JP2016013189A - Photoacoustic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoacoustic apparatus capable of reducing a time required from the completion of reception of a photoacoustic wave to the acquisition of a space distribution of subject information in a reconfiguration using a Fourier transformation method.SOLUTION: A photoacoustic apparatus includes: a light source for emitting light at first and second timings; a probe for receiving a photoacoustic wave generated by the irradiation of light to a subject at the first and second timings, and outputting first and second time series reception signals; and a processing part for starting conversion from the first time series reception signal to a first wavenumber component between the first timing and the second timing, converting the second time series reception signal to a second wavenumber component, synthesizing the first wavenumber component and the second wavenumber component to acquire a third wavenumber component, and acquiring a space distribution of subject information based on the third wavenumber component.

Description

  The present invention relates to a photoacoustic apparatus that acquires subject information using a photoacoustic effect.

  Conventionally, photoacoustic apparatuses such as a photoacoustic imaging apparatus and an ultrasonic echo imaging apparatus have been proposed as techniques for receiving acoustic waves and acquiring information inside a subject such as a living body.

  For example, the photoacoustic imaging apparatus has been shown to be particularly useful in the diagnosis of skin cancer and breast cancer, and as a medical device that replaces an ultrasonic echo diagnostic apparatus, an X-ray apparatus, an MRI apparatus, etc. that have been used in the diagnosis. Expectations are growing.

  When measuring light such as visible light or near-infrared light is irradiated to a living tissue, a light-absorbing substance inside the living body, for example, a substance such as hemoglobin in the blood absorbs the energy of the measuring light and instantaneously expands. It is known that acoustic waves are generated. This phenomenon is called a photoacoustic effect, and the generated acoustic wave is also called a photoacoustic wave.

  The photoacoustic imaging apparatus visualizes information on a living tissue by measuring the photoacoustic wave. Such a tomographic technique using the photoacoustic effect is also referred to as photoacoustic imaging (PAI).

  In photoacoustic imaging, object information related to the light absorption coefficient inside the object can be imaged. The light absorption coefficient is a rate at which living tissue absorbs light energy. For example, the initial sound pressure that is the sound pressure at the moment when the photoacoustic wave is generated can be imaged. Since the initial sound pressure is proportional to the product of the light energy and the light absorption coefficient, the light absorption coefficient can be imaged by performing appropriate processing. Furthermore, since the light absorption coefficient depends on the concentrations of the components constituting the living tissue, those concentrations can be acquired. In particular, the concentration ratio of oxyhemoglobin and reduced hemoglobin, that is, the oxygen saturation can be acquired based on the light absorption coefficient acquired by each of the light of different wavelengths. When a tumor tissue is present in a living body, it is known that the oxygen saturation is reduced at the location. Therefore, it is expected that a tumor can be diagnosed by measuring a light absorption coefficient.

  Non-Patent Document 1 and Non-Patent Document 2 disclose a Fourier transform method as a method (reconstruction method) for acquiring a spatial distribution of object information related to a light absorption coefficient from a received signal of a photoacoustic wave. In these documents, the received signal of the photoacoustic wave is converted into a wave number component of the photoacoustic wave generated by the subject, and the spatial distribution of the subject information is acquired by performing inverse Fourier transform on the wave number component. In particular, Non-Patent Document 1 discloses a Fourier transform method when a photoacoustic wave is received on a plane. Non-Patent Document 2 discloses a Fourier transform method when a photoacoustic wave is received on a spherical surface.

Journal of Biomedical Optics 15 (2), 021314 (March / April 2010) Physics in Medicine and Biology 57 (2012) N493-N499

  However, in the Fourier transform methods described in these documents, it may take a long time to acquire the spatial distribution of the subject information after all the photoacoustic wave measurements are completed.

  Therefore, the present invention provides a photoacoustic apparatus capable of reducing the time required to acquire the spatial distribution of subject information after the completion of reception of photoacoustic waves in reconstruction using a Fourier transform method. For the purpose.

  The photoacoustic apparatus disclosed in this specification includes a light source that emits light at a first timing and a second timing that is later than the first timing, and the subject is irradiated with light at the first timing. The photoacoustic wave generated by the first time-series received signal is output, and the photoacoustic wave generated by irradiating the subject with light at the second timing is received at the second time. A probe that outputs a series of received signals, and a processing unit that acquires a spatial distribution of the subject information. The processing unit includes a first timing and a second timing between the first timing and the second timing. Starts conversion from time-series received signal to first wavenumber component, converts second time-series received signal to second wavenumber component, and combines first wavenumber component and second wavenumber component To obtain a third wavenumber component, and obtain a spatial distribution of the subject information based on the third wavenumber component. To.

  Another photoacoustic apparatus disclosed in this specification receives a light source that emits light at a plurality of timings, and a photoacoustic wave generated at each timing by irradiating the subject with the light at the plurality of timings. A probe that outputs a time-series received signal corresponding to the plurality of timings, and a processing unit that acquires a spatial distribution of subject information, and the processing unit irradiates light at the plurality of timings. Wave number components related to some dimensions of the plurality of dimensions related to the time-series received signal are acquired before completion of light irradiation, and after the light irradiation at the plurality of timings is completed, the wave number components related to the remaining dimensions of the plurality of dimensions are acquired. To obtain wave number components related to the plurality of dimensions, and obtain a spatial distribution of the subject information based on the wave number components related to the plurality of dimensions.

  According to the photoacoustic apparatus disclosed in the present specification, in reconstruction using the Fourier transform method, the time required to acquire the spatial distribution of the subject information after completion of all photoacoustic wave measurements is reduced. can do.

The figure which shows the measurement sequence which concerns on a comparative example and 1st embodiment. The schematic diagram of the photoacoustic apparatus which concerns on 1st embodiment. The figure which shows the detail of the process part which concerns on 1st embodiment, and the structure of the periphery. The figure which shows the structure of the probe which concerns on 1st embodiment. The figure which shows the movement of the probe which concerns on 1st embodiment. The figure which shows the flow of the subject information acquisition method which concerns on 1st embodiment. The figure which shows the flow of the subject information acquisition method which concerns on 2nd embodiment. The schematic diagram of the photoacoustic apparatus which concerns on 3rd embodiment. The figure which shows the structure of the probe which concerns on 3rd embodiment. The figure which shows the movement of the probe which concerns on 3rd embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same component in principle, and description is abbreviate | omitted.

