Patent Publication Number: US-2011077520-A1

Title: Ultrasonic diagnostic apparatus and ultrasonic diagnostic method

Description:
FIELD OF THE INVENTION 
     The present invention relates to an ultrasonic diagnostic apparatus and an ultrasonic diagnostic method for performing diagnosis of a lesion based on a B/A coefficient obtained from a harmonic component of echo waves. 
     BACKGROUND OF THE INVENTION 
     Medical diagnosis using an ultrasonic diagnostic apparatus is commonly performed. The ultrasonic diagnostic apparatus is composed of an ultrasonic probe and an ultrasonic observation device. At a tip of the ultrasonic probe, a plurality of ultrasonic transducers (hereinafter abbreviated as UTs) are arranged. Each UT is composed of a backing material, a piezoelectric element, a pair of electrodes, an acoustic matching layer, and an acoustic lens. The UTs transmit ultrasonic waves to a subject (human body) and receive echo waves therefrom. Thereby detection signals are outputted from the UTs. The detection signals are electrically processed in an ultrasonic observation device or imaging device. Thus, an ultrasonic image is produced. 
     Emission with scanning of ultrasonic waves produces an ultrasonic cross-sectional image. To produce the ultrasonic cross-sectional image, a mechanical scan method and an electronic scan method are known. In the mechanical scan method, the UTs are mechanically rotated, swung, or slid. In the electronic scan method, the UTs are arranged in an array (hereinafter referred to as UT array), and the UT to be driven is selectively switched or changed using an electronic switch, for example, a multiplexer. 
     The ultrasonic waves from the UTs become distorted as they propagate inside the body of a patient. As a result, the ultrasonic waves propagating through the inside of the body of a patient have a fundamental component having the original frequency and nth harmonic components having a frequency n times as high as that of the fundamental component. For example, when ultrasonic waves (5 MHz) are transmitted from the UTs, the ultrasonic waves having a fundamental component (5 MHz) and second, third, fourth, . . . to nth harmonic components (10 MHz, 15 MHz, 20 MHz, . . . to 5×n MHz) propagate through the body of a patient. The UTs receive the echo waves, mostly composed of the fundamental component and partly the harmonic components. 
     Recently in the field of ultrasonic diagnosis, harmonic imaging attracts attention. The harmonic imaging uses the harmonic component of the echo waves for imaging. (see Japanese Patent Laid-Open Publication No. 08-0187245 corresponding to U.S. Pat. No. 5,724,976, Japanese Patent Laid-Open Publication No. 11-155863, PCT Publication No. WO 00/30543 corresponding to Japanese Patent Application Publication No. 2002-530145 and U.S. Pat. No. 6,645,145, Japanese Patent Laid-Open Publication No. 2003-169800, Japanese Patent Laid-Open Publication No. 2003-210464, PCT publication No. WO 2005/084267 corresponding to Japanese Patent Application Publication No. 2007-531357 and U.S. Pat. No. 7,612,483). The harmonic imaging, known as THI (Tissue Harmonic Imaging) and CHI (Contrast Harmonic Imaging), is used for clinical examinations of various diseases. The THI creates images that are derived solely from the harmonic component of the echo waves. The CHI creates images that are derived from the harmonic components of the harmonic resonance and disruption of microbubbles of an ultrasonic contrast agent. With the analysis of the harmonic components, a B/A coefficient (also referred to as non-linear parameter or non-linear acoustic parameter B/A) is acquired. The B/A coefficient indicates properties specific to living tissue, for example, density and stiffness. Application of the B/A coefficient to a new method of diagnosing a lesion is expected. 
     Conventionally, elastography and ARFI (Acoustic Radiation Force Impulse) are well known as methods for observing stiffness of living tissue, which is specific to living tissue. However, since elastography is performed with an ultrasonic probe being pushed against the body of a patient, observation results vary among operators or doctors and patients. Accordingly, it is difficult to obtain quantitative and reproducible values. Specifically, ARFI requires to emit extremely strong sound waves called push pulse to the human body for observation. It has been pointed out that the push pulse has adverse effects of to the human body. 
     The B/A coefficient has been researched because it is capable of clearing up the problems of the above described elastography and ARFI. For example, “Reflection type ultrasonic nonlinear parameter imaging system for medical diagnoses” [Takuso SATO et al, Report of Research Results for Grant-in-Aid for Scientific Research of the Japanese Ministry of Education, Culture, Sports, Science and Technology (Research Project No: 61420032), 1986-1987] discloses a technique to apply sound waves called “pump waves” to living tissue to create images derived from distribution of magnitude (B/A coefficient) of perturbation of living tissue. 
