Abstract:
A dynamic change detecting apparatus allows canceling the influence of environmental change or an individual difference between a plurality of laser elements so as to perform a stable detection. This apparatus has a laser, including a laser resonator, for emitting a laser beam while causing frequency modulation in accordance with dimensional change of the laser resonator; a partial reflection mirror for splitting the laser beam emitted by the laser into a plurality of split-beams and guiding the plurality of split-beams to a plurality of optical paths having mutually different optical path lengths respectively; a frequency shifter for causing frequency shift in at least one of the plurality of split-beams; a lens for combining the plurality of split-beams with each other to obtain interference light; an photodetector for detecting the interference light to obtain an intensity signal; a demodulation unit for demodulating the intensity signal to generate a demodulated signal; and an integration processing unit for obtaining a signal corresponding to the dynamic change on the basis of the demodulated signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and an apparatus for detecting dynamic change in ultrasonic wave or the like propagating through a medium. Further, the present invention relates to an ultrasonic diagnostic apparatus having such a dynamic change detecting apparatus. 
     2. Description of a Related Art 
     In an ultrasonic diagnostic apparatus for a so-called ultrasonic echo observation or the like, it is the general practice to use piezoelectric materials typically represented by PZT (Pb (read) zirconate titanate) for an ultrasonic sensor portion (probe). 
     FIGS. 12A and 12B schematically show the structure of a conventional probe. FIG. 12A is a whole perspective view of the probe, and FIG. 12B is an enlarged perspective view of array vibrator included in the probe. 
     As shown in FIG. 12A, the probe  301  has a thin box shape as a whole, and has a slender rectangular probing surface  302 . The probing surface  302  is brought into contact with a human body and an ultrasonic wave is transmitted so as to receive an ultrasonic echo reflected from the depths of the body. A cable  307 , which transmits a drive signal for transmitting an ultrasonic wave and a detection signal of the ultrasonic wave, is connected to the upper side of the probe  301 . 
     A comb-shaped array vibrator  303  serving as both a transmitter and a receiver of ultrasonic wave is housed in the probing surface  302 . As shown in FIG. 12B, the array vibrator  303  is provided a number of slits  306  (having a width of, for example, 0.1 mm) in a thin strip-shaped PZT sheet (having a thickness of, for example, 0.2 to 0.3 mm) so as to form a number of (for example, 256) comb-teeth-shaped individual vibrator  305  (having, for example, a width of 0.2 mm and a length of 20 mm). 
     An electrode is formed in each individual vibrator  305 , and a signal line is connected thereto. An acoustic lens layer or an acoustic matching layer made of resin material such as rubber is attached to the surface side (lower side in the drawing) of the array vibrator  303 , and a backing material is attached to the back side. The acoustic lens layer converges the transmitted ultrasonic waves effectively. The acoustic matching layer improves the transmission efficiency of ultrasonic waves. The backing material has a function of holding the vibrator and causes vibration of the vibrator to be finished earlier. 
     Such ultrasonic probe and ultrasonic diagnostic apparatus are described in detail in “Ultrasonic Observation Method and Diagnostic Method”, Toyo Publishing Co., or “Fundamental Ultrasonic Medicine”, Ishiyaku Publishing Co. 
     In the field of ultrasonic diagnostic, it is desired to collect three-dimensional data in order to obtain more detailed information about the interior of an object&#39;s body. In order to comply with such a demand, it is required to make ultrasonic detecting elements (ultrasonic sensors) into a two-dimensional array. In the aforementioned PZT, however, it is difficult to fine the devices down and integrate them in the present conditions for the following reasons. That is, processing technology of PZT materials (ceramics) is almost on a limit level, and further fining down leads to an extreme decrease in processing yield. Moreover, if the number of wires increases, electrical impedance of the element and crosstalk between the elements (individual vibrators) would increase. It is therefore considered difficult to realize a two-dimensional array probe using PZT at the present level of the art. 