  The photoacoustic apparatus according to the present embodiment can acquire subject information by detecting a photoacoustic wave generated by the photoacoustic effect.

  In this embodiment, the subject information includes the initial sound pressure of the photoacoustic wave, the light energy absorption density derived from the initial sound pressure, the light absorption coefficient, and the concentration of the substance constituting the subject. Here, the concentration of the substance includes oxygen saturation, oxyhemoglobin concentration, deoxyhemoglobin concentration, total hemoglobin concentration, and the like. The total hemoglobin concentration is the sum of the oxyhemoglobin concentration and the deoxyhemoglobin concentration.

  In the present embodiment, the subject information may be distribution information instead of numerical data. That is, distribution information such as a light absorption coefficient distribution and an oxygen saturation distribution may be used as the subject information.

  By the way, in the Fourier transform method using the received signal data obtained by performing light irradiation at a plurality of timings, there are many processes from the completion of all the photoacoustic wave measurements until the acquisition of the spatial distribution of the subject information. The inventor has found that this may take time. Hereinafter, this problem will be described with reference to FIG.

  FIG. 1 shows a flow of photoacoustic wave measurement and reconstruction processing arranged in time series. Mn represents the nth measurement. Kn represents a conversion process from a time-series received signal obtained in the n-th measurement to a wave number component. IF represents inverse Fourier transform processing for obtaining the spatial distribution of the subject information from the wave number component. That is, FIG. 1 shows the time required for the Fourier transform for obtaining the wave number component from the time-series received signal and the time required for the inverse Fourier transform for obtaining the spatial distribution from the waveform component.

  In this specification, measurement refers to receiving light and receiving a photoacoustic wave generated by the light irradiation. Further, the measurement position refers to the position of the probe when light is irradiated.

(Comparative Example 1)
FIG. 1A shows the measurement sequence from the first time to the n-th time and the sequence of each process in the first comparative example. In the first comparative example, a case where a conversion process from a time-series received signal to a wave number component and a conversion process from a wave number component to a spatial distribution of subject information is performed for each light irradiation is considered.

  As can be understood from FIG. 1A, in the first comparative example, the time required for converting the time-series received signal into the wave number component and the time required for acquiring the spatial distribution of the subject information from the wave number component are calculated as light. It is necessary to acquire the spatial distribution of the subject information for the time multiplied by the number of irradiations. Therefore, the calculation cost for acquiring the spatial distribution of the subject information from the time-series received signal increases. In addition, as shown in FIG. 1A, when the process for one irradiation is not completed between measurements, it takes a lot of time to acquire the spatial distribution of the subject information from the completion of the reception of the photoacoustic wave. . In particular, when reconstructing a large amount of three-dimensional volume data, it takes a lot of time to acquire the spatial distribution of the subject information from the wave number component.

(Comparative Example 2)
FIG. 1B shows the measurement sequence from the first time to the n-th time in Comparative Example 2 and the sequence of each process. In the second comparative example, after the reception of the photoacoustic waves at all measurement positions is completed, the conversion process from the time-series received signal to the wave number component and the conversion process from the wave number component to the spatial distribution of the subject information are performed. Think. As can be understood from FIG. 1B, in the comparative example 2, after the reception of the photoacoustic wave at all the measurement positions is completed, the conversion process from the time-series received signal for the n times of light irradiation to the wave number component is performed. Therefore, it takes a lot of time from the completion of reception of photoacoustic waves to acquisition of object information.

  In both cases of Comparative Example 1 and Comparative Example 2, it may take a long time from the completion of reception of photoacoustic waves at all measurement positions until the spatial distribution of subject information is acquired. Therefore, when the spatial distribution of the subject information is used for the diagnostic image, it takes a redundant time from the completion of the measurement to the presentation of the diagnostic image, which may cause inconvenience in diagnosis.

  In Comparative Example 1 and Comparative Example 2, it is possible to perform parallel processing using pipeline processing to convert a time-series received signal into a wave number component or to acquire a spatial distribution of subject information from the wave number component. However, in this case, since the parallel processing is performed, the apparatus scale of the processing unit becomes large.

(First embodiment)
As a result of earnestly examining the above problems, the present inventor has been able to reduce the time required from acquisition of the photoacoustic wave to acquisition of the spatial distribution of the subject information while suppressing the apparatus scale of the processing unit. Inspired by the device. Hereinafter, the photoacoustic apparatus according to the present embodiment will be described with reference to FIG. FIG. 1C shows a measurement sequence from the first time to the n-th time and a sequence of each process in the present embodiment.

  If the number of volume data when converting the wave number component to the spatial distribution of the subject information is the same, the time required for the inverse Fourier transform is almost the same. That is, even when the spatial distribution of the same region is obtained from different wave number components, the time required for the inverse Fourier transform does not change substantially. On the other hand, the time required for the process of converting the time series received signal into the wave number component increases as the data amount of the time series received signal increases.

  Therefore, based on the above knowledge, the present inventor converts the received signal data of the photoacoustic wave from the received signal data to the first wave number component before receiving the photoacoustic wave at all measurement positions. Inspired to start. For example, in FIG. 1C, the time-series received signal obtained by the first measurement is converted into a wave number component (K1) before the reception of the nth photoacoustic wave is completed.

  Further, the present inventor has conceived of converting received signal data obtained at the remaining measurement positions into a second wave number component. In FIG. 1C, the time-series received signals obtained by other measurements are similarly converted into wave number components before the completion of the n-th photoacoustic wave reception (K1 to Kn−). 1).

  The inventor has also conceived of synthesizing the first wave number component and the second wave number component and converting the synthesized third wave number component into a spatial distribution of the subject information. In FIG. 1C, after the reception of the nth photoacoustic wave is completed, the time-series received signal obtained by the nth measurement is converted into a wave number component (Kn). Subsequently, after the wave number components obtained by the 1st to n-th measurements are synthesized, a process of converting the synthesized wave number components into a spatial distribution of the subject information is performed (IF).

