JP2016101393A - Subject information acquisition apparatus and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoacoustic imaging technique using multi-wavelength light, with excellent measurement accuracy but yet cost increase suppressed.SOLUTION: An subject information acquisition apparatus is used, which comprises: a light source for emitting pulsed light of a first wavelength and pulsed light of a second wavelength different from the first wavelength at a different timing; a delay optical system for delaying the pulsed light of the first wavelength relative to the pulsed light of the second wavelength; a conversion element for receiving photoacoustic waves generated by a subject irradiated with each of the pulsed light of the first and second wavelengths and outputting reception signals; a photodetector for detecting the light quantity of each of the pulsed light of the first and second wavelengths; and a processing unit for acquiring characteristic information of the subject, on the basis of the reception signal output from the conversion element and deriving from each of the pulsed light of the first and second wavelengths and the photodetector-detected light quantity of each of the pulsed light of the first and second wavelengths.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a subject information acquisition apparatus and a control method thereof.

  One of imaging techniques using light is a photoacoustic imaging technique. In photoacoustic imaging, first, pulsed light generated from a light source is irradiated onto a subject. The irradiation light propagates and diffuses in the subject, and the energy of the light is absorbed at a plurality of locations in the subject to generate an acoustic wave (hereinafter referred to as a photoacoustic wave). The photoacoustic wave is received by the transducer, and the received signal is analyzed in the processing device, whereby information regarding the optical characteristics inside the subject is acquired as image data. Thereby, the optical characteristic distribution in the subject is visualized.

  In recent years, in order to image a finer light absorber using photoacoustics, improvement in resolution has been demanded. Then, development of a photoacoustic microscope has been promoted that images an absorber such as a microvessel near the surface of a subject with high resolution by focusing sound or condensing pulsed light. In Patent Document 1, the resolution is improved by condensing pulsed light with a lens and placing the subject at the focal position of the light.

  In addition, by irradiating with light having different wavelengths, it is possible to obtain a distribution related to the concentration of a substance present in the subject. In this case, the distribution related to the concentration of the substance can be imaged using the value of the light absorption coefficient in the subject obtained for each wavelength and the wavelength dependency of the light absorption specific to the substance to be obtained. In particular, the oxygen saturation of blood can be obtained based on the concentrations of oxyhemoglobin HbO and deoxyhemoglobin Hb.

ここで、μ_ａ ^λ１は波長λ_１における吸収係数、μ_ａ ^λ２は波長λ_２における吸収係数を示す。また、ε_Ｈｂ０ ^λ１は波長λ_１におけるオキシヘモグロビンのモル吸光係数、ε_Ｈｂ ^λ１は波長λ１におけるデオキシヘモグロビンのモル吸光係数を示す。ε_Ｈｂ０ ^λ２は波長λ_２におけるオキシヘモグロビンのモル吸光係数、ε_Ｈｂ ^λ２は波長λ_２におけるデオキシヘモグロビンのモル吸光係数を示す。ε_Ｈｂ０ ^λ１、ε_Ｈｂ ^λ１、ε_Ｈｂ０ ^λ２、ε_Ｈｂ ^λ２は既知の値である。なお、ｒは位置座標を示す。式（１）のように、血液の酸素飽和度を求めるためには、２波長における吸収係数の比が必要となる。 When two wavelengths are used, the oxygen saturation SO ₂ can be obtained by the following formula (1).

Here, μ _a ^λ1 represents an absorption coefficient at the wavelength λ ₁ , and μ _a ^λ2 represents an absorption coefficient at the wavelength λ ₂ . Ε _Hb0 ^λ1 represents the molar extinction coefficient of oxyhemoglobin at the wavelength λ ₁ , and ε _Hb ^λ1 represents the molar extinction coefficient of deoxyhemoglobin at the wavelength λ1. ε _Hb0 ^λ2 represents the molar extinction coefficient of oxyhemoglobin at the wavelength λ ₂ , and ε _Hb ^λ2 represents the molar extinction coefficient of deoxyhemoglobin at the wavelength λ ₂ . ε _Hb0 ^λ1 , ε _Hb ^λ1 , ε _Hb0 ^λ2 , and ε _Hb ^λ2 are known values. Note that r indicates position coordinates. As in equation (1), in order to determine the oxygen saturation of blood, a ratio of absorption coefficients at two wavelengths is required.

  When calculating the oxygen saturation distribution using two wavelengths, first, photoacoustic measurement is performed at the first wavelength, and then photoacoustic measurement is performed at the second wavelength. Distribution is obtained. However, since the living body has body movement, pulsation, respiration, and the like, the subject moves between the measurement of the first wavelength and the second wavelength. This shifts the light absorption distribution obtained at each wavelength, that is, the position of the blood vessel at each wavelength. When the position shift occurs, the ratio of the absorption coefficient between the two wavelengths at each position becomes an incorrect value, so that an incorrect oxygen saturation is obtained.

  In order to cope with this problem, there is a method of alternately irradiating the subject with light of each wavelength (hereinafter referred to as alternate irradiation). By alternately irradiating, it is possible to suppress positional deviation between wavelengths due to body movement at each measurement point. Each measurement is performed as the light emission interval between two wavelengths, that is, the interval between the pulse light of the first wavelength being irradiated on the subject and the pulse light of the second wavelength being irradiated on the subject is shorter. The effect of positional shift between wavelengths due to body movement at the point is reduced, and the accuracy of the oxygen saturation distribution is increased.

Special table 2011-519281 gazette

In order to perform the alternate irradiation, a method of using two light sources having different emission wavelengths and irradiating pulsed light alternately by shifting the light emission timing is conceivable. However, this method requires a cost for mounting two light sources, and further requires light emission control between the two light sources.
A method of performing alternate irradiation using a wavelength variable mechanism of one wavelength variable light source is also conceivable. However, in order to prevent positional shift such as pulsation and respiration, it is necessary to shorten the light emission interval of the pulsed light between the two wavelengths, so that an advanced technique for high-speed wavelength variable control is required.

