JP2018187234A - Photoacoustic apparatus and photoacoustic image generation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize a measurement condition to obtain a photoacoustic image, which cannot be optimized by a conventional art of generating a reconstitution image with a cycle of a refresh rate of a display device.SOLUTION: A photoacoustic apparatus according to this invention irradiates a subject with light with a first cycle, averages reception signals obtained by the irradiation, generates reconstitution image data by a frame rate of a second cycle on the basis of an averaged signal, and converts a display rate of an image based on the reconstitution image data generated by the frame rate of the second cycle to a frame rate of a third cycle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photoacoustic apparatus and a method for processing subject information obtained using a photoacoustic effect.

  A photoacoustic apparatus that images the inside of a subject using a photoacoustic effect is known.

  Patent Document 1 describes a photoacoustic imaging apparatus provided with a handheld probe, similarly to an ultrasonic diagnostic apparatus. The photoacoustic imaging apparatus described in Patent Document 1 causes the light-emitting semiconductor element to emit light at a sampling period shorter than the refresh rate period with respect to the refresh rate, which is the number of times the screen is rewritten per unit time. At that time, detection signals obtained by receiving photoacoustic waves emitted from the subject when light enters the subject are added and averaged to generate an image displayed on the display unit. The image displayed on the display unit is an image generated at a cycle equivalent to the refresh rate cycle.

JP-A-2006-47102

  However, in the apparatus described in Patent Document 1, since the cycle of generating an image is limited by the refresh rate, a photoacoustic image such as the light emission cycle of a light source or selection of a signal used for generating an image is acquired. It is considered difficult to change the conditions. If a photoacoustic signal cannot be obtained under appropriate conditions, the S / N ratio of the generated image may be insufficient, or blurring caused by movement of the subject may occur.

  Therefore, an object of the present invention is to improve the degree of freedom for acquiring a photoacoustic image and improve the image quality of the obtained image.

  A photoacoustic apparatus according to an aspect of the present invention includes a light irradiation unit that irradiates a subject with light, and an acoustic that receives an acoustic wave generated from the subject and outputs a reception signal when the light is irradiated. A photoacoustic apparatus comprising: a wave receiving unit; and an image generating unit that generates an image inside the subject based on the received signal, wherein the light irradiating unit applies the light to the subject first. The image generation unit synthesizes a plurality of received signals obtained by the plurality of times of light irradiation, and generates image data at a frame rate of a second period based on the synthesized signals. And a frame rate conversion unit that converts an image display rate based on the image data generated at the frame rate of the second period to a frame rate of the third period.

  According to the present invention, it is possible to improve the degree of freedom for acquiring a photoacoustic image and improve the image quality of the obtained image.

The block diagram of the photoacoustic apparatus which concerns on 1st Embodiment. Schematic diagram of the handheld probe according to the first embodiment 1 is a block diagram showing a computer and a peripheral configuration according to a first embodiment Timing chart for explaining the operation in the first embodiment Timing chart for explaining the operation in the second embodiment Timing chart for explaining the operation in the third embodiment Timing chart for explaining the operation in the fourth embodiment The block diagram which shows the computer and peripheral structure which concern on 5th Embodiment Timing chart for explaining the operation in the fifth embodiment The figure which shows the display screen which displays the measurement conditions of this invention

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described below should be 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 subject information acquisition apparatus or a control method thereof, a subject information acquisition method, or a signal processing method. The present invention can also be understood as a display method for generating and displaying an image indicating characteristic information inside a subject. The present invention can also be understood as a program that causes an information processing apparatus including hardware resources such as a CPU and a memory to execute these methods, and a non-transitory storage medium that stores the program and is readable by a computer.

  The subject information acquisition apparatus of the present invention receives an acoustic wave generated in a subject by irradiating the subject with light (electromagnetic waves), and acquires the subject's characteristic information as image data. Including a photoacoustic imaging apparatus using In this case, the characteristic information is information on characteristic values corresponding to each of a plurality of positions in the subject, generated using a signal derived from the received photoacoustic wave.

  The photoacoustic image data according to the present invention is a concept including all image data derived from photoacoustic waves generated by light irradiation. For example, the photoacoustic image data includes at least one subject such as a sound pressure generated by the photoacoustic wave (initial sound pressure), an absorption energy density, an absorption coefficient, and a concentration of a substance constituting the subject (such as oxygen saturation). It is image data representing the spatial distribution of information. Note that photoacoustic image data indicating spectral information such as the concentration of a substance constituting the subject is obtained based on photoacoustic waves generated by light irradiation with a plurality of different wavelengths. The photoacoustic image data indicating the spectral 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, the photoacoustic image data indicating the spectral information may be a glucose concentration, a collagen concentration, a melanin concentration, or a volume fraction of fat or water.

  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 referred to in the present invention is typically an ultrasonic wave and includes an elastic wave called a sound wave or an acoustic wave. An electric signal converted from an acoustic wave by a transducer 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. The distribution data is also called photoacoustic image data or reconstructed image data.

  In the following embodiments, a photoacoustic apparatus that irradiates a subject with pulsed light, receives a photoacoustic wave from the subject, and generates a blood vessel image (structure image) in the subject as the subject information acquisition device. take up. In the following embodiment, a photoacoustic apparatus having a handheld probe is taken up, but the present invention can also be applied to a photoacoustic apparatus that mechanically scans by providing a probe on a mechanical stage.

<First Embodiment>
(Device configuration)
Hereinafter, the configuration of the photoacoustic apparatus 1 according to the present embodiment will be described with reference to the block diagram of FIG. 1. The photoacoustic apparatus 1 includes a probe 180, a signal collection unit 140, a computer 150, a display unit 160, and an input unit 170. The probe 180 includes a light source unit 200, an optical system 112, a light irradiation unit 113, and an acoustic wave receiving unit 120. The computer 150 includes a calculation unit 151, a storage unit 152, a control unit 153, and a frame rate conversion unit 159.

  The light source unit 200 supplies light pulses to the light irradiation unit 113 via the optical system 112 such as an optical fiber (bundle fiber) in the first period. The light irradiation unit 113 irradiates the subject 100 with the supplied light. Thereby, a photoacoustic wave is generated from the subject 100 in the first period. The acoustic wave receiving unit 120 receives a photoacoustic wave generated from the subject 100 in the first period, and outputs an electrical signal (hereinafter also referred to as a reception signal or a photoacoustic signal) as an analog signal. That is, the acoustic wave receiving unit 120 receives photoacoustic waves at intervals defined by the first period. The signal collecting unit 140 converts the analog signal output from the acoustic wave receiving unit 120 into a digital signal and outputs the digital signal to the computer 150.

  The computer 150 uses the arithmetic unit 151, the storage unit 152, and the control unit 153 to convert the digital signal output from the signal collection unit 140 in the first cycle by the multiple times of light irradiation into the second cycle (hereinafter, referred to as “second cycle”). And is also stored in the storage unit 152 as an electrical signal (photoacoustic signal) derived from a photoacoustic wave. Here, synthesis is not limited to simple addition, but includes weighted addition, addition average, moving average, and the like. In the following, an explanation will be given mainly using the addition average, but a synthesis method other than the addition average may be applied. The computer 150 performs processing such as image reconstruction on the digital signal stored in the storage unit 152, thereby obtaining photoacoustic image data within a period defined by the second period (the period of the imaging frame rate). Generate. In other words, the computer 150 functions as an image generation unit that generates an image inside the subject based on the received signal.

  The computer 150 outputs the generated photoacoustic image data to the frame rate conversion unit 159 according to the second period. The frame rate converter converts the photoacoustic image data generated according to the second period into photoacoustic image data of a third period (hereinafter also referred to as a display frame rate period) suitable for display on the display unit 160. Convert. That is, the computer 150 can also be rephrased as converting the image display rate based on the image data generated in the second cycle to the frame rate of the third cycle. Further, the computer 150 controls the entire photoacoustic apparatus 1 using the control unit 153.

