Light measurement device and light measurement method

Abstract

Provided are a light measurement device and a light measurement method capable of completing measurement carried out by an image sensor within a decorrelation time. The light measurement device comprises: a laser source (1); an ultrasonic wave source (2); a camera (3); a control circuit (4); and a data analysis unit (5). The control circuit (4) that controls the emission timing such that a first laser beam and a second laser beam are emitted at a time interval shorter than the time of a single frame of an image sensor (3a), and such that the emission time point of the first laser beam and the emission time point of the second laser beam correspond to different exposure time of continuous frames. The ultrasonic wave source (2) emits an ultrasonic wave such that ultrasonic wave arrives at a measurement position at the emission time point of the first laser beam or the second laser beam. The data analysis unit (5) extracts a signal component modulated by the ultrasonic wave on the basis of a detection signal of the first laser beam and a detection signal of the second laser beam detected by the image sensor (3a).

Description

Optical measurement device and optical measurement method

[0001] The present disclosure relates to an optical measurement device and an optical measurement method for measuring light modulated by ultrasonic waves.

[0002] Many optical techniques have been developed as minimally invasive methods for measuring tissues in vivo. For example, by irradiating light from outside the body and measuring the light that propagates through the body and is emitted, it is possible to obtain biological information such as morphological information and metabolic information (e.g., blood oxygen saturation) of the tissues in vivo. However, because tissues in vivo are light-scattering media, the light irradiated from outside the body is scattered by the tissues in vivo, resulting in poor spatial resolution and inability to measure deep tissues. Therefore, optical measurement devices using ultrasound-modulated optical tomography (UOT) have been developed, which combines ultrasound, which propagates with low scattering within the body, with light (Non-Patent Documents 1 and 2). UOT acquires biological information by measuring light modulated by ultrasound.

[0003] Non-Patent Document 3 discloses that a CCD camera is used to capture images of speckle patterns both when a focused pulsed ultrasound is irradiated and when it is not irradiated, and a change in the speckle pattern is determined based on the difference between the images, thereby obtaining information on a local area indexed by ultrasound.

[0004] Wang, LV; Ku, G.; "Frequency-swept ultrasound-modulated optical tomography of scattering media," Optics Letters 23(12) 975-977 (1998) Elson, Daniel S., et al. "Ultrasound-mediated optical tomography: a review of current methods." Interface Focus 1.4 (2011): 632-648. Sasakura, Y; Hisaka, M., Reflection-type ultrasound-modulated speckle optical measurement method, Biomedical Engineering, 2007, 45.4: 235-241

[0005] However, when measuring tissue in a living body, the autocorrelation of the measured speckle pattern is lost (called decorrelation) due to random changes in the state of the tissue in the living body caused by biological activity (biological fluctuations).As in Patent Document 3, when a speckle pattern is photographed both with and without ultrasound irradiation and a difference is calculated, the difference output is affected by decorrelation.

[0006] The effect of decorrelation can be reduced by using image sensors with short frame times, but such image sensors are relatively expensive.

[0007] The present disclosure has been made to solve such problems, and aims to suppress the influence of biological fluctuations on the measured speckle pattern in an optical measurement device and optical measurement method using ultrasound-modulated optical tomography.

[0008] The optical measurement device disclosed herein includes a light source that irradiates a living body with pulsed laser light, an ultrasound source that irradiates an ultrasound wave at a measurement position located at a predetermined depth within the living body, an image sensor that detects the laser light that has passed through a region within the living body including the measurement position, a control circuit that controls the irradiation timing of the laser light from the light source, and an arithmetic circuit that extracts a signal component modulated by ultrasound from the laser light detected by the image sensor. The control circuit irradiates a first laser light and a second laser light at a time interval shorter than the time of one frame of the image sensor and controls the irradiation timing so that the irradiation time of the first laser light and the irradiation time of the second laser light correspond to different exposure times of consecutive frames. The ultrasound source irradiates ultrasound so that the ultrasound reaches the measurement position at the irradiation time of the first laser light or the second laser light. The arithmetic circuit extracts the signal component modulated by ultrasound based on the detection signal of the first laser light and the detection signal of the second laser light detected by the image sensor.

