Abstract:
This photoacoustic imaging device ( 100 ) comprises: a display unit ( 40 ) that rewrites a screen ( 40   a ) at a predetermined refresh rate (RC) and that displays an image on the screen; and a control unit ( 30 ) that performs the acquisition of a detection signal and irradiation with light by a semiconductor light-emitting-element light-source unit at a sampling cycle (SC) shorter than the cycle of the predetermined refresh rate, and that creates an image to be displayed on the display unit from the detection signal detected according to the sampling cycle.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a photoacoustic imaging apparatus, specifically, to a photoacoustic imaging apparatus including a display portion. 
       BACKGROUND ART 
       [0002]    A photoacoustic imaging apparatus including a display portion has conventionally been known. Such a photoacoustic imaging apparatus is disclosed in Japanese Patent Laying-Open No. 2012-250019, for example. 
         [0003]    Japanese Patent Laying-Open No. 2012-250019 discloses a photoacoustic imaging apparatus including: a light source that generates pulsed light at certain light emission frequencies (20 Hz and 40 Hz); a receiver that detects an acoustic wave generated by a detection target in a test object when the detection target absorbs the pulsed light and converts the detected acoustic wave to a receiving signal; a signal processing portion that generates an image by executing averaging processing on the receiving signal; and a monitor (display portion) on which the image is displayed. A screen of this monitor (display portion) is generally updated at a certain refresh rate (60 Hz, for example). 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: Japanese Patent Laying-Open No. 2012-250019 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    In the above-described photoacoustic imaging apparatus described in Japanese Patent Laying-Open No. 2012-250019, light emission frequencies (20 Hz and 40 Hz) are lower than a general refresh rate (60 Hz, for example). This makes a light emission cycle (a sampling cycle) longer than a cycle of updating the screen of the display portion (a cycle of a refresh rate). Hence, in some cases, both light emission and acquisition of a detection signal cannot be achieved within a cycle of updating the screen. In these cases, a detection signal is not acquired within the cycle of updating the screen. This makes it impossible for the signal processing portion to generate a new image within the cycle of updating the screen, causing an unfavorable issue of failing to update the screen (displaying one image continuously). In this case, the cycle of updating the screen is substantially extended and this is considered to cause a problem of awkward motion of moving images displayed on the screen (loss of smoothness). 
         [0006]    The present invention has been made to solve the above-described problem. It is one object of the present invention to provide a photoacoustic imaging apparatus capable of suppressing awkward motion of moving images displayed on a screen. 
       Solution to Problem 
       [0007]    A photoacoustic imaging apparatus according to one aspect of the present invention includes: a semiconductor light-emitting element light source portion; a detecting portion that detects an acoustic wave generated from a detection target in a test object when the detection target absorbs light emitted from the semiconductor light-emitting element light source portion and outputs a detection signal; a display portion having a screen to be updated at a certain refresh rate and on which an image is to be displayed; and a control portion that makes the semiconductor light-emitting element light source portion emit light in a sampling cycle shorter than a cycle of the certain refresh rate, acquires the detection signal in the sampling cycle, and generates an image to be displayed on the display portion using the detection signal detected in the sampling cycle. 
         [0008]    As described above, in the photoacoustic imaging apparatus according to the aforementioned aspect of the present invention, the control portion is provided that makes the semiconductor light-emitting element light source portion emit light in the sampling cycle shorter than the cycle of the certain refresh rate, acquires the detection signal in the sampling cycle, and generates an image to be displayed on the display portion using the detection signal detected in the sampling cycle. As the sampling cycle is set to be shorter than the cycle of the certain refresh rate, a detection signal can be acquired within the cycle of the certain refresh rate. Thus, the detection signal acquired within the cycle of the certain refresh rate can be used for generating an image. This can easily reduce the likelihood of failing to update the screen of the display portion (displaying one image continuously) due to failing to acquire a detection signal during a cycle of updating the screen (cycle of the certain refresh rate). This can easily make it less likely that the cycle of updating the screen will be substantially extended. As a result, awkward motion of moving images displayed on the screen (loss of smoothness) can be suppressed. Further, provision of the semiconductor light-emitting element light source portion can shorten the sampling cycle easily, compared to use of a solid-laser light source portion having difficultly in shortening a light emission cycle (sampling cycle). 
         [0009]    In the photoacoustic imaging apparatus according to the aforementioned aspect, the control portion is preferably configured to generate an image to be displayed on the display portion by taking an arithmetic average of the detection signals detected in the sampling cycles. In this configuration, an arithmetic average of the detection signals detected in the sampling cycles is taken, so that an image can be generated with an increased S/N ratio (signal-to-noise ratio). 
         [0010]    In the aforementioned configuration of generating an image to be displayed on the display portion by taking an arithmetic average of the detection signals, the sampling cycle preferably has a length that allows the semiconductor light-emitting element light source portion to emit light several times while allowing the detection signal to be acquired several times within the cycle of the certain refresh rate. In this configuration, the several detection signals can be acquired within the cycle of the certain refresh rate. This can more easily reduce the likelihood of failing to update the screen of the display portion due to failing to acquire a detection signal during a cycle of updating the screen (cycle of the certain refresh rate). As a result, awkward motion of moving images displayed on the screen can be suppressed more easily. 
         [0011]    In the aforementioned configuration of generating an image to be displayed on the display portion by taking an arithmetic average of the detection signals, the control portion is preferably configured to generate an image to be displayed on the display portion by taking an arithmetic average of the detection signals with the number of additions that makes a value obtained by multiplying the sampling cycle and the number of additions during taking of an arithmetic average exceed the cycle of the certain refresh rate. This configuration can reduce the likelihood of the occurrence of a detection signal out of the acquired detection signals and not to be reflected in generation of an image, compared to a case where a value obtained by multiplying the sampling cycle and the number of additions during taking of an arithmetic average does not exceed the cycle of the certain refresh rate. 
         [0012]    In the aforementioned configuration of generating an image to be displayed on the display portion by taking an arithmetic average of the detection signals, the control portion is preferably configured to generate an image to be displayed on the display portion by taking a moving average as an arithmetic average. This configuration makes it possible to generate an image in such a manner as to smoothen a motion (difference) between individual generated images, unlike the case of taking a average as an arithmetic average. Thus, moving images formed of the individual images can be displayed smoothly. This configuration works effectively, particularly in displaying moving images of the inside of the test object to change constantly such as a human body. 
         [0013]    In this case, the control portion is preferably configured to take a moving average each time the detection signal is acquired. In this configuration, averaging processing is executed on every occasion on each detection signal by taking a moving average of detection signals, so that averaging processing for generating an image can be executed reliably at each certain refresh rate. As a result, an image can be generated reliably during update of the screen, making it possible to reliably reduce the likelihood of failing to update the screen. Thus, awkward motion of moving images displayed on the screen can be suppressed reliably. 
         [0014]    In the aforementioned configuration of generating an image to be displayed on the display portion by taking an arithmetic average of the detection signals, the control portion is preferably configured to generate an image to be displayed on the display portion by taking a average as an arithmetic average. This configuration makes it possible to reduce the number of detection signals to be stored in a memory, compared to taking a moving average as an arithmetic average. This achieves a corresponding saving of the volume of the memory. 
         [0015]    In the aforementioned configuration of generating an image to be displayed on the display portion by taking an arithmetic average of the detection signals, the control portion is preferably configured to generate an image to be displayed on the display portion by taking an arithmetic average of the detection signals with the number of additions that makes a value obtained by multiplying the sampling cycle and the number of additions during taking of an arithmetic average 125 msec or less. In this configuration, the redundancy of averaging time can be suppressed. This can suppress awkward motion of moving images formed of individual images due to redundancy of averaging time. 
         [0016]    In the photoacoustic imaging apparatus according to the aforementioned aspect, the control portion is preferably configured to generate a average signal by taking a average of detection signals from a detection signal acquired first to a detection signal acquired last within the cycle of the certain refresh rate and to generate an image to be displayed on the display portion based on the average signal. In this configuration, all detection signals acquired within the cycle of the certain refresh rate can be used for generating an image. This can reduce the likelihood of the occurrence of a detection signal out of acquired detection signals and not to be reflected in an image to be displayed on the screen of the display portion. As a result, the acquired detection signals can be used efficiently for generating an image. 
