JP2016083044A - Photoacoustic imaging apparatus and photoacoustic image construction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoacoustic imaging apparatus capable of acquiring a clear image by a reverse projection method.SOLUTION: A photoacoustic imaging apparatus 100 includes: a light source part 10; a detection part 20 for detecting a photoacoustic wave signal attributed to a photoacoustic wave AW generated from a detection object Q in a subject P that has absorbed light from the light source part 10; and a signal processing part 31 for correcting a decrease in the signal strength of the photoacoustic wave signal attributed to the attenuation of the photoacoustic wave AW, and generating an image by a reverse projection method based on the corrected photoacoustic wave signal.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a photoacoustic imaging apparatus and a photoacoustic image construction method, and more particularly to a photoacoustic imaging apparatus including a signal processing unit that generates an image and the photoacoustic image construction method.

  Conventionally, a reception data device for a photoacoustic imaging apparatus including a signal processing unit that generates an image is known (see, for example, Patent Document 1).

  In Patent Document 1, a photoacoustic tomography diagnosis that generates an image based on a received photoacoustic wave signal (photoacoustic wave signal) generated by irradiating a subject with light and received by a receiving array. A reception data processing device for a device (for a photoacoustic imaging device) is disclosed. This received data processing apparatus is configured to generate an image by phasing and adding photoacoustic wave signals by a signal processing unit such as an arithmetic circuit.

  Conventionally, a back projection method (Back Projection method) is known as a technique of imaging processing of a radiographic imaging apparatus. In the received data processing device for the photoacoustic imaging device described in Patent Document 1 and the conventional radiographic imaging device, imaging processing techniques such as phasing addition and back projection are used to obtain a clear image. It is used.

JP 2010-57730 A

  In the received data processing apparatus described in Patent Document 1, an image is obtained by applying a back projection method, which is an imaging processing technique of a conventional radiographic imaging apparatus, instead of phasing addition as an imaging processing technique. It is possible.

  However, in general, the intensity of photoacoustic waves generated by light irradiation is small. In addition, the signal intensity of the detected photoacoustic wave signal is further reduced due to the attenuation of the photoacoustic wave that occurs between generation and detection in the subject. For this reason, there is a problem that a sufficiently clear image cannot be obtained by simply applying the back projection method to the received data processing apparatus described in Patent Document 1 as an imaging processing technique.

  The present invention has been made to solve the above-described problems, and one object of the present invention is a photoacoustic imaging apparatus and a photoacoustic image capable of obtaining a clear image by a back projection method. It is to provide a construction method.

  A photoacoustic imaging apparatus according to a first aspect of the present invention detects a photoacoustic wave signal caused by a photoacoustic wave generated from a light source unit and a detection target in a subject that has absorbed light from the light source unit. A detection unit, a signal processing unit that corrects a decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave, and generates an image by back projection based on the corrected photoacoustic wave signal; Is provided.

  In the photoacoustic imaging apparatus according to the first aspect of the present invention, as described above, the reduction in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave is corrected, and the corrected photoacoustic wave signal is converted into the corrected photoacoustic wave signal. Based on this, a signal processing unit for generating an image by back projection is provided. Thereby, even if the photoacoustic wave generated in the subject is attenuated before reaching the detection unit, the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave can be corrected. As a result, imaging processing by the back projection method can be performed by the photoacoustic wave signal in which the decrease in signal intensity is corrected, and thus a clear image can be obtained by the back projection method.

  In the photoacoustic imaging apparatus according to the first aspect, preferably, the signal processing unit is at least one of a detection time until the photoacoustic wave signal is detected by the detection unit, or a signal frequency of the photoacoustic wave signal. Is configured to correct a decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave. Here, the decrease (decrease amount) in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave changes according to the detection time or the signal frequency. Therefore, if comprised as mentioned above, based on the reduction | decrease (decrease amount) of the signal strength of the photoacoustic wave signal resulting from attenuation | damping of a photoacoustic wave, the reduction | decrease in the signal strength of a photoacoustic wave signal is correct | amended reliably. be able to.

  In this case, the signal processing unit preferably attenuates the photoacoustic wave by increasing the signal intensity of the photoacoustic wave signal as the detection time or at least one of the signal frequencies increases. It is configured to correct a decrease in the signal intensity of the photoacoustic wave signal caused by it. If comprised in this way, the signal of the photoacoustic wave signal resulting from attenuation of a photoacoustic wave according to the reduction | decrease (decrease amount) of the signal strength which becomes large as the value of at least one of detection time or a signal frequency becomes large. Strength can be increased. As a result, it is possible to more reliably correct the decrease in the signal intensity of the photoacoustic wave signal according to the decrease (decrease amount) in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave.

In the configuration for increasing the signal intensity of the photoacoustic wave signal, preferably, the signal processing unit sets h as a constant relating to the sound speed, t as a detection time, f as a signal frequency, and k1 as a constant relating to the detection time and the signal frequency. When the unit of the detection time t is μs, the unit of the signal frequency f is MHz, and the constant k1 is 0.002 or more and 0.009 or less, the correction coefficient Z1 represented by the following formula (1) is By multiplying the photoacoustic wave signal, the signal intensity of the photoacoustic wave signal is increased as the detection time and the signal frequency increase.
Z1 = h × t × 10 ^{k1 × t × f} (1)

  If comprised in this way, the signal intensity | strength of a photoacoustic wave signal can be increased according to both detection time and a signal frequency by using said Formula (1). As a result, the decrease in the signal intensity of the photoacoustic wave signal can be more reliably corrected according to the decrease (decrease amount) in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave. Moreover, the correction coefficient Z1 can be appropriately acquired by setting the constant k1 to be not less than 0.002 and not more than 0.009. In addition, by providing the term (h × t) in the above formula (1), it is possible to appropriately perform an imaging process in accordance with the characteristics of the back projection method.

  In this case, preferably, the constant h is 0.1 or more and 0.2 or less when the unit is (cm / μs), and a value obtained by multiplying the constant h and the detection time t is smaller than a predetermined value. In this case, a value obtained by multiplying the constant h and the detection time t is set as a predetermined value. With this configuration, the value of the constant h is appropriately set, so that the correction coefficient Z1 can be acquired more appropriately.

  In the configuration in which the value obtained by multiplying the constant h and the detection time t is a predetermined value, the predetermined value is preferably 0.5 or more and 1.5 or less. With this configuration, the value of the constant h is set more appropriately, so that the correction coefficient Z1 can be acquired more appropriately.

  In the photoacoustic imaging apparatus according to the first aspect, preferably, the detection unit includes a detection element that receives the photoacoustic wave and detects a photoacoustic wave signal caused by the photoacoustic wave, and performs signal processing. In addition to correcting the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave, the unit uses the back projection method in consideration of the sensitivity due to the incident direction of the photoacoustic wave with respect to the detection element. It is configured to generate an image. According to this configuration, when the image is generated by the back projection method, it is possible to consider the difference in the sensitivity of the detection element due to the incident direction of the photoacoustic wave. Can be obtained. As a result, the sensitivity due to the incident direction of the photoacoustic wave with respect to the detection element is considered while improving the sharpness of the image by correcting the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave. Thus, an image close to the actual condition in the subject can be obtained.

  In the photoacoustic imaging apparatus according to the first aspect, preferably, the light source unit includes at least one of a light emitting diode element, a semiconductor laser element, and an organic light emitting diode element as a light source. With this configuration, it is possible to obtain advantages such as a reduction in power consumption of the light source and a reduction in size of the light source unit as compared with the case where a solid laser light source is used. Here, when a light-emitting diode element, a semiconductor laser element, or an organic light-emitting diode element is used as a light source, the output of light emitted from the light source is smaller than when a solid-state laser light source is used. For this reason, the signal intensity of the photoacoustic wave signal detected by the detector is further reduced. Therefore, when using a light emitting diode element, a semiconductor laser element, or an organic light emitting diode element as a light source, the present invention that a clear image can be obtained by correcting a decrease in signal intensity is particularly effective.

  In the photoacoustic imaging apparatus according to the first aspect, preferably, the signal processing unit corrects a decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave, and further, a light source for the subject. Configured to correct a decrease in signal intensity of the photoacoustic wave signal caused by attenuation of light from the light source unit as the distance from the light irradiation position by the unit to a predetermined position in the subject increases Has been. With this configuration, even if the light from the light source unit attenuates before reaching the detection target in the subject, the signal intensity of the photoacoustic wave signal is reduced due to the attenuation of the light from the light source unit. It can be corrected. As a result, in addition to correcting the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave, the signal intensity decrease due to the attenuation of the light from the light source is also corrected. can do. Therefore, the decrease in the signal intensity of the photoacoustic wave signal can be corrected more appropriately.

In this case, preferably, the signal processing unit corrects the following expression (2) when the constant related to the irradiation position is k2 and the distance from the irradiation position to a predetermined position in the subject is d. By multiplying the photoacoustic wave signal by the coefficient Z2, the signal of the photoacoustic wave signal resulting from the attenuation of light from the light source unit as the distance from the irradiation position to the predetermined position in the subject increases. It is configured to compensate for the decrease in intensity.
Z2 = 10 ^{k2 × d} (2)

  If comprised in this way, attenuation | damping of the light from a light source part will be ensured according to the reduction | decrease (decrease amount) of the signal intensity resulting from attenuation | damping of the light from a light source part by using said Formula (2). It is possible to correct a decrease in the signal intensity of the photoacoustic wave signal caused by.