     At present, the B/A coefficient is not effectively used for the diagnosis of a lesion because measurement of an absolute value of the B/A coefficient still has uncertain factors. An apparatus disclosed in “Reflection type ultrasonic nonlinear parameter imaging system for medical diagnoses” has not been developed for commercial use. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an ultrasonic diagnostic apparatus and an ultrasonic diagnostic method in which a B/A coefficient is effectively utilized for diagnosis of a lesion. 
     According to the present invention, the inventors of the present invention focused on temperature dependence of the B/A coefficient to utilize this property for the diagnosis of a lesion. The temperature dependence of the B/A coefficient is disclosed in “In vitro measurement of B/A in animal tissue using thermodynamics” (Tetsuya ASAHINA, Nobuyuki ENDOH, Jpn. J. Med. Ultrasonics Vol. 17 No. 4 (1990) p. 358). For example, the B/A coefficient of bovine fat increases 0.03 per degree rise in temperature. The B/A coefficient of bovine liver increases 0.05 per degree rise in temperature. The temperature dependence of the B/A coefficients of water, physiological saline solution, and agar is measured as reference samples. The B/A coefficients of water and physiological saline solution increase 0.028 per degree rise in temperature. The B/A coefficient of agar increases 0.032 per degree rise in temperature. 
     An ultrasonic diagnostic apparatus of the present invention includes an ultrasonic transducer, a harmonic image processor, and an acquisition section. The ultrasonic transducer transmits ultrasonic waves to an object of interest, and receive echo waves from the object of interest to output a detection signal. The harmonic image processor calculates a B/A coefficient based on a signal component corresponding to a harmonic component in the detection signal. The acquisition section acquires information on a change in the B/A coefficient relative to a temperature change of the object of interest. 
     It is preferable that the ultrasonic diagnostic apparatus further includes a display controller which makes a monitor to display the information acquired by the acquisition section. 
     It is preferable that the display controller makes the monitor to display an ultrasonic image produced based on a fundamental component of the detection signal. 
     It is preferable that the ultrasonic diagnostic apparatus further includes a temperature controller for changing the temperature of the object of interest. 
     It is preferable that the temperature controller heats the object of interest with sound waves. 
     It is preferable that the temperature controller heats the object of interest with ultrasonic waves. 
     It is preferable that the temperature controller is the ultrasonic transducer. 
     It is preferable that the ultrasonic diagnostic apparatus further includes a controller for controlling at least one of a level, a frequency, a transmission time, a transmission area, and a focal region of the ultrasonic waves to adjust an irradiation energy amount of the ultrasonic waves transmitted to the object of interest. 
     It is preferable that the ultrasonic diagnostic apparatus further includes a designation section for designating a region of interest from the object of interest, and the temperature controller selectively changes the temperature of the designated region of interest. 
     It is preferable that the acquisition section acquires at least one of the relative values of the B/A coefficient when the temperature of the object of interest is constant, a rate of increase of the B/A coefficient while the object of interest is being heated, and a rate of decrease of the B/A coefficient while the object of interest is being cooled from the acquired information. 
     An ultrasonic diagnostic method of the present invention includes a transmission step, a reception step, an extraction step, a calculation step, and information obtaining step. In the transmission step, ultrasonic waves are transmitted to an object of interest. In the reception step, the echo waves from the object of interest are received and a detection signal is outputted. In the extraction step, a signal component corresponding to a harmonic component is extracted from the detection signal. In the calculation step, a B/A coefficient is calculated based on the signal component. In the information obtaining step, the above steps are repeated while the temperature of the object of interest changes, and information on temporal changes in the B/A coefficient is obtained. 
     According to the present invention, temporal changes in the B/A coefficient are obtained while the temperature of the object of interest changes. The obtained B/A coefficient is effectively utilized for a diagnosis of a lesion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and advantages of the present invention will be more apparent from the following detailed description of the preferred embodiments when read in connection with the accompanied drawings, wherein like reference numerals designate like or corresponding parts throughout the several views, and wherein: 
         FIG. 1  is a perspective view of an ultrasonic diagnostic apparatus; 
         FIG. 2  is a partly exploded perspective view of an ultrasonic transducer array; 
         FIG. 3  is a block diagram of an electrical configuration of the ultrasonic diagnostic apparatus; 
         FIG. 4  shows a monitor in a state of displaying a pop-up window; 
         FIG. 5  shows the monitor in a state of displaying a pop-up window; 
         FIG. 6  is a perspective view of an ultrasonic transducer array of another embodiment; and 
         FIG. 7  is a block diagram of an electrical configuration of ultrasonic transducers of another embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , an ultrasonic diagnostic apparatus  2  is composed of a portable ultrasonic observation device  10  or imaging device and an external ultrasonic probe  11 . The portable ultrasonic observation device  10  is composed of a housing  12  and a cover  13 . An operation section  14  is provided on the top surface of the housing  12 . The operation section  14  has buttons and a trackball to input various operation instructions to the portable ultrasonic observation device  10 . On an inner surface of the cover  13 , a monitor  15  is provided. The monitor  15  displays various operation screens including an ultrasonic image. 