     On the other hand, Japanese patent application publication JP-A-10-501893 discloses an ultrasonic detecting apparatus including an array of vertical cavity surface emission laser (VCSEL) excited electrically (pumping). A cavity length of each laser is modulated by the acoustic field propagated from an object. As a result, the laser beam obtained thereby is frequency modulated by the acoustic field. The modulated laser beam is converted into amplitude modulation signal by a detector head, and thereafter, detected by a CCD array. Then, information of the signal is transmitted electrically to the signal processing assembly and processed. It is stated that this ultrasonic apparatus can achieve high level detection of frequency bandwidth, high resolving power of space and simplification of electric wiring. 
     Further, a paper entitled “High Frequency Ultrasound Imaging Using an Active Photodetector” by James D. Hamilton et al. appears in IEEE TRANSACTIONS ON ULTRASCONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 45, NO. 3, MAY 1998. This paper discloses an ultrasonic detecting apparatus including laser and optical modulator having a waveguide made of neodymium doped glass. 
     However, the detection system using change in a length of the laser resonator due to the ultrasonic wave have no practicality without compensation for environmental changes such as temperature change because such a detection system has high sensitivity for displacement. In the case of arraying the sensors, since variance will be inevitably generated in oscillation frequencies at respective laser element, it would be difficult to put the sensors to practical use as an array, unless a measuring method which is not affected by the variance in oscillation frequencies of laser elements is used. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished in view of these problems. A first object of the present invention is to provide a dynamic change detecting method and apparatus for detecting dynamic change stably by canceling influence of environmental change or an individual difference between a plurality of laser elements. A second object of the present invention is to provide an ultrasonic diagnostic apparatus using such a dynamic change detecting apparatus and appropriate for collection of three-dimensional data. 
     In order to solve the aforementioned problems, a dynamic change detecting method according to the present invention comprises steps of: (a) emitting a laser beam while causing frequency modulation to the laser beam to be generated in accordance with change in a size of a laser resonator by propagating the dynamic change to a total reflection mirror included in the laser resonator to cause dynamic displacement to the total reflection mirror; (b) separating the laser beam into a plurality of split-beams and guiding the plurality of split-beams to a plurality of optical paths having mutually different optical path lengths, respectively; (c) causing frequency shift in at least one of the plurality of split-beams; (d) combining the plurality of split-beams with each other to obtain interference light, and detecting the interference light to obtain an intensity signal corresponding to intensity of the interference light; (e) demodulating the intensity signal to generate a demodulated signal; and (f) obtaining a signal corresponding to the dynamic change on the basis of the demodulated signal. 
     Moreover, a dynamic change detecting apparatus according to the present invention comprises a laser including a laser resonator having a total reflection mirror where a dynamic perturbation is generated by propagation of dynamic change, the laser emitting a laser beam while causing frequency modulation to the laser beam to be generated in accordance with change in a size of the laser resonator; first means for separating the laser beam emitted from the laser into a plurality of split-beams and guiding the plurality of split-beams to a plurality of optical paths having mutually different optical path lengths, respectively; second means for causing frequency shift in at least one of the plurality of split-beams; third means for combining the plurality of split-beams with each other to obtain interference light; a photodetector for detecting the interference light to obtain an intensity signal corresponding to intensity of the interference light; fourth means for demodulating the intensity signal to generate a demodulated signal; and fifth means for obtaining a signal corresponding to the dynamic change on the basis of the demodulated signal. 
