WO2013031586A1

WO2013031586A1 - Object information acquiring apparatus and object information acquiring method

Info

Publication number: WO2013031586A1
Application number: PCT/JP2012/071114
Authority: WO
Inventors: Kenji Oyama
Original assignee: Canon Kabushiki Kaisha
Priority date: 2011-08-30
Filing date: 2012-08-15
Publication date: 2013-03-07
Also published as: JP2013048671A; JP5818582B2

Abstract

Provided is an object information acquiring apparatus including: a holding plate which holds an object; a probe which detects an acoustic wave propagated from the inside of the object irradiated with measurement light and converts the acoustic wave into an electric signal; an image processor which generates an image inside the object from the electric signal; a photodetector which detects light reflected by a peripheral part as a region that does not come into contact with the holding plate in the object; and a discerning unit which discerns a contact state between the holding plate and the object using a detection result of the photodetector.

Description

DESCRIPTION

Title of Invention

OBJECT INFORMATION ACQUIRING APPARATUS AND OBJECT INFORMATION ACQUIRING METHOD

Technical Field

[ 0001 ]

The present invention relates to an object information acquiring apparatus and an object

information acquiring method.'

Background Art

[ 0002 ]

Regarding a technique of acquiring a tomographic image using light, many techniques have been proposed so far. As one of these techniques, PTL 1 discloses a photoacoust ic imaging apparatus. This apparatus uses a technique of a photoacoustic tomography (PAT) . The photoacoustic imaging apparatus is particularly valid in the diagnosis of a skin cancer or a breast cancer, and has gained attention as a medical instrument which may be used instead of an ultrasonic imaging apparatus, an X-ray apparatus, or an MRI apparatus that has been used so far for the same diagnosis.

[0003]

When measurement light such as visible light or near infrared light is irradiated to a tissue of a living body, a light absorbing material inside the living body, and particularly, a material such as hemoglobin in blood instantly expands by absorbing the energy of the measurement light, thereby generating an acoustic wave. This phenomenon is called a photoacoustic effect, and the generated acoustic wave is called a photoacoustic wave. In the photoacoustic imaging apparatus, informat i on of the tissue of the living body is visualized by measuring the photoacoustic wave. By the technique of the photoacoustic imaging apparatus, a light energy absorption density distribution, that is, a distribution of density of a light absorbing material inside the living body may be measured quantitatively and

three-dimensionally.

[ 000 ]

Further, since light is used to acquire the tomographic image, the photoacoustic imaging apparatus may provide diagnostic imaging without any radiation exposure and invasion. Accordingly, this apparatus has l rge competitiveness from the viewpoint of the patient ' s burden. Therefore, instead of the X-ray apparatus which may not easily conduct repeated diagnosis, the photoacoustic imaging apparatus may screen and early diagnose the breast cancer.

[0005]

In the photoacoustic imaging apparatus, based on the principle of the photoacous t ic measurement, the initial acoustic pressure P₀ of the photoacous tic wave which is generated when the light absorbing material absorbs the measurement light is calculated by the following equation (1) .

[Math. 1]

Ρ_α=Γ-μ_α·Φ ( i )

Here, Γ is a Gruneisen coefficient, and is obtained by dividing the product of a square of a volume expansion coefficient β and an acoustic speed c by an isobaric specific heat C_p . It is known that Γ becomes a substantially constant value due to the object. μ₃ is a light absorption coefficient of the light absorbing material. Φ is a light-amount in a local region inside the object, that is, the amount of light (optical f luence) that actually reaches the light absorbing material.

[0006]

According to Equation (1) , the distribution of the product of μ₃ and Φ, that is, the light energy absorption density distribution may be calculated by dividing the distribution of the initial acoustic pressure P₀ by the

Gruneisen coefficient Γ. The distribution of the initial acoustic pressure P₀ may be obtained by measuring a change in time of the acoustic pressure P of the pho toacous tic wave that is propagated inside the object and reaches the probe. Further, in order to calculate the distribution of the light absorption coefficient μ₃ inside the object as the diagnosis subject, there is a need to calculate the distribution of the light amount Φ inside the object. Since the measurement light penetrates the object to the deep portion thereof while being strongly diffused and attenuated inside the object, the light amount Φ that actually reaches the light absorbing material is calculated from the light attenuation amount and the penetration depth in the object.

[ 0007 ]

In a case where a region which is sufficiently large with respect to the object holding distance is irradiated with measurement light having a uniform light amount, when a boundary condition is set on the assumption that light is propagated inside the object as a planar wave, the light amount Φ inside the object may be expressed by the following equation (2) .

[Math. 2]

Here, μ_Βίί is an average effective light attenuation coefficient of the object. Φ₀ is a light amount of the measurement light irradiated to the object, that is, a light amount of the surface of the object. Further, d is a distance from a measurement light irradiation region of the surface of the object to the light absorbing material emitting a photoacous t ic wave.

[ 0008 ]

As described above, according to Equation (1) and Equation (2), it is possible to quantitatively measure a density distribution of the light absorbing material inside the object as the diagnosis subject.

Citation List

Patent Literature

[0009]

PTL 1: US Patent No. 5713356

Summary of Invention

Technical Problem

[0010]

In the photoacous tic imaging apparatus which acquires thephotoacoustic image while holding the object by the holding plate, the shape of the object is uni formly fixed in a wide area due to the holding operation. Accordingly, according to Equation (2) , the light amount distribution inside the object may be calculated. In the surface of the object, the position where the measurement light is incident to the object and starts to be strongly diffused and attenuated may be assumed as the boundary surface with respect to the holding plate . Accordingly, the distance d from the measurement light irradiation region of the surface of the object to the light absorbing material may be calculated from the gap between the holding plates.

[0011]

However, in the photoacoust ic imaging apparatus which two- dimens iona 11 y scans a photoacoust ic

measurement position and acquires a three-dimensional photoacoust ic image, the shape of the object changes in accordance with the measurement position, and does not match the boundary condition of the light amount distribution calculation equation of Equation (2) in some cases .

[ 0012 ]

For example, in a mammary department, a subject of a diagnosis of abreast cancer corresponds to a peripheral part of a breast as an object. In the peripheral part of the breast, there is a gap between the breast and a holding plate since the breast is away from the holding plate. For this reason, in the peripheral part, the distance d from the surface of the object to the light absorbing material does not match the holding gap of the holding plate. The measurement light is irradiated to the object without any attenuation and with high energy while traveling the gap between the holding plate and the surface of the breast. For this reason, when the light amount distribution calculation equation

(Equation 2) is appliedwithout discerning the peripheral part, the quant itativeness of the light absorbing material distribution may not be ensured in the peripheral part and the other regions.

[0013]

As described above, in the diagnosis of the breast cancer, like the peripheral part of the breast, there is a region in which the quantitat iveness of the acquired image lacks. However, there is not any method of discerning the region so far.

[ 001 ]

The invention is made in consideration of the above-described problems, and it is an object of the invention to provide a pho toacous t i c imaging apparatus that holds an object by a holding plate, where the quant itativeness of the measurement is ensured by discerning the region of the peripheral part of the object.

Solution to Problem

[0015]

The invention provides an object information acquiring apparatus comprising:

a holding plate which holds an object;

a probe which detects an acoustic wave propagated from the inside of the object irradiated with measurement light and converts the acoustic wave into an electric signal ;

an image processor which generates an image inside the object from the electric signal;

a photode tector which detects light reflected by a peripheral part as a region of the object that does not come into contact with the holding plate; and a discerning unit which discerns a contact state between the holding plate and the object using a detection result of the photodet ector .