  The present invention has been made in view of the above problems, and an object of the present invention is to realize accurate measurement while suppressing cost in photoacoustic imaging using light of a plurality of wavelengths.

The present invention employs the following configuration. That is,
A light source that emits pulsed light of a first wavelength and pulsed light of a second wavelength different from the first wavelength at different timings;
A delay optical system that delays the pulsed light of the first wavelength with respect to the pulsed light of the second wavelength;
A conversion element that receives a photoacoustic wave generated by irradiating a subject with each of the pulsed light beams having the first and second wavelengths and outputs a reception signal;
A photodetector for detecting the amount of each of the pulsed light of the first and second wavelengths;
The received signal derived from each of the first and second wavelength pulse lights output from the conversion element, and each of the first and second wavelength pulse lights detected by the photodetector. A processing unit for acquiring characteristic information of the subject based on the light amount;
A subject information acquisition apparatus characterized by comprising:

The present invention also employs the following configuration. That is,
A light source that emits pulsed light of a plurality of wavelengths at different timings;
A delay optical system that delays the pulsed light of each wavelength with a different delay time for each wavelength;
A conversion element that receives a photoacoustic wave generated by irradiating a subject with each of the pulsed light beams of each wavelength that has passed through the delay optical system, and outputs a received signal;
A photodetector for detecting the respective light amounts of the pulsed light of each wavelength;
Based on the received signal derived from the pulsed light of each wavelength output from the conversion element and the light quantity of the pulsed light of each wavelength detected by the photodetector, characteristic information of the subject A processing unit for acquiring
Have
The delay optical system is an object information acquisition apparatus in which the pulsed light of each wavelength passes through optical paths having different optical path lengths.

The present invention also employs the following configuration. That is,
A light source emitting pulsed light of a first wavelength and pulsed light of a second wavelength different from the first wavelength at different timings;
A delay optical system delaying the pulsed light of the first wavelength with respect to the pulsed light of the second wavelength;
A conversion element that receives a photoacoustic wave generated by irradiating the subject with each of the pulsed light beams having the first and second wavelengths and outputs a reception signal;
A photodetector detecting the respective light amounts of the pulsed light of the first and second wavelengths;
The received signal derived from each of the first and second wavelength pulse lights output from the conversion element by the processing unit, and the first and second wavelength pulses detected by the photodetector Obtaining characteristic information of the subject based on the respective light quantities of light;
A control method for a subject information acquiring apparatus.

The present invention also employs the following configuration. That is,
A light source emitting pulsed light of a plurality of wavelengths at different timings;
A delay optical system delaying the pulsed light of each wavelength with a different delay time for each wavelength;
A conversion element that receives a photoacoustic wave generated by irradiating a subject with each of the pulsed light of each wavelength that has passed through the delay optical system and outputs a reception signal;
A photodetector detecting the respective light amounts of the pulsed light of each wavelength;
Based on the received signal derived from the pulsed light of each wavelength output from the conversion element and the light quantity of the pulsed light of each wavelength detected by the photodetector, the processing unit Obtaining specimen characteristic information; and
Have
In the delaying step, the subject information acquiring apparatus control method is characterized in that the pulsed light of each wavelength passes through optical paths having different optical path lengths.

  According to the present invention, in photoacoustic imaging using light of a plurality of wavelengths, accurate measurement can be realized while suppressing cost.

Schematic diagram showing the configuration of the photoacoustic apparatus The flowchart which shows an example of the acquisition flow of object information Time chart showing an example of measurement of a photoacoustic apparatus Graph showing received signal of light irradiation and generated photoacoustic wave Partially enlarged graph showing received signal of photoacoustic wave generated by light irradiation Partially enlarged graph showing received signal of photoacoustic wave generated by light irradiation

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described below should be changed as appropriate according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the following description.

  The present invention relates to a technique for detecting acoustic waves propagating from a subject, generating characteristic information inside the subject, and acquiring the characteristic information. Therefore, the present invention can be understood as a subject information acquisition apparatus or a control method thereof, a subject information acquisition method, or a signal processing method. The present invention can also be understood as a program that causes an information processing apparatus including hardware resources such as a CPU to execute these methods, and a storage medium that stores the program. The present invention can also be understood as an acoustic wave measuring device and a control method thereof.

  The subject information acquiring apparatus of the present invention irradiates a subject with light (electromagnetic waves), and receives (detects) an acoustic wave generated and propagated in the subject or on the subject surface according to the photoacoustic effect. Includes devices that use. Such an object information acquiring apparatus can be called a photoacoustic imaging apparatus, a photoacoustic image apparatus, or simply a photoacoustic apparatus because it obtains characteristic information inside the object in the form of image data or the like based on photoacoustic measurement.

Characteristic information in the photoacoustic device is composed of the source distribution of acoustic waves generated by light irradiation, the initial sound pressure distribution in the subject, or the optical energy absorption density distribution, absorption coefficient distribution, and tissue derived from the initial sound pressure distribution. Concentration distribution of substances to be included. Specifically, it includes blood component distribution such as oxyhemoglobin / deoxyhemoglobin concentration distribution and oxygen saturation distribution obtained from them. Further, fat, glucose concentration, collagen concentration, melanin concentration, fat or water volume fraction, and the like may be used.
Further, the characteristic information may be obtained as distribution information of each position in the subject, not as numerical data. That is, two-dimensional or three-dimensional distribution information such as an absorption coefficient distribution and an oxygen saturation distribution may be used.

  The acoustic wave referred to in the present invention is typically an ultrasonic wave and includes an elastic wave called a sound wave or an acoustic wave. An acoustic wave generated by the photoacoustic effect is called a photoacoustic wave or an optical ultrasonic wave. An electrical signal converted from an acoustic wave by the probe is also called an acoustic signal, and an acoustic signal derived from the photoacoustic wave is particularly called a photoacoustic signal.

