JP2017046823A - Photoacoustic imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoacoustic imaging apparatus capable of controlling frequency characteristics of a detected photoacoustic wave so as to conform to a frequency bandwidth of a detection unit (ultrasonic probe) by a method other than a method in which a pulse width of a pulse light is controlled.SOLUTION: A photoacoustic imaging apparatus includes: a light source unit 11; a detection unit 12 for detecting an acoustic wave A generated from the inside of a subject P and attributed to the irradiation of light onto a subject P by the light source unit 11; and a light source drive unit 21 for supplying power to the light source unit 11 and driving the light source unit 11. The light source drive unit 21 sets a ratio of a rising inclination of a pulse waveform of the light irradiated from the light source unit 11 to a falling inclination thereof based on a detection frequency (frequency bandwidth) of the detection unit 12, and makes an absolute value of the ratio of the inclinations larger as the range of the detection frequency of the detection unit 12 is wider.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a photoacoustic imaging apparatus, and more particularly, to a photoacoustic imaging apparatus including a light source driving unit that controls pulsed light from a light source unit based on a detection frequency band of a detection unit.

  2. Description of the Related Art Conventionally, a photoacoustic imaging apparatus including a light source driving unit that controls pulsed light from a light source unit based on a detection frequency band of a detection unit is known (see, for example, Patent Document 1).

  Patent Document 1 discloses a photoacoustic imaging apparatus including a light source unit. This photoacoustic imaging apparatus is provided with an ultrasonic probe and an imaging unit. The light source unit includes a Q-switch pulse laser light source. The photoacoustic imaging apparatus is configured to irradiate a subject with laser light by a light source unit and detect an acoustic wave signal generated from the subject by an ultrasonic probe. The imaging unit is configured to image the acoustic wave signal detected by the ultrasonic probe. The photoacoustic imaging apparatus is configured to adjust the pulse width of the pulsed light from the Q-switch pulse laser light source in accordance with the frequency band of the ultrasonic probe.

JP 2013-128722 A

  However, the photoacoustic imaging apparatus of Patent Document 1 is configured to adjust the pulse width of the pulsed light from the light source according to the frequency band of the ultrasonic probe. Here, depending on the frequency band of the ultrasonic probe, the frequency characteristic of the detected acoustic wave is controlled so as to match the frequency band of the ultrasonic probe only by controlling the pulse width of the pulsed light. The problem is that it is difficult.

  The present invention has been made to solve the above-described problems, and one object of the present invention is to provide a detection unit (ultrasonic probe) by a method other than the method for controlling the pulse width of pulsed light. The photoacoustic imaging apparatus is capable of controlling the frequency characteristics of the detected acoustic wave so as to be adapted to the frequency band.

  In the photoacoustic imaging apparatus according to one aspect of the present invention, a light source unit, a detection unit that detects an acoustic wave generated from the inside of the subject due to light being irradiated on the subject by the light source unit, and a light source A light source driving unit that drives the light source unit by supplying power to the unit, and the light source driving unit is configured to start rising of a pulse waveform of light emitted from the light source unit based on a detection frequency (frequency band) of the detection unit. The ratio between the inclination and the falling inclination is set, and the absolute value of the inclination ratio is increased as the detection frequency range of the detection unit is wider.

  In the photoacoustic imaging apparatus according to one aspect of the present invention, based on the detection frequency of the detection unit, while setting the ratio of the rising slope and the falling slope of the pulse waveform of the light emitted from the light source unit, The absolute value of the ratio of the inclination is increased as the detection frequency range of the detection unit is wider. Here, the frequency range (frequency characteristics) of the detected acoustic wave can be expanded by increasing the absolute value of the ratio of the slopes of the pulse waveforms. According to the configuration of the present invention, even when the detection frequency range of the detection unit is wide, it is possible to adapt the frequency range of the acoustic wave and the detection frequency of the detection unit by increasing the absolute value of the slope of the pulse waveform. Therefore, the frequency characteristic of the detected acoustic wave can be controlled by a method other than the method of controlling the pulse width of the pulsed light so as to be adapted to the frequency band of the detection unit.

  In the photoacoustic imaging apparatus according to the above aspect, preferably, the light source driving unit is configured such that one of the absolute value of the rising slope or the absolute value of the falling slope is 1.5 times or more and 10 times or less of the other. It is comprised so that it may become. If comprised in this way, the frequency range of the detected acoustic wave is made by making one of the absolute value of the rising slope or the absolute value of the falling slope 1.5 times or more and 10 times or less of the other. Since it can be easily expanded, the frequency characteristic of the detected acoustic wave can be easily controlled so as to be adapted to the frequency band of the detector by a method other than the method of controlling the pulse width of the pulsed light.