[0016]

The invention also provides an object information acquiring method comprising:

holding an object by a holding plate;

detecting, by a probe, an acoustic wave propagated from the inside of the object irradiated by measurement light and converting the acoustic wave into an electric signal ;

generating, by an image processor, an image inside the object from the electric signal;

detecting, by a pho todetecto r , light reflected by a peripheral part as a region which does not come into contact with the holding plate in the object; and discerning, by a discerning unit, a contact state between the holding plate and the object using a detection result of the pho todetector .

Advantageous Effects of Invention

[ 0017 ]

According to the configuration of the invention, in the photoacoust ic imaging apparatus which holds the object by the holding plate, the region of the object peripheral part is discerned, and hence the

quant i t at ivene s s of the measurement may be ensured.

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

[ 0018 ]

Fig. 1 is an entire diagram illustrating a configuration of a photoacoust ic imaging system of a first embodiment.

Figs .2A and 2B are conceptual diagrams illustrating a method of acquiring photoacous tic image acquired data of the first embodiment.

Fig. 3 is a conceptual diagram illustrating an object peripheral part of the first embodiment.

Figs. 4A to 4C are conceptual diagrams illustrating a light distribution correction appropriate region of the first embodiment.

Figs. 5A to 5C are conceptual diagrams illustrating a light distribution correction inappropriate region of the first embodiment.

Figs. 6A to 6C are conceptual diagrams illustrating a position where an object is not present in the first embodiment .

Fig. 7 is a flowchart illustrating an operation of acquiring a pho to acous t i c image of the first embodiment .

Fig. 8 is an entire diagram illustrating a configuration of a pho toacous t i c imaging system of a second embodiment.

Figs . 9Aand 9B are conceptual diagrams illustrating a method of discerning an object peripheral part in the second embodiment.

Figs. 1 OA and 10B are conceptual diagrams illustrating discerning of the object peripheral part of the second embodiment.

Fig. 11 is a flowchart illustrating an operation of acquiring a photoacoust ic image of the second embodiment .

Description of Embodiments

[0019]

Hereinafter, referring to the drawings, preferred embodiments of the invention will be exemplarily described .

Furthermore, a photoacoust ic image acquiring operation in the description below indicates that a photoacous tic wave propagated from the inside of an object is received and photoacous tic data corresponding to characteristics inside the object is acquired. Further, an image constructing process which generates an image corresponding to a distribution of information on characteristics inside the object, and part i cu 1 ar 1 y , optical characteristic information using the

photoacoustic data also may be included in the photoacoustic image acquiring operation. From the photoacoustic data, an initial acoustic pressure distribution, a light energy absorption density distribution, a distribution of a light absorption coefficient or a material density, and the like may be calculated, and these information items may be called object information which represents an object state. Accordingly, a photoacoustic imaging apparatus of the invention may be called an object information acquiring apparatus which acquires object information.

[0020]

A first embodiment which uses a photoacoustic imaging apparatus and a photoacoustic imaging method of the invention will be described according to the drawings .

[ 0021 ]

Fig. 1 is an entire diagram of a configuration of the photoacoustic imaging system of the first embodiment .

A photoacoustic imaging apparatus of the first embodiment includes a holding plate 102 which holds an object 101, a holding control unit 103 which controls the holding in a state suitable for the image acquiring operation, an irradiation unit 104 which irradiates measurement light, and a photoacous t ic wave detection unit 105 which detects a photoacous tic wave. Further, the photoacoustic imaging apparatus includes a photoacous t i c measurement unit 106 which amplifies a signal detected by the photoacoustic wave detection unit 105 and converts the result into a digital signal, a signal process unit 107 which performs an integration process, a storage process, or the like of the detected photoacoustic wave signal, and a scanning control unit 110 which two- dimens i ona 11 y controls the measurement position. Furthermore, the photoacoustic imaging apparatus includes a control unit 111 which receives an image acquiring instruction from an image processing device 120 serving as an external process device and an I/F 112 with respect to the image processing device 120.

Furthermore, the photoacoustic imaging apparatus of the embodiment particularly includes a side light detection unit 108 which detects light reflected to the lateral side of the obj ect by the surface of the peripheral part of the object 101 and a peripheral part discerning unit 109 which is a characteristic of the invention.

[ 0022 ]

The object 101 which is an image acquiring subject is a breast in the diagnosis of a mammary department.

Furthermore, the photoacoustic imaging apparatus o f the invent i on may be us ed for , for example, amalignant tumor, a blood vessel disease, or the like of a human or an animal. Accordingly, as the object, a diagnosis object portion such as hands and feet or fingers of a human or an animal may be supposed other than the breast .

[0023]

The holding plate 102 includes a pair of holding plates 102A and 102B, and is controlled at a holding gap which is best suitable for the measurement by the holding control unit 103. In a case where there is no need to distinguish the holding plates 102A and 102B from each other, they are referred to as the holding plate 102. Since the object 101 is fixed to the apparatus while being interposed between the holding plates 102, a measurement error which is caused by the movement of the object 101 may be reduced.

Furthermore, since the holding plate 102 is positioned on the optical path of the measurement light, it is desirable to have high t ransmi s s ivi t y with respect to the measurement light. Also, since the holding plate 102B is particularly positioned on a path where the photoacous tic wave is propagated, it is desirable to use a member that has a high acoustic matching property with respect to an ultrasonic probe inside the photoacous tic wave detection unit 105. Further, when an acoustic matching material such as a gel sheet for measuring an ultrasonic wave is used, it is possible to obtain the stronger acoustic coupling between the ultrasonic probe and the holding plate 102B.

The holding control unit 103 adjusts the state where the object 101 is held in a holding gap and a pressure best suitable for the photoacous t ic image acquiring operation so as to match a burden on a subject or a penetration depth of the measurement light.

[ 0024 ]

The irradiation unit 104 irradiates measurement light to the object 101. The irradiation unit 104 includes an irradiation optical system which guides measurement light from a laser beam source, generating pulsed light (having a width of 100 nsec or less) having a central wavelength in a near-infrared region of 530 to 1300 nm, to the object and a movement mechanism which moves the irradiation position of the measurement light with respect to the holding plate.

As the irradiation optical system which is used to guide light, a mirror which reflects light, a lens which collects or broadens light or changes a shape thereof, a prism which disperses, refracts, or reflects light, an optical fiber which propagates light, a diffusion plate, andthe likemaybe exemplified. As such an optical system, any type may be used when the light radiated from the light source is irradiated in a desired shape to the obj ect .

As a light source (not illustrated), solid-state laser (for example, Yttrium-Aluminium-Garnet laser or Titan-Sapphire laser) capable of generating pulsed light generally having a central wavelength in a near- infrared region is used.

[0025]

Furthermore, the wavelength of the measurement light is selected from 530 nm to 1300 nm in response to a light absorbing material (for example, hemoglobin, glucose, cholesterol, and the like) inside a living body serving as a measurement object.

Hemoglobin in a neovascular vessel of a breast cancer as a measurement object generally absorbs light of 600 to 1000 nm. On the other hand, since the light absorption of water constituting the living body is the smallest near 830 nm, the light absorption relatively increases from 750 to 850 nm . Further, since the light absorption rate changes due to the hemoglobin state (the oxygen saturation degree), there is a possibility that a functional change of a living body may be also measured by using the wavelength dependency.

[0026]

Further, in the inside of the irradiation unit 104, an optical configuration ( not i 1 lus t rat ed ) for detecting the measurement light is provided in order to control the storage of the photoacoustic wave signal in synchronization with the irradiation of the measurement light. The detection of the measurement light is performed in a manner such that a part of the measurement light actually irradiated to the object 101 is divided by an optical system such as a half mirror and the divided light is guided to an installed optical sensor. When the measurement light is detected, the detection synchronization signal of the photoacoust ic wave signal is transmitted to the photoacous ti c wave detection unit 105·.