  The main purpose of the device of the present invention is the diagnosis of vascular diseases and malignant tumors in humans and animals, and the follow-up of chemical treatment. Therefore, a part of a living body, specifically, a subject to be inspected, such as a human or animal skin or a subcutaneous part, a breast, a neck, or an abdomen, is assumed as a subject. In particular, a shallow region within a few millimeters from the skin surface is suitable as an inspection target. However, the subject is not limited to this, and other parts of the living body and non-biological materials can be measured.

  Examples of the light absorber in a subject typically include oxyhemoglobin or deoxyhemoglobin in a living body, blood vessels containing many of them, and malignant tumors containing many new blood vessels. As the light absorber, one having a relatively high light absorption coefficient inside the subject is preferable. In addition, melanoma and carotid artery plaque also serve as light absorbers.

[Embodiment 1]
The configuration and processing of the subject information acquisition apparatus according to the first embodiment will be described below.

[Device configuration]
FIG. 1 is a schematic diagram showing the configuration of the photoacoustic apparatus of the present embodiment. The photoacoustic apparatus of the present embodiment includes a light source 100 including an oscillation unit 110 and a wavelength conversion unit 120, a probe 200 including a conversion element 210, and a delay optical system 300 for delaying light emitted from the oscillation unit 110. Prepare. The photoacoustic apparatus also includes a waveguide optical system 400 for guiding light of a plurality of wavelengths to a subject, a photodetector 500, a water tank 600, a processing unit 700, a control unit 800, a scanning mechanism 900, and a display unit 1000.

The pulsed light 1200 having the first wavelength emitted from the oscillation unit 110 is guided to the delay optical system 300.
The pulsed light 1200 having the first wavelength delayed through the delay optical system 300 and the pulsed light 1300 having the second wavelength excited by the pulsed light 1210 from the oscillation unit 110 and emitted from the wavelength conversion unit 120 are obtained by an optical element. Guided to the same optical path. The optical element is, for example, a dichroic mirror 360. At this time, the pulsed light 1200 having the first wavelength reaches the pulsed light 1300 having the second wavelength after being delayed by the amount propagated through the delay optical system 300. Then, the pulsed light 1400 of each wavelength guided to the same optical path is alternately irradiated to the subject 1100 through the waveguide optical system 400 and reaches the light absorber 1110 in the subject 1100.

The light absorber 1110 absorbs the energy of light of each wavelength and generates a photoacoustic wave for each wavelength. The generated photoacoustic wave propagates through the subject and reaches the conversion element 210.
The conversion element 210 outputs a time-series reception signal by receiving a photoacoustic wave. In the present embodiment, the conversion element 210 (receiving surface) of the probe 200 is immersed in water 610 as an acoustic matching material in the water tank 600. Thereby, acoustic matching between the subject 1100 and the conversion element 210 is achieved.

The photodetector 500 detects a part of the pulsed light 1400 and outputs a reception signal.
The scanning mechanism 900 scans the measurement unit 1500 including the probe 200, a part of the optical system 400, and the photodetector 500 during photoacoustic measurement.
The control unit 800 controls each constituent block by supplying necessary control signals and data to each constituent block in the photoacoustic apparatus.
Reception signals output from the conversion element 210 and the photodetector 500 are sequentially input to the processing unit 700. The processing unit 700 generates subject information using signals input from the conversion element 210 and the photodetector 500. Then, the processing unit 700 transmits the generated object information data to the display unit 1000 to display an image or numerical value of the object information.

Hereinafter, each component block will be described in detail.
(Light source 100)
The light source 100 includes an oscillation unit 110 and a wavelength conversion unit 120. The light generated in the oscillation unit 110 and the wavelength conversion unit 120 is preferably pulsed light on the order of nanoseconds to microseconds. A specific pulse width is preferably about 1 to 100 nanoseconds. The wavelength is preferably in the range of about 300 nm to 1600 nm. In particular, when imaging blood vessels near the surface of a living body with high resolution, light having a wavelength in the visible region (400 nm or more and 700 nm or less) is preferable. On the other hand, when imaging a deep part of a living body, light having a wavelength (700 nm or more and 1100 nm or less) with less absorption in the background tissue of the living body is preferable. However, it is possible to use terahertz waves, microwaves, and radio waves.

As the oscillation unit 110, various lasers such as a solid laser, a semiconductor laser, and a gas laser can be used, but a solid laser is particularly preferable. Specifically, an Nd: YAG laser (laser using a yttrium / aluminum / garnet crystal doped with neodymium) using a semiconductor laser or a flash lamp as excitation light can be used. Furthermore, it is preferable that these lasers can generate a second harmonic and a third harmonic and can emit light of each wavelength. In addition to Nd: YAG laser, Nd: YVO ₄ laser (laser using neodymium-doped yttrium vanadate crystal), Nd: YLF laser (laser using neodymium-doped yttrium-lithium fluoride crystal), etc. are also used. obtain.

One of the light of the fundamental wave, the second harmonic wave, and the third harmonic wave oscillated in the oscillation unit 110
One is emitted from the oscillation unit 110 as pulsed light 1200 of the first wavelength. Similarly, one of the fundamental wave, the second harmonic wave, the third harmonic wave, and the like oscillated in the oscillation unit 110 is guided to the wavelength conversion unit 120 as the pulsed light 1210, and the pulsed light 1200 having the first wavelength Becomes the pulsed light 1300 of the second wavelength having a different wavelength. The pulsed light 1200 and the pulsed light 1210 may have the same wavelength or different wavelengths.