     Further, an ultrasonic diagnostic apparatus according to the present invention comprises transmitting means for transmitting an ultrasonic wave; receiving means for receiving an ultrasonic echo to convert the ultrasonic echo into an electric signal, the receiving means comprising a laser, including a laser resonator having a total reflection mirror where a dynamic perturbation is generated by propagation of dynamic change, for emitting a laser beam while causing frequency modulation to the laser beam to be generated in accordance with change in a size of the laser resonator, means for separating the laser beam emitted from the laser into a plurality of split-beams and guiding the plurality of split-beams to a plurality of optical paths having mutually different optical path lengths respectively, means for causing frequency shift in at least one of the plurality of split-beams, means for combining the plurality of split-beams with each other to obtain interference light; a photodetector for detecting the interference light to obtaining an intensity signal corresponding to intensity of the interference light, means for demodulating the intensity signal to generate a demodulated signal, and means 45 for obtaining a signal corresponding to the dynamic change on the basis of the demodulated signal; and image processing and displaying means for image processing of the signal corresponding to the dynamic change and displaying an image on the basis of the signal. 
     According to the present invention, the separated laser beams pass through the optical paths having different optical path lengths respectively and the frequency shift is generated in at least one of the separated laser beams, and thereafter, the separated laser beams are combined with each other so as to cause interfere light (so-called heterodyne interference) even if the detection environment, for instance, the temperature is changed in the laser resonator. Therefore, intensity of the interfere light is hardly affected by the temperature change and the dynamic change of an object can be detected stably. In addition, in the case where the laser resonator is constructed as an array, the dynamic change of an object can be detected stably even if oscillation frequencies of respective resonator units have dispersion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram schematically showing a dynamic change detecting apparatus (ultrasonic detecting apparatus) according to a first embodiment of the present invention; 
     FIG. 2 is an enlarged schematic view showing displacement of a part of a laser resonator included in the dynamic change detecting apparatus as shown in FIG. 1; 
     FIG. 3 is a graph showing an example of displacement of a reflection mirror included in the laser resonator oscillating due to propagation of an ultrasonic wave; 
     FIG. 4 is a graph showing the oscillation frequency ν (t) of a laser beam oscillated from the laser resonator, when a reflection mirror in the laser resonator shifts with the displacement d(t) as shown in FIG. 3; 
     FIG. 5 is a graph showing a waveform of a beat signal in a photodetector when the reflection mirror in the laser resonator shifts with the displacement d(t) as shown in FIG. 3; 
     FIG. 6 is a graph showing a demodulated signal obtained by demodulating the beat signal as shown in FIG. 5; 
     FIG. 7 is a graph showing the displacement d(t) of the reflection mirror in the laser resonator reproduced on the basis of the demodulated signal as shown in FIG. 6; 
     FIG. 8 is a diagram schematically showing a dynamic change detecting apparatus (ultrasonic detecting apparatus) according to a second embodiment of the present invention; 
     FIG. 9 is a diagram schematically showing a dynamic change detecting apparatus (ultrasonic detecting apparatus) according to a third embodiment of the present invention; 
     FIG. 10 is a diagram schematically showing a dynamic change detecting apparatus (ultrasonic detecting apparatus) having a surface-emitting laser array, according to a fourth embodiment of the present invention; 
     FIG. 11 is a block diagram showing an ultrasonic diagnostic apparatus according to one embodiment of the present invention; and 
     FIG.  12 A and FIG. 12B schematically show the structure of a conventional probe. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, embodiments of the present invention will be described in detail with reference to the drawings. The same reference numerals designate the same components, and explanation about the same components is omitted. 
     FIG. 1 is a diagram showing a dynamic change detecting apparatus (ultrasonic detecting apparatus) according to a first embodiment of the present invention. 
     This dynamic change detecting apparatus  1  includes a laser  7  having a laser resonator and receives an ultrasonic wave  5  propagating in an object  3  at a total reflection mirror  21  of the laser resonator. Laser light L 1  emitted from the laser  7  is incident upon a heterodyne interference optical system  9 , and the light having passed through the heterodyne interference optical system  9  is detected by an photodetector  11 . An electric signal output from the photodetector  11  is conducted various processing in an electric signal processing unit  13 . 
     The laser  7  has a total reflection mirror  21 , a chamber  23  housing laser medium and so on, and a partial reflection mirror  25 , which are arranged from the left to the right in the drawing. This laser  7  is excited by electricity, lamp, laser light, or the like. 