[ 0027 ]

The photoacous tic wave detection unit 105 detects the p otoacoustic wave emitted and propagated inside the object 101 and converts the photoacoustic wave into an electric signal in accordance with the detection synchronization signal transmitted from the irradiation unit 104. The photoacoustic wave detection unit 105 includes an ultrasonic probe which includes a plurality of acoustic elements arranged in a two-dimensional shape and a scanning mechanism which scans the holding plate using the probe.

Furthermore, the photoacoustic wave indicates a wave which is emitted by the photoacoustic effect in the acoustic wave. The acoustic wave is a kind of elastic waves, and is also called a sound wave. The acoustic wave is typically an ultrasonic wave, and the

photoacoustic wave in this case is also called a photo-ultrasonic wave.

[ 0028 ]

In the invention, any type of probe may be used. For example, a conversion element which is used in a general ultrasonic diagnosis apparatus and uses piezoelectric ceramics (PZT), a microphone capacitance type conversion element, or the like is used.

Furthermore, hereinafter, the probe which measures an ultrasonic wave is s impl y eferredtoasaprobe. Further, a capacitance type capacitive micromachined ultrasonic transducer ( CMUT ) , a magnetic MUT (MMUT) us ing a magne t i c film, and the like may be also used. Further, a piezoelectric MUT (PMUT) which uses a piezoelectric thin film and the like may be also used.

[0029]

The photoacoustic measurement unit 106 amplifies a weak photoacoustic wave signal generated in the photoacoustic wave detection unit 105, converts the photoacoustic wave signal into a digital signal, and generates one photoacoustic data constituting , photoacoustic image acquired data. The photoacoustic measurement unit 106 includes a signal amplifying unit which amplifies an analog signal output from the photoacoustic wave detection unit 105 and an A/D conversion unit which converts an analog signal into a digital signal. In the signal amplifying unit, in order to obtain a photoacoustic image having uniform contrast regardless of the measurement depth, a control and the like are performed which increases or decreases an amplification gain in response to a time from the irradiation of the measurement light to the arrival of the photoacoust ic wave to the probe.

[ 0030 ]

The signal process unit 107 performs a sensitivity variation correction of an acoustic detection element of a probe, a process of complementing a physically or electrically defective element, an integration process for a noise reduction, a storage of a photoacoust ic wave signal in a recording medium (not illustrated) , and the like with respect to the photoacous tic wave signal measured by the photoacous tic measurement unit 106. In the integration process, the measurement is repeatedly performed at the same position of the object 101, and an averaging process is performed so as to reduce system noise, thereby improving the S/N ratio of the

photoacous tic wave signal. The photoacoustic image acquired data which is emitted by the photoacoustic wave signal process is transmitted to the image processing device 120 through the I/F 112. Further, according to the discerning result of the peripheral part discerning unit 109, the discerning information of the peripheral part is stored together with the photoacoustic image acquired data.

[ 0031 ]

The side light detection unit 108 detects the side light which is reflected laterally by the peripheral part of the object 101. As the side light detection unit 108 of the embodiment, side light detection units 108A and 108B are arranged in the axis perpendicular to the direction in which the object 101 is held. In a case where there is no need to distinguish the side light detection units 108A and 108B from each other, they are referred to as the side light detection unit 108. In the embodiment , the side light detection unit corresponds to a pho tode tector of the invention.

Furthermore, the side light detection unit 108 includes an optical configuration and a sensor capable of only detecting light having a wavelength of the same region as that of the measurement light, and performs a side light detection operation according to the instruction of the scanning control unit 110.

The peripheral part discerning unit 109 discerns whether the current measurement position is the object peripheral part based on the detection result of the side light using the side light detection unit 108, andoutputs the discerning result to the signal process unit 107. Furthermore, the method of discerning the object peripheral part will be described later. The peripheral part discerning unit corresponds to a discerning unit of the invention.

[ 0032 ]

The scanning control unit 110 s imul t aneous ly drives the irradiation unit 104 and the photoacous t i c wave detection unit 105 so that the measurement position is two-dimensionally scanned on the holding plate, and performs control so that the optical axis of the measurement light is equal to the center of the probe. By two-dimensionally scanning the measurement position with respect to the object 101, the wide image acquiring area may be obtained even in a small probe. For exampl e , in the diagnosis of the breast cancer, the full breast photoacoust ic image may be acquired.

Furthermore, when the scanning control unit 110 which receives the instruction from the control unit 111 controls the photoacous tic image acquiring operation and reaches the very appropriate measurement position by the scanning control, the control unit respectively instruct the irradiation unit 104 and the side light detection unit 108 to perform the irradiation of the measurement light and the side light detection operation.

[ 0033 ]

The control unit 111 receives an image acquiring start instruction or various demands from the image processing device 120, and manages and controls the entire photoacoustic imaging apparatus. In addition to the transmission of the start of the image acquiring operation to the scanning control unit 110, the control unit manages the discerning information for discerning each apparatus or individually set information, monitors the state of the apparatus, and transmits such information to the image processing device 120. [003 ]

The I/F 112 is an interface (simply referred to as an I/F) which transmits photoacoustic image acquired data and a holding state acquired image to the image processing device 120 serving as an external device. Further, the interface transmits various instructions from the image processing device 120 to the photoacoustic imaging apparatus. The I/F 112 serves as an interface which performs data communication between the photoacoustic imaging apparatus and the image processing device 120 together with the I/F 121 of the image processing device 120. It is desirable to adopt a communication standard capable of ensuring a real-time performance and transmitting a large amount of data.

[0035]

The image processing device 120 forms or displays the photoacoustic image based on the photoacoustic image acquired data transmitted from the photoacoustic imaging apparatus. The image processing device includes the I/F 121 with respect to the photoacoustic imaging apparatus, an image constructing unit 122 which forms a

photoacoustic image from photoacoustic image acquired data, a display unit 123 which displays a photoacoustic image, and an operation unit 124 which is used for an examiner as a user to operate the image processing device 120 and the photoacoustic imaging apparatus . In general, an apparatus such as a PC or a workstation having a ^' high-per ormance calculation process function or a graphic display function is used.

[0036]

The I/F 121 has the same function as that of the I/F 112 of the photoacous t ic imaging apparatus, and transmits and receives the pho to acous t i c image acquired data or the control instruction of the apparatus in cooperation with the I/F 112.

The image constructing unit 122 forms a

photoacoust ic image by image acquiring information on an optical characteristic distribution of the object 101 based on the transmitted photoacous tic image acquired data. Further, the image constructing unit forms information which is more desirable for the diagnosis by applying brightness adjustment or distortion correction and various correction processes such as clipping of an interested region on the formed photoacoust ic image. Further, in accordance with the user' s operation of the operation unit 124, the parameter for constructing the photoacous tic image, the display image, or the like is adjusted. The image constructing unit corresponds to an image processor of the invention.

The display unit 123 displays the photoacous tic image which is formed by the image constructing unit 122.

The operation unit 124 is an input device through which a user performs a designation of an image acquiring position of photoacoust ic image acquiring operation, an operation of an apparatus such as adjustment of a scanning area, or an image processing operation with respect to a photoacoust ic image on operation software of an image processing device (not illustrated) .

[ 0037 ]

When the image of the object 101 is acquired based on the principle of photoacoustic tomography using a photoacoust ic imaging system having the above-described configuration, the optical characteristic distribution of the object 101 may be acquired as an image and a photoacoustic image may be provided. Furthermore, in Fig. 1, the image processing device 120 is formed as an external device. Although the photoacoustic imaging apparatus and the image processing device are

respectively formed as different hardware, they may be integrated by integrating the functions thereof.