[0009] The optical measurement method disclosed herein is an optical measurement method for an optical measurement device including a light source that irradiates a living body with pulsed laser light, an ultrasound source that irradiates an ultrasound wave at a measurement position located at a predetermined depth within the living body, an image sensor that detects the laser light that has passed through a region within the living body including the measurement position, a control circuit that controls the irradiation timing of the laser light from the light source, and an arithmetic circuit that extracts a signal component modulated by the ultrasound from the laser light detected by the image sensor. The optical measurement method includes the steps of: irradiating a first laser light and a second laser light at a time interval shorter than the time of one frame of the image sensor, and controlling the irradiation timing so that the irradiation times of the first laser light and the irradiation times of the second laser light correspond to different exposure times of consecutive frames, respectively; irradiating ultrasound from the ultrasound source so that the ultrasound reaches the measurement position at the irradiation time of the first laser light or the second laser light; and extracting the signal component modulated by the ultrasound based on the detection signals of the first laser light and the second laser light detected by the image sensor.

[0010] The optical measurement device and optical measurement method disclosed herein irradiate a first laser light and a second laser light at a time interval shorter than the time of one frame of the image sensor, and the first exposure time for irradiating the first laser light and the second exposure time for irradiating the second laser light are different exposure times for consecutive frames, so that it is possible to complete measurement by the image sensor within the decorrelation time, thereby reducing the effects of decorrelation and improving measurement accuracy.

[0011] Fig. 1 is a schematic diagram of an optical measurement device according to an embodiment. Fig. 2 is a flowchart showing an optical measurement method according to an embodiment. Fig. 3 is a timing chart showing the turn-on timing of a pulse laser of the optical measurement device according to an embodiment. Fig. 4 is a schematic diagram showing a turn-on form of the pulse laser of the optical measurement device according to an embodiment. Fig. 5 is a timing chart showing another turn-on timing of the pulse laser of the optical measurement device according to an embodiment. Fig. 6 is a schematic diagram of a measurement system of a modified example using the optical measurement device according to an embodiment. Fig. 7 is a block diagram of the measurement system of the modified example.

[0012] Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and description thereof will not be repeated.

[0013] [Optical Measurement Device] In this embodiment, an optical measurement device that measures light modulated by ultrasound to measure tissue in a living body in a minimally invasive manner will be described below. The optical measurement device according to this embodiment can be applied to, for example, an optical measurement device that performs minimally invasive optical measurement of a subject's brain activity using near-infrared spectroscopy (NIRS). Of course, the optical measurement device according to this embodiment can also be applied to a measurement device that measures blood oxygen saturation, in addition to an optical measurement device that measures brain activity using near-infrared spectroscopy.

[0014] 1 is a schematic diagram of an optical measurement device 10 according to an embodiment. The optical measurement device 10 is composed of a laser source 1, an ultrasound source 2, a camera 3, a control circuit 4, and a data analysis unit 5. The control circuit 4 and the data analysis unit 5 can be configured on a single computer (not shown), and external devices such as a memory or a printer can be connected as needed. The laser source 1, ultrasound source 2, camera 3, etc. can also be configured integrally, and these and the control circuit 4 can also be configured integrally so that they can be worn by a subject.

[0015] The laser source 1 is a light source that irradiates the inside of the living body 20 with laser light, and is, for example, a semiconductor laser element. In this embodiment, the laser source 1 is controlled to generate pulsed laser light (pulsed laser light). The laser source 1 irradiates laser light in the near-infrared wavelength region (e.g., 780 nm, etc.) that has high transmittance through the living body 20. The laser light irradiated from the laser source 1 to the living body 20 is scattered by tissue within the living body 20 and reaches the measurement position, as shown in FIG. 1 . Furthermore, the laser source 1 can irradiate pulsed laser light of approximately several tens of nanoseconds to several nanoseconds.

[0016] The ultrasound source 2 is an ultrasound generator that irradiates ultrasound waves at a measurement position located at a predetermined depth within the living body 20. The ultrasound source 2 is equipped with a converger 2a for converging the irradiated ultrasound waves at the measurement position within the living body 20. Here, speckle fluctuations increase as the sound pressure of the ultrasound waves increases. Therefore, by converging the ultrasound waves at the measurement position within the living body 20 using the converger 2a, the measurement position is limited to an area with high sound pressure, thereby reducing speckle fluctuations that occur in areas where ultrasound waves exist other than the measurement position. The ultrasound waves irradiated from the ultrasound source 2 may be continuous or pulsed. However, by using pulsed ultrasound waves irradiated from the ultrasound source 2, the length of the ultrasound waves in the propagation direction can be shortened, thereby limiting the area where the ultrasound waves exist to the measurement position. Furthermore, when pulsed ultrasound waves are irradiated from the ultrasound source 2, a delay time (delay time) is required for the pulsed ultrasound waves irradiated from the surface of the living body 20 to reach the measurement position. Therefore, it is necessary to control the timing (second timing) of emitting ultrasonic waves from the ultrasonic source 2 so that the pulsed ultrasonic waves reach the measurement position in accordance with the time when the pulsed laser light irradiated from the laser source 1 reaches the measurement position. Note that, since the distance to the measurement position is sufficiently short compared to the speed of light, the time when the pulsed laser light irradiated from the laser source 1 reaches the measurement position is approximately the same as the irradiation time of the pulsed laser light irradiated from the laser source 1.