         [0017]    In the aforementioned configuration of generating an image to be displayed on the display portion based on the average signal, the control portion is preferably configured to generate an image to be displayed on the display portion by defining the average signal generated by taking a average as one unit and acquiring average signals as a plurality of units, and by taking an arithmetic average of the acquired average signals as the plurality of units. This configuration achieves generation of an image by executing averaging processing on more detection signals, so that the image can be generated with an increased S/N ratio (signal-to-noise ratio). As a result, a clear image can be generated through efficient use of acquired detection signals. 
         [0018]    In this case, the control portion is preferably configured to generate an image to be displayed on the display portion by taking a moving average as an arithmetic average. In this configuration, while the average signals are generated by taking a average, a moving average of these average signals is taken. This makes it possible to generate an image in such a manner as to smoothen a motion (difference) between individual images. Thus, moving images formed of the individual images can be displayed smoothly while acquired detection signals are used efficiently. This configuration of taking a moving average works effectively, particularly in displaying moving images of the inside of the test object to change constantly such as a human body. 
         [0019]    In the aforementioned configuration of taking a moving average as an arithmetic average, the control portion is preferably configured to take a moving average each time the average signal is acquired. In this configuration, averaging processing is executed on every occasion on each average signal by taking a moving average of the average signals, so that averaging processing for generating an image can be executed reliably at each certain refresh rate. As a result, an image can be generated reliably during update of the screen, making it possible to reliably reduce the likelihood of failing to update the screen. In this way, while an image is generated by efficiently using acquired detection signals, awkward motion of moving images displayed on the screen can be suppressed reliably. 
         [0020]    In the aforementioned configuration of generating an image to be displayed on the display portion based on the average signal, the control portion is preferably configured to generate an image to be displayed on the display portion by taking a average as an arithmetic average. This configuration makes it possible to reduce the number of detection signals to be stored in the memory, compared to taking a moving average as an arithmetic average. This achieves a corresponding saving of the volume of the memory. 
         [0021]    In the aforementioned configuration of taking an arithmetic average of the average signals as the plurality of units, the control portion is preferably configured to acquire the average signals as the plurality of units in such a manner that a value obtained by multiplying the sampling cycle and the number of detection signals to be subjected to averaging processing by taking of an arithmetic average is 125 msec or less. In this configuration, the redundancy of averaging time can be suppressed. This can suppress awkward motion of moving images formed of individual images due to redundancy of averaging time. 
         [0022]    In the photoacoustic imaging apparatus according to the aforementioned aspect, the control portion is preferably configured to acquire the detection signal in a certain sampling cycle, and the control portion is preferably configured to synchronize timing of start of the cycle of the certain refresh rate and timing of start of the certain sampling cycle with each other for each cycle of the certain refresh rate. In this configuration, non-uniformity of the number of detection signals between cycles of the certain refresh rate can be less likely to occur in each cycle of the certain refresh rate. In this way, the number of detection signals to form the average signal can be less likely to vary between the cycles of the certain refresh rate, making it possible to reduce the likelihood of the occurrence of a difference in an image quality between individual images to be generated. 
         [0023]    In this case, the control portion is preferably configured to synchronize timing of start of the cycle of the certain refresh rate and timing of start of the certain sampling cycle with each other by changing the length of a last sampling cycle within the certain refresh cycle. In this configuration, timing of start of the cycle of the certain refresh rate and timing of start of the certain sampling cycle can be synchronized with each other only by changing the length of the last sampling cycle within the certain sampling cycle. As a result, timing of start of the cycle of the certain refresh rate and timing of start of the certain sampling cycle can be synchronized with each other easily. 
         [0024]    In the photoacoustic imaging apparatus according to the aforementioned aspect, the control portion is preferably configured to define the average signal generated by taking a average as one unit and acquire the average signal as one unit or acquire the average signals as a plurality of units in such a manner that the number of the detection signals reaches a certain number or more, and to generate an image to be displayed on the display portion based on the acquired average signal as one unit or the acquired average signals as the plurality of units. This configuration makes it possible to execute averaging processing reliably using the detection signals of the certain number or more, so that an S/N ratio (signal-to-noise ratio) can be increased reliably during generation of an image. As a result, a clear image can be generated reliably. 
         [0025]    In the photoacoustic imaging apparatus according to the aforementioned aspect, the semiconductor light-emitting element light source portion preferably includes a light-emitting diode element as the semiconductor light-emitting element. This configuration of using the light-emitting diode element of relatively low power consumption can reduce power consumption. 
         [0026]    In the photoacoustic imaging apparatus according to the aforementioned aspect, the semiconductor light-emitting element light source portion preferably includes a semiconductor laser element as the semiconductor light-emitting element. In this configuration, a laser beam of relatively high directivity can be emitted to the test object, compared to using the light-emitting diode element. Thus, much of the beam from the semiconductor laser element can be applied reliably to the test object. 
         [0027]    In the photoacoustic imaging apparatus according to the aforementioned aspect, the semiconductor light-emitting element light source portion preferably includes an organic light-emitting diode element as the semiconductor light-emitting element. This configuration of using the organic light-emitting diode element capable of being reduced in thickness easily facilitates size reduction of the semiconductor light-emitting element light source portion. 
       Advantageous Effects of Invention 
       [0028]    As described above, according to the present invention, a photoacoustic imaging apparatus capable of suppressing awkward motion of moving images displayed on a screen can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0029]      FIG. 1  is a view showing the overall configuration of a photoacoustic imaging apparatus according to a first embodiment and a second embodiment of the present invention. 
           [0030]      FIG. 2  is a schematic view showing a state of measuring an acoustic wave by the photoacoustic imaging apparatus according to the first and second embodiments of the present invention. 
           [0031]      FIG. 3  is a view for explaining a case where the number of additions during averaging processing by taking of a moving average is small. 
           [0032]      FIG. 4  is a view for explaining a case where the number of additions during averaging processing by taking of a moving average is large. 
           [0033]      FIG. 5  is a view for explaining averaging processing by taking of a average by a photoacoustic imaging apparatus according to the second embodiment of the present invention. 
           [0034]      FIG. 6  is a view showing the overall configuration of a photoacoustic imaging apparatus according to a third embodiment, a fourth embodiment, and a fifth embodiment of the present invention. 
           [0035]      FIG. 7  is a schematic view showing a state of measuring an acoustic wave by the photoacoustic imaging apparatus according to the third embodiment of the present invention. 
           [0036]      FIG. 8  is a view for explaining a average signal generated by the photoacoustic imaging apparatus according to the third embodiment of the present invention. 
           [0037]      FIG. 9  is a view for explaining generation of an image using a average signal by the photoacoustic imaging apparatus according to the third embodiment of the present invention. 
           [0038]      FIG. 10  is a view for explaining generation of an image using a average signal by the photoacoustic imaging apparatus according to the fourth embodiment of the present invention. 
           [0039]      FIG. 11  is a view for explaining a average signal generated by the photoacoustic imaging apparatus according to the fifth embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0040]    Embodiments of the present invention will be described below by referring to the drawings. 
       First Embodiment 
       [0041]    The configuration of a photoacoustic imaging apparatus  100  according to a first embodiment of the present invention will be described first by referring to  FIGS. 1, 2 , and  4 . 
         [0042]    As shown in  FIGS. 1 and 2 , the photoacoustic imaging apparatus  100  according to the first embodiment of the present invention includes an apparatus body  1  and a probe portion  2 . The apparatus body  1  and the probe portion  2  are connected through a wire  51  and a wire  52 . The apparatus body  1  includes a control portion  30  and a display portion  40 . The probe portion  2  includes a semiconductor light-emitting element light source portion  10  (hereinafter called a light source portion  10 ) and a detecting portion  20 . 
         [0043]    As shown in  FIGS. 1 and 2 , the light source portion  10  includes two light sources  11  and is configured to emit pulsed light for measurement from each of the two light sources  11  toward a test object P. Each of the two light sources  11  is connected through the wire  51  to the control portion  30  and is configured to receive power and a control signal supplied from the control portion  30  through the wire  51 . 
         [0044]    The two light sources  11  are arranged near the detecting portion  20  and on opposite sides of the detecting portion  20  so as to sandwich the detecting portion  20  therebetween. In this way, the two light sources  11  are configured to emit pulsed light toward the test object P from different positions. 
         [0045]    As shown in  FIG. 1 , each of the two light sources  11  includes a light source substrate  11   a  and a semiconductor light-emitting element  11   b . For example, a light-emitting diode element, a semiconductor laser element, or an organic light-emitting diode element is applicable as the semiconductor light-emitting element  11   b . The light source substrate  11   a  has a lower surface holding a plurality of semiconductor light-emitting elements  11   b  mounted in an array pattern. The light source substrate  11   a  has a light source drive circuit and is configured to make the semiconductor light-emitting element  11   b  emit a pulse based on a control signal output from the control portion  30 . 