  That is, after the n-th measurement, a conversion process (Kn) from a time-series received signal for one measurement to a wave number component and a conversion process (IF) from the wave number component to a spatial distribution of subject information are performed. Only. After the reception of the photoacoustic waves at all measurement positions is completed, the subject information can be acquired simply by performing these two processes.

  1 that the time required to acquire the spatial distribution of the subject information from the completion of reception of photoacoustic waves at all measurement positions is reduced according to the present embodiment as compared with the comparative example. Is done.

  In the present embodiment shown in FIG. 1C, a time-series received signal obtained for each light irradiation is converted into a wave number component.

<Configuration of photoacoustic apparatus>
FIG. 2 is a schematic diagram of a photoacoustic apparatus according to an embodiment of the present invention. Hereinafter, each component of the apparatus will be described. Note that the photoacoustic apparatus according to the present embodiment is a photoacoustic imaging apparatus using a photoacoustic effect.

  The photoacoustic apparatus according to the present embodiment includes a light source 110, an optical system 120, a probe 130, a moving unit 140, a processing unit 150, and a display unit 160 in order to acquire subject information of the subject 100.

  FIG. 3 is a schematic diagram showing details of the processing unit 150 and a configuration around the processing unit 150. As illustrated in FIG. 3, the processing unit 150 includes a control unit 151, a general-purpose storage unit 152, a wave number component calculation unit 153, a wave number component storage unit 154, and an inverse Fourier transform unit 155. Note that the wave number component storage unit 154 and the general-purpose storage unit 152 are made independent in order to facilitate understanding of the configuration and effects of the present invention, but the wave number component storage unit 154 may be part of the general-purpose storage unit 152.

  The control unit 151 controls the operation of each component constituting the photoacoustic apparatus via the bus 200. In addition, the control unit 151 reads a program in which a later-described subject information acquisition method stored in the general-purpose storage unit 152 is described, and causes the photoacoustic apparatus to execute the subject information acquisition method.

  In addition to storing a program in which the object information acquisition method is described, the general-purpose storage unit 152 temporarily stores input / output data from each unit when performing an imaging operation of the entire apparatus, and enables data exchange between the units. . However, each unit may have a data storage unit for performing each process independently of the general-purpose storage unit 152.

  First, light generated from the light source 110 is irradiated to the subject 100 as pulsed light 121 through the optical system 120. Then, a photoacoustic wave is generated in the subject 100 due to the photoacoustic effect. Subsequently, the propagated photoacoustic wave is received by the probe 130 to acquire a time-series electrical signal, which is stored in the general-purpose storage unit 152 and used as reception signal data.

  Further, the above process is performed by changing the position of the probe 130 by the moving unit 140, and reception signal data is generated at a plurality of measurement positions. Here, the measurement position refers to a position where the probe 130 is positioned when the subject 100 is irradiated with the pulsed light 121. Further, the positions where the probe 130 is positioned at each timing when the subject 100 is irradiated with the pulsed light 121 at a plurality of timings are collectively referred to as “a plurality of measurement positions”.

  Further, the processing unit 150 acquires the spatial distribution of the subject information in the subject 100 by the Fourier transform method based on the time-series received signal output from the probe 130. That is, the processing unit 150 converts the time-series received signal into a wave number component related to the spatial wave number and the angular frequency. Subsequently, the processing unit 150 converts the converted wave number component into an initial sound pressure distribution as a spatial distribution of the subject information. Note that the processing unit 150 performs light amount distribution correction in the subject 100 on the converted initial sound pressure distribution and the like, and a space for subject information such as a light absorption coefficient distribution and a substance concentration distribution in the subject 100. Distribution can be obtained.

  Hereafter, the detail of each structure of the photoacoustic apparatus which concerns on this embodiment is demonstrated.

(Subject 100)
These do not constitute a part of the photoacoustic apparatus of the present invention, but will be described below. The main purpose of the photoacoustic apparatus of the present invention is to diagnose a human or animal malignant tumor or vascular disease, or to observe the course of chemotherapy. Therefore, the subject is assumed to be a living body, specifically, a target site for diagnosis such as the breast, neck and abdomen of a human body or animal.

  The light absorber inside the subject is assumed to have a relatively high light absorption coefficient inside the subject. For example, if the human body is an object to be measured, oxyhemoglobin, deoxyhemoglobin, a blood vessel containing many of them, or a malignant tumor containing many new blood vessels becomes a light absorber. In addition, plaques on the carotid artery wall are also targeted.

(Light source 110)
The light source 110 is preferably a pulse light source capable of generating pulsed light on the order of several nanoseconds to several microseconds. Specifically, in order to efficiently generate a photoacoustic wave, the light source 110 is preferably capable of generating light having a pulse width of about 10 nanoseconds. As the wavelength of light that can be emitted from the light source 110, it is desirable to use a wavelength at which the light propagates to the inside of the subject. Specifically, when the subject is a living body, a suitable wavelength is 500 nm or more and 1200 nm or less. However, when obtaining the optical characteristic value distribution of the living tissue relatively near the surface of the living body, it is also possible to use a wavelength region having a wider range than the above wavelength region, for example, a wavelength region of 400 nm to 1600 nm.

  Further, a laser or a light emitting diode can be used as the light source. As the laser, various lasers such as a solid laser, a gas laser, a dye laser, and a semiconductor laser can be used. For example, the laser used in the present embodiment includes an alexandrite laser, a Yttrium-Aluminium-Garnet laser, a Titan-Sapphire laser, and the like.

  The light source 110 may be provided separately from the photoacoustic apparatus. Moreover, the light source 110 may be comprised from a single light source, and may be comprised from several light source.

(Optical system 120)
The light emitted from the light source 110 is typically molded into a desired light distribution shape and guided to the subject 100 by the optical system 120 including optical components such as lenses and mirrors. In addition, it is also possible to propagate using an optical waveguide such as an optical fiber. Optical components include, for example, mirrors that reflect light, lenses that condense and enlarge light, and change shapes, prisms that disperse, refract, and reflect light, optical fibers that propagate light, and diffuse that diffuse light Such as a board. Any optical component may be used as long as it can irradiate the subject with light emitted from the light source 110 in a desired shape.

  Note that the optical system 120 does not need to be used when the light emitted from the light source 110 can be irradiated onto the subject as desired light.