  As the wavelength conversion unit 120, a dye laser, a Ti: sa (titanium sapphire) laser, an OPO (Optical Parametric Oscillators) laser, or the like can be used. The dyes and crystals in these lasers are excited by pulsed light 1210 and oscillate pulsed light 1300 having a second wavelength different from that of pulsed light 1200 having the first wavelength. In the case of using a dye laser, for example, Pyrromethene 597 can be used as the dye. At this time, as the pulsed light 1210, a second harmonic wave of an Nd: YAG laser having a wavelength of 532 nm can be used. When an OPO laser is used, a second harmonic of an Nd: YAG laser or a third harmonic of 355 nm is used as the pulsed light 1210 in accordance with the wavelength of the pulsed light 1300 having the second wavelength. Further, when a Ti: sa laser is used, the pulsed light 1210 can be a double wave of an Nd: YAG laser.

Further, when measuring using light of various wavelengths, the wavelength conversion unit 120 is more preferably a laser capable of changing the oscillation wavelength. When selecting the first and second wavelengths in the wavelength tunable laser, it is preferable to use light having a wavelength that is efficiently absorbed by each of oxyhemoglobin and deoxyhemoglobin.
Thus, although the laser is preferable as the light source 100, a light emitting diode or a flash lamp can be used instead of the laser.

(Probe 200)
The probe 200 includes one or more conversion elements 210 and a casing. The conversion element 210 receives an acoustic wave, such as a piezoelectric element using a piezoelectric phenomenon such as lead zirconate titanate (PZT), a conversion element using optical resonance, or a capacitive conversion element such as CMUT. Any conversion element may be used as long as it can be converted into an electric signal.
When the photoacoustic apparatus is a photoacoustic microscope as shown in FIG. 1, the probe 200 is preferably a focus type probe. That is, an acoustic lens is preferably provided on the receiving surface of the conversion element 210.

In order to acquire a wide range of object information, it is preferable that the probe 200 can be mechanically moved with respect to the object 1100 by the scanning mechanism 900. At that time, it is preferable that a part of the optical system 400 (irradiation position of the pulsed light 1400) and the probe 200 move in synchronization.
In the case where the probe 200 is a handheld type, the user has a gripping part for gripping the probe 200.

When the photoacoustic apparatus is a photoacoustic tomography apparatus, the probe 200 is preferably provided with a plurality of conversion elements 210. In the case of including a plurality of conversion elements 210, it is preferable that they are arranged so as to be arranged in a plane or a curved surface called a 1D array, 1.5D array, 1.75D array, or 2D array.
In the probe 200, an amplifier that amplifies the analog signal output from the conversion element 210 may be provided.

(Delay optical system 300)
The delay optical system 300 includes the pulsed light 1 having the first wavelength with respect to the pulsed light 1300 having the second wavelength.
This is an optical system for delaying 200. The delay optical system 300 includes an optical mirror 310, a lens 320, an optical fiber 330, a collimator lens 340, an optical mirror 350, and a dichroic mirror 360.

  The first wavelength pulsed light 1200 emitted from the oscillation unit 110 is guided to the lens 320 by the optical mirror 310, condensed, and incident on the optical fiber 330. Note that when light of the same wavelength is used as the pulsed light 1200 and the pulsed light 1210, it is preferable to place a beam splitter at the position of the optical mirror 310 to branch the same light.

Since the delay optical system 300 needs an optical path length for delaying the pulsed light 1200 having the first wavelength for a desired time, an optical fiber 330 having a long optical path length is used.
In order to separate the photoacoustic signals of the respective wavelengths generated by the alternate irradiation between the two wavelengths due to the optical delay, it is preferable that the generation of the photoacoustic signals of the respective wavelengths is separated by at least about 1 μs. For this reason, an optical delay of at least 1 μs is necessary. Since the speed of light in the optical fiber is 200 m / μs, it is preferable to use an optical fiber of at least 200 m. The optical fiber 330 is preferably used in a state of being wound around a bobbin.
The light passing through the optical fiber 330 is converted into parallel light by the collimator lens 340 and reflected by the optical mirror 350.

As the dichroic mirror 360, one that reflects the pulsed light 1200 having the first wavelength and transmits the pulsed light 1300 having the second wavelength is used.
With the above configuration, the pulsed light 1400 having the first wavelength and the pulsed light 1300 having the second wavelength are guided to the same optical path, and the pulsed light having the first wavelength and the second wavelength are alternately irradiated. It becomes. In addition, other optical elements (for example, a polarizing mirror) may be used instead of the dichroic mirror as long as the pulsed light of the first wavelength and the second wavelength can be multiplexed.

For example, consider a case where the oscillation unit 110 oscillates pulsed light 1200 having the first wavelength at 100 Hz and uses an optical fiber 330 of 400 m. In each oscillation, the pulsed light 1200 having the first wavelength reaches the dichroic mirror 360 with a delay of 2 μs from the pulsed light 1300 having the second wavelength. As a result, a set (pulsed light 1400) of the pulsed light 1200 having the first wavelength and the pulsed light 1300 having the second wavelength spaced apart by 2 μs is emitted every 10 ms. That is, the subject 1100 is irradiated with a set of pulsed light of the first wavelength and pulsed light of the second wavelength with a spacing of 2 μs at a repetition frequency of 100 Hz.
Since the photoacoustic measurement receives an acoustic wave generated by the expansion of the light absorber that has absorbed the light energy, the subject contracts between the light pulse of the first wavelength and the light pulse of the second wavelength. It is preferable to take the interval necessary to do so.

  In this embodiment, the first wavelength pulse light 1200 and the second wavelength pulse light 1300 are delayed by delaying the first wavelength pulse light 1200 with respect to the second wavelength pulse light 1300. Alternating irradiation was performed. However, conversely, the pulsed light 1300 having the second wavelength may be delayed with respect to the pulsed light 1200 having the first wavelength. In that case, a delay optical system is applied to the pulsed light 1300 having the second wavelength emitted from the wavelength conversion unit 120.

  In the present embodiment, a long optical path length is obtained using the optical fiber 330, but other methods may be used. For example, instead of the lens 320, the optical fiber 330, and the collimator lens 340, the optical path length can be obtained by repeatedly reflecting using an optical mirror.