         [0046]    The two semiconductor light-emitting elements  11   b  are both configured to generate light of a measurement wavelength in an infrared region suitable for measurement of the test object P such as a human body (light having a center wavelength from about 700 to about 1000 nm, for example). The two semiconductor light-emitting elements  11   b  may be configured to generate light of different measurement wavelengths or light of the substantially same measurement wavelength. A measurement wavelength may be determined properly in a manner that depends on an intended detection target to be detected. 
         [0047]    As shown in  FIGS. 1 and 2 , the detecting portion  20  is an ultrasonic probe and connected to the control portion  30  through the wire  52 . The detecting portion  20  includes an ultrasonic vibrator  20   a . In the detecting portion  20 , the ultrasonic vibrator  20   a  includes a plurality of ultrasonic vibrators  20   a  arranged in an array pattern. The detecting portion  20  is configured to detect an acoustic wave (ultrasonic wave) AW in response to vibration of the ultrasonic vibrator  20   a  caused by an acoustic wave generated from a detection target Q in the test object P when the detection target Q absorbs pulsed light emitted from the light source portion  10 . The detecting portion  20  is configured to be capable of generating an ultrasonic wave UW by making the ultrasonic vibrator  20   a  vibrate based on a control signal output from the control portion  30 . The detecting portion  20  is also configured to detect the ultrasonic wave UW in response to vibration of the ultrasonic vibrator  20   a  caused by this ultrasonic wave UW reflected in the test object P. The detecting portion  20  is configured to output a detection signal corresponding to the detected acoustic wave AW or the detected ultrasonic wave UW to the control portion  30  through the wire  52 . 
         [0048]    In this description, for the convenience of explanation, an ultrasonic wave generated by absorption of pulsed light by the detection target Q in the test object P will be called an “acoustic wave,” an ultrasonic wave generated by the ultrasonic vibrator  20   a  and reflected in the test object P will be called an “ultrasonic wave,” and the “acoustic wave” and the “ultrasonic wave” will be described distinctively. 
         [0049]    The control portion  30  includes a CPU and a storage portion  30   a  such as a ROM or a RAM. As shown in  FIG. 1 , the control portion  30  is configured to form an image of the inside of the test object P based on a detection signal output from the detecting portion  20 . More specifically, the control portion  30  is configured to generate a photoacoustic image based on a detection signal resulting from the acoustic wave AW and to generate an ultrasonic image based on a detection signal resulting from the ultrasonic wave UW. The control portion  30  is configured to be capable of forming an image of various types of information in the test object P by synthesizing the photoacoustic image and the ultrasonic image. Generation of the photoacoustic image resulting from the acoustic wave AW will be described in detail later. 
         [0050]    As shown in  FIG. 1 , the display portion  40  is formed of a general liquid crystal type monitor or a scanning type monitor. The display portion  40  has a screen  40   a  and is configured to display an image such as an image of the inside of the test object P on the screen  40   a  formed by the control portion  30 . As shown in  FIG. 4 , the display portion  40  is configured in such a manner that the screen  40   a  is updated at a certain refresh rate (frequency). The certain refresh rate to be applied is generally about 50 Hz or more (about 50 Hz, about 60 Hz, or about 120 Hz, for example), and these values are applicable as the certain refresh rate. 
         [0051]    The refresh rate mentioned herein is a value indicating the number of times the screen  40   a  is refreshed (updated) per unit time (one second, for example). This means that, if the refresh rate is about 60 Hz, the screen  40   a  is refreshed (updated) about 60 times in one second. In other words, this means that the screen  40   a  is refreshed (updated) in each cycle of a refresh rate (hereinafter called a refresh cycle) RC of about 16.7 msec (milliseconds). In  FIG. 4 , timing of refresh (update) of the screen  40   a  is schematically shown by a substantially rectangular pulse wave. In the case of a liquid crystal type monitor, for example, the screen  40   a  is refreshed at the time of rising of a substantially rectangular pulse wave. In the case of a scanning type monitor, for example, the monitor is scanned within the refresh cycle RC to refresh the screen  40   a.    
         [0052]    The following describes the details of acquisition of a detection signal resulting from the acoustic wave AW and generation of a photoacoustic image based on the acquired detection signal by the photoacoustic imaging apparatus  100  by referring to  FIG. 4 . The following description is about acquisition of a detection signal resulting from the acoustic wave AW and generation of a photoacoustic image. Thus, a signal simply called a detection signal means a detection signal resulting from the acoustic wave AW. 
         [0053]    As shown in  FIG. 4 , in the photoacoustic imaging apparatus  100 , the control portion  30  is configured to acquire a detection signal at a sampling frequency that determines a sampling cycle SC to be one cycle. 
         [0054]    In the first embodiment, the control portion  30  is configured to make the light source portion  10  emit pulsed light and to acquire a detection signal resulting from the acoustic wave AW in the sampling cycle SC shorter than the refresh cycle RC. The control portion  30  is also configured to generate a photoacoustic image (photoacoustic image data) by executing averaging processing by taking a moving average using the detection signal detected in the sampling cycle SC. 
         [0055]    More specifically, the control portion  30  is configured to make the light source portion  10  emit pulsed light and to acquire a detection signal in a detecting section belonging to the sampling cycle SC and shown schematically by a substantially rectangular pulse wave. 
         [0056]    The control portion  30  is configured to execute the following in a signal processing section belonging to the sampling cycle SC and following the detecting section of the same sampling cycle SC: storing of a detection signal acquired in this sampling cycle SC into the storage portion  30   a , averaging processing by taking of a moving average using a plurality of stored detection signals, etc. The control portion  30  is also configured to generate photoacoustic image data by executing averaging processing by taking a moving average, to output the generated photoacoustic image data to the display portion  40 , and to make the display portion  40  display a photoacoustic image. 
         [0057]    In the first embodiment, the sampling cycle SC has a length shorter than that of the refresh cycle RC and allowing the light source portion  10  to emit pulsed light several times while allowing a detection signal to be acquired several times within the refresh cycle RC. Specifically, in the first embodiment, several detecting sections exist within one refresh cycle RC, as shown in  FIG. 4 . 
         [0058]    The length of the sampling cycle SC is preferably determined in consideration of an MPE (maximum permission exposure) of skin. The reason for this is that decrease in the length of the sampling cycle SC reduces an MPE value. If a measurement wavelength is 750 nm, the pulse width of pulsed light is 1 microsecond, and the sampling cycle SC is 0.1 msec, for example, an MPE value of skin is about 14 J/m 2 . If the peak power of pulsed light emitted from the light source portion  10  is 3 kW and an area of emission from the light source portion  10  is 250 mm 2 , for example, the energy of light emitted from the light source portion  10  to the test object P such as a human body is about 12 J/m 2 . Thus, the energy of light emitted from the light source portion  10  described in this example does not exceed the MPE value, so that the sampling cycle SC can be set at 0.1 msec or more. Specifically, the sampling cycle SC is preferably set in a range not to cause excess over the MPE value. 
         [0059]    As shown in  FIG. 4 , in the first embodiment, the control portion  30  is configured to generate a photoacoustic image (photoacoustic image data) to be displayed on the display portion  40  by taking a moving average of detection signals during averaging processing by taking of a moving average, with the number of additions (in  FIG. 4 , five) that makes a value (time) obtained by multiplying the time of the sampling cycle SC and the number of additions during taking of a moving average exceed the time of the refresh cycle RC. If the refresh cycle RC is 16.7 msec and the sampling cycle SC is 0.1 msec, for example, the number of additions satisfying this requirement is 168 or more. 
         [0060]    The control portion  30  is configured to generate a photoacoustic image (photoacoustic image data) to be displayed on the display portion  40  by taking a moving average of detection signals with the number of additions that makes a value (time) obtained by multiplying the time of the sampling cycle SC and the number of additions during taking of a moving average about 125 msec or less. If the sampling cycle SC is 0.1 msec, for example, the number of additions satisfying this requirement is 1250 or less. Thus, if the refresh cycle RC is 16.7 msec and the sampling cycle SC is 0.1 msec, for example, the number of additions satisfying the aforementioned requirements is set in a range from 168 to 1250. 