  In the configuration in which the constant related to the irradiation position is k2, preferably, the constant k2 is a unit of distance d from the irradiation position to a predetermined position in the subject when the irradiation position of the light source unit is on the detection unit side. , And the constant k2 is a constant k2 when the irradiation position of the light source unit is on the side opposite to the detection unit, and the irradiation position of the light source unit is on the detection unit side. -0.8 or more when the distance from the irradiation position to a predetermined position in the subject is d and the unit of the distance d from the irradiation position to the predetermined position in the subject is cm -0.2 or less. If comprised in this way, the correction coefficient Z2 can be appropriately acquired according to the irradiation position of the light by a light source part. As a result, it is possible to appropriately increase the signal intensity of the photoacoustic wave signal resulting from the attenuation of light from the light source unit.

  In the photoacoustic imaging apparatus according to the first aspect, preferably, the detection unit includes a plurality of detection elements that receive the photoacoustic wave and detect a photoacoustic wave signal caused by the photoacoustic wave. The width of the light source unit in the arrangement direction in which the plurality of detection elements are arranged is larger than the width in the arrangement direction of the plurality of detection elements. If comprised in this way, the light from a light source part can be reliably irradiated over the whole region of the sequence direction of a some detection element. As a result, sufficient photoacoustic waves are generated from the detection object within the range detectable by the plurality of detection elements due to the small amount of light irradiation within the range detectable by the plurality of detection elements. Can not be suppressed. Thereby, it can suppress that detection of the detection target object within the range which can be detected with a plurality of detection elements is not appropriately performed by the plurality of detection elements.

  In the photoacoustic image construction method according to the second aspect of the present invention, the detection unit detects a photoacoustic wave signal caused by a photoacoustic wave generated from a detection target in the subject that has absorbed light from the light source unit. And a step of correcting the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave by the signal processing unit, and an image by the back projection method based on the corrected photoacoustic wave signal by the signal processing unit. Generating.

  In the photoacoustic image construction method according to the second aspect of the present invention, as described above, the signal processing unit corrects the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave, and the correction is performed. Based on the photoacoustic wave signal, a step of generating an image by a back projection method by a signal processing unit is performed. Thereby, also in the photoacoustic image construction method of the second aspect, a clear image can be obtained by the back projection method.

  According to the present invention, as described above, it is possible to provide a photoacoustic imaging apparatus and a photoacoustic image construction method capable of obtaining a clear image by back projection.

It is a block diagram which shows the whole structure of the photoacoustic imaging device of the 1st-3rd embodiment of this invention. It is a figure for demonstrating acquisition of the photoacoustic wave signal by the photoacoustic imaging device of 1st Embodiment of this invention. It is a figure for demonstrating acquisition of the photoacoustic wave signal corresponding to the light emission period and light emission period by the photoacoustic imaging device of 1st Embodiment of this invention. It is a figure for demonstrating the NM coordinate data before correction | amendment in the photoacoustic imaging device of 1st Embodiment of this invention. It is a figure for demonstrating the NM coordinate data after correction | amendment in the photoacoustic imaging device of 1st Embodiment of this invention. It is a figure for demonstrating the imaging process by the back projection method in the photoacoustic imaging device of 1st Embodiment of this invention. It is a figure for demonstrating the determination method of the signal value of the imaging area | region by the back projection method in the photoacoustic imaging device of 1st Embodiment of this invention. It is a flowchart for demonstrating the photoacoustic wave image construction process by the photoacoustic imaging device of 1st Embodiment of this invention. It is a figure for demonstrating the sensitivity resulting from the incident direction of the detection element in the photoacoustic imaging device of 2nd Embodiment of this invention. It is a figure for demonstrating the imaging process by the back projection method in consideration of the sensitivity resulting from the incident direction of the detection element in the photoacoustic imaging device of 2nd Embodiment of this invention. It is a flowchart for demonstrating the photoacoustic wave image construction process by the photoacoustic imaging device of 2nd Embodiment of this invention. It is a figure which shows the case where the irradiation position of the light by the light source part in the photoacoustic imaging device of 3rd Embodiment of this invention is a detection part side. It is a figure for demonstrating the NM coordinate data after correction | amendment in the photoacoustic imaging device of 3rd Embodiment of this invention. It is a figure which shows the case where the irradiation position of the light by the light source part in the photoacoustic imaging device of 3rd Embodiment of this invention is the other side of a detection part. It is a graph for demonstrating attenuation | damping of the light by the photoacoustic imaging device of 3rd Embodiment of this invention. It is a flowchart for demonstrating the photoacoustic wave image construction process by the photoacoustic imaging device of 3rd Embodiment of this invention.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings.

(First embodiment)
First, the configuration of the photoacoustic imaging apparatus 100 according to the first embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the photoacoustic imaging apparatus 100 according to the first embodiment of the present invention includes a light source unit 10, a detection unit 20, and a photoacoustic imaging apparatus main body (hereinafter referred to as an apparatus main body) 30. ing. The light source unit 10 and the detection unit 20 are provided outside the apparatus main body 30 and are connected to the apparatus main body 30 by wiring (not shown). Through this wiring, the photoacoustic imaging apparatus 100 outputs a control signal from the apparatus main body 30 to the light source unit 10, and detects a photoacoustic wave signal detected by the detection unit 20 from the detection unit 20 to the apparatus main body 30. A signal such as an output can be transmitted.

  As shown in FIG. 1, the light source unit 10 is a light source unit for irradiating a subject P (see FIG. 2) with light. When measuring the photoacoustic wave AW (see FIG. 2), the light source unit 10 is used in a state of being in contact with the surface of the subject P.

  The light source unit 10 includes a light source 11 and is configured to emit light for measurement from the light source 11 toward the subject P. The light source 11 of the light source unit 10 repeats pulsed light having a pulse width ta (see FIG. 3) with a light emission period Ta (see FIG. 3) based on a control signal of a light source driving unit 33 described later of the apparatus main body 30. It is configured to emit light. Then, after the emission of the pulsed light, the photoacoustic wave signal for a predetermined period before the emission of the next pulsed light is repeatedly acquired by the apparatus main body 30.

  The light source 11 is configured to generate light having a measurement wavelength in the infrared region suitable for measurement of a subject P such as a human body (see FIG. 2) (for example, light having a center wavelength of about 700 nm to about 1000 nm). ing. As such a light source 11, it is possible to use a light emitting diode element, a semiconductor laser element, or an organic light emitting diode element, for example. In this case, since the light source unit 10 can be reduced in size, the photoacoustic wave AW can be measured by bringing the light source unit 10 provided with the light source 11 into direct contact with the subject P. . Note that the measurement wavelength of the light source 11 may be appropriately determined according to the detection target Q desired to be detected.

  As shown in FIG. 1, the detection unit 20 is a probe for receiving a photoacoustic wave AW (see FIG. 2). In addition to receiving the photoacoustic wave AW, the detecting unit 20 can be configured to transmit and receive ultrasonic waves. When measuring the photoacoustic wave AW, the detection unit 20 is used in a state of being in contact with the surface of the subject P.

  The detection unit 20 includes a plurality of detection elements 21. The plurality of detection elements 21 include piezoelectric elements, and are arranged in an array in the vicinity of the tip inside the housing (not shown). In the first embodiment, N (also referred to as Nch (channel)) detection elements 21 are provided. As the number N of the detection elements 21, for example, 64, 128, 192, or 256 can be used.

  Further, the detection unit 20 vibrates the detection element 21 by the photoacoustic wave AW generated from the detection object Q (see FIG. 2) in the subject P (see FIG. 2) that has absorbed the light emitted from the light source unit 10. Thus, the photoacoustic wave AW is received and the photoacoustic wave signal is detected. The detection unit 20 is configured to output the detected photoacoustic wave signal to the apparatus main body 30.

  Here, in the first embodiment, the apparatus main body 30 is provided with a signal processing unit 31. The signal processing unit 31 is configured to generate a photoacoustic wave image based on the photoacoustic wave signal by correcting and backprojecting the photoacoustic wave signal output from the detection unit 20. Specifically, the signal processing unit 31 corrects the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW, and based on the corrected photoacoustic wave signal, the back projection method (back The photoacoustic wave image is generated by a projection method (Back Projection method).

  In general, the signal processing unit 31 acquires a photoacoustic wave signal, corrects the acquired photoacoustic wave signal, backprojects the corrected photoacoustic wave signal, and light based on the backprojected photoacoustic wave signal. It is configured to perform signal processing related to generation of an acoustic wave image. Hereinafter, the configuration of the signal processing unit 31 will be described in detail.

  As shown in FIG. 1, the signal processing unit 31 includes a receiving unit 41, a first memory 42, an averaging processing unit 43, a correction processing unit 44, a second memory 45, a back projection unit 46, 3 memory 47. The function of the signal processing unit 31 is realized by, for example, a combination of a dedicated circuit, a general-purpose CPU, a hardware such as a field programmable gate array (FPGA), a nonvolatile memory, a volatile memory, and software such as various programs. be able to.

  The receiving unit 41 includes a plurality (N) of amplifying units 51 corresponding to a plurality (N) of detection elements 21 of the detection unit 20 and a plurality (N) of analog-digital conversion units (hereinafter referred to as A / D). 52) (referred to as a conversion unit).