  The display unit 160 displays a photoacoustic image based on the photoacoustic image data of the third period (display frame rate period).

  The computer 150 may perform image processing for display and graphic processing for GUI on the obtained photoacoustic image data as necessary. This process may be performed on the photoacoustic image data generated in the second cycle, or may be performed on the photoacoustic image data generated in the third cycle.

  In the present invention, the embodiments will be described using terms such as a first period, a second period (an imaging frame rate period), and a third period (a display frame rate period). The “cycle” does not have to be “the repetition time is completely constant”. In other words, in the present invention, the term “cycle” is used even when it is repeated at non-constant time intervals. Further, the first cycle includes a case where there is a rest period, as will be described later. In the present invention, a repetition time in a time that does not include a pause period is called a period.

  A user (such as a doctor or engineer) checks the photoacoustic image displayed on the display unit 160. The image displayed on the display unit 160 may be stored in a memory in the computer 150 or a data management system connected to the photoacoustic apparatus via a communication network based on a storage instruction from the user or the computer 150. The input unit 170 receives an instruction from the user.

(Detailed configuration of each block)
Subsequently, a preferable configuration of each block will be described in detail.

(Probe 180)
FIG. 2A is a schematic diagram of the probe 180 according to the present embodiment. The probe 180 includes a light source unit 200, an optical system 112, a light irradiation unit 113, an acoustic wave receiving unit 120, and a housing 181. The housing 181 is a housing that surrounds the light source unit 200, the optical system 112, the light irradiation unit 113, and the acoustic wave receiving unit 120. A user can use the probe 180 as a handheld probe by gripping the housing 181. The light irradiation unit 113 irradiates the subject with the light pulse propagated by the optical system 112. Note that the XYZ axes in the figure indicate coordinate axes when the probe is left stationary, and do not limit the orientation when the probe is used.

  The probe 180 shown in FIG. 2A is connected to the signal collecting unit 140 via the cable 182. The cable 182 includes wiring for supplying power to the light source unit 200, light emission control signal wiring, and wiring for outputting an analog signal output from the acoustic wave receiving unit 120 to the signal collecting unit 140 (not shown). It is good also as a structure which can provide a connector in the cable 182 and can isolate | separate the probe 180 and the other structure of a photoacoustic apparatus. In addition, as shown in FIG. 2B, a semiconductor laser, a light emitting diode, or the like may be used as the light source unit 200, and the subject may be directly irradiated with light pulses without using the optical system 112. In this case, the light emitting portion 113 is a light emitting end portion (housing front end) of a semiconductor laser, LED, or the like.

(Light source unit 200)
The light source unit 200 generates light for irradiating the subject 100. The light source unit 200 is preferably a light source capable of outputting a plurality of wavelengths when generating pulsed light and acquiring a substance concentration such as oxygen saturation. Further, since it is necessary to mount the probe 180 in the housing, it is preferable to use a semiconductor light emitting element such as a semiconductor laser or a light emitting diode as shown in FIG. The output of a plurality of wavelengths can be realized by switching light emission using a plurality of types of semiconductor lasers or light emitting diodes that generate light of different wavelengths.

  The pulse width of the light emitted from the light source unit 200 is, for example, 10 ns or more and 1 μs or less. Further, the wavelength of light is preferably 400 nm or more and 1600 nm or less, but the wavelength may be determined according to the light absorption characteristics of the light absorber to be imaged. When a blood vessel is imaged with high resolution, a wavelength (400 nm or more and 800 nm or less) having a large absorption in the blood vessel may be used. When imaging a deep part of a living body, light having a wavelength (700 nm or more and 1100 nm or less) with less absorption in a background tissue (water, fat, etc.) of the living body may be used. In the present invention, since a semiconductor light emitting element is used as the light source of the light source unit 200, the amount of light is insufficient. That is, the photoacoustic signal obtained by one irradiation does not reach a desired S / N ratio. Therefore, light is emitted in the first period, the photoacoustic signals are added and averaged, the S / N ratio is improved, and the photoacoustic is generated in the second period (the period of the imaging frame rate) based on the added and averaged photoacoustic signal. Calculate the image.

  As an example of the wavelength of the light source unit 200 used in the present embodiment, a wavelength of 797 nm is preferable. That is, it is a wavelength that reaches the deep part of the subject, and is suitable for detecting a blood vessel structure because the absorption coefficients of oxyhemoglobin and deoxyhemoglobin are substantially equal. If a 756 nm light source is used as the second wavelength, the oxygen saturation can be determined using the difference in absorption coefficient between oxyhemoglobin and deoxyhemoglobin.

(Light irradiation unit 113)
The light irradiation unit 113 is an emission end for irradiating the subject with light. As the light irradiation part 113, when a bundle fiber is used as the optical system 112, a terminal part can be used. In addition, when a part of a living body (such as a breast) is used as the subject 100, a diffuser plate that diffuses light may be used in order to irradiate with an expanded beam diameter of pulsed light. When a semiconductor light emitting element is used as the light source unit 200 shown in FIG. 2B, the light emitting end portions (housing front ends) of a plurality of semiconductor light emitting elements are arranged to form the light irradiating unit 113 so that the subject can be measured over a wide range. Can be irradiated.

(Acoustic wave receiving unit 120)
The acoustic wave receiving unit 120 includes a transducer that receives a photoacoustic wave generated with light emission of the first period and outputs an electrical signal, and a support that supports the transducer. For example, a piezoelectric material, a capacitive micro-machined ultrasonic transducer (CMUT), a transducer using a Fabry-Perot interferometer, or the like can be used as a member constituting the transducer. Examples of the piezoelectric material include a piezoelectric ceramic material such as PZT (lead zirconate titanate) and a polymer piezoelectric film material such as PVDF (polyvinylidene fluoride).

  The electrical signal obtained by the transducer in the first period is a time-resolved signal. Therefore, the amplitude of the electric signal represents a value based on the sound pressure received by the transducer at each time (for example, a value proportional to the sound pressure).

  In addition, as a transducer, what can detect the frequency component (typically 100 KHz to 10 MHz) which comprises a photoacoustic wave is preferable. It is also preferable to arrange a plurality of transducers side by side on the support to form a plane or curved surface called a 1D array, 1.5D array, 1.75D array, or 2D array.

  The acoustic wave receiving unit 120 may include an amplifier that amplifies a time-series analog signal output from the transducer. The acoustic wave receiving unit 120 may include an A / D converter that converts a time-series analog signal output from the transducer into a time-series digital signal. That is, the acoustic wave receiving unit 120 may include the signal collecting unit 140.

  In order to improve acoustic accuracy by detecting acoustic waves from various angles, a transducer arrangement that surrounds the subject 100 from the entire circumference is preferable. In addition, when the subject 100 is large enough not to surround the entire periphery, the transducer may be arranged on a hemispherical support. The probe 180 including the acoustic wave receiving unit 120 having such a shape is not a handheld type, but is suitable for a mechanical scanning type photoacoustic apparatus that moves the probe relative to the subject 100. A scanning unit such as an XY stage may be used for moving the probe. The arrangement and number of transducers and the shape of the support are not limited to the above, and may be optimized according to the subject 100.

  In the space between the acoustic wave receiving unit 120 and the subject 100, a medium for propagating photoacoustic waves may be disposed. As a result, the acoustic impedance at the interface between the subject 100 and the transducer is matched. Examples of the medium include water, oil, and ultrasonic gel.

  The photoacoustic apparatus 1 may include a holding member that holds the subject 100 and stabilizes the shape. As the holding member, a material having both high light transmittance and acoustic wave transmittance is preferable. For example, polymethylpentene, polyethylene terephthalate, acrylic, or the like can be used.