         [0061]    Averaging processing by taking of a moving average and display of a generated photoacoustic image will be described next by referring to  FIGS. 3 and 4  and giving specific examples. In a case described first by referring to  FIG. 3 , a value (time) obtained by multiplying the time of the sampling cycle SC and the number of additions during taking of a moving average does not exceed the time of the refresh cycle RC (sampling cycle SC×the number of additions≦refresh cycle RC). Conditions such as numerical values given in the following description are illustrative and not restrictive. 
         [0062]      FIG. 3  shows averaging processing by taking of a moving average schematically using an arrow B 1 , an arrow B 2 , an arrow B 3 , an arrow B 4 , and an arrow B 5 . Specifically, the arrows B 1  to B 5  show that averaging processing by taking of a moving average is executed on every occasion (each time a detection signal is acquired), with the number of additions set at three. For example, the arrow B 4  shows that averaging processing is being executed by taking a moving average of detection signals acquired in a detecting section (2), a detecting section (3), and a detecting section (4) respectively. The arrow B 5  shows that averaging processing is being executed by taking a moving average of detection signals acquired in the detecting section (3), the detecting section (4), and a detecting section (5) shifted subsequently by one detecting section from those shown by the arrow B 4 . Averaging processing executed by taking a moving average is also executed before the arrow B 1  and after the arrow B 5 . However, for the sake of simplicity, such averaging processing is omitted from the drawing. 
         [0063]    In the photoacoustic imaging apparatus  100 , an image displayed on the screen  40   a  of the display portion  40  (see  FIG. 1 ) is a photoacoustic image generated by averaging processing (a photoacoustic image already generated) to coincide with timing of refresh (update) of the screen  40   a  in the refresh cycle RC. Specifically, in  FIG. 3 , images displayed on the screen  40   a  of the display portion  40  are photoacoustic images generated by averaging processing corresponding to the arrow B 1  shown as a black arrow and averaging processing corresponding to the arrow B 5  shown as a black arrow. Specifically, the photoacoustic image generated by the averaging processing corresponding to the arrow B 1  is displayed. Then, the photoacoustic image generated by the averaging processing corresponding to the arrow B 5  is displayed as a next photoacoustic image. 
         [0064]    If sampling cycle SC×the number of additions≦refresh cycle RC, while detection signals are acquired in the detecting sections (2) to (5) in a period from the arrow B 1  to the arrow B 5 , a detection signal to contribute to a photoacoustic image includes only the detection signals corresponding to the detecting sections (3), (4), and (5) covered by the arrow B 5  out of those corresponding to the detecting sections (2) to (5). This unfortunately generates a detection signal such as one corresponding to the detecting section (2) not to be reflected in generation of a photoacoustic image. 
         [0065]    By contrast, unlike the case of  FIG. 3 , in the case of  FIG. 4 , the photoacoustic imaging apparatus  100  according to the first embodiment does not generate a detection signal not to be reflected in generation of a photoacoustic image. In a case described next by referring to  FIG. 4 , a value (time) obtained by multiplying the time of the sampling cycle SC and the number of additions during taking of a moving average exceeds the time of the refresh cycle RC (sampling cycle SC×the number of additions &gt;refresh cycle RC). 
         [0066]      FIG. 4  shows averaging processing by taking of a moving average schematically using an arrow B 11 , an arrow B 12 , an arrow B 13 , an arrow B 14 , an arrow B 15 , and an arrow B 16 . Specifically, the arrows B 11  to B 16  show that averaging processing by taking of a moving average is executed on every occasion (each time a detection signal is acquired), with the number of additions set at five. Averaging processing by taking of a moving average is also executed before the arrow B 11  and after the arrow B 16 . However, for the sake of simplicity, such averaging processing is omitted from the drawing. 
         [0067]    In  FIG. 4 , averaging processing corresponding to the arrow B 11  shown as a black arrow and averaging processing corresponding to the arrow B 16  shown as a black arrow are executed to coincide with timing of refresh (update) of the screen  40   a  in the refresh cycle RC. Thus, images displayed on the screen  40   a  of the display portion  40  are photoacoustic images generated by the averaging processing corresponding to the arrow B 11  shown as the black arrow and the averaging processing corresponding to the arrow B 16  shown as the black arrow. Specifically, the photoacoustic image generated by the averaging processing corresponding to the arrow B 11  is displayed. Then, the photoacoustic image generated by the averaging processing corresponding to the arrow B 16  is displayed as a next photoacoustic image. 
         [0068]    In the case of the photoacoustic imaging apparatus  100  according to the first embodiment where sampling cycle SC×the number of additions &gt;refresh cycle RC, the arrow B 16  covers all the detection signals corresponding to the detecting sections (6) to (10) acquired in a period from the arrow B 11  to the arrow B 16 . Thus, there will be no detection signal not to be reflected in generation of a photoacoustic image. For the convenience of illustration, the arrows B 11  and B 16  have been described as examples. However, detection signals acquired before the arrow B 11  and detection signals acquired after the arrow B 16  also do not include a detection signal not to be reflected in generation of a photoacoustic image. As described above, in the photoacoustic imaging apparatus  100  according to the first embodiment, a value (time) obtained by multiplying the time of the sampling cycle SC and the number of additions during taking of a moving average is set to exceed the time of the refresh cycle RC, thereby reducing the likelihood of the occurrence of a detection signal not to be reflected in generation of a photoacoustic image. 
         [0069]    The first embodiment achieves the following effect. 
         [0070]    As described above, in the first embodiment, the control portion  30  is provided that makes the semiconductor light-emitting element light source portion  10  emit light and acquires a detection signal in the sampling cycle SC shorter than the refresh cycle RC. Further, the control portion  30  generates a photoacoustic image to be displayed on the display portion  40  using the detection signal detected in the sampling cycle SC. As the sampling cycle SC is set to be shorter than the refresh cycle RC, a detection signal can be acquired within the refresh cycle RC. Thus, the detection signal acquired within the refresh cycle RC can be used for generating an image. This can easily reduce the likelihood of failing to update the screen  40   a  of the display portion  40  (displaying one image continuously) due to failing to acquire a detection signal during a cycle of updating the screen  40   a  (refresh cycle RC). This can easily make it less likely that the cycle of updating the screen  40   a  will be substantially extended. As a result, awkward motion of moving images displayed on the screen  40   a  (loss of smoothness) can be suppressed. Further, provision of the semiconductor light-emitting element light source portion  10  can shorten the sampling cycle SC easily, compared to use of a solid-laser light source portion having difficultly in shortening a light emission cycle (sampling cycle SC). 
         [0071]    As described above, in the first embodiment, the control portion  30  is configured to generate a photoacoustic image to be displayed on the display portion  40  by taking a moving average of detection signals detected in the sampling cycles SC. By doing so, a moving average of the detection signals detected in the sampling cycles SC is taken, so that a photoacoustic image can be generated with an increased S/N ratio (signal-to-noise ratio). 
         [0072]    As described above, in the first embodiment, the sampling cycle SC has a length that allows the semiconductor light-emitting element light source portion  10  to emit light several times while allowing a detection signal to be acquired several times within the refresh cycle RC. Thus, the several detection signals can be acquired within the refresh cycle RC. This can more easily reduce the likelihood of failing to update the screen  40   a  of the display portion  40  due to failing to acquire a detection signal during a cycle of updating the screen  40   a  (refresh cycle RC). As a result, awkward motion of moving images displayed on the screen  40   a  can be suppressed more easily. 
         [0073]    As described above, in the first embodiment, the control portion  30  is configured to generate a photoacoustic image to be displayed on the display portion  40  by taking a moving average of detection signals with the number of additions that makes a value obtained by multiplying the sampling cycle SC and the number of additions during taking of a moving average exceed the refresh cycle RC. This can reduce the likelihood of the occurrence of a detection signal out of acquired detection signals and not to be reflected in generation of a photoacoustic image as shown in  FIG. 4 , compared to the case of  FIG. 3  where a value obtained by multiplying the sampling cycle SC and the number of additions during taking of a moving average does not exceed the refresh cycle RC. 
         [0074]    As described above, in the first embodiment, the control portion  30  is configured to generate a photoacoustic image to be displayed on the display portion  40  by taking a moving average as an arithmetic average. This makes it possible to generate a photoacoustic image in such a manner as to smoothen a motion (difference) between individual generated photoacoustic images, unlike the case of taking a average as an arithmetic average. Thus, moving images formed of the individual photoacoustic images can be displayed smoothly. This configuration works effectively, particularly in displaying moving images of the inside of the test object P to change constantly such as a human body. 
