Abstract:
In an ultrasonic probe to be used in an ultrasonic diagnostic apparatus for medical use, ultrasonic transducers are cooled while sufficiently absorbing ultrasonic waves released to the back of the ultrasonic transducers without causing attenuation of ultrasonic waves transmitted or received by the ultrasonic transducers. The ultrasonic probe includes: an ultrasonic transducer array including plural ultrasonic transducers for transmitting and receiving ultrasonic waves; an acoustic matching layer provided on a front of the ultrasonic transducer array; a cooling mechanism directly or indirectly provided on a back of the ultrasonic transducer array and including a porous member; a backing material provided on the back of the ultrasonic transducer array via at least the cooling mechanism; and channels for circulation of a liquid heat transfer material in the cooling mechanism.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an ultrasonic probe to be used when intracavitary scanning or extracavitary scanning is performed on an object to be inspected, and an ultrasonic endoscope to be inserted into a body cavity of the object. Further, the present invention relates to an ultrasonic diagnostic apparatus including such an ultrasonic probe or ultrasonic endoscope and an ultrasonic diagnostic apparatus main body. 
         [0003]    2. Description of a Related Art 
         [0004]    In medical fields, various imaging technologies have been developed in order to observe the interior of an object to be inspected for making diagnoses. Especially, ultrasonic imaging for acquiring interior information of the object by transmitting and receiving ultrasonic waves enables image observation in real time and provides no exposure to radiation unlike other medical image technologies such as X-ray photography or RI (radio isotope) scintillation camera. Accordingly, ultrasonic imaging is utilized as an imaging technology at a high level of safety in a wide range of departments including not only the fetal diagnosis in the obstetrics, but gynecology, circulatory system, digestive system, etc. 
         [0005]    The ultrasonic imaging is an image generation technology utilizing the nature of ultrasonic waves that the ultrasonic waves are reflected at a boundary between regions with different acoustic impedances (e.g., a boundary between structures). Typically, an ultrasonic diagnostic apparatus (or referred to as an ultrasonic imaging apparatus or an ultrasonic observation apparatus) is provided with an ultrasonic probe to be used in contact with the object or ultrasonic probe to be inserted into a body cavity of the object. Alternatively, the apparatus may be provided with an ultrasonic endoscope in combination of an endoscope for optically observing the interior of the object and an ultrasonic probe for intracavitary. 
         [0006]    Using such an ultrasonic probe or ultrasonic endoscope, ultrasonic beams are transmitted toward the object such as a human body and ultrasonic echoes generated by the object are received, and thereby, ultrasonic image information is acquired. On the basis of the ultrasonic image information, ultrasonic images of structures (e.g., internal organs, diseased tissues, or the like) existing within the object are displayed on a display unit of the ultrasonic diagnostic apparatus. 
         [0007]    In the ultrasonic probe, a vibrator (piezoelectric vibrator) having electrodes formed on both sides of a material (a piezoelectric material) that expresses piezoelectric effect is generally used as an ultrasonic transducer for transmitting and receiving ultrasonic waves. As the piezoelectric material, a piezoelectric ceramics represented by PZT (Pb(lead)zirconate titanate), a polymeric piezoelectric material represented by PVDF (polyvinylidene difluoride), or the like is used. 
         [0008]    When a voltage is applied to the electrodes of the vibrator, the piezoelectric material expands and contracts due to the piezoelectric effect to generate ultrasonic waves. Accordingly, plural vibrators are one-dimensionally or two-dimensionally arranged and the vibrators are sequentially driven, and thereby, an ultrasonic beam transmitted in a desired direction can be formed. Further, the vibrator receives the propagating ultrasonic waves, expands and contracts to generate an electric signal. The electric signal is used as a reception signal of ultrasonic waves. 
         [0009]    When ultrasonic waves are transmitted, drive signals having great energy are supplied to the ultrasonic transducers. Not the whole energy of the drive signals is converted into acoustic energy and the considerable amount of energy turns into heat. Thus, there has been a problem of rising temperature of the ultrasonic probe during its use. However, the ultrasonic probe for medical use is used in direct contact with a living body of human or the like, and the surface temperature of the ultrasonic probe is requested to be 43° C. or below for safety reasons of prevention of low-temperature burn. 
         [0010]    As a related technology, Japanese Patent Application Publication JP-P2002-291737A discloses an ultrasonic probe having an ultrasonic probe head part for transmitting and receiving ultrasonic waves, a cable electrically connected to the ultrasonic probe head part, and a cable cooling part thermally connected to at least part of the cable. 
         [0011]    However, in JP-P2002-291737A, only a small portion of the ultrasonic probe head part is indirectly cooled via the cable by the cable cooling, and therefore, the cooling efficiency is not very good. 
         [0012]    Japanese Patent Application Publication JP-A-63-242246 discloses an ultrasonic probe for intracavitary to be inserted into a body cavity for imaging ultrasonic images, and the ultrasonic probe is provided with cooling means for cooling the heat generated by an ultrasonic converter during operation of the ultrasonic probe, in a predetermined position of a sound absorbing material. In JP-A-63-242246, a cooling pipe is provided in the ultrasonic probe and a cooling medium such as water is flown through the pipe, and thereby, the group of ultrasonic vibrators are cooled. 
         [0013]    However, when the cooling pipe is provided on the side of the group of ultrasonic vibrators ( FIG. 3 ), the thermal coupling between the cooling pipe and the group of ultrasonic vibrators becomes weaker and the cooling efficiency is not good. On the other hand, when the cooling pipe is provided on the back of the group of ultrasonic vibrators ( FIGS. 4-6 ), there is a fear that the ultrasonic waves released to the back of the group of ultrasonic vibrators may not be sufficiently absorbed. 
