TITLE OF INVENTION OBJECT INFORMATION ACQUIRING APPARATUS AND METHOD OF CONTROLLING

THE SAME

Technical Field

[0001] The present invention relates to an object information acquiring apparatus and a method of controlling the same .

Background Art

[0002] A photoacoustic imaging technique is known as one of imaging techniques which use light. In the photoacoustic imaging technique, first, an object is irradiated with a pulsed light generated from a light source. The irradiation beam propagates through and diffuses into the object and the energy of the beam is absorbed by a plurality of portions inside the object, whereby an acoustic wave (hereinafter referred to as a photoacoustic wave) is generated. A transducer receives the photoacoustic wave and the received signal is analyzed by a processing device, whereby information on optical

characteristics inside the object is acquired as image data. As a result, a optical characteristic distribution inside the object is visualized.

[0003] Recently, in order to image a finer light absorber using photoacoustic waves, the imaging resolution needs to be improved. Moreover, a photoacoustic microscope that focuses sound or a pulsed light to image light absorbers such as fine blood vessels near the surface of an object with high resolution has been developed. Patent Literature 1 improves resolution by focusing a pulsed light using lenses so that an object is disposed at a focal position of the beam.

[0004] Moreover, by radiating light having different wavelengths, a concentration distribution of a substance present inside an object can be obtained. In this case, it is possible to image a concentration distribution of a substance using the value of an absorption coefficient of light inside the object obtained for each wavelength and the wavelength dependency of optical absorption unique to the substance. In particular, the oxygen saturation of the blood can be acquired based on the concentration of oxyhemoglobin HbO and deoxyhemoglobin Hb.

[0005] When two wavelengths are used, the oxygen saturation

S0 ₂ can be acquired by Equation (1) .

[Math. 1]

Here, μ _Ά represents an absorption coefficient at a wavelength λι and μ _Ά represents an absorption coefficient at a wavelength λ ₂ . Moreover, B _H bo ^Xl represents a molar absorption coefficient of oxyhemoglobin at the wavelength λ _χ and s _H ^l represents a molar absorption coefficient of deoxyhemoglobin at the wavelength λχ . Moreover, E _H o represents a molar absorption coefficient of oxyhemoglobin at the wavelength λ ₂ and 8 _Hb represents a molar absorption coefficient of deoxyhemoglobin at the wavelength λ ₂ . The coefficients ε _Η ι>ο ^λ1 _/ £nb ^l , ε _Η ΐ ₃ θ ^λ2 , and z _Ri> ^X2 are known values. In addition, r represents a position coordinate. As illustrated in Equation (1), the ratio of the absorption coefficients at two wavelengths is required to obtain the oxygen saturation of the blood.

[0006] When the oxygen saturation distribution is calculated using two wavelengths, photoacoustic measurement is performed based on the first wavelength and photoacoustic measurement is performed based on the second wavelength, whereby the optical absorption distribution of the blood in the object at the respective wavelengths is obtained. However, since a living body has motions, pulsations, and breaths, the like, the object may move during the measurement based on the first and second wavelengths. As a result, the optical absorption distribution obtained at the respective wavelengths (that is, the position of the blood vessel measured based on the respective wavelengths) may shift. When a positional shift occurs, since the ratio of absorption coefficients of two wavelengths at respective positions has a wrong value, a wrong oxygen saturation is obtained.

[0007] In order to solve such a problem, a method of alternately irradiating an object with light of respective wavelengths is known (this method is hereinafter referred to as alternate irradiation) . With the alternate irradiation, it is possible to suppress a positional shift of respective wavelengths resulting from the motion at the respective measurement positions. The shorter the emission interval of the pulsed lights of two wavelengths (that is, the shorter the interval between the time at which an object is irradiated with a pulsed light of a first wavelength and the time at which the object is irradiated with a pulsed light of a second wavelength) , the less the influence of a positional shift of the wavelengths due to the motion at the respective measurement position and the more accurate the obtained oxygen saturation distribution.

Citation List

Patent Literature

[0008] PTL 1: Japanese Translation of PCT Application No.

2011-519281

SUMMARY OF INVENTION

Technical Problem

[0009] In order to perform the alternate irradiation, a method of alternately radiating pulsed lights at different points in time using two light sources that emit light of different wavelengths. However, this method incurs the cost for mounting two light sources and needs to control the emission of the two light sources.

Moreover, a method of performing alternate irradiation using one wavelength-variable mechanism such as a

wavelength-variable light source. However, in order to prevent a positional shift due to pulsations or breaths, it is necessary to shorten the emission interval of the pulsed lights of the two wavelengths. Thus, a complex high-speed wavelength-variable control technique is required.

[0010] In view of the above problems, it is an object of the present invention to provide a photoacoustic imaging technique which uses light having a plurality of wavelengths, capable of performing high-accuracy measurement while reducing the cost.

Solution to Problem

[0011] The present invention provides an object

information acquiring apparatus comprising:

a light source that emits a pulsed light of a first wavelength and a pulsed light of a second wavelength, which is different from the first wavelength, at different points in time; a delay optical system that delays the pulsed light of the first wavelength relative to the pulsed light of the second wavelength;

a conversion element that receives photoacoustic waves generated when the pulsed lights of the first and second wavelengths are radiated to an object and outputs reception signals;

a photodetector that detects light quantities of the pulsed lights of each of the first and second wavelengths; and a processor that acquires characteristics information on the object based on the reception signals originating from the pulsed lights of each of the first and second wavelengths, which have been output from the conversion element, and the light quantities of the pulsed lights of each of the first and second wavelengths, which have been detected by the photodetector .