         [0075]    As described above, in the first embodiment, the control portion  30  is configured to take a moving average each time a detection signal is acquired. By doing so, averaging processing is executed on every occasion on each detection signal by taking a moving average of detection signals, so that averaging processing for generating a photoacoustic image can be executed reliably at each refresh rate. As a result, a photoacoustic image can be generated reliably during update of the screen  40   a , making it possible to reliably reduce the likelihood of failing to update the screen  40   a . Thus, awkward motion of moving images displayed on the screen  40   a  can be suppressed reliably. 
         [0076]    As described above, in the first embodiment, the control portion  30  is configured to generate a photoacoustic image to be displayed on the display portion  40  by taking an arithmetic average of detection signals with the number of additions that makes a value obtained by multiplying the sampling cycle SC and the number of additions during taking of an arithmetic average about 125 msec or less. Thus, the redundancy of averaging time can be suppressed. This can suppress awkward motion of moving images formed of individual photoacoustic images due to redundancy of averaging time. 
         [0077]    As described above, in the first embodiment, the semiconductor light-emitting element  11   b  includes at least one of a light-emitting diode element, a semiconductor laser element, and an organic light-emitting diode element. If the light-emitting diode element is used as the semiconductor light-emitting element  11   b , using the light-emitting diode element of relatively low power consumption can reduce power consumption. If the semiconductor laser element is used as the semiconductor light-emitting element  11   b , a laser beam of relatively high directivity can be emitted to the test object. Thus, much of the beam from the semiconductor laser element can be applied reliably to the test object P. If the organic light-emitting diode element is used as the semiconductor light-emitting element  11   b , using the organic light-emitting diode element capable of being reduced in thickness easily facilitates size reduction of the semiconductor light-emitting element light source portion  10  to include the organic light-emitting diode element. 
       Second Embodiment 
       [0078]    A second embodiment will be described next by referring to  FIGS. 1 and 5 . In an example described in the second embodiment, unlike the aforementioned configuration of the first embodiment where averaging processing is executed by taking a moving average, averaging processing is executed by taking a average. Structures comparable to those of the first embodiment will be given the same signs and description of such structures will be omitted. 
         [0079]    As shown in  FIG. 1 , a photoacoustic imaging apparatus  200  according to the second embodiment of the present invention includes a control portion  130 . 
         [0080]    As shown in  FIG. 5 , like in the first embodiment, the sampling cycle SC has a length shorter than that of the refresh cycle RC and allowing the semiconductor light-emitting element light source portion  10  (hereinafter called the “light source portion  10 ”) to emit light several times while allowing a detection signal to be acquired several times within the refresh cycle RC. In the second embodiment, the control portion  130  is configured to make the light source portion  10  emit pulsed light and to acquire a detection signal resulting from the acoustic wave AW in the sampling cycle SC shorter than the refresh cycle RC. The control portion  130  is also configured to generate a photoacoustic image (photoacoustic image data) by executing averaging processing by taking a average using a detection signal detected in the sampling cycle SC. 
         [0081]    The control portion  130  is configured to generate a photoacoustic image (photoacoustic image data) to be displayed on the display portion  40  by taking a average of detection signals during averaging processing by taking of a average, with the number of additions (in  FIG. 5 , five) that makes a value (time) obtained by multiplying the time of the sampling cycle SC and the number of additions during taking of a average exceed the time of the refresh cycle RC. 
         [0082]    Averaging processing by taking of a average and display of a generated photoacoustic image will be described next by referring to  FIG. 5  using specific examples. Conditions such as numerical values given in the following description are illustrative and not restrictive. 
         [0083]      FIG. 5  shows averaging processing by taking of a average schematically using an arrow B 21  and an arrow B 22 . Specifically, the arrows B 21  and B 22  show that averaging processing by taking of a average is executed in units of detection signals of a number corresponding to the number of additions. For example, the arrow B 21  shows that averaging processing is being executed by taking a average of detection signals acquired in a detecting section (1), a detecting section (2), a detecting section (3), a detecting section (4), and a detecting section (5) respectively. The arrow B 22  shows that averaging processing is being executed by taking a average of detection signals acquired in a detecting section (6), a detecting section (7), a detecting section (8), a detecting section (9), and a detecting section (10) respectively after the arrow B 21 . Averaging processing by taking of a average is also executed before the arrow B 21  and after the arrow B 22 . 
         [0084]    In the photoacoustic imaging apparatus  200 , an image displayed on the screen  40   a  of the display portion  40  is a photoacoustic image generated by averaging processing (a photoacoustic image already generated) to coincide with timing of refresh (update) of the screen  40   a  in the refresh cycle RC. Specifically, in  FIG. 5 , images displayed on the display portion  40  are photoacoustic images generated by averaging processing corresponding to the arrow B 21  shown as a black arrow and averaging processing corresponding to the arrow B 22  shown as a black arrow. 
         [0085]    Thus, in the case of the photoacoustic imaging apparatus  200  according to the second embodiment, the arrow B 22  also covers all the detection signals corresponding to the detecting sections (6) to (10) acquired in a period from the arrow B 21  to the arrow B 22 . Thus, there will be no detection signal not to be reflected in generation of a photoacoustic image. For the convenience of illustration, the arrows B 21  and B 22  have been described as examples. However, detection signals acquired before the arrow B 21  and detection signals acquired after the arrow B 22  also do not include a detection signal not to be reflected in generation of a photoacoustic image. 
         [0086]    The configuration of the second embodiment is the same in the other respects as that of the first embodiment. 
         [0087]    The second embodiment achieves the following effect. 
         [0088]    As described above, in the second embodiment, the control portion  130  is provided that makes the semiconductor light-emitting element light source portion  10  emit light and acquires a detection signal in the sampling cycle SC shorter than the refresh cycle RC. Further, the control portion  130  generates a photoacoustic image to be displayed on the display portion  40  by taking a average of detection signals detected in the sampling cycles SC. As a result, like in the first embodiment, awkward motion of moving images displayed on the screen  40   a  (loss of smoothness) can be suppressed in the second embodiment. 
         [0089]    As described above, in the second embodiment, the control portion  130  is configured to generate a photoacoustic image to be displayed on the display portion  40  by taking a average as an arithmetic average. This makes it possible to reduce the number of detection signals to be stored (recorded) in the storage portion  30   a  (memory), compared to taking a moving average as an arithmetic average. This achieves a corresponding saving of the volume of the storage portion  30   a  (memory). 
         [0090]    The other effect of the second embodiment is the same as that achieved by the first embodiment. 
       Third Embodiment 
       [0091]    A third embodiment will be described next by referring to  FIGS. 6 to 8 . In an example described in the third embodiment, a average signal is generated using a detection signal and an image to be displayed on a display portion is generated based on the generated average signal. 
         [0092]    The configuration of a photoacoustic imaging apparatus  300  according to the third embodiment of the present invention will be described by referring to  FIGS. 6 to 8 . 
         [0093]    As shown in  FIGS. 6 and 7 , the photoacoustic imaging apparatus  300  according to the third embodiment of the present invention includes an apparatus body  201  and a probe portion  202 . The apparatus body  201  and the probe portion  202  are connected through a wire  251  and a wire  252 . The apparatus body  201  includes a control portion  230  and a display portion  240 . The probe portion  202  includes a light source portion  210  and a detecting portion  220 . The light source portion  210  is an example of a “semiconductor light-emitting element light source portion” according to the present invention. 
         [0094]    As shown in  FIGS. 6 and 7 , the light source portion  210  includes two light sources  211  and is configured to emit pulsed light for measurement from each of the two light sources  211  toward a test object P. Each of the two light sources  211  is connected through the wire  251  to the apparatus body  201  and is configured to receive power and a control signal supplied from the apparatus body  201  through the wire  251 . 
         [0095]    The two light sources  211  are arranged near the detecting portion  220  and on opposite sides of the detecting portion  220  so as to sandwich the detecting portion  220  therebetween. In this way, the two light sources  211  are configured to emit pulsed light toward the test object P from different positions. 
         [0096]    Each of the two light sources  211  includes a light source substrate  211   a  and a semiconductor light-emitting element  211   b . For example, a light-emitting diode element, a semiconductor laser element, or an organic light-emitting diode element is applicable as the semiconductor light-emitting element  211   b . The light source substrate  211   a  has a lower surface holding a plurality of semiconductor light-emitting elements  211   b  mounted in an array pattern. The light source substrate  211   a  is configured to make the semiconductor light-emitting element  211   b  emit a pulse based on a control signal output from the control portion  230 . 