(Probe 130)
The probe 130 includes a transducer 131 that is an element capable of detecting an acoustic wave, and a support body 132 that supports the transducer. The support body 132 in this embodiment is hemispherical. In the measurement, as shown in FIG. 2, the subject 100 is placed inside the probe 130 to receive a photoacoustic wave.

  The transducer 131 receives a photoacoustic wave and converts it into an electrical signal. The transducer 131 may be anything as long as it can receive photoacoustic waves, such as one using a piezoelectric phenomenon, light resonance, change in capacitance, or the like.

  Since the frequency component constituting the photoacoustic wave is typically 100 KHz to 100 MHz, it is preferable to employ a transducer 131 that can detect these frequencies.

  The support 132 is preferably configured using a metal material having high mechanical strength.

  The probe 130 preferably includes a plurality of transducers 131. As a result, photoacoustic waves generated by a single light irradiation can be acquired at a plurality of positions, so that the amount of information used for imaging increases and the image quality can be improved. FIG. 4 is a view of the probe 130 as viewed from the z-axis direction of FIG. 2, and shows an arrangement example of a plurality of transducers 131. The transducers may be arranged in a spiral shape as shown in FIG. 4A, or the transducers may be arranged on concentric circles as shown in FIG. 4B. In order to keep the image quality spatially uniform, it is preferable that the transducers are arranged uniformly on the spherical surface. Such an arrangement is known to be spiral, and is preferably arranged as shown in FIG.

  Generally, a transducer has the highest receiving sensitivity in the normal direction of its receiving surface (surface). An area (hereinafter, referred to as a directivity axis) of the plurality of transducers 131 along the direction with the highest reception sensitivity is collected near the center of curvature of the hemispherical shape so that it can be visualized in the vicinity of the center of curvature with high accuracy ( High sensitivity region) is formed.

  FIG. 4 is an example of transducer arrangement, and the arrangement is not limited to this. Any transducer arrangement may be used as long as the directional axes are gathered in a predetermined region and a predetermined high-sensitivity region can be formed. That is, a plurality of transducers 131 may be arranged along a curved surface shape so as to form a predetermined high-sensitivity region. Further, in this specification, the curved surface includes a spherical surface having an opening such as a true spherical shape or a hemispherical surface. Further, it includes a surface with irregularities on the surface that can be regarded as a spherical surface, and a surface on an ellipsoid that can be regarded as a spherical surface (a shape in which the ellipse is expanded to three dimensions, and the surface is a quadric surface).

  Further, when the plurality of transducers 131 are arranged along the support 132 having a shape obtained by cutting the sphere in an arbitrary cross section, the directional axis is most concentrated at the center of curvature of the shape of the support. The hemispherical support 132 described in the present embodiment is also an example of a support having a shape obtained by cutting a sphere in an arbitrary cross section. In this specification, a shape obtained by cutting a sphere in an arbitrary cross section is called a shape based on a sphere. In addition, the plurality of transducers supported by the support body having a shape based on the sphere is supported on the spherical surface.

  Note that the support 132 may support a plurality of transducers 131 on a plane, as will be described in a third embodiment described later.

  The space between the probe 130 and the subject 100 is filled with a medium capable of propagating photoacoustic waves. It is preferable that this medium can transmit the photoacoustic wave, and at the same time, the acoustic characteristics are matched at the interface with the subject 100 and the transducer 131, and the transmittance of the photoacoustic wave is as high as possible. Further, a holding member that holds the subject 100 may be provided in a space between the probe 130 and the subject 100. The material of the holding member is preferably a material having high acoustic matching with the subject 100 and the above-described medium.

(Moving unit 140)
The moving unit 140 moves the probe 130 and the optical system 120 relative to the subject 100. The moving unit 140 includes a driving unit such as a motor and mechanical parts that transmit the driving force. The moving unit 140 moves the light irradiation position and the photoacoustic wave receiving position by moving the probe 130 relative to the subject 100 in accordance with a control signal from the control unit 151. Obtaining received signal data for obtaining a wide range of target object information by repeatedly obtaining received signal data while moving the light irradiation position and the photoacoustic wave receiving position with respect to the subject 100 Can do. That is, since photoacoustic waves can be received in more angular directions, the amount of information for acquiring subject information increases, and the accuracy of subject information can be improved. In particular, when imaging subject information, resolution, contrast, and the like can be improved.

  In addition, the moving unit 140 can output position information of the probe 130 to the processing unit 150 at the time of light irradiation, that is, at the time of receiving a photoacoustic wave, in synchronization with one-time light irradiation control by the optical system 120. it can.

  FIG. 5 is a view of the subject 100 and the probe 130 viewed from the z-axis direction of FIG. 2, and shows an example of movement of the probe 130. Examples of the movement of the probe 130 include movement along a spiral trajectory 410 as shown in FIG. 5A, movement along a circular trajectory 420 as shown in FIG. 5B, and FIG. The movement along a straight track as shown in FIG. FIG. 5 is an example of movement and is not limited to this. In addition to the movement in the xy plane, the range of the attention area may be expanded by moving in the z-axis direction.

(Processing unit 150)
As illustrated in FIG. 3, the processing unit 150 includes a control unit 151, a general-purpose storage unit 152, a wave number component calculation unit 153, a wave number component storage unit 154, and an inverse Fourier transform unit 155.

  The control unit 151 is typically composed of an element such as a CPU.

  The general-purpose storage unit 152 and the wave number component storage unit 154 are typically configured from a storage medium such as a ROM, a RAM, and a hard disk. Note that the general-purpose storage unit 152 is not limited to a single storage medium, and may be configured from a plurality of storage media.

  The calculation unit 156 including the wave number component calculation unit 153, the wave number component storage unit 154, and the inverse Fourier transform unit 155 is typically configured by elements such as a CPU, GPU, A / D converter, and circuits such as an FPGA and an ASIC. Is done. In addition to a single element or circuit, it may be composed of a plurality of elements or circuits. In addition, any element or circuit may execute each process performed in the subject information acquisition method. Devices that execute each process are collectively referred to as a calculation unit according to the present embodiment.

  Further, the processing unit 150 is preferably configured to be able to pipeline process a plurality of signals at the same time. As a result, it is possible to shorten the time until the object information is acquired.