[0012] The present invention also provides an object information acquiring apparatus comprising:

a light source that emits pulsed lights having a plurality of wavelengths at different points in time;

a delay optical system that delays the pulsed lights of the respective wavelengths by different delay periods for respective wavelengths;

a conversion element that receives photoacoustic waves generated when the pulsed lights of respective wavelengths that have passed through the delay optical system are radiated to an object and outputs reception signals;

a photodetector that detects light quantities of the pulsed lights of the respective wavelengths; and

a processor that acquires characteristics information on the object based on the reception signals originating from the pulsed lights of the respective wavelengths, which have been output from the conversion element, and the light quantities of the pulsed lights of the respective wavelengths, which have been detected by the photodetector, wherein

the delay optical system is configured such that optical paths through which the pulsed lights of the respective wavelengths pass have different optical path lengths.

[0013] The present invention also provides a method of controlling an object information acquiring apparatus, the method comprising:

allowing a light source to emit a pulsed light of a first wavelength and a pulsed light of a second wavelength, which is different from the first wavelength, at different points in time; allowing a delay optical system to delay the pulsed light of the first wavelength relative to the pulsed light of the second wavelength;

allowing a conversion element to receive photoacoustic waves generated when the pulsed lights of each of the first and second wavelengths are radiated to an object and output reception signals ;

allowing a photodetector to detect light quantities of the pulsed lights of each of the first and second wavelengths; and allowing a processor to acquire characteristics information on the object based on the reception signals originating from the pulsed lights of each of the first and second wavelengths, which have been output from the conversion element, and the light quantities of the pulsed lights of each of the first and second wavelengths, which have been detected by the photodetector.

[0014] The present invention also provides a method of controlling an object information acquiring apparatus, the method comprising:

allowing a light source to emit pulsed lights having a plurality of wavelengths at different points in time;

allowing a delay optical system to delay the pulsed lights of the respective wavelengths by different delay periods for respective wavelengths;

allowing a conversion element to receive photoacoustic waves generated when the pulsed lights of respective wavelengths that have passed through the delay optical system are radiated to an object and output reception signals;

allowing a photodetector to detect light quantities of the pulsed lights of the respective wavelengths; and

allowing a processor to acquire characteristics

information on the object based on the reception signals originating from the pulsed lights of the respective wavelengths, which have been output from the conversion element, and the light quantities of the pulsed lights of the respective wavelengths, which have been detected by the photodetector, wherein

the pulsed lights of the respective wavelengths pass though optical paths having different optical path lengths.

Advantageous Effects of Invention

[0015] According to the present invention, it is possible to provide a photoacoustic imaging technique which uses light having a plurality of wavelengths, capable of performing high-accuracy measurement while reducing the cost.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS [0016] Fig. 1 is a schematic diagram illustrating a configuration of a photoacoustic apparatus.

Fig. 2 is a flowchart illustrating an example of the flow of acquiring object information.

Fig. 3 is a timing chart illustrating an example of measurement by a photoacoustic apparatus.

Fig. 4A is a graph illustrating light irradiation and reception signals of generated photoacoustic waves.

Fig. 4B is a partially enlarged graph illustrating light irradiation and reception signals of generated photoacoustic waves.

Fig. 4C is a partially enlarged graph illustrating light irradiation and reception signals of generated photoacoustic waves.

DESCRIPTION OF EMBODIMENTS

[0017] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Dimensions, materials, shapes, relative arrangements, and the like of constituent components described below are to be appropriately changed according to the configuration and various conditions of an apparatus to which the present invention is applied, and the scope of the present invention is not limited to those described below.

[0018] The present invention relates to a technique of detecting acoustic waves having propagated from an object, and generating and acquiring specific information on the interior of the object. Thus, the present invention can be understood as an object information acquiring apparatus or a control method thereof, and alternatively, as an object information acquiring method and a signal processing method. Moreover, the present invention can be understood as a program for allowing an information processing apparatus having hardware resources such as a CPU to execute these methods and a storage medium having the program stored therein. Further, the present invention can be understood as an acoustic wave measurement apparatus and a control method thereof.

[0019] The object information acquiring apparatus according to the present invention includes an apparatus which uses a photoacoustic technique to irradiate an object with light (electromagnetic waves) to receive (detect) acoustic waves having propagated through the object after being generated inside or on the surface of the object according to a

photoacoustic effect. Such an object information acquiring apparatus can be referred to as a photoacoustic imaging apparatus, a photoacoustic image apparatus, or simply a photoacoustic apparatus as characteristics information on the interior of the object is obtained in a format such as image data based on photoacoustic measurement.

[0020] The characteristics information in the

photoacoustic apparatus indicates a generation source

distribution of the acoustic waves generated by light

irradiation, an initial acoustic pressure distribution inside the object, an optical energy absorption density distribution and an absorption coefficient distribution derived from the initial acoustic pressure distribution, or a concentration distribution of a substance that constitutes a tissue. Specific examples of the characteristics information include a blood component distribution such as oxyhemoglobin and

deoxyhemoglobin concentration distributions or an oxygen saturation distribution derived from the distributions. The characteristics information may be a fat concentration, a glucose concentration, a collagen concentration, a melanin concentration, and a volume fraction of fats and water.