(Waveguide optical system 400)
The waveguide optical system 400 guides the pulsed light 1400 of each wavelength guided to the same optical path by the dichroic mirror 360 to the subject 1100 and the photodetector 500.
The waveguide optical system 400 can use optical elements such as lenses, mirrors, and optical fibers. In the photoacoustic microscope, in order to increase the resolution, it is preferable that the light emitting portion of the waveguide optical system 400 is constituted by a lens or the like, and the irradiation is performed while focusing the diameter of the beam light. In addition, the waveguide optical system 400 may be moved with respect to the subject 1100, thereby enabling imaging of the subject 1100 over a wide range.

In the present embodiment, the waveguide optical system 400 includes an optical fiber 410, a lens 420, a collimator lens 430, a beam splitter 440, an axicon lens 450, and an optical mirror 460. The optical mirror 460 is arranged so that the pulsed light 1400 guided in an annular shape by the axicon lens 450 is condensed at the target position of the subject 1100. Further, it is preferable to use a beam splitter 440 having a reflectance within 5% at an incident angle of 45 degrees.
Further, in the biological information acquisition apparatus for examining the breast or the like, it is preferable that the light emitting unit of the waveguide optical system 400 is irradiated with a beam light having a diameter increased by a lens or the like.

(Photodetector 500)
A photodiode or a light energy meter can be used as the photodetector 500. A light detector other than these may be used as long as it can detect a part of the irradiation light guided by the beam splitter 440.

(Water tank 600)
The water tank 600 is a container capable of holding water 610 as an acoustic matching material. In the present embodiment, the conversion element 210 provided in the probe 200 is immersed in water 610. Thereby, acoustic matching between the subject 1100 and the conversion element 210 can be achieved via the water 610. The contact surface with the subject 1100 is preferably made of a film that is thinner than the wavelength of the photoacoustic wave so that the photoacoustic wave can easily pass therethrough. More preferably, the contact surface has a thickness that is ¼ of the wavelength of the photoacoustic wave. In addition, as the acoustic matching material and the material for the contact surface, a material that hardly absorbs the pulsed light 1400 is preferable. For example, water, ultrasonic gel, oil, or the like is preferable as the acoustic matching material, and polyethylene or the like is preferable as the contact surface.
In addition, it is preferable that the object 1100 and the contact surface are acoustically matched with an ultrasonic gel or the like.

(Processing unit 700)
The processing unit 700 includes a photoacoustic signal collection unit 710, a light amount signal collection unit 720, and a characteristic information calculation unit 730.

  The photoacoustic signal collection unit 710 collects time-series analog reception signals output from the conversion element 210, and signals such as reception signal amplification, analog reception signal AD conversion, and digitized reception signal storage Process. As the photoacoustic signal collection unit 710, a circuit generally called a DAS (Data Acquisition System) can be used. The photoacoustic signal collection unit 710 includes, for example, an amplifier that amplifies the received signal and an AD converter that digitizes the analog received signal.

  The light amount signal collecting unit 720 collects the reception signal output from the photodetector 500. The light amount signal collecting unit 720 performs signal processing such as amplification of received signals, AD conversion of analog received signals, storage of digitized received signals, and processing of converting the obtained received signals into light amount values as necessary. I do. The light amount signal collecting unit 720 is configured by, for example, an amplifier that amplifies the received signal and an AD converter that digitizes the analog received signal.

The characteristic information calculation unit 730 uses the received signals output from the photoacoustic signal collection unit 710 and the light amount signal collection unit 720 to acquire characteristic information related to the absorption coefficient in the subject, the concentration of the substance constituting the tissue, and the like. To do. In particular, information on oxygen saturation is acquired. Hereinafter, the characteristic information related to the oxygen saturation at each position in the subject is also referred to as the oxygen saturation distribution in the subject. Further, the characteristic information relating to the light absorption rate at each position in the subject is also referred to as a light absorption distribution in the subject.

The characteristic information calculation unit 730 includes a CPU, a processor such as a GPU (Graphics Processing Unit), an FPGA (Field Programmable).
An arithmetic circuit such as a Gate Array chip can be used. In addition, it may be comprised not only from one processor and an arithmetic circuit but from several processors and arithmetic circuits. Further, a memory for storing a received signal, generated distribution data, display image data, various measurement parameters, and the like may be provided. The memory is typically composed of one or more storage media such as a ROM, a RAM, and a hard disk.

(Control unit 800)
The control unit 800 supplies necessary control signals and data to each component block. Specifically, a signal for instructing the light source 100 to emit light, a reception control signal for the conversion element 200, and a control signal for the scanning mechanism 900 are supplied. Furthermore, signal amplification control, AD conversion timing control, reception signal storage control, and the like of the processing unit 700 are performed.

  Similarly to the processing unit 700, the control unit 800 can be configured by combining one or a plurality of circuits such as a processor such as a CPU and a GPU and an FPGA chip. Moreover, you may provide the memory which memorize | stores various measurement parameters. The memory is typically composed of one or more storage media such as a ROM, a RAM, and a hard disk. These can be used together with the processing unit 700.

(Scanning mechanism 900)
For example, an automatic stage using a stepping motor or a servo motor can be used as the scanning mechanism 900. In the configuration of FIG. 1, the scanning mechanism 900 scans the measurement unit 1500. As a result, photoacoustic measurement is performed while scanning measurement points on the subject 1100. However, such a configuration is not necessarily required, and it is only necessary to perform measurement while scanning measurement points on the subject 1100.
Further, the irradiation light 1400 may be applied to a wide range of the subject 1100, and the scanning mechanism 900 may scan only the probe 200.