         [0097]    The two semiconductor light-emitting elements  211   b  are both configured to generate light of a measurement wavelength in an infrared region suitable for measurement of the test object P such as a human body (light having a center wavelength from about 700 to about 1000 nm, for example). The two semiconductor light-emitting elements  211   b  may be configured to generate light of different measurement wavelengths or light of the substantially same measurement wavelength. A measurement wavelength may be determined properly in a manner that depends on an intended detection target Q to be detected. 
         [0098]    As shown in  FIGS. 6 and 7 , the detecting portion  220  is an ultrasonic probe and connected to the apparatus body  201  through the wire  252 . The detecting portion  220  includes an ultrasonic vibrator  220   a . In the detecting portion  220 , the ultrasonic vibrator  220   a  includes a plurality of ultrasonic vibrators  220   a  arranged in an array pattern. The detecting portion  220  is configured to detect an acoustic wave (ultrasonic wave) AW in response to vibration of the ultrasonic vibrator  220   a  caused by an acoustic wave generated from the detection target Q in the test object P when the detection target Q absorbs pulsed light emitted from the light source portion  210 . The detecting portion  220  is configured to be capable of generating an ultrasonic wave UW by making the ultrasonic vibrator  220   a  vibrate based on a control signal output from the control portion  230 . The detecting portion  220  is also configured to detect the ultrasonic wave UW in response to vibration of the ultrasonic vibrator  220   a  caused by this ultrasonic wave UW reflected in the test object P. The detecting portion  220  is configured to output a detection signal corresponding to the detected acoustic wave AW or the detected ultrasonic wave UW to the control portion  230  through the wire  252 . 
         [0099]    In this description, for the convenience of explanation, an ultrasonic wave generated by absorption of pulsed light by the detection target Q in the test object P will be called an “acoustic wave,” an ultrasonic wave generated by the ultrasonic vibrator  220   a  and reflected in the test object P will be called an “ultrasonic wave,” and the “acoustic wave” and the “ultrasonic wave” will be described distinctively. 
         [0100]    The control portion  230  includes a CPU and a storage portion  230   a  such as a ROM or a RAM. As shown in  FIG. 6 , the control portion  230  is configured to form an image of the inside of the test object P based on a detection signal output from the detecting portion  220 . More specifically, the control portion  230  is configured to generate a photoacoustic image based on a detection signal resulting from the acoustic wave AW and to generate an ultrasonic image based on a detection signal resulting from the ultrasonic wave UW. The control portion  230  is configured to be capable of forming an image of various types of information in the test object P by synthesizing the photoacoustic image and the ultrasonic image. Generation of the photoacoustic image resulting from the acoustic wave AW will be described in detail later. 
         [0101]    As shown in  FIG. 6 , the display portion  240  is formed of a general liquid crystal type monitor or a scanning type monitor. The display portion  240  has a screen  240   a  and is configured to display an image such as an image of the inside of the test object P on the screen  240   a  formed by the control portion  230 . As shown in  FIG. 8 , the display portion  240  is configured in such a manner that the screen  240   a  is updated at a certain refresh rate (frequency). The certain refresh rate to be applied is generally about 50 Hz or more (about 50 Hz, about 60 Hz, or about 120 Hz, for example), and these values are applicable as the certain refresh rate. 
         [0102]    The refresh rate mentioned herein is a value indicating the number of times the screen  240   a  is refreshed (updated) per unit time (one second, for example). This means that, if the refresh rate is about 60 Hz, the screen  240   a  is refreshed about 60 times in one second. In other words, this means that the screen  240   a  is refreshed in each cycle of a refresh rate (hereinafter called a refresh cycle) RC of about 16.7 msec. In  FIG. 8 , timing of refresh of the screen  240   a  is schematically shown by a substantially rectangular pulse wave. In the case of a liquid crystal type monitor, for example, the screen  240   a  is refreshed at the time of rising of a substantially rectangular pulse wave. In the case of a scanning type monitor, for example, the monitor is scanned within the refresh cycle RC to refresh the screen  240   a.    
         [0103]    The following describes the details of generation of a photoacoustic image by the photoacoustic imaging apparatus  300  according to the third embodiment by referring to  FIGS. 8 and 9 . The following description is about acquisition of a detection signal resulting from the acoustic wave AW and generation of a photoacoustic image. Thus, a signal simply called a detection signal means a detection signal resulting from the acoustic wave AW. 
         [0104]    In outline, the photoacoustic imaging apparatus  300  acquires detection signals resulting from the acoustic waves AW and executes averaging processing on the acquired detection signals. Then, the photoacoustic imaging apparatus  300  generates a photoacoustic image based on the detection signals having been subjected to the averaging processing. This averaging processing is intended to increase an S/N ratio by executing averaging processing on individual detection signals. The following describes these processing steps sequentially. 
         [0105]    As shown in  FIG. 8 , in the photoacoustic imaging apparatus  300 , the control portion  230  is configured to acquire a detection signal at a sampling frequency (any frequency from 1 to 10 kHz, for example) that determines a certain sampling cycle (hereinafter simply called a sampling cycle) SC to be one cycle. 
         [0106]    More specifically, the control portion  230  is configured to make the light source portion  210  emit pulsed light and to acquire a detection signal in a detecting section belonging to the sampling cycle SC and shown by a substantially rectangular pulse wave. 
         [0107]    The control portion  230  is configured to execute the following in a signal processing section belonging to the sampling cycle SC and following the detecting section of the same sampling cycle SC: storing of a detection signal acquired in this sampling cycle SC into the storage portion  230   a , averaging processing by using a plurality of stored detection signals, etc. 
         [0108]    The sampling cycle SC has a length shorter than that of the refresh cycle RC and allowing the light source portion  210  to emit pulsed light several times while allowing a detection signal to be acquired several times within the refresh cycle RC. 
         [0109]    As shown in  FIG. 8 , in the third embodiment, the control portion  230  is configured to generate a average signal S (S 1 , S 2 , and S 3  shown in  FIG. 8 ) by taking a average of a plurality of detection signals from a detection signal acquired first to a detection signal acquired last within one refresh cycle RC.  FIG. 8  schematically shows the average signal S (S 1  to S 3 ) by surrounding detection signals by chain double-dashed lines that are used for a average. The detection signal to be acquired first can be a detection signal acquired immediately after timing of one refresh (at the time of rising of a substantially rectangular pulse wave), for example. The detection signal to be acquired last can be a detection signal acquired immediately before timing of refresh subsequent to the timing of the former refresh. 
         [0110]    As shown in  FIG. 9 , in the third embodiment, the control portion  230  is configured to generate a photoacoustic image (photoacoustic image data) by defining the average signal S as one unit and acquiring the average signals S as a plurality of units (in  FIG. 9 , thee units), and by executing averaging processing further by taking a moving average using the acquired average signals S as the plurality of units. The control portion  230  is configured to display the photoacoustic image on the screen  240   a  of the display portion  240  by outputting the generated photoacoustic image data to the display portion  240 . 
         [0111]    In the third embodiment, the control portion  230  is configured to acquire the average signals S as a plurality of units in such a manner that the number of detection signals to be subjected to averaging processing (in other words, the number of detecting sections shown in  FIG. 8 ) reaches a certain number or more during averaging processing by taking of a moving average of the average signals S. If the certain number is 100 and one average signal S includes 20 detection signals on average, for example, average signal S as five units or more are acquired. The certain number is determined properly by experiment conducted in consideration of an S/N ratio desirable for imaging, for example. 
         [0112]    The control portion  230  is configured to acquire the average signals S as a plurality of units in such a manner that a value (averaging time) obtained by multiplying the time of the sampling cycle SC and the number of detection signals to be subjected to averaging processing is about 125 msec or less. If the sampling cycle SC is about 1 msec, for example, the number of detection signals to be subjected to averaging processing is 125 (125 times) or less. Thus, if the average signal S includes 20 detection signals on average, the average signals S of less than seven units are acquired. By doing so, the redundancy of averaging time can be suppressed. This can suppress awkward motion of moving images formed of individual photoacoustic images due to redundancy of averaging time. 
         [0113]    The aforementioned processing will be described next by referring to  FIGS. 8 and 9  and giving specific examples. Conditions such as numerical values given in the following description are illustrative and not restrictive. 
         [0114]      FIG. 8  shows generation of the average signal S by taking a average of detection signals within the refresh cycle RC.  FIG. 8  shows three average signals S 1  to S 3  acquired as the average signal S. 