  In the photoacoustic imaging apparatus according to the above aspect, the light source driving unit is preferably configured such that the half width of the pulse waveform is 12.5 nsec or more and 500 nsec or less. Here, if the pulse width is too narrow, less than 12.5 nsec, even if the absolute value of the slope ratio is increased, only the wide band that does not affect reception spreads and the peak frequency decreases. If the pulse width exceeds 500 nsec and is too wide, the amplitude of the peak frequency becomes small. Therefore, if the half width of the pulse waveform is set to 12.5 nsec or more and 500 nsec or less, the amplitude of the peak frequency can be ensured, so that the acoustic wave from the subject can be detected efficiently.

  In this case, it is preferable that the half width of the pulse waveform is 50 nsec or more and 200 nsec or less. With this configuration, the amplitude of the peak frequency can be ensured more reliably by setting the half width of the pulse waveform to 50 nsec or more and 200 nsec or less, so that the acoustic wave from the subject can be detected more efficiently. Can do.

  In the photoacoustic imaging apparatus according to the above aspect, the light source driving unit is preferably configured such that the absolute value of the falling slope is larger than the absolute value of the rising slope. Here, the response characteristic of the light emitting element (for example, LED) generally falls faster than the rising edge, and falls sharply only by stopping the supply of current flowing through the light emitting element. Therefore, by configuring as described above, the absolute value of the slope of the falling edge of the pulse waveform can be increased, so that the frequency characteristics of the detected acoustic wave can be easily adapted to the frequency band of the detection unit. Can be controlled.

  The photoacoustic imaging apparatus according to the above aspect is preferably configured such that the light source driving unit sets the pulse width to be smaller as the maximum frequency of the acoustic wave that can be detected by the detection unit is larger. . Here, the acoustic wave generated from the subject is generated as an acoustic wave having a frequency equal to or lower than the maximum frequency with a frequency having a reciprocal value of the pulse width irradiated to the subject as a maximum frequency. Focusing on this point, in the present invention, the light source driving unit is configured to set the pulse width to be smaller as the maximum frequency of the acoustic wave that can be detected by the detection unit is larger. The maximum frequency of the acoustic wave generated from the subject can be increased as the maximum frequency is increased. As a result, since the maximum frequency of the acoustic wave that can be detected by the detection unit and the maximum frequency of the acoustic wave generated from the subject can be substantially matched, the acoustic wave can be generated efficiently. . In the specification of the present application, the maximum frequency is the maximum frequency among the frequencies that are -6 dB relative to the peak value (0 dB) of the frequency component of the acoustic wave that can be detected by the detection unit. It is described as a frequency.

  In the photoacoustic imaging apparatus according to the above aspect, the maximum frequency that can be detected by the detection unit is preferably 1 MHz or more and 20 MHz or less. Here, when the detection frequency of the detection unit is higher than 20 MHz, the ultrasonic wave is attenuated, so that the depth becomes shallow and only the surface layer of the subject can be observed. On the other hand, when the detection frequency is lower than 1 MHz, the resolution becomes worse while the depth becomes deeper. Therefore, if the maximum frequency that can be detected by the detection unit is configured to be 1 MHz or more and 20 MHz or less, each of the depth and the resolution can be ensured.

  In the photoacoustic imaging apparatus according to the above aspect, preferably, the light source driving unit is configured such that a pulse waveform of light emitted from the light source unit is either a triangular shape or a trapezoidal shape. With this configuration, the pulse waveform of the light emitted from the light source unit has either a triangular shape or a trapezoidal shape, so that the rising slope and falling slope of the pulse waveform can be easily controlled. .

  In the photoacoustic imaging apparatus according to the above aspect, the light source unit is preferably configured to include a semiconductor light emitting element. If configured in this way, unlike the case of using a solid-state laser element (Q-switch pulse laser light source), an optical surface plate and a strong housing for suppressing characteristic fluctuation due to vibration of the optical system are not required. Therefore, the structure of the photoacoustic imaging apparatus can be prevented from increasing in size.

  According to the present invention, as described above, the frequency of the photoacoustic wave detected by the method other than controlling the pulse width of the pulsed light so as to conform to the frequency band of the detection unit (ultrasound probe). A photoacoustic imaging apparatus capable of controlling characteristics can be provided.