Moreover, the characteristics information may be obtained as distribution information relative to respective positions inside an object rather than as numerical data. That is, the characteristics information may be 2-dimensional or

3-dimensional distribution information such as an absorption coefficient distribution or an oxygen saturation distribution.

[0021] Acoustic waves referred in the present invention are typically ultrasound waves, and include elastic waves called sound waves and acoustic waves. The acoustic waves generated by the photoacoustic effect are referred to as photoacoustic waves or light-induced ultrasound waves. Electrical signals converted from acoustic waves by a probe are also referred to as acoustic signals, and acoustic signals originating from photoacoustic waves are referred to as photoacoustic signals in particular.

[0022] A main object of the apparatus of the present invention is to examine blood diseases or malignant tumors of a person or an animal or to perform follow-up examination of chemotherapy. Thus _f the object may be a part of a living body, and specifically, the skin, hypodermic segments, breast, neck, and abdomen of a person or an animal may be the examination obj ect . In particular, a segment within several millimeters from the surface of the skin is ideal as the examination object. The object is not limited thereto, however, and other segments of a living body and non-living materials can be also measured.

[0023] Typical examples of the light absorber inside the object include oxyhemoglobin or deoxyhemoglobin inside a living body, a blood vessel that contains many oxyhemoglobins or deoxyhemoglobins , and a malignant tumor that contains many angiogenesis . The light absorber preferably has a relatively high absorption coefficient inside the object. Besides this, melanoma, plaque on the carotid wall, or the like may be the light absorber .

[0024] <First Embodiment>

Hereinafter, a configuration and a process of an object information acquiring apparatus according to a first embodiment will be described.

[0025] (Apparatus Configuration)

Fig. 1 is a schematic diagram illustrating a configuration of a photoacoustic apparatus according to the present embodiment. The photoacoustic apparatus according to the present embodiment includes a light source 100 including an oscillating unit 110 and a wavelength converting unit 120, a probe 200 including a conversion element 210, and a delay optical system 300 for delaying light emitted from the oscillating unit 110. The photoacoustic apparatus further includes a guiding optical system 400 for guiding light having a plurality of wavelengths to an object, a photodetector 500, a water tank 600, a processor 700, a controller 800, a scanning mechanism 900, and a display unit 1000.

[0026] A pulsed light 1200 of a first wavelength emitted from the oscillating unit 110 is guided to the delay optical system 300.

The pulsed light 1200 of the first wavelength delayed by the delay optical system 300 and a pulsed light 1300 of a second wavelength excited by a pulsed light 1210 from the oscillating unit 110 and emitted from the wavelength converting unit 120 are guided to the same optical path by an optical element. The optical element is a dichroic mirror 360, for example. In this case, the pulsed light 1200 of the first wavelength arrives at a delay corresponding to the period, in which the pulsed light 1200 propagates through the delay optical system 300, relative to the pulsed light 1300 of the second wavelength. The pulsed lights 1400 of the respective wavelengths guided to the same optical path are alternately radiated to an object 1100 through the guiding optical system 400 and reach a light absorber 1110 in the object 1100.

[0027] The light absorber 1110 absorbs the energy of the light of the respective wavelengths to generate photoacoustic waves of respective wavelengths. The generated photoacoustic waves propagate through the object to reach the conversion element 210.

Upon receiving the photoacoustic waves, the conversion element 210 outputs time-sequential reception signals. In the present embodiment, the conversion element 210 (the reception surface) of the probe 200 is immersed in water 610 as an acoustic matching material in the water tank 600. In this way, acoustic matching between the object 1100 and the conversion element 210 is realized.

[0028] The photodetector 500 detects a portion of the pulsed lights 1400 and outputs a reception signal.

The scanning mechanism 900 scans a measurement unit 1500 including the probe 200, a portion of the optical system 400, and the photodetector 500 during photoacoustic measurement.

The controller 800 controls respective constituent blocks in the photoacoustic apparatus by supplying necessary control signals and data to the constituent blocks.

The processor 700 sequentially receives the reception signals output from the conversion element 210 and the photodetector 500. The processor 700 generates object information using the signals input from the conversion element 210 and the photodetector 500. The processor 700 transmits data of the generated object information to the display unit 1000 to display images and numerical values of the object information.

[0029] Hereinafter, the respective constituent blocks will be described in detail.

(Light Source 100)

The light source 100 includes the oscillating unit 110 and the wavelength converting unit 120. The light generated by the oscillating unit 110 and the wavelength converting unit 120 is preferably a pulsed light on the order of nanoseconds to microseconds. A specific pulse width is preferably

approximately between 1 to 100 nanoseconds. Moreover, the wavelength of the light is preferably between approximately 300 nm and 1600 nm. When a blood vessel near the surface of a living body is imaged with high resolution, light in the visible wavelength region (between 400 nm and 700 nm) is preferred. On the other hand, when a deep portion of a living body is imaged, light having a wavelength (700 nm or more and 1100 nm or smaller) in which the light is rarely absorbed in the background tissue of a living body is preferred. However, light in the terahertz, microwave, and radio wave regions can be also used.

[0030] Although various lasers such as a solid-state laser, a semiconductor laser, or a gas laser can be used as the oscillating unit 110, a solid-state laser is particularly preferable. Specifically, a Nd:YAG laser (a laser which uses the crystal structure of the neodymium-doped yttrium aluminum garnet) which uses a semiconductor laser or a flash lamp as excitation light can be used. Further, these lasers are preferably capable of generating second harmonics and third harmonics and emitting light of respective wavelengths.