  When the apparatus according to the present embodiment generates an ultrasonic image by transmitting and receiving an acoustic wave in addition to the photoacoustic image, the transducer may function as a transmission unit that transmits the acoustic wave. The transducer as the reception means and the transducer as the transmission means may be a single (common) transducer or may have different configurations.

(Signal collection unit 140)
The signal collection unit 140 amplifies an electrical signal that is an analog signal output from the acoustic wave reception unit 120 and is generated along with light emission in the first period, and converts the analog signal output from the amplifier into a digital signal. An A / D converter for conversion. The signal collection unit 140 may be configured by an FPGA (Field Programmable Gate Array) chip or the like.

  The operation of the signal processing unit 140 will be described in more detail. The analog signals output from a plurality of transducers arranged in an array of the acoustic wave receiving unit 120 are amplified by a plurality of amplifiers corresponding to each, and converted into digital signals by a plurality of A / D converters corresponding to each. The The A / D conversion rate is at least twice the bandwidth of the input signal. As described above, if the frequency component constituting the photoacoustic wave is 100 KHz to 10 MHz, the A / D conversion rate is 20 MHz or higher, preferably 40 MHz. The signal collecting unit 140 synchronizes the timing of light irradiation and the timing of signal collection processing by using the light emission control signal. That is, A / D conversion is started at the above-described A / D conversion rate with reference to the light emission time for each first period, and an analog signal is converted into a digital signal. As a result, a digital data string for each time interval (A / D conversion interval) that is 1 / A / D conversion rate from the light emission time can be acquired for each of the plurality of transducers.

  The signal collection unit 140 is also referred to as a data acquisition system (DAS). In this specification, an electric signal is a concept including both an analog signal and a digital signal.

  As described above, the signal collection unit 140 may be disposed inside the housing 181 of the probe 180. With such a configuration, since the information between the probe 180 and the computer 150 is propagated as a digital signal, noise resistance is improved. Further, by using a high-speed digital signal, the number of wires can be reduced and the operability of the probe 180 is improved as compared with the case of transmitting an analog signal.

  In addition, the signal collection unit 140 may perform addition averaging described later. In this case, it is preferable to perform addition averaging using hardware such as FPGA.

(Computer 150)
The computer 150 includes a calculation unit 151, a storage unit 152, a control unit 153, and a frame rate conversion unit 159. The unit responsible for the calculation function as the calculation unit 151 can be configured by a processor such as a CPU or a GPU (Graphics Processing Unit), or an arithmetic circuit such as an FPGA (Field Programmable Gate Array) chip. These units may be composed of a single processor or arithmetic circuit, or may be composed of a plurality of processors or arithmetic circuits.

  The computer 150 synthesizes data having the same time difference with respect to the light emission time of the light source 200 in the digital data sequence output from the signal collection unit 140 for each first period. The computer 150 stores the synthesized digital data string in the storage unit 152 as a synthesized electric signal (photoacoustic signal) derived from the photoacoustic wave for each second period (period of the imaging frame rate). Remember.

  The arithmetic unit 151 then generates photoacoustic image data (structure image and function) by image reconstruction based on the addition average photoacoustic signal stored in the storage unit 152 for each second period (imaging frame rate period). Image) and other various arithmetic processes. The calculation unit 151 may receive input of various parameters such as the sound velocity of the subject and the configuration of the holding unit from the input unit 170 and use them for calculation.

  The reconstruction algorithm used when the calculation unit 151 converts the electrical signal into three-dimensional volume data includes arbitrary algorithms such as a back projection method in the time domain, a back projection method in the Fourier domain, and a model base method (repetitive calculation method). Can be used. As a back projection method in the time domain, there is a universal back-projection (UBP), a filtered back-projection (FBP), or a phasing addition (Delay-and-Sum).

  When the light source unit 200 is configured to be able to switch and emit light of two wavelengths, the calculation unit 151 obtains the first initial sound pressure distribution from the photoacoustic signal derived from the light of the first wavelength by image reconstruction processing. The second initial sound pressure distribution may be generated from the photoacoustic signal derived from the light of the second wavelength. Further, by correcting the first initial sound pressure distribution with the light amount distribution of the light of the first wavelength, the first absorption coefficient distribution is obtained, and the second initial sound pressure distribution is replaced with the light amount distribution of the light of the second wavelength. The second absorption coefficient distribution is obtained by correcting. Furthermore, an oxygen saturation distribution can be obtained from the first and second absorption coefficient distributions. In addition, since it is only necessary to finally obtain the oxygen saturation distribution, the contents and order of the calculations are not limited to this.

  The storage unit 152 includes a volatile memory such as a RAM (Random Access Memory), a non-temporary storage medium such as a ROM (Read only memory), a magnetic disk, and a flash memory. Note that the storage medium storing the program is a non-temporary storage medium. The storage unit 152 includes a plurality of storage media.

  The storage unit 152 is a photoacoustic signal that is added and averaged in the second period (period of the imaging frame rate), photoacoustic image data generated by the arithmetic unit 151, and reconstructed image data based on the photoacoustic image data. Various data can be saved.

  The control unit 153 includes an arithmetic element such as a CPU. The control unit 153 controls the operation of each component of the photoacoustic apparatus. The control unit 153 may control each component of the photoacoustic apparatus in response to instruction signals from various operations such as measurement start from the input unit 170. The control unit 153 reads the program code stored in the storage unit 152 and controls the operation of each component of the photoacoustic apparatus.

  In addition, the control unit 153 performs image adjustment on the display unit 160 and the like. Thereby, an oxygen saturation distribution image is sequentially displayed with the movement of the probe and the photoacoustic measurement.

  The frame rate conversion unit 159 converts the photoacoustic image data (structure image or functional image) generated at the frame rate (imaging frame rate) of the second cycle into an image of the frame rate (display frame rate) of the third cycle. Output to the display unit as a signal. In FIG. 1, the frame rate conversion unit 159 has an independent configuration, but the reconstructed image data is stored in the storage unit 152 at the frame rate (imaging frame rate) of the second period, and the stored reconstructed image data is stored. You may implement | achieve by reading at a 3rd frame rate (display frame rate). In this case, it can be considered that the control unit 153 and the storage unit 152 also function as the frame rate conversion unit 159. In the present invention, even when the frame rate conversion is realized by using the configuration for realizing other functions as described above, the corresponding part is also referred to as a frame rate conversion unit.

  As the frame rate (display frame rate) of the third period, for example, it is preferable to select a frame rate of 50 Hz, 60 Hz, 72 Hz, or 120 Hz that can be input by a general-purpose display. By adopting such a configuration, it is possible to independently select the frame rate (imaging frame rate) of the second period suitable for measurement and the frame rate (display frame rate) of the third period suitable for image display. it can. In other words, the frame rate (imaging frame rate) suitable for the second measurement can be freely selected irrespective of the frame rate (display frame rate) suitable for the image display. In addition, a configuration in which the frame rate (imaging frame rate) of the second period is changed by, for example, a user instruction can be easily realized.

  The display unit 160 rewrites the real screen in synchronization with the frame rate (display frame rate) of the third period input to the display unit 160. In this case, the frame rate (display frame rate) of the third period is the same as the rewrite rate (refresh rate) of the real screen. In recent years, some liquid crystal displays have a function corresponding to input of a plurality of frame rates (frame frequencies). Some of such liquid crystal displays have a built-in frame rate converter that converts an input frame rate into a rewrite rate (refresh rate) of a real screen. In the case of such a configuration having the display unit 160, the display unit 160 further converts the frame rate (display frame rate) of the third period into a rate (refresh rate) for rewriting the real screen. It can be said that the converter is mounted on the display unit 160.