[ 0038 ]

Fig. 2 is a conceptual diagram illustrating a method of acquiring photoacoustic image acquired data of the first embodiment. Fig. 2A illustrates the acquisition of photoacoustic data which is measured by once irradiation of the measurement light, and Fig. 2B illustrates an example of a method of acquiring photoacoustic image acquired data by two - dimens ional 1 y scanning the measurement position. Furthermore, in the second embodiment , an example has been described in which the image acquiring area matches the size of the holding plate 102B.

[0039]

The shape of the measurement light 201 which is irradiated from the irradiation unit 104 may be two-dimens i onal 1 y broadened so as to be substantiall equal to the shape of the probe 105 since the strength of the photoacous tic wave signal is dependent on the directivity of each acoustic element constituting the probe 105. When the object positioned directly above the probe 105 is illuminated by the measurement light 201, it is possible to acquire photoacous t i c data which is necessary to reconstruct an image of the rectangular parallelepiped image acquired region 202 directly above the probe 105 by once irradiation of the measurement light 201.

[0040]

When the photoacoust ic data is repeatedly acquired by moving the measurement position as in the image acquired regions 202A, 202B, and 202C along a movement trace 203 of the measurement position on the holding plate 102B, the photo acous t i c image acquired data may be acquired. Furthermore, the image acquired regions 202A, 202B, and 202C respectively overlap each other because an integration process is performed on one voxel of photoacoust ic data.

[0041]

In the two-dimensional scanning of the measurement position, primary probe scanning (primary scanning) is performed in which photoacoustic data is repeatedly acquired at a position corresponding to a voxel pitch while first moving the probe in the x direction along the movement trace 203. Subsequently, secondary probe scanning (secondary scanning) is performed which moves the probe by a predetermined distance in the positive y direction. The two-dimensional scanning is performed by repeating the primary scanning and the secondary scanning .

[0042]

Fig. 3 is a conceptual diagram illustrating the peripheral part of the interested object 101 of the first embodiment .

The peripheral part of the object 101 maybe divided into several regions in accordance with the relation between the measurement light irradiation side holding plate 102A and the object 101 and the relation between the probe side holding plate 102B and the object 101. Furthermore, there is provided a region 301 to which the measurement light 201 is irradiated by the

two-dimensional scanning of the photoacoustic

measurement. That is, the region illustrates a region which corresponds to the image acquiring area.

[ 0043 ]

In the region 301, there are two regions, that is, a region 302 in which the object 101 and the holding plate 102A come into contact with each other and a region 303 in which the object and the holding plate do not come into contact with each other by the relation between the holding plate 102A and the object 101. The region 302 is a normal irradiation region in which the surface layer of the object is maintained so as to be perpendicular to the measurement light 201, and is a region whi ch matche s a boundary condition of an optical distribution correction calculation equation (Equation 2) . On the other hand, the region 303 is the side reflection region 303 in which the object 101 moves away from the holding plate 102A, the normal vector of the surface layer of the object is directed to the lateral side, and the measurement light 201 is reflected to the lateral side. In the side reflection region 303, the distance d in the optical distribution calculation equation (Equation 2) does not match the holding gap of the holding plate.

[ 0044 ]

In the same way, even in the holding plate 102B and the object 101, there are two divided regions, that is, a region 304 in which the object 101 and the holding plate 102B come into contact with each other and a region 306 in which the object and the holding plate do not come into contact with each other. Further, the region 306 is in a contact state where the photoacoust ic wave emitted from the inside of the object 101 may not reach the probe due to a gap and the photoacoust ic wave signal may not be measured. The normal measurement region 304 which maymeasure the photoacoustic wave signal is divided into a region 305 and a region 307 due to the relation between the side reflection region 303 and the normal irradiation region 302 on the irradiation side of the measurement light 201.

[0045]

The region 305 is a light distribution correction appropriate region in which the boundary condition of the optical distribution calculation equation (Equation 2) matches due to the normal irradiation region 302 and the optical distribution correction may be appropriately performed, and the region 307 is a region which is not appropriate for the boundary condition of the optical distribution correction due to the presence of the gap 309. The photoacoustic imaging apparatus of the first embodiment recognizes the light distribution correction inappropriate region 307. Then, di scerning in format ion which represents whether the optical distribution correction may be correctly applied for the image acquired region 308 is stored so that a user who sees the photoacoustic image discerns a difference in quant itativeness (particularly with the region 305) .

[0046]

In the first embodiment, the peripheral part discerning unit 109 discerns the side reflection region 303 by detecting the lateral reflection light of the measurement light 201 due to the side reflection region 303, and outputs a discerning result to the signal process unit 107. Furthermore, since the light distribution correction inappropriate region 307 does not match the side reflection region 303, the light distribution correction inappropriate region 307 may not be directly discerned. However, the light distribution correction inappropriate region 307 may be discerned by using a fact that the photoacoustic wave may not be detected and only photoacoust ic data of a noise level may be acguired in the region 306.

[ 0047 ]

Further, the peripheral part region 306 in which the photoacoustic wave signal may not be detected may be set as the interested light distribution correction inappropriate region 307 of. the first embodiment by filling an acoustic matching material such as a gel sheet between the object 101 and the holding plate 102B. As a result, an image acquired region is obtained in which the quant it at i veness may not be ensured.

[0048]

The invention is characterized in that^' a unit for discerning the light distribution correction

inappropriate region 307 described in Fig. 3 is provided. That is, since only photoacoustic data of a noise level may be acquired in the region 306, it is apparent that the measurement result is not appropriate. However, since normal photoacous tic data which may not be distinguished at first glance from that of the region 305 is acquired in the region 307, there is a need to discern the region.

[0049]

Fig. 4 is a conceptual diagram illustrating a photoacous tic wave signal which is measured in the light distribution correction appropriate region 305 of the first embodiment. Fig. 4A illustrates an example of a method of measuring a photoacoust ic wave, Fig. 4B illustrates examples of a detection signal of the irradiation of measurement light inside the irradiation unit 104 and a side light detection signal using a side light detection unit 108B, and Fig. 4C illustrates an example of a detectedphotoacoustic wave signal . In Figs 4B and 4C, the vertical axes respectively indicate the optical detection signal and the pho t oacous t i c wave signal, and the horizontal axes indicate the time.

[ 0050 ]

The measurement light 201 which is irradiated to the object 101 penetrates the deep portion of the object 101 while being strongly diffused and attenuated inside the object 101. For this reason, the energy of light which illuminates the tissue inside the object 101 becomes smaller as it moves closer to the deep portion of the object.

A light absorbing material 401 is provided which absorbs the measurement light 201 and emits a

photoacoustic wave. In the diagnosis of the breast cancer, the light absorbing material corresponds to a breast cancer. The tissue of the breast cancer has a light absorption rate higher than that of the normal tissue due to an increase in blood flow volume caused by active angiogene s i s , and expands due to heat by absorbing the energy of pulsed light, thereby emitting photoacoustic wave.

An acoustic detection element 402 is provided which constitutes the probe of the photoacoustic wave detection unit 105. The acoustic detection element detects a reaching photoacoustic wave, and generates a

photoacoustic wave signal shown in Fig. 4C. Since the detection frequency bandwidth of the acoustic detection element is limited and the sensitivity at the low frequency is low, a signal which mainly includes a high-frequency element is formed.

[ 0051 ]

A detection signal 421 at the upper portion of Fig. 4B is obtained by a detection unit (not shown) provided inside the irradiation unit 104. The detection unit detects whether the measurement light 201 is actually irradiated .