  Here, with reference to FIG. 2, the process from the detection of the photoacoustic wave signal by the detection unit 20 to the reception of the photoacoustic wave signal by the reception unit 41 will be described. When pulsed light is irradiated toward the subject P by the light source unit 10 (see FIG. 1), a photoacoustic wave AW is generated from the detection target Q in the subject P as shown in FIG. At this time, a photoacoustic wave AW is generated from a wide range at a time by light irradiation. In FIG. 2, only one detection object Q is shown for easy understanding.

  And the detection part 20 (refer FIG. 1) receives the photoacoustic wave AW generate | occur | produced from the detection target object Q by each of the N detection elements 21, and detects a photoacoustic wave signal. In FIG. 2, the photoacoustic wave signals detected by the respective detection elements 21 are shown as photoacoustic wave signals L1 to LN. The photoacoustic wave signals L <b> 1 to LN detected by the detection element 21 are output from the detection unit 20 to the apparatus main body 30 and received by the reception unit 41 of the apparatus main body 30. Hereinafter, the photoacoustic wave signals are appropriately referred to as photoacoustic wave signals L1 to LN.

  The receiving unit 41 includes the photoacoustic wave detected by the nth detection element 21 by the nth (1 ≦ n ≦ N) th amplification unit 51 and the nth A / D conversion unit 52 corresponding thereto. The signal Ln (L1 to LN) is configured to be received.

  Each amplification unit 51 is configured to amplify the received photoacoustic wave signals L <b> 1 to LN (for example, about 300 times to about 30000 times) and output the signals to each A / D conversion unit 52. .

  Each A / D converter 52 converts each of the photoacoustic wave signals L1 to LN in a state amplified by each amplifier 51 from an analog signal to a digital signal with a predetermined sampling frequency and a predetermined bit resolution. It is configured. Each A / D converter 52 is configured to output the photoacoustic wave signals L <b> 1 to LN as digital signals to the first memory 42.

  The first memory 42 is configured to store the photoacoustic wave signals L <b> 1 to LN output from each A / D conversion unit 52. Further, as shown in FIG. 4, the first memory 42 stores the photoacoustic wave signals L1 to LN as NM coordinate data.

Here, the NM coordinate data is data in which information related to the width direction of the detection unit 20 and information related to the depth direction from the surface of the subject P are configured in a matrix. Specifically, the NM coordinate data is composed of a matrix of the number of detection elements 21 (number of detection elements) N and the number of samplings M. Here, the sampling number M is the number of samplings of the signals up to the depth at which imaging is desired in each of the photoacoustic wave signals L1 to LN. For example, the depth desired to be imaged is 6 cm (0.06 m) from the surface of the subject P, the sound velocity in the human body is 1530 (m / s), and the predetermined sampling frequency of the A / D converter 52 is 20 In the case of × 10 ⁶ Hz, the sampling number M is M = (0.06 / 1530) × 20 × 10 ⁶ = about 800. The sampling number M indicates the number of pixels in the depth direction. For example, in the case of the above calculation example, the number of samplings M has about 800 pixels in the depth direction.

In the NM coordinate data, each point of the M coordinate is arranged at a time interval corresponding to the sampling time p. The sampling time p is a time corresponding to one cycle of a predetermined sampling frequency of the A / D conversion unit 52. For example, when the predetermined sampling frequency of the A / D converter 52 is 20 × 10 ⁶ Hz, the sampling time p is 0.05 μs. That is, in the NM coordinate data, the M coordinate corresponds to the detection time t in the detected photoacoustic wave signals L1 to LN. For example, when the M coordinate is m (1 ≦ m ≦ M), the detection time t is obtained by t = m × p. Therefore, this NM coordinate data can be said to be data having information at each detection time t of the photoacoustic wave signals L1 to LN detected by the respective detection elements 21. Specifically, the coordinate point (n, m) of the NM coordinate data has information on the signal value X _nm at the detection time t (= m × p) of the photoacoustic wave signal Ln. One NM coordinate data is obtained for one pulse emission by the light source 11 of the light source unit 10. And this pulse light emission is performed for every light emission period Ta, and the photoacoustic wave signals L1-LN based on each pulse light are stored in the 1st memory 42, respectively.

  As shown in FIG. 3, the averaging processing unit 43 (see FIG. 1) corresponds to each of a plurality (P sets) of photoacoustic wave signals L1 to LN received based on a plurality (P times) of pulsed light. A plurality (P pieces) of NM coordinate data is averaged. As a result, a photoacoustic wave image (image data) can be generated in a state in which the S / N ratio (signal / noise ratio) of the photoacoustic wave signals L1 to LN is improved by the averaging process. It is possible to generate a photoacoustic wave image in which the state in P is accurately reflected. The averaging processing unit 43 is configured to store the averaged NM coordinate data in the first memory 42. The first memory 42 is configured to be able to output the stored NM coordinate data to the correction processing unit 44.

  Here, in the first embodiment, the correction processing unit 44 corrects the decrease in the signal intensity of the photoacoustic wave signals L1 to LN due to the attenuation of the photoacoustic wave AW based on the detection time t and the signal frequency f. It is configured as follows. The detection time t is the time from the time of pulse light irradiation by the light source unit 10 to the time of detection when the photoacoustic wave signals L1 to LN are detected by the detection unit 20. Note that the start point of the detection time t does not have to be strictly the time of pulse light irradiation by the light source unit 10. For example, as shown in FIG. 3, it may be the sampling start time of the photoacoustic wave signals L1 to LN after the irradiation time of the pulsed light from the light source unit 10. In the first embodiment, the detection time t is a value obtained by multiplying the M coordinate m of the NM coordinate data and the sampling time p as described above. The signal frequency f is a signal frequency that the photoacoustic wave signals L1 to LN have. In the first embodiment, the signal frequency f is a signal frequency at a predetermined coordinate point in the NM coordinate data. Such a signal frequency f can be obtained, for example, by analyzing the photoacoustic wave signals L1 to LN by a Fourier transform method or the like.

In the first embodiment, the correction processing unit 44 has the following constants regarding the sound speed as h, and constants regarding the detection time t (μs: microseconds) and the signal frequency f (MHz: megahertz) as k1. By multiplying the photoacoustic wave signals L1 to LN by the correction coefficient Z1 expressed by the equation (1), the signal intensity of the photoacoustic wave signal is increased as the values of the detection time t and the signal frequency f increase. It is configured to increase.
Z1 = h × t × 10 ^{k1 × t × f} (1)
Here, the constant k1 is a constant for correcting the attenuation (reduction in signal intensity) of the photoacoustic wave AW generated in the subject P with respect to the detection time t and the signal frequency f, and the subject P (human body or other) And the like, and the measurement site of the subject P can be appropriately determined. In view of this point, the constant k1 is preferably 0.002 or more and 0.009 or less.

For example, the constant k1 for measuring a living body (human body) soft part is obtained as follows as an example. First, the attenuation in the soft body of the living body is set to −0.6 dB / (cm × MHz), and the time for the sound (photoacoustic wave AW) to travel through the distance of 1 cm in the soft body of the living body is 6.536 μs (= 0.01 m / 1530 (m / S) = 1 cm / sound velocity), the attenuation in the soft body part is 10 ^{−0.00459 × t × f} (= 10 ^ ((− 0.6 / 20) /6.536) × t × f )). Corresponding to this equation, the constant k1 is obtained as k1 = ((0.6 / 20) /6.536) = 0.00459 ((μs × MHz) ⁻¹ ). That is, the constant k1 can be said to be a constant for correcting the attenuation (decrease in signal intensity) of the photoacoustic wave AW generated around the detection time t and the signal frequency f. The correction coefficient Z1 according to the above equation (1) can be said to be a correction coefficient that can increase the attenuation (decrease in signal intensity) of the photoacoustic wave AW generated in the subject P. Accordingly, by multiplying the photoacoustic wave signal by the correction coefficient Z1, the photoacoustic wave AW (see FIG. 2) generated in the subject P (see FIG. 2) is attenuated until it reaches the detection element 21 of the detection unit 20. Even if it does, it is possible to correct | amend the reduction | decrease of the signal intensity of the photoacoustic wave signals L1-LN resulting from attenuation | damping of this photoacoustic wave AW.

  The constant h is a value determined from the speed of sound in the subject P, and can be appropriately determined according to measurement conditions such as the subject P (human body or other animals) and the measurement site of the subject P. Is possible. In view of this point, the constant h is preferably 0.1 or more and 0.2 or less. For example, as a constant h when measuring a living body (human body) soft part, h = about 0.15 (cm / μs) can be used by converting sound velocity 1530 (m / s) in the soft body part as a unit. is there.

  Here, in the correction coefficient Z1, the term (h × t) multiplies the constant h (cm / μs) relating to the sound speed and the detection time t (μs), so that the depth in the subject P with respect to the detection element 21 is increased. It represents the distance (cm) in the vertical direction. Then, by providing this (h × t) term, it becomes possible to appropriately perform imaging processing by a back projection method to be described later.