     An ultrasonic wave  5 , which is propagating in an object  3  to be inspected (human body, for instance) from the left side in the drawing, is received by the total reflection mirror  21 . An acoustic matching layer or a seal layer is disposed on the surface of the total reflection mirror  21 . In the laser  7 , the propagation of the ultrasonic wave  5  causes dynamic displacement of the total reflection mirror  21 , which in turn causes perturbation in the optical resonator formed by the total reflection mirror  21  and the partial reflection mirror  25  so that the laser light L 1  emitted from the laser  7  is frequency-modulated. The detail of modulation process of sound against light in the laser  7  will be described after, referring to FIG.  2 . 
     In this embodiment, laser  7  of an external resonator type wherein an optical resonator is arranged outside a chamber  23  enclosing laser medium and so on is used. In this case, the perturbation due to the ultrasonic wave is propagated only to the total reflection mirror  21 . Alternatively, a resonator LD of a vertical type (surface-emission laser) for emitting light in a direction perpendicular to the composition direction of the chamber  23  may be used. In this case, the composition of the optical resonator including the chamber  23  can be shortened. If length of the optical resonator is equal to or less than ½ of the ultrasonic wavelength, the whole optical resonator receives perturbation due to the ultrasonic waves so that the length of the optical resonator is extended or shortened. 
     Laser light L 1  emitted from the laser  7  is incident upon the heterodyne interference optical system  9 . A beam splitter  31  is disposed on the nearest position to the laser  7  in the heterodyne interference system  9 . The laser light L 1  is partially reflected and partially passes through the beam splitter  31 . A partial reflection mirror  33  is disposed beyond the beam splitter  31 . The partial reflection mirror  33  reflects light L 2  that is a part of the laser light L 1 . A part of reflected light L 2  is reflected downward in the drawing by the beam splitter  31 . 
     A frequency shifter  35  including an acoustic optical module (AOM) or the like is disposed at the exit side of the partial reflection mirror  33 . The frequency shifter  35  shifts a frequency of the incident light L 1  slightly. The laser light L 1  having passed through the partial reflection mirror  33  is frequency-shifted by the frequency shifter  35  and becomes light L 3 . 
     A reflection prism  37  is disposed at the exit side of the frequency shifter  35 . The reflection prism  37  reflects the frequency-shifted light L 3  to the left side. 
     A part of the light L 3  passes through the partial reflection mirror  33  and is reflected downward in the drawing by the beam splitter  31 . 
     The light L 2  and the light L 3  both reflected downward by the beam splitter  31  are converged on the photodetector by a lens  39  and combined with each other so that they interfere with each other on the photodetector  11 . The photodetector  11  converts intensity (amplitude) of the interference light into an electric signal. 
     The electric signal output from photodetector  11  is transmitted to an electric signal-processing unit  13  and processed. 
     The electric signal processing unit  13  includes an amplifier  41  for amplifying the electric signal output from photodetector  11 , a demodulation unit  43  for demodulating the amplified signal, an integration processing unit  45  for integrating the demodulated signal, a waveform display unit  47  for displaying the integrated signal as a waveform, and a waveform storage unit  49  for storing the waveform. 
     FIG. 2 is an enlarged schematic view showing displacement of a part of a laser resonator included in the dynamic change detecting apparatus as shown in FIG.  1 . In FIG. 2, reflection mirror  21 , laser medium  23  and partial reflection mirror  33  of the laser  7  are shown. The ultrasonic wave  5  is received by the total reflection mirror  21 , and the total reflection mirror  21  vibrates in the right and left directions in the drawing. As a result, the length L of the resonator varies. Here, change of the resonator length L, that is, displacement of the total reflection mirror of the resonator is supposed to be d(t). 