In the measurement of the light distribution correction appropriate region of the object shown in Fig. 4A, no reflection of the measurement light 201 directed to the lateral side of the object occurs . For this reason, as shown in the lower portion of Fig. 4B, no detection signal of the side light is generated.

[0052 ]

A threshold value 441 is determined in advance so as to detect the irradiation of the measurement light 201. In the example of the upper portion of Fig. 4B, the signal 421 exceeds the threshold value 441, thereby detecting the irradiation of the measurement light.

A threshold value 442 is determined in advance so as to detect the lateral reflection light of the measurement light 201.

A threshold value 443 is determined in advance so as to determine whether the object 101 is not present between the holding plates at the current measurement position. The threshold value is larger than the threshold values 441 and 442.

[ 0053 ]

A photoacoust ic wave signal 461 of the light absorbing material 401 is shown in Fig. 4C. The signal 461 is a first signal whi ch is detected after the detection of the photoacoust ic wave starts in the measurement of the light distribution appropriate region.

Aphotoacousticwave signal 462 is generated at the boundary surface between the holding plate 102A on the side of the irradiation unit 104 and the object 101. The surface layer of the object 101 is formed of a normal tissue of which the light absorption rate is

comparatively small, but since the measurement light 201 is incident with the high light energy, the photoacous tic wave emitted from the surface layer of the obj ect is large . For this reason, the photoacous tic signal 462 which is generated at the boundary surface becomes a very large signal compared to the signal 461.

Since the detection time of the signal 462 is determined by the configuration of the apparatus (mainly, the thickness of the holding plate 102A) and the signal strength is determined by the light energy of the measurement light 201 and the light absorption rate of the object 101, the same signal characteristics are detected without any change in each measurement as long as the holding state is not changed.

[0054]

Subsequently, referring to Fig. 5, the

characteristics of the photoacous tic- wave signal measured in the light distribution correction

inappropriate region 307 are illustrated, and the difference will be described.

As in Fig. 4, Fig. 5A illustrates an example of a method of measuring a photoacous tic wave, Fig. 5B illustrates examples of a measurement light detection signal and a side light detection signal, and Fig. 5C illustrates an example of a detected photoacous tic wave signal. In Figs. 5B and 5C, the vertical axes respectively indicate the optical detection signal and the photoacous tic wave signal, and the horizontal axes indicate the time.

[0055]

A light absorbing material 501 is present in the light distribution correction inappropriate region 307 in the peripheral part of the object 101. Furthermore, the light absorbing material is present at the same position as that of the light absorbing material 402 in the light distribution correction appropriate region with respect to the optical axis of the measurement light 201, and has the same optical characteristics such as a size or a light absorption coefficient.

[0056]

In the light distribution correction inappropriate region, a gap is present between the object. 101 and the holding plate 102A, and a side reflection region having a curved surface shape is present therebetween. For this reason, the measurement light 201 penetrates the object 101, and a part thereof is reflected by the surface layer of the object to the lateral side thereof. In addition, the position in which the measurement light 201 is incident to the object 101 and starts to be strongly diffused and attenuated also moves toward the probe. For this reason, there is a difference in the energy between the light which penetrates the light absorbing material 501 in the light distribution correction inappropriate region and the light which penetrates the light absorbing material 401 in the appropriate region. That is, in the light distribution correction inappropriate region, the variable d in the light amount distribution calculation equation shown in Equation (2) does not match the holding gap distance. For this reason, the light amount distribution correction may not be accurately applied in the holding distance, and the quant i tat ivene s s lacks in the photoacous t ic image.

[ 0057 ]

A detection signal 521 of side light 502 which is reflected by the side reflection region to the lateral side is shown at the lower portion of Fig. 5B . Since the signal 521 exceeds the threshold value 442, the presence of the side light 502 is detected. Furthermore, since the side light detection unit 108B has directivity in the detection sensitivity so that only the side light 502 from the side reflection region may be detected, an erroneous operation caused by the light other than the side reflection region is inhibited.

[ 0058 ]

A photoacous tic wave signal 561 of the light absorbing material 501 is shown in Fig. 5C. The signal 561 is a first signal which is detected after the detection of the photoacoust ic wave starts in the measurement of the light distribution correction inappropriate region as in' Fig. 5A, and is detected at the substantially same timing as that of the signal 461 in the light distribution correction appropriate region. However, since there is a difference in the penetration light energy amount between the light absorbing materials 501 and 401, the signal 561 and the signal 461 in the light distribution correction appropriate region are detected as signals of different magnitudes. That is, the signal 561 which has small scattering and attenuating amounts due to the object has large signal strength.

[0059]

Aphotoacousticwave signal 562 of the surface layer of the object on the side of the irradiation unit 104 is illustrated in Fig. 5C. Since the surface layer of the object is present at a close position in relation to the gap of the holding plate when seen from the acoustic detection element 403, the propagation distance of the photoacous t ic wave in the object is short compared to Fig. AC. As a result, the timing of detecting the signal 562 is earlier than that of the object surface layer signal 462. Further, in the light distribution correction inappropriate region having the side reflection region on the irradiation side of the measurement light 201, the surface layer of the object is formed in a curved surface shape, and hence the photoacous tic wave which is generated on the surface layer of the object is not formed as a planar wave. As a result, the signal 562 becomes a signal having a width compared to the signal 462 in the light distribution correction appropriate region having the normal irradiation region.

[0060]

As described above by referring to Figs. 4 and 5, there is a difference in the side light detection signal outputting from the side light detection unit 108 between the light distribution correction appropriate region and the light distribution correction inappropriate region of the object 101. Accordingly, based on a difference in the signal characteristic, the sub ect side reflection region may be discerned.

[ 0061 ]

Fig. 6 is a conceptual diagram illustrating a characteristic of the photoacoustic signal at a position where the object is not present in the first embodiment. As in Fig. 4, Fig. 6A illustrates an example of a method of measuring a photoacoustic wave, Fig. 6B illustrates examples of a measurement light detection signal and a side light detection signal, and Fig. 6C illustrates an example of a detected photoacoustic wave signal. The vertical axes of Figs. 6B and 6C respectively indicate the optical detection signal and the photoacoustic wave signal, and the horizontal axes indicate the time.

[ 0062 ]

At the upper portion of Fig. 6B, the object 101 is not present and the measurement light 201 is not interrupted. Fo r t hi s r e as on , the measurement light 201 which is irradiated from the irradiation unit 104 directly reaches the probe of the facing photoacoustic wave detection unit 105., Furthermore, as shown in the lower portion of Fig. 6B, there is no reflection light directed to the lateral side of the object 101, and hence the side light detection signal is not detected.

[0063]

A photoacoustic wave signal 661 of Fig. 6C is generated in the surface of the probe of the photoacoustic wave detection unit 105. In general, an acoustic matching material is attached to the surface of the probe so as to improve the detection efficiency of the elastic wave. Since the acoustic matching material has a light absorption rate with respect to the measurement light 201, the surface of the probe becomes a source of the photoacoustic wave. Furthermore, even when the surface of the probe is protected by a reflection film, since the reflection film itself has several percentage of a light absorption rate (for example, about 3% in the case of Au), the reflection film emits a large photoacoustic wave by receiving the measurement light 201 having large light energy.

[0064]

Since the signal 661 is a signal which is caused by the photoacoustic wave generated on the surface of the probe, the signal is detected immediately after the measurement thereof starts, and the strength thereof is very large. Furthermore, since the signal 661 is a photoacous tic signal which is caused by the structure of the probe, the signal is detected as the same signal characteristics without any change in the detection time and the signal strength for each measurement. By using the threshold value 443 based on the signal

characteristics, it is possible to recognize whether the measurement position is deviated from the object 101.