It is the block diagram which showed the whole structure of the photoacoustic imaging device by the 1st-3rd embodiment of this invention. It is the block diagram which showed the structure regarding irradiation of the pulsed light of the photoacoustic imaging device by the 1st-3rd embodiment of this invention. It is a figure for demonstrating the characteristic of the detection frequency of the detection part by 1st-3rd embodiment of this invention. It is a figure for demonstrating the relationship between the pulse response whose absolute value ratio of the inclination of the photoacoustic imaging device by 1st Embodiment of this invention is 1-3 times, and the frequency response of the acoustic wave detected in each. . Relationship between pulse waveform in which absolute value of rising slope is larger than absolute value of falling slope and frequency response of detected acoustic wave of photoacoustic imaging apparatus according to modifications of first to third embodiments of the present invention It is a figure for demonstrating. It is a figure for demonstrating the relationship between the pulse response whose absolute value ratio of the inclination of the photoacoustic imaging device by 1st Embodiment of this invention is 10 times, and 20 times, and the frequency response of the acoustic wave detected in each. is there. It is a figure for demonstrating the relationship between the pulse waveform of the half value width of 12.5 nsec of the photoacoustic imaging device by 2nd Embodiment of this invention, and the frequency response of the detected acoustic wave. It is a figure for demonstrating the relationship between the pulse waveform of the half value width of 500 nsec of the photoacoustic imaging device by 2nd Embodiment of this invention, and the frequency response of the detected acoustic wave. It is a figure for demonstrating the relationship between the pulse waveform of the half value width of 50 nsec of the photoacoustic imaging device by 3rd Embodiment of this invention, and the frequency response of the detected acoustic wave. It is a figure for demonstrating the relationship between the pulse waveform of the half width 200nsec of the photoacoustic imaging device by 3rd Embodiment of this invention, and the frequency response of the detected acoustic wave. It is a figure in case the pulse waveform of the photoacoustic imaging device by the modification of the 1st-3rd embodiment of this invention is trapezoid.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
(Overall configuration of photoacoustic imaging apparatus)
With reference to FIGS. 1-6, the whole structure of the photoacoustic imaging device 100 by 1st Embodiment of this invention is demonstrated. As shown in FIG. 1, the photoacoustic imaging apparatus 100 detects an acoustic wave A from a detection target (blood, organ, puncture needle, etc.) inside a subject P (human body, etc.), and photoacoustic It has a function of imaging a wave signal.

  The photoacoustic imaging apparatus 100 according to the first embodiment of the present invention is provided with a probe main body 1 and an apparatus main body 2 as shown in FIG. The photoacoustic imaging apparatus 100 is provided with a cable 3 for connecting the probe main body 1 and the apparatus main body 2.

  The probe main body 1 is configured to be disposed on the surface of a subject P (such as a human body surface) while being held by an operator. The probe main body 1 is provided with a light source 11 and a detector 12.

  The light source unit 11 is configured to irradiate the subject P with light. The detection unit 12 is configured to detect an acoustic wave A generated from within the subject P due to the light being irradiated to the subject P by the light source unit 11. The detection unit 12 is configured to transmit the acoustic wave A as a photoacoustic wave signal to the apparatus main body unit 2 via the cable 3.

  The apparatus main body 2 is provided with a light source driving unit 21, a control unit 22, an imaging unit 23, an image display unit 24, and an operation unit 25. The light source drive unit 21 is configured to drive the light source unit 11 by supplying power to the light source unit 11 based on a command from the control unit 22. The control unit 22 is configured to control each unit of the photoacoustic imaging apparatus 100. The imaging unit 23 is configured to process and image the photoacoustic wave signal detected by the probe main body unit 1. The image display unit 24 includes, for example, a liquid crystal monitor and is configured to display an imaged photoacoustic wave signal. The operation unit 25 includes, for example, a keyboard and is configured to accept an input operation from the operator.

(Configuration of each part of the photoacoustic imaging apparatus)
<Configuration of pulsed light irradiation>
Here, in 1st Embodiment, as shown in FIG. 2, the light source part 11 contains the some LED element 11a. The LED element 11a is configured, for example, as a plurality of light emitting element groups 11b in which a plurality (n) of LED elements 11a are connected in series with each other. Three rows are connected in parallel. The LED element 11a is an example of the “semiconductor light emitting element” in the claims.

  The light source unit 11 emits pulsed light having an infrared wavelength (for example, a wavelength of 600 nm to 1000 nm, preferably a wavelength of about 850 nm) when power is supplied from the light source driving unit 21. It is configured to be possible. The light source unit 11 is configured to irradiate the subject P with light emitted from the plurality of LED elements 11a.

  As shown in FIG. 1, the pulsed light applied to the subject P from the light source unit 11 is absorbed by a detection target (for example, hemoglobin) in the subject P. The detection target object expands and contracts (returns from the expanded size to the original size) according to the irradiation intensity (light quantity and absorption amount) of the pulsed light, thereby detecting the detection target object (subject P). To generate an acoustic wave A.

