitudinal direction of the foot bath 20 while keeping the irradiation port of the light irradiation unit 50 facing vertically upward, thereby scanning the subject's foot from the toes to the heel from the sole side without contact (Figures 7(B) and (C)).

[0067] At this time, when the light source probe unit 12 slides, the signal processing device 3 (unit control unit 60) uses the distance measurement unit 70 to adjust the height position of the light source probe unit 12 so that it always maintains a constant close distance to the sole of the subject's foot while compensating for the discrepancy between the set scan path and the actual slide movement.

[0068] In this way, in the photoacoustic imaging device 1, the light source probe unit 12 in the 3D automatic scanning device 2 automatically scans the sole of the subject's foot, detects photoacoustic waves generated from the optical absorber inside the foot, and the signal processing device 3 images the optical absorber based on the photoacoustic waves.

[0069] Next, the signal processing device 3 (unit control unit 60) moves the light source probe unit 12 to a default position at the bottom of the front end of the foot bath section 20 of the device main body section 10, and then when the extremity holding section 11 is positioned at a second position in the foot bath section 20, the light source probe unit 12 is slid along the instep of the subject's foot along the scanning path set on the instep of the subject's foot, with the irradiation port of the light irradiation section 50 facing diagonally downward and facing the instep of the subject's foot, to scan the subject's foot from the toes to just before the ankle from the instep side without contact (Figure 7(D)).

[0070] At this time, when the light source probe unit 12 slides, the signal processing device 3 (unit control unit 60) uses the distance measurement unit 70 to adjust the height position of the light source probe unit 12 so as to always maintain a constant close distance to the instep of the subject's foot while compensating for any discrepancy between the set scan path and the actual slide movement.

[0071] At the same time, the signal processing device 3 (unit control unit 60) controls the orientation of the light source probe unit 12 so that the incident angle of the light irradiation unit 50 in the light source probe unit 12 remains perpendicular to the scanning direction when the light source probe unit 12 slides.

[0072] In this way, in the photoacoustic imaging device 1, the light source probe unit 12 in the 3D automatic scanning device 2 automatically scans the instep side of the subject's foot, detects photoacoustic waves generated from a light absorber inside the foot, and the signal processing device 3 images the light absorber based on the photoacoustic waves.

[0073] As a result, the photoacoustic imaging device 1 eliminates the cumbersome manual process required in the past; the subject simply places their foot in the tank of the device main body 10, and the entire foot is automatically scanned according to its shape.Since it is non-contact, pressure on the skin of the foot is avoided, and highly reproducible 3D photoacoustic images of peripheral blood vessels can be generated in a uniform state at all times.

[0074] In this case, by always facing the irradiation port of the light irradiation section 50 in the light source probe unit 12 to the surface of the subject's foot and always irradiating light at a perpendicular angle to the subject's foot, it is possible to stably generate three-dimensional photoacoustic images of peripheral blood vessels even in the case of a three-dimensional shape such as a foot.

[0075] (6) Other embodiments In this embodiment, the photoacoustic imaging device 1 is described as being divided into a 3D automatic scanning device 2 (including the device main body 10 and the light source probe unit 12) and a signal processing device 3 (including the unit control unit 60 and the image generation unit 62), but the present invention is not limited to this, and the signal processing device 3 may be included in the 3D automatic scanning device 2 and integrated.

[0076] In addition, in this embodiment, in the signal processing device 3 of the photoacoustic imaging device 1, the unit control unit 60 uses the image evaluation unit 63 to evaluate the clarity of the image based on the photoacoustic waves generated by the image generation unit 62 for each scan path, and if the clarity of the evaluated image is below a predetermined level, the light source probe unit 12 may be slid again along the corresponding scan path.

[0077] Specifically, the image evaluation unit 63 analyzes the images generated by the image generation unit 62 for each scan path, and detects peripheral blood vessels inside the skin and body tissue at the extremities of the subject shown in the images.