Furthermore, in the photoacoust ic measurement of the region 306 in which the photoacoustic signal may not be detected due to a lack in the acoustic coupling between the object 101 and the holding plate 102B, the side light detection signal is detected and thephotoacoustic signal is not detected.

[0065]

As described above so far by referring to Figs. 4, 5, and 6, it is possible to discern the respective regions in the peripheral part of the object 101, and particularly, the light distribution correction inappropriate regions by the combination of the side light detection signal and the measured photoacoustic signal.

[0066]

Fig. 7 is a flowchart illustrating a flow of an operation acquiring the photoacoustic image in the first embodiment. A series of processes indicated by the flowchart is provided to discern the respective regions of the peripheral part of the object as described so far and to realize a photoacoustic image acquiring operation while in particular storing the discerning information of the light distribution correction inappropriate region. Furthermore, it is assumed that an operation such as an operation of holding the object is completed by an examiner before the flowchart is performed.

[ 0067 ]

In step S701, an examiner instructs an image acquiring operation using the operation unit 124 of the image processing device 120. The control unit 111 which receives the image acquiring instruction instructs the scanning control unit 110 to start a photoacoustic image acquiring operation.

In step S702, the scanning control unit 110 simultaneously moves the irradiation unit 104 and the photoacoustic wave detection unit 105 in the primary scanning direction (x direction) to the next measurement position.

In step S703, when the irradiation unit and the photoacoustic wave detection unit reach the next measurement position, the scanning control unit 110 activates the side light detection unit 108A or 108B in response to the measurement position.

[0068]

In step S704, the irradiation unit 104 controls the emission of light of the light source, and irradiates a pulsed laser beam of a near- infrared region as measurement light toward the object.

In step S705, the peripheral part discerning unit 109 determines whether the side light detection unit 108 detects the side light. In the case of the detection, the process proceeds to step S706. In the case of no detection, the process proceeds to step S707.

In step S706, the signal process unit 107 stores the discerning information of the peripheral part based on the discerning result of the peripheral part discerning unit 109. Furthermore, the discerning information herein is a detection result of the side reflection region in the peripheral part of the object.

[0069]

In step S707, the scanning control unit 110 inactivates the side light detection unit 108 when the period is not valid for the detection of the side light due to the configuration of the apparatus.

In step S708 , the probe of the photoacous tic wave detection unit 105 detects (samples) the pho toacous t i c wave which is generated by the irradiation of the measurement light in step S704. Then, the photoacous tic measurement unit 106 amplifies and A/D converts the photoacoustic wave signal which is detected by the photoacous tic wave detection unit 105, and outputs the signal to the signal process unit 107. By repeating the sampling of the photoacoustic wave signal as many as the number of samples necessary for once measurement corresponding to the measurement depth, the photoacous t ic data of the image acquired region 202 is obtained .

[0070]

In step S709, the signal process unit 107 performs a sensitivity variation correction of an acoustic detection element of a probe, a process of complementing a physically or electrically defective element, an integration process for a noise reduction, a storage of a photoacoust ic signal in a recording medium, and the like based on the photoacoust ic data acquired in the precedent step. Further, the light distribution correction inappropriate region is discerned based on the measured photoacoust ic signal and the discerning result from the peripheral part discerning unit 109. Then, the discerning information of the peripheral part stored in step S706 is updated and stored so as to be correlated to the measurement position, and then the discerning data of the object peripheral part is generated .

[ 0071 ]

In step S710, the scanning control unit 110 determines whether once scanning operation in the primary scanning direction is completed. The completion of the scanning operation is determined based on whether the movement in the primary scanning direction is completed with respect to the image acquiring region which is designated by the examiner . When the scanning operation is completed, the process proceeds to step S711. When the scanning operation is not completed, the process proceeds to step S702 and the photoacoustic measurement is repeated at the next measurement position.

In step S711, the scanning control unit 110 determines whether the full scanning operation is completed. The completion of the full scanning operation is determined based on whether the primary scanning operation and the secondary scanning operation are completed in the image acquiring area designated by the examiner and all scanning operations are completed. When the full scanning operation is completed, the photoacoustic image acquired data and the discerning data of the object peripheral part are transmitted to the image processing device 120, and the process, proceeds to step S713. When the full scanning operation is not comp leted, the process proceeds to step S712.

[0072]

In step S712, the scanning control unit 110 simultaneously moves the irradiation unit 104 and the photoacoustic wave detection unit 105 in the secondary scanning direction so as to continue the measurement operation at the next primary scanning line.

In step S713, the image constructing unit 122 forms a photoacoustic acquired image based on the photoacoustic image acquired data. In step S714, the formed photoacoustic acquired image is displayed on the display unit 123.

[ 0073 ]

By the above-described processes, in the

photoacoustic measurement in which the measurement position may be two-dimensionally scanned, a

photoacoustic diagnosis image which is very suitable for the image diagnosis may be obtained, and the discerning information of the object peripheral part may be stored so as to be correlated to the measurement position.

[ 0074 ]

According to the embodiment, in the photoacoustic imaging apparatus which performs a measurement by a configuration in which the light source and the probe face each other with the object interposed therebetween while the object is held by the holding plate, it is possible to discern the peripheral part of the object by providing a unit which detects the reflection light of the measurement light directed to the lateral side of the ob e ct .

Further, it is possible to acquire and store information for discerning a region in which the quant itativeness is different on the photoacoustic image by providing a unit which discerns a region which is not appropriate for the boundary condition of the light distribution correction in the peripheral part of the object. When the stored discerning information is correlated with the measurement position, is stored together with the photoacoust ic image acquired data, and is transmitted to the image processing device,, it is possible to discern a region in which the

quant i tat i vene s s is different on the photoacoust ic image and to provide the region for the examiner.

[0075]

A second embodiment which uses an ultrasonic measurement apparatus and an ultrasonic measurement method of the invention will be described according to the drawings .

[0076]

In the first embodiment, when the reflection of the measurement light directed to the lateral side of the object is detected by the side reflection region in the object peripheral part, the light distribution correction inappropriate region may be sequentially discerned at the respective measurement positions during the photoacous tic image acquiring operation. As a result, the discerning information may be checked after the photoacous tic image acquiring operation ends.

On the other hand, when the discerning information of the light distribution correction inappropriate region may be provided for the examiner before the photoacous tic image acquiring operation, it is possible to provide an option whether the image acquiring operation is performed so as to include the same region or only the light distribution correction appropriate region excluding the same region is acquired as an image.

The second embodiment is characterized in that the peripheral part of the object may be discerned before the photoacoustic image acquiring operation and may be provided for the examiner.

[ 0077 ]

Based on the characteristics, the second embodiment will be described. Fig. 8 is an entire diagram illustrating an apparatus configuration of the photoacoustic imaging system of the second embodiment. Compared to the photoacoustic imaging apparatus of Fig. 1 of the first embodiment, in the photoacoustic imaging apparatus of the second embodiment, a holding and image acquiring unit 801, a side illuminator 802 , and a control unit 803 are newly provided. Further, the image processing device 820 is newly provided with a peripheral part discerning unit 821. The operation of the control unit 803 is different from that of the control unit 111 of Fig . 1.