  The control unit 22 is configured to transmit an optical trigger signal to the light source driving unit 21. And the light source drive part 21 is comprised so that light may be irradiated from the light source part 11 according to a light trigger signal. The control unit 22 is configured to transmit a sampling trigger signal synchronized with the light trigger signal to the imaging unit 23.

  As shown in FIG. 2, the light source drive unit 21 includes a drive power supply unit 21 a and switch units 21 b to 21 d.

  The drive power supply unit 21a is formed of, for example, a DC / DC converter or the like, and is configured to acquire power from an external power supply (not shown) and to acquire a control signal from the control unit 22. And the drive power supply part 21a is comprised so that the acquired electric power may be converted into the direct-current electric power which has the voltage value V according to the acquired control signal. The drive power supply unit 21a is connected to the anode side of the light emitting element group 11b of the light source unit 11, and is configured to supply generated power (apply a voltage value V) to the anode side of the LED element 11a. ing.

  One side of each of the switch units 21b to 21d is connected to the cathode side of the LED element 11a of the light source unit 11, and the other side thereof is grounded. And switch part 21b-21d contains FET (Field Effect Transistor), for example, and it is comprised so that on and off can be switched based on the pulse-form optical trigger signal from the control part 22, respectively.

  When the switch portions 21b to 21d are turned on, the voltage value on the cathode side of the LED element 11a decreases (is grounded), so that a potential difference (substantially voltage value) occurs between the anode side and the cathode side of the LED element 11a. V) is generated, and the current flows through the LED element 11a. That is, the time during which the switch units 21 b to 21 d are turned on corresponds to the size of the pulse width tw of the pulsed light emitted from the light source unit 11, and the magnitude of the current value flowing through the LED element 11 a is emitted from the light source unit 11. This corresponds to the amount of pulsed light.

<Configuration for acoustic wave detection>
The detection unit 12 is configured by a piezoelectric element (for example, lead zirconate titanate (PZT)). And the detection part 12 is comprised so that it may vibrate and produce a voltage (signal), when the above-mentioned acoustic wave A is acquired. And the detection part 12 is comprised so that a photoacoustic wave signal may be transmitted to the apparatus main body part 2, as shown in FIG.

  Here, as shown in FIG. 3, the maximum frequency fmax that can be detected by the detection unit 12 is determined from the frequency characteristic (detection frequency characteristic) of the acoustic wave A that can be detected by the detection unit 12. The In the case of the example shown in FIG. 3, the maximum frequency fmax that can be detected by the detection unit 12 is a frequency (7.5 MHz and 2.5 MHz) that is 6 dB smaller (being −6 dB) with reference to the peak value (0 dB). The higher frequency is 7.5 MHz. In the present specification, as described above, the maximum frequency fmax is a frequency having a value of −6 dB with respect to the peak value (0 dB) of the frequency component of the acoustic wave A that can be detected by the detection unit 12. Among these, a large frequency is described as the maximum frequency fmax.

  Here, in the first embodiment, the detection unit 12 is configured such that the maximum frequency fmax that can be detected is 20 MHz or less. In general, as the frequency of the acoustic wave A increases, the resolution increases, while the attenuation rate when the acoustic wave A propagates inside the subject P increases. For example, when an acoustic wave A greater than 20 MHz is generated from the subject P (for example, a living body), the acoustic wave A greater than 20 MHz generated from a portion deeper than the surface layer portion may reach the detection unit 12. It becomes difficult. That is, when the maximum frequency fmax that can be detected by the detection unit 12 is greater than 20 MHz, the sound that is substantially detected when the maximum frequency fmax that can be detected by the detection unit 12 is 20 MHz. The frequency of the wave A is equivalent. Therefore, it is preferable to configure the detection unit 12 so that the maximum frequency fmax of the detection unit 12 is 20 MHz or less.

  In the first embodiment, the maximum frequency fmax that can be detected by the detection unit 12 is configured to be 1 MHz or more. In general, the smaller the frequency of the acoustic wave A, the greater the distance (depth) that the acoustic wave A can propagate through the subject P, but the smaller the resolution. For example, when imaging using 1 MHz acoustic wave A, the resolution is about 1.5 mm. Generally, when an image of acoustic wave A is used for diagnosis, it is desirable that the resolution is 1.5 mm or less. Therefore, by configuring the detection unit 12 so that the maximum frequency fmax is 1 MHz or more, it is possible to suppress difficulty in diagnosis using the photoacoustic imaging apparatus 100.