As a correction process caused by the attenuation of the photoacoustic wave AW of the specific photoacoustic wave signals L1 to LN, the correction processing unit 44 acquires the NM coordinate data stored in the first memory 42 and has been acquired. The signal value (signal intensity) at each coordinate point in the NM coordinate data is configured to be multiplied by a correction coefficient Z1. Thereby, the correction | amendment process part 44 is comprised so that the signal strength of the photoacoustic wave signals L1-LN may be increased according to the value of the detection time t and the signal frequency f becoming large. For example, as shown in FIGS. 4 and 5, the signal value X _nm of the coordinate point (n, m) in the NM coordinate data is multiplied by the correction coefficient Z1 at the coordinate point (n, m) to obtain the coordinate point. A corrected signal value Y _nm (= Z1 × X _nm ) at (n, m) is obtained. Similarly, at all coordinate points of the NM coordinate data from the coordinate point (1, 1) to the coordinate point (N, M), the signal value at each coordinate point is multiplied by the correction coefficient Z1 at each coordinate point. Thus, the corrected NM coordinate data shown in FIG. As shown in FIG. 1, the correction processing unit 44 is configured to output the acquired corrected NM coordinate data to the second memory 45.

  Note that the photoacoustic wave signals L1 to LN corrected by the correction processing unit 44 may be either RF (Radio Frequency) signals (high frequency signals) or RF signals obtained by detecting the original RF signals. That is, the correction processing by the correction processing unit 44 may be performed on either the RF signal or the detected RF signal. In addition, in the case where correction processing is performed on the detected RF signal, it is possible to perform correction processing on the detected RF signal by providing a detection processing unit before the correction processing unit 44. .

  The second memory 45 is configured to store the corrected NM coordinate data (see FIG. 5) output from the correction processing unit 44. The second memory 45 is configured to be able to output the stored NM coordinate data to the back projection unit 46.

  The back projection unit 46 is configured to perform back projection based on the corrected NM coordinate data. Hereinafter, back projection by the back projection unit 46 will be described with reference to FIGS. 6 and 7.

  As shown in FIG. 6, the back projection unit 46 performs back projection based on the corrected NM coordinate data (see FIG. 5), thereby distributing the signal value in the imaging region AR corresponding to the inside of the subject P. Is configured to determine. Schematically, the back projection unit 46 has an imaging region AR based on a virtual setting of a plurality of semicircular distributed data D centered on the detection element 21 and an overlapping state of the set distributed data D. And the distribution of signal values at. First, virtual setting of a plurality of semicircular distributed data D centered on the detection element 21 by the back projection unit 46 will be described.

  Here, in the back projection method, the signal intensity of the photoacoustic wave signal at the detection time t is represented by an integrated value of the sound field at a distance (c × t) with respect to the detection element 21 where c is the speed of sound. . Specifically, in the back projection method, the signal intensity of the photoacoustic wave signal at the detection time t is expressed by an integral value of a sound field on a semicircular arc having a radius r = (c × t) with respect to the detection element 21. . In the first embodiment, the back projection unit 46 treats a sound field on a semicircular arc as distributed data D having a semicircular (band) region.

As shown in FIG. 6, the back projection unit 46 first virtually sets a plurality of distributed data D having a semi-annular region centered on the detection element 21. The plurality of distributed data D is virtually set in each detection element 21. In FIG. 6, a plurality (M pieces) of distributed data D _{n1 to} D _nM of the n-th detection element 21 are shown.

Here, each of the plurality of distributed data D has a signal value (signal intensity) corresponding to a coordinate point in the NM coordinate data. Specifically, each of the plurality of distributed data D has a signal value obtained by dividing the signal value Y _nm of the corresponding coordinate point by the area of the distributed data D. That is, it can be said that the signal values Y _nm of the corresponding coordinate points are evenly (uniformly) distributed in the semicircular (band-like) regions of the plurality of distributed data D. Further, the distributed data D can be composed of a plurality of unit pixels, for example. In this case, by assigning a value obtained by dividing the signal value Y _nm by the number of unit pixels included in the distributed data D to each unit pixel, it is possible to correspond in a semicircular (band) region of the plurality of distributed data D. It is possible to uniformly (uniformly) distribute the signal value Y _nm of the coordinate points.

The distributed data D will be specifically described with reference to FIG. For example, the first distributed data D _n1 in the nth detection element 21 has a signal value obtained by dividing the signal value Y _n1 of the coordinate point (n, 1) in the NM coordinate data by the area of the distributed data D _n1. Yes. That is, the signal value Y _{n1 at} the coordinate point (n, 1) is uniformly (uniformly) distributed in the semicircular region of the distributed data D _n1 . Similarly, 2 to M-th distributed data _D n2 _{to D nM} in the n-th detector element 21, the coordinate point in NM coordinate data signal values _Y n2 _{to Y nM} of (n, 2) ~ (n , M) Each has a signal value divided by the area of the distributed data D _{n2 to} D _nM .

The first dispersion data D _n1 in the nth detection element 21 corresponds to a detection time of 1 × p from the nth detection element 21 in the depth direction in the subject P in the subject P. It is virtually arranged at a distance. In addition, the second dispersion data D _n2 is virtually located in the subject P at a position corresponding to the detection time 2 × p from the nth detection element 21 in the depth direction in the subject P. Has been placed. That is, each of the distributed data D _{n1 to} D _nM in the nth detection element 21 is a distance (= p × c) corresponding to the sampling time p from the nth detection element 21 toward the depth direction in the subject P. ) At equal intervals.

  The back projection unit 46 virtually sets a plurality of semicircular distributed data D in each of the first to Nth detection elements 21 as in the case of the nth detection element 21. It is configured.

At this time, the area of the distributed data D increases as the distance in the depth direction increases. As a result, when the signal value Y _nm of the corresponding coordinate point is divided by the area of the dispersion data D, the signal value after the division greatly decreases as the distance in the depth direction increases. Therefore, in the first embodiment, in the correction coefficient Z1 of the above equation (1), a term (h × t) representing the distance in the depth direction in the subject P is provided, and the distance in the depth direction is increased. Accordingly, correction is performed in advance so that the signal value of each coordinate point in the NM coordinate data becomes large. As a result, it is possible to suppress the signal value after division from being greatly reduced as the distance in the depth direction increases. As a result, it is possible to appropriately perform the imaging process by the back projection method.

  In the first embodiment, the correction processing unit 44, when the value obtained by multiplying the constant h (cm / μs) and the detection time t (μs) in the term (h × t) is smaller than a predetermined value ( In other words, when the distance in the depth direction is less than a predetermined distance (cm), a value obtained by multiplying the constant h and the detection time t is set as the predetermined value. Here, when the light source unit 10 is disposed adjacent to the detection unit 20, the light from the light source unit 10 does not easily reach the vicinity of the detection element 21 of the detection unit 20. As a result, it is considered that a photoacoustic wave signal having a relatively small signal intensity can be easily obtained from a position where the distance in the depth direction is less than the predetermined distance. In view of this point, the predetermined value can be 0.5 or more and 1.5 or less (the predetermined distance is 0.5 cm or more and 1.5 cm or less). In the first embodiment, as described above, when the distance in the depth direction is less than the predetermined distance (when smaller than the predetermined value), a value obtained by multiplying the constant h and the detection time t is set as the predetermined value. To do. Thereby, it is possible to multiply the correction coefficient Z1 having a larger value than normal (value of h × t). As a result, it is possible to appropriately acquire the correction coefficient Z1 in consideration of a case where the light from the light source unit 10 is less than a predetermined distance that is difficult to reach.

  Next, with reference to FIG. 7, determination of the distribution of signal values in the imaging region AR based on the overlap state of the distributed data D set by the back projection unit 46 will be described.

  As shown in FIG. 7, the back projection unit 46 determines the signal value of each area of the imaging area AR based on the set overlapping state of the respective pieces of distributed data D, and thereby the signal in the imaging area AR. Determine the distribution of values. Hereinafter, with reference to FIG. 7, it demonstrates based on a specific example.

In FIG. 7, the dispersion data D _{1ma of} the first detection element 21 (data corresponding to the signal value of the coordinate point (1, ma)) and the dispersion data D _2mb of the second detection element 21 (coordinate point (2, mb) (data corresponding to the signal value), the dispersion data D _{nmc of the} nth detection element 21 (data corresponding to the signal value of the coordinate point (n, mc)), and the dispersion data of the Nth detection element 21 D _Nmd (data corresponding to the signal value of the coordinate point (N, md)). Note that the coordinate points ma to md of the M coordinate may be the same coordinate point or may be different from each other. As shown in FIG. 7, distributed data _{D 1ma,} D _2mb, the _{portion D nmc} and _{D Nmd} overlap each other (regions), overlapping distributed data _{D 1ma,} D _2mb, the signal values of _{D nmc} and _{D Nmd} are added As a result, the signal value of the imaging area AR of that portion is determined. In the non-overlapping portion, the signal value of the imaging area AR of the portion is determined by the value of the single distributed data D _1ma , D _2mb , D _nmc or D _Nmd . In FIG. 7, a portion where more distributed data D overlaps (in other words, a portion where the signal value is large) is illustrated so as to appear dark. Then, the distribution of signal values in the imaging area AR is determined by performing the above processing based on the overlapping state of all the distributed data D of each detection element 21. As a result, signal value distribution data (signal distribution data) in the imaging region AR is generated by the back projection unit 46. Then, a photoacoustic wave image is constructed (generated) based on the generated signal distribution data. That is, the constructed photoacoustic wave image is an image obtained by back projecting the signal value corrected by the correction processing unit 44. As shown in FIG. 1, the back projection unit 46 is configured to output a photoacoustic wave image (image data) based on the signal distribution data to the third memory 47.