[0017] The camera 3 includes an image sensor 3a that detects laser light from the measurement position and a lens 3b that forms an image on the image sensor 3a. Because the optical measurement device 10 needs to capture a speckle pattern, it uses the image sensor 3a, which is a multi-element photodetector such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) sensor, rather than a single-element photodetector such as a photomultiplier tube. Using a CCD sensor or a CMOS sensor for the image sensor 3a can reduce the manufacturing cost of the optical measurement device 10. The speckle pattern is a collection of speckle grains (spot-like particles) that are generated by multiple interference of light that is multiply scattered within tissue within the living body 20. Therefore, it is preferable that the pixel size of the image sensor 3a be smaller than the average size of the speckle grains to be captured.

[0018] Image sensors 3a such as CCD sensors generally have a frame rate of several tens to several hundred fps. In contrast, the frequency of ultrasound is as fast as several MHz, and the image sensor 3a cannot keep up with changes in the ultrasound. Therefore, the optical measurement device 10 uses stroboscopic photography to irradiate the tissue in the living body 20 irradiated with ultrasound with pulsed laser light, and captures the speckle pattern with the exposed image sensor 3a. Furthermore, the optical measurement device 10 controls the irradiation timing (first timing) at which the laser source 1 irradiates the laser light so that measurement can be completed within the decorrelation time to prevent the autocorrelation of the measured speckle pattern from being lost due to fluctuations in the living body.

[0019] The control circuit 4 controls the first timing at which the laser source 1 emits laser light and the second timing at which the ultrasound source 2 emits ultrasonic waves. Specifically, the control circuit 4 includes a control unit 4a and a signal generator 4b. The control unit 4a sets the first timing at which the first laser light and the second laser light are emitted for different exposure times for consecutive frames at a time interval shorter than the frame time of the image sensor 3a, based on the frame rate of the image sensor 3a. The control unit 4a also sets the second timing so that the ultrasound reaches the measurement position at the time of emission of the second laser light. Note that, although the present disclosure describes the control unit 4a controlling the timing (second timing) at which the ultrasound source 2 emits ultrasound, the ultrasound source 2, rather than the control unit 4a, may control the timing of ultrasound emission so that the ultrasound reaches the measurement position at the time of emission of the first laser light or the second laser light. Here, the laser light is pulsed and therefore has a pulse width. Therefore, the laser light emission time is defined, for example, as the rise time of the pulse. Of course, the irradiation time of the laser light may be defined as, for example, the time of the center value of the pulse or the fall time of the pulse.

[0020] The signal generator 4b supplies a drive signal to the laser source 1 so that the first laser beam and the second laser beam are emitted at the first timing set by the control unit 4a, and also supplies a drive signal to the ultrasonic source 2 so that the ultrasonic beam is emitted at the second timing set by the control unit 4a.

[0021] The data analyzer 5 is an arithmetic circuit that extracts signal components modulated by ultrasound from the laser light detected by the camera 3. Specifically, the data analyzer 5 extracts signal components (speckle patterns) modulated by ultrasound based on the detection signals of the first laser light and the second laser light detected by the camera 3. Specifically, the data analyzer 5 obtains a first speckle pattern not modulated by ultrasound from the detection signal of the first laser light, and a second speckle pattern modulated by ultrasound from the detection signal of the second laser light. The first speckle pattern and the second speckle pattern are speckle patterns captured within a decorrelation time during which no biological fluctuations occur. Therefore, the data analyzer 5 can obtain a speckle pattern with a high S / N ratio by calculating the difference between the first speckle pattern and the second speckle pattern.

[0022] [Optical Measurement Method] A method for obtaining a speckle pattern modulated by ultrasonic waves using optical measurement device 10 will be described. Fig. 2 is a flowchart showing an optical measurement method according to an embodiment. Fig. 3 is a timing chart showing the timing of turning on the pulse laser of optical measurement device 10 according to an embodiment.

[0023] First, the optical measurement device 10 sets the first timing for irradiating laser light from the laser source 1 and the second timing for irradiating ultrasound from the ultrasound source 2 using the control unit 4a (step S101). First, the first timing is the timing for turning on the pulse laser so that optical measurement by UOT can be performed within the decorrelation time using the camera 3 using the image sensor 3a. Specifically, as shown in FIG. 3 , the first timing is the timing for irradiating two pulse laser beams, the first laser beam and the second laser beam, from the laser source 1 at a time interval shorter than the time for one frame of the image sensor 3a, at the timing of frame switching of the image sensor 3a. Furthermore, the irradiation times of the first laser beam and the second laser beam correspond to different exposure times of consecutive frames, respectively. Note that the irradiation time of the first laser beam corresponds to the exposure time of the first frame (first exposure time), and the irradiation time of the second laser beam corresponds to the exposure time of the second frame (second exposure time).

