JP2019195583A - Photoacoustic apparatus and subject information acquisition method - Google Patents

Abstract

To provide a photoacoustic apparatus capable of performing imaging in a wide range and acquiring a stable signal.SOLUTION: A photoacoustic apparatus includes: a light irradiation unit for irradiating a subject with light; a probe for receiving a photoacoustic wave generated from the subject due to irradiation of the light; and a movement control unit for controlling a first movement mechanism for moving the probe to the subject, and a second movement mechanism for moving a light irradiation position to the subject. The movement control unit switches the control between first control for moving the light irradiation position and the probe on a surface of the subject while causing them to follow each other, and second control for moving the probe while fixing the light irradiation position on the surface of the subject.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photoacoustic apparatus.

Photoacoustic tomography (PAT) is known as a technique for imaging structural information in a subject and physiological information, that is, functional information.
When light such as laser light is irradiated on a living body that is a subject, an acoustic wave (typically, an ultrasonic wave) is generated when the light is absorbed by a living tissue in the subject. This phenomenon is called a photoacoustic effect, and an acoustic wave generated by the photoacoustic effect is called a photoacoustic wave. Since the absorption rate of light energy varies depending on the tissue constituting the subject, the sound pressure of the generated photoacoustic wave varies depending on the tissue. In PAT, the generated photoacoustic wave is received by a probe, and the received signal is mathematically analyzed, whereby characteristic information in the subject can be acquired.

  As an example of a photoacoustic apparatus, for example, Patent Document 1 discloses a microscope-type compact device that acquires photoacoustic information in a subject by irradiating the subject with light and scanning a probe with an acoustic lens. A photoacoustic device is disclosed.

Japanese Patent Laying-Open No. 2006-70801

In the apparatus described in Patent Document 1, a member (light irradiation unit) that irradiates a subject with light is fixed to the apparatus. According to such a configuration, since the light amount distribution of the light irradiated to the subject does not change with each irradiation, there is an advantage that the intensity relationship of the photoacoustic signal generated from within the subject is stabilized according to the multiple times of light irradiation. .
On the other hand, when it is desired to receive a photoacoustic wave from a wide range, it is necessary to move the light irradiation unit in order to expand the light irradiation range. However, when the measurement is performed while moving the light irradiation unit, the light quantity distribution of the light irradiated to the subject fluctuates, which causes a problem that the quantitativeness of the measurement deteriorates.

  The present invention has been made in view of such a problem of the prior art, and an object of the present invention is to provide a photoacoustic apparatus capable of imaging in a wide range and acquiring a stable signal.

In order to solve the above problems, a photoacoustic apparatus according to the present invention includes:
A light irradiating unit for irradiating the subject with light; a probe for receiving an acoustic wave generated from the subject due to the irradiation of the light; and a first moving the probe relative to the subject. A movement control unit that controls one movement mechanism and a second movement mechanism that moves the irradiation position of the light with respect to the subject, and the movement control unit is arranged on the surface of the subject. A first control for moving the light irradiation position and the probe following each other, and a second control for fixing the light irradiation position on the surface of the subject and moving the probe. It is characterized by switching.

Further, the subject information acquisition method according to the present invention includes:
A light irradiating unit for irradiating the subject with light; a probe for receiving an acoustic wave generated from the subject due to the irradiation of the light; and a first moving the probe relative to the subject. An object information acquisition method performed by a photoacoustic apparatus having one movement mechanism and a second movement mechanism that moves an irradiation position of the light with respect to the subject, the method comprising: Control for switching between first control for moving the irradiation position and the probe following each other and second control for fixing the light irradiation position on the surface of the subject and moving the probe Including steps.

  ADVANTAGE OF THE INVENTION According to this invention, the photoacoustic apparatus which can image widely and can acquire the stable signal can be provided.

The system block diagram of the photoacoustic apparatus which concerns on 1st embodiment. The figure explaining the function structure of the data processing part. The figure explaining the light quantity distribution of the light with respect to the light absorber. The figure which showed the relationship between a light irradiation area and an imaging area. The 2nd figure which showed the relationship between a light irradiation area and an imaging area. The process flowchart figure in 1st embodiment. The figure explaining the acquisition timing of a photoacoustic signal, and the display timing of a reconstruction image. The figure showing the position of the probe for every acquisition timing of a photoacoustic signal. The figure showing the position of the probe for every acquisition timing of a photoacoustic signal. A diagram showing the light distribution on the imaging area The process flowchart figure in 2nd embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described below should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions. Therefore, the scope of the present invention is not intended to be limited to the following description.

  The present invention relates to a technique for detecting acoustic waves propagating from a subject, generating characteristic information inside the subject, and acquiring the characteristic information. Therefore, the present invention can be understood as a photoacoustic apparatus or a control method thereof. The present invention can also be regarded as a program that causes a device including hardware resources such as a CPU and a memory to execute these methods, and a computer-readable non-transitory storage medium that stores the program.

  The photoacoustic apparatus according to the embodiment receives acoustic waves generated in a subject by irradiating the subject (for example, breast, face, palm) with light (electromagnetic waves), and obtains characteristic information of the subject as image data. It is a device using the photoacoustic effect acquired as follows. In this case, the characteristic information is characteristic value information corresponding to each of a plurality of positions in the subject, which is generated using a reception signal obtained by receiving a photoacoustic wave.

The characteristic information acquired by photoacoustic measurement is a value reflecting the absorption rate of light energy. For example, a generation source of an acoustic wave generated by light irradiation, an initial sound pressure in a subject, a light energy absorption density or absorption coefficient derived from the initial sound pressure, and a concentration of a substance constituting a tissue are included.
Further, information such as the concentration of a substance constituting the subject can be obtained based on photoacoustic waves generated by light having different wavelengths. This information may be oxygen saturation, a value obtained by weighting the oxygen saturation with an intensity such as an absorption coefficient, a total hemoglobin concentration, an oxyhemoglobin concentration, or a deoxyhemoglobin concentration. Further, it may be glucose concentration, collagen concentration, melanin concentration, or volume fraction of fat or water.
In the embodiment described below, by irradiating a subject with light having a wavelength assumed to be hemoglobin as an absorber, blood vessel distribution / shape data in the subject and oxygen saturation distribution data in the blood vessel are obtained. Assume a photoacoustic imaging device that acquires and images.