     The cover  13  is attached to the housing  12  through a hinge  16 . The cover  13  is rotatable between an open position and a closed position. In the open position, the operation section  14  and the monitor  15  are exposed. In the closed position, the inner surface and the top surface of the housing  12  face each other to cover the operation section  14  and the monitor  15  with each other. On a side of the housing  12 , a grip (not shown) is provided. With the grip, the portable ultrasonic observation device  10  can be carried in the closed position. On the other side of the housing  12  opposite to the grip, a probe connector  17  is provided. The ultrasonic probe  11  is detachably connected to the probe connector  17 . 
     The ultrasonic probe  11  is composed of a scan head  18 , a connector  19 , and a cable  20 . The scan head  18  is held by an operator or doctor and gently pressed against a patient. The connector  19  is connected to the probe connector  17 . The cable  20  connects the scan head  18  and the connector  19 . At the tip of the scan head  18 , an ultrasonic transducer array (hereinafter abbreviated as UT array)  21  is incorporated. 
     In  FIG. 2 , the UT array  21  has a flat base  25  made from glass-epoxy resin or the like, a backing material  26 , ultrasonic transducers (hereinafter abbreviated as UTs)  27 , acoustic matching layers  28   a  and  28   b , and an acoustic lens  29  layered in this order from the bottom. 
     The backing material  26  is made from, for example, epoxy resin or silicone resin, and absorbs the ultrasonic waves emitted from the UTs  27  toward the base  25 . The backing material  26  has a convex surface with a substantially dome-like cross-section in an elevation direction (hereinafter abbreviated as EL direction) (see  FIG. 1 ). 
     Each of the UTs  27  has a plate-like shape, long in the EL direction. The UTs are spaced at regular intervals in an azimuth direction (scan direction of ultrasonic waves, hereinafter abbreviated as AZ direction) orthogonal to the EL direction. A filler  30  is filled between and around the UTs  27 . 
     The acoustic matching layers  28   a  and  28   b  are made from, for example, epoxy resin. The acoustic matching layers  28   a  and  28   b  reduce a difference in acoustic impedance between the UTs  27  and the patient. The acoustic lens  29  is made from silicone resin or the like. The acoustic lens  29  converges the ultrasonic waves emitted from the UTs  27  onto an object of interest inside the body of the patient. It should be noted that the acoustic lens  29  may not be used. Instead of the acoustic lens  29 , a protection layer may be provided. 
     Each UT  27  transmits ultrasonic waves and receives echo waves as a single channel. Since the UT array  21  is composed of the UTs  27  arranged in the AZ direction, the UT array  21  has multiple transmission and reception channels. 
     Each UT  27  has a piezoelectric ceramics thick film (inorganic piezoelectric element)  31  of PZT (lead zirconate titanate) sandwiched between first and second electrodes  32   a  and  32   b . When a voltage (excitation pulse) is applied to the electrodes  32   a  and  32   b , the inorganic piezoelectric element  31  oscillates or vibrates in the thickness direction to generate ultrasonic waves. Thereby, the ultrasonic waves are transmitted to an object of interest of the patient. When the UT  27  receives echo waves, the inorganic piezoelectric element  31  oscillates or vibrates to generate a voltage. The voltage is output as a detection signal from the UT  27  via the electrodes  32   a  and  32   b.    
     The second electrode  32   b  is separated on a channel-by-channel basis, and individually provided for each UT  27 . The first electrode  32   a  is provided all over the interface between the backing material  26  and the UTs  27 . The first electrode  32   a  covers all the UTs  27 . 
     In  FIG. 3 , the first electrode  32   a  is connected to a ground. The second electrode  32   b  is connected to one end of a switch (hereinafter abbreviated as SW)  40 . The SW  40  is a dual switch. A pulser  41  and a reception amplifier  42  are connected to the other ends of the SW  40 . 