[0078] The image evaluation unit 63 can use, for example, a so-called deep learning method, a so-called template matching method, a machine learning method using SVM (Support Vector Machine) and AdaBoost, etc., as a method for detecting peripheral blood vessels inside the skin and body tissue at the extremities of the subject.

[0079] Next, the image evaluation unit 63 calculates the sharpness of the edges in the detected image of the skin and peripheral blood vessels inside the body tissue at the extremities of the subject, and evaluates whether the calculated sharpness is below a predetermined level.

[0080] When the clarity of the image evaluated by the image evaluation unit 63 is equal to or lower than a predetermined level, the signal processing device 3 (unit control unit 60) slides the light-source probe unit 12 again along the corresponding scan path. The predetermined level of clarity of the image at this time is set based on a level that allows the examiner to visually recognize and judge the image as a three-dimensional photoacoustic image of the superficial peripheral blood vessels in the subject's foot in a practically sufficient manner.

[0081] As a result, in the photoacoustic imaging device 1, if slight vibrations such as tremors or convulsions occur in the subject's foot when the light source probe unit 12 is slid, causing the image of the foot to become unclear, the device can automatically scan again, thereby stably generating a three-dimensional photoacoustic image of the peripheral blood vessels, even for a three-dimensional shape such as a foot.

[0082] The image evaluation unit 63 may be configured to evaluate the clarity of the shape and state of the peripheral blood vessels inside the skin and body tissue of the subject's foot for each scan path among the images generated by the image generation unit 62.

[0083] As a result, the photoacoustic imaging device 1 evaluates images obtained without contact and without applying pressure to the skin of the subject's foot, thereby enabling the generation of three-dimensional photoacoustic images of peripheral blood vessels that are always homogeneous and highly reproducible.

[0084] Furthermore, in this embodiment, the limb holding unit 11 provided on the device main body 10 of the 3D automatic scanning device 2 is described as being configured to be movable up and down so that it can be positioned in two stages, from a predetermined starting position to a first position and a second position.However, the means for this up and down movement for positioning may be a support method using a locking mechanism that manually engages at each position, or a support method that stops at each position by actuator drive in response to external operation.In short, as long as the limb holding unit 11 can be moved and supported in stages to the first position and the second position, either a manual or automatic support method may be adopted.

[0085] Furthermore, in this embodiment, the 3D automatic scanning device 2 is described as being configured to automatically scan the entire foot of a subject while detecting photoacoustic waves generated from an optical absorber inside the foot, but the present invention is not limited to this, and it is also possible to apply a configuration to automatically scan the entire hand of a subject while detecting photoacoustic waves generated from an optical absorber inside the hand. [Explanation of symbols]

[0086] 1...Photoacoustic imaging device, 2...3D automatic scanning device, 3...Signal processing device, 10...Device main body, 11...Extremity holding section, 12...Light source probe unit, 13...Image display section, 20...Foot bath section, 21...Lid-shaped opening frame, 21A, 21B...Protrusion, 22...Ankle holding section, 30A, 30B...Slide rail, 31A, 31B...Support frame, 40...Slide drive section, 41...Lift drive section, 42...Rotation drive section, 50...Light irradiation section, 51...Photoacoustic wave detection section, 52...Light source drive section, 60...Unit control section, 61...Memory section, 62...Image generation section, 63...Image evaluation section, 70...Distance measurement section.