[0024] Here, the time for one frame of the image sensor 3a includes an exposure time and a readout time for the data captured during the exposure time. The period during which the frame signal is in an ON state is the exposure time, and the period during which the frame signal is in an OFF state is the readout time. The time interval between the irradiation of the first laser light and the second laser light is also referred to as a pulse interval. This pulse interval may be any interval as long as it is equal to or shorter than the decorrelation time. It is known that the decorrelation time is generally less than 1 ms, and it is preferable to calculate an average value of the decorrelation times of multiple subjects and set the pulse interval to, for example, 500 μs or less.

[0025] In the optical measurement device 10, the control unit 4a controls the timing of laser light irradiation so that the timing of laser light irradiation corresponds to the exposure times of different frames, as will be described later. Specifically, the control unit 4a synchronizes the laser source 1, the ultrasound source 2, and the camera 3 in advance using a signal (e.g., a synchronization signal) output from the signal generator 4b, and controls the laser source 1 so that the laser light is irradiated at the timing corresponding to the exposure times of different frames. Of course, in addition to synchronously controlling the laser source 1, the ultrasound source 2, and the camera 3, the control unit 4a may determine that the exposure times of the frames are different and control the timing of laser light irradiation. For example, the control unit 4a determines the exposure times of different frames using a signal (e.g., a trigger signal) for each frame output from the camera 3, and controls the timing of laser light irradiation.

[0026] The period during which the first laser beam and the second laser beam are lit (the period during which the laser drive signal is ON) is also referred to as the pulsed illumination time. By setting the pulsed illumination time shorter than the ultrasonic wave period (e.g., 1 / 8 or less of the ultrasonic wave period), the optical measurement device 10 can measure the speckle fluctuations caused by the ultrasonic waves within a time width in which the fluctuations can be considered stationary. Therefore, the optical measurement device 10 can obtain a direct difference between a speckle pattern not modulated by ultrasonic waves and a speckle pattern modulated by ultrasonic waves in a certain state, enabling measurements with a high signal-to-noise ratio. However, setting the pulsed illumination time shorter than the ultrasonic wave period reduces the amount of light detectable by the image sensor 3a. To obtain an amount of light detectable by the image sensor 3a, it is preferable to configure the first laser beam and the second laser beam to include multiple pulsed laser beams.

[0027] 4A and 4B are schematic diagrams showing the lighting modes of the pulsed laser of the optical measurement device 10 according to the embodiment. In FIG. 4A, a first laser beam including one pulsed laser beam is emitted in a first frame, and a second laser beam including one pulsed laser beam is emitted in a second frame. The time interval (pulse interval) between the first laser beam and the second laser beam is 10 μs. As shown in FIG. 4A, the pulse lighting times of the first laser beam and the second laser beam are shorter than the period of the ultrasonic waves. The first laser beam and the second laser beam shown in FIG. 3 adopt the lighting mode of the pulsed laser shown in FIG. 4A, but the lighting modes of the pulsed laser shown in FIG. 4B and FIG. 4C described below may also be adopted.

[0028] In FIG. 4( b), a first laser beam including four pulsed laser beams is irradiated in the first frame, and a second laser beam including four pulsed laser beams is irradiated in the second frame. The time interval (pulse interval) from the first pulsed laser beam of the first laser beam to the fourth pulsed laser beam of the second laser beam is 10 μs. As shown in FIG. 4( b), the pulsed lighting times of each of the first pulsed laser beam and the second pulsed laser beam are shorter than the ultrasonic wave period. However, since the total pulsed lighting time of the four pulsed laser beams is four times the pulsed lighting time of FIG. 4( a), the amount of light detectable by the image sensor 3 a increases. However, since the four pulsed laser beams are irradiated so as to correspond to the same peak position of each ultrasonic wave, a speckle pattern modulated by the ultrasonic wave portion at the same peak position is obtained, enabling optical measurement that is not affected by the speckle pattern modulated by the ultrasonic wave portion other than the peak. Note that the number of pulsed laser beams included in the first laser beam and the second laser beam is not limited to four; any number may be used.