     Under the control of the CPU  43 , the pulser  41  is driven by the scan controller  44 . The scan controller  44  selects a group of pulsers  41  to be driven from among all the pulsers  41 . The group of the pulsers  41  to be driven is changed at a predetermined time interval. To be more specific, for example, in the case where there are 128 transmission and reception channels, adjacent 48 channels are selected as a block to be driven. The channels are driven sequentially on a block-by-block basis. In each block, each of the UTs  27  is driven with a delay. Every time a transmission of ultrasonic waves and reception of echo waves takes place, the block to be driven is switched or changed. Because adjacent blocks partly overlap with each other, the blocks are switched such that the channels to be driven are shifted or changed at a pitch or interval of one to several channels. Based on the drive signal from the scan controller  44 , the pulser  41  transmits the UT  27  an excitation pulse to generate the ultrasonic waves. 
     An A/D converter (hereinafter abbreviated as A/D)  45  is connected to an output end of the reception amplifier  42 . The reception amplifier  42  may be a voltage feedback type or a charge storage type. The reception amplifier  42  amplifies the detection signal (detection voltage) outputted from the UT  27  that received echo waves. The A/D  45  converts the detection signal from the reception amplifier  42  into a digital signal. Although only a single group of one reception amplifier  42 , one A/D  45 , one pulser  41 , and one SW  40  is shown in the drawing, this group is provided for each channel. 
     As shown in  FIG. 3 , to transmit the ultrasonic waves, the SW  40  is turned to the pulser  41  side, namely, the pulser  41  and the UT  27  are connected, while the UT  27  and the reception amplifier  42  are disconnected. When the excitation pulse is applied from the pulser  41  to the UT  27 , ultrasonic waves are emitted from the surface of the acoustic lens  29 . 
     To receive the echo waves, on the other hand, the SW  40  is turned to the reception amplifier  42  side to disconnect the pulser  41  and the UT  27 , and connect the UT  27  and the reception amplifier  42 . When the echo waves are incident on the surface of the acoustic lens  29 , the detection signal corresponding to the echo waves is outputted from the UT  27 . The detection signal outputted from the UT  27  mainly represents a fundamental component of the echo waves and includes a harmonic component. The switching operation of the SW  40  is controlled by the scan controller  44 . 
     The A/D  45  is connected to a parallel/serial converter (hereinafter abbreviated as P/S)  46 . The P/S  46  converts the detection signal (parallel data) from each A/D  45  into serial data. The serial data is inputted to a serial/parallel conversion circuit (hereinafter abbreviated as S/P)  50  of the portable ultrasonic observation device  10  through the cable  20 , the connector  19 , and the probe connector  17 . 
     The S/P  50  converts the serial data sent from the ultrasonic probe  11  back into the original parallel data. A beamformer (hereinafter abbreviated as BF)  51  performs phase matching operation to the detection signal converted back into the parallel data. A log compression and detection circuit  52  performs log compression to the detection signal outputted from the BF  51  to detect its level (amplitude). The detection signal outputted from the log compression and detection circuit  52  is temporarily stored in a memory (not shown). 
     Under the control of a CPU  54 , a digital scan converter (hereinafter abbreviated as DSC)  53  converts the detection signal into a TV signal. The TV signal is subjected to D/A conversion by a D/A converter (not shown), and thus an ultrasonic image is displayed on the monitor  15 . 
     The CPU  54  controls overall operations of the portable ultrasonic observation device  10 . The CPU  54  operates each section based on an operation input signal from the operation section  14 . The CPU  54  controls power supply to the ultrasonic probe  11 . 
     The ultrasonic diagnostic apparatus  2  is provided with a normal mode, a harmonic imaging mode (hereinafter abbreviated as HI mode), and B/A coefficient acquisition mode. In the normal mode, an ultrasonic image is generated solely from a fundamental component of the echo waves. In the HI mode, an ultrasonic image is generated using a harmonic component of the echo waves. In the B/A coefficient acquisition mode, a B/A coefficient (non-linear parameter B/A) of a region of interest (abbreviated as ROI) is acquired. The operation section  14  is operated to select the mode and to designate the ROI. 
     A harmonic imaging processor (hereinafter abbreviated as the HI processor)  55  is actuated in the HI mode and the B/A coefficient acquisition mode. 
     In the normal mode, the DSC  53  generates an ultrasonic image based on the detection signal, obtained by the UT  27 , representing the fundamental component of the echo waves. On the other hand, in the HI mode, the HI processor  55  actuates. Through filtering, the HI processor  55  extracts a signal component representing or corresponding to the harmonic component of the echo waves, obtained by the UT  27 , from the detection signal. The DSC  53  generates an ultrasonic image using the harmonic component based on the detection signal extracted by the HI processor  55 . An ultrasonic image may be generated using a combination of the fundamental component and the harmonic component. 