     When the total reflection mirror of the laser resonator shifts by d(t) due to the ultrasonic wave, the frequency ν (t) of the laser oscillation deviates, and this deviation Δν (t) is expressed as follows:                Δ                   v        (   t   )         =       -     v   c       ·       d        (   t   )       L               (   1   )                                
     Out of laser light L 1  incident upon the heterodyne interference optical system  9  as shown in FIG. 1, the light L 2 , which has been transmitted through the beam splitter  31  and reflected by the partial reflection mirror  33 , is thereafter reflected from the beam splitter  31  so as to be incident upon the photodetector  11  through a lens  39 . Consequently, the laser light L 2  in a state where an ultrasonic wave is received to generate dynamic change in the total reflection mirror  21  can be expressed as follows: 
     
       
           f   1 ( t )=cos {2πν( t )· t+φ   1 }  (2) 
       
     
     where φ 1  designates an initial phase. 
     On the other hand, the light L 3  having passed through the partial reflection mirror  33  and the frequency shifter  35  is reflected from a reflection prism  37  and thereafter transmitted again through the partial reflection mirror  33 . Then, the light L 3  is reflected by the beam splitter  31  and incident upon the photodetector  11  through the lens  39 . Supposing that ΔX represents a difference of optical pass lengths between light L 2  and light L 3 , a time delay Δt=Δx/c is generated between light L 2  and light L 3  both incident upon the photodetector  11 . Where, “c” represents a velocity of the light. Therefore, the light L 3  is expressed as follows: 
     
       
           f   2 ( t )=cos {(Ω 0 +2πν( t−Δt ))· t+φ   2 }  (3) 
       
     
     where Ω 0  represents an amount of change in a shifted angular frequency caused by frequency shifter  35  and φ 2  represents an initial phase. 
     Supposing that Δν represents a difference between the oscillation frequency ν (t) at the time “t” and the oscillation frequency ν (t−Δt) at the time (t−Δt), the following expression can be obtained. 
     
       
         Δν( t )=ν( t )−ν( t−Δt )  (4) 
       
     
     Consequently, it can be expressed as follows: 
     
       
         ν( t−Δt )=ν( t )−Δν( t )  (5) 
       
     
     Therefore, the expression (3) can be rewrote as follows: 
     
       
           f   2 ( t )=cos {(Ω 0 +2π(ν( t )−Δν( t )))· t+φ   2 }  (6) 
       
     
     Since light L 2  and light L 3  are combined (superposed) with each other by the lens  39  on the photodetector  11 , Light L 2  and light L 3  interfere with each other on the photodetector  11 . From the expression (2) and (6), this superposition can be expressed as follows:                      g        (   t   )       =                    f   1          (   t   )       +       f   2          (   t   )                     =                2      cos                   1   2          {         (       ω   0     +     2        π        (       v        (   t   )       -     Δ                   v        (   t   )           )           )     ·   t     +     φ   2     -                                      (       2      π                     v        (   t   )       ·   t       +     φ   1       )     }     ·   cos                     1   2          {       (       ω   0     +     2        π        (       v        (   t   )       -     Δ                   v        (   t   )           )           )     ·                                t   +     φ   2     +     (       2      π                     v        (   t   )       ·   t       +     φ   1       )       }               =                2      cos                   1   2            {         (       ω   0     -     2      πΔ                   v        (   t   )           )     ·   t     +     φ   2     -     φ   1       }     ·                                cos                   1   2          {         (       ω   0     +     2      π                   (       2        v        (   t   )         -     Δ                   v        (   t   )           )         )     ·   t     +     φ   2     +     φ   1       }                     (   7   )                                
     Consequently, the amplitude variation A(t) generated by the superposition of light L 2  and light L 3  is expressed as follows:                A        (   t   )       =     2      cos                   1   2          {         (       ω   0     -     2      π                 Δ                   v        (   t   )           )     ·   t     +     φ   2     -     φ   1       }               (   8   )                                