         [0014]    Japanese Patent Application Publication JP-A-11-299775 discloses an ultrasonic diagnostic apparatus including transferring means for guiding heat generated in a sound absorbing member to a position apart from the sound absorbing member, and releasing means provided at the position apart from the sound absorbing member, for releasing the heat guided by the transferring means. In the sound absorbing member, a surface opposite to a surface on which ultrasonic vibrators have been provided is formed in a curved configuration having a focus for reflecting and concentrating ultrasonic waves radiated from the ultrasonic vibrators toward the sound absorbing member, and a heat absorbing part of the transferring means is provided in the focus position within the sound absorbing member ( FIG. 6 ). 
         [0015]    In JP-A-11-299775, the temperature of the vibrator part at the leading end of an insertion part is controlled by electronic cooling means provided within the grip part of an ultrasonic probe via a heat pump ( FIG. 5 ). Therefore, the vibrator part is indirectly cooled via the heat pump and so on, and therefore, the cooling efficiency is not good. 
         [0016]    Japanese Patent Application Publication JP-A-61-58643 discloses an ultrasonic probe having ultrasonic vibrators and a case accommodating the vibrators, and the ultrasonic probe has means for guiding a cooling material to the object contact side of the ultrasonic vibrators. 
         [0017]    However, when a cooling medium is flown along a front face of an acoustic lens, that is, through partition walls between the object contact side and the acoustic lens of the ultrasonic probe ( FIG. 1 ), the distance between the ultrasonic vibrators and the object becomes longer and causes attenuation of ultrasonic waves transmitted and received by the ultrasonic vibrators. On the other hand, when a channel for the cooling medium is provided within a back acoustic absorbing material ( FIG. 3 ), there is a fear that the ultrasonic waves released to the back of ultrasonic vibrators may not be sufficiently absorbed. Further, when a channel for the cooling medium is provided between the back acoustic absorbing material and the case ( FIG. 5 ), the thermal coupling between the ultrasonic vibrators and the cooling medium becomes weaker, and therefore, the cooling efficiency is not good. 
         [0018]    Japanese Utility Model Application Publication JP-U-57-88073 discloses an ultrasonic probe provided with a path for a cooling medium in contact with the object outside of ultrasonic vibrators. 
         [0019]    However, as shown in FIG. 1 of JP-U-57-88073, the path for the cooling medium is provided apart from the space where the ultrasonic vibrators are provided, and therefore, only the periphery of the ultrasonic vibrators is cooled on the object contact surface, and the fact that the object is directly affected by the heat generation of the ultrasonic vibrators is unchanged. 
         [0020]    Further, Japanese Utility Model Application Publication JP-U-57-88074 discloses an ultrasonic probe provided, outside of ultrasonic vibrators, with a thermoelectric cooling element in contact with the object, and the thermoelectric cooling element is temperature-controllable for heating or cooling the object by changing the direction of a current flow. 
         [0021]    However, as shown in FIG. 1 of JP-U-57-88074, the cooling medium is provided apart from the space where the ultrasonic vibrators are provided, and therefore, only the periphery of the ultrasonic vibrators is cooled on the object contact surface, and the fact that the object is directly affected by the heat generation of the ultrasonic vibrators is unchanged. 
         [0022]    Japanese Patent Application Publication JP-P2003-38485A discloses an ultrasonic diagnostic apparatus including an ultrasonic probe provided with ultrasonic vibrators for transmitting and receiving ultrasonic waves, and a channel, through which a medium for transferring heat from the ultrasonic vibrators flows, is formed in the ultrasonic probe and a circulation mechanism for circulating the medium is connected to the channel. 
         [0023]    However, in JP-P2003-38485A, a water bag to be filled with water as the cooling medium is disposed at the living body side of the probe (i.e., before the ultrasonic vibrators), and thereby, the distance between the ultrasonic vibrators and the object becomes longer and causes the attenuation of ultrasonic waves to be transmitted and received by the ultrasonic vibrators. 
       SUMMARY OF THE INVENTION 
       [0024]    Accordingly, in view of the above-mentioned problems, a purpose of the present invention is, in an ultrasonic probe or an ultrasonic endoscope to be used in an ultrasonic diagnostic apparatus for medical use, to cool ultrasonic transducers while sufficiently absorbing ultrasonic waves released to the back of the ultrasonic transducers without causing attenuation of ultrasonic waves transmitted or received by the ultrasonic transducers. 
         [0025]    In order to accomplish the purpose, an ultrasonic probe according to one aspect of the present invention includes: an ultrasonic transducer array including plural ultrasonic transducers for transmitting and receiving ultrasonic waves; an acoustic matching layer provided on a front of the ultrasonic transducer array; a cooling mechanism directly or indirectly provided on a back of the ultrasonic transducer array and including a porous member; a backing material provided on the back of the ultrasonic transducer array via at least the cooling mechanism; and channels for circulation of a liquid heat transfer material in the cooling mechanism. 
         [0026]    Further, an ultrasonic endoscope according to one aspect of the present invention includes: an ultrasonic transducer array provided in an insertion part formed of a material having flexibility to be inserted into a body cavity of an object to be inspected and including plural ultrasonic transducers for transmitting and receiving ultrasonic waves; an acoustic matching layer provided on a front of the ultrasonic transducer array; a cooling mechanism directly or indirectly provided on a back of the ultrasonic transducer array and including a porous member; a backing material provided on the back of the ultrasonic transducer array via at least the cooling mechanism; and channels for circulation of a liquid heat transfer material in the cooling mechanism. 
         [0027]    Furthermore, an ultrasonic diagnostic apparatus according to one aspect of the present invention includes: the above-mentioned ultrasonic probe or ultrasonic endoscope; drive signal supply means for supplying drive signals to the plural ultrasonic transducers, respectively; signal processing means for generating image data representing an ultrasonic image by processing reception signals outputted from the plural ultrasonic transducers, respectively; and heat transfer material circulating means connected to the channels of the ultrasonic probe or ultrasonic endoscope, for collecting the heat transfer material from the ultrasonic probe or ultrasonic endoscope, cooling the collected heat transfer material, and supplying the cooled heat transfer material to the ultrasonic probe or ultrasonic endoscope. 