  The third memory 47 is configured to store the photoacoustic wave image (image data) output from the back projection unit 46. The third memory 47 is configured to output the stored photoacoustic wave image to the monitor 32. As a result, the monitor 32 displays a clear photoacoustic wave image generated by the back projection method based on the photoacoustic wave signal in which the decrease in signal intensity is corrected. An image processing unit that performs image processing such as gradation adjustment can be further provided between the third memory 47 and the monitor 32.

  The apparatus main body 30 is provided with a monitor 32 including a general liquid crystal monitor. The monitor 32 is configured to display a photoacoustic wave image, various operation screens, and the like.

  The apparatus main body 30 is provided with a light source driving unit 33. The light source driving unit 33 is configured to perform control to cause the light source 11 of the light source unit 10 provided outside the apparatus main body 30 to emit light in pulses. Specifically, the light source driving unit 33 is configured to perform control so that the light source 11 of the light source unit 10 repeatedly emits pulsed light having a pulse width ta with a light emission period Ta. The light source driving unit 33 is configured to be able to adjust the pulse width ta, the light emission period Ta, and the current value for driving the light source 11 based on a control signal from the control unit 34 of the apparatus main body 30. That is, the photoacoustic imaging apparatus 100 is configured to be able to change the light irradiation condition by the light source unit 10 by changing the setting of the light source driving unit 33.

  The apparatus main body 30 is provided with a control unit 34. The control unit 34 includes a CPU and is configured to control each component of the apparatus main body 30. The control unit 34 is configured to control, for example, irradiation conditions of the light source unit 10 by the light source driving unit 33 and signal processing conditions by the signal processing unit 31.

  Next, with reference to FIG. 8, the photoacoustic wave image construction processing by the signal processing unit 31 of the apparatus main body 30 will be described based on a flowchart.

  First, in step S1, a photoacoustic wave signal is acquired. Specifically, the photoacoustic wave signals L1 to LN (see FIG. 4) are received by the receiving unit 41 (see FIG. 1) and stored in the first memory 42 (see FIG. 1), so that the signal processing unit 31. Obtained by At this time, the photoacoustic wave signals L1 to LN are stored in the first memory 42 as NM coordinate data before correction (see FIG. 4).

  In step S2, averaging processing of a plurality (P sets) of photoacoustic wave signals is performed. Specifically, a plurality (P pieces) of NM coordinate data corresponding to each of a plurality (P sets) of photoacoustic wave signals L1 to LN stored in the first memory 42 are averaged by the averaging processing unit 43. It is processed.

In step S3, the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW is corrected. Specifically, the acquisition of the NM coordinate data stored in the first memory 42 and the correction by multiplying the signal value (signal intensity) X _nm of each coordinate point in the acquired NM coordinate data by the correction coefficient Z1. This is performed by the correction processing unit 44. Thereby, the NM coordinate data (refer FIG. 5) by which the reduction | decrease of the signal strength of the photoacoustic wave signal resulting from attenuation | damping of the photoacoustic wave AW was correct | amended is obtained.

  In step S4, the corrected photoacoustic wave signal is backprojected. That is, in step S4, the back projection unit 46 performs back projection based on the corrected NM coordinate data obtained by the process of step S3. As a result, the signal distribution data in the imaging region AR is generated based on the overlapping state of the respective dispersion data D of each detection element 21 as shown in FIG. 7, and the photoacoustic wave image based on the signal distribution data is generated. Built.

  In step S 5, the photoacoustic wave image constructed by back projection is output from the third memory 47 to the monitor 32. As a result, a clear photoacoustic wave image obtained by the correction process is displayed on the monitor 32. And it returns to step S1 and acquisition of the following photoacoustic wave signal is performed.

  In the first embodiment, the following effects can be obtained.

  In the first embodiment, as described above, the reduction in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW is corrected, and light is projected by back projection based on the corrected photoacoustic wave signal. A signal processing unit 31 that generates an acoustic wave image is provided. Thereby, even if the photoacoustic wave AW generated in the subject is attenuated before reaching the detection unit 20, the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW can be corrected. it can. As a result, since the imaging process by the back projection method can be performed by the photoacoustic wave signal in which the decrease in signal intensity is corrected, a clear photoacoustic wave image can be obtained by the back projection method.

  In the first embodiment, as described above, the photoacoustic wave is based on both the detection time t until the photoacoustic wave signal is detected by the detection unit 20 and the signal frequency f of the photoacoustic wave signal. The signal processing unit 31 is configured to correct a decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the wave AW. Thereby, the decrease in the signal intensity of the photoacoustic wave signal can be reliably corrected based on the decrease (decrease amount) in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW.

  In the first embodiment, as described above, the signal intensity of the photoacoustic wave signal is increased by increasing the value of the detection time t and the signal frequency f, so that the photoacoustic wave AW is increased. The signal processing unit 31 is configured to correct a decrease in signal intensity of the photoacoustic wave signal due to attenuation. Thereby, the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW is increased in accordance with the decrease (decrease amount) of the signal intensity that increases as the values of the detection time t and the signal frequency f increase. be able to. As a result, the decrease in the signal intensity of the photoacoustic wave signal can be more reliably corrected in accordance with the decrease (decrease amount) in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW.

  In the first embodiment, as described above, when the unit of the detection time t is μs, the unit of the signal frequency f is MHz, and the constant k1 is 0.002 or more and 0.009 or less, the above formula is used. By multiplying the photoacoustic wave signal by the correction coefficient Z1 represented by (1), the signal intensity of the photoacoustic wave signal is increased as the values of the detection time t and the signal frequency f increase. The signal processing unit 31 is configured. Thereby, by using said Formula (1), the signal strength of a photoacoustic wave signal can be increased according to both detection time t and signal frequency f. As a result, the decrease in the signal intensity of the photoacoustic wave signal can be corrected more reliably according to the decrease (decrease amount) in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW. Moreover, the correction coefficient Z1 can be appropriately acquired by setting the constant k1 to be not less than 0.002 and not more than 0.009. In addition, by providing the term (h × t) in the above formula (1), it is possible to appropriately perform an imaging process in accordance with the characteristics of the back projection method.

  In the first embodiment, as described above, when the unit is (cm / μs) and the unit of the detection time t is μs, the constant h is set to 0.1 or more and 0.2 or less. If the value obtained by multiplying the constant h by the detection time t is smaller than the predetermined value, the value obtained by multiplying the constant h by the detection time t is set as the predetermined value. Thereby, since the value of the constant h is appropriately set, the correction coefficient Z1 can be acquired more appropriately.

  In the first embodiment, as described above, the predetermined value is 0.5 or more and 1.5 or less. Thereby, since the value of the constant h is set more appropriately, the correction coefficient Z1 can be acquired more appropriately.

  In the first embodiment, as described above, the light source 11 of the light source unit 10 is configured by at least one of a light emitting diode element, a semiconductor laser element, and an organic light emitting diode element. Thereby, compared with the case where a solid-state laser light source is used, advantages, such as reduction of the power consumption of the light source 11, and size reduction of the light source part 10, can be acquired. Here, when a light-emitting diode element, a semiconductor laser element, or an organic light-emitting diode element is used as the light source 11, the output of light emitted from the light source 11 is smaller than when a solid laser light source is used. For this reason, the signal intensity of the photoacoustic wave signal detected by the detection unit 20 is further reduced. Therefore, when a light emitting diode element, a semiconductor laser element or an organic light emitting diode element is used as the light source 11, the present invention that a clear photoacoustic wave image can be obtained by correcting a decrease in signal intensity is particularly effective. .

(Second Embodiment)
Next, a second embodiment will be described with reference to FIGS. 1, 2, 5, 6 and 9 to 11. In the second embodiment, in addition to the configuration of the first embodiment, an example in which a photoacoustic wave image is generated by a back projection method in consideration of sensitivity due to the incident direction of the photoacoustic wave AW with respect to the detection element 21. Will be described. In addition, about the structure same as the said 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  As shown in FIG. 1, the photoacoustic imaging apparatus 200 according to the second embodiment of the present invention includes a light source unit 10, a detection unit 20, and a photoacoustic imaging apparatus main body (hereinafter referred to as an apparatus main body) 130. ing. The apparatus main body 130 is provided with a signal processing unit 131. The signal processing unit 131 has the same configuration as the signal processing unit 31 of the first embodiment except that a back projection unit 146 is provided.

  As shown in FIG. 9, the detection element 21 has different sensitivity (detection sensitivity) depending on from which direction (incident direction) the photoacoustic wave AW (see FIG. 2) is incident. For example, the rectangular detection element 21 shown in FIG. 9 has the highest sensitivity when the photoacoustic wave AW is incident on the detection surface of the detection element 21 from the vertical direction. The sensitivity decreases as the incident angle θ, which is an angle formed between the direction perpendicular to the detection surface and the incident direction of the photoacoustic wave AW, increases. In FIG. 9, the magnitude of the sensitivity of the first detection element 21 with respect to the incident angle θ is conceptually represented by the length of the arrow.

  In the second embodiment, as shown in FIG. 1, the back projection unit 146 performs the back projection based on the corrected NM coordinate data (see FIG. 5), and the incident direction of the photoacoustic wave AW with respect to the detection element 21. The signal distribution data in the imaging area AR (see FIG. 6) is generated in consideration of the sensitivity due to the above.