  When using the display unit 160 incorporating such a frame rate converter, the frame rate conversion unit 159 shown in FIG. 1 does not use the configuration of the computer 150, and the frame rate conversion unit 159 displays the display unit 160. It is realizable with the structure which has. In the present invention, the frame rate conversion unit 159 may not be included in the computer 150 but may be included in the display unit 160. In the case where the frame rate conversion unit is included in the display unit 160, there is an advantage that the configuration of the computer 150 can be simplified.

  The computer 150 may be a specially designed workstation. The computer 150 may also be a computer in which a general-purpose PC or workstation is operated according to instructions of a program stored in the storage unit 152. Each configuration of the computer 150 may be configured by different hardware. Further, at least a part of the configuration of the computer 150 may be configured by the same hardware.

  FIG. 3 shows a specific configuration example of the computer 150 according to the present embodiment. A computer 150 according to this embodiment includes a CPU 154, a GPU 155, a RAM 156, a ROM 157, an external storage device 158, and a frame rate conversion unit 159. In addition, a liquid crystal display 161 as a display unit 160, a mouse 171 and a keyboard 172 as input units 170 are connected to the computer 150.

  Further, the computer 150 and the acoustic wave receiving unit 120 may be provided in a configuration housed in a common housing. Alternatively, a part of signal processing may be performed by a computer housed in a housing, and the rest of the signal processing may be performed by a computer provided outside the housing. In this case, the computers provided inside and outside the housing can be collectively referred to as the computer according to the present embodiment. That is, the hardware constituting the computer may not be housed in a single housing. As the computer 150, an information processing apparatus provided in a cloud computing service or the like installed in a remote place may be used.

  The computer 151 corresponds to the processing unit of the present invention. In particular, the function of the processing unit is realized mainly by the calculation unit 151.

(Display unit 160)
The display unit 160 is a display such as a liquid crystal display or an organic EL (Electro Luminescence). This is an apparatus for displaying an image based on subject information obtained by the computer 150, a numerical value at a specific position, and the like. The display unit 160 inputs and displays the reconstructed image data having the frame rate (display frame rate) of the third period described above. The frame rate (display frame rate) of the third period is, for example, a frame rate of 50 Hz, 60 Hz, 72 Hz, or 120 Hz. The display unit 160 may display an image or a GUI for operating the device. Image processing (such as adjustment of luminance values) may be performed on the display unit 160 or the computer 150.

(Input unit 170)
As the input unit 170, an operation console that can be operated by the user and configured with a mouse, a keyboard, a dedicated knob, and the like can be employed. The display unit 160 may be configured with a touch panel, and the display unit 160 may be used as the input unit 170. The input unit 170 receives input from the user such as instructions and numerical values, and transmits them to the computer 150.

  In addition, each structure of a photoacoustic apparatus may be comprised as a respectively different apparatus, and may be comprised as one apparatus united. Moreover, you may comprise as one apparatus with which at least one part structure of the photoacoustic apparatus was united.

  The computer 150 also performs drive control of the configuration included in the photoacoustic apparatus by the control unit 153. The display unit 160 may display a GUI or the like in addition to the image generated by the computer 150. The input unit 170 is configured so that a user can input information. Using the input unit 170, the user can perform operations such as measurement start and end, designation of a frame rate (imaging frame rate) of a second period, and a creation image saving instruction, which will be described later.

(Subject 100)
The subject 100 does not constitute a photoacoustic apparatus, but will be described below. The photoacoustic apparatus according to the present embodiment can be used for the purpose of diagnosing malignant tumors, vascular diseases, etc. of humans and animals, and monitoring the progress of chemical treatment. Therefore, the subject 100 is assumed to be a target site for diagnosis such as a living body, specifically breasts of human bodies or animals, each organ, blood vessel network, head, neck, abdomen, extremities including fingers and toes. The For example, if the human body is a measurement target, oxyhemoglobin or deoxyhemoglobin, a blood vessel containing many of them, or a new blood vessel formed in the vicinity of a tumor may be used as a light absorber. Further, a plaque of the carotid artery wall or the like may be a target of the light absorber. In addition, a dye such as methylene blue (MB) or indocyanine green (ICG), gold fine particles, or a substance introduced from the outside, which is accumulated or chemically modified, may be used as the light absorber. Moreover, it is good also considering the light absorber attached | subjected to the puncture needle and the puncture needle as an observation object. The subject may be an inanimate object such as a phantom or a test object.

(Description of operation)
FIGS. 4A, 4B, and 4C are timing diagrams for easily explaining the operation in the first embodiment of the present invention. 4A, 4B, and 4C, the horizontal axis is the time axis. The first embodiment of the present invention will be described with reference to FIGS. 4 (a), 4 (b), and 4 (c). These controls are performed by the computer 150, the FPGA, or dedicated hardware.

  First, the acquisition of the photoacoustic signal of the photoacoustic apparatus of the present invention and a method for generating a photoacoustic image based on the acquired photoacoustic signal will be described in detail with reference to FIG. FIG. 4A illustrates the case where the frame rate of the second period (imaging frame rate) and the frame rate of the third period (display frame rate) have the same frequency for easy understanding.

  As shown in FIG. 4 (a) T1, in the photoacoustic apparatus, the light source unit 200 emits light with a first period (first period: tw1), and a photoacoustic signal associated with light emission has a first period: tw1. get.

Note that the length of the first cycle: tw1 is preferably set in consideration of the maximum permissible exposure (MPE: Maximum Permissible Exposure) for the skin. This is because the MPE value decreases as the length of the first period tw1 decreases. For example, when the measurement wavelength is 750 nm, the pulse width of the pulsed light is 1 μsec, and the first period tw1 is 0.1 msec, the MPE value for the skin is about 14 J / m ² . On the other hand, when the peak power of the pulsed light emitted from the light emitting unit 113 is 2 kW and the irradiation area from the light emitting unit 113 is 150 mm ² , the light emitted from the light source unit 200 to the subject 100 such as a human body. The energy will be about 13.3 J / m ² . In this case, the light energy irradiated from the light emission part 113 becomes below MPE value. Thus, if the first period tw1 is 0.1 msec or more, it can be guaranteed that it is equal to or less than the MPE value. Thus, it sets in the range which does not exceed MPE value from the 1st period tw1, the peak power of pulsed light, and an irradiation area.

  As shown in FIG. 4 (a) T1 to T3, the light irradiation from the light irradiation unit to the subject is performed eight times in the first period: tw1, and the photoacoustic generated from the subject with each light irradiation. Make a signal ((1) to (8)). The obtained photoacoustic signals are added and averaged, and the added and averaged photoacoustic signal A1 is obtained for each cycle of the imaging frame rate: tw2. As described above, a simple average, a moving average, a weighted average, or the like may be performed instead of the addition average. As an example of specific numerical values, when the time of the first cycle tw1 is 0.1 msec and the imaging frame rate is 60 Hz, the cycle of the imaging frame rate: tw2 is 16.7 msec, which is within the cycle of the imaging frame rate. The average number of additions can be set to 167 times.

  Reconstructed image data R1 is obtained by performing processing for reconstruction based on the photoacoustic signal A1 that has been averaged during the time interval defined by the second period tw2. Here, the reconstructed image data is sequentially calculated by the calculation unit at a cycle of the imaging frame rate tw2.

  Thereafter, the reconstructed image data R1 calculated by the calculation unit is output as an image 1 from the frame rate conversion unit 159 to the display unit according to the third frame rate. As described above, in the example shown in FIG. 4A, the imaging frame rate and the display frame rate are the same frequency. Therefore, the frame rate conversion unit 159 outputs the reconstructed image data R1 obtained at T3 as display image data at a display frame rate period: tw3. Then, the display unit 160 displays the display image data input at the display frame rate cycle: tw3.