     Now, for simplification, supposing that the ultrasonic waveform is a triangular waveform, the displacement d(t) of the total reflection mirror of the laser resonator  21  due to the ultrasonic wave is shown in FIG.  3 . The deviation of the laser oscillation frequency ν (t) becomes to have an opposite form to the displacement d(t) as shown in FIG.  4 . When a light beam whose oscillation frequency is deviating with time as shown in FIG. 4 is incident upon an heterodyne interference optical system as shown in FIG. 1, an amplitude modulation having a frequency F(t) is generated. The frequency F(t) is shifted by an amount of change in the oscillation frequency corresponding to a time delay due to an optical path difference against the original frequency Ω 0 /4π of heterodyne interference signal as a center frequency when the oscillation frequency is constant as shown in FIG.  5 . Here, F(t) is expressed as follows:          F        (   t   )       =             ω   0     /   2        π     ±     Δ                   v        (   t   )           2                            
     By detecting the light beam, an intensity signal corresponding to an intensity of the light, that is, a beat signal suffering the frequency modulation is obtained. Further, by demodulating the beat signal in the demodulation unit, the demodulated signal as shown in FIG. 6 can be obtained. The demodulated signal originally represents the change in the oscillation frequency corresponding to the time delay, and therefore, the displacement d(t) of the total reflection mirror  21  shift d(t) as shown in FIG. 7, that is, the ultrasonic waveform can be reproduced by conducting integration processing for the demodulated signal. 
     Dynamic change generated by various physical energy including an ultrasonic wave can be detected by displaying the waveform obtained by the integration processing on a display unit  47 . Further, the waveform obtained by such processing may be stored in a storing unit  49 . 
     For the matters concerning general signal processing in the electric signal processing unit  13 , it may be referred to “Ultrasonic observation method and diagnostic method”, Toyo Publishing Co., or “Fundamental ultrasonic medicine”, Ishiyaku Publishing Co. 
     Next, a dynamic change detecting apparatus (ultrasonic detecting apparatus) according to a second embodiment of the present invention will be described referring to FIG.  8 . FIG. 8 is a diagram schematically showing the apparatus. 
     A laser  7  similar to that in FIG. 1 is shown at the left end section as shown in FIG.  8 . Light emitted from the laser  7  is incident upon an optical fiber  51  through a lens  26 . 
     The optical fiber  51  extends to the right side in FIG. 8 passing through an optical coupler  53 . An optical fiber Bragg grating  55  is connected to the end of the optical fiber  51 . This grating  55  splits the incident light L 1  into light L 2  and light L 3 , similarly to the function of the partial reflection mirror  33  in the apparatus as shown in FIG. 1. A frequency shifter  59  is connected ahead of the grating  55 . The frequency shifter  59 , composed by winding an optical fiber  57  around a piezoelectric element  60 , shifts the frequency of the light passing through the optical fiber  57  according to the variation of the piezoelectric element diameter. A total reflection mirror  61  is disposed ahead of the frequency shifter  59 . 
     Light L 2  reflected from the grating  55  and light L 3  reflected from the total reflection mirror are superposed by the optical coupler  53 , and incident upon an optical fiber  63 . Further, the superposed light L 2  and L 3  are incident upon the photodetector  11  and converted into an electric signal. The following electric signal processing is performed similarly as in the apparatus as shown in FIG.  1 . 
     Next, a dynamic change detecting apparatus (ultrasonic detecting apparatus) according to a third embodiment of the present invention will be described referring to FIG.  9 . FIG. 9 is a diagram schematically showing the apparatus. 
     In this dynamic change detecting apparatus, a total reflection mirror  64  is disposed at the end of the optical fiber  63  in place of the optical fiber Bragg grating  55  in the apparatus as shown in FIG.  8 . Light L 2 , which is a part of light L 1  emitted from the laser  7  and having passed through the optical fiber  51 , is incident upon the optical fiber  63  at the optical coupler  53 , and light L 3 , which is another part of the light L 1 , transmits in the optical fiber  51  as it is. The light L 2  is reflected by the total reflection mirror  64 . On the other hand, the light L 3  is reflected by the total reflection mirror  61  and frequency-modulated by passing through the frequency shifter  59 . Those light L 2  and L 3  are superposed in the optical coupler  52  to be transmitted in the optical fiber  63  and incident upon the photodetector  11 . The other components of this apparatus are similar to the apparatus as shown in FIG.  1 . 