  In the first embodiment, the light source driving unit 21 is configured such that the pulse waveform of the light emitted from the light source unit 11 has either a triangular shape or a trapezoidal shape. Specifically, as shown in the pulse waveform graphs of FIGS. 4 to 6, after the pulse waveform rises with a linear gradient and the light intensity reaches a maximum, the pulse waveform falls with a linear gradient. That is, the pulse waveform has a triangular shape.

  In the first embodiment, the light source driving unit 21 sets the ratio between the rising slope and the falling slope of the pulse waveform of the light emitted from the light source unit 11 based on the detection frequency of the detection unit 12. It is configured as follows. In addition, the absolute value of the ratio of the inclination is increased as the detection frequency range of the detection unit 12 is wider. Specifically, as shown in FIG. 2, the slope of the pulse waveform is controlled by controlling the gate voltage of the FETs of the switch units 21b to 21d. That is, when the gate voltage is sharply raised, the switch portions 21b to 21d are quickly turned on, so that the rising slope of the pulse waveform is increased. Further, since the switch portions 21b to 21d are quickly turned off by sharply lowering the gate voltage, the slope of the fall of the pulse waveform is increased. Conversely, by smoothing the change in the gate voltage, the on / off operation of the switch portions 21b to 21d is slowed down, so that the slope of the pulse waveform becomes small. 4A to 4D show the pulse waveform and the sound when the absolute value of the falling slope is 1, 2, 3 and 1.5 times the absolute value of the rising slope, respectively. 2 is a graph of the frequency response of a wave A. As shown in the frequency response graphs of FIGS. 4A to 4D, as the absolute value of the ratio of the slopes of the pulse waveforms increases, the wideband amplitude (intensity of the acoustic wave A) of the frequency response graph increases. It has become. That is, the frequency range of the acoustic wave A is wide in the order of (c), (b), (d), and (a) in FIG. Note that the slope is, for example, the difference between the minimum value (Imin) of the light intensity (I) and the difference ΔI (= Imax−Imin) between the maximum value (Imax) and the minimum value of the light intensity. The slope of the increase (decrease) in the light intensity between the time of 10% plus (Imin + 0.1 × ΔI) and the time of 90% plus (Imin + 0.9 × ΔI) is there.

  5A and 5B are graphs of the pulse waveform and the frequency response of the acoustic wave A when the absolute value of the rising slope is twice and three times the absolute value of the falling slope, respectively. is there. Since there is no significant difference between FIG. 4B and FIG. 5A and between FIG. 4C and FIG. 5B, the rise of the pulse waveform Substantially equivalent frequency response characteristics can be obtained even if the relationship between the slope and the slope of the fall is reversed.

  In the first embodiment, one of the absolute value of the rising slope and the absolute value of the falling slope of the pulse waveform is configured to be 1.5 to 10 times the other. Specifically, as shown in FIGS. 4A to 4D, the peak frequency is obtained when the absolute value of the falling slope of the pulse waveform is 1.5 times or more the absolute value of the rising slope. The frequency range is expanded by increasing the intensity of the acoustic wave A at the above frequencies. 6A and 6B are graphs of the pulse waveform and the frequency response when the absolute value of the falling slope of the pulse waveform is 10 times and 20 times the absolute value of the rising slope, respectively. It is. As shown in the frequency response graphs of FIGS. 6A and 6B, the ratio between the absolute value of the falling slope and the absolute value of the rising slope of the pulse waveform was increased from 10 times to 20 times. However, there is no significant effect on the frequency response characteristics. Based on these results, it is desirable that one of the absolute value of the rising slope or the falling slope of the pulse waveform be 1.5 to 10 times the other.

  Further, in the first embodiment, the light source driving unit 21 is configured such that the absolute value of the falling slope is larger than the absolute value of the rising slope. Specifically, for example, as shown in FIGS. 4B to 4D and FIGS. 6A and 6B, the absolute value of the falling slope is the absolute value of the rising slope, respectively. They are 2 times, 3 times, 1.5 times, 10 times, and 20 times, and the slope of falling is larger.

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

  In the first embodiment, as described above, the light source unit 11 and the detection unit 12 that detects the acoustic wave A generated from within the subject P due to the light being irradiated on the subject P by the light source unit 11. And a light source drive unit 21 that supplies power to the light source unit 11 to drive the light source unit 11. The light source drive unit 21 is irradiated from the light source unit 11 based on the detection frequency (frequency band) of the detection unit 12. The ratio between the rising slope and the falling slope of the pulse waveform of the light to be set is set, and the absolute value of the slope ratio is increased as the detection frequency range of the detector 12 is wider. Thereby, even when the detection frequency range of the detection unit 12 is wide, the frequency range of the acoustic wave A and the detection frequency of the detection unit 12 can be adapted by increasing the absolute value of the slope of the pulse waveform. The frequency characteristic of the detected acoustic wave A can be controlled by a method other than the method of controlling the pulse width tw of the pulsed light so as to be adapted to the frequency band of the detection unit 12.