Besides the Nd:YAG laser, a Nd:YV0 ₄ laser (a laser which uses the crystal structure of the neodymium-doped yttrium vanadate) , a Nd:YLF laser (a laser which uses the crystal structure of the neodymium-doped yttrium lithium fluoride) , and other lasers can be used.

[0031] One of the light beams such as a fundamental wave, a second harmonic, a third harmonic, and the like oscillated by the oscillating unit 110 is emitted from the oscillating unit 110 as the pulsed light 1200 of the first wavelength. Similarly, one of the laser beams such as a fundamental wave, a second harmonic, a third harmonic, and the like oscillated by the oscillating unit 110 is guided to the wavelength converting unit 120 as the pulsed light 1210 and becomes the pulsed light 1300 of the second wavelength different from the first wavelength of the pulsed light 1200. The pulsed light 1200 and the pulsed light 1210 may have the same wavelength and different wavelengths.

[0032] A dye laser, a Ti:sa (titanium-sapphire) laser, an optical parametric oscillators (OPO) laser, or the like can be used as the wavelength converting unit 120. The dye or crystal in these lasers is excited by the pulsed light 1210 to oscillate the pulsed light 1300 of the second wavelength different from the first wavelength of the pulsed light 1200. When a dye laser is used, Pyrromethene 597, for example, can be used as the dye. In this case, a second harmonic of a Nd:YAG laser having a wavelength of 532 nm can be used as the pulsed light 1210. Moreover, when the OPO laser is used, a second harmonic of the Nd:YAG laser or a third harmonic having a wavelength of 355 nm is used as the pulsed light 1210 depending on the second wavelength of the pulsed light 1300. Further, when the Ti:sa laser is used, the second harmonic of the Nd:YAG laser can be used as the pulsed light 1210. [0033] Moreover, when measurement is performed using light having various wavelengths, a laser capable of changing an oscillating wavelength is more preferably used as the wavelength converting unit 120. When the first and second wavelengths of a wavelength-variable laser are selected, light having a wavelength in which the light is efficiently absorbed in oxyhemoglobin and deoxyhemoglobin is preferred.

As described above, although a laser is preferred as the light source 100, a light-emitting diode, a flash lamp, or the like can be used instead of the laser.

[0034] (Probe 200)

The probe 200 includes one or more conversion elements 210 and a housing. An arbitrary conversion element capable of receiving acoustic waves and converting the acoustic waves into electrical signals, such as a piezoelectric element (for example, lead zirconate titanate (PZT) ) which uses a piezoelectric phenomenon, a conversion element which uses resonance of light, or a capacitive conversion element (for example, CMUT) can be used as the conversion element 210.

When the photoacoustic apparatus is a photoacoustic microscope as illustrated in Fig. 1, the probe 200 is preferably a focus-type probe. That is, an acoustic lens is preferably mounted on a reception surface of the conversion element 210.

[0035] Moreover, in order to acquire object information of a wide range of areas, the probe 200 is preferably mechanically movable in relation to the object 1100 by the scanning mechanism 900. In this case, a portion (an irradiation position of the pulsed lights 1400) of the optical system 400 and the probe 200 are preferably moved in synchronism.

Moreover, when the probe 200 is a handheld-type probe, the probe 200 has a holding portion with which a user holds the probe 200.

[0036] When the photoacoustic apparatus is a photoacoustic tomography apparatus, a plurality of conversion elements 210 is preferably provided in the probe 200. When a plurality of conversion elements 210 is provided, the conversion elements are preferably disposed so as to be aligned in a flat surface or a curved surface referred to as a ID. 1.5D, 1.75D, or 2D array.

Moreover, an amplifier for amplifying analog signals output from the conversion element 210 may be provided in the probe 200.

[0037] (Delay Optical System 300)

The delay optical system 300 is an optical system for delaying the pulsed light 1200 of the first wavelength in relation to the pulsed light 1300 of the second wavelength. 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.

[0038] The pulsed light 1200 of the first wavelength emitted from the oscillating unit 110 is guided to the lens 320 by the optical mirror 310 and is concentrated and incident on the optical fiber 330. When light having the same wavelength is used as the pulsed lights 1200 and 1210, a beam splitter is preferably disposed at the position of the optical mirror 310 so as to split the same light.

[0039] Since the delay optical system 300 requires an optical path length for delaying the pulsed light 1200 of the first wavelength by a desired period, an optical fiber having a large optical path length is used as the optical fiber 330.

Moreover, in order to separate the photoacoustic signals of the respective wavelengths, occurring due to alternate radiation of light having two wavelengths with an optical delay, the occurrences of the photoacoustic signals of the respective wavelengths are preferably separated by at least 1 με . Thus, an optical delay of at least 1 is required. Since the velocity of light in an optical fiber is 200 ιη/μ3, it is preferable to use an optical fiber having a length of at least 200 m. The optical fiber 330 is preferably used in a state of being wound around a bobbin.

The light having passed through the optical fiber 330 is collimated by the collimator lens 340 and is reflected by the optical mirror 350.

[0040] A mirror capable of reflecting the pulsed light 1200 of the first wavelength and transmitting the pulsed light 1300 of the second wavelength is used as the dichroic mirror 360.