[0078]

The holding and image acquiring unit 801 acquires an image of the held object 101 from the side of the irradiation unit 101 through the holding plate 102A. In the holding and image acquiring unit 801, a general imaging element such as a CCD (charge coupled device) oraCMOS ( compl ement ary me t a 1 ox i de s emi conduc to r ) image sensor having a detection sensitivity in the visible or infrared region is used. The image which is acquired by the holding and image acquiring unit 801 is transmitted to the image processing device 120 through the I/F 112, and is used to designate the image acquiring area by the examiner. For this reason, it is desirable to perform an image acquiring operation at a field angle in which the maximum image acquiring area determined as the apparatus is included.

Further, in order to reduce an influence of external light, it is desirable to have detection s ens i t ivi t y wi th respect to the same wavelength in response to the wavelength used in the illumination light so that only the illumination light of the side illuminator 802 may be detected. In the embodiment, the holding and image acquiring unit and the image processing device correspond to a photode tector of the invention.

[0079]

The side illuminator 802 irradiates light of a visible region or an infrared region from the lateral side of the object 101 in accordance with the instruction of the control unit 803. As for the .side illuminator 802 of the embodiment, side illuminators 802A and 802B are arranged in a direction in which the object 101 is held, that is, a direction perpendicular to the measurement light irradiation direction. In the image which is acquiredby the holding and image acquiring unit

801 using the illumination from the lateral side of the object, the side reflection region of the object 101 may be emphasized.

[ 0080 ]

The control unit 803 receives a demand from the image processing device 820 and controls the side illuminator

802.

The peripheral part discerning unit 821 performs an imaging process on the image acquired by the holding and image acquiring unit 801, discerns the side reflection region of the object 101, and displays the discerning information on the display unit 123. The detail thereof will be described later.

By the photoacous tic imaging apparatus having the above-described configuration, the examiner may visually recognize the informa t ion of the peripheral part of the object 101 before the photoacous tic image acquiring operation.

[0081]

Fig. 9 is a conceptual diagram illustrating a method of discerning the peripheral part of the object of the second embodiment. Fig. 9A illustrates an example of a region which is acquired as an image by the holding and image acquiring unit 801, and Fig. 9B illustrates an example of the lateral illumination.

[0082] The portion 901 of Fig. 9A is obtained by projecting the image acquiring area acquiredby the holding and image acquiring unit 801 onto the holding plate 102A. When the image acquiring operation is performed at the field angle in which the maximum image acquiring area defined as the apparatus is included, the entire object including the peripheral part of the object may be recognized.

[ 0083 ]

The portions 902 and 903 of Fig. 9B are respectively the normal irradiation region of the measurement light and the light distribution correction appropriate region described in Fig. 3. Further, the portions 904, 905, and 906 respectively indicate the side reflection region, the light distribution correction appropriate region, and the region where the photoacoust ic wave may not be detected .

Further, the portions 911 and 912 respectively indicate the illumination light of the side illuminator 802B and the reflection light of the side reflection region 904. It is desirable that the illumination light has directivity in which only the peripheral part of the object 101 may be illuminated. The light 911 which illuminates the object 101 from the lateral side thereof is reflected by the side reflection region 904 of the object 101, and the reflection light 912 is acquired as an image by the holding and image acquiring unit 801.

[ 0084 ] In the second embodiment, the peripheral part discerning unit 821 detects the reflection light 912 in which the illumi ation light 911 is reflected by the side reflection region 904 toward the holding and image acquiring unit 801. By detecting the reflection light, the side reflection region 904 is discerned, and the discerning result is output to the signal process unit 107. Furthermore, although the light distribution correction inappropriate region 905 and the side reflection region 904 do not match each other, a boundary line 907 between the light distribution correction appropriate region 903 and the inappropriate region 905 is equal to the boundary line between the normal irradiation region 902 and the side reflection region 904. For this reason, the 1 i ght di s t r ibut i on cor r e c t i on inappropriate region 905 may be estimated.

[0085]

Fig. 10 is a conceptual diagram illustrating a method of discerning the peripheral part of the object and designating the photoacous t ic image acquiring area of the second embodiment. Fig. 10A illustrates an example of the discerned image of the side reflection region using the holding and image acquiring unit 801, and Fig. 10B illustrates an exam le of a relation between the discerning result and the image acquiring area.

[0086]

The portion 1001 of Fig. 1 OA illustrates an example of the discerned image which is acquired by the holding and image acquiring unit 801 in a state where the side reflection region is illuminated by the side illuminator 802.

The portion 1002 is a region where the illumination light of the side illuminator 802 does not reach, and corresponds to the normal irradiation region 902 of the measurement light which is acquired as a dark image.

The portion 1003 is a region which corresponds to the side reflection region 904 reflecting the

illumination light of the side illuminator 802 toward the holding and image acquiring unit 801. Furthermore, the peripheral part discerning unit 821 may easily discern the side reflection region 1003 by performing an imaging process such as an emphasis process or a binarization process which is very suitable for the discerning operation.

The portion 1004 is a region in which the object 101 is not present, and becomes a dark region by the emphasis process of the side reflection region 1003.

Furthermore, the discerned image 1001 is an image which is used inside the peripheral part discerning unit 821 so as to discern the side reflection region 1003, and is not provided for the examiner.

[0087]

The portion 1011 of Fig. 10B is an image in which the image acquiring area based on the discerning result of the peripheral part of the object is superimposed on the image acquired by the holding and image acquiring unit 801 so as to observe the holding state of the object 101 in a state where there is no illumination of the side illuminator 802. Furthermore, the acquired image 1011 is provided for the user through the display unit 123 in accordance with the information of the peripheral part discerning unit 821.

The portions 1012 and 1013 respectively illustrate an example of the image acquiring area provided for the examiner based on the result in which the peripheral part discerning unit 821 discerns the side reflection region 904 of the object 101. The image acquiring area 1012 illustrates a region which internally contacts the boundary line 907 between the normal irradiation region 902 of the measurement light and the side reflection region 904. The image acquiring area 1013 illustrates a area which internally contacts the outline of the object 101.

At this time, additional information items such as time necessary for the image acquiring operation may be provided together with the image acquiring area. The examiner may select several image acquiring areas and designate an arbitrary image acquiring area by referring to two provided image acquiring areas . Furthermore, the image acquiring area provided in the invention is not limited to two image acquiring areas 1012 and 1013. Then, based on the image acquiring areas 1012 and 1013, for example, several image acquiring areas which are very suitable for the image diagnosis, such as an intermediate image acquiring area may be provided.

[ 0088 ]

As described above, since the normal irradiation region 903 and the side reflection region 904 caused by the side illuminator 802 are acquired as regions having different brightness on the image acquiredby the holding and image acquiring unit 801. For this reason, the side reflection region 904 of the object may be discerned based on a difference in the region. That is, as described in Fig. 9, the light distribution correction

inappropriate region 905 corresponding to the side reflection region 904 may be discerned.

Further, when the discerning information of the light distribution correction inappropriate region 905 of the object 101 is provided for the user before the photoacoust ic image acquiring operation starts, an arbitrary image acquiring area may be designated in consideration of the state of the peripheral part of the obj ect .

Furthermore, in the embodiment , the per ipheral part is discerned in the more emphasized state by the lateral illumination. However, the di s co lo r ed pe r ipher a 1 part of the held object may be discerned even in a state where there is no side light. Since there is a difference in color of a skin between the normal irradiation region

902 of the breast as the object 101 which is pressed by the holding plate and the peripheral part which is not pressed by the holding plate 102, the color difference may be discerned by the image processing.

[0089]

Fig. 11 is a flowchart illustrating a flow of an operation of acquiring the photoacoustic image of the second embodiment.

In step S1101, there is a need to discern the state of the peripheral part of the object in the photoacoustic imaging apparatus in accordance with the input from the operation unit 124 by the examiner before the

photoacoustic image acquiring operation starts. The control unit 803 which receives a request simultaneously controls the lighting of the side illuminator 802.