     In the B/A coefficient acquisition mode, every time a transmission of ultrasonic waves and reception of echo waves takes place, the ultrasonic waves for heating are transmitted to heat the object of interest. The ultrasonic waves for heating are, for example, burst waves or continuous waves. The ultrasonic waves for heating differ from the ultrasonic waves for generating an ultrasonic image in various parameters such as a level, a frequency, and a transmission time. Needless to say, the above parameters are set such that an irradiation energy amount of the ultrasonic waves for heating remains within a range specified by a standard such as MI (Mechanical Index) or TI (Thermal Index) based on FDA 510k or IEC standards. The CPU  43  and the scan controller  44  drive the UTs  27  with predetermined parameters to transmit the ultrasonic waves for heating and to transmit the ultrasonic waves and receive the echo waves. 
     The irradiation energy amount of the ultrasonic waves may be adjusted by changing the number of the UTs  27  to be driven (radiation range) or by making a change in a focal region in the AZ direction or in the EL direction between the ultrasonic waves for heating and those for generating an ultrasonic image. 
     The object of interest is gradually heated with heat energy of the ultrasonic waves for heating every time a transmission of ultrasonic waves and reception of echo waves takes place. Within a range of allowable temperature limit of the living tissue, the object of interest is heated for a predetermined time with the ultrasonic waves for heating. When the heating stops, the temperature increase of the object of interest stops, and the object of interest starts to dissipate heat. After a while, the temperature of the object of interest returns to the original temperature. 
     In the B/A coefficient acquisition mode, the HI processor  55  monitors temporal changes of the B/A coefficient relative to temperature changes of the object of interest. The results are outputted to the DSC  53 . First, the HI processor  55  calculates the B/A coefficient based on the signal component representing or corresponding to the harmonic component of the echo waves of the detection signal received by the UTs  27 . For the calculation of the B/A coefficient, a mathematical expression (1) is used. 
     
       
         
           
             
               
                 
                   
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     In the mathematical expression (1), P 2  represents a level of generation of the second harmonic component (a level of the signal component representing the second harmonic component of the detection signal), P 0  represents a level of sound pressure of the ultrasonic waves, ρ 0  represents density of living tissue, Co represents propagation sound velocity of small amplitude ultrasonic waves inside the living tissue, α 1  represents an attenuation coefficient of the fundamental component, α 2  represents an attenuation coefficient of the second harmonic component. P 2  is derived from the detection signal acquired by the UTs  27 . The rest of the parameters are known. Accordingly, B/A in the parentheses of the mathematical expression, that is, the B/A coefficient is calculated by substituting the parameters in the mathematical expression (1). The B/A coefficient indicates properties such as density and stiffness of living tissue. 
     The HI processor  55  obtains data of temporal changes in the B/A coefficient from immediately before the start of the transmission of the ultrasonic waves for heating until the object of interest returns to its original temperature after the transmission of the ultrasonic waves for heating stops. For example, the HI processor  55  creates table data of the B/A coefficient associated with the time at which the B/A coefficient is obtained. The HI processor  55  obtains the B/A coefficient (base value) immediately before the start of the transmission of the ultrasonic waves for heating, the rate of increase of the B/A coefficient during the transmission of the ultrasonic waves for heating, and the rate of decrease of the B/A coefficient until the object of interest returns to its original temperature after the transmission of the ultrasonic waves for heating stops. The HI processor  55  calculates data related to the B/A coefficient with respect to the ROI designated using the operation section  14 , and the calculated data is outputted to the DSC  53 . 
     The detection signals outputted from the log compression and detection circuit  52  are stored in the memory in a state that the detection signals are sorted according to the channel received and with the fundamental component and harmonic component separated from each other. The HI processor  55  reads the signal component of the detection signal representing the harmonic component corresponding to an ROI designated using the operation section  14  to obtain the B/A coefficient. 
     The B/A coefficient (base value) is, for example, a value standardized with a maximum or an average value of all the B/A coefficients of living tissue around the ROI. For example, in the case where the B/A coefficient of the ROI is “10”, and the maximum or the average value of the B/A coefficients around the ROI is “12.5”, the B/A coefficient (base value) of the ROI is 10/12.5=0.8. The harmonic component of the echo waves detected by the UTs  27  is at an extremely weak level, so the obtained B/A coefficient itself is not reliable. For this reason, the base value obtained by relative comparison of the B/A coefficients in different areas is used. 