With this configuration, the pulsed lights 1200 and 1300 of the first and second wavelengths are guided to the same optical path and become the pulsed lights 1400 which radiate the pulsed lights of the first and second wavelengths alternately.

i

Moreover, another optical element (for example, a deflecting mirror) may be used instead of the dichroic mirror as long as the element can couple the pulsed lights of the first and second wavelengths .

[0041] For example, a case, in which the oscillating unit

110 oscillates the pulsed light 1200 of the first wavelength at a frequency of 100 Hz and the optical fiber 330 having a length of 400 m is used, will be considered. In each oscillation, the pulsed light 1200 of the first wavelength reaches the dichroic mirror 360 with a delay of 2 μβ from the pulsed light 1300 of the second wavelength. As a result, a set (the pulsed lights 1400) of the pulsed lights 1200 and 1300 of the first and second wavelengths with an interval of 2 ε is emitted every 10 ms . That is, the object 1100 is irradiated with the set of the pulsed lights of the first and second wavelengths with an interval of 2 μ≤ at a repetition frequency of 100 Hz.

Since the photoacoustic measurement involves receiving acoustic waves generated by expansion of a light absorber having absorbed the optical energy, the pulsed lights of the first and second wavelengths preferably occur at an interval required for the object to be contracted.

[0042] In the present embodiment, the pulsed light 1200 of the first wavelength is delayed in relation to the pulsed light 1300 of the second wavelength so that the pulsed lights 1200 and 1300 of the first and second wavelengths are alternately radiated. However, conversely, the pulsed light 1300 of the second wavelength may be delayed in relation to the pulsed light 1200 of the first wavelength. In this case, the delay optical system is applied to the pulsed light 1300 of the second wavelength emitted from the wavelength converting unit 120.

[0043] Moreover, in the present embodiment, although a large optical path length is obtained using the optical fiber 330, another method may be used. For example, the large optical path length may be obtained by repeatedly reflecting light using an optical mirror instead of using the lens 320, the optical fiber 330, and the collimator lens 340.

[0044] (Guiding Optical System 400)

The guiding optical system 400 guides the pulsed lights- 1400 of the respective wavelengths guided to the same optical path by the dichroic mirror 360 to the object 1100 and the photodetector 500.

An optical element such as a lens, a mirror, and an optical fiber can be used as the guiding optical system 400. In a photoacoustic microscope, in order to increase the resolution, a light output portion of the guiding optical system 400 is preferably formed of a lens or the like so that the diameter of an irradiation light beam is focused. Moreover, the guiding optical system 400 may be moved in relation to the object 1100, whereby a large area of the object 1100 can be imaged.

[0045] Moreover, in the present embodiment, the guiding 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 disposed so that the pulsed light 1400 guided in a ring form by the axicon lens 450 is focused at a target position of the object 1100. Moreover, a beam splitter having a reflectivity smaller than 5% at an inclination angle of 45° is preferably used as the beam splitter 440.

Moreover, in a living body information acquiring apparatus that examines the breast or the like, the light output portion of the guiding optical system 400 preferably radiates a light beam, with the diameter thereof being increased by a lens or the like .

[0046] (Photodetector 500)

A photodiode and an optical energy meter can be used as the photodetector 500. A photodetector other than these elements may be used as long as the photodetector can detect a portion of the irradiation light guided by the beam splitter 440.

[0047] (Water Tank 600)

The water tank 600 is a container capable of storing the water 610 as an acoustic matching material. In the present embodiment, the conversion element 210 provided in the probe 200 is immersed in the water 610. In this way, acoustic matching between the object 1100 and the conversion element 210 can be realized by the water 610. Moreover, a surface of the tank in contact with the object 1100 is preferably formed of a film thinner than the wavelength of the photoacoustic wave so that the photoacoustic wave can easily pass from the film. More preferably, the contacting surface preferably has a thickness of 1/4 of the wavelength of the photoacoustic wave. Moreover, the acoustic matching material and the contacting surface are preferably formed of a material that rarely absorbs the pulsed light 1400. For example, water, ultrasound gel, oil, or the like is ideally used as the acoustic matching material, andpolyethylene or the like is ideally used as the contacting surface.

Moreover, acoustic matching is preferably realized between the object 1100 and the contacting surface by ultrasound gel or the like.

[0048] (Processor 700)

The processor 700 includes a photoacoustic signal collecting unit 710, a light quantity signal collecting unit 720, and a characteristics information calculating unit 730.

[0049] The photoacoustic signal collecting unit 710 performs signal processing of collecting time-sequential analog reception signals output from the conversion element 210, amplifying the reception signals, A/D converting the analog reception signals, and storing the digital reception signals. A circuit generally called a data acquisition system (DAS) can be used as the photoacoustic signal collecting unit 710. The photoacoustic signal collecting unit 710 includes an amplifier that amplifies reception signals and an A/D converter that digitalizes analog reception signals, for example.

[0050] The light quantity signal collecting unit 720 collects reception signals output from the photodetector 500. The light quantity signal collecting unit 720 performs signal processing of amplifying reception signals, A/D converting analog reception signals, storing digital reception signals, and converting the obtained reception signals into light quantity values, as necessary. The light quantity signal collecting unit 720 includes an amplifier that amplifies reception signals and an A/D converter that digitalizes analog reception signals, for example .