         [0028]    According to the present invention, since the cooling mechanism including the porous member is provided between the ultrasonic transducer array and the backing material, and thereby, the ultrasonic transducers can be cooled while providing matching of acoustic impedances. Therefore, ultrasonic waves released to the back of the ultrasonic transducers can be sufficiently absorbed without causing attenuation of ultrasonic waves transmitted or received by the ultrasonic transducers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a perspective view showing an exterior appearance and part of an interior of an ultrasonic probe according to the first embodiment of the present invention; 
           [0030]      FIG. 2  shows a configuration of an ultrasonic diagnostic apparatus main body to which the ultrasonic probe according to any one of the first to third embodiments of the present invention is connected; 
           [0031]      FIG. 3  shows the interior of the ultrasonic probe according to the first embodiment of the present invention; 
           [0032]      FIG. 4  is a partially sectional perspective view showing a single-layer ultrasonic transducer; 
           [0033]      FIG. 5  shows an interior of a head part of an ultrasonic probe according to the second embodiment of the e present invention; 
           [0034]      FIG. 6  is a partially sectional perspective view showing a multilayered ultrasonic transducer; 
           [0035]      FIG. 7  is a diagram for explanation of a modified example of the ultrasonic diagnostic apparatus main body to which the ultrasonic probe according to any one of the first to third embodiments of the present invention is connected; 
           [0036]      FIG. 8  is a plan view showing an interior of an ultrasonic probe according to the fourth embodiment of the present invention; 
           [0037]      FIG. 9  shows a configuration of an ultrasonic diagnostic apparatus main body to which the ultrasonic probe shown in  FIG. 8  is connected; 
           [0038]      FIG. 10  is a schematic diagram showing a configuration of an ultrasonic endoscope according to one embodiment of the present invention; and 
           [0039]      FIG. 11  is an enlarged view showing the leading end of an insertion part shown in  FIG. 10 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings. The same reference numbers will be assigned to the same component elements and the description thereof will be omitted. 
         [0041]      FIG. 1  is a perspective view showing an exterior appearance and part of an interior of an ultrasonic probe according to the first embodiment of the present invention. The ultrasonic probe  1  is used in contact with an object to be inspected when extracavitary scanning is performed. As shown in  FIG. 1 , a head part of the ultrasonic probe  1  includes a casing  10 , an ultrasonic transducer array  12  including plural ultrasonic transducers (vibrators)  11 , a first acoustic matching layer  13 , an acoustic lens  14 , a second acoustic matching layer  15 , a micro-channel  16  as a cooling mechanism for cooling the plural ultrasonic transducers  11 , a third acoustic matching layer  17 , a backing material  18 , flexible printed circuits (FPCs)  19  connected to a common electrode of the plural ultrasonic transducers  11 , and FPCs  20  connected to signal electrodes of the plural ultrasonic transducers  11 . 
         [0042]    In the embodiment, in order to cool the plural ultrasonic transducers  11 , the micro-channel  16  is formed on the back of the ultrasonic transducer array  12  between the second acoustic matching layer  15  and the third acoustic matching layer  17 , and a liquid heat transfer material (heat transfer medium) flowing through the micro-channel  16  cools the ultrasonic transducer array  12 . Here, the second acoustic matching layer  15  and the third acoustic matching layer  17  are provided for matching of acoustic impedances in a transfer path of ultrasonic waves from the ultrasonic transducer array  12  via the micro-channel  16  to the backing material  18 . Thereby, the ultrasonic waves released to the back of the ultrasonic transducers  11  can be sufficiently absorbed by the backing material  18 . 
         [0043]    Specifically, given that the acoustic impedance of the vibrators is Z 1 , the acoustic impedance of the micro-channel  16  filled with the heat transfer material is Zm, the acoustic impedance of the second acoustic matching layer  15  is Z 2 , the acoustic impedance of the third acoustic matching layer  17  is Z 3 , and the acoustic impedance of the backing material  18  is Z 4 , it is desirable that the materials of the respective parts are selected such that Z 1 &gt;Z 2 &gt;Zm&gt;Z 3 &gt;Z 4  is satisfied. 
         [0044]    Here, given that the center wavelength of the ultrasonic waves to be transmitted and received is λ, it is desirable that the thickness of the vibrator is set to λ/2. Further, it is desirable that the thickness of the second acoustic matching layer  15  and the thickness of the third acoustic matching layer  17  are respectively set to λ/4. When the thickness of the micro-channel  16  is larger and the attenuation of ultrasonic waves in the heat transfer material within the micro-channel  16  is larger, the third acoustic matching layer  17  may be omitted. Further, the second acoustic matching layer  15  may be omitted depending on the acoustic impedance values of the respective parts. 
         [0045]    Two circulation tubes  3   a  and  3   b  for circulation of the heat transfer material through the micro-channel  16 , an electric cable  4  including plural coaxial cables and/or single wire cables, and a cable cover  5  for protecting them are connected to the casing  10 . Here, the circulation tube  3   a  and an inflow hole formed in the third acoustic matching layer  17  and the backing material  18  forms a lead-in channel for leading in the heat transfer material, and the circulation tube  3   b  and an outflow hole formed in the third acoustic matching layer  17  and the backing material  18  forms a lead-out channel for leading out the heat transfer material. 