An acoustic focus type configuration in which a probe capable of receiving a wide range of photoacoustic waves (for example, a single transducer or an array type transducer with a wide focus range) is fixed is also possible. In this case, the irradiation light 1400 is condensed and irradiated onto the subject 1100, and the scanning mechanism 900 scans only a part of the waveguide optical system 400, thereby scanning the measurement point.
Thus, when the probe 200 is not scanned, it is not always necessary to use a liquid such as water as the acoustic matching material. For example, instead of the water tank 600 and the water 610, a gel member (for example, polyurethane-based gel) or the like can be used.

As a scanning method by the scanning mechanism 900, there are a method of changing the position of a part of the probe 210 and the waveguide optical system 400, and a method of changing the angle.
Further, the scanning mechanism 900 may scan the photoacoustic wave detection position and the irradiation position of the irradiation light 1400 by moving the mirror using a mirror that reflects the photoacoustic wave and the irradiation light 1400. Even in this case, both a method of scanning both the irradiation light 1400 and the detection position of the photoacoustic wave and a method of scanning only one of them can be employed. When moving the mirror, the angle or position of the mirror may be changed. As a mirror capable of such an operation, for example, there is a galvanometer mirror or a MEMS mirror.

(Display unit 1000)
As the display unit 1000, a display such as an LCD (Liquid Crystal Display), a CRT (Cathode Ray Tube), or an organic EL display can be used. The display unit 1000 may be prepared separately from the photoacoustic apparatus of the present embodiment and connected to the photoacoustic apparatus.

(Handheld type)
The present invention can also be applied to a handheld photoacoustic apparatus. In that case, the member surrounded by the dotted line 1600 may be held as one casing.

[Subject information acquisition method]
Next, a flow in which the photoacoustic apparatus according to the present embodiment acquires object information will be described with reference to FIG. The control unit 800 reads a program describing the object information acquisition method stored in the processing unit 700, and causes the photoacoustic apparatus to execute the following object information acquisition method.

(S110: Step of starting photoacoustic measurement)
In this step, the control unit 800 instructs each component unit to start photoacoustic measurement. Specifically, the scanning mechanism 900 starts scanning, and the oscillation unit 110 oscillates the pulsed light 1200 having the first wavelength using a signal output from the scanning mechanism 900 as a trigger.

(S120: Step of collecting photoacoustic signals)
In this step, during the photoacoustic measurement, the photoacoustic signal collection unit 710 collects time-series analog reception signals output from the conversion element 210 at each measurement position.
During the photoacoustic measurement, the oscillation unit 110 oscillates the pulsed light 1200 of the first wavelength using a signal output every time the scanning mechanism 900 performs equidistant scanning, thereby collecting photoacoustic signals at regular intervals. It is preferable.

  FIG. 3 is an example of a timing chart of photoacoustic measurement processing. In FIG. 3, the upper stage is a trigger signal during photoacoustic measurement, the middle stage is the irradiation timing of the pulse light 1200 of the first wavelength and the pulse light 1300 of the second wavelength to the subject 1100, and the lower stage is the light generated by each pulse light. This is the timing at which the acoustic signal reaches the conversion element 210. In this example, the oscillation unit 110 oscillates pulsed light 1200 having the first wavelength at a pulse repetition frequency (PRF) of 100 Hz.

  Since the trigger signal 301 is input to the oscillation unit 110 at 100 Hz, the input interval 302 is 10 ms. When the trigger signal 301 is input to the oscillation unit 110, the oscillation unit 110 oscillates, and first irradiates the subject 1100 with the pulsed light 303 with the second wavelength and then with the pulsed light 304 with the first wavelength. The irradiation interval 305 between the pulse light 303 having the second wavelength and the pulse light 304 having the first wavelength is a delay time generated by the delay optical system 300. For example, when the 400 m optical fiber 330 is used, the irradiation interval 305 is 2 μs. A set of the pulsed light 303 having the second wavelength and the pulsed light 304 having the first wavelength is irradiated to the subject 1100 every 10 ms.

Then, after an interval 306 from the irradiation of the pulsed light 303 having the second wavelength, the photoacoustic signal 307 generated by the pulsed light 303 having the second wavelength reaches the conversion element 210. The interval 306 is determined by the distance between the conversion element and the light absorber and the sound velocity of the medium, and can be obtained by calculation if these values are known. Then, the photoacoustic signal 308 generated by the pulsed light 304 having the first wavelength reaches the conversion element 210 with a delay of the interval 309. The interval 309 is the same time as the irradiation interval 305.
The photoacoustic signal collection unit 710 receives a photoacoustic signal using a pulsed light emitted from the light source 100 as a trigger. The trigger signal can be created based on the light detection result by the photodiode.

(S130: Step of collecting light quantity signal)
In this step, during the photoacoustic measurement, the light amount signal collection unit 720 collects the reception signal output from the photodetector 500 at each measurement position.

  4A to 4C show examples of received signals in the photoacoustic signal collection unit 710 and the light amount signal collection unit 720. FIG. In this example, an Nd: YAG laser capable of emitting a second harmonic and a third harmonic is used as the oscillation unit 110, an OPO unit is used as the wavelength conversion unit 120, and a 54 m optical fiber is used as the optical fiber 410. At this time, the first wavelength pulsed light is pumped by the OPO unit by the pulsed light having a wavelength of 532 nm, which is the second harmonic of the Nd: YAG laser, and the pulsed light of the second wavelength is excited by the third harmonic of the Nd: YAG laser. The 556 nm pulsed light was used. A black body printed on the film was used as the light absorber.

In FIG. 4A, the series indicated by the dotted line is the light intensity received by the light quantity signal collecting unit 720, and corresponds to the left axis. In this series, the signal 401 is a received signal of pulsed light of the second wavelength, and the signal 402 is a received signal of pulsed light of the first wavelength.
A series indicated by a solid line is the photoacoustic signal intensity received by the photoacoustic signal collection unit 710 and corresponds to the right axis. In this series, the signal 403 is a photoacoustic signal derived from pulsed light of the second wavelength, and the signal 404 is a photoacoustic signal derived from pulsed light of the first wavelength. The photoacoustic signal of each wavelength is received with a delay from the time of light irradiation for the time required for the generated photoacoustic wave to reach the conversion element 210 from the light absorber (about 7.5 μs here). I understand.