     The rate of increase of the B/A coefficient is obtained by dividing the difference between the B/A coefficient obtained when the transmission of the ultrasonic waves for heating is stopped and the B/A coefficient immediately before the start of the transmission of the ultrasonic waves for heating, by the transmission time of the ultrasonic waves for heating. The rate of decrease of the B/A coefficient is obtained by dividing the difference between the B/A coefficient obtained when the transmission of the ultrasonic waves for heating is stopped and the B/A coefficient immediately before the start of the transmission of the ultrasonic waves for heating, by the time between when the transmission of the ultrasonic waves for heating stops and when the B/A coefficient returns to its original value. The rates of increase and decrease of the B/A coefficient describe tendency for heating and thermal diffusion, in other words, specific heat which depends on proximity of surrounding tissue and heat diffusion due to blood flow. 
     Generally, living tissue in a malignant tumor is stiffer than that in a benign tumor. Accordingly, the B/A coefficient (base value) of a malignant tumor becomes higher than that in a benign tumor. Compared to a benign tumor, a malignant tumor has a large amount of blood flow and is likely to diffuse heat. As a result, the rate of increase of the B/A coefficient in a malignant tumor is lower than that in the benign tumor, meaning that a malignant tumor is heated slower than the benign tumor. On the other hand, the rate of decrease of the B/A coefficient in a malignant tumor is higher than that in the benign tumor, meaning that a malignant tumor is cooled faster than the benign tumor. Temporal changes in the B/A coefficient, the base value of the B/A coefficient, the rates of increase and decrease of the B/A coefficient, and the like are used as indices for the diagnosis of a lesion. 
     As shown in  FIG. 4 , in the B/A coefficient acquisition mode, a field  61  for displaying the B/A coefficient is displayed on a display screen on the monitor  15 , in addition to an ultrasonic image  60  and information such as patient information and examination site. On the ultrasonic image  60 , one or more markings  62  are superimposed. Each marking  62  is composed of a mark “x”, indicating an ROI designated via the operation section  14 , and a letter such as “a”. 
     In the field  61  for displaying the B/A coefficient, graphs  63  of spots “a” to “c” in the ROI are displayed in addition to transmission status of the ultrasonic waves for heating. The transmission status includes, for example, frequency and transmission time. In the graph  63 , the horizontal axis represents time and the vertical axis represents the B/A coefficient (base value). The graph  63  plots changes in the B/A coefficient (base value) with time based on the table data of time and B/A coefficient obtained from the HI processor  55 . Inside the graph  63 , dotted lines  64  show the transmission time. 
     For the graph  63  of each spot, a detail button  65  is provided. When the detail button  65  is selected via the operation section  14 , a pop-up window  70  shown in  FIG. 5  appears on the side of the field  61  for displaying the B/A coefficient. In the pop-up window  70 , the B/A coefficient (base value) and the rates of increase and decrease of the B/A coefficient are displayed in list form. In  FIG. 5 , a part of the ultrasonic image  60  is covered with the pop-up window  70  just for the sake of convenience in explanation. Actually, the pop-up window  70  is displayed in a layout not covering the ultrasonic image  60 . 
     In graphs  63  of the spots “a” and “c”, changes in the B/A coefficient are substantially the same. On the spot “b”, changes in the B/A coefficient are obviously different from those on the spots “a” and “c”. On the spot “b”, the B/A coefficient (base value) is large. The rate of increase of the B/A coefficient is low, whereas the rate of decrease is high. A doctor analyzes changes in the B/A coefficient while observing the ultrasonic image  60 , and uses the pop-up window  70  to check the B/A coefficient (base value) and the rates of increase and decrease of the B/A coefficient as necessary. Thus, diagnosis of the lesion is performed. 
     An operation of the ultrasonic diagnostic apparatus  2  having the above configuration is described. First, the connector  19  of the ultrasonic probe  11  is inserted and fixed in the probe connector  17  of the portable ultrasonic observation device  10 . Thus, the portable ultrasonic observation device  10  and the ultrasonic probe  11  are connected. The operation section  14  is operated to turn on the portable ultrasonic observation device  10 , and the power is supplied from the portable ultrasonic observation device  10  to the ultrasonic probe  11 . The doctor observes an ultrasonic image displayed on the monitor  15  of the portable ultrasonic observation device  10  to perform diagnosis while he/she gently presses the scan head  18  of the ultrasonic probe  11  against the patient. 
     An excitation pulse is transmitted from the pulser  41  selected by the scan controller  44  of the ultrasonic probe  11  to the UT  27  of the corresponding channel. Thereby, the ultrasonic waves are emitted from the UT  27  to the patient. The scan controller  44  sequentially shifts the pulser  41  to be driven after a transmission of the ultrasonic waves and reception of the echo waves takes place. Thus, the patient is scanned with the ultrasonic waves. For the transmission, the scan controller  44  turns the SW  40 , connected to the UT  27  which emits the ultrasonic waves, to the pulser  41  side. 