  Each process performed by the subject information acquisition method can be stored in the general-purpose storage unit 152 as a program to be executed by the calculation unit 156. However, the general-purpose storage unit 152 in which the program is stored is a non-temporary recording medium.

  The processing unit 150 and the plurality of transducers 131 may be provided in a configuration housed in a common housing. However, a part of the processing may be performed by the processing unit housed in the housing, and the remaining processing may be performed by the processing unit provided outside the housing. In this case, the processing units provided inside and outside the housing can be collectively referred to as the processing unit according to the present embodiment.

(Display unit 160)
The display unit 160 serving as a display unit is a device that displays subject information output from the processing unit 150. The display unit 160 is typically a liquid crystal display or the like, but may be another type of display such as a plasma display, an organic EL display, or an FED.

<Subject information acquisition method>
Next, each step of the subject information acquisition method according to the present embodiment will be described with reference to the flowchart of FIG. In addition, each process is performed when the control part 151 controls the action | operation of each structure of a photoacoustic apparatus.

(S100: Step of irradiating the subject with light)
The light generated by the light source 110 is applied to the subject 100 as pulsed light 121 through the optical system 120. Then, the pulsed light 121 is absorbed inside the subject 100, and a photoacoustic wave is generated by the photoacoustic effect.

(S200: Step of receiving photoacoustic wave)
In this step, the probe 130 detects a photoacoustic wave, and each transducer 131 outputs a time-series received signal p (r _j , t). r _j is a position vector of the j-th transducer 131 used for imaging, and t is time. In this embodiment, the light emission timing is set to t = 0.

(S300: Step of storing the received signal)
In this step, the time-series received signal p (r _j , t) output from each transducer 131 is stored in the general-purpose storage unit 152.

(S400: Step of moving the measurement position)
In this step, the probe 130 and the optical system 120 are moved to the next measurement position. Steps S100 to S300 are performed at the next measurement position, and a time-series received signal is obtained at each measurement position. When the measurement is finished at all positions, the movement is finished.

  In this embodiment, in addition to S100 to S300, S500 described later is also executed at each measurement position.

(S500: Step of acquiring wave number component)
In this step, the wave number component for reconstructing the initial sound pressure distribution, which is the subject information of the region of interest, is calculated using the time-series received signal obtained in S300. The details of the wave number component calculation will be described below.

According to Non-Patent Document 2, the equation for obtaining the wave number component p ^ (k) of the initial sound pressure distribution, which is subject information of the region of interest, from the received signal p (r _S , t) detected by the spherical transducer is: It is represented by Formula (1).

k [rad / m] is the spatial wave number, ω is the angular frequency [rad / s], c [m / s] is the speed of sound in the subject, and Rs is the radius of the spherical surface. F ₁ represents a one-dimensional Fourier transform with respect to time t [s], and Re {·} represents taking a real part. r _S is a position vector on the spherical surface.

  In actual calculation, Formula (1) can be discretized and Formula (2) corresponding to a plurality of measurements as described later can be used.

  In equation (2), n is the number of transducers 131, j is the number of the transducer 131 used for imaging (j = 0,..., N−1), N is the total number of measurements, and l (l = 0,. .., N-1) indicates a measurement number.

Furthermore, from r _j ^l = (x _j ^l , y _j ^l , z _j ^l ) and k = (k _x , k _y , k _z ), Expression (2) is expressed by Expression (3).

  In the present embodiment, this step is executed for each light irradiation. That is, the wave number component calculation unit 153 converts the time-series received signal obtained for each measurement position into a wave number component according to Expression (4), and stores the wave number component in the wave number component storage unit 154.

That is, the wave number component corresponding to each measurement position represented by the equation (4) calculated by the wave number component calculation unit 153 is stored in the wave number component storage unit 154. At this time, if the wave numbers (k _x , k _y , k _z , ω) of the wave number components obtained at each measurement position match, they can be combined and stored in a common coordinate area of the wave number component storage unit 154. it can. For example, the wave number component calculation unit 153 can add or average the wave number components obtained at each measurement position and store them. A weight may be applied when combining wave number components. For example, when the SN of the wave number component differs depending on the measurement position, the SN of the subject information can be improved by applying a large weight to the wave number component having a high SN. As described above, the wave number component calculation unit 153 combines the wave number components obtained for each measurement position at different timings, and stores them in the wave number component storage unit 154.

  In addition, it is preferable to complete this process between light irradiation timings. That is, it is preferable that the wave number component calculation unit 153 completes the calculation according to the equation (4) while the probe 130 and the optical system 120 are moved to the next measurement position.

In the calculation of Expression (4), the calculation may be performed only for ω necessary for calculating p _j ^ (k _x , k _y , k _z ) of Expression (4). In general, ω where ω = c | k | needs to be interpolated from discrete ω. Therefore, it is preferable to calculate only ω necessary for interpolation. By limiting the calculation to the required ω, the calculation can be performed at a higher speed.

(S600: Step of acquiring subject information)
In this step, the inverse Fourier transform unit 155 performs inverse Fourier transform on the wave number component p ^ (k) obtained by synthesizing the wave number components for all measurements, and obtains subject information on the region of interest. The inverse Fourier transform from the wave number component to the spatial distribution of the subject information is expressed by Expression (5).

r represents a position vector in the region of interest, and p (r) | _{t = 0} represents the sound pressure distribution of the region of interest at time t = 0, that is, the initial sound pressure distribution. F ₃ ^-1 indicates a three-dimensional inverse Fourier transform. In this embodiment, three-dimensional inverse Fourier transform is used to calculate a three-dimensional initial sound pressure distribution. However, it is preferable to use inverse Fourier transform according to the dimension of necessary subject information.

(S700: Step of displaying subject information)
In this step, the initial sound pressure distribution of the attention area acquired in S600 is displayed on the display unit 160. For example, the processing unit 150 may generate image data by performing processing for displaying the initial sound pressure distribution of the attention area on the display unit 160 such as luminance value conversion, and output the image data to the display unit 160.

  Note that S600 and 700 may be performed during the measurement. Thus, it is possible to display object information obtained from a part of data using a wave number component in the middle of measurement. In this case, since only a part of the received signal is used, the displayed information is simple information and an image as compared with the case where the received signal obtained by all measurements is used. However, it is useful for quickly making a provisional diagnosis of a region of interest or for confirming whether the measurement has been performed correctly during the measurement.