         [0115]    The average signal S 1  is a signal generated by taking a average of four detection signals from a detection signal acquired first in a detecting section (3) within a refresh cycle RC 1  to a detection signal acquired last in a detecting section (6) within the refresh cycle RC 1 . Likewise, the average signal S 2  is a signal generated by taking a average of five detection signals from a detection signal acquired first in a detecting section (7) within a refresh cycle RC 2  to a detection signal acquired last in a detecting section (11) within the refresh cycle RC 2 . Likewise, the average signal S 3  is a signal generated by taking a average of five detection signals from a detection signal acquired first in a detecting section (12) within a refresh cycle RC 3  to a detection signal acquired last in a detecting section (16) within the refresh cycle RC 3 . The average signal S is also generated before generation of the average signal S 1  and after generation of the average signal S 3 . However, for the sake of simplicity, generation of such average signals is omitted from the drawing. 
         [0116]      FIG. 9  shows generation of a photoacoustic image by executing averaging processing further by taking a moving average using the average signals S as a plurality of units.  FIG. 9  shows averaging processing by taking of a moving average schematically using an arrow B 201 , an arrow B 202 , and an arrow B 203 . Specifically, the arrows B 201  to B 203  show that averaging processing on the average signals S is executed by taking a moving average on every occasion (in units of average signals S), with the number of additions set at three. For example, the arrow B 203  shows that averaging processing is being executed by taking a moving average of the average signals S 1  to S 3 . 
         [0117]    In the photoacoustic imaging apparatus  300 , an image displayed on the screen  240   a  of the display portion  240  is a photoacoustic image generated by averaging processing (a photoacoustic image already generated) to coincide with timing of refresh (update) of the screen  240   a  in the refresh cycle RC. As described above, the photoacoustic imaging apparatus  300  generates a photoacoustic image by executing averaging processing while defining the average signal S as one unit, so that all acquired detection signals can be used for generating the photoacoustic image. 
         [0118]    The third embodiment achieves the following effect. 
         [0119]    As described above, in the third embodiment, the control portion  230  is provided that generates the average signal S by taking a average of detection signals from a detection signal acquired first within the refresh cycle RC to a detection signal acquired last within this refresh cycle RC. The control portion  230  generates a photoacoustic image to be displayed on the display portion  240  based on the average signal S. By doing so, all detection signals acquired within the refresh cycle RC can be used for generating a photoacoustic image. This can reduce the likelihood of the occurrence of a detection signal out of acquired detection signals and not to be reflected in a photoacoustic image to be displayed on the screen  240   a  of the display portion  240 . As a result, the acquired detection signals can be used efficiently for generating a photoacoustic image. 
         [0120]    As described above, in the third embodiment, the control portion  230  is configured to generate a photoacoustic image to be displayed on the display portion  240  by defining the average signal S generated by taking a average as one unit and acquiring the average signals S as a plurality of units (three units), and by taking an arithmetic average of the acquired average signals S as the plurality of units. This achieves generation of a photoacoustic image by executing averaging processing on more detection signals, so that the photoacoustic image can be generated with an increased S/N ratio (signal-to-noise ratio). As a result, a clear photoacoustic image can be generated through efficient use of acquired detection signals. 
         [0121]    As described above, in the third embodiment, the control portion  230  is configured to generate a photoacoustic image to be displayed on the display portion  240  by taking a moving average as an arithmetic average for taking an arithmetic average of the average signals S. By doing so, while the average signals S are generated by taking a average, a moving average of these average signals S is taken. This makes it possible to generate a photoacoustic image in such a manner as to smoothen a motion (difference) between individual photoacoustic images. Thus, moving images formed of the individual photoacoustic images can be displayed smoothly while acquired detection signals are used efficiently. This configuration of taking a moving average works effectively, particularly in displaying moving images of the inside of the test object P to change constantly such as a human body. 
         [0122]    As described above, in the third embodiment, the control portion  230  is configured to take a moving average each time the average signal S is acquired. By doing so, averaging processing is executed on every occasion on each average signal S by taking a moving average of the average signals S, so that averaging processing for generating a photoacoustic image can be executed reliably at each refresh rate. As a result, a photoacoustic image can be generated reliably during update of the screen  240   a , making it possible to reliably reduce the likelihood of failing to update the screen  240   a . In this way, while an image is generated by efficiently using acquired detection signals, awkward motion of moving images displayed on the screen  240   a  can be suppressed reliably. 
         [0123]    As described above, in the third embodiment, the control portion  230  is configured to acquire the average signals S as a plurality of units in such a manner that a value obtained by multiplying the sampling cycle SC and the number of detection signals to be subjected to averaging processing by taking of an arithmetic average is about 125 msec or less. By doing so, the redundancy of averaging time can be suppressed. This can suppress awkward motion of moving images formed of individual photoacoustic images due to redundancy of averaging time. 
         [0124]    As described above, in the third embodiment, the control portion  230  is configured to define the average signal S generated by taking a average as one unit and acquire the average signals S as a plurality of units in such a manner that the number of detection signals reaches a certain number or more. The control portion  230  is also configured to generate a photoacoustic image to be displayed on the display portion  240  based on the acquired average signals S as the plurality of units. This makes it possible to execute averaging processing reliably using detection signals of the certain number or more, so that an S/N ratio (signal-to-noise ratio) can be increased reliably during generation of a photoacoustic image. As a result, a clear photoacoustic image can be generated reliably. 
         [0125]    As described above, in the third embodiment, the semiconductor light-emitting element  211   b  includes at least one of a light-emitting diode element, a semiconductor laser element, and an organic light-emitting diode element. If the light-emitting diode element is used as the semiconductor light-emitting element  211   b , using the light-emitting diode element of relatively low power consumption can reduce power consumption. If the semiconductor laser element is used as the semiconductor light-emitting element  211   b , a laser beam of relatively high directivity can be emitted to the test object. Thus, much of the beam from the semiconductor laser element can be applied reliably to the test object P. If the organic light-emitting diode element is used as the semiconductor light-emitting element  211   b , using the organic light-emitting diode element capable of being reduced in thickness easily facilitates size reduction of the light source portion  210  to include the organic light-emitting diode element. 
       Fourth Embodiment 
       [0126]    A fourth embodiment will be described next by referring to  FIGS. 6 to 8 and 10 . In an example described in the fourth embodiment, unlike the aforementioned configuration of the third embodiment where averaging processing on the average signals S is executed by taking a moving average, averaging processing on the average signals S is executed by taking a average. Structures comparable to those of the third embodiment will be given the same signs and description of such structures will be omitted. 
         [0127]    As shown in  FIG. 6 , a photoacoustic imaging apparatus  400  according to the fourth embodiment of the present invention (see  FIG. 7 ) includes a control portion  330 . 
         [0128]    As shown in  FIG. 8 , like in the third embodiment, the control portion  330  is configured to generate the average signal S (S 1 , S 2 , and S 3  shown in  FIG. 8 ) by taking a average of a plurality of detection signals from a detection signal acquired first to a detection signal acquired last within one refresh cycle RC. 
         [0129]    As shown in  FIG. 10 , in the fourth embodiment, the control portion  330  is configured to generate a photoacoustic image (photoacoustic image data) by defining the average signal S as one unit and acquiring the average signals S as a plurality of units (in  FIG. 10 , three units), and by executing averaging processing further by taking a average using the acquired average signals S as the plurality of units. The control portion  330  is configured to display the photoacoustic image on the screen  240   a  of the display portion  240  by outputting the generated photoacoustic image data to the display portion  240 . 
         [0130]    The aforementioned processing will be described next by referring to  FIG. 10  and giving specific examples. Conditions such as numerical values given in the following description are illustrative and not restrictive. Processing of generating the average signal S shown in  FIG. 8  is the same as the above-described processing of the third embodiment, so that description of this processing will be omitted. 
         [0131]      FIG. 10  shows generation of a photoacoustic image by executing averaging processing further by taking a average using the average signals S as a plurality of units.  FIG. 10  shows averaging processing by taking of a average schematically using an arrow B 211  and an arrow B 212 . Specifically, the arrows B 211  and B 212  show that averaging processing on the average signals S is executed by taking a average in units of average signals S of a number corresponding to the number of additions, with the number of additions set at three. For example, the arrow B 212  shows that averaging processing is being executed by taking a average of the average signals S 1  to S 3 . 
         [0132]    In the photoacoustic imaging apparatus  400 , an image displayed on the screen  240   a  of the display portion  240  is also a photoacoustic image generated by averaging processing (a photoacoustic image already generated) to coincide with timing of refresh (update) of the screen  240   a  in the refresh cycle RC. As described above, the photoacoustic imaging apparatus  400  also generates a photoacoustic image by executing averaging processing while defining the average signal S as one unit, so that all acquired detection signals can also be used for generating the photoacoustic image. 