  In the first embodiment, as described above, the light source driving unit 21 is configured such that one of the absolute value of the rising slope or the absolute value of the falling slope is 1.5 to 10 times the other. Configure as follows. Accordingly, the frequency range of the detected acoustic wave A can be easily expanded by setting one of the absolute value of the rising slope and the absolute value of the falling slope to 1.5 times to 10 times the other. Therefore, the frequency characteristic of the detected acoustic wave A can be easily controlled by a method other than the method of controlling the pulse width tw of the pulsed light so as to easily match the frequency band of the detection unit 12.

  In the first embodiment, as described above, the light source driving unit 21 is configured such that the absolute value of the falling slope is larger than the absolute value of the rising slope. Here, the response characteristic of the light emitting element (for example, LED) generally falls faster than the rising edge, and falls sharply only by stopping the supply of current flowing through the light emitting element. As a result, the absolute value of the slope of the falling edge of the pulse waveform can be increased, so that the frequency characteristics of the detected acoustic wave A can be easily controlled to match the frequency band of the detection unit 12. .

  In the first embodiment, as described above, the maximum frequency fmax that can be detected by the detection unit 12 is 1 MHz or more and 20 MHz or less. Here, when the detection frequency of the detection unit 12 increases, the ultrasonic wave attenuates, so that the depth becomes shallower, and only the surface layer of the subject P can be observed. Further, when the detection frequency is lowered, the depth is increased while the resolution is deteriorated. Therefore, if the maximum frequency fmax that can be detected by the detection unit 12 is configured to be 1 MHz or more and 20 MHz or less, each of the depth and the resolution can be ensured.

  In the first embodiment, as described above, the light source driving unit 21 is configured such that the pulse waveform of the light emitted from the light source unit 11 has either a triangular shape or a trapezoidal shape. Since the pulse waveform of the light emitted from the light source unit 11 is either triangular or trapezoidal, the rising slope and falling slope of the pulse waveform can be easily controlled.

  Moreover, in 1st Embodiment, as mentioned above, the light source part 11 is comprised so that a semiconductor light-emitting device may be included. As a result, unlike the case of using a solid-state laser element (Q-switched pulse laser light source), an optical surface plate and a strong housing for suppressing characteristic fluctuations due to vibration of the optical system are not required. An increase in the size of the imaging apparatus 100 can be suppressed.

[Second Embodiment]
Next, the configuration of the photoacoustic imaging apparatus 200 according to the second embodiment will be described with reference to FIGS. 1 to 3, 7 and 8. In the second embodiment, an example in which the half width of the pulse waveform is 12.5 nsec or more and 500 ns or less will be described in addition to the configuration of the first embodiment. In addition, about the structure same as the said 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

(Overall configuration of photoacoustic imaging apparatus)
As shown in FIG. 1, the apparatus main body unit 22 includes a light source driving unit 221, a control unit 222, an imaging unit 23, an image display unit 24, and an operation unit 25. The light source driving unit 221 is configured to drive the light source unit 11 by supplying power to the light source unit 11 based on a command from the control unit 222. The control unit 222 is configured to control each unit of the photoacoustic imaging apparatus 200.

  Here, in the second embodiment, the half width of the pulse waveform is configured to be 12.5 nsec or more and 500 nsec or less. Specifically, as shown in FIG. 2, the photoacoustic imaging apparatus 200 controls the time during which the switch units 21 b to 21 d are turned on based on the light trigger signal from the control unit 222, thereby generating a pulse waveform. The full width at half maximum is configured to be 12.5 nsec or more and 500 nsec or less.

  FIG. 7A shows a pulse waveform in which the half width is 12.5 nsec and the absolute value of the falling slope is one time the absolute value of the rising slope. FIG. 7B shows a pulse waveform in which the half width of the pulse waveform is 12.5 nsec and the absolute value of the falling slope is four times the absolute value of the rising slope. As shown in the graphs of the frequency response in FIGS. 7A and 7B, by increasing the absolute value of the ratio of the slope, a wide band that does not affect reception spreads, and the amplitude at the peak frequency (acoustic wave A Strength) is small. If the full width at half maximum is further reduced, the absolute value of the ratio of the slope is increased, whereby the amplitude of the peak frequency is further reduced, and it is difficult to efficiently detect the acoustic wave A.