  In the present embodiment, the case where the processing unit 150 acquires the initial sound pressure distribution as the spatial distribution of the subject information has been described. However, other information related to the light absorption coefficient inside the subject is acquired, and the display unit 160 May be displayed. For example, the processing unit 150 can acquire the light absorption coefficient distribution based on Expression (7).

In formula (6), μ _a (r) represents the light absorption coefficient distribution in the subject, and φ (r) represents the light fluence distribution in the subject caused by the light irradiated from the optical system 120. Γ is an amount called a Gruneisen coefficient, which is a product of the product of the volume expansion coefficient and the square of the speed of sound divided by a constant pressure specific heat, and is known to take a substantially constant default value in living bodies. The light absorption coefficient distribution μ _a (r) can be acquired by dividing the initial sound pressure distribution p (r) | _{t = 0} acquired in S700 by the light fluence distribution φ (r) and the Gruneisen coefficient.

  Further, the processing unit 150 may acquire subject information for a plurality of wavelengths and display it on the display unit 160. Further, the processing unit 150 may acquire the concentration of the substance in the subject using the subject information corresponding to a plurality of wavelengths, and display it on the display unit 160 as the subject information. For example, the processing unit 150 can acquire light absorption coefficient distributions corresponding to a plurality of wavelengths, and can acquire oxygen saturation as a substance concentration from these light absorption coefficient distributions.

  As described above, in this embodiment, the conversion processing from the time-series received signal to the wave number component is performed in parallel with the measurement, and after the measurement at all measurement positions is completed, the wave number component is converted into the spatial distribution of the subject information. And convert. Thereby, it is possible to shorten the time required from the completion of the measurement to acquiring the spatial distribution of the subject information while suppressing the apparatus scale of the processing unit. In particular, by calculating the wave number component for each light irradiation, the processing that is left after the measurement is completed is limited. Therefore, the time required to acquire the spatial distribution of the subject information after the measurement can be greatly shortened.

(Second embodiment)
In the present embodiment, an example will be described in which, when measurement for a certain dimension of a time-series received signal is completed, the time-series received signal is converted into a wave number component related to that dimension. In addition, the same code | symbol is attached | subjected to the component same as 1st embodiment in principle, and description is abbreviate | omitted.

  In the first embodiment, since a time-series received signal obtained at one measurement position is converted into a wave number component for each light irradiation, there is a case where sufficient information cannot be converted into a wave number component. In this case, since the quantitativeness of the converted wavenumber component is low, the quantitativeness of the spatial distribution of the subject information obtained from such a wavenumber component is also low.

  Therefore, the present inventor stores the time-series received signal obtained at each measurement position, and selectively converts the time-series received signal from the time-series received signal to the wave number component for the dimension in which the measurement range measurement is completed. I was inspired by that. Here, the dimension of the time-series received signal is the photoacoustic wave reception position coordinate, that is, the transducer position coordinate (for example, x, y, z in the orthogonal coordinate system) and the photoacoustic wave reception timing, that is, the time-series reception signal. This is the reception time t of the received signal. In addition, the measurement range is a movement width when performing measurement if it is a dimension of position coordinates, and a sampling time width if it is a dimension of reception time.

  In this embodiment, among the dimensions (position, time) of the time-series received signal, the dimension for sequentially calculating the wave number component is limited to the dimension for which the generation of the received signal in the measurement range has been completed. Information accuracy and image quality can be improved.

  In general, the wave number resolution ΔK is determined by equation (7).

  ΔX is the sampling interval of the variable X indicating a certain dimension, and S is the number of samplings of that dimension. For example, when X is time t, ΔX = Δt is the sampling time interval, and ΔK = Δω is the angular frequency resolution. When X is position x, ΔX = Δx is the sampling distance interval, and ΔK = Δk is the spatial wavenumber resolution. From equation (7), it is understood that the resolution of the wave number is lowered when only a part of the points S ′ (<S) is used without using the total number of points S in the measurement range. In the present embodiment, the wave number component is calculated after the generation of the reception signal in the measurement range for each dimension is completed, so that high wave number resolution is achieved using the total number S, and the accuracy and image quality of the subject information are improved. be able to.

<Subject information acquisition method>
Hereinafter, step S510 in the flow of the subject information acquisition method according to the present embodiment illustrated in FIG. 7 will be described in detail. In the present embodiment, the wave number component calculation unit 153 sequentially calculates the wave number component related to the dimension for which the generation of the reception signal in the measurement range is completed before all the measurements are completed in S510.

(S510: Step of acquiring wave number component)
With respect to the dimension of time t in one measurement at a certain measurement position, generation of the reception signal in the measurement range is completed. Therefore, the wave number component calculation unit 153 sequentially calculates the wave number component regarding the angular frequency ω corresponding to the part of the equation (8) in the equation (3), that is, the dimension of the time t, for each measurement position.

Further, in the calculation of Expression (8), calculation may be performed only for ω necessary for calculating p _j ^ (k _x , k _y , k _z ) of Expression (8) as in the first embodiment. .

  If the probe is moved only on the xy plane in FIG. 5 and not moved in the z direction, the generation of the reception signal in the measurement range in the z direction is completed by one measurement at a certain measurement position. That is, when the probe 130 is moved two-dimensionally, measurement in the direction orthogonal to the moving direction is completed at each light irradiation timing. In this case, the wave number component calculation unit 153 can calculate the wave number component in the z direction by applying Expression (9) to Expression (8) at each light irradiation timing.

Further, for example, in FIGS. 5A and 5B, the generation of reception signals in the measurement range X in the x direction and the measurement range Y in the y direction is completed when all measurements are completed. In this case, the wave number component calculation unit 153 calculates p _j ^ (x _j ^l , y _j ^l , k _z , ω) of the equation (9) stored in the wave number component storage unit 154 when all the measurements are completed. By applying to (10), the wave number component p ^ (k _x , k _y , k _z ) is calculated.