  Here, an example of how to set the first period tw1 and the period tw2 of the imaging frame rate will be described. As described above, the first period tw1 is determined from the peak power of the pulsed light and the irradiation area on the subject due to the limitation by the MPE value. The average number of times of addition is determined from the S / N ratio of the photoacoustic signal obtained by one irradiation of the pulsed light and the ratio of the S / N ratio of the photoacoustic signal determined from the image quality requested by the user. For example, if the S / N ratio of the photoacoustic signal obtained by one irradiation of the pulsed light is 1/10 times the S / N of the required photoacoustic signal, the S / N ratio is improved by 10 times. There is a need. Therefore, it is necessary to perform averaging 100 times. For example, if the first cycle tw1 is 0.1 msec, the cycle of the imaging frame rate is 10 msec or more, that is, the imaging frame rate is 100 Hz or less.

  The first period tw1 is also limited by the heat generated by the semiconductor light emitting element. That is, if the thermal resistance of the probe is determined, the temperature is determined from the power consumption of the semiconductor light emitting element. It is necessary to lengthen the first period tw1 so that the temperature of the semiconductor light emitting element does not exceed the allowable temperature.

  On the other hand, if the number of averaging times is increased, the photoacoustic signals are averaged over a long period of time. Therefore, when there is a body motion or the like in the subject, blur due to movement occurs. In order to reduce motion blur, it is advantageous to reduce the average number of additions as much as possible. Specifically, it is preferable to design so that motion blur is suppressed to ½ or less of the required resolution. For example, if the required resolution is 0.2 mm and the body motion of the subject is 5 mm / sec, the number of addition averaging is 200 times or less, that is, the imaging frame rate when the first cycle tw1 is 0.1 msec. The period tw2 is set to 20 msec or less. Considering such a plurality of conditions, the first cycle tw1 and the imaging frame rate cycle tw2 may be determined. Of course, if all conditions cannot be met, priorities are determined and these parameters are determined. Further, the user can input desired conditions such as resolution and S / N ratio via the input unit, and the control unit determines the first period and the second period according to the input conditions. You may comprise a photoacoustic apparatus.

  FIGS. 4B and 4C are timing diagrams of the first embodiment of the present invention when the imaging frame rate and the display frame rate are different frequencies. Based on FIG.4 (b), the detail of the acquisition of the photoacoustic signal of the photoacoustic apparatus which is the 1st Embodiment of this invention, and the method of producing | generating photoacoustic image data based on the acquired photoacoustic signal is demonstrated. explain.

  4 (b) and 4 (c), the operations shown in FIG. 4 (a) and T1 to T3 are the same. That is, from the irradiation of light pulses to the acquisition of reconstructed image data, the operations shown in FIGS. 4B and 4C are the same acquisition conditions (the same measurement conditions) as the operations shown in FIG. Can be done. Therefore, the same reconstructed image data can be obtained under the same measurement conditions regardless of the display frame rate of the display unit.

  FIG. 4B is an example of a display frame rate of 72 Hz, and the display frame rate period tw3 is about 13.8 msec. That is, this is an example in which the cycle of the imaging frame rate that is the second cycle is longer than the cycle of the display frame rate that is the third cycle. On the other hand, FIG. 4 (c) T4 is an example of a display frame rate of 50 Hz, and the display frame rate period tw3 is 20 msec. That is, this is an example in which the cycle of the imaging frame rate that is the second cycle is longer than the cycle of the display frame rate that is the third cycle. As described above, the reconstructed image data acquired under the same measurement conditions is converted from the imaging frame rate (60 Hz) to the display frame rate (72 Hz or 50 Hz) by the frame rate conversion unit 159. Here, the case where the period of the imaging frame rate that is the second period is 20 ms has been described as an example, but the present invention is not limited to this condition. Actually, since the first period needs to be longer than the time determined by the distance from the receiving unit to the object to be observed, in other words, the distance to receive the photoacoustic wave, the first period is from 0.1 A few milliseconds is practical. Further, in order to improve the S / N ratio of the photoacoustic signal, if the photoacoustic signal obtained by irradiation of several tens or more of light pulses is acquired and averaged, the imaging frame rate is preferably set to 240 Hz or less. . Conveniently, the frame rate conversion unit converts the frame rate by synthesizing an image between a plurality of frames, thinning out the frames, or overwriting the frames. If the probe movement is fast and the sense of interference is noticeable, the frame rate conversion unit should perform frame rate conversion such as inter-frame interpolation using a motion vector or the like to generate an interpolated frame. .

In simple frame rate conversion, frame decimation and frame overwriting are performed, so that when the display frame rate cycle tw3 is shorter than the imaging frame rate cycle tw2, reconstructed image data that is not displayed may be generated. Therefore, when only reconstructed image data is displayed, the reconstructed image data may be wasted. Therefore, in such a case, in order to avoid wasteful generation of reconstructed image data,
Imaging frame rate cycle tw2 ≧ display frame rate cycle tw3
Is more desirable.

  In addition, when the cycle of the imaging frame rate is longer than the cycle of the display frame rate, by executing the reconstruction process for a plurality of frames in parallel, the cycle of the imaging frame rate is effectively set to the display frame rate. It can be shorter than the period. In other words, during the period when the reconstruction process relating to the image R1 is being performed, the arithmetic unit starts the reconstruction process relating to the image R2, so that the reconstruction image data for one frame can be acquired within the cycle of the display frame rate. Become.

  On the other hand, there is also a method in which the acquired reconstructed image data is displayed and simultaneously stored in the storage unit 152 and the reconstructed image data sequentially stored in the storage unit 152 is displayed at another time. That is, the reconstructed image data is read from the storage unit 152 at the imaging frame rate period tw2, the frame rate conversion unit 159 performs the frame rate conversion, and the display frame data is output as display data to the display unit 200 at the display frame rate period tw3. The reconstructed image data stored in the unit 152 can be displayed. On the other hand, the reconstructed image data stored sequentially in the storage unit 159 can be read from the storage unit 159 at the display frame rate cycle tw3 and output to the display unit 200 as display data. In the present invention, such processing is also called frame rate conversion. In this case, although the displayed time is extended or shortened (slow motion shooting or high-speed shooting is performed), there is no reconstructed image data that is not displayed as an image. The condition of the period tw3 is not always necessary.

  4A to 4C described above can be switched based on a user instruction or based on a predetermined determination performed by the computer 150. That is, the user can switch the operation mode according to the frequency at which the image is to be refreshed.

  In the apparatus described in Patent Document 1, the timing for obtaining reconstructed image data, that is, the measurement condition is determined by the refresh rate of the display. In contrast, according to the present embodiment, the imaging frame rate and the display frame rate are independent, and the frame rate conversion unit 159 converts the reconstructed image data of the imaging frame rate into the display frame rate. It is a configuration. For this reason, reconstructed image data can be acquired under the same measurement conditions regardless of the display frame rate used. As a result, reconstructed image data can be obtained under the same measurement conditions regardless of the display used, and a plurality of reconstructed image data can be easily compared. Further, since the operation is performed at the same timing except for the display frame rate T4 regardless of the display refresh rate, there is also an advantage that the device configuration of the photoacoustic apparatus is simplified. Moreover, even when only the display is changed, there is an advantage that it can be easily performed without changing the measurement conditions.

<Second Embodiment>
Next, a second embodiment of the present invention will be described.

  In the apparatus described in Patent Literature 1, since reconstructed image data is generated for each cycle of the display refresh rate, it is not easy to change measurement conditions. In the present embodiment, a configuration will be described in which measurement conditions can be changed according to a subject or a region of interest even when a reconstructed image is displayed on a display with a fixed display frame rate.

  The operation of the photoacoustic apparatus according to the second embodiment of the present invention will be described in detail with reference to FIGS. 4 (a), 5 (a) and 5 (b).