  A two-dimensional or three-dimensional characteristic information distribution is obtained based on the characteristic information of each position in the subject. The distribution data can be generated as image data. The characteristic information may be obtained not as numerical data but as distribution information of each position in the subject. That is, distribution information such as initial sound pressure distribution, energy absorption density distribution, absorption coefficient distribution, and oxygen saturation distribution.

  The acoustic wave in this specification is typically an ultrasonic wave, and includes an elastic wave called a sound wave or a photoacoustic wave. An electric signal converted from an acoustic wave by a probe or the like is also called an acoustic signal. However, the description of ultrasonic waves or acoustic waves in this specification is not intended to limit the wavelength of those elastic waves. An acoustic wave generated by the photoacoustic effect is called a photoacoustic wave or an optical ultrasonic wave. An electrical signal derived from a photoacoustic wave is also called a photoacoustic signal. In this specification, the photoacoustic signal is a concept including both an analog signal and a digital signal. The distribution data is also called photoacoustic image data or reconstructed image data.

  In the following embodiments, a photoacoustic apparatus that picks up a subject with pulsed light, receives acoustic waves from the subject by the photoacoustic effect, and analyzes them to acquire distribution information of the light absorber in the subject will be taken up. The subject is assumed to be the subject's breast. However, the subject is not limited to the breast, and other parts such as the subject's limbs, non-human animals, inanimate objects, phantoms, and the like can also be considered. The photoacoustic apparatus in the following embodiments is suitable for diagnosing malignant tumors and vascular diseases of humans and animals, and for monitoring the progress of chemical treatment.

(First embodiment)
FIG. 1 is a diagram illustrating a system configuration of the photoacoustic apparatus according to the first embodiment. The photoacoustic apparatus according to this embodiment includes a light source 101, an optical system 102, a light irradiation unit 104, a probe 106, a signal acquisition unit 110, a control unit 111, a first scanning mechanism 112, a second scanning mechanism 113, and data processing. The unit 120 is configured.

Each component included in the apparatus will be described.
The light source 101 is a device that generates pulsed light that irradiates a subject. The light source 101 is preferably a laser light source in order to obtain a large output, but a light emitting diode or a flash lamp can be used instead of the laser. When a laser is used as the light source, various lasers such as a solid laser, a gas laser, a dye laser, and a semiconductor laser can be used.
The laser used for the light source 101 is preferably one having a strong output and capable of continuously changing the wavelength. For example, an Nd: YAG laser, an alexandrite laser, or the like can be suitably used. Further, a Ti: sa laser excited by Nd: YAG or an OPO laser may be used.
The wavelength of the pulsed light is preferably a specific wavelength that is absorbed by a specific component among the components constituting the subject, and is a wavelength at which light propagates to the inside of the subject. Specifically, the thickness is desirably 400 nm or more and 1600 nm or less.
In particular, when imaging a deep part of a living body, light having a wavelength that is absorbed by a specific substance (for example, hemoglobin) to be examined among components constituting the living body and less absorbed by other substances is used. Specifically, 700 nm or more and 1100 nm or less are preferable. On the other hand, a visible light region can also be used when imaging blood vessels near the surface of a living body with high resolution. However, it is possible to use terahertz waves, microwaves, and radio waves. Note that in the case of irradiating light with a plurality of wavelengths, the light source 101 may include a plurality of single wavelength lasers with different wavelengths.
In order to effectively generate photoacoustic waves, light must be irradiated in a sufficiently short time according to the thermal characteristics of the subject. When the subject is a living body as shown in the present embodiment, the pulse width of the pulsed light generated from the light source is preferably about 1 to 100 nanoseconds.
Note that the timing, waveform, intensity, and the like of light irradiation are controlled by the control unit 111 described later.

The optical system 102 is a member that transmits pulsed light emitted from a light source. The light emitted from the light source is guided to the subject while being processed into a predetermined light distribution shape by an optical component such as a lens or a mirror, and is irradiated from the light irradiation unit 104. It is also possible to propagate light using an optical waveguide such as an optical fiber.
The optical system 102 may have a configuration in which, for example, a plurality of hollow waveguides are connected by a joint including a mirror, and the inside of the waveguide is guided. Moreover, the structure which propagates in the space by optical elements, such as a mirror and a lens, and light-guides may be sufficient.
The optical system 102 may include optical devices such as a lens, a mirror, a prism, an optical fiber, a diffusion plate, a shutter, and a filter, for example. Any optical component may be used in the optical system as long as the light emitted from the light source 101 can be irradiated onto the subject in a desired shape. In addition, by expanding the light to a certain area, the safety to the living body can be improved and the diagnostic area can be expanded. Conversely, the resolution can be increased by focusing and irradiating the diameter of the beam light with a lens or the like.

In the present embodiment, the light irradiation unit 104 is configured to be movable in a two-dimensional direction (XY direction in the drawing) by the first scanning mechanism 112. By moving the light irradiation unit 104 by the scanning mechanism, it is possible to irradiate light at an arbitrary position on the subject, and a wide range of imaging is possible.
In the following description, a position defined by the position where the optical axis of the light irradiated on the subject surface intersects the subject surface and the intensity distribution of the light is referred to as a light irradiation area (reference numeral 115 in FIG. 1). .

  The first scanning mechanism 112 includes a mechanism for moving the light irradiation unit 104 in the plane direction with respect to the subject and a mechanism for changing the inclination of the light irradiation unit 104. As a mechanism for moving the light irradiation unit 104, for example, a mechanism that combines a biaxial linear stage or a pulse motor and a ball screw can be cited, but any moving mechanism can be used as long as the light irradiation unit 104 can be moved. Also good. An actuator may be used as a mechanism for changing the inclination of the light irradiation unit 104. These mechanisms operate based on commands from the control unit 111 (movement control unit in the present invention).