     Next, a dynamic change detecting apparatus according to a fourth embodiment of the present invention will be described referring to FIG.  10 . FIG. 10 is a schematic view showing the dynamic change detecting apparatus according to this embodiment. 
     In this dynamic change detecting apparatus, the dynamic change detecting systems, one of which is shown in FIG. 8, are composed to form an array. This dynamic change detecting apparatus has a surface emission laser array  73  wherein a number of laser reflection mirrors  71  are arranged in a matrix shape. A heterodyne interference optical system  70  similar to that in the dynamic change detecting apparatus as shown in FIG. 8 is connected to each laser reflection mirror  71 . The interference light of each interference system  70  is transmitted to a photodetector array  75  through the optical fiber  63 , and detected individually. The electric signals generated by the photodetector array  75  are transmitted to a signal-processing array  77  and processed. 
     By arraying the dynamic change detecting systems, scanning, deviation, or conversion of ultrasonic waves can be performed dynamically and simultaneously in parallel. Therefore, it becomes easy to collect three-dimensional data. In the dynamic change detecting apparatus, since signals are derived by using fine optical fibers, an array having high integration can be realized. Further, since light is used as a signal, the signal transmission impedance does not increase. Furthermore, such an apparatus may be realized by arraying the dynamic change detecting system as shown in FIG.  9 . 
     Next, an ultrasonic diagnostic apparatus according to an embodiment of the present invention will be described referring to FIG.  11 . FIG. 11 is a block diagram schematically showing the ultrasonic diagnostic apparatus. 
     This ultrasonic diagnostic apparatus includes a transmitting unit  201 , a probe  209 , a receiving unit  211 , a TV scan converting unit  213  and a display unit (television monitor)  215 . 
     The transmitting unit  201  transmits an ultrasonic drive signal of a pulse type to an ultrasonic transmission transducer  203  including PZT, PVDF, or the like. The transducer  203  transmits an ultrasonic wave and causes the ultrasonic wave to propagate into an object body  206 . An ultrasonic partial reflection mirror  205  (a plate made of resin, or the like) is arranged on downside of the transducer  203  in the drawing. In the object body  206 , an ultrasonic echo  207  reflected upward in the drawing from depth  216  of the object body  206  is reflected to the right side by a partial reflection mirror  205  in the probe  209  and incident upon an ultrasonic detecting unit  208  of a two-dimensional array type. The ultrasonic detecting unit  208  converts an ultrasonic wave into an optical signal and transmits it to a receiving unit  211 . The receiving unit  211  converts the optical signal from the ultrasonic detecting unit  208  into an electric signal. The TV scan-converting unit  213  amplifies or otherwise processes the electric signal from the receiving unit  211 , and thereafter, performs the imaging processing. The signal after the imaging processing is transmitted to the display unit (TV monitor)  215  and is displayed. 
     According to this embodiment, the effect of the environmental change or individual difference between a plurality of laser elements can be cancelled so as to provide a dynamic change detecting apparatus that performs a stable detection. Therefore, an ultrasonic diagnostic apparatus appropriate for three-dimensional data can be realized. By using such an ultrasonic diagnostic apparatus, a high-resolution image of internal of an object&#39;s body can be obtained. 
     Although embodiments of the present invention have been explained above referring to drawings, the present invention is not limited to the above embodiments and various additions or modifications can be made. In the above embodiments, the dynamic change to be detected is described as an ultrasonic wave propagating in an object as an example. However, according to the present invention, it is also possible to detect a sound wave, acceleration, distortion, temperature, displacement, or other phenomena.