  FIG. 5A is a timing chart for illustrating an example of the operation of the present embodiment. The timing chart shown in FIG. 5A is different from the timing chart shown in FIG. 4A in the timing chart shown in T1 to T3. On the other hand, the display frame rate T4 is the same as that in FIG. The operation shown in the timing chart of FIG. 5A is effective for improving the S / N ratio of the reconstructed image. It is also effective when the region of interest is at a relatively deep position in the sensory body.

  As shown at T1 in FIG. 5A, in the photoacoustic apparatus, the light source unit 200 emits light with a first period: tw1, and acquires a photoacoustic signal associated with light emission with a first period: tw1. The first period tw1 is the same as the time shown in FIG. 4 (a) T1. As described above, the length of the first period: tw1 is related to the maximum exposure allowance (MPE) for the skin, and is the same as the time shown in FIG. 4 (a) T1 here. The length of the first cycle: tw1 may be changed within a range not exceeding MPE. In order to further increase the S / N ratio of the reconstructed image, the number of addition averages was increased from 8 times to 10 times in the first embodiment. As shown to Fig.5 (a), a signal collection part acquires a photoacoustic signal 10 times by the 1st period: tw1 ((1)-(10)), and a calculating part obtains the obtained photoacoustic signal. Are added and averaged to obtain a photoacoustic signal A1 that is added and averaged every period tw2. Then, for each period tw2 of the imaging frame rate, the calculation unit calculates reconstructed image data. As a result, the cycle of the imaging frame rate: tw2 is longer than that in the case of FIG. 4A, but the frame rate conversion unit 159 displays the output cycle of the reconstructed image data R1, R2,. Rate cycle: converted to tw3 and output as display image data. Then, the display unit 160 displays the display image data input at the display frame rate cycle: tw3.

  On the other hand, the operation shown in the timing diagram of FIG. 5B is an operation that is effective when the movement of the subject or the movement of the probe is fast. As indicated by T1 in FIG. 5 (b), in this operation, the number of photoacoustic signals to be subjected to addition averaging is reduced from 8 times to 6 times in FIG. 4 (a). By reducing the number of times of addition averaging, the time width for averaging the photoacoustic data (sampling effective time) is shortened, so that motion blur can be reduced compared to the operation shown in FIG.

  In the example shown in FIG. 5B, the signal collection unit acquires the photoacoustic signal six times at the first period: tw1 ((1) to (6)), and the calculation unit obtains the obtained photoacoustic signal. Are added and averaged to obtain a photoacoustic signal A1 that is added and averaged every period tw2. Then, for each period tw2 of the imaging frame rate, the calculation unit calculates reconstructed image data. As a result, the cycle of the imaging frame rate: tw2 is shorter than that in FIG. 4A, but the frame rate conversion unit 159 sets the output cycle of the reconstructed image data R1, R2,. : Convert to tw3 and output as display image data. Then, the display unit 160 displays the display image data input at the display frame rate cycle: tw3. The operation shown in FIG. 5B is more effective in reducing motion blur as compared with FIG.

  Also in the present embodiment, the user may be able to select an operation mode according to whether priority is given to reduction of motion blur or S / N ratio of a photoacoustic image. Further, the computer 150 may automatically determine the operation mode.

  When the computer 150 automatically sets the operation mode, for example, the control unit can detect the movement of the probe with an acceleration sensor or the like provided in the probe and switch the operation mode according to the result. When the movement of the probe is faster than a predetermined threshold value, measurement in the operation mode shown in the timing diagram of FIG. 5B is performed (reducing the number of photoacoustic signals to be added and averaged) in order to reduce motion blur. To do). On the other hand, when the movement of the probe is slower than a predetermined threshold value, measurement in the operation mode shown in the timing diagram of FIG. 5A is executed in order to improve the S / N ratio of the photoacoustic image. (Increase the number of photoacoustic signals to be averaged). Thus, it may be determined automatically by sensing the movement of the probe.

  As another method of automatically switching the operation mode by the computer 150, it is conceivable to use the depth of the attention area. When the depth of the region of interest is deeper than a predetermined threshold, priority is given to the S / N ratio of the photoacoustic image, and the measurement in the operation mode shown in the timing diagram of FIG. Increase the number of acoustic signals). On the other hand, when the depth of the attention area is shallower than the predetermined threshold, priority is given to the reduction of motion blur, and measurement in the operation mode shown in the timing diagram of FIG. Less). Thus, it may be automatically determined according to the depth of the attention area.

  Further, a pressure sensor may be added to the probe, and switching between giving priority to the S / N ratio of the photoacoustic image or giving priority to reduction of motion blur may be switched by the pressing force of the probe. That is, when the pressing force of the probe is larger than a predetermined threshold, it is considered that the region of interest is deep and the moving speed of the probe is slow. Increase the number of signals. On the other hand, when the pressing force of the probe is smaller than a predetermined threshold value, it is considered that the region of interest is shallow and the moving speed of the probe is fast.Therefore, priority is given to the reduction of motion blur, and the number of photoacoustic signals to be averaged Reduce. Thus, it may be automatically determined by sensing the pressing force of the probe.

  According to the present embodiment, by providing the frame rate conversion unit, it is possible to easily change the measurement conditions for acquiring the reconstructed image data by user designation or automatically without changing the display frame rate of the display. .

<Third Embodiment>
The third embodiment according to the present invention is different from the operation shown in the first embodiment in the target of the photoacoustic signal to be added and averaged when generating the reconstructed image.

  In FIG. 6, the timing from T1 to T4 is the same as FIG. In the operation shown in FIG. 4A, the photoacoustic signals acquired within a time equal to the imaging frame rate period tw2 are averaged. In this embodiment, however, they are acquired over a period longer than the imaging frame rate period. The obtained photoacoustic signals ((1) to (10)) are averaged. By performing the addition averaging in this manner, the addition averaging of the photoacoustic signals can be performed over a period longer than the period tw2 of the imaging frame rate, and the S / N ratio can be improved. In addition, since the photoacoustic signal obtained over a period longer than the cycle tw2 of the imaging frame rate is used, the timing at which the reconstructed image data R1 is generated is delayed as compared with the operation illustrated in FIG. That is, the waiting time from when the subject is irradiated with light until the image is displayed is longer than the operation shown in FIG.

  In contrast to the operation of FIG. 6, only a part of the photoacoustic acquired during the imaging frame rate period tw2 may be averaged to generate reconstructed image data. For example, among the photoacoustic signals shown in FIG. 6, (7) to (10) may be averaged without using (1) to (6). By doing so, it is possible to average the photoacoustic signals for a time shorter than the cycle of the imaging frame rate, and to reduce motion blur.

  By performing such processing, it is possible to easily change the measurement conditions for acquiring the reconstructed image data as shown in the second embodiment, that is, the advantage that the apparatus configuration can be further simplified. is there.

<Fourth Embodiment>
The fourth embodiment is an embodiment in which the timing for acquiring the photoacoustic signal is changed. FIG. 7 is a timing chart for explaining the operation according to the present embodiment.

  FIG. 7 illustrates the case where the imaging frame rate and the display frame rate have the same frequency, as in FIG. 4A of the first embodiment. Of course, the present invention can also be applied to the case where the imaging frame rate and the display frame rate are different from each other as shown in FIGS.

  The fourth embodiment shown in FIG. 7 differs greatly from the first embodiment in the sampling time of the photoacoustic signal to be averaged, that is, the light emission time of the light source 200. In the first embodiment, the first period is fixed. In the fourth embodiment, as shown at T1 in FIG. 7, the time for acquiring the photoacoustic signal is concentrated at a time having a period of the imaging frame rate, that is, the period of the imaging frame rate is the target. There is a rest period in which the sample is not irradiated with light. Also in this example, it is preferable that the first period and the like are determined under the condition that satisfies the above-described MPE.