  The probe 106 is a unit that receives an acoustic wave generated from a subject. The probe 106 is configured by arranging a plurality of (for example, 512) conversion elements 105 in a spiral shape on the inner surface of a hemispherical support member.

  The support member is a substantially hemispherical container that supports the plurality of conversion elements 105. In the present embodiment, a plurality of conversion elements 105 are installed on the inner surface of the hemisphere. An acoustic matching material (for example, water) may be stored inside the hemisphere. In order to support these members, the support member is preferably configured using a metal material having high mechanical strength. More preferably, when the probe 106 is moved by the second scanning mechanism 113, the support member is configured to have a mechanical strength that can maintain the posture of the probe 106.

The conversion element 105 is a means for receiving an acoustic wave coming from inside the subject due to light irradiation and converting it into an electrical signal (hereinafter referred to as a photoacoustic signal). The conversion element is also called a probe, an acoustic wave detection element, an acoustic wave detector, an acoustic wave receiver, or a transducer.
Since the acoustic wave generated from the living body is an ultrasonic wave of 100 KHz to 100 MHz, an element capable of receiving the above frequency band is used for the acoustic wave probe. Specifically, a transducer using a piezoelectric phenomenon, a transducer using optical resonance, a transducer using a change in capacitance, or the like can be used.

  In addition, it is desirable to use an acoustic wave probe having high sensitivity and a wide frequency band. Specifically, piezoelectric elements using PZT (lead zirconate titanate), polymer piezoelectric film materials such as PVDF (polyvinylidene fluoride), CMUT (capacitive micromachined ultrasonic transducer), Fabry-Perot interferometer were used. Things. However, the present invention is not limited to those listed here, and any one may be used as long as it satisfies the function as a probe.

  The plurality of conversion elements 105 are arranged in an array so that the direction (directing axis) in which each element has the highest reception sensitivity is concentrated in a certain region consisting of a substantially hemispherical curvature center and its vicinity. By arranging the plurality of conversion elements 105 in this way, a high resolution can be obtained at the center of curvature of the hemisphere.

  Thus, by arranging the plurality of conversion elements 105 in a multidimensional manner, acoustic waves can be received at a plurality of positions at the same time, so that the measurement time can be shortened. Note that the support member is not limited to a hemispherical shape as long as the direction of high reception sensitivity of the plurality of conversion elements 105 can be concentrated in a predetermined region. For example, the support member may have a shape obtained by cutting an ellipsoid in an arbitrary cross section, or may be a polyhedron.

The probe 106 is configured to be movable in a two-dimensional direction (XY direction in the figure) by the second scanning mechanism 113. By moving the probe 106 by the scanning mechanism, it is possible to receive photoacoustic waves at a plurality of different positions with respect to the subject, and a wide range of imaging is possible.
The second scanning mechanism 113 is configured to have a mechanism for moving the probe 106 in the plane direction with respect to the subject. As a mechanism for moving the probe 106, for example, a mechanism that combines a two-axis linear stage or a pulse motor and a ball screw can be cited. Any moving mechanism can be used as long as the probe 106 can be moved. Also good. These mechanisms operate based on commands from the control unit 111.

The holding member 103 is a member that holds the subject. By holding the subject by the holding member 103, the subject being imaged can be fixed. This facilitates the estimation of the light irradiation position on the subject, the estimation of the acoustic wave propagation path, and the like, and improves the measurement accuracy.
The holding member 103 is preferably made of a material having the strength to support the subject and the property of transmitting light and acoustic waves. For example, a transparent resin such as acrylic, polycarbonate, or PET, a rubber sheet such as silicone rubber, natural rubber, or urethane rubber, or a mesh material having a uniform opening in a wide range can be used.
Note that the shape of the holding member 103 is not limited as long as the subject can be fixed in an arbitrary shape. For example, when the subject has a convex shape such as a breast, a cup-shaped holding member protruding toward the probe 106 may be used. Further, when the subject has a planar shape such as a palm or a sole, a flat holding member may be used.
In the present embodiment, a planar PET plate installed in parallel with the scanning plane of the second scanning mechanism 113 is used as the holding member 103. Thereby, the distance between the conversion element 105 and the subject can be kept constant.

Note that the holding member 103 is not an essential component. Without the holding member 103, the surface position of the subject becomes indefinite, so that the measurement accuracy is reduced, but the subject information can be acquired. In this case, other means for acquiring the shape of the subject may be used. For example, a method of estimating the shape of the subject based on the result of analyzing the camera image or the acoustic information of the blood vessels near the skin or the skin surface can be used.

  In addition, you may store an acoustic matching material inside the holding member 103 as needed. The acoustic matching material is a member for acoustically matching the subject or the holding member 103 and the probe 106. The acoustic matching material preferably propagates an acoustic wave and does not hinder scanning of the probe 106. For example, liquids such as water, DIDS (sebacate diisodecyl ester), PEG (polyethylene glycol), silicone oil, castor oil can be used. In this embodiment, water is used. In the present embodiment, the inside of the holding member 103 and the space between the holding member 103 and the conversion element 105 are filled with the acoustic matching material.

The signal acquisition unit 110 is means for amplifying the electric signal acquired by the conversion element 105 and converting it into a digital signal.
The signal acquisition unit 110 is configured using an amplifier that amplifies the received signal, an A / D converter that digitally converts the analog received signal, a memory such as a FIFO that stores the received signal, and an arithmetic circuit such as an FPGA chip. Also good. Further, the signal acquisition unit 110 may be composed of a plurality of processors and arithmetic circuits.

The data processing unit 120 is means (image generation unit in the present invention) that reconstructs the digital signal output from the signal acquisition unit 110 and generates image data representing characteristic information in the subject. Details of the data processing unit 120 will be described with reference to FIG.
The data processing unit 120 reconstructs the photoacoustic signal, generates a volume data representing the characteristic information of the subject (information acquisition unit 121), and converts the volume data into an image (image processing). Part 122).
The data processing unit 120 may be configured by a computer having a CPU, a RAM, a nonvolatile memory, and a control port. Control is performed by executing a program stored in the nonvolatile memory by the CPU. The data processing unit 120 may be realized by a general-purpose computer or a dedicated workstation. The unit responsible for the calculation function of the data processing unit 120 may be configured by a processor such as a CPU or GPU, or an arithmetic circuit such as an FPGA chip. These units are not only composed of a single processor and arithmetic circuit, but may be composed of a plurality of processors and arithmetic circuits.