[0029] In FIG. 4( c), a first laser beam including one pulsed laser beam is irradiated in the first frame, and a second laser beam including one pulsed laser beam is irradiated in the second frame. The time interval (pulse interval) between the first laser beam and the second laser beam is 10 μs. However, the pulsed illumination time of the first laser beam and the second laser beam is 4 μm, which corresponds to the length of four cycles of ultrasonic waves, as shown in FIG. 4( c). Because the pulsed illumination time is four cycles of ultrasonic waves, the amount of light detectable by the image sensor 3 a increases. However, because the speckle patterns of the first laser beam and the second laser beam modulated by four cycles of ultrasonic waves are superimposed, a time average of the speckle patterns modulated by four cycles of ultrasonic waves is obtained.

[0030] Returning to Fig. 3 , the second timing is the timing at which the ultrasonic source 2 emits ultrasonic waves so that the ultrasonic waves reach the measurement position at the emission time of the second laser light. Specifically, as shown in Fig. 3 , the second timing is the timing at which the ultrasonic source 2 emits pulsed ultrasonic waves before the ultrasonic delay time from the emission time of the second laser light. Note that the ultrasonic delay time can be calculated from the distance from the ultrasonic source 2 to the measurement position. Furthermore, since the ultrasonic waves emitted by the ultrasonic source 2 are pulsed ultrasonic waves, the period during which the ultrasonic waves are emitted (the period during which the ultrasonic drive signal is in the ON state) is also referred to as the ultrasonic pulse width. Of course, the ultrasonic waves emitted by the ultrasonic source 2 are not limited to pulsed ultrasonic waves and may be continuous ultrasonic waves.

[0031] 3, ultrasonic waves are emitted in synchronization with the time when the second laser light irradiates the measurement position, but ultrasonic waves may also be emitted in synchronization with the time when the first laser light irradiates the measurement position. When ultrasonic waves are emitted in synchronization with the time when the first laser light irradiates the measurement position, the second timing is the timing at which the ultrasonic source 2 irradiates ultrasonic waves so that the ultrasonic waves reach the measurement position at the irradiation time of the first laser light. The ultrasonic source 2 may irradiate ultrasonic waves so that the ultrasonic waves reach the measurement position in synchronization with either the irradiation time of the first laser light or the irradiation time of the second laser light.

[0032] Returning to FIG. 2, the optical measurement device 10 supplies a laser drive signal from the signal generator 4b to the laser source 1 based on the first timing set by the control unit 4a, causing the laser source 1 to irradiate the first laser light (step S102).

[0033] Next, the optical measurement device 10 supplies an ultrasonic drive signal from the signal generator 4b to the ultrasonic source 2 based on the second timing set by the control unit 4a, causing the ultrasonic source 2 to emit ultrasonic waves (step S103).

[0034] Next, the optical measurement device 10 supplies a laser drive signal from the signal generator 4b to the laser source 1 based on the first timing set by the control unit 4a, causing the laser source 1 to irradiate the second laser light (step S104).

[0035] Next, the optical measurement device 10 causes the data analysis unit 5 to extract signal components modulated by ultrasonic waves from the speckle patterns of the two detected frames (step S105). The data analysis unit 5 obtains a first speckle pattern that is not modulated by ultrasonic waves from the detection signal of the first laser beam, and obtains a second speckle pattern modulated by ultrasonic waves from the detection signal of the second laser beam. The data analysis unit 5 can extract signal components (speckle patterns) with a high S / N ratio by calculating the difference value between the first speckle pattern and the second speckle pattern.

[0036] [Variations of Illumination Timing] The time for one frame of the image sensor 3a shown in FIG. 3 includes an exposure time and a readout time for data captured during the exposure time. However, the configuration of one frame of the image sensor varies depending on the type of sensor, the readout method, etc., and is not limited to the configuration shown in FIG. 3. FIG. 5 is a timing chart showing another illumination timing of the pulse laser of the optical measurement device 10 according to the embodiment. The time for one frame of the image sensor shown in FIG. 5 includes an exposure time and a readout time for data captured in a frame prior to the exposure time. In the image sensor shown in FIG. 5, data captured during the first exposure time of the first frame is read out during the readout time of the second frame. Therefore, in the second frame, the second exposure time of the second frame and the readout time for reading the data of the first frame occur during the same time period.

[0037] 5, two pulsed laser beams, the first laser beam and the second laser beam, are irradiated at a time interval shorter than one frame time of the image sensor. Also, at the first timing shown in Fig. 5, the first exposure time for irradiating the first laser beam and the second exposure time for irradiating the second laser beam are exposure times for different frames. The first exposure time is the exposure time for the first frame, and the second exposure time is the exposure time for the second frame.

[0038] In Fig. 5, the period during which the exposure signal is in the ON state is the exposure time, and the period during which the readout signal is in the ON state is the readout time. Also, in the first laser beam and the second laser beam shown in Fig. 5, the pulse interval is equal to or shorter than the decorrelation time, and the pulse lighting time is shorter than the ultrasonic period.