  In the operation illustrated in FIG. 7, in the first half of the cycle of the imaging frame rate, the photoacoustic apparatus emits the light source unit 200 in the first cycle: tw1 and acquires the photoacoustic signal accompanying the light emission in the first cycle: tw1. To do. Next, in this example, the calculation unit obtains the photoacoustic signal A1 obtained by averaging the photoacoustic signals ((1) to (8)) obtained eight times. The calculation unit further sequentially calculates the reconstructed image data R1, R2,... According to the period defined by the second period, based on the photoacoustic signal A1 that has been averaged. Then, the frame rate conversion unit 159 converts the reconstructed image data R1, R2,... Into a display frame rate period: tw3, and outputs it as display image data. Then, the display unit 160 displays the display image data input at the display frame rate cycle: tw3.

  According to the operation according to the present embodiment, the photoacoustic signal is acquired at a certain time within the imaging frame rate and the averaging is performed. Therefore, in the photoacoustic image, compared with the operation illustrated in the first embodiment. Reduce motion blur. Moreover, the useless photoacoustic signal generated in the third embodiment does not occur. Further, as shown in FIG. 7, the time for performing photoirradiation to acquire the photoacoustic signal is only a part of the period of the imaging frame rate, and the time for not acquiring the photoacoustic signal in the period of the imaging frame rate. Occurs. As a result, within the period of the imaging frame rate, a photoacoustic signal can be obtained, an addition average can be performed, and a reconstruction process can be performed. As a result, the delay from the acquisition of the photoacoustic signal to the output of the reconstructed image data can be reduced.

  In the fourth embodiment, since the time width for averaging the photoacoustic data can be shortened, motion blur can be reduced.

<Fifth Embodiment>
In the fifth embodiment, a configuration in which measurement conditions are determined according to the subject will be described. Specifically, a photoacoustic apparatus that operates in synchronization with a periodic activity of a living body, for example, a heartbeat, that is, an electrocardiogram waveform, will be described.

  FIG. 8 is a block diagram showing a computer and a peripheral configuration according to the fifth embodiment. In FIG. 8, the same components as those in FIG. 3 are given the same reference numerals as those in FIG. In FIG. 8, an electrocardiograph 173 detects an electrical signal transmitted through the heart of a patient, who is the subject, and outputs it to the computer 150. The computer 150 determines the imaging frame rate so as to be synchronized with the output of the electrocardiograph (electrocardiogram waveform), acquires a photoacoustic signal, and calculates reconstructed image data. This will be described in more detail with reference to FIG.

  In FIG. 9, the imaging frame rate cycle tw2 and the display frame rate cycle tw3 are different. The computer 150 synchronizes the cycle tw2 of the imaging frame rate with the RR cycle: tw4 of the electrocardiogram waveform T5 detected by the electrocardiograph 173. Specifically, the period tw2 of the imaging frame rate is started based on the R wave that is the maximum amplitude of the electrocardiogram waveform T5.

  As illustrated in FIG. 9, in the photoacoustic apparatus, the light source unit 200 emits light at a first period: tw1 and acquires a photoacoustic signal accompanying light emission at a first period: tw1. However, the period for acquiring the photoacoustic signal is acquired during the sampling effective period SW after the delay time DLY has passed with reference to the R wave. The sampling effective period SW is a value obtained by multiplying the first cycle tw1 by the number of times of light emission (in this case, 8 times). As described above, the first period tw1 is preferably determined according to the MPE restriction or the like.

  Next, the signal collecting unit acquires the photoacoustic signal eight times in the first period: tw1 ((1) to (8)), and the arithmetic unit averages the obtained photoacoustic signal, and the averaging is performed. Calculated photoacoustic signal A1. The arithmetic unit further performs processing for reconstruction. The reconstructed image data R1 is sequentially calculated according to the cycle tw2 of the imaging frame rate. The frame rate conversion unit 159 outputs the reconstructed image data R1, R2,... With the calculated imaging frame rate period: tw2 as display image data with the display frame rate period: tw3. Then, the display unit 160 displays the display image data input at a display frame rate cycle: tw3.

  Note that the timing shown in FIG. 9 is merely an example, and in an actual apparatus, the first period is about 0.1 to several milliseconds, the imaging frame rate period is about 0.4 to 2 seconds, and the display frame rate Is considered to be about 50 to 240 Hz.

  As described above, it is preferable that the delay time DLY and the sampling effective time SW can be freely set by the user via the input unit 170, for example.

  Blood vessels move periodically as the heart beats. Therefore, by receiving a photoacoustic signal in synchronization with an electrocardiogram waveform, that is, heartbeat, and obtaining a reconstructed image, it is possible to reduce motion blur due to blood vessel contraction and movement due to heartbeat. In the electrocardiogram waveform T5 in FIG. 9, the ventricle contracts in the QRS wave, and blood is ejected from the S wave to the T wave. That is, it is a period in which the blood pressure of the artery is high. When viewing a reconstructed image of a blood vessel in such a period, as shown in FIG. 9, the delay time DLY and the sampling effective time SW are set so as to acquire a photoacoustic signal between the S wave and the T wave. Set. Then, by reconstructing the photoacoustic signal for the set period, a clear reconstructed image without motion blur can be acquired.

  In addition, since the distance from the heart differs depending on the site from which the photoacoustic image is acquired, the time (the phase with respect to tw4) at which the blood pressure changes with respect to the electrocardiogram waveform. Moreover, the change in blood pressure is also different (the change in blood pressure decreases with distance from the heart). Therefore, it is preferable that the user can adjust the delay time DLY and the sampling effective time SW so that a good value can be set while viewing the reconstructed image. Further, by making it possible to adjust the delay time DLY and the sampling effective time SW, for example, reconstructed image data whose timing is changed (measurement conditions are changed) such as a blood vessel image at the timing of atrial inflation is obtained. be able to.

  In the above-described embodiment, the photoacoustic signal is acquired in synchronization with the heartbeat based on the electrocardiogram waveform, but the fifth embodiment of the present invention is synchronized with the heartbeat in addition to the electrocardiogram waveform. Biosignals can be used. Specifically, an arterial pressure waveform or a sound wave (heart sound) emitted from the heart may be used instead of the electrocardiographic waveform. Further, the fifth embodiment can be applied to a periodic activity of a living body other than the heartbeat.

  As described above, according to the fifth embodiment of the present invention, the reconstructed image data is generated at the cycle of the imaging frame rate synchronized with the electrocardiogram waveform or the like different from the cycle of the display frame rate, and the frame rate conversion unit The period is converted into a display frame rate by 159 and displayed by the display unit 160. With such a configuration, it is possible to acquire a good reconstructed image with less blood vessel motion blur due to a periodic physiological phenomenon depending on a living body such as an electrocardiogram waveform. In particular, arterial motion blur can be reduced and a photoacoustic image of the artery can be clearly obtained.

<Sixth Embodiment>
In the sixth embodiment according to the present invention, a user interface (UI) centering on a display screen for displaying measurement conditions will be specifically described. A display screen for displaying measurement conditions, which is this user interface, which is an example of an input unit that receives input from the user, may be displayed on the liquid crystal display 161 of the display unit 160 described above together with the reconstructed image. In addition, a plurality of windows may be displayed on the liquid crystal display 161, and a reconstructed image and a display screen for displaying measurement conditions may be displayed in separate windows. Furthermore, a different liquid crystal display or the like may be added, and the added liquid crystal display or the like may be assigned and used for display dedicated to the user interface. The user can set various measurement parameters including the first period, the second period, and the third period via the user interface. The configuration may be such that the user inputs all of these imaging parameters, or only a part of the imaging parameters may be set by the user.