         [0046]      FIG. 2  shows a configuration of an ultrasonic diagnostic apparatus main body to which the ultrasonic probe according to any one of the first to third embodiments of the present invention is connected. As shown in  FIG. 2 , the circulation tubes  3   a  and  3   b  extending from the ultrasonic probe  1  are connected to an ultrasonic diagnostic apparatus main body  2  via a heat transfer material connector  21 . In the ultrasonic diagnostic apparatus main body  2 , a cooler  29  with a circulation pump cools the heat transfer material and supplies the cooled heat transfer material to the micro-channel  16  ( FIG. 1 ) via the circulation tube  3   a  for heat transfer medium circulation, and collects the heat transfer material that has passed through the micro-channel  16  via the circulation tube  3   b  for heat transfer medium circulation. Thereby, the heat transfer material circulates between the ultrasonic probe  1  and the ultrasonic diagnostic apparatus main body  2 . 
         [0047]    Further, the ultrasonic probe  1  is electrically connected to the ultrasonic diagnostic apparatus main body  2  via the electric cable  4  and an electric connector  22 . The electric cable  4  transmits drive signals generated in the ultrasonic diagnostic apparatus main body  2  to the respective ultrasonic transducers and transmits reception signals outputted from the respective ultrasonic transducers to the ultrasonic diagnostic apparatus main body  2 . 
         [0048]    The ultrasonic diagnostic apparatus main body  2  includes a control unit  23  for controlling the operation of the entire system including the ultrasonic probe  1  and the ultrasonic diagnostic apparatus main body  2 , a drive signal generating unit  24 , a transmission and reception switching unit  25 , a reception signal processing unit  26 , an image generating unit  27 , a display unit  28 , and the cooler  29  with the circulation pump. The drive signal generating unit  24  includes plural drive circuits (pulsers or the like), for example, and generates drive signals to be used for respectively driving the plural ultrasonic transducers. The transmission and reception switching unit  25  switches output of drive signals to the ultrasonic probe  1  and input of reception signals from the ultrasonic probe  1 . 
         [0049]    The reception signal processing unit  26  includes plural preamplifiers, plural A/D converters, and a digital signal processing circuit or CPU, for example, and performs predetermined signal processing of amplification, phasing addition, detection, etc. on the reception signals outputted from the respective ultrasonic transducers. The image generating unit  27  generates image data representing an ultrasonic image based on the reception signals on which the predetermined signal processing has been performed. The display unit  28  displays the ultrasonic image based on thus generated image data. 
         [0050]      FIG. 3  ( a ) is a plan sectional view of the ultrasonic probe  1  according to the first embodiment of the present invention Further,  FIG. 3  ( b ) is a side sectional view of the ultrasonic probe along the dashed-dotted line  3 B- 3 B′ shown in  FIG. 3  ( a ), and  FIG. 3  ( c ) is a front sectional view along the dashed-dotted line  3 C- 3 C′ shown in  FIG. 3  ( a ). In  FIG. 3  ( a ) to ( c ), the arrows indicate the flow directions of the heat transfer material. 
         [0051]    As shown in  FIG. 3  ( a ), the ultrasonic transducer array  12  includes the plural ultrasonic transducers  11  arranged in a one-dimensional form. As shown in  FIG. 4 , each ultrasonic transducer includes a piezoelectric material  31  such as PZT (Pb(lead)zirconate titanate) and electrodes  32  and  33  formed on two opposite surfaces of the piezoelectric material. One of the electrodes  32  and  33  may be commonly connected among the plural ultrasonic transducers as a common electrode. 
         [0052]    Referring to  FIG. 3  again, the plural ultrasonic transducers  11  generate ultrasonic waves based on the drive signals respectively supplied from the ultrasonic diagnostic apparatus main body. Further, the plural ultrasonic transducers  11  receive ultrasonic echoes propagating from the object and generate electric signals. The electric signals are outputted to the ultrasonic diagnostic apparatus main body and processed as reception signals of the ultrasonic echoes. In order to reduce the interference among the plural ultrasonic transducers  11  and suppress the lateral vibration of the ultrasonic transducers  11  to allow the ultrasonic transducers  11  to vibrate only in the longitudinal direction, the spaces between the plural ultrasonic transducers  11  may be filled with a filling material. 
         [0053]    At least one wiring pattern connected to the common electrode of the plural ultrasonic transducers  11  is formed on the two FPCs  19 . One end of the wiring pattern is connected to the common electrode of the plural ultrasonic transducers  11  and the other end of the wiring pattern is connected to the ground lines of the plural coaxial cables. Further, plural wiring patterns respectively connected to the signal electrodes of the plural ultrasonic transducers  11  are formed on the two FPCs  20 . One ends of the wiring patterns are respectively connected to the signal electrodes of the plural ultrasonic transducers  11  and the other ends of the wiring patterns are respectively connected to the hot lines of the coaxial cables. In  FIG. 3 , the cable for transmission of electric signals is omitted for easy understanding of the flow of the heat transfer material. 
         [0054]    The first acoustic matching layer  13  formed on the front of the ultrasonic transducers  11  is formed of Pyrex (registered trademark) glass or an epoxy resin including metal powder, which easily propagates ultrasonic waves, for example, and provides matching of acoustic impedances between the object as a living body and the ultrasonic transducers  11 . Thereby, the ultrasonic waves transmitted from the ultrasonic transducers  11  efficiently propagate within the object. Although the single-layer acoustic matching layer has been shown on the front of the ultrasonic transducers  11  in  FIGS. 1 and 3 , plural acoustic matching layers may be provided according to need. 
         [0055]    The acoustic lens  14  is formed of silicone rubber, for example, and focuses an ultrasonic beam transmitted from the ultrasonic transducer array  12  and propagating through the acoustic matching layer  13 , at a predetermined depth within the object. 
         [0056]    The second acoustic matching layer  15  and the third acoustic matching layer  17  are also formed of Pyrex (registered trademark) glass or an epoxy resin including metal powder, and their acoustic impedances satisfy the above explained condition. 
         [0057]    The backing material  18  is formed of a material having large acoustic attenuation such as an epoxy resin including ferrite powder, metal powder, or PZT powder, or rubber including ferrite powder, and promotes attenuation of unwanted ultrasonic waves generated from the ultrasonic transducers  11 . 