Thus, the calculation of Expression (3) is completed, and the wave number components p ^ (k _x , k _y , k _z ) can be obtained. According to this method, conversion to a spatial wave number in the z direction and conversion to an angular frequency component are sequentially performed until all measurements are completed, so the time from the completion of measurement to the acquisition of the spatial distribution of the subject information Can be shortened. Furthermore, for each dimension of (x, y, z, t), since conversion to wave number components is performed using a large amount of information after the measurement of the measurement range is completed, the quantification of each wave number component is performed. Is expensive. Therefore, the quantitativeness of the spatial distribution of the subject information obtained using this wave number component is also improved.

Further, in the case of FIG. 5C, the generation of the received signal in the measurement range X in the x direction is completed with a part of the measurements before performing all measurements as indicated by the horizontal arrow in FIG. To do. In this case, p _j ^ (x _j ^l , y _j ^l , k _z , ω) of Expression (8) stored in the wave number component storage unit 154 is read out when the measurement in the x direction at each y coordinate is completed. . Then, the wave number component calculation unit 153 applies Expression (11) to p _j ^ (x _j ^l , y _j ^l , k _z , ω) of the read Expression (9), and sequentially determines the wave number related to k _x. Calculate the components.

Here, q and r are numbers indicating the x-direction movement position and the y-direction movement position, respectively. A total of N = Q × R times is measured Q times in the x direction and R times in the y direction. The calculated wave number component p _j ^ (k _x , y _j ^r , k _z , ω) is stored in the wave number component storage unit 154.

After the completion of all measurements, the wave number component calculation unit 153 reads the wave number component of Equation (11) from the wave number component storage unit 154 and applies Equation (12), and p _j ^ (k _x , k _y , k _z ) Get.

  The wave number component calculation unit 153 may acquire the spatial wave number in the y direction at each x coordinate when the measurement of each x coordinate is completed in parallel with the movement of the probe 130 in the last x direction. Good.

The wave number component calculation unit 153 applies the equation (13) to the wave number component of the equation (12), completes the calculation of the equation (3), and obtains the wave number components p ^ (k _x , k _y , k _z ).

  In FIG. 5C, conversion to a spatial wave number in the x direction, conversion to a spatial wave number in the z direction, and conversion to an angular frequency are sequentially performed before all measurements are completed. For this reason, it is possible to shorten the time from the completion of the measurement until the acquisition of the spatial distribution of the subject information. Further, as shown in FIG. 5C, it is preferable to move the probe so that the wave number component related to one dimension can be obtained by calculating the wave number component related to one dimension when all measurements are completed. That is, this makes it possible to shorten the time from the completion of measurement until the acquisition of the spatial distribution of the subject information. Furthermore, for each dimension of (x, y, z, t), since conversion to wave number components is performed using a large amount of information after the measurement of the measurement range is completed, the quantification of each wave number component is performed. Is expensive. Therefore, the quantitativeness of the spatial distribution of the subject information obtained using this wave number component is also improved.

  As described above, in this embodiment, before all measurements are completed, the time-series received signal is converted into a wave number component for the dimension for which the generation of the received signal in the measurement range is completed. Thereby, it is possible to acquire the spatial distribution of the subject information with high quantitativeness while suppressing the apparatus scale of the processing unit and shortening the time from the completion of the measurement to the acquisition of the spatial distribution of the subject information.

(Third embodiment)
In this embodiment, a photoacoustic apparatus having a probe in which a transducer for receiving a photoacoustic wave is arranged on a plane will be described. In addition, the same code | symbol is attached | subjected to the component similar to 1st embodiment in principle, and description is abbreviate | omitted.

<Configuration of photoacoustic apparatus>
FIG. 8 is a schematic diagram of a photoacoustic apparatus according to an embodiment of the present invention. Hereinafter, each component of the apparatus will be described. Note that the photoacoustic apparatus according to the present embodiment is a photoacoustic imaging apparatus using a photoacoustic effect.

  In the probe 730 in this embodiment, the support body 732 supports the plurality of transducers 731 on a plane. For example, the probe 730 can be a two-dimensional array shown in FIG. 9A or a one-dimensional array shown in FIG. The probe 730 is preferably a two-dimensional array in order to receive photoacoustic waves at more points. However, the probe 730 can also be used as a one-dimensional array in order to reduce electrical signal transmission lines and reduce hardware load. Good.

  Between the probe 730 and the subject 100, a medium capable of propagating photoacoustic waves and a holding member for holding the subject can be provided. These preferably have high photoacoustic wave transmittance.

  The moving unit 140 moves the probe 730 and the optical system 120 relative to the subject 100. You may have the drive means for a movement, and the separate control part for a movement control further. The transducer 731 generally has the highest reception sensitivity in the front direction. Further, although the pulsed light 121 irradiated from the optical system 120 is scattered and spreads within the subject, the amount of light irradiated in the front direction is high. Since the amplitude of the photoacoustic wave is proportional to the amount of light, if the photoacoustic wave generated in the front direction irradiated with light is received in the front direction with good reception sensitivity of the transducer 731, the SN can be increased. For this reason, it is preferable that the moving unit 140 moves in synchronization so that the probe 730 and the optical system 120 face each other.

  FIG. 10 is a diagram illustrating an example of a method for moving the probe 730. 10A shows a case where the probe 730 of FIG. 9A is scanned in both the x and y directions along the linear trajectory 1000, and FIG. 10B shows the case of FIG. A case where the probe 730 is scanned in the y direction along the linear trajectory 1010 is shown. FIG. 10 is an example of scanning and is not limited to this.

  Note that time-series signals obtained by receiving photoacoustic waves at the same position at different light irradiation timings may be combined. For example, by adding or averaging time-series received signals obtained at the same position, a time-series received signal at that position can be obtained.

  Hereinafter, a calculation example for obtaining the spatial distribution of the subject information from the time-series received signal when the planar array is used will be described. In the present embodiment, as described in the second embodiment, a method for preferentially calculating the wave number component from the dimension in which the generation of the reception signal in the measurement range is completed will be described.