  An example of the display screen will be specifically described with reference to FIGS. 10 (a), 10 (b), and 10 (c).

  FIG. 10A is an example of a display screen according to the present embodiment. In FIG. 10A, U1 is a diagram schematically showing an image displayed on the display. U101 is a waveform schematically showing the timing of the display frame rate, and U102 is a number (unit: msec) indicating the period DT of the display frame rate. U103 is a waveform schematically showing the imaging frame rate, and U104 is a number (unit: msec) indicating the period FT of the imaging frame rate. U105 is a waveform indicating the delay time DLY and the sampling effective time SW. U106 is a number (unit: msec) indicating the delay time DLY from the start of the imaging frame rate U103 to the start of the sampling effective time SW, and U107 is a number (unit: msec) indicating the sampling effective time SW.

  The user can change the measurement conditions by changing each numerical value using a mouse or a keyboard while viewing the screen shown in U1 displayed on the screen. Instead of a mouse or a keyboard, a dedicated knob for changing each parameter may be provided and adjusted. When such adjustment is performed, the software is designed so that the waveform and the numerical value of the screen of U1 change interactively in response to a user instruction.

  FIG. 10B is another example of the display screen. In FIG. 10B, U2 is a diagram schematically showing an image to be displayed on the display. U201 is a waveform schematically showing the timing of the display frame rate, and U202 is a number (unit: Hz) indicating the display frame rate DR. U203 is a waveform schematically showing the imaging frame rate, and U204 is a number (unit: Hz) indicating the imaging frame rate FR. U205 is a waveform indicating the delay time DLY and the sampling effective time SW. U206 is a number (unit: °, period: 360 °) indicating the ratio of the delay time DLY from the start of the frame rate to the start of the sampling effective time with respect to the period of the imaging frame rate U203, U207 is sampling effective It is a number (unit:%) indicating the time SW as a ratio of the period FT of the imaging frame rate U203. With such a display screen, even when the user converts the imaging frame rate, the time to start acquisition of the photoacoustic signal and the sampling effective time can be intuitively understood. The display screen may be a combination of these or other expression methods.

  The user can interactively change the measurement conditions while viewing the displayed screen indicated by U2.

  The display frame rate is generally fixed once the display unit 160 is determined. Therefore, waveforms (U101, U201) schematically showing the timing of the display frame rate shown in the images (U1, U2) to be displayed shown in FIGS. 10A and 10B, and numbers indicating the display frame rate. (U102, U202) may not be displayed. In this way, the display content is reduced, and the user can more easily set and grasp the measurement conditions.

  FIG. 10C shows still another example of the display screen. FIG. 10C is an embodiment in which the measurement conditions (imaging frame rate) shown in the fifth embodiment are determined according to the subject. More specifically, this is a display screen for displaying a measurement condition suitable for a photoacoustic apparatus in which the cycle of the frame rate is synchronized with the periodic activity of the living body, for example, the heartbeat, that is, the electrocardiogram waveform.

  In FIG. 10C, U3 is a diagram schematically showing an image to be displayed on the display. U301 is a waveform schematically showing the imaging frame rate, and U302 is a number (unit: Sec) indicating the period FT of the imaging frame rate. U303 is a waveform indicating the delay time DLY and the sampling effective time SW. U304 is a number (unit: °, period: 360 °) indicating the ratio of the time from the start of the frame rate to the start of the sampling effective time SW with respect to the period of the imaging frame rate U301, U305 is sampling effective It is a number (unit:%) indicating the time SW as a ratio of the period FT of the imaging frame rate U303. U306 is a waveform indicating an electrocardiogram waveform. U307 is a line indicating the trigger level set for the electrocardiogram waveform U306. The trigger level can be set by the user with the mouse, keyboard, or dedicated knob. As another method, the computer 150 can automatically set 90% of the peak value of the amplitude. In the case of the example shown in FIG. 10C, the trigger is activated at the rising time of the electrocardiographic waveform exceeding the set trigger level amplitude. When a trigger is applied, the computer 150 generates an imaging frame rate with one cycle until the next trigger. That is, the user cannot set the imaging frame rate. While viewing the electrocardiogram waveform, the user can adjust the sampling start phase and the sampling effective time SW, which are measurement conditions, to desired values, and obtain a reconstructed image.

  According to the sixth embodiment described above, the user can easily grasp and set the measurement conditions. Therefore, there is an advantage that the user can easily set the optimum measurement conditions according to the state of the living body as the subject.

(Other)
The light source unit 200 may be configured to irradiate a plurality of wavelengths as described above. When light of a plurality of wavelengths is used, oxygen saturation as functional information can be calculated. For example, a photoacoustic signal is acquired by alternately irradiating a subject with two wavelengths for each imaging frame rate, and reconstructed image data is calculated for each wavelength. The oxygen saturation can be calculated from the constituent image data. For the calculation of the oxygen saturation, a known method can be used, such as JP-A-2015-142740.

  Further, the plurality of embodiments described above may be realized by a single photoacoustic apparatus and used by switching. In addition, the photoacoustic apparatus may be additionally provided with a function of transmitting ultrasonic waves from a transducer and performing measurement using reflected waves. In that case, the ultrasonic echo image and the photoacoustic image may be displayed side by side, or may be superimposed and displayed in alignment.

DESCRIPTION OF SYMBOLS 100 Subject 112 Optical system 113 Light emitting part 120 Acoustic wave receiving part 140 Signal collecting part 150 Computer 151 Calculation part 152 Storage part 153 Control part 159 Frame rate conversion part 160 Display part 170 Input part 180 Probe 181 Housing 200 Light source part

Claims (10)

A light irradiation unit for irradiating the subject with light;
An acoustic wave receiving unit that receives an acoustic wave generated from the subject by being irradiated with the light and outputs a reception signal; and
An image generation unit that generates an image inside the subject based on the received signal,
The light irradiation unit repeatedly irradiates the subject with the light in a first cycle,
The image generation unit synthesizes a plurality of the reception signals obtained by irradiating the light a plurality of times, generates image data at a frame rate of a second period based on the synthesized signals,
The photoacoustic apparatus further comprises a frame rate conversion unit that converts an image display rate based on the image data generated at the frame rate of the second period to a frame rate of the third period.   The photoacoustic apparatus according to claim 1, wherein the first period is shorter than the second period.   The photoacoustic apparatus according to claim 1, wherein the second period is longer than the third period.   The photoacoustic apparatus according to any one of claims 1 to 3, wherein the frame rate of the second period is synchronized with a periodic activity of a living body.   The photoacoustic apparatus according to claim 1, wherein the frame rate conversion unit causes the display unit to display the image in the third period. A storage unit that stores the image data generated at the frame rate of the second period;
The photoacoustic apparatus according to claim 5, wherein the frame rate conversion unit outputs the stored reconstructed image data to the display unit at a frame rate of a third period.   The photoacoustic apparatus according to claim 5, wherein the control unit causes the display unit to display information regarding the third period.   The photoacoustic according to claim 1, further comprising an input unit that receives at least one input of the first period, the second period, and the third period. apparatus. A light irradiation step for irradiating the subject with light;
An acoustic wave receiving step of receiving an acoustic wave generated from the subject by being irradiated with the light and outputting a reception signal;
An image generation step of generating an image inside the subject based on the received signal, and a photoacoustic image generation method comprising:
The light irradiation step repeatedly irradiates the subject with the light in a first cycle,
The image generation step combines a plurality of the reception signals obtained by a plurality of times of the light irradiation, generates image data at a frame rate of a second period based on the combined signals,
The photoacoustic image generation method further includes a frame rate conversion step of converting an image based on the image data generated at the frame rate of the second period into a frame rate of the third period. An image generated by the photoacoustic image generation method according to claim 9,
A method for displaying a photoacoustic image, which is displayed on the display unit in the third period.

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