         [0058]    The micro-channel  16  is formed of a porous material such as porous ceramics. In  FIG. 3 , the micro-channel  16  is formed between the second acoustic matching layer  15  and the third acoustic matching layer  17 , and both side surfaces and both end surfaces of the micro-channel  16  are covered by the backing material  18  for preventing outflow of the heat transfer material. Alternatively, a coating may be formed by employing a resin material or the like to cover both side surfaces and both end surfaces of the micro-channel  16  and further cover the upper surfaces and/or lower surfaces of the micro-channel  16  in the drawing. As the resin material, epoxy resin, urethane resin, silicone resin, polyimide resin, acrylic resin, or the like may be used. 
         [0059]    The heat transfer material is a liquid for passing through the micro-channel  16  to absorb the heat generated from the ultrasonic transducers  11 . As the heat transfer material, a material having good heat transference is used. For example, liquid paraffin, silicone oil, water, alcohol, mixture of water and alcohol, and fluorinated inert liquid may be used. Among them, liquid paraffin, silicone oil, and a fluorinated inert liquid (e.g., FLUORINERT (registered trademark) manufactured by Sumitomo 3M) are preferable, and in the embodiment, the liquid paraffin is used. 
         [0060]    The inflow hole  6   a  and the outflow hole  6   b  for the heat transfer material are formed in the third acoustic matching layer  17  and the backing material  18 . Further, the circulation tube  3   a  is connected to the inflow hole  6   a  and the circulation tube  3   b  is connected to the outflow hole  6   b  in the lower surface of the backing material  18 . The heat transfer material introduced from the ultrasonic diagnostic apparatus main body via the circulation tube  3   a  into the ultrasonic probe sequentially passes the inflow hole  6   a , the micro-channel  16 , and the outflow hole  6   b , and is collected in the ultrasonic diagnostic apparatus main body via the circulation tube  3   b.    
         [0061]    As described above, in the embodiment, the heat transfer material cooled in the ultrasonic diagnostic apparatus main body  2  is flown through the micro-channel  16  of the ultrasonic probe  1 . Although the micro-channel  16  contacts the plural ultrasonic transducers  11  via the second acoustic matching layer  15 , the thickness of the second acoustic matching layer  15  is smaller than (about one-half of) the thickness of the ultrasonic transducers (vibrators)  11 , and thus, the heat generated by the ultrasonic transducers  11  is efficiently absorbed by the heat transfer material. 
         [0062]    Therefore, the plural ultrasonic transducers  11  can be uniformly cooled, and the central part of the ultrasonic transducer array  12 , in which heat especially tends to stay, can be sufficiently and evenly cooled. Thereby, the temperature distribution in the plural ultrasonic transducers  11  is averaged and the influence by the temperature on the ultrasonic transmission and reception operation (sensitivity variations or the like) can be reduced. 
         [0063]    Next, the second embodiment of the present invention will be explained. 
         [0064]      FIG. 5  ( a ) is a front view showing an interior of a head part of the ultrasonic probe according to the second embodiment of the present invention. Further,  FIG. 5  ( b ) is a plan sectional view of the ultrasonic probe along the dashed-dotted line  5 B- 5 B′ shown in  FIG. 5  ( a ), and  FIG. 5  ( c ) is a side sectional view of the ultrasonic probe along the dashed-dotted line  5 C- 5 C′ shown in  FIG. 5  ( a ). In  FIG. 5  ( a ), an acoustic matching layer  43  and an acoustic lens  44  shown in  FIG. 5  ( b ) are omitted. 
         [0065]    As shown in  FIG. 5  ( a ), the ultrasonic probe according to the second embodiment of the present invention has an ultrasonic transducer array  42  in which plural ultrasonic transducers  11  are two-dimensionally arranged, and accordingly, the micro-channel configuration formed within the ultrasonic probe is different from that in the first embodiment. The connection configuration between the ultrasonic probe and the ultrasonic diagnostic apparatus main body are the same as that have been explained with reference to  FIG. 2 . 
         [0066]    The head part of the ultrasonic probe according to the second embodiment of the present invention includes a casing  40 , the ultrasonic transducer array  42  including plural ultrasonic transducers  11 , a first acoustic matching layer  43 , an acoustic lens  44 , a second acoustic matching layer  45 , a micro-channel  46  for flowing a liquid heat transfer material (heat transfer medium), a third acoustic matching layer  47 , a backing material  48 , flexible printed circuits (FPCs)  49  connected to a common electrode of the plural ultrasonic transducers  11 , and FPCs  50  connected to signal electrodes of the plural ultrasonic transducers  11 . Further, the ultrasonic probe is connected to the ultrasonic diagnostic apparatus main body via circulation tubes  3   a  and  3   b  and an electric cable. The materials forming the first acoustic matching layer  43 , the acoustic lens  44 , the second acoustic matching layer  45 , the third acoustic matching layer  47 , and the backing material  48  and functions thereof are the same as those in the first embodiment. 
         [0067]    In the ultrasonic transducer array  42 , plural ultrasonic transducers  11  are arranged in a two-dimensional matrix form. As shown in  FIG. 4 , each ultrasonic transducer  11  includes a piezoelectric material  31  and electrodes  31  and  32  formed both sides of the piezoelectric material  31 . One of the electrodes  31  and  32  may be commonly connected among the plural ultrasonic transducers as a common electrode. In order to reduce the interference among the plural ultrasonic transducers  11  and suppress the lateral vibration of the ultrasonic transducers  11  to allow the ultrasonic transducers  11  to vibrate only in the longitudinal direction, the spaces between the plural ultrasonic transducers  11  may be filled with a filling material. 