Claims

1. 1. A photoacoustic imaging apparatus that detects photoacoustic waves generated from a light absorber in a subject and images the light absorber based on the photoacoustic waves, an apparatus main body having a tank-like structure for immersing the extremity of the subject in a liquid; a limb holder provided in the device body and configured to hold the limb of the subject in a tank of the device body; a light source probe unit that is provided so as to be movable within the tank of the device main body along a two-dimensional coordinate system in which the longitudinal direction and the vertical direction of the device main body are mutually orthogonal axes, and that integrally includes a light irradiator that irradiates pulsed light of a wavelength that is absorbed inside the subject, and a photoacoustic wave detector that detects photoacoustic waves generated from the light absorber; a path setting unit that sets scan paths in the two-dimensional coordinate system on the back side and the back side of the extremity of the subject, using the extremity holder as a reference; a distance measurement unit attached to the light source probe unit and configured to measure a proximity distance from an object facing a detection port of the photoacoustic wave detection unit; a unit control unit that controls the light irradiation unit and the photoacoustic wave detection unit of the light source probe unit while sliding the light source probe unit along the outer surface of the extremity of the subject in a non-contact manner, in accordance with the scan paths on the back and back sides of the extremity of the subject set by the path setting unit, so that the proximity distance measured by the distance measurement unit keeps a predetermined distance approximately uniformly relative to the outer surface of the extremity of the subject; A photoacoustic imaging device comprising:

2. The unit control unit controls the orientation of the light source probe unit so that the incident angle of the light irradiating unit in the light source probe unit is kept perpendicular to the sliding direction when the light source probe unit is slid.

2. The photoacoustic imager according to claim 1.

3. an image generating unit that generates an image based on the photoacoustic wave detected by the photoacoustic wave detecting unit; an image evaluation unit that evaluates the clarity of the image generated by the image generation unit for each of the scan paths; and when the clarity of the image evaluated by the image evaluation unit is equal to or lower than a predetermined level, the unit control unit slides the light source probe unit again along the corresponding scan path.

3. The photoacoustic imager according to claim 1, wherein the light source is a photoacoustic imaging device.

4. The image evaluation unit evaluates the clarity of the shape and state of the peripheral blood vessels inside the skin and body tissue of the extremity of the subject for each of the scan paths in the images generated by the image generation unit.

4. The photoacoustic imager according to claim 3.

5. 1. A photoacoustic imaging method for detecting a photoacoustic wave generated from an optical absorber in a subject and imaging the optical absorber based on the photoacoustic wave, an apparatus main body having a tank-like structure for immersing the extremity of the subject in a liquid, the apparatus main body being provided with an extremity holder for holding the extremity of the subject in the tank of the apparatus main body; a light source probe unit integrally including a light irradiator that irradiates pulsed light of a wavelength absorbed inside the subject and a photoacoustic wave detector that detects photoacoustic waves generated from the light absorber, is provided so as to be movable along a two-dimensional coordinate system within the tank of the device body, the axes of which are perpendicular to each other in the longitudinal direction and the vertical direction of the device body; a first step of setting scan paths in the two-dimensional coordinate system on the back side and the back side of the extremity of the subject, with the extremity holder as a reference; a second step of measuring a proximity distance from an object attached to the light source probe unit and facing a detection port of the photoacoustic wave detection unit; a third step of controlling the light irradiating unit and the photoacoustic wave detecting unit of the light source probe unit while sliding the light source probe unit in a non-contact manner along the outer surface of the extremity of the subject, in accordance with the scan paths on the back and back sides of the extremity of the subject set in the first step, so that the proximity distance measured in the second step is kept at a substantially uniform predetermined distance from the outer surface of the extremity of the subject; A photoacoustic imaging method comprising:

6. In the third step, the orientation of the light source probe unit is controlled so that the incident angle of the light irradiating portion of the light source probe unit is kept perpendicular to the sliding direction when the light source probe unit is slid.

6. The photoacoustic imaging method of claim 5.

7. a fourth step of generating an image based on the photoacoustic wave detected by the photoacoustic wave detection unit; a fifth step of evaluating the clarity of the image generated by the fourth step for each of the scan paths; and in the third step, if the clarity of the image evaluated in the fifth step is equal to or lower than a predetermined level, sliding the light source probe unit again along the corresponding scanning path.

7. The photoacoustic imaging method according to claim 5 or 6.

8. In the fifth step, the clarity of the shape and state of the peripheral blood vessels inside the skin and body tissue of the extremity of the subject in the images generated in the fourth step is evaluated for each of the scan paths.

8. The photoacoustic imaging method of claim 7.

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