FIG. 4B is an enlarged graph of a pulsed light signal for each wavelength in the light amount signal collecting unit 720 in FIG. 4A. It can be seen that the signal 402 is received delayed from the signal 401 by about 270 ns for the optical path of the 54 m optical fiber.
4C is an enlarged graph of the photoacoustic signal received by the photoacoustic signal collection unit 710 in FIG. 4A. It can be seen that the signal 404 is received with a delay of about 270 ns from the signal 403, reflecting the delay of light irradiation between wavelengths.

(S140: Step of calculating photoacoustic signal intensity distribution of each wavelength)
In this step, the characteristic information calculation unit 730 calculates a photoacoustic signal intensity distribution (also referred to as a sound pressure distribution) for each wavelength based on the reception signals for each wavelength collected by the photoacoustic signal collection unit 710.

  Consider a case where the photoacoustic signal collection unit 710 receives a photoacoustic signal using either the pulsed light 1300 having the second wavelength or the pulsed light 1200 having the first wavelength as a trigger. In this case, the photoacoustic wave derived from the pulsed light 1300 having the second wavelength and the photoacoustic wave derived from the pulsed light 1200 having the first wavelength delayed by the optical delay time are collected as a series of photoacoustic signals. Output from the unit 710.

In this case, the characteristic information calculation unit 730 needs to separate the photoacoustic wave derived from the pulsed light 1200 having the first wavelength from the photoacoustic wave derived from the pulsed light 1300 having the second wavelength. As a separation method, a method of separating a received signal by time, pattern matching, threshold processing, or the like can be used. Note that this processing is not necessary when the photoacoustic signal collection unit 710 receives a photoacoustic signal using both the pulsed light 1300 having the second wavelength and the pulsed light 1200 having the first wavelength as triggers.

  When the photoacoustic apparatus is a photoacoustic microscope as in the present embodiment, the characteristic information calculation unit 730 performs envelope detection on the obtained photoacoustic reception signal for each wavelength with respect to time change, and then an optical pulse. The time axis direction in each signal is converted into the depth direction and plotted on the space coordinates. Then, sound pressure distribution data is acquired by performing this for each measurement position (scanning position).

On the other hand, when the photoacoustic apparatus is a photoacoustic tomography apparatus, the characteristic information calculation unit 730 performs image reconstruction using the obtained photoacoustic reception signal for each wavelength. Thereby, generated sound pressure data corresponding to a position on a two-dimensional or three-dimensional spatial coordinate can be acquired. Image reconstruction methods include Universal Back Projection (UBP) and Filtered
A known method such as Back Projection (FBP) can be used. As an image reconstruction method, a delay and sum process may be used.

(S150: Step of calculating irradiation light quantity of each wavelength)
In this step, the characteristic information calculation unit 730 calculates the light amount for each wavelength at each measurement position based on the reception signals for each wavelength collected by the light amount signal collection unit 720.
For example, when the photodetector 500 is a photodiode, the characteristic information calculation unit 730 uses the peak value of the received signal for each wavelength output from the photodiode at each measurement point as the light amount. Further, the integrated value of the received signal may be calculated to obtain the light amount.
Furthermore, it is preferable that the light can be converted into the amount of light irradiated on the subject 1100 based on the peak value and the integrated value for each wavelength. In that case, it is preferable that the characteristic information calculation part 730 memorize | stores such a conversion coefficient and a conversion formula.

(S160: Step of calculating light absorption distribution of each wavelength)
In this step, the characteristic information calculation unit 730 calculates a light absorption distribution of each wavelength from the photoacoustic signal intensity distribution of each wavelength obtained in S140 and the irradiation light amount of each wavelength at each measurement position obtained in S150.

  When the photoacoustic apparatus is a photoacoustic microscope as in the present embodiment, the characteristic information calculation unit 730 uses the light amount value at each measurement position for each wavelength obtained in S150, and each measurement position obtained in S140. The sound pressure distribution data at is corrected. Thereby, light absorption distribution data at each measurement position is obtained. For example, the light absorption distribution data at each measurement position for each wavelength is obtained by dividing the sound pressure distribution data by the light amount value.

  On the other hand, when the photoacoustic apparatus is a photoacoustic tomography apparatus, the characteristic information calculation unit 730 calculates the light amount distribution for each wavelength in the subject 1100 using the light amount value at each measurement position for each wavelength obtained in S150. . Then, the light absorption distribution data at each measurement position for each wavelength is calculated by dividing the sound pressure distribution data for each wavelength obtained in S140 by the light amount distribution for each wavelength. The light quantity distribution for each wavelength in the subject 1100 can be calculated using a finite element method or a Monte Carlo method based on the light transport equation or the light diffusion equation.

(S170: Step of calculating oxygen saturation distribution)
In this step, the characteristic information calculation unit 730 obtains a distribution related to the concentration of the substance present in the subject using the light absorption distribution data of each wavelength obtained in S160. In particular, the oxygen saturation distribution of blood is obtained based on the concentrations of oxyhemoglobin HbO and deoxyhemoglobin Hb.

(S180: An oxygen saturation distribution image is displayed)
In this step, the characteristic information calculation unit 730 transmits the characteristic information data obtained in S170 to the display unit 1000, and causes the display unit 1000 to display an image of the subject information. Note that the display unit 1000 can display various information such as numerical values of subject information, diagrams and symbols indicating tissues or functions in the body, instead of or together with images.