         [0068]    At least one wiring pattern connected to the common electrode of the plural ultrasonic transducers  11  are formed on the two FPCs  49 . One end of the wiring pattern is connected to the common electrode of the plural ultrasonic transducers  11  and the other end of the wiring pattern is connected to the ground lines of the plural coaxial cables. Further, plural wiring patterns respectively connected to the signal electrodes of the plural ultrasonic transducers  11  are formed on the two FPCs  50 . One ends of the wiring patterns are respectively connected to the signal electrodes of the plural ultrasonic transducers  11  and the other ends of the wiring patterns are respectively connected to the hot lines of the coaxial cables. In  FIG. 5 , the cable for transmission of electric signals is omitted for easy understanding of the flow of the heat transfer material. 
         [0069]    The micro-channel  46  is formed of a porous material such as porous ceramics. In  FIG. 5 , the micro-channel  46  is formed between the second acoustic matching layer  45  and the third acoustic matching layer  47 , and four side surfaces of the micro-channel  46  are covered by the backing material  48  for preventing outflow of the heat transfer material. Alternatively, a coating may be formed by employing a resin material or the like to cover four side surfaces of the micro-channel  46  and further cover the upper surfaces and/or lower surfaces of the micro-channel  46  in the drawing. As the resin material, epoxy resin, urethane resin, silicone resin, polyimide resin, acrylic resin, or the like may be used. 
         [0070]    In the embodiment, FLUORINERT is used as the heat transfer material. The inflow hole  6   a  and the outflow hole  6   b  for the heat transfer material are formed in the third acoustic matching layer  47  and the backing material  48 . Further, the circulation tube  3   a  is connected to the inflow hole  6   a  and the circulation tube  3   b  is connected to the outflow hole  6   b  in the lower surface of the backing material  48 . The heat transfer material introduced from the ultrasonic diagnostic apparatus main body via the circulation tube  3   a  into the ultrasonic probe is led into the micro-channel  46  through the inflow hole  6   a , and two-dimensionally spreads as shown in  FIG. 5  ( a ). Then, the heat transfer material flows into the outflow hole  6   b  formed in a position diagonally opposing the inflow hole  6   a  on the front of the ultrasonic probe, and is collected in the ultrasonic diagnostic apparatus main body via the circulation tube  3   b.    
         [0071]    In the two-dimensional ultrasonic transducer array as shown in  FIG. 5  ( a ), the heat generated from the ultrasonic transducers located inner side is especially hard to disperse, and the heat especially tends to stay around the center. However, according to the embodiment, the heat transfer material is flown through the micro-channel  46  in contact with the plural ultrasonic transducers  11  via the second acoustic matching layer  45  having a relatively small thickness, and thereby, even the ultrasonic transducers around the center where the heat tends to stay can be sufficiently cooled. Therefore, the production of a temperature gradient can be suppressed in the two-dimensional ultrasonic transducer array, and thus, the influence due to temperature (e.g., sensitivity variations or the like) can be reduced. 
         [0072]    In the embodiment, the inflow hole  6   a  and the outflow hole  6   b  are formed in two locations at corners of the third acoustic matching layer  47  and the backing material  48 , however, the inflow hole and the outflow hole may be formed in other locations as long as the heat transfer material can be smoothly circulated. Further, two or more inflow holes and/or two or more outflow holes may be provided. 
         [0073]    Next, the third embodiment of the present invention will be explained. In the third embodiment, an ultrasonic transducer including a multilayered piezoelectric material shown in  FIG. 6  is used in place of the ultrasonic transducer including the single-layer piezoelectric material shown in  FIG. 4  in the ultrasonic probe shown in  FIG. 3  or  FIG. 5 . 
         [0074]    The multilayered ultrasonic transducer shown in  FIG. 6  includes plural piezoelectric material layers  71  formed of PZT or the like, a lower electrode layer  72 , internal electrode layers  73  and  74 , an upper electrode layer  75 , insulating films  76 , and side electrodes  77  and  78 . 
         [0075]    The lower electrode layer  72  is connected to the side electrode  77  on the left side in the drawing and insulated from the side electrode  78  on the right side in the drawing. Further, the internal electrode layers  73  and  74  are alternately inserted between the plural piezoelectric material layers  71 . The internal electrode layers  73  are connected to the side electrode  78  and insulated from the side electrode  77  by the insulating films  76 . On the other hand, the internal electrode layers  74  are connected to the side electrode  77  and insulated from the side electrode  78  by the insulating films  76 . Furthermore, the upper electrode layer  75  is connected to the side electrode  78  and insulated from the side electrode  77 . The plural electrodes of the ultrasonic transducer are thus formed, and thereby, five sets of electrodes for applying electric fields to the five layers of piezoelectric material layers  71  are connected in parallel. The number of the piezoelectric material layers is not limited to five as shown in  FIG. 6 , but two to four or six or more layers may be provided. 
         [0076]    In the multilayered ultrasonic transducer (here, also referred to as “element”), areas of facing electrodes are larger than those in the single-layer element, and the electric impedance becomes lower. Therefore, the multilayered element operates more efficiently for an applied voltage than the single-layer element. Specifically, given that the number of the piezoelectric material layers is N (N=5 in  FIG. 6 ), the number of the piezoelectric material layers is N times the number of the single-layer element and the thickness of each piezoelectric material layer is 1/N times the thickness thereof, and the electric impedance of the element is 1/N 2  times the electric impedance thereof. Therefore, the electric impedance of the element can be adjusted by increasing and decreasing the number of stacked layers of the piezoelectric material layers, and thus, the electric impedance matching with the drive circuit and/or the preamplifier can be easily provided and the sensitivity can be improved. On the other hand, the capacitance increases due to stacked form of the element, and the amount of heat generated from each element increases. 
         [0077]    According to the embodiment, the heat transfer material is flown through the micro-channel  16  shown in  FIG. 3  or the micro-channel  46  shown in  FIG. 5  and the respective elements can be efficiently cooled, even when the amount of heat generated from the multilayered element increases. Therefore, the temperature rise of the ultrasonic probe can be suppressed. 