[0051] The characteristics information calculating unit

730 acquires characteristics information relative to the absorption coefficient inside an object and the concentration of substances that form tissues using the reception signals output from the photoacoustic signal collecting unit 710 and the light quantity signal collecting unit 720. In particular, the characteristics information calculating unit 730 acquires information on the oxygen saturation. Hereinafter, the characteristics information relative to the oxygen saturation at respective positions in the object is also referred to as an oxygen saturation distribution inside an object. Moreover, the characteristics information on the absorption coefficient of light at respective positions inside an object is also referred to as an optical absorption distribution inside an object.

[0052] A processor such as a CPU or a graphics processing unit (GPU) or an arithmetic circuit such as a field programmable gate array (FPGA) chip can be used as the characteristics information calculating unit 730. The characteristics information calculating unit 730 may be formed of one processor or arithmetic circuit and may be formed of a plurality of processors or arithmetic circuits. Moreover, the

characteristics information calculating unit 730 may include a memory that stores reception signals, generated distribution data, display image data, and various measurement parameters. The memory is typically formed of at lease one storage media such as a ROM, a RAM, or a hard disk.

[0053] (Controller 800)

The controller 800 supplies necessary control signals or data to the respective constituent blocks. 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. Further, the controller 800 controls signal amplification, AD conversion timing, and storage of reception signals, of the processor 700.

[0054] The controller 800 can be also formed of one or a plurality of processors, such as a CPU or a GPU, or circuits, such as a FPGA chip, in combination similarly to the processor 700. Moreover, the controller 800 may include a memory that stores various measurement parameters and the like. The memory is typically formed of at least one storage media such as a ROM, a RAM, or a hard disk. These elements may be shared by the processor 700.

[0055] (Scanning Mechanism 900)

An automated stage formed of a stepping motor and a servo motor, for example, can be used as the scanning mechanism 900. In the configuration.of Fig. 1, the scanning mechanism 900 scans the measurement unit 1500. In this way, the scanning mechanism 900 performs photoacoustic measurement while scanning measurement positions on the object 1100. However, such a configuration is not essential , and measurement may be performed while scanning the measurement positions on the object 1100.

Moreover, the irradiation light 1400 may be radiated to a large area of the object 1100 and the scanning mechanism 900 may scan the probe 200 only.

[0056] Moreover, an acoustic focusing configuration in which a probe (for example, a single transducer or an array transducer having a wide focusing range) capable of receiving a photoacoustic wave in a wide range is fixed may be used. In this case, the irradiation light 1400 is focused and radiated to the object 1100 and the scanning mechanism 900 scans only a portion of the guiding optical system 400, whereby the measurement positions are scanned.

When the probe 200 is not scanned as described above, it is not always necessary to use liquid such as water as the acoustic matching material. For example, a gel member (for example, polyurethane-based gel) or the like may be used instead of the water tank 600 and the water 610.

[0057] A method of changing the position or the angle of a portion of the probe 210 or the guiding optical system 400 may be used as the scanning method of the scanning mechanism 900.

Further, the scanning mechanism 900 may scan the detection position of photoacoustic waves and the irradiation position of the irradiation light 1400 by moving a mirror that reflects the photoacoustic waves and the irradiation light 1400. In this case, both the method of scanning both detection positions of the irradiation light 1400 and the photoacoustic waves and the method of scanning only one of both positions can be employed. The mirror may be moved by changing the position or the angle of the mirror. For example, a galvanic mirror or a MEMS mirror may be used as the mirror capable of performing such an operation.

[0058] (Display Unit 1000)

A display such as a liquid crystal display (LCD) , a cathode ray tube (CRT) , or an organic EL display can be used as the display unit 1000. The display unit 1000 may be provided separately from the photoacoustic apparatus of the present embodiment and be connected to the photoacoustic apparatus .

[0059] (Handheld Type)

The present invention can be applied to a handheld photoacoustic apparatus. In this case, members surrounded by dot line 1600 may be stored in one housing.

[0060] (Object Information Acquisition Method)

Next, the flow in which the photoacoustic apparatus according to the present embodiment acquires object information will be described with reference to Fig. 2. The controller 800 reads a program which is stored in the processor 700 and in which an object information acquisition method is described and allows the photoacoustic apparatus to execute the following object information acquisition method.

[0061] (S110: Photoacoustic Measurement Starting Step)

In this step, the controller 800 instructs the respective constituent blocks to start photoacoustic measurement.

Specifically, when the scanning mechanism 900 starts scanning and the scanning mechanism 900 outputs a signal, the oscillating unit 110 oscillates the pulsed light 1200 of the first wavelength using the signal as a trigger signal.

[0062] (S120: Photoacoustic Signal Collecting Step)

In this step, during photoacoustic measurement, the photoacoustic signal collecting unit 710 collects the time-sequential analog reception signals output from the conversion element 210 at respective measurement positions.

During photoacoustic measurement, the oscillating unit 110 preferably oscillates the pulsed light 1200 of the first wavelength using the signal output whenever the scanning mechanism 900 scans an equal distance as a trigger signal, whereby the photoacoustic signals are collected at equal intervals .

[0063] Fig. 3 illustrates an example of the timing chart of a photoacoustic measurement process. In Fig. 3, a trigger signal during photoacoustic measurement is illustrated at the top, the timing at which the pulsed lights 1200 and 1300 of the first and second wavelengths are radiated to the object 1100 is illustrated at the middle, and the timing at which the photoacoustic signals occurring due to the respective pulsed lights reach the conversion element 210 is illustrated at the bottom. In this example, the oscillating unit 110 oscillates the pulsed light 1200 of the first wavelength at a pulse repetition frequency (PRF) of 100 Hz.