  In the present embodiment, the apparatus configuration and flow for alternately irradiating pulsed light of two wavelengths have been described. However, when the light source can emit pulsed light of 3 wavelengths or more, irradiation with light of 3 wavelengths or more can be performed by using a delay optical system having a different optical path length for the pulsed light of each wavelength. Is possible. In that case, a delay optical system having a plurality of optical fibers having different lengths corresponding to the respective wavelengths is preferable. Thereby, it can comprise so that the optical path length of the optical path along which the light of each wavelength passes mutually differs.

  As described above, according to the photoacoustic apparatus according to the present embodiment, light of two wavelengths can be alternately irradiated at short intervals, so that the positional deviation between wavelengths due to body movement of the subject is reduced. As a result, the oxygen saturation calculation accuracy is improved. In addition, since light of a plurality of wavelengths can be irradiated from a single oscillation unit, cost and device scale can be suppressed.

  The present invention has been described in detail above with reference to specific embodiments. However, the present invention is not limited to the specific form described above, and the embodiments can be modified without departing from the technical idea of the present invention.

  100: Light source, 200: Probe, 300: Delay optical system, 400: Waveguide optical system, 500: Photo detector, 700: Processing unit

Claims (17)

A light source that emits pulsed light of a first wavelength and pulsed light of a second wavelength different from the first wavelength at different timings;
A delay optical system that delays the pulsed light of the first wavelength with respect to the pulsed light of the second wavelength;
A conversion element that receives a photoacoustic wave generated by irradiating a subject with each of the pulsed light beams having the first and second wavelengths and outputs a reception signal;
A photodetector for detecting the amount of each of the pulsed light of the first and second wavelengths;
The received signal derived from each of the first and second wavelength pulse lights output from the conversion element, and each of the first and second wavelength pulse lights detected by the photodetector. A processing unit for acquiring characteristic information of the subject based on the light amount;
A subject information acquisition apparatus characterized by comprising: The object information acquiring apparatus according to claim 1, wherein the light source emits pulsed light having a plurality of wavelengths including at least the first wavelength and the second wavelength. The light source has an oscillation unit and a wavelength conversion unit,
The at least one of the first wavelength pulsed light and the second wavelength pulsed light is emitted from the oscillation unit and then converted in wavelength by the wavelength conversion unit. 3. The subject information acquisition apparatus according to 1 or 2. 4. The object information acquiring apparatus according to claim 1, wherein the light source repeatedly emits a set of pulsed light having a first wavelength and pulsed light having a second wavelength. 5. The object information acquiring apparatus according to claim 1, wherein the delay optical system includes an optical fiber. The object information acquiring apparatus according to claim 5, wherein the length of the optical fiber is 200 m or more. The processing unit has a light absorption distribution of the subject at the first wavelength based on the received signal derived from the pulsed light of the first wavelength and the light quantity of the pulsed light of the first wavelength. And obtaining the light absorption distribution of the subject at the second wavelength based on the received signal derived from the pulsed light of the second wavelength and the light quantity of the pulsed light of the second wavelength. The object information acquiring apparatus according to claim 1, wherein the object information acquiring apparatus is acquired. The object information acquiring apparatus according to claim 7, wherein the processing unit acquires a concentration distribution of a substance in the object using the light absorption distributions at the first and second wavelengths. . 9. The object information acquiring apparatus according to claim 8, wherein the concentration distribution of the substance is an oxygen saturation distribution. The object information acquiring apparatus according to claim 3, wherein the oscillation unit emits at least one of a fundamental wave, a second harmonic wave, and a third harmonic wave. The object information acquiring apparatus according to claim 3, wherein the oscillation unit is an Nd: YAG laser. The object information acquiring apparatus according to claim 1, wherein the processing unit separates the reception signal output from the conversion element for each wavelength. The object information acquiring apparatus according to claim 1, further comprising a display unit configured to display characteristic information of the object. A light source that emits pulsed light of a plurality of wavelengths at different timings;
A delay optical system that delays the pulsed light of each wavelength with a different delay time for each wavelength;
A conversion element that receives a photoacoustic wave generated by irradiating a subject with each of the pulsed light beams of each wavelength that has passed through the delay optical system, and outputs a received signal;
A photodetector for detecting the respective light amounts of the pulsed light of each wavelength;
Based on the received signal derived from the pulsed light of each wavelength output from the conversion element and the light quantity of the pulsed light of each wavelength detected by the photodetector, characteristic information of the subject A processing unit for acquiring
Have
2. The object information acquiring apparatus according to claim 1, wherein the delay optical system is configured such that optical path lengths of optical paths through which the pulsed light beams having different wavelengths pass are different from each other. The object information acquiring apparatus according to claim 14, wherein the delay optical system includes a plurality of optical fibers having different lengths. A light source emitting pulsed light of a first wavelength and pulsed light of a second wavelength different from the first wavelength at different timings;
A delay optical system delaying the pulsed light of the first wavelength with respect to the pulsed light of the second wavelength;
A conversion element that receives a photoacoustic wave generated by irradiating the subject with each of the pulsed light beams having the first and second wavelengths and outputs a reception signal;
A photodetector detecting the respective light amounts of the pulsed light of the first and second wavelengths;
The received signal derived from each of the first and second wavelength pulse lights output from the conversion element by the processing unit, and the first and second wavelength pulses detected by the photodetector Obtaining characteristic information of the subject based on the respective light quantities of light;
A method for controlling a subject information acquiring apparatus, comprising: A light source emitting pulsed light of a plurality of wavelengths at different timings;
A delay optical system delaying the pulsed light of each wavelength with a different delay time for each wavelength;
A conversion element that receives a photoacoustic wave generated by irradiating a subject with each of the pulsed light of each wavelength that has passed through the delay optical system and outputs a reception signal;
A photodetector detecting the respective light amounts of the pulsed light of each wavelength;
Based on the received signal derived from the pulsed light of each wavelength output from the conversion element and the light quantity of the pulsed light of each wavelength detected by the photodetector, the processing unit Obtaining specimen characteristic information; and
Have
In the delaying step, the pulse information of each wavelength passes through optical paths having different optical path lengths.

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