[0039] [Application to Brain Function Measuring Device] The optical measurement device 10 according to this embodiment can be applied to a measurement device that measures brain function, and can measure the brain activity of a subject in a minimally invasive manner using near-infrared spectroscopy. When the optical measurement device 10 is applied to a measurement device that measures brain function, a laser source 1, an ultrasound source 2, and a camera 3 shown in FIG. 1 are placed on the surface of the subject's head. In other words, the living body 20 shown in FIG. 1 is the surface of the subject's head. This allows the optical measurement device 10 to measure the brain activity of the subject in a minimally invasive manner, and can visualize the activity state near the brain surface in real time using functional near-infrared spectroscopy (fNIRS).

[0040] The laser source 1 is configured to irradiate a first laser beam and a second laser beam, as shown in FIG. 3, from the surface of the subject's head to a measurement position. The laser source 1 includes, for example, a semiconductor laser and is configured to be able to irradiate laser beams of multiple wavelengths (e.g., light of three wavelengths: 780 nm, 805 nm, and 830 nm) in the near-infrared wavelength range, which has high biological transmittance. The camera 3 includes an image sensor such as a CCD sensor and detects the laser beam from the measurement position. The camera 3 outputs an electrical signal corresponding to the detected light. The ultrasound source 2 irradiates ultrasound waves to the measurement position on the subject's head.

[0041] The data analysis unit 5 then analyzes changes in hemoglobin amount (oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin) associated with brain activity based on the speckle pattern measured by the camera 3. This enables the optical measurement device 10 to minimally invasively obtain changes in hemoglobin amount associated with brain activity, i.e., changes in blood flow and the activation state of oxygen metabolism.

[0042] [Modification] When the optical measurement device 10 is applied to a measurement system for measuring brain function, it may be configured so that measurement light is irradiated onto the subject's head from multiple measurement probes placed on the subject's head, and measurement light scattered within the brain of the subject's head is received. Fig. 6 is a schematic diagram of a measurement system 100 of a modification using the optical measurement device according to the embodiment. Fig. 7 is a block diagram of the measurement system 100 of the modification.

[0043] 6, a measurement system 100 for measuring brain function is configured as a brain function imaging device that can minimally measure brain activity of a subject P and visualizes the activity state near the brain surface in real time using functional near-infrared spectroscopy. The measurement system 100 is also configured, for example, with a main unit 10A worn by the subject P and a data analysis unit 5, which is a computer that receives and analyzes data measured by the main unit 10A via wireless communication.

[0044] As a result, in the measurement system 100, the subject P is not constrained to the vicinity of the data analysis unit 5 even during brain function measurement, and the subject P can move freely while carrying the main unit 10A, making it possible to perform brain function measurement in an environment closer to everyday life.

[0045] The main unit 10A is composed of a laser source 1, an ultrasound source 2, a camera 3, and a control circuit 4. The measurement system 100 also includes a holder 6 that is attached to the head of the subject P and includes a plurality of attachment portions 61 for attaching a light-transmitting probe 6a, a light-receiving probe 6b, and an ultrasound probe 6c. The light-transmitting probe 6a, the light-receiving probe 6b, and the ultrasound probe 6c are each attached to the holder 6 attached to the head of the subject P, and thereby positioned on the surface of the head of the subject P.

[0046] The light-transmitting probe 6a is connected to the laser source 1 via an optical fiber and irradiates the first laser light and the second laser light shown in Fig. 3 from the surface of the head of the subject P to the measurement position. The light-receiving probe 6b is connected to the camera 3 via an optical fiber and detects the laser light from the measurement position. The ultrasound probe 6c is connected to the ultrasound source 2 via wiring and irradiates ultrasound from the surface of the head of the subject P to the measurement position.

[0047] The laser source 1 is configured to irradiate the head of the subject P with first and second laser lights from the light-transmitting probe 6a via an optical fiber. The laser source 1 includes, for example, a semiconductor laser and is configured to be able to irradiate laser lights of multiple wavelengths in the near-infrared wavelength range, which has high biological transmittance. The camera 3 includes an image sensor such as a CCD sensor and is configured to acquire and detect light incident on the light-receiving probe 6b via an optical fiber. The camera 3 outputs an electrical signal corresponding to the detected light. The ultrasound source 2 irradiates ultrasound from the ultrasound probe 6c to a measurement position on the head of the subject P.