[0064] Since a trigger signal 301 is input to the oscillating unit 110 at the frequency of 100 Hz, the input interval 302 is 10 ms . When the trigger signal 301 is input to the oscillating unit 110, the oscillating unit 110 oscillates so that a pulsed light 303 of the second wavelength and a pulsed light 304 of the first wavelength are radiated to the object 1100 in that order. The irradiation interval 305 between the pulsed light 303 of the second wavelength and the pulsed light 304 of the first wavelength is a delay period caused by the delay optical system 300, and the irradiation interval 305 is 2 μ3 when the optical fiber 330 having the length of 400 m is used, for example. The set of the pulsed light 303 of the second wavelength and the pulsed light 304 of the first wavelength is radiated to the object 1100 at intervals of 10 ms .

[0065] After the elapse of the interval 306 from irradiation of the pulsed light 303 of the second wavelength, a photoacoustic signal 307 occurring due to the pulsed light 303 of the second wavelength reaches the conversion element 210. Since the interval 306 is determined by the distance between the conversion element and the light absorber and the velocity of sound in a medium, the interval can be acquired by computation if these values are known. A photoacoustic signal 308 occurring due to the pulsed light 304 of the first wavelength reaches the conversion element 210 with a delay of the interval 309. The interval 309 is the same period as the irradiation interval 305.

The photoacoustic signal collecting unit 710 receives the photoacoustic signal using the pulsed light emitted by the light source 100 as a trigger signal . The trigger signal can be created based on the photo detection result obtained by the photodiode.

[0066] (S130: Light Quantity Signal Collecting Step)

In this step, during photoacoustic measurement, the light quantity signal collecting unit 720 collects the reception signals output from the photodetector 500 at respective measurement positions.

[0067] Figs. 4A to 4C illustrate examples of reception signals received by the photoacoustic signal collecting unit 710 and the light quantity signal collecting unit 720. In this example, a Nd:YAG laser capable of outputting second and third harmonics was used as the oscillating unit 110, an OPO unit was used as the wavelength converting unit 120, and an optical fiber having the length of 54 m was used as the optical fiber 410. In this case, a pulsed light having the wavelength of 532 nm which is the second harmonic of the Nd:YAG laser was used as the pulsed light of the first wavelength and a pulsed light having the wavelength of 556 nm excited by the OPO unit with the third harmonic of the Nd:YAG laser was used as the pulsed light of the second wavelength. A black body printed on a film was used as the light absorber.

[0068] In Fig. 4A, a group of signals indicated by dot lines is the light intensity received by the light quantity signal collecting unit 720 and corresponds to the left axis. In this group of signals, a signal 401 is the reception signal of the pulsed light of the second wavelength and a signal 402 is the reception signal of the pulsed light of the first wavelength.

Moreover, a group of signals indicated by -solid lines is the photoacoustic signal intensity received by the photoacoustic signal collecting unit 710 and corresponds to the right axis. In this group of signals, a signal 403 is a photoacoustic signal originating from the pulsed light of the second wavelength and a signal 404 is a photoacoustic signal originating from the pulsed light of the first wavelength. It can be understood that the photoacoustic signals of the respective wavelengths are received with a delay from the irradiation time, corresponding to a period (in this example, approximately 7.5 μβ ) required for the generated photoacoustic waves reach the conversion element 210 from the light absorber.

[0069] Fig. 4B is an enlarged graph of the pulsed light signals of respective wavelengths received by the light quantity signal collecting unit 720 in Fig. 4A. It can be understood that the signal 402 is received with a delay of approximately 270 ns from the signal 401 corresponding to the optical path length of 54 m of the optical fiber.

Fig. 4C is an enlarged graph of the photoacoustic signals received by the photoacoustic signal collecting unit 710 in Fig. 4A. It can be understood that the signal 404 is received with a delay of approximately 270 ns from the signal 403 by reflecting the delay of light radiations between wavelengths.

[0070] (S140: Wavelength-Based Photoacoustic Signal

Intensity Distribution Calculating Step)

In this step, the characteristics information calculating unit 730 calculates a photoacoustic signal intensity

distribution (also referred to as an acoustic pressure distribution) of each wavelength based on the reception signals of respective wavelengths collected by the photoacoustic signal collecting unit 710. [0071] ^' A case in which the photoacoustic signal collecting unit 710 receives the photoacoustic signal using any one of the pulsed lights 1200 and 1300 of the first and second wavelengths as a trigger signal will be considered. In this case, a photoacoustic wave originating from the pulsed light 1300 of the second wavelength and a photoacoustic wave originating from the pulsed light 1200 of the first wavelength delayed by an optical delay period are output from the photoacoustic signal collecting unit 710 as a series of photoacoustic signals.

[0072] In this case, the characteristics information calculating unit 730 may need to separate the photoacoustic wave originating from the pulsed light 1200 of the first wavelength and the photoacoustic wave originating from the pulsed light 1300 of the second wavelength. A method of segmenting the reception signals by time to separate the reception signals, a pattern matching method, a threshold processing method, and the like can be used as the separating method. This process is not necessary when the photoacoustic signal collecting unit 710 receives photoacoustic signals using both the pulsed lights 1200 and 1300 of the first and second wavelengths as a trigger signal.

[0073] As in the present embodiment, when the photoacoustic apparatus is a photoacoustic microscope, the characteristics information calculating unit 730 detects the envelope with time of the obtained photoacoustic reception signals of respective wavelengths, converts the time-axis direction of the pulsed light signals to a depth direction, and plots the photoacoustic reception signals on spatial coordinates. This process is performed for respective measurement positions (scanning positions) whereby acoustic distribution data is acquired.