The information acquisition unit 121 acquires characteristic information inside the subject for each position based on the digitally converted signal (photoacoustic signal). Specifically, by performing reconstruction using time-series received signals acquired by a plurality of conversion elements 105, data of characteristic values (distribution data) corresponding to positions on two-dimensional or three-dimensional spatial coordinates Ask for.
The unit area of reconstruction is called a pixel or voxel. As a reconstruction method, a known reconstruction method such as a filtered back projection (FBP), a time reversal method, a model-based method, or a Fourier transform method can be used. Further, a delay and sum process used in ultrasonic imaging may be used.

When the present invention is applied to an optical focus type photoacoustic microscope or a photoacoustic microscope using a focus type probe, distribution data can also be generated without performing reconstruction processing.
Specifically, the probe 106 is moved relative to the subject by the second scanning mechanism 113, and the probe 106 receives photoacoustic waves at a plurality of positions. And the information acquisition part 121 converts the time-axis direction into a depth direction after plotting the obtained photoacoustic signal with respect to a time change, and plots it on a space coordinate. By performing this for each scanning position, distribution data can be configured.

The image processing unit 122 generates image data to be output to the display unit 114 based on the characteristic information and distribution data generated by the information acquisition unit 121. Specifically, image processing such as luminance conversion, distortion correction, region of interest extraction, blood vessel extraction processing, arterial and vein separation processing, logarithmic compression processing, and the like is performed.

  The unit responsible for the storage function of the data processing unit 120 may be a non-temporary storage medium such as a ROM, a magnetic disk or a flash memory, or a volatile medium such as a RAM. Note that the storage medium storing the program is a non-temporary storage medium. Note that these units may be configured not only from one storage medium but also from a plurality of storage media.

  The control unit 111 is a unit that gives commands related to overall control of the apparatus, such as light irradiation control on the subject, movement control of the light irradiation unit 104, movement control of the probe 106, and the like.

  The display unit 114 is a means for displaying the information acquired by the data processing unit 120 and its processing information, and is typically a display device using liquid crystal, organic EL, or the like. The display unit 114 may not constitute the photoacoustic apparatus according to the present invention.

Next, an outline of processing for acquiring subject information performed by the photoacoustic apparatus according to the present embodiment will be described.
The pulsed light emitted from the light source 101 is irradiated to the subject E via the optical system 102 and the light irradiation unit 104. When a part of the energy of the light propagated inside the subject is absorbed by a light absorber such as blood, blood vessel, tumor, etc., an acoustic wave is generated from the light absorber due to thermal expansion. When cancer is present in a living body, light is specifically absorbed in the new blood vessels of the cancer like other normal blood, and an acoustic wave is generated.
When measuring concentration information in a living body such as oxygen saturation, a plurality of pulse lights having different wavelengths may be output at different timings.
The photoacoustic wave generated in the living body is received by the conversion element 105 included in the probe 106 and output as a time-series analog electric signal.

  In the present embodiment, light irradiation can be performed while changing the light irradiation position on the subject by the first scanning mechanism 112. Further, the acoustic wave can be acquired while the relative positional relationship between the probe 106 and the subject is changed by the second scanning mechanism 113. That is, photoacoustic signals can be acquired at a plurality of positions while irradiating light at different positions on the subject a plurality of times.

  In the following description, the light irradiation position on the subject refers to a position where the optical axis of the irradiation light intersects the surface of the subject, and is synonymous with “center coordinates of the light irradiation area”. In the present embodiment, the coordinate corresponding to the optical axis is the center of the light irradiation area. However, the center of gravity of the light irradiation area may be the luminance gravity center position of the light amount distribution.

  The signal output from the conversion element 105 is amplified and digitally converted by the signal acquisition unit 110 and then analyzed by the data processing unit 120. The analysis result is volume data representing in-vivo characteristic information (for example, initial sound pressure distribution and absorption coefficient distribution), and is converted to a two-dimensional image and then output via the display unit 114.

Next, processing unique to the photoacoustic apparatus according to the present embodiment will be described.
The photoacoustic apparatus according to the present embodiment has a configuration in which a plurality of imaging area sizes are set in advance, and the user of the apparatus can specify and select the imaging center coordinates and the imaging area size. For example, a wide-range image of the surface of the subject is displayed on the display unit 114, a frame having an imaging area size selected by the user is displayed around the selected coordinates, and the imaging location can be visually recognized. Yes. By determining the center coordinates of the imaging and the size of the imaging area, an imaging target area (hereinafter referred to as an imaging area) on the subject surface is determined. The imaging area is an area obtained by projecting an area to be imaged by reconstruction onto the subject surface.

Based on the determined coordinates and size of the imaging area, the movement pattern of the probe 106 when imaging is determined. The movement pattern is information indicating on which route the probe 106 moves and at which position the acoustic wave is received when the subject is imaged. The movement pattern may be generated dynamically or selected from preset ones.
Note that the photoacoustic apparatus according to the present embodiment can perform control to move the probe 106 and the light irradiation position so as to follow each other. In this case, the movement pattern can be said to be information indicating on what route the irradiation position of light on the subject moves and at which position the light irradiation is performed.

  The control unit 111 issues a command to the light source 101, the first scanning mechanism 112, and the second scanning mechanism 113 according to the set movement pattern, thereby controlling the light irradiation to the subject and the light irradiation position. Control and position control of the probe 106 are performed.

  By the way, when reconstructing the object information, it is preferable to move the probe 106 as much as possible and receive acoustic waves at a plurality of positions. This is because, by acquiring acoustic waves at a plurality of locations and reconstructing an image, a good S / N ratio can be obtained and high resolution can be achieved. Further, it is possible to reduce artifacts generated depending on the position of the conversion element 105. Furthermore, when the present invention is applied to an optical focus type photoacoustic microscope or a photoacoustic microscope using a focus type probe, a wide range can be reconfigured according to the movement range of the probe 106. .