[0048] The data analysis unit 5 is configured to analyze changes in hemoglobin amount due to brain activity based on the speckle pattern measured by the camera 3. This enables the measurement system 100 to minimally invasively acquire changes in hemoglobin amount due to brain activity, i.e., changes in blood flow and the activation state of oxygen metabolism. The measurement system 100 is also configured to measure brain activity and acquire a two-dimensional distribution at each measurement point (measurement channel) formed by the light-transmitting probe 6 a, light-receiving probe 6 b, and ultrasound probe 6 c.

[0049] In the measurement system 100, the ultrasonic probe 6c may be an ultrasonic phased array to enable steering and scanning of ultrasonic waves. Also, in the measurement system 100, a bundle fiber may be used as the optical fiber for receiving light that connects the light-receiving probe 6b and the camera 3.

[0050] Aspects It will be understood by those skilled in the art that the above-described embodiments are specific examples of the following aspects.

[0051] (Item 1) An optical measurement device according to one aspect includes a light source that irradiates a living organism with pulsed laser light, an ultrasound source that irradiates an ultrasound wave at a measurement position located at a predetermined depth within the living organism, an image sensor that detects the laser light that has passed through a region within the living organism that includes the measurement position, a control circuit that controls the irradiation timing of the laser light from the light source, and an arithmetic circuit that extracts a signal component modulated by the ultrasound wave from the laser light detected by the image sensor. The control circuit irradiates a first laser light and a second laser light at a time interval shorter than the time of one frame of the image sensor, and controls the irradiation timing so that the irradiation time of the first laser light and the irradiation time of the second laser light correspond to different exposure times of consecutive frames. The ultrasound source irradiates ultrasound so that the ultrasound reaches the measurement position at the irradiation time of the first laser light or the second laser light. The arithmetic circuit extracts the signal component modulated by the ultrasound wave based on the detection signal of the first laser light and the detection signal of the second laser light detected by the image sensor.

[0052] According to the optical measurement device described in paragraph 1, the first laser light and the second laser light are irradiated at a time interval shorter than the time of one frame of the image sensor, and the first exposure time for irradiating the first laser light and the second exposure time for irradiating the second laser light are different exposure times for consecutive frames, so it is possible to complete measurement by the image sensor within the decorrelation time, thereby reducing the effects of decorrelation and improving measurement accuracy.

[0053] (Item 2) In the optical measurement device according to item 1, the first laser light and the second laser light are configured by a plurality of pulsed laser lights.

[0054] According to the optical measurement device described in paragraph 2, since a plurality of pulsed laser beams are irradiated onto the measurement position, the amount of laser beam detected by the image sensor can be increased.

[0055] (Item 3) In the optical measurement device according to item 1 or 2, the pulse lighting time of the first laser light and the second laser light is shorter than the period of the ultrasonic wave.

[0056] According to the optical measurement device described in paragraph 3, by making the pulse lighting time shorter than the period of the ultrasonic waves, it is possible to regard the speckle fluctuations caused by the ultrasonic waves as stationary.

[0057] (4) In the optical measurement device according to any one of the above items 1 to 3, the light source can emit laser light having different peak wavelengths.

[0058] According to the optical measurement device described in paragraph 4, the light source can emit laser light with different peak wavelengths, making it possible to measure various things such as blood oxygen saturation.

[0059] (Item 5) In the optical measurement device according to any one of items 1 to 4, the ultrasonic source can emit pulsed ultrasonic waves.

[0060] According to the optical measurement device described in item 5, the ultrasonic source irradiates pulsed ultrasonic waves, thereby making it possible to reduce speckle fluctuations caused by ultrasonic waves.

[0061] (Item 6) In the optical measurement device according to any one of items 1 to 5, the ultrasonic source irradiates ultrasonic waves so that the ultrasonic waves converge at the measurement position.

[0062] According to the optical measurement device described in paragraph 6, the ultrasonic source irradiates ultrasonic waves so that the ultrasonic waves converge at the measurement position, thereby reducing speckle fluctuations caused by ultrasonic waves at positions other than the measurement position.

[0063] (7) In the optical measurement device according to any one of the above items 1 to 6, the time interval between the irradiation of the first laser light and the irradiation of the second laser light is 500 μs or less.

[0064] According to the optical measurement device described in paragraph 7, by setting the time interval for irradiating the first laser light and the second laser light to 500 μs or less, measurement within the decorrelation time becomes easy.

[0065] (Item 8) In the optical measurement device according to item 4, the light source can emit laser light of a plurality of wavelengths in the near-infrared wavelength region.

[0066] According to the optical measurement device described in paragraph 8, the light source irradiates laser light of a plurality of wavelengths in the near-infrared wavelength region, thereby making it possible to measure the oxygen saturation level in the blood.