         [0133]    The configuration of the fourth embodiment is the same in the other respects as that of the third embodiment. 
         [0134]    The fourth embodiment achieves the following effect. 
         [0135]    As described above, in the fourth embodiment, the control portion  330  is provided that generates a photoacoustic image to be displayed on the display portion  240  based on the average signal S. By doing so, in the fourth embodiment, all acquired detection signals can be used efficiently for generating a photoacoustic image, like in the third embodiment. 
         [0136]    As described above, in the fourth embodiment, the control portion  330  is configured to generate a photoacoustic image to be displayed on the display portion  240  by taking a average as an arithmetic average for taking an arithmetic average of the average signals S. This makes it possible to reduce the number of detection signals to be stored (recorded) in the storage portion  230   a  (memory), compared to taking a moving average as an arithmetic average. This achieves a corresponding saving of the volume of the storage portion  230   a  (memory). 
         [0137]    The other effect of the fourth embodiment is the same as that achieved by the third embodiment. 
       Fifth Embodiment 
       [0138]    A fifth embodiment will be described next by referring to  FIGS. 6, 7, and 11 . In an example described in the fifth embodiment, unlike the aforementioned configuration of the third embodiment, averaging processing is executed while the refresh cycle RC and the sampling cycle SC are synchronized with each other. Structures comparable to those of the third embodiment will be given the same signs and description of such structures will be omitted. 
         [0139]    As shown in  FIG. 6 , a photoacoustic imaging apparatus  500  according to the fifth embodiment of the present invention (see  FIG. 7 ) includes a control portion  430 . 
         [0140]    As shown in  FIG. 11 , in the fifth embodiment, the control portion  430  is configured to synchronize timing of start of the refresh cycle RC and timing of start of the sampling cycle SC with each other for each refresh cycle RC. More specifically, in  FIG. 11 , timing of start of the refresh cycle RC and timing of start of the sampling cycle SC are synchronized with each other at a moment t1, a moment t2, a moment t3 a moment t4, a moment t5, and at subsequent moments. In this case, as shown in  FIG. 11 , only the last sampling cycle SC within the refresh cycle RC is changed in length from the other sampling cycles SC within the same refresh cycle RC. This makes it possible to synchronize timing of start of the refresh cycle RC and timing of start of the sampling cycle SC with each other easily. 
         [0141]    Like in the third embodiment, the control portion  430  is configured to generate the average signal S (S 11 , S 12 , and S 13  shown in  FIG. 11 ) by taking a average of a plurality of detection signals from a detection signal acquired first to a detection signal acquired last within one refresh cycle RC. This allows all the average signals S (S 11  to S 13 ) to cover the same number of detection signals (the same number of detecting sections). 
         [0142]    More specifically, as shown in  FIG. 11 , the average signal S 11  includes five detection signals from a detection signal acquired in a detecting section (1) to a detection signal acquired in a detecting section (5). The average signal S 12  includes five detection signals from a detection signal acquired in a detecting section (6) to a detection signal acquired in a detecting section (10). The average signal S 12  includes five detection signals from a detection signal acquired in a detecting section (11) to a detection signal acquired in a detecting section (15). As described above, in the fifth embodiment, a photoacoustic image can be generated while all the average signals S (S 11  to S 13 ) cover the same number of detecting sections (the same number of detection signals). 
         [0143]    The configuration of the fifth embodiment is the same in the other respects as that of the third embodiment. 
         [0144]    The fifth embodiment achieves the following effect. 
         [0145]    As described above, in the fifth embodiment, the control portion  430  is provided that generates a photoacoustic image to be displayed on the display portion  240  based on the average signal S. By doing so, in the fifth embodiment, all acquired detection signals can be used efficiently for generating a photoacoustic image, like in the third embodiment. 
         [0146]    As described above, in the fifth embodiment, the control portion  430  is configured to synchronize timing of start of the refresh cycle RC and timing of start of the sampling cycle SC with each other for each refresh cycle RC. Thus, non-uniformity of the number of detection signals between the refresh cycles RC can be less likely to occur in each refresh cycle RC. In this way, the number of detection signals to form the average signal S can be less likely to vary between the refresh cycles RC, making it possible to reduce the likelihood of the occurrence of a difference in an image quality between individual photoacoustic images to be generated. 
         [0147]    As described above, in the fifth embodiment, the control portion  430  is configured to synchronize timing of start of the refresh cycle RC and timing of start of the sampling cycle SC with each other by changing the length of the last sampling cycle SC within the refresh cycle RC. Thus, timing of start of the refresh cycle RC and timing of start of the sampling cycle SC can be synchronized with each other only by changing the length of the last sampling cycle SC within the sampling cycle SC. As a result, timing of start of the refresh rate cycle RC and timing of start of the sampling cycle SC can be synchronized with each other easily. 
         [0148]    The other effect of the fifth embodiment is the same as that achieved by the third embodiment. 
         [0149]    The embodiments disclosed herein must be considered to be illustrative in all aspects and not restrictive. The range of the present invention is understood not by the above description of the embodiments but by the scope of claims for patent. All changes (modifications) within the meaning and range equivalent to the scope of claims for patent are to be embraced. 
         [0150]    For example, in the example shown in the above-described first and second embodiments, during averaging processing by taking of a moving average (average), the control portion  30  ( 130 ) takes a moving average (average) of detection signals with the number of additions that makes a value (time) obtained by multiplying the time of the sampling cycle SC and the number of additions during taking of a moving average (average) exceed the time of the refresh cycle RC. However, this is not to limit the present invention. In the present invention, as shown in  FIG. 3 , during averaging processing by taking of a moving average (average), a control portion may also take a moving average (average) of detection signals with the number of additions that makes a value (time) obtained by multiplying the time of a sampling cycle and the number of additions during taking of a moving average (average) equal to the time of a refresh cycle or less. In this case, a smaller number of additions achieves a corresponding saving of the volume of a storage portion (memory), compared to the case of  FIG. 4 . 
         [0151]    In the example shown in the above-described first embodiment, the control portion  30  takes a moving average of detection signals with the number of additions that makes a value (time) obtained by multiplying the time of the sampling cycle SC and the number of additions during taking of a moving average about 125 msec or less. However, this is not to limit the present invention. In the present invention, a control portion may also take a moving average of detection signals with the number of additions that makes a value (time) obtained by multiplying the time of a sampling cycle and the number of additions during taking of a moving average exceed 125 msec. 
         [0152]    In the example shown in the above-described first and second embodiments, several detecting sections exist within one refresh cycle RC. However, this is not to limit the present invention. In the invention, a refresh cycle covering only one detecting section may be present. 
         [0153]    In the example shown in the above-described third and fourth embodiments, a photoacoustic image is generated through averaging processing executed by taking a moving average (average) of the average signals S. However, this is not to limit the present invention. In the invention, a photoacoustic image may also be generated through processing other than averaging processing such as taking a moving average or a average. 
         [0154]    In the example shown in the above-described third and fourth embodiments, a photoacoustic image is generated by acquiring the average signals S as a plurality of units and using the acquired average signals S as the plurality of units as a basis. However, this is not to limit the present invention. In the invention, if the average signal S includes detection signals of a certain number or more, for example, a photoacoustic image may also be generated based on a average signal as one unit without acquiring the average signals S as a plurality of units. 
         [0155]    In the example shown in the above-described first to fifth embodiments, an arithmetic average is taken by taking a average or a moving average. However, this is not to limit the present invention. In the invention, an arithmetic average may be different from a average or a moving average. For example, an arithmetic average may be taken by weighted averaging (weighting averaging) of taking an average of detection signals each given a weight. 
       REFERENCE SINGS LIST 
       [0000]    
       
         
           
               10  Semiconductor light-emitting element light source portion 
               11   b ,  211   b  Semiconductor light-emitting element 
               20 ,  220  Detecting portion 
               30 ,  130 ,  230 ,  330 ,  430  Control portion 
               40 ,  240  Display portion 
               40   a ,  240   a  Screen 
               100 ,  200 ,  300 ,  400 ,  500  Photoacoustic imaging apparatus 
               210  Light source portion (semiconductor light-emitting element light source portion) 
             RC Refresh cycle (cycle of certain refresh rate) 
             SC Sampling cycle 
             S, S 1 , S 2 , S 3 , S 11 , S 12 , S 13  Average signal