     The ultrasonic waves transmitted from the UTs  27  are reflected by the object of interest. The detection signal generated from the echo waves is outputted from the UT  27  of the corresponding channel. The scan controller  44  turns the SW  40 , connected to the UT  27  for receiving the echo waves, to the reception amplifier  42  side. The detection signal from the UT  27  is amplified by the reception amplifier  42 , and then subjected to the A/D conversion by the A/D  45 . Thus, the detection signal is digitized. The digital detection signal is converted into serial data by the P/S  46 , and then sent to the portable ultrasonic observation device  10 . 
     In the portable ultrasonic observation device  10 , the detection signal is converted back into the parallel data by the S/P  50 . Then, the detection signal is sent to the BF  51  and subjected to the phase matching operation therein. Thereafter, the detection signal is subjected to the log compression and detection in the log compression and detection circuit  52 , and then temporarily stored in the memory. 
     After the log compression and the detection, the detection signal is converted into the TV signal in the DSC  53 . The TV signal is subjected to the D/A conversion and then displayed as an ultrasonic image on the monitor  15 . 
     In the B/A coefficient acquisition mode, the ultrasonic waves for heating are emitted to the object of interest every time a transmission of the ultrasonic waves and reception of the echo waves takes place. Thus, the object of interest is heated. The HI processor  55  obtains the B/A coefficient from the signal component, representing the harmonic component of the echo waves, of the detection signal. Then, the HI processor  55  acquires the B/A coefficient (base value) and rates of increase and decrease of the B/A coefficient. The data is outputted to the DSC  53 . 
     Based on the data from the HI processor  55 , the DSC  53  controls the display of the B/A coefficient (base value) and the rates of increase and decrease of the B/A coefficient using a graph  63  in the field  61  for displaying the B/A coefficient and a pop-up window  70 . The graph  63  and the pop-up window  70  are displayed on the monitor  15  together with the ultrasonic image  60 . 
     As described above, attention is focused not on the B/A coefficient itself but on the temperature dependence of the B/A coefficient. While the object of interest is heated with the ultrasonic waves for heating, changes in the B/A coefficient are monitored. The results are displayed on the monitor  15 . Thus, a new way of diagnosing a lesion using the B/A coefficient as an index becomes available. 
     Conventionally, elastography, ARFI, and color Doppler imaging are used in combination to examine stiffness of tissue and a state of blood flow. The present invention enables to examine the stiffness of tissue and a state of blood flow at a time. 
     The tissue may be judged normal or not, using a comparison between the acquisition result of the B/A coefficient and a predetermined threshold value. The judgment result may be displayed on the monitor or the like to notify the doctor. 
     In the above embodiment, the changes in the B/A coefficient are displayed using the field  61  for displaying the B/A coefficient and the pop-up window  70 . Alternatively, the B/A coefficient (base value) and the rates of increase and decrease of the B/A coefficient may be superimposed on or around the marking  62  on the ultrasonic image  60 . The ultrasonic image  60  may be displayed as a gray scale image to express the magnitudes of B/A coefficient (base value) and the rates of increase and decrease of the B/A coefficient with colors (for example, an area of the object of interest with maximum values may be colored in red, an area with medium values may be colored in pink, and an area with minimum values may be colored in white, and the like.). Temporal changes in the B/A coefficient (base value) may be expressed using lightness and darkness of a color, and the color may be superimposed on a moving image of the ultrasonic image  60  and made reproducible. 
     In the above embodiment, to heat the object of interest, the ultrasonic waves for heating are transmitted every time a transmission of the ultrasonic waves and reception of echo waves takes place. The number of cycles of transmission of the ultrasonic waves for heating can be changed. The ultrasonic waves for heating can be transmitted, for example, five times in every transmission and reception, or once in every 1 cycle of the transmission and reception. The B/A coefficient may be acquired several times with the different transmission conditions of ultrasonic waves for heating. The acquired data may be displayed in a comparative manner. Alternatively, the B/A coefficient may be obtained several times with the same transmission condition. An average of the acquired B/A coefficients may be obtained. 
     The ultrasonic waves for heating may be transmitted for a predetermined time. The transmission and reception of the ultrasonic waves may be performed only when the B/A coefficient starts to decrease. Thereby, only a rate of decrease is obtained. The ultrasonic waves for heating may be only transmitted to an area designated as an ROI. 
     In the above embodiment, the ultrasonic waves for heating are generated from the UTs for imaging. Alternatively, the UTs specifically used for transmitting the ultrasonic waves for heating may be provided. Instead of using ultrasonic waves, sound waves at a frequency of less than 20 kHz or electromagnetic waves (infrared rays) may be used, for example. Alternatively or in addition, a heater may be directly placed on the body surface. 