[0067] (Item 9) An optical measurement method according to one aspect is an optical measurement method for an optical measurement device including a light source that irradiates a living organism with pulsed laser light, an ultrasound source that irradiates an ultrasound wave at a measurement position located at a predetermined depth within the living organism, an image sensor that detects the laser light that has passed through a region within the living organism that includes the measurement position, a control circuit that controls the irradiation timing of the laser light from the light source, and an arithmetic circuit that extracts a signal component modulated by the ultrasound wave from the laser light detected by the image sensor. The optical measurement method includes the steps of: irradiating a first laser light and a second laser light at a time interval shorter than the time of one frame of the image sensor, and controlling the irradiation timing so that the irradiation times of the first laser light and the irradiation times of the second laser light correspond to different exposure times of consecutive frames, respectively; irradiating ultrasound from the ultrasound source so that the ultrasound reaches the measurement position at the irradiation time of the first laser light or the second laser light; and extracting the signal component modulated by the ultrasound wave based on the detection signal of the first laser light and the detection signal of the second laser light detected by the image sensor.

[0068] According to the optical measurement method described in paragraph 9, the first laser light and the second laser light are irradiated at a time interval shorter than the time of one frame of the image sensor, and the first exposure time for irradiating the first laser light and the second exposure time for irradiating the second laser light are different exposure times for consecutive frames, so it is possible to complete measurement by the image sensor within the decorrelation time, thereby reducing the effects of decorrelation and improving measurement accuracy.

[0069] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0070] 1 Laser source, 2 Ultrasound source, 2a Converger, 3 Camera, 3a Image sensor, 3b Lens, 4 Control circuit, 4a Control unit, 4b Signal generator, 5 Data analysis unit, 6 Holder, 6a Light transmitting probe, 6b Light receiving probe, 6c Ultrasound probe, 10 Optical measurement device, 10A Main unit, 20 Living body, 61 Mounting unit, 100 Measurement system.

Claims

1. a light source that irradiates the inside of a living body with pulsed laser light; an ultrasound source that irradiates ultrasound so that the ultrasound converges at a measurement position at a predetermined depth within the living body; an image sensor that detects the laser light that has passed through a region in the living body that includes the measurement position; a control circuit for controlling the timing of irradiation of the laser light from the light source; an arithmetic circuit that extracts a signal component modulated by the ultrasonic wave from the laser light detected by the image sensor, The control circuit irradiating the first laser light and the second laser light at a time interval shorter than a time for one frame of the image sensor, and controlling the irradiation timing so that the irradiation time of the first laser light and the irradiation time of the second laser light correspond to different exposure times of successive frames, respectively; the ultrasonic wave source irradiates the ultrasonic wave so that the ultrasonic wave reaches the measurement position at the irradiation time of the first laser light or the second laser light; The arithmetic circuit comprises: extracting a signal component modulated by the ultrasonic wave based on a detection signal of the first laser beam and a detection signal of the second laser beam detected by the image sensor; the light source can irradiate the laser light with different peak wavelengths, an optical measurement device, wherein a time interval between irradiating the first laser light and the second laser light is 500 μs or less.

2. the first laser beam and the second laser beam are constituted by a plurality of pulsed laser beams, a pulse lighting time of the first laser light and the second laser light is shorter than a period of the ultrasonic wave; The optical measurement device according to claim 1 , wherein the ultrasonic source is capable of emitting the ultrasonic waves in pulses.

3. 3. The optical measurement device according to claim 1, wherein the light source is capable of irradiating the laser light of a plurality of wavelengths in the near-infrared wavelength region.

4. An optical measurement method in an optical measurement device comprising: a light source that irradiates a living body with pulsed laser light; an ultrasound source that irradiates ultrasound so that the ultrasound converges at a measurement position at a predetermined depth within the living body; an image sensor that detects the laser light that has passed through a region within the living body that includes the measurement position; a control circuit that controls the irradiation timing of the laser light from the light source; and an arithmetic circuit that extracts a signal component modulated by the ultrasound from the laser light detected by the image sensor, irradiating a first laser beam and a second laser beam at a time interval shorter than a time period for one frame of the image sensor, and controlling the irradiation timing so that an irradiation time of the first laser beam and an irradiation time of the second laser beam correspond to different exposure times of successive frames, respectively; the ultrasonic source irradiating the ultrasonic wave so that the ultrasonic wave reaches the measurement position at the irradiation time of the first laser light or the second laser light; extracting a signal component modulated by the ultrasonic wave based on a detection signal of the first laser beam and a detection signal of the second laser beam detected by the image sensor, the light source can irradiate the laser light with different peak wavelengths, an optical measurement method, wherein a time interval between irradiating the first laser light and the second laser light is 500 μs or less;