         [0078]    Next, a modified example of the ultrasonic diagnostic apparatus main body, to which the ultrasonic probe according to any one of the first to third embodiments of the present invention is connected, will be explained with reference to  FIG. 7 . 
         [0079]    The ultrasonic diagnostic apparatus main body  2   a  shown in  FIG. 7  further has a temperature sensor  91  and a temperature control unit  92  compared to the ultrasonic diagnostic apparatus main body  2  shown in  FIG. 2 . The rest of the configuration is the same as that shown in  FIG. 2 . 
         [0080]    The temperature sensor  91  includes a thermistor, thermocouple, or the like. The temperature sensor  91  is attached to the cooler  29  with the circulation pump, and senses the temperature of the heat transfer material collected from the ultrasonic probe  1  via the circulation tube  3   b . The temperature control unit  92  obtains a value on the temperature of the heat transfer material based on a signal outputted from the temperature sensor  91 , and controls the operation of the cooler  29  with the circulation pump based on the obtained value. For example, when the obtained value on the temperature of the heat transfer material exceeds a predetermined value, the temperature control unit  92  lowers the preset temperature of the cooler or increases the pressure of the circulation pump for increasing the flow rate of the heat transfer material within the ultrasonic probe  1 . Alternatively, the cooler  29  with the circulation pump may be operated only when the obtained value on the temperature of the heat transfer material exceeds the predetermined value. 
         [0081]    According to the embodiment, since the operation of the cooler  29  with the circulation pump is feedback-controlled based on the temperature of the heat transfer material, the temperature of the heat transfer material can be easily kept in a certain range and the operation cost of the cooler  29  with the circulation pump can be reduced. As a modified example of the ultrasonic diagnostic apparatus main body shown in  FIG. 7 , a calculating unit for calculating the temperature based on the sensing result of the temperature sensor  91  is provided in place of the temperature control unit  92 , and the control unit  23  may control the cooler  29  with the circulation pump based on a calculation result thereof. 
         [0082]    Next, an ultrasonic probe according to the fourth embodiment of the present invention will be explained with reference to  FIGS. 8 and 9 .  FIG. 8  is a plan view showing an interior of the ultrasonic probe according to the fourth embodiment of the present invention, and  FIG. 9  shows a configuration of an ultrasonic diagnostic apparatus main body to which the ultrasonic probe shown in  FIG. 8  is connected. 
         [0083]    As shown in  FIG. 8 , the ultrasonic probe  1   a  according to the embodiment further includes a temperature sensor  93  for sensing the temperature within the ultrasonic probe compared to the ultrasonic probe  1  shown in  FIGS. 1 and 3 . The rest of the configuration is the same as the ultrasonic probe  1  shown in  FIGS. 1 and 3 . 
         [0084]    The temperature sensor  93  includes a thermistor, thermocouple, or the like, and is attached to the surface of the FPC  20 . Alternatively, the temperature sensor  93  may be disposed in or on the backing material. In either case, the temperature sensor  93  is desirably located as close as possible to the micro-channel ( 16  in  FIG. 3  or  46  in  FIG. 5 ) or the ultrasonic transducer  11 . The temperature sensor  93  is electrically connected to an ultrasonic diagnostic apparatus main body  2   b  ( FIG. 9 ) by a lead wire  94 . 
         [0085]    As shown in  FIG. 9 , the ultrasonic diagnostic apparatus main body  2   b  to be used in the embodiment has a temperature control unit  95 . The rest of the configuration of the ultrasonic diagnostic apparatus main body  2   b  is the same as that of the ultrasonic diagnostic apparatus main body  2  shown in  FIG. 2 . 
         [0086]    The temperature control unit  95  obtains a value on the temperature of the heat transfer material based on a sensing result of the temperature sensor  93  received via the lead wire  94 , and controls the operation of the cooler  29  with the circulation pump based on the obtained value such that the temperature of a head part  4  falls within a desired range. For example, when the obtained value on the temperature within the head part  4  exceeds a predetermined value, the temperature control unit  95  lowers the preset temperature of the cooler or increases the pressure of the circulation pump. Alternatively, the cooler  29  with the circulation pump may be operated only when the obtained value on the temperature within the head part  4  exceeds the predetermined value. 
         [0087]    According to the embodiment, since the operation of the cooler  29  with the circulation pump is feedback-controlled based on the temperature within the head part of the ultrasonic probe  1   a , the temperature within the head part can be controlled more accurately and the operation cost of the cooler  29  with the circulation pump can be reduced. Also in the embodiment, a calculating unit for calculating the temperature within the head part based on the sensing result of the temperature sensor  93  may be provided in place of the temperature control unit  95 , and the control unit  23  may control the cooler  29  with the circulation pump based on a calculation result thereof. 
         [0088]    Next, an ultrasonic endoscope according to one embodiment of the present invention will be explained with reference to  FIGS. 10 and 11 . The ultrasonic endoscope is an instrument having an ultrasonic probe for intracavitary provided at the leading end of an insertion part of an endoscopic examination device for optical observation of the intracavitary of the object. The ultrasonic endoscope is connected to the ultrasonic diagnostic apparatus main body in the same way as the ultrasonic probe in  FIG. 2 ,  7  or  9  to configure an ultrasonic diagnostic apparatus. 
         [0089]      FIG. 10  is a schematic diagram showing an appearance of the ultrasonic endoscope. As shown in  FIG. 10 , the ultrasonic endoscope  100  includes an insertion part  101 , an operation part  102 , a connecting cord  103 , a universal cord  104 , a circulation medium cable  105 , and a circulation medium connector  106 . The insertion part  101  of the ultrasonic endoscope  100  is an elongated tube formed of a material having flexibility for insertion into the body of the object. The operation part  102  is provided at the base end of the insertion part  101 , connected to the ultrasonic diagnostic apparatus main body via the connecting cord  103 , and connected to a light source unit via the universal cord  104 . 