  On the other hand, it is preferable to fix the light irradiation position on the subject as much as possible. This is because the light amount distribution of the light irradiated to the subject is not uniform, and an intensity difference occurs in the light amount in the same light irradiation area. When such a light irradiation area moves, the magnitude relationship of signals generated from a plurality of light absorbers changes, and depending on the combination of signals at the time of reconstruction, the photoacoustic signals generated from the same light absorber are uneven. It will occur.

  This will be described with reference to FIG. FIG. 3 shows an example in which light is irradiated to different positions on the linear light absorber 301. As illustrated, the intensity of the photoacoustic signal generated from Pos1 and Pos2 in the light absorber is reversed depending on the amount of irradiation light. That is, the reproducibility of the reconstructed image can be stabilized by fixing the light irradiation position with respect to the imaging target. For example, after determining the light irradiation position, the reconstructed image can be stabilized by performing imaging while the first scanning mechanism 112 is stopped.

  However, if the light irradiation position on the subject is fixed, the photoacoustic signal cannot be acquired from a wide range. Therefore, the photoacoustic apparatus according to the present embodiment switches between fixing the light irradiation position and moving the irradiation position following the probe 106 based on the set size of the imaging area.

As described above, the light irradiation area is a region defined by the position where the optical axis of the light irradiated on the subject surface intersects the subject surface and the intensity distribution of the light.
How the light irradiation area is formed on the subject can be acquired based on the shape of the subject and the position of the light irradiation unit 104. In the present embodiment, the subject is held by the holding member 103 parallel to the scanning plane of the first scanning mechanism 112, and the light irradiation unit 104 moves in parallel with a fixed inclination. The intensity distribution of the emitted light does not change regardless of the position of the light irradiation area. Therefore, the control part 111 can acquire a light irradiation area using a prescribed profile.

  When the scanning surface of the first scanning mechanism 112 and the surface of the subject are not parallel, the surface shape of the subject is assumed, and the light irradiation area is calculated or obtained on the assumption that the intensity distribution does not change. Also good. By doing in this way, the acquisition process of a light irradiation area can be simplified.

  In the present embodiment, control for moving the probe 106 and the light irradiation position on the subject to follow each other is referred to as first control, and the light irradiation position on the subject is fixed. The control for moving only this is referred to as second control.

Whether to perform the first control or the second control when imaging the subject can be determined by the following method.
That is, the second control is performed when the region on the subject that can be irradiated with light at a predetermined intensity or higher completely includes the region on the subject corresponding to the imaging area, and otherwise The first control is performed. An area on the subject irradiated with light having a predetermined intensity or higher is hereinafter referred to as a high intensity area.

This will be described with reference to FIG. In this example, a region where the energy of the irradiated light is 1 / e ² or more of the peak energy is defined as a high intensity region. In the example of FIG. 4A, the region defined by the radius R1 is a high intensity region. The energy of the irradiated light can be estimated based on a profile that approximates a Gaussian distribution, for example. FIG. 4B is a diagram showing the size of the imaging area.

When the diameter of the high intensity region (that is, R1 × 2) is larger than the diagonal length Ld of the imaging area, it can be seen that light having a predetermined intensity or more can be irradiated to all positions in the imaging area. In this embodiment, in this case, the second control, that is, the control for imaging while fixing the light irradiation position on the subject is performed.
On the other hand, when the diameter of the high-intensity region is smaller than the diagonal length Ld of the imaging area, it can be seen that light of a predetermined intensity or more cannot be irradiated to all positions in the imaging area. In the present embodiment, in such a case, the first control, that is, the control of imaging by causing the light irradiation position on the subject and the probe 106 to follow each other is performed.
In other words, whether to perform the first control or the second control is determined based on the result of comparing the area of the high-intensity region and the area of the imaging area.

  By the way, only the method described above may cause an inappropriate determination depending on the position of the light irradiation unit 104 with respect to the subject. Therefore, the photoacoustic apparatus according to the present embodiment determines whether or not the high-intensity region covers the imaging area before starting imaging, and if not, the light irradiation unit 104 (that is, high-intensity) Control to move the position of the area.

  FIG. 4C is a diagram illustrating a positional relationship between the light irradiation area and the imaging area in the initial state. In this example, the distance from the center coordinate of the light irradiation area to the farthest point in the imaging area is Rd1. When the diameter of the high-intensity region in the initial state (that is, R1 × 2) exceeds Rd1, it is possible to irradiate light of a predetermined intensity or more to all positions in the imaging area without moving the light irradiation unit 104. I understand.

On the other hand, when the diameter of the strong intensity region in the initial state is smaller than the diagonal length Rd1 of the imaging area, it can be seen that light of a predetermined intensity or more cannot be irradiated to all positions in the imaging area. In such a case, the light irradiation area is moved by changing the position of the light irradiation unit 104 by the first scanning mechanism 112.
The movement destination of the light irradiation area can be, for example, near the center of the imaging area. For example, as shown in FIG. 5A, the light irradiation unit 104 may be moved by controlling the first scanning mechanism 112 so that the center coordinates of the light irradiation area are moved by L _next .
As described above, in addition to the area, the positional relationship between the high-intensity region and the imaging area may be further determined as a criterion for determining whether to perform the first control or the second control.

  In the method described above, the comparison is performed using the diameter of the strong intensity region. However, when the light intensity distribution in the light irradiation area is not uniform, the comparison may be performed using a diameter other than the diameter of the strong intensity region. . FIG. 5B shows an example in which the intensity distribution in the light irradiation area of the irradiation light is not uniform. When the intensity distribution in the light irradiation area is not uniform, the above-described comparison may be performed using, for example, the minimum value, maximum value, average value, etc. of the width of the strong intensity region. Further, the above-described comparison may be performed using the minimum value, the maximum value, the average value, and the like of the distance from the center of the light irradiation area to the edge of the strong intensity region. Further, the comparison may be performed in consideration of the direction in the longitudinal direction of the imaging area and the moving direction of the probe 106.