Specifically, as shown in FIG. 10, when the back projection unit 146 first sets a plurality of semicircular distributed data D centering on the detection element 21, the photoacoustic for the detection element 21 is set. In consideration of the sensitivity due to the incident direction of the wave AW, the signal values of the plurality of dispersion data D are set. For example, as shown in FIG. 10, in the dispersion data D _nm in the nth detection element 21, the signal value (corresponding coordinate point) when the signal value Y _nm corresponding to the coordinate point in the NM coordinate data is evenly dispersed. in signal value the signal value obtained by dividing the Y _nm in the area of the distributed data D) a is a, the sensitivity at an incident angle theta = 0 of the detecting element 21 is 1, the incident angle _{θ = θ 1 (0 <θ} 1) The sensitivity is 0.7, and the sensitivity at an incident angle θ = θ ₂ (θ ₁ <θ ₂ ) is 0.5. In this case, as shown in FIG. 10, the signal value is set to a × 1 in the region corresponding to the incident direction of the incident angle θ = 0 in the semicircular region of the dispersion data D _nm . Similarly, in the region corresponding to the incident direction of the incident angle theta = theta _1, sets the signal value to a × 0.7, in the region corresponding to the incident direction of the incident angle theta = theta ₂ is a signal value a × Set to 0.5. In this way, the back projection unit 146 considers the sensitivity due to the incident direction of the photoacoustic wave AW with respect to the detection element 21, and the signal value of the region corresponding to the incident direction of the incident angle θ in the plurality of dispersion data D. Set.

  And in 2nd Embodiment, the back projection part 146 is based on the overlapping state of the dispersion data D set in consideration of the sensitivity resulting from the incident direction of the photoacoustic wave AW with respect to the detection element 21. The signal value distribution in the AR is determined. The method for generating signal distribution data by determining the distribution of signal values is the same as in the first embodiment. Thereafter, the photoacoustic wave image based on the signal distribution data is stored in the third memory 47 as in the first embodiment.

  That is, in the second embodiment, the correction processing unit 44 corrects the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW using the correction coefficient Z1 according to the equation (1). In consideration of the sensitivity due to the incident direction of the photoacoustic wave AW with respect to the detection element 21, signal distribution data in the imaging region AR is generated by the back projection unit 146, and photoacoustics are generated based on the signal distribution data. A wave image is constructed (generated).

  Next, with reference to FIG. 11, the photoacoustic wave image construction process by the signal processing unit 131 of the apparatus main body 130 of the second embodiment will be described based on a flowchart.

  First, in step S1, a photoacoustic wave signal is acquired, and then in step S2, a plurality (P sets) of photoacoustic wave signals are averaged. In step S3, the correction processing unit 44 corrects the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW. The processing in steps S1 to S3 is the same as that in the first embodiment.

  In step S4a, the back projection unit 146 performs back projection in consideration of the sensitivity due to the incident direction with respect to the detection element 21. Specifically, acquisition of NM coordinate data after correction by the correction processing unit 44 stored in the second memory 45, virtual setting of the distributed data D based on the acquired NM coordinate data, and the set variance The back projection unit 146 generates the signal distribution data in the imaging area AR based on the overlapping state of the data D. In addition, when the dispersion data D is virtually set based on the acquired NM coordinate data, the dispersion data D is virtually set in consideration of the sensitivity due to the incident direction with respect to the detection element 21. As a result of the processing of steps S3 and S4a, an imaging region in which a decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW is corrected and the sensitivity due to the incident direction with respect to the detection element 21 is considered Signal distribution data in the AR is obtained. In step S4a, a photoacoustic wave image based on the signal distribution data is constructed.

  Thereafter, the process of step S5 is performed as in the first embodiment. As a result, also in the second embodiment, a clear photoacoustic wave image is displayed on the monitor 32. And it returns to step S1 and acquisition of the following photoacoustic wave signal is performed.

  In addition, the other structure of 2nd Embodiment is the same as that of the said 1st Embodiment.

  In the second embodiment, the following effects can be obtained.

  In the second embodiment, as described above, in addition to correcting the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW, it is caused by the incident direction of the photoacoustic wave AW with respect to the detection element 21. In consideration of the sensitivity, the signal processing unit 131 is configured to generate a photoacoustic wave image by the back projection method. Thereby, when generating a photoacoustic wave image by the back projection method, the difference in sensitivity of the detection element 21 due to the incident direction of the photoacoustic wave AW can be taken into consideration, so that the subject P (see FIG. 2). A photoacoustic wave image close to the actual condition can be obtained. As a result, the sharpness of the photoacoustic wave image is improved by correcting the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW, and in the incident direction of the photoacoustic wave AW with respect to the detection element 21. By taking into account the resulting sensitivity, a photoacoustic wave image close to the actual condition in the subject P can be obtained. Therefore, in the second embodiment, a photoacoustic wave image that is clear and close to the actual condition in the subject P can be obtained by the back projection method.

  The remaining effects of the second embodiment are similar to those of the aforementioned first embodiment.

(Third embodiment)
Next, a third embodiment will be described with reference to FIGS. 1 and 12 to 16. In the third embodiment, in addition to the configuration of the first embodiment, an example in which a decrease in signal intensity of a photoacoustic wave signal due to attenuation of light from the light source unit 10 is corrected will be described. In addition, about the structure same as the said 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  As shown in FIG. 1, the photoacoustic imaging apparatus 300 according to the third embodiment of the present invention includes a light source unit 10, a detection unit 20, and a photoacoustic imaging apparatus main body (hereinafter referred to as apparatus main body) 230. ing. The apparatus main body 230 is provided with a signal processing unit 231. The signal processing unit 231 has the same configuration as the signal processing unit 31 of the first embodiment except that the correction processing unit 244 is provided.

  In the third embodiment, the correction processing unit 244 corrects the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW, and in addition, corrects the light due to the attenuation of the light from the light source unit 10. It is configured to correct a decrease in the signal intensity of the acoustic wave signal. That is, in the third embodiment, the attenuation of the photoacoustic wave AW that occurs in the subject P (see FIG. 12) and reaches the detection element 21 of the detection unit 20 and the light source unit 10 are irradiated. The correction processing by the correction processing unit 244 is performed in consideration of both the attenuation of light until reaching the detection target Q (see FIG. 12) in the subject P.

  Specifically, the correction processing unit 244 corrects the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW by the correction coefficient Z1 according to the equation (1), as in the first embodiment. Is configured to do. In the third embodiment, the correction processing unit 244 is further configured based on the distance d from the light irradiation position of the light source unit 10 to the subject P to a predetermined position in the subject P from the light source unit 10. The photoacoustic wave signal due to light attenuation is corrected for reduction. In the third embodiment, the distance d is obtained corresponding to the NM coordinate data. For example, the distance d to the predetermined position Po in the subject P shown in FIG. 12 is as shown in FIG. 13 with respect to the detection time t = m × p of the coordinate point (1, m) in the NM coordinate data. , By multiplying by the sound speed c, d = m × p × c. That is, the distance d from the light irradiation position by the light source unit 10 to a predetermined position in the subject P is obtained by replacing the distance d from the detection element 21 to the predetermined position in the subject P. For other coordinate points, the distance d can be obtained by the same calculation.

  In the configuration for obtaining the distance d in this way, as shown in FIGS. 12 and 14, the width W1 of the light source 11 of the light source unit 10 in the arrangement direction in which the plurality of detection elements 21 are arranged is equal to the plurality of detection elements 21. It is configured to be larger than the overall width W2 in the arrangement direction. Thus, even if the distance d from the light irradiation position by the light source unit 10 to a predetermined position in the subject P is replaced with the distance from the detection element 21 to the predetermined position in the subject P, the light source 11 is larger than the width W2 in the arrangement direction of the plurality of detection elements 21, it is possible to reliably correspond the positional relationship between the light irradiation position by the light source unit 10 and the detection elements 21.

In the third embodiment, the correction processing unit 244 uses the correction coefficient Z2 expressed by the following equation (2) as the photoacoustic wave signal when the constant related to the light irradiation position by the light source unit 10 is k2. , The photoacoustic wave signal resulting from the attenuation of the light from the light source unit 10 as the distance d from the light irradiation position by the light source unit 10 to the predetermined position in the subject P increases. It is configured to correct for a decrease in signal strength.
Z2 = 10 ^{k2 × d} (2)

Specifically, the correction processing unit 244 applies the signal value (signal intensity) of each coordinate point in the NM coordinate data stored in the first memory 42 as in the case of the correction coefficient Z1 of the first embodiment. Thus, by multiplying by Z2, the photoacoustic attributed to the attenuation of light from the light source unit 10 as the distance d from the light irradiation position by the light source unit 10 to a predetermined position in the subject P increases. It is configured to correct a decrease in signal strength of the wave signal. That is, in the third embodiment, both the correction coefficients Z1 and Z2 are multiplied by the signal value (signal intensity) of each coordinate point in the NM coordinate data stored in the first memory 42. For example, as shown in FIG. 13, by multiplying the signal value X _nm of the coordinate point (n, m) in the NM coordinate data by both the correction coefficients Z1 and Z2 at the coordinate point (n, m), the coordinates A corrected signal value Y _nm (= Z1 × Z2 × X _nm ) at the point (n, m) is obtained. Similarly, at all the coordinate points of the NM coordinate data from the coordinate point (1, 1) to the coordinate point (N, M), the correction coefficients Z1 and Z2 at each coordinate point with respect to the signal value at each coordinate point. Both are multiplied, and the corrected NM coordinate data shown in FIG. 13 is acquired by the correction processing unit 244. Then, the corrected NM coordinate data is output from the correction processing unit 244 to the second memory 45. Thereafter, as in the first embodiment, back projection is performed by the back projection unit 46, and a photoacoustic wave image is constructed (generated).