  FIG. 8A shows a pulse waveform in which the half-value width of the pulse waveform is 500 nsec and the absolute value of the falling slope is one time the absolute value of the rising slope. FIG. 8B shows a pulse waveform in which the half width of the pulse waveform is 500 nsec and the absolute value of the falling slope is four times the absolute value of the rising slope. As shown in the frequency response graphs of FIGS. 8A and 8B, the frequency range of the acoustic wave A is expanded by increasing the absolute value of the ratio of the slopes. However, in each of FIGS. 8A and 8B, the amplitude of the peak frequency is reduced by increasing the half width. Further, if the amplitude of the peak frequency is further reduced by increasing the half width, it becomes difficult to detect the acoustic wave A efficiently. From these results, it is preferable that the half width of the pulse waveform is 12.5 nsec or more and 500 nsec or less.

  In the second embodiment, the light source driving unit 221 is configured to set the half width of the pulse waveform to be smaller as the maximum frequency fmax of the acoustic wave A that can be detected by the detection unit 12 is larger. . Specifically, as shown in FIGS. 7 and 8, the frequency range is wider in FIG. 7 where the half width of the pulse waveform is smaller.

  Other configurations of the photoacoustic imaging apparatus 200 according to the second embodiment are the same as those of the photoacoustic imaging apparatus 100 according to the first embodiment.

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

  In the second embodiment, as described above, the light source driving unit 221 is configured so that the half width of the pulse waveform is 12.5 nsec or more and 500 nsec or less. Here, if the pulse width tw is too narrow, even if the absolute value of the slope ratio is increased, only the wide band that does not affect reception spreads and the peak frequency decreases. Further, if the pulse width tw is too wide, the amplitude of the peak frequency becomes small. Thus, if the half-width of the pulse waveform is configured to be 12.5 nsec or more and 500 nsec or less, the amplitude of the peak frequency can be secured, so that the acoustic wave A from the subject P can be detected efficiently. it can.

  In the second embodiment, as described above, the light source drive unit 221 is configured to set the pulse width tw to be smaller as the maximum frequency fmax of the acoustic wave A that can be detected by the detection unit 12 is larger. To do. Here, the acoustic wave A generated from the subject P is generated as an acoustic wave A having a frequency equal to or lower than the maximum frequency fmax, with the frequency having a reciprocal value of the pulse width tw irradiated to the subject P being the maximum frequency fmax. To do. Focusing on this point, the light source driving unit 221 is configured to set the pulse width tw to be smaller as the maximum frequency fmax of the acoustic wave A that can be detected by the detection unit 12 is larger. The maximum frequency fmax of the acoustic wave A generated from the subject P can be increased as the maximum frequency fmax of 12 is increased. As a result, the maximum frequency fmax of the acoustic wave A that can be detected by the detection unit 12 and the maximum frequency fmax of the acoustic wave A generated from the subject P can be substantially matched. A can be generated.

  Other effects of the photoacoustic imaging apparatus 200 according to the second embodiment are the same as those of the photoacoustic imaging apparatus 100 according to the first embodiment.

[Third Embodiment]
Next, the configuration of the photoacoustic imaging apparatus 300 according to the third embodiment will be described with reference to FIGS. 1 to 3, 9, and 10. In the third embodiment, unlike the configuration of the second embodiment, an example in which the half width of the pulse waveform is 50 nsec or more and 200 nsec or less 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.

(Overall configuration of photoacoustic imaging apparatus)
As shown in FIG. 1, the apparatus main body unit 32 is provided with a light source driving unit 321, a control unit 322, an imaging unit 23, an image display unit 24, and an operation unit 25. The light source driving unit 321 is configured to drive the light source unit 11 by supplying power to the light source unit 11 based on a command from the control unit 322. The control unit 322 is configured to control each unit of the photoacoustic imaging apparatus 300.

  Here, in the third embodiment, the half width of the pulse waveform is configured to be 50 nsec or more and 200 nsec or less. Specifically, as shown in FIG. 2, the photoacoustic imaging apparatus 300 controls the time for which the switch units 21 b to 21 d are turned on based on the light trigger signal from the control unit 322, thereby generating a pulse waveform. The half width is configured to be 50 nsec or more and 200 nsec or less.