According to Non-Patent Document 1, the wave number of the initial sound pressure distribution, which is subject information in the region of interest, from the received signal p (r _S , t) = p (x, y, t) detected by a planar probe. An expression for obtaining the component p ^ (k) is expressed by Expression (14).

p (x, y, t) is a time-series received signal output from the transducer 731 at the position (x, y) when the probe plane is z = 0. F _xy represents a two-dimensional Fourier transform with respect to xy, and F _t represents a one-dimensional Fourier transform with respect to time. From equation (14), a wave number component p ^ (k _x , k _y , ω) using the angular frequency ω as an argument instead of the wave number component k _{z in} the z direction is calculated from the received signal p (x, y, t). The Next, p ^ (k _x , k _y , ω) is interpolated using the relationship of ω = c | k | to calculate the wave number component p ^ (k _{x, k} y, _{k z)} is calculated.

  In the actual calculation, the wave number component calculation unit 153 calculates the wave number component using Expression (15) obtained by discretizing Expression (14).

  In Expression (15), q represents the number in the x direction of the transducer 731 when the reception signal generation in the measurement range in the x direction is completed. r indicates the number of the transducer 731 in the y direction when the generation of the reception signal in the measurement range in the y direction is completed. q and r are numbers related to the synthesized received signal. As shown in FIGS. 10C and 10D, there are Q transducers 731 in the measurement range in the x direction and R transducers 731 in the measurement range in the y direction. Indicates to do.

In the case of FIG. 10A, when the generation of the combined received signal of each one-dot chain line is completed, the generation of the received signal in the measurement range of the angular frequency ω at time t and the spatial wave number k _x at position x is completed. . Therefore, the wave number component calculation unit 153 sequentially calculates the wave number component related to the angular frequency ω at time t and the spatial wave number k _{x at the} position x in parallel with the measurement. In the case of FIG. 10B, the reception signal generation in the measurement range in the direction of the time t and the position x is completed in one measurement at the measurement position. Therefore, the wave number component calculation unit 153 calculates the wave number component related to the angular frequency ω and the spatial wave number k _{x in the} x direction for each measurement.

  For example, the wave number component calculation unit 153 calculates the wave number component in the x direction according to the equation (16), and stores it in the wave number component storage unit 154.

Similar to the first embodiment, in the calculation of Expression (16), only ω necessary for the calculation of p _j ^ (k _x , k _y , k _z ) of Expression (15) may be calculated.

When all the measurements are completed and the generation of the reception signal is completed for all q in the y direction, the wave number component calculation unit 153 calculates the wave number components related to k _y and k _{z according} to Equation (17), and obtains the final wave number. The component p ^ (k _x , k _y , k _z ) is obtained.

  Even when the planar array probe 730 is used, the wave number component is acquired at each light irradiation timing as in the first embodiment, and the spatial distribution of the subject information is acquired from the synthesized wave number component. You can also.

  As described above, in the third embodiment, the wave number component can be calculated in parallel with the measurement even in the apparatus using the planar probe 730 different from the first or second embodiment. . Thereby, the time from the completion of the measurement to the acquisition of the spatial distribution of the subject information can be shortened. In addition, when calculating the wave number component in parallel with the measurement, the accuracy of the subject information is limited by limiting the dimension of the received signal (position, time) to the dimension for which the generation of the received signal in the measurement range has been completed. And image quality can be improved.

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

100 Subject 110 Light source 130 Probe 150 Processing unit

Claims (14)

A light source that emits light at a first timing and a second timing after the first timing;
The photoacoustic wave generated by irradiating the subject with light at the first timing is received and a first time-series received signal is output, and the light is irradiated to the subject at the second timing. A probe that receives a photoacoustic wave generated by the output and outputs a second time-series received signal;
A processing unit for acquiring a spatial distribution of subject information;
Have
The processor is
Between the first timing and the second timing, start conversion from the first time-series received signal to the first wave number component,
Converting the second time-series received signal into a second wavenumber component;
Combining the first wavenumber component and the second wavenumber component to obtain a third wavenumber component;
A photoacoustic apparatus that acquires a spatial distribution of the subject information based on the third wave number component. The processor is
By adding or averaging components related to the same wave number of the first wave number component and the second wave number component, the first wave number component and the second wave number component are combined to form the third wave number component. The photoacoustic apparatus according to claim 1, wherein: The processing unit completes the conversion from the first time-series received signal to the first wavenumber component between the first timing and the second timing. The photoacoustic apparatus according to 1. A light source that emits light at multiple timings;
A probe that receives photoacoustic waves generated at each timing by irradiating the subject with light at the plurality of timings and outputs reception signals in a time series corresponding to the plurality of timings;
A processing unit for acquiring a spatial distribution of subject information;
Have
The processor is
Before the light irradiation at the plurality of timings is completed, a wave number component related to a part of a plurality of dimensions related to a time-series received signal is obtained,
After the light irradiation at the plurality of timings is completed, by acquiring the wave number component related to the remaining dimensions of the plurality of dimensions, the wave number component related to the plurality of dimensions is acquired,
A photoacoustic apparatus that acquires a spatial distribution of the subject information based on wave number components related to the plurality of dimensions. The processor is
The photoacoustic apparatus according to claim 4, wherein a wave number component related to an angular frequency corresponding to each of the plurality of timings is acquired. A moving unit for moving the probe in two dimensions;
6. The photoacoustic apparatus according to claim 4, wherein the processing unit acquires a wave number component related to a direction orthogonal to a moving direction of the probe corresponding to each of the plurality of timings. After the light irradiation at the plurality of timings is completed, the processing unit acquires the wave number component related to the plurality of dimensions by acquiring the wave number component related to one dimension of the plurality of dimensions, so that the subject and the probe are acquired. The photoacoustic apparatus according to claim 4, further comprising a moving unit that relatively moves the tactile element. The said processing part synthesize | combines the time series received signal obtained by receiving at the same position, and acquires as a time series received signal in the position. The photoacoustic apparatus of description. The photoacoustic apparatus according to claim 1, further comprising a moving unit that relatively moves the subject and the probe. The photoacoustic apparatus according to claim 9, wherein the moving unit moves the probe. The photoacoustic apparatus according to claim 1, wherein the probe includes a plurality of transducers and a support body that supports the plurality of transducers. The photoacoustic apparatus according to claim 11, wherein the support supports the plurality of transducers on a plane. The photoacoustic apparatus according to claim 11, wherein the support supports the plurality of transducers on a spherical surface. The photoacoustic apparatus according to any one of claims 1 to 13, wherein the processing unit acquires three-dimensional volume data as a spatial distribution of the subject information.

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