         [0090]      FIG. 11  is an enlarged schematic diagram showing the leading end of the insertion part  101  shown in  FIG. 10 .  FIG. 11  ( a ) is a plan view showing the upper surface of the leading end of the insertion part  101 , and  FIG. 11  ( b ) is a side sectional view showing the side surface of the leading end of the insertion part  101 . In  FIG. 11  ( a ), the acoustic matching layer  130  shown in  FIG. 11  ( b ) is omitted. 
         [0091]    As shown in  FIG. 11 , at the leading end of the insertion part, an observation window  111 , an illumination window  112 , a treatment tool passage opening  113 , a nozzle hole  114 , and an ultrasonic transducer array  120  are provided. A punctuation needle  115  is provided in the treatment tool passage opening  113 . In  FIG. 11  ( a ), an objective lens is fit in the observation window  111 , and an input end of an image guide or a solid-state image sensor such as a CCD camera is provided in the imaging position of the objective lens. These configure an observation optical system. Further, an illumination lens for outputting illumination light to be supplied from the light source unit via a light guide is fit in the illumination window  112 . These configure an illumination optical system. 
         [0092]    The treatment tool passage opening  113  is a hole for leading out a treatment tool or the like inserted from a treatment tool insertion opening  107  provided in the operation part  102  shown in  FIG. 10 . Various treatments are performed within a body cavity of the object by projecting the treatment tool such as the punctuation needle  115  or forceps from the hole and operating it with the operation part  102 . The nozzle hole  114  is provided for injecting a liquid (water or the like) for cleaning the observation window  111  and the illumination window  112 . The ultrasonic transducer array  120  is a convex-type multi row array and includes plural ultrasonic transducers  121 - 123  arranged in five rows on a curved surface. 
         [0093]    As shown in  FIG. 11  ( b ), an acoustic matching layer  130  is provided in front of the ultrasonic transducer array  120 . An acoustic lens is provided on the acoustic matching layer  130  according to need. Further, on the back of the ultrasonic transducer array  120 , a second acoustic matching layer  131 , a micro-channel  132  as a cooling mechanism for cooling plural ultrasonic transducers, a third acoustic matching layer  133 , and a backing material  134  are provided. 
         [0094]    In the embodiment, in order to cool the plural ultrasonic transducers, the micro-channel  132  is formed between the second acoustic matching layer  131  and the third acoustic matching layer  132 , and a heat transfer material flowing through the micro-channel  132  cools the ultrasonic transducer array  120 . Here, the second acoustic matching layer  131  and the third acoustic matching layer  133  are provided for matching of acoustic impedances in a transfer path of ultrasonic waves from the ultrasonic transducer array  120  via the micro-channel  132  to the backing material  134 . Thereby, the ultrasonic waves released to the back of the ultrasonic transducers can be sufficiently absorbed by the backing material  134 . 
         [0095]    Also in the embodiment, as is the case of the first embodiment, given that the center wavelength of the ultrasonic waves to be transmitted and received is λ, it is desirable that the thickness of the ultrasonic transducer (vibrator) is set to λ/2. Further, it is desirable that the thickness of the second acoustic matching layer  131  and the thickness of the third acoustic matching layer  133  are respectively set to λ/4. when the thickness of the micro-channel  132  is larger and the attenuation of ultrasonic waves in the heat transfer material within the micro-channel  132  is larger, the third acoustic matching layer  133  may be omitted. Further, the second acoustic matching layer  131  may be omitted depending on the acoustic impedance values of the respective parts. 
         [0096]    The micro-channel  132  is formed of a porous material such as porous ceramics. In  FIG. 11 , the micro-channel  132  is formed between the second acoustic matching layer  131  and the third acoustic matching layer  133 , and both side surfaces of the micro-channel  132  are covered by the backing material  134  for preventing outflow of the heat transfer material. Alternatively, a coating may be formed by employing a resin material or the like to cover both side surfaces of the micro-channel  132  and further cover the upper surfaces and/or lower surfaces of the micro-channel  132  in the drawing. As the resin material, epoxy resin, urethane resin, silicone resin, polyimide resin, acrylic resin, or the like may be used. 
         [0097]    A circulation tube  7   a  for supplying the heat transfer material is connected to one end surface of the micro-channel  132  via an inflow hole formed on the backing material  134 , and a circulation tube  7   b  for collecting the heat transfer material is connected to the other end surface of the micro-channel  132  via an outflow hole formed on the backing material  134 . The circulation tubes  7   a  and  7   b  are accommodated in a heat transfer material cable  105  (see  FIG. 10 ) and connected to a cooling unit provided inside or outside of the ultrasonic diagnostic apparatus main body. The heat transfer material circulates between the micro-channel  132  and the cooling unit via the circulation tubes  7   a  and  7   b.    
         [0098]    As described above, since the heat transfer material is flown through the micro-channel  132 , the respective ultrasonic transducers  121 - 123  can be directly cooled. Thereby, the temperature rise of the ultrasonic endoscope is suppressed and the safety in ultrasonic endoscopic examination can be improved. 
         [0099]    In  FIG. 11 , the convex-type multirow array is shown as the ultrasonic transducer array  120 , however, a radial-type ultrasonic transducer array in which plural ultrasonic transducers are arranged on a cylindrical surface or an ultrasonic transducer array in which plural ultrasonic transducers are arranged on a spherical surface may be used. Further, also in the ultrasonic endoscopic shown in  FIG. 11 , the temperature sensor for sensing the temperature in the leading end of the insertion part  101  may be provided in the vicinity of the micro-channel  132  or the ultrasonic transducer so as to feedback-control the cooling unit of the heat transfer material based on the signal outputted from the temperature sensor.