In step S1102, the peripheral part discerning unit 821 discerns the side reflection region 1003 of the object 101 by acquiring the image acquired by the holding and image acquiring unit 801 as a result of the lateral illumination in step S1101. Further, the peripheral part discerning unit 821 outputs info rma t ion of the image acquiring area which is a candidate indicated in Fig.

10 based on the discerning result.

[ 0090 ]

In step S1103, the examiner determines an arbitrary image acquiring area by the operation unit 124 of the image processing device 820 from the candidates of the provided image acquiring area or by referring to the candidates .

In step S1104, the examiner instructs an image acquiring operation by the operation unit 124 of the image processing device 820. The control unit 803 which receives the pho toacous t i c image acquiring instruction causes the scanning control unit 110 to start the pho toacous tic image acquiring operation, and completely acquires the photoacous t ic image acquired data throughout the full region of the image acquiring area designated in step S1102.

The processes in step S713 and step S714 are the same as those of the first embodiment.

[ 0091 ]

In the photoacoust ic imaging apparatus which performs a photoacoustic measurement while

two-dimens iona 11 y scanning the measurement position by the above-described process, the light distribution correction inappropriate region of the object may be provided for the examiner prior to the photoacoustic image acqui r ing operation, and the examine r may designate an arbitrary image acquiring area in consideration of the same region.

[0092]

In the embodiment, in the photoacoustic imaging apparatus which performs a measurement with a configuration in which the light source and the probe face each other with the object interposed therebetween while holding the object by the holding plate, an illumination unit which illuminates the lateral side of the object and a unit which acquires an image of the held object are provided. Accordingly, the light

distribution correction inappropriate region may be discerned before the start of the image acquiring operation, and may be provided for the user.

[ 0093 ]

Further, the object of the invention is also attained by the following method. That is, a storage medium (or a recording medium) which stores a program code of software realizing the function of the above-described embodiments is provided for a system or an apparatus. Then, a computer (or a CPU or an MPU) of the system or the apparatus reads the program code stored in the storage medium and executes the program code. In this case, the program code which is read from the storage medium realizes the functions of the above-described embodiments, and the storage medium which stores the program code constitutes the invention.

[ 009 ]

Further, when the program code which is read by the computer is executed, a part or the entirety of the actual process such as an operating system (OS) which is operated on the computer is performed based on the instruction of the program code. Even when the functions of the above-described embodiments are realized by the process, the process is included in the invention.

[0095]

Further, the program code which is read from the storage medium is written in a memory of a function extension card inserted into the computer or a function extension unit connected to the computer . Subsequently, a CPU or the like included in the function extension card or the function extension unit performs a part or the entirety of the actual process based on the instruction of the program code, and the functions of the

above-described embodiments are realized. Even this case is included in the invention.

When the invention is applied to the storage medium, the storage medium stores the program code which corresponds to the flowchart described above.

[0096]

A new system may be easily obtained by the person skilled in the art by appropriately combining various techniques of the above-described embodiments, and the system which is obtained by various combinations is also included in the scope of the invention.

[ 0097 ]

For example, in the first and second embodiments, an example has been described in which the invention is applied to the photoacoustic imaging system that disposes one light source and one probe with the object interposed therebetween and performs a photoacoustic measurement only by the irradiation of the measurement light from the opposite side of the probe . That is, the 1 i ght source is disposed in one holdingplate, and the probe is disposed in the other holding plate. However, a configuration may be supposed in which the light source and the probe are disposed on the same side and the photoacoustic measurement is performed using the measurement light at the same side as that of the probe. Even in such a configuration, when the optical axis of the measurement light does not match the propagation path of the photoacoustic wave generated inside the object to the probe, the light distribution correction inappropriate region is present, and hence similarly, the peripheral part of the object may be discerned. Furthermore, in this case, the holding and image acquiring unit of the second embodiment needs to be provided in the probe. As described above, a configuration in whi ch the measurement light is irradiated to the object from the same side as that of the probe is also included in the scope of the invention .

[0098]

Further, in the first and second embodiments, an example has been described in which the invention is applied to the photoacoustic imaging system that disposes the light source only at one side of the object and performs the measurement only by the irradiation of the measurement light from one side. However, as a configuration which improves the measurement depth and obtains the photoacoustic image having high contrast and high image quality, a configuration may be supposed in which the light source is disposed at both sides of the object and the measurement is performed by using the measurement light from both sides. Even in such a configuration, the peripheral part of the object may be analyzed similarly by the combination of the first and second embodiments and the above-described configuration in which the measurement light and the probe are disposed on the same side. Accordingly, the configuration in which the measurement light is irradiated to the object from both sides thereof is also included in the scope of the invention.

[0099]

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 modi f i cat i ons and equivalent structures and functions.

[0100] This application claims the benefit of Japanese Patent Application No . 2011-187296, filed on August 30, 2011, which is hereby incorporated by reference herein in its entirety.

Claims

1. An object information acquiring apparatus comprising :

a holding plate which holds an object;

a phot ode t ect or which detects light reflected by a peripheral part as a region of the object that does not come into contact with the holding plate; and a discerning unit which discerns a contact state between the holding plate and the object using a detection result of the pho tode t ector .

2. The object information acquiring apparatus according to claim 1,

wherein the photodet ector is a sensor which is disposed at the lateral side of the object when seen from the holding direction by the holding plate, and detects reflection light in which the measurement light is reflected by the peripheral part.

3. The object information acquiring apparatus according to claim 2,

wherein the discerning unit discerns a non-contact state between the holding plate and the object when the intensity of the reflection light exceeds a pr ede t e rmined threshold value.

4. The object information acquiring apparatus according to anyone of claims 1 to 3, further compr i sing: a scanning unit which moves a light- source of the measurement light and the probe with respect to the holding plate ,

where in the discerning unit discerns a contact state between the holding plate and the object at each movement position of the light source of the measurement light.

5. The object information acquiring apparatus according to claim 4,

wherein the holding plate is two plates which hold the object in a sandwiched state,

wherein the probe is disposed in one of two holding plates and the light source of the measurement light is disposed in the other thereof, and

whe r e in the discerning unit discerns a contact state between the object and the holding plate at the side of the light source of the measurement light.

6. The object information acquiring apparatus according to claim 5,

wherein the discerning unit discerns a region of the object, which does not come into contact with the holding plate at the side of the light source of the measurement light but comes into contact with the holding plate at the side of the probe, based on the intensity of the acoustic wave detected by the probe.

7. The object information acquiring apparatus according to claim 1, further comprising:

a side illuminator which is disposed at the lateral side of the object when seen from the holding direction by the holding plate and illuminate the object,

wherein the pho todetector captures an image of the object from the irradiation direction of the measurement light, and processes the captured image, thereby detecting illumination light reflected by peripheral part of the object.

8. The object information acquiring apparatus according to .claim 7, further comprising:

a scanning unit which moves the light source of the measurement light and the probe with respect to the holding plate;

a display unit which displays the contact state between the holding plate and the object discerned by the discerning unit for a user; and an operation unit from which an object information acquiring area as a region, detecting an acoustic wave by moving the light source of the measurement light and the probe using the scanning unit, is input from the user .

9. An ob ect information acqui r ing method compri sing: holding an object by a holding plate;

detecting, by a probe, an acoustic wave propagated from the inside of the object irradiated by measurement light and converting the acoustic wave into an electric signal;

detecting, by a pho tode t ector , light reflected by a peripheral part as a region which does not come into contact with the holding plate in the object; and discerning, by a discerning unit, a contact state between the holding plate and the object using a detection result of the pho tode t ector .