Next, a flowchart of processing performed by the photoacoustic apparatus according to the present embodiment will be described with reference to FIG.
First, in step S101, the user of the apparatus designates the size and position of the imaging area. As a result, the imaging area and the movement pattern of the probe 106 are determined.
Next, in step S102, the control unit 111 acquires the position and intensity distribution of the light irradiation area in the initial state based on the shape of the subject and the position information of the first scanning mechanism 112 in the initial state. The position and intensity distribution of the light irradiation area in the initial state may be calculated, or a predefined one based on a profile or the like may be read.

Next, in step S103, based on the information regarding the light irradiation area and the imaging area in the initial state, (1) the central coordinates of the light irradiation area, (2) the size of the strong intensity region, and (3) the position of the imaging area And get the size. In the present embodiment, the size of the strong intensity region is acquired based on the profile.
Next, in step S104, it is determined whether the high intensity region in the initial state includes the entire imaging area. As described above, this determination can be performed by comparing the distance (Rd1) from the center coordinate of the light irradiation area to the farthest point in the imaging area and the diameter (R1 × 2) of the strong intensity region. it can.
Here, when the high intensity region in the initial state includes the entire imaging area, the process proceeds to step S106.
In step S106, by driving the second scanning mechanism 113, only the probe 106 is moved to a position corresponding to the imaging area. This position is the initial position in the movement pattern.

On the other hand, if the strong intensity region in the initial state does not include the entire imaging area, the process proceeds to step S105.
In step S105, the first scanning mechanism 112 and the second scanning mechanism 113 are driven to move both the probe 106 and the light irradiation unit 104 to a position corresponding to the imaging area. This position is the initial position in the movement pattern.

In step S107, it is determined whether the first control is performed or the second control is performed by determining whether the high-intensity region includes the entire imaging area based on the center coordinates of the light irradiation area. . Here, when the high-intensity region includes the entire imaging area, the process proceeds to step S109 in order to perform the second control.
In step S109, imaging of the subject is performed while performing second control, that is, control for moving only the probe 106. Specifically, light irradiation and acoustic wave reception are performed while moving the probe 106 to a plurality of signal acquisition positions included in the movement pattern.

On the other hand, when the high intensity region does not include the entire imaging area, the process proceeds to step S108 in order to perform the first control.
In step S108, imaging of the subject is performed while performing the first control, that is, the control of causing the light irradiation position on the subject and the probe 106 to follow each other. Specifically, light irradiation and acoustic wave reception are performed while moving the probe 106 and the center of the light irradiation area to a plurality of signal acquisition positions included in the movement pattern.

The acoustic wave generated from the subject is received by the conversion element 105, converted into an electrical signal, and then output to the signal acquisition unit 110. The photoacoustic signal that has undergone processing such as A / D conversion and amplification is output to the data processing unit 120, and the data processing unit 120 (information acquisition unit 121) generates an initial sound pressure distribution in the subject (step S110). ).
In this example, light of a single wavelength is irradiated, but light of a plurality of different wavelengths (for example, two wavelengths of λ1 and λ2) is alternately irradiated, and an initial sound pressure distribution corresponding to each wavelength. , Data representing the concentration distribution of the light absorber may be generated.
In step S <b> 111, the image processing unit 122 generates image data based on the initial sound pressure distribution and density distribution, and outputs the image data to the display unit 114.

  As described above, according to the first embodiment, based on the positional relationship between the imaging area and the high intensity region, imaging is performed with the light irradiation position fixed, or the light irradiation position and the probe are It is determined whether to perform imaging while following each other. According to this mode, it is possible to achieve both acquisition of a stable photoacoustic signal and widening of the imaging area.

(Second embodiment)
The photoacoustic apparatus according to the first embodiment reconstructs an image upon completion of acquisition of the photoacoustic signal, and outputs an image (still image) including subject information to the display unit 114. On the other hand, the second embodiment is an embodiment in which the subject information is sequentially output as a continuous image (moving image). The configuration of the photoacoustic apparatus according to the second embodiment is the same as that of the first embodiment, except that the reconstruction is sequentially performed based on the acquired photoacoustic signal and the generated image is periodically output. Is different.

  The photoacoustic apparatus according to the second embodiment is a mode for outputting the acquired subject information as a moving image in addition to the mode for outputting the acquired subject information as a still image as in the first embodiment (video mode). ) Can be selected.

FIG. 7 is a diagram for explaining the timing at which an acoustic wave is received and a photoacoustic signal is generated, and the display timing of a reconstructed image. The photoacoustic apparatus according to the second embodiment generates and outputs a reconstructed image for one frame based on photoacoustic signals generated at a plurality of timings.
FIG. 7A shows an example in which one reconstructed image is obtained using all the photoacoustic signals generated between the start of imaging and the end of imaging. This example corresponds to the first embodiment.
On the other hand, FIG. 7B and FIG. 7C are examples in which a reconstructed image is generated based on one or more photoacoustic signals and displayed each time. In this example, newly reconstructed images (F1, F2, F3...) Are successively displayed like a moving image.

  When the moving image mode is selected, the photoacoustic signal used for image reconstruction is smaller than that in the still image mode as shown in FIG. However, by moving the probe 106 as much as possible and receiving signals at a plurality of locations, artifacts can be reduced and the quality of the reconstructed image can be improved. In the present embodiment, light irradiation and acoustic wave reception are performed at a cycle of 10 Hz, and the probe 106 is moved along the circumferential orbit at a cycle of 2 Hz.

FIG. 8 is a diagram showing the positional relationship of the probe 106 in the example of FIG. In the present embodiment, acoustic waves are received at a frequency of 10 Hz, and the probe 106 moves at a frequency of 2 Hz. Therefore, each time the acoustic wave is received, the probe 106 is 72 degrees on the circumferential path. Moving.
In the example of FIG. 7B, image reconstruction is performed using three sets of photoacoustic signals per frame. That is, a reconstructed image for one frame is generated using photoacoustic signals received at three locations. As can be seen from the figure, in this example, the combination of the three positions changes for each frame.