  Here, the constant k2 is a constant related to the light irradiation position by the light source unit 10 as described above. Specifically, the constant k2 is a constant related to the distance d from the irradiation position of the light from the light source unit 10 to the subject P to a predetermined position in the subject P. That is, it is a constant for correcting light attenuation (decrease in light intensity) generated in the subject P with respect to the distance d. Then, it is possible to correct the decrease in the signal intensity of the photoacoustic wave signal caused by the attenuation of the light by correcting the attenuation (the decrease in the light intensity) of the light generated in the subject P with respect to the distance d. It is.

  The constant k2 can be appropriately determined according to measurement conditions such as the subject P (human body or other animals) and the measurement site of the subject P. In view of this point, as illustrated in FIG. 12, when the light irradiation position by the light source unit 10 is on the detection unit 20 side (in other words, the light source unit 10 is disposed adjacent to the detection unit 20, and the light source unit 10 When the unit of the distance d (= m × p × c) is cm, the constant k2 is 0.2 or more and 0.8. The following is preferable. When the constant k2 is a positive value, the correction coefficient Z2 is larger than 1. In this case, the signal intensity of the photoacoustic wave signal is increased from the light source unit 10 by increasing the signal intensity of the photoacoustic wave signal as the distance d from the light irradiation position by the light source unit 10 to the predetermined position in the subject P increases. A decrease in signal intensity of the photoacoustic wave signal due to light attenuation is corrected. That is, in this case, by increasing the signal intensity of the photoacoustic wave signal, each coordinate of the NM coordinate data due to a decrease in the signal intensity of the photoacoustic wave signal caused by attenuation of light from the light source unit 10 is obtained. Corrections are made to reduce the relative signal strength differences at the points.

  Further, as shown in FIG. 14, when the light irradiation position by the light source unit 10 is on the side opposite to the detection unit 20 (in other words, the light source unit 10 is arranged to face the detection unit 20, and the light source unit 10 When the unit of the distance d is cm when the light irradiation position faces the detection unit 20), the constant k2 is preferably −0.8 or more and −0.2 or less. Even when the irradiation position of the light source unit 10 is on the side opposite to the detection unit 20, the virtual irradiation position in the subject P from the virtual irradiation position when the light irradiation position by the light source unit 10 is on the detection unit 20 side is also used. The distance to the predetermined position is d (= m × p × c). When the constant k2 is a negative value, the correction coefficient Z2 is less than 1. In this case, the light from the light source unit 10 is reduced by reducing the signal intensity of the photoacoustic wave signal as the distance d from the virtual light irradiation position to a predetermined position in the subject P increases. The decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of is corrected. In other words, the signal intensity of the photoacoustic wave signal is decreased so that the amount of decrease in the signal intensity of the photoacoustic wave signal decreases as the distance from the light irradiation position by the actual light source unit 10 increases. Thus, the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of light from the light source unit 10 is corrected. Thereby, in this case, by reducing the signal intensity of the photoacoustic wave signal, each of the NM coordinate data due to the decrease in the signal intensity of the photoacoustic wave signal caused by the attenuation of the light from the light source unit 10 is obtained. Correction is made so that the relative signal intensity difference at the coordinate points is reduced.

  As a result, the distance d according to the same equation is used when the light irradiation position by the light source unit 10 is on the detection unit 20 side and when the light irradiation position by the light source unit 10 is on the side opposite to the detection unit 20. It is possible to correct so that the difference in relative signal intensity at each coordinate point of the NM coordinate data is reduced.

Here, with reference to FIG. 15, the result of an experiment performed to determine the constant k2 will be described. FIG. 15 shows a semilogarithmic graph in which the horizontal axis is thickness (cm), the vertical axis is light transmittance (%), and the vertical axis is logarithmic. Experiments were performed on air (air layer), agar, chicken and pork. In the experiment, near infrared light (light having a center wavelength of 850 nm) was used. As shown in FIG. 15, the degree of decrease in transmittance (light attenuation) is the smallest in the case of air, and the degree of decrease in light transmittance (light attenuation) is the largest in the case of pork. In the case of pork, the thickness was 3 cm and the transmittance was 1.5%. Therefore, the constant k2 is k2 = −Log (1.5 / 100) / 3 = about 0.6 (cm ⁻¹ ) in terms of attenuation of light per 1 cm in the case of pork. In the case of air, the thickness was 3 cm and the transmittance was 33%. Therefore, the constant k2 becomes k2 = −Log (33/100) / 3 = about 0.2 (cm ⁻¹ ) in terms of attenuation of light per 1 cm in the case of air. In consideration of light attenuation in the subject P such as a human body, the constant k2 is 0.2 or more and 0.6 or less (the light irradiation position by the light source unit 10 shown in FIG. 12 is on the detection unit 20 side). ), Or -0.6 or more and -0.2 or less (when the light irradiation position by the light source unit 10 shown in FIG. 14 is opposite to the detection unit 20) is more preferable.

  Next, with reference to FIG. 16, the photoacoustic wave image construction process by the signal processing unit 231 of the apparatus main body 230 of the third embodiment will be described based on a flowchart.

  First, in step S1, a photoacoustic wave signal is acquired, and then in step S2, a plurality (P sets) of photoacoustic wave signals are averaged. Steps S1 and S2 are the same as those in the first embodiment.

  In step S3a, the correction of the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW and the correction of the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the light from the light source unit 10 are performed. And both are done. Specifically, the acquisition of NM coordinate data stored in the first memory 42 and the signal value (signal intensity) of each coordinate point in the acquired NM coordinate data are multiplied by both of the correction coefficients Z1 and Z2. Correction is performed by the correction processing unit 244. Thereby, both the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW and the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the light from the light source unit 10 were corrected. NM coordinate data is obtained.

  In step S4, the photoacoustic wave signal subjected to the two corrections is back-projected. Thereafter, the process of step S5 is performed as in the first embodiment. As a result, also in the third embodiment, a clear photoacoustic wave image is displayed on the monitor 32. And it returns to step S1 and acquisition of the following photoacoustic wave signal is performed.

  The remaining configuration of the third embodiment is similar to that of the aforementioned first embodiment.

  In the third embodiment, the following effects can be obtained.

  In the third embodiment, as described above, in addition to correcting the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW, the light emission position from the light source unit 10 with respect to the subject P is determined. As the distance d to the predetermined position (Po) in the subject P increases, the signal processing is performed so as to correct the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the light from the light source unit 10. The unit 231 is configured. Thereby, even if the light from the light source unit 10 is attenuated before reaching the detection target Q in the subject P, the signal intensity of the photoacoustic wave signal due to the attenuation of the light from the light source unit 10 is reduced. It can be corrected. As a result, in addition to correcting the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW, the signal intensity of the photoacoustic wave signal due to the attenuation of the light from the light source unit 10 is reduced. It can be corrected. Therefore, the decrease in the signal intensity of the photoacoustic wave signal can be corrected more appropriately. Therefore, in the third embodiment, a clearer photoacoustic wave image can be obtained by back projection.

  In the third embodiment, as described above, the photoacoustic wave signal is multiplied by the correction coefficient Z2 represented by the above equation (2), so that the position from the irradiation position to a predetermined position in the subject P is obtained. As the distance d increases, the signal processing unit 231 is configured to correct a decrease in signal intensity of the photoacoustic wave signal due to attenuation of light from the light source unit 10. Thereby, by using the above formula (2), the light intensity from the light source unit 10 is surely caused by the light attenuation from the light source unit 10 according to the decrease (decrease amount) of the signal intensity due to the light attenuation from the light source unit 10. It is possible to correct a decrease in the signal intensity of the photoacoustic wave signal.

  In the third embodiment, as described above, when the irradiation position of the light source unit 10 is on the detection unit 20 side, the unit of the distance d from the irradiation position to a predetermined position in the subject P is cm. In this case, the constant k2 is set to 0.2 or more and 0.8 or less. Further, when the irradiation position of the light source unit 10 is on the side opposite to the detection unit 20, from the irradiation position when the irradiation position of the light source unit 10 is on the detection unit 20 side to a predetermined position in the subject P. When the distance is d and the unit of the distance d from the irradiation position to the predetermined position in the subject P is cm, the constant k2 is set to −0.8 or more and −0.2 or less. Thereby, according to the irradiation position of the light by the light source part 10, the correction coefficient Z2 can be acquired appropriately. As a result, the signal intensity of the photoacoustic wave signal resulting from the attenuation of light from the light source unit 10 can be appropriately increased.

  In the third embodiment, as described above, the width W1 of the light source unit 10 in the arrangement direction in which the plurality of detection elements 21 are arranged is larger than the width W2 in the arrangement direction of the plurality of detection elements 21. Thereby, the light from the light source part 10 can be reliably irradiated over the entire region in the arrangement direction of the plurality of detection elements 21. As a result, the photoacoustic wave AW is sufficiently generated from the detection object Q within the range detectable by the plurality of detection elements 21 due to the small amount of light irradiation within the range detectable by the plurality of detection elements 21. It is possible to suppress the failure to occur. Thereby, it is possible to suppress the detection of the detection target Q within the range detectable by the plurality of detection elements 21 from being appropriately performed by the plurality of detection elements 21.