     Instead of heating the object of interest, the object of interest may be cooled. Changes in the B/A coefficient become the inverse of the above. Regardless of increase or decrease, changes in the B/A coefficient can be used as the index of the diagnosis of a lesion. To cool the object of interest, the ultrasonic probe may be provided with air supply/water supply functions to apply cool air or cool water to the body. A cooling pad may be placed on the body surface. 
     In the above embodiment, the UTs with the inorganic piezoelectric ceramics thick film are used for transmission of the ultrasonic waves and the reception of the echo waves as an example. The UTs may have a different configuration. 
     For example, a UT array  75  shown in  FIG. 6  may be used. Basic configuration of the UT array  75  is the same or similar to that of the UT array  21  shown in  FIG. 2 . In the UT array  75 , the UTs  27  are overlaid with the UTs  76 . The UTs  27  are turned upside down from those shown in  FIG. 2 , namely, the first electrode  32   a  is on top of the UTs  27 , and the second electrode  32   b  is on the bottom of the UTs  27 . 
     Each UT  76  has an organic piezoelectric element  77  made from PVDF (Polyvinylidene difluoride) sandwiched between first and third electrodes  32   a  and  32   c . The organic piezoelectric element  77  functions as the acoustic matching layer. Unlike the UTs  27 , the UTs  76  only receive echo waves and do not transmit ultrasonic waves. The UTs  76  mainly output detection signals based on the harmonic component, for example, the secondary harmonic component of the echo waves. 
     In  FIG. 7 , the third electrode  32   c  is connected to an end of a SW  80 . The other end of the SW  80  is connected to a reception amplifier  81  and an A/D  82 . The reception amplifier  81  is the same as or similar to the reception amplifier  42 . The A/D  82  is the same as or similar to the A/D  45 . To transmit the ultrasonic waves, the SW  80  is turned off. Conversely, to receive the echo waves, the SW  80  is turned on. The signal component, of the detection signal, representing or corresponding to the harmonic component of the echo waves received by the UTs  76  is inputted to the reception amplifier  81 . The harmonic component is effectively acquired and acquisition accuracy of the B/A coefficient is improved when the UTs  76  using the organic piezoelectric element  77  are used for the reception of the harmonic component. 
     Alternatively, pMUT (Piezoelectric Micromachined Ultrasonic Transducer) may be used for the reception of the harmonic component. The pMUT has piezoelectric oxide thin film. Although the pMUTs are not suitable for the transmission of ultrasonic waves, they function sufficiently for the reception of echo waves. Additionally, other harmonic components including secondary harmonic components can be acquired by pMUT with changes in diameter and thickness. A dielectric constant of the pMUT is approximately 500 to 1000 times higher than that of organic piezoelectric elements such as PVDF. Because the pMUT has a membrane structure, capacitance of the pMUT is drastically higher than that of the organic piezoelectric elements. Accordingly, a level of the detection signal is higher than in the case where a material with relatively low capacitance is used. As a result, the harmonic component of the echo waves are effectively acquired. 
     In the above embodiment, the portable ultrasonic observation device and the ultrasonic probe are connected with the cable as an example. Alternatively, wireless data communication can be performed between the portable ultrasonic observation device and the ultrasonic probe. In this case, to transmit and receive the detection signals by radio, a wireless transmitter is provided at an output of the P/S  46 , and a wireless receiver is provided at an input of the S/P  50 . In addition, a battery is incorporated in the ultrasonic probe. The power from the battery is supplied to the each section of the ultrasonic probe. 
     A multiplexer may be inserted between the UT array and the pulser or between the pulser and the reception amplifier. The multiplexer selectively switches or changes the UTs to be driven. For example, in the case where 128 transmission and reception channels are used, and adjacent 48 channels are driven as one block, the multiplexer can select the block to be driven and adjust the delay timing of each UT. The number of pulsers is equal to the number of the channels to be driven at a time (in this case, 48). Thereby, the ultrasonic probe is further downsized. The scan control becomes easy because the scan controller only needs to transmit a switch signal to the multiplexer. 
     In the above embodiment, an external ultrasonic probe of a so-called convex electronic scan type is described as an example. Alternatively, an ultrasonic probe of a linear electronic scan type or a radial electronic scan type may be used. The present invention is also applicable to an internal ultrasonic probe inserted in a forceps channel of an electronic endoscope and an ultrasonic endoscope integrated with an electronic endoscope. 
     Various changes and modifications are possible in the present invention and may be understood to be within the present invention.