FIG. 9 is a diagram showing the positional relationship of the probe 106 in the example of FIG.
In the example of FIG. 7C, image reconstruction is performed using five sets of photoacoustic signals per frame. That is, a reconstructed image for one frame is generated using photoacoustic signals received at five locations. As can be seen from the figure, in this example, the combination of the five positions is the same for each frame.

In the example of FIG. 7C, since the number of photoacoustic signals used for reconstruction is larger than in the example of FIG. 7B, a good S / N ratio can be obtained, and artifacts are reduced. However, a large processing load is applied due to the large scale of computation.
On the other hand, in the example of FIG. 7B, compared with the example of FIG. 7C, the number of photoacoustic signals used for reconstruction is small, so the image quality is relatively lowered, but the processing load is reduced. Therefore, there is an advantage that the update of the moving image becomes smooth and the time change of the absorber can be easily observed.
The photoacoustic apparatus according to the second embodiment is configured so that the user of the apparatus can select the number of photoacoustic signals used per frame in consideration of such advantages and disadvantages.

  In the example of FIGS. 7B and 7C, the acquisition of the photoacoustic signal and the reconstruction of the image are executed in parallel. However, as shown in FIG. 7D, the acquisition of the photoacoustic signal is performed. And image reconstruction may be performed alternately.

  FIG. 10 is a diagram illustrating a light amount distribution of light with respect to an imaging area. FIG. 10A shows a light irradiation area corresponding to one shot. In this example, the imaging area is represented by a broken line, and the light intensity is represented by a white region.

  FIG. 10B is a diagram showing the positions of the light irradiation areas corresponding to the images F1, F2, and F3 in FIG. This example shows an example in which the light irradiation position and the probe are made to follow each other. As can be seen from the figure, the light amount distribution of the light corresponding to each frame can be considered to be equivalent to the sum of the light amount distributions of the three times of light irradiation. However, in the case of this example, since the position of the light irradiation area is different in each of the frames F1, F2, and F3, the integrated light amount distribution changes for each frame. That is, since the signal corresponding to the acoustic wave generated from the light absorber varies from frame to frame, the displayed moving image flickers. The reason why such flickering occurs is that a combination of positions where light is irradiated (hereinafter referred to as a light irradiation pattern) changes from frame to frame.

  On the other hand, FIG. 10C shows the position of the light irradiation area corresponding to the images F1, F2, and F3 in FIG. In the case of this example, the light amount distribution of the light corresponding to each frame can be considered to be equivalent to the sum of the light amount distributions of five times of light irradiation. That is, since the integrated light quantity distribution does not change for each frame, no flickering occurs in the moving image.

  The photoacoustic apparatus according to the second embodiment determines that the light irradiation pattern changes for each frame, and in such a case, the light irradiation position is fixed and imaging is performed. Thereby, as shown in FIG. 10A, it is possible to prevent the deviation of the light amount distribution.

  Actually, even if the irradiation position of light is fixed, the amount of light for each irradiation is not completely the same. For this reason, the light amount may be corrected by measuring the light amount change for each irradiation and adjusting the gain of the photoacoustic signal.

The acoustic wave reception position, reception period, light irradiation position, light irradiation period, probe rotation period, and the like are not limited to those illustrated.
Further, as in the first embodiment, when the range to be reconstructed is smaller than the high intensity region, the light irradiation area may be fixed even if the light irradiation pattern between frames is the same. . However, in this case, the area irradiated with light is narrowed with respect to the imaging area.

Next, a flowchart of processing performed by the photoacoustic apparatus according to the second embodiment will be described with reference to FIG.
First, in step S201, the user of the apparatus sets the size and position of the imaging area. As a result, the imaging area and the movement pattern of the probe 106 are determined. In this step, whether to use the moving image mode is set. In this step, the frame rate of the moving image may be set.
Next, in step S202, it is determined whether to use the moving image mode. If the moving image mode is not used, the process proceeds to step S102. When the moving image mode is used, the process proceeds to step S203.

In step S203, a light irradiation pattern for each frame is determined. For example, as described above, the number of photoacoustic signals per frame, the movement angle of the probe 106 in one light irradiation, and the like are determined.
Next, in step S204, it is determined whether to perform the first control or the second control during imaging. In this step, when the combination of the light irradiation patterns is different between frames, it is determined to perform the second control. Further, when the combination of light irradiation patterns is the same between frames, it is determined to perform the first control.

  In step S206, imaging of the subject is performed while performing the second control, that is, the control for moving only the probe 106. Specifically, light irradiation and acoustic wave reception are performed while moving the probe 106 to a plurality of signal acquisition positions included in the movement pattern. This step continues until the number of photoacoustic signals necessary for reconstructing one frame image can be acquired.

  In step S205, imaging is performed on the subject while performing the first control, that is, the control for causing the probe 106 and the light irradiation position to follow each other. Specifically, light irradiation and acoustic wave reception are performed while moving the probe 106 and the center of the light irradiation area to a plurality of signal acquisition positions included in the movement pattern. This step continues until the number of photoacoustic signals necessary for reconstructing one frame image can be acquired.

The acoustic wave generated from the subject is received by the conversion element 105, converted into an electrical signal, and then output to the signal acquisition unit 110. The photoacoustic signal that has undergone processing such as A / D conversion and amplification is output to the data processing unit 120, and the data processing unit 120 (information acquisition unit 121) generates an initial sound pressure distribution in the subject (step S207). ).
In step S <b> 208, the image processing unit 122 generates image data based on the initial sound pressure distribution and density distribution, and outputs the image data to the display unit 114.
In step S209, it is determined whether or not to end imaging. If the imaging is continued, the process proceeds to step S204.

  In the second embodiment, as described above, in the photoacoustic apparatus that outputs the reconstructed image as a moving image, control is performed so that the integrated light amount distribution is the same for each frame. Thereby, variation in the light amount distribution can be suppressed and the accuracy of the reconstructed image can be improved. In addition, since images using photoacoustic signals obtained with the same light amount distribution can be sequentially updated, a moving image with less flicker can be displayed.