  FIG. 9A shows a pulse waveform in which the half-value width is 50 nsec and the absolute value of the falling slope is one time the absolute value of the rising slope. FIG. 9B shows a pulse waveform in which the half width is 50 nsec and the absolute value of the falling slope is four times the absolute value of the rising slope. As shown in the frequency response graphs of FIGS. 9 (a) and 9 (b), by increasing the absolute value of the ratio of the slope, the low band affecting reception is expanded compared to FIG. A decrease in the amplitude of the peak frequency is suppressed. FIG. 10A shows a pulse waveform in which the half-value width is 200 nsec and the absolute value of the falling slope is one time the absolute value of the rising slope. FIG. 10B shows a pulse waveform in which the half width is 200 nsec and the absolute value of the falling slope is four times the absolute value of the rising slope. As shown in the frequency response graphs of FIGS. 10A and 10B, the frequency range is expanded by increasing the absolute value of the ratio of the slopes. Further, in each of (a) and (b) of FIG. 10, a decrease in the amplitude of the peak frequency is suppressed as compared with FIG. From these results, it is more preferable that the half width of the pulse waveform is 50 nsec or more and 200 nsec or less.

  The other configuration of the photoacoustic imaging apparatus 300 according to the third embodiment is the same as that of the photoacoustic imaging apparatus 100 according to the first embodiment.

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

  In the third embodiment, as described above, the half width of the pulse waveform is configured to be 50 nsec or more and 200 nsec or less. Thus, by setting the half-value width of the pulse waveform to 50 nsec or more and 200 nsec or less, the amplitude of the peak frequency can be more reliably ensured, so that the acoustic wave A from the subject P can be detected more efficiently. .

  Other effects of the photoacoustic imaging apparatus 300 according to the third embodiment are the same as those of the photoacoustic imaging apparatus 100 according to the first embodiment.

[Modification]
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 LED element is used for the light source unit has been described, but the present invention is not limited thereto. In the present invention, a semiconductor laser may be used.

  Moreover, in the said 1st-3rd embodiment, although the pulse waveform of pulsed light showed the example which is triangular shape, this invention is not limited to this. In the present invention, the pulse waveform may be trapezoidal as shown in FIG. FIG. 11 is a graph in which the absolute value of the rising slope of the pulse waveform is twice and three times the absolute value of the falling slope.

  In the first to third embodiments, the absolute value of the falling slope of the pulse waveform is larger than the absolute value of the rising slope. However, the present invention is not limited to this. In the present invention, as shown in FIG. 5, the absolute value of the rising slope of the pulse waveform may be larger than the absolute value of the falling slope.

  In the first to third embodiments, an example is shown in which the on / off of the switch unit is controlled as a method for controlling the slope of the pulse waveform of the pulsed light. However, the present invention is not limited to this. In the present invention, for example, the slope of the pulse waveform of the pulsed light may be controlled by controlling the voltage from the drive power supply unit (control unit).

  Moreover, in the said 1st-3rd embodiment, although the example which provides a light source drive part in an apparatus main body part was shown, this invention is not limited to this. For example, the light source driving unit may be provided in the probe main body.

11 Light source part 11a LED element 11a (light emitting element)
12 detectors 21, 221, 321 light source driver 100, 200, 300 photoacoustic imaging device

Claims (9)

A light source unit;
A detection unit for detecting an acoustic wave generated from within the subject due to light being irradiated to the subject by the light source unit;
A light source driving unit that supplies power to the light source unit to drive the light source unit,
The light source driving unit sets a ratio of a rising slope and a falling slope of a pulse waveform of light emitted from the light source unit based on a detection frequency of the detection unit, and a detection frequency of the detection unit. The photoacoustic imaging device is configured to increase the absolute value of the ratio of inclination as the range of is wide.   2. The light source driving unit according to claim 1, wherein one of an absolute value of a rising slope or an absolute value of a falling slope is configured to be 1.5 times or more and 10 times or less of the other. Photoacoustic imaging device.   3. The photoacoustic imaging apparatus according to claim 1, wherein the light source driving unit is configured such that a half width of the pulse waveform is 12.5 nsec or more and 500 nsec or less.   4. The photoacoustic imaging apparatus according to claim 3, wherein the light source driving unit is configured such that a half width of the pulse waveform is 50 nsec or more and 200 nsec or less.   5. The photoacoustic imaging apparatus according to claim 1, wherein the light source driving unit is configured such that an absolute value of a falling slope is larger than an absolute value of a rising slope.   The said light source drive part is comprised so that the half value width of the said pulse waveform may be set small, so that the maximum frequency of the said acoustic wave which the said detection part can detect is large. The photoacoustic imaging apparatus of Claim 1.   The photoacoustic imaging apparatus of any one of Claims 1-6 whose maximum frequency which the said detection part can detect is 1 MHz or more and 20 MHz or less.   The said light source drive part is comprised so that the said pulse waveform of the light irradiated from the said light source part may become any one of a triangle shape or a trapezoid shape. Photoacoustic imaging device.   The photoacoustic imaging apparatus according to claim 1, wherein the light source unit is configured to include a semiconductor light emitting element.

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