[0074] On the other hand, when the photoacoustic apparatus is a photoacoustic tomography apparatus, the characteristics information calculating unit 730 reconstructs an image using the obtained photoacoustic reception signals of respective wavelengths. In this way, it is possible to acquire data on acoustic pressure corresponding to the positions on

2-dimensional or 3-dimensional spatial coordinates. An existing method such as universal back projection (UBP) or filtered back projection (FBP) may be used as the image reconstruction method. A delay and sum process may be used as the image reconstruction method.

[0075] (S150: Wavelength-Based Irradiation Light Quantity

Calculating Method)

In this step, the characteristics information calculating unit 730 calculates the light quantities of respective wavelength at respective measurement positions based on the reception signals of respective wavelengths collected by the light quantity signal collecting unit 720.

For example, when the photodetector 500 is a photodiode, the characteristics information calculating unit 730 calculates the peak values the reception signals of respective wavelengths output from the photodiode at the respective measurement positions as the light quantities. Moreover, the integration value of the reception signals may be calculated as the light quantity . Further, it is preferable to convert the peak value and the integration value of respective wavelengths into the light quantity of light radiated to the object 1100. In this case, the characteristics information calculating unit 730 preferably stores such a conversion coefficient and a conversion formula.

[0076] (S160: Wavelength-Based Optical Absorption

Distribution Calculating Step)

In this step, the characteristics information calculating unit 730 calculates the optical absorption distributions of respective wavelengths based on the photoacoustic signal intensity distortions of respective wavelengths calculated in S140 and the irradiation light quantities of respective wavelengths at respective measurement positions calculated in S150.

[0077] As in the present embodiment, when the photoacoustic apparatus is a photoacoustic microscope, the characteristics information calculating unit 730 corrects the acoustic pressure distribution data at respective measurement positions calculated in S140 using the light quantity values at respective measurement positions of respective wavelengths calculated in S150. By doing so, the optical absorption distribution data at respective measurement positions is obtained. For example, the acoustic pressure distribution data is divided by the light quantity value, whereby the optical absorption distribution data at respective measurement position of respective wavelengths is acquired.

[0078] On the other hand, when the photoacoustic apparatus is a photoacoustic tomography apparatus, the characteristics information calculating unit 730 calculates a light quantity distribution of respective wavelengths in the- object 1100 using the light quantity values at respective measurement positions of respective wavelengths calculated in S150. The acoustic pressure distribution data of respective wavelengths calculated in S140 is divided by the light quantity distribution of respective wavelengths, whereby the optical absorption distribution data at respective measurement positions of respective wavelengths is calculated. The light quantity distribution of respective wavelengths in the object 1100 can be calculated using a finite element method or a Monte Carlo method based on a light transport equation or a light diffusion equation .

[0079] (S170: Oxygen Saturation Distribution Calculating

Step)

In this step, the characteristics information calculating unit 730 calculates a distribution of concentrations of substances present inside an object using the optical absorption distribution data of respective wavelengths calculated in S160. In particular, the oxygen saturation distribution of the blood is calculated based on the concentrations of oxyhemoglobin HbO and deoxyhemoglobin Hb.

[0080] (S180: Oxygen Saturation Distribution Image

Displaying Step)

In this step, the characteristics information calculating unit 730 transmits the data of the characteristics information calculated in S170 to the display unit 1000 so that the image of the object information is displayed on the display unit 1000. The display unit 1000 may display various types of information such as the values of the object information or the figures or symbols indicating the tissues or functions inside the body instead of or together with images.

[0081] In the present embodiment, the configuration and the flow of operations of the apparatus that alternately radiates pulsed lights of two wavelengths have been described. However, when a light source can emit pulsed lights of three wavelengths or more, a set of pulsed lights having three wavelengths or more may be radiated using delay optical systems having different optical path lengths. In this case, a delay optical system having a plurality of optical fibers having different lengths corresponding to the respective wavelengths may be ideally used. By doing so, the light of respective wavelengths passes through optical paths having different optical path lengths.

[0082] As described above, according to the photoacoustic apparatus of the present embodiment, since light of two wavelengths can be alternately radiated at a short interval, a positional shift between wavelengths resulting from the motion of an object. As a result, the calculation accuracy of the oxygen saturation is improved. Moreover, since light of a plurality of wavelengths can be radiated from a single oscillating unit, it is possible to decrease the cost and the apparatus size.

[0083] The present invention has been described in detail with reference to specific embodiments. However, the present invention is not limited to the specific embodiments and. the embodiments may be modified without departing from the technical scope and spirit of the present invention.

[0084] Other Embodiments

Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions recorded on a storage medium (e.g., non-transitory computer-readable storage medium) to perform the functions of one or more of the above-described embodiment (s) of the present invention, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment (s) . The computer may comprise one or more of a central processing unit (CPU) , micro processing unit (MPU) , or other circuitry, and may include a network of separate computers or separate computer processors . The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM) , a read only memory (ROM) , a storage of distributed computing systems, an optical disk (such as a compact disc (CD) , digital versatile disc (DVD) , or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.

[0085] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

[0086] This application claims the benefit of Japanese

Patent Application No . 2014-242172, filed on November 28 , 2014, which is hereby incorporated by reference herein in its entirety.