  FIG. 11 illustrates an example in which an image is output while alternately acquiring photoacoustic signals and reconstructing an image. However, the process of acquiring a photoacoustic signal corresponding to the (n + 1) th frame and the nth frame are described. The image reconstruction processing may be executed in parallel.

  In the description of the second embodiment, light having a single wavelength is irradiated. However, light having a plurality of different wavelengths (for example, two wavelengths of λ1 and λ2) is irradiated, and an initial value corresponding to each wavelength is irradiated. Data representing the concentration distribution of the light absorber may be generated after obtaining the sound pressure distribution. In this case, the light irradiation pattern may be determined for each wavelength.

(Modification)
It should be noted that the description of the embodiment is an example for explaining the present invention, and the present invention can be implemented with appropriate modifications or combinations without departing from the spirit of the invention.
For example, the present invention can be implemented as a photoacoustic apparatus including at least a part of the above means. The present invention can also be implemented as a subject information acquisition method including at least a part of the above processing. The above processes and means can be freely combined and implemented as long as no technical contradiction occurs.

For example, in the description of the embodiment, the range in which the energy is 1 / e ² or more of the peak energy is set as the strong intensity region, but the reference value for defining the strong intensity region may be other than this. For example, the half value of peak energy may be used. The reference value can be determined according to, for example, the S / N ratio required for the photoacoustic signal.
In the description of the embodiment, it is expressed that the light irradiation position and the probe follow each other. However, if the light irradiation position and the probe can be moved simultaneously, one movement is not necessarily changed to the other. There is no need to provide feedback.

  In the description of the embodiment, it is determined whether to perform the first control or the second control based on the result of comparing the high intensity region and the imaging area. The determination may be made. For example, it may be determined whether to perform the first control or the second control based only on information indicating the region to be imaged, the imaging range, and the like. Information on the subject may be obtained from, for example, an electronic medical record, or there is data recorded when a measurement is performed on the subject in the past (for example, data attached to a medical image) , May be obtained from the data.

  The present invention is also realized by executing the following processing. That is, a program that realizes one or more functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and one or more processors in the computer of the system or apparatus read the program. It can also be realized by processing to be executed. It can also be realized by a circuit (for example, FPGA or ASIC) that realizes one or more functions.

  101: Light source, 102: Optical system, 104: Light irradiation unit, 106: Probe, 111: Control unit, 112: First scanning mechanism, 113: Second scanning mechanism

Claims (13)

A light irradiation unit for irradiating the subject with light;
A probe for receiving an acoustic wave generated from the subject due to the light irradiation;
A movement control unit that controls a first movement mechanism that moves the probe with respect to the subject, and a second movement mechanism that moves the irradiation position of the light with respect to the subject;
Have
The movement control unit fixes the light irradiation position on the subject surface and the probe to move the probe so as to follow each other, and fixes the light irradiation position on the subject surface. A photoacoustic apparatus, wherein the second control for moving the child is switched. An acquisition unit that acquires information on a strong intensity region that is an area of the subject surface irradiated with the light with an intensity stronger than a predetermined value, and information on an imaging area;
The movement control unit performs the first control when the strong intensity region completely includes the imaging area, and performs the second control when the strong intensity region does not completely include the imaging area. It performs. The photoacoustic apparatus of Claim 1 characterized by the above-mentioned. The movement control unit moves the strong intensity region to a position corresponding to the imaging area when the strong intensity region is not included in the imaging area.
3. The method according to claim 2, wherein whether to perform the first control or the second control is determined based on the high-intensity region disposed at the position and the imaging area. The photoacoustic apparatus of description. An acquisition unit that acquires information on a strong intensity region that is an area of the subject surface irradiated with the light with an intensity stronger than a predetermined value, and information on an imaging area;
The movement control unit, based on the first area that is the area of the high-intensity region and the second area that is the area of the region of the subject surface corresponding to the imaging area, The photoacoustic apparatus according to claim 1, wherein it is determined whether to perform control or to perform the second control. The movement control unit performs the first control when the second area exceeds the first area, and the second control area performs the first control when the second area is less than the first area. The photoacoustic apparatus according to claim 4, wherein the second control is performed. The movement control unit determines whether to perform the first control or the second control based on a positional relationship between the strong intensity region and the imaging area. The photoacoustic apparatus according to claim 4. The photoacoustic apparatus according to any one of claims 2 to 6, wherein the strong intensity region is a region in which light intensity is 1 / e ² or more of peak energy. A holding member that is disposed between the subject and the light irradiation unit and holds the subject;
The said acquisition part acquires the position and magnitude | size of the said high intensity | strength area | region based on the profile of the light irradiated to the said holding member. The one of Claim 2 to 7 characterized by the above-mentioned. Photoacoustic device. It further has an acquisition unit that acquires information about the imaging area,
The movement control unit performs the first control when the region of the subject surface corresponding to the imaging area exceeds a predetermined area, and the region of the subject surface corresponding to the imaging area is a predetermined area. The photoacoustic apparatus according to claim 1, wherein the second control is performed when the value is lower than the value. 10. The light according to claim 1, further comprising an image generation unit configured to generate a reconstructed image representing characteristic information in the subject based on the received acoustic wave. Acoustic device. The image generation unit generates a reconstructed image for one frame based on acoustic waves received by the probe at a plurality of reception positions, and sequentially outputs the generated reconstructed image. The photoacoustic apparatus according to claim 10. The movement control unit performs the second control when the combination of the plurality of reception positions corresponding to the reconstructed image for one frame is different for each frame. The photoacoustic apparatus of description. A light irradiating unit for irradiating the subject with light; a probe for receiving an acoustic wave generated from the subject due to the irradiation of the light; and a first moving the probe relative to the subject. An object information acquisition method performed by a photoacoustic apparatus having one movement mechanism and a second movement mechanism that moves an irradiation position of the light with respect to the object,
First control for moving the light irradiation position on the subject surface and the probe to follow each other, and second control for fixing the light irradiation position on the subject surface and moving the probe And a control step for switching between the control and the subject information acquisition method.