  The remaining effects of the third embodiment are similar to those of the aforementioned first embodiment.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiment but by the scope of claims for patent, and further includes all modifications (modifications) within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the first to third embodiments, the example in which the control unit 34 is provided separately from the signal processing unit 31 (131, 231) is shown, but the present invention is not limited to this. In the present invention, a part of the function of the signal processing unit may be performed by the control unit.

  In the second embodiment, the reduction in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW is corrected, and the sensitivity due to the incident direction of the photoacoustic wave AW with respect to the detection element 21 is considered. In the third embodiment, the correction of the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW and the photoacoustic wave signal due to the attenuation of light from the light source unit 10 are performed. Although an example in which back-projection is performed while performing two corrections, i.e., correction of a decrease in signal intensity of the present invention, the present invention is not limited to this. In the present invention, there are two corrections: a correction of a decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave, and a correction of a decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the light from the light source unit. While performing correction, back projection may be performed in consideration of the sensitivity due to the incident direction of the photoacoustic wave with respect to the detection element. Thereby, a clearer image close to the actual condition in the subject can be obtained by back projection.

  In the first to third embodiments, the correction of the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave AW is performed based on both the detection time t and the signal frequency f. Although shown, the present invention is not limited to this. In the present invention, the correction of the decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave may be performed based on at least one of the detection time and the signal frequency.

  In the first to third embodiments, the receiving unit 41 includes a plurality (N) of amplifying units 51 and a plurality (N) corresponding to the plurality (N) of detecting elements 21 of the detecting unit 20. However, the present invention is not limited to this. In the present invention, the receiving unit may be provided with an amplifying unit and an A / D conversion unit with a smaller number than the plurality of detecting elements of the detecting unit. In this case, the N photoacoustic wave signals detected by the plurality of detection elements of the detection unit may be divided and received multiple times. Thereby, since the structure of a receiving part can be simplified, the structure of a photoacoustic imaging device can be simplified correspondingly.

  Moreover, although the example which provided the one light source 11 in the light source part 10 was shown in the said 1st-3rd embodiment, this invention is not limited to this. In the present invention, a plurality of light sources may be provided in the light source unit, and each of the plurality of light sources may be configured to emit light having a plurality of different wavelengths. In this case, the photoacoustic wave signal by a plurality of wavelengths or the synthesized photoacoustic wave signal obtained by synthesizing the respective photoacoustic wave signals by a plurality of wavelengths is corrected, and photoacoustic is performed by back projection. You may comprise so that a wave image may be produced | generated. As a result, even in a configuration in which a plurality of photoacoustic wave signals are obtained with light of a plurality of wavelengths, a photoacoustic wave is obtained based on a photoacoustic wave signal of a single wavelength light while obtaining a clear photoacoustic wave image by back projection. Compared to the case of obtaining an image, a photoacoustic wave image including more various information in the subject can be obtained.

  In the first embodiment, the correction coefficient Z1 expressed by the equation (1) is used for correction. In the third embodiment, the correction coefficient Z2 expressed by the equation (2) is used for correction. The present invention is not limited to this. In the present invention, the equations of the correction coefficients Z1 and Z2 may be used in a simplified manner. For example, in the case of the first embodiment, the correction coefficient Z1 may be simplified and used as Z1 = h × t × 2.3 × (1+ (k1 × t × f)). In the case of the second embodiment, the correction coefficient Z1 × Z2 is simplified to Z1 × Z2 = h × t × 2.3 × (1+ (k1 × t × f) + (k2 × d)). May be used. As a result, the processing time related to the correction processing can be shortened by the amount of simplification of the correction coefficient.

  Moreover, in the said 1st-3rd embodiment, it demonstrates using the flow drive type flowchart which processes for the process of the signal processing part 31 (131,231) of this invention in order along a processing flow for convenience of explanation. However, the present invention is not limited to this. In the present invention, the processing operation of the signal processing unit 31 (131, 231) may be performed by event-driven (event-driven) processing that executes processing for each event. In this case, it may be performed by a complete event drive type or a combination of event drive and flow drive.

DESCRIPTION OF SYMBOLS 10 Light source part 11 Light source 20 Detection part 21 Detection element 31, 131, 231 Signal processing part 100, 200, 300 Photoacoustic imaging device L1-LN Photoacoustic wave signal

Claims (13)

A light source unit;
A detection unit for detecting a photoacoustic wave signal caused by a photoacoustic wave generated from a detection target in a subject that has absorbed light from the light source unit;
A signal processing unit that corrects a decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave, and generates an image by back projection based on the corrected photoacoustic wave signal; A photoacoustic imaging apparatus.   The signal processing unit is caused by attenuation of the photoacoustic wave based on at least one of a detection time until the photoacoustic wave signal is detected by the detection unit or a signal frequency of the photoacoustic wave signal. The photoacoustic imaging apparatus according to claim 1, configured to correct a decrease in signal intensity of the photoacoustic wave signal.   The signal processing unit is caused by attenuation of the photoacoustic wave by increasing the signal intensity of the photoacoustic wave signal in accordance with an increase in at least one value of the detection time or the signal frequency. The photoacoustic imaging apparatus according to claim 2, wherein the photoacoustic imaging apparatus is configured to correct a decrease in signal intensity of the photoacoustic wave signal. The signal processing unit sets a constant related to sound speed as h, the detection time as t, the signal frequency as f, a constant as to the detection time and the signal frequency as k1, and a unit of the detection time t as μs, When the unit of the signal frequency f is MHz and the constant k1 is 0.002 or more and 0.009 or less, the photoacoustic wave signal is multiplied by the correction coefficient Z1 represented by the following formula (1). The photoacoustic imaging apparatus according to claim 3, configured to increase a signal intensity of the photoacoustic wave signal as the detection time and the signal frequency increase.
Z1 = h × t × 10 ^{k1 × t × f} (1) The constant h is 0.1 or more and 0.2 or less when the unit is (cm / μs),
The light according to claim 4, wherein when the value obtained by multiplying the constant h and the detection time t is smaller than a predetermined value, a value obtained by multiplying the constant h and the detection time t is set as the predetermined value. Acoustic imaging device.   The photoacoustic imaging apparatus according to claim 5, wherein the predetermined value is not less than 0.5 and not more than 1.5. The detection unit includes a detection element for receiving the photoacoustic wave and detecting the photoacoustic wave signal caused by the photoacoustic wave;
In addition to correcting a decrease in signal intensity of the photoacoustic wave signal due to attenuation of the photoacoustic wave, the signal processing unit considers sensitivity due to the incident direction of the photoacoustic wave with respect to the detection element. And the photoacoustic imaging device of any one of Claims 1-6 comprised so that an image may be produced | generated by the back projection method.   8. The photoacoustic imaging apparatus according to claim 1, wherein the light source unit includes at least one of a light emitting diode element, a semiconductor laser element, and an organic light emitting diode element as a light source.   The signal processing unit corrects a decrease in the signal intensity of the photoacoustic wave signal due to the attenuation of the photoacoustic wave, and in addition, from the irradiation position of the light by the light source unit to the subject, As the distance to the predetermined position increases, the signal intensity decrease of the photoacoustic wave signal due to attenuation of light from the light source unit is corrected. 9. The photoacoustic imaging apparatus according to any one of items 8. The signal processing unit has a correction coefficient Z2 expressed by the following equation (2), where k2 is a constant related to the irradiation position and d is a distance from the irradiation position to a predetermined position in the subject. Is multiplied by the photoacoustic wave signal, and the photoacoustic wave resulting from attenuation of light from the light source unit as the distance from the irradiation position to a predetermined position in the subject increases. The photoacoustic imaging device according to claim 9, configured to correct a decrease in signal strength of the signal.
Z2 = 10 ^{k2 × d} (2) The constant k2 is 0.2 when the unit of the distance d from the irradiation position to a predetermined position in the subject is cm when the irradiation position of the light source unit is on the detection unit side. Is 0.8 or less,
When the irradiation position of the light source unit is on the side opposite to the detection unit, the constant k2 is calculated from the irradiation position in the case where the irradiation position of the light source unit is on the detection unit side. When the distance to the predetermined position is d and the unit of the distance d from the irradiation position to the predetermined position in the subject is cm, it is −0.8 or more and −0.2 or less. The photoacoustic imaging apparatus according to claim 10. In the detection unit, a plurality of detection elements for receiving the photoacoustic wave and detecting the photoacoustic wave signal resulting from the photoacoustic wave are arranged,
The photoacoustic image according to any one of claims 1 to 11, wherein a width of the light source unit in an arrangement direction in which the plurality of detection elements are arranged is larger than a width in the arrangement direction of the plurality of detection elements. Device. A step of detecting a photoacoustic wave signal caused by a photoacoustic wave generated from a detection target in a subject that has absorbed light from the light source unit, by a detection unit;
Correcting a decrease in signal intensity of the photoacoustic wave signal due to attenuation of the photoacoustic wave by a signal processing unit;
Generating a back projection image based on the corrected photoacoustic wave signal by the signal processing unit, and a photoacoustic image construction method.

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