Patent Publication Number: US-2012046552-A1

Title: Ultrasonic diagnostic apparatus, ultrasonic probe, and ultrasonic diagnostic method

Description:
TECHNICAL FIELD 
     The present invention relates to an ultrasonic diagnostic apparatus and a receiver circuit which amplifies a signal from a subject received by an ultrasonic transducer and in particular, to an ultrasonic diagnostic technique including a circuit which has both a transmission and reception separating function and a transmitted signal amplifying function. 
     RELATED ART 
     An ultrasonic diagnostic apparatus is mainly formed of a piezoelectric material, and an electric signal is applied to transducers arrayed in the shape of a straight line or a specific curve. In addition, an element group corresponding to transmission/reception wave size is selected, and signal transmission and reception are performed while scanning them sequentially. Various kinds of information are extracted from the reflected signals to acquire information regarding the inside of a subject in a non-invasive manner. 
     Conventionally, a transmitter circuit which applies a voltage to transducers which have 100 or more elements is provided in the apparatus body. Generally, the number of transmitter circuits is equivalent to a phasing size of tens of channels. Ideally, independent transmitted and received signals are needed for all transducers. However, if a transmitter circuit and a receiver circuit are used for each element, the required number of components, the length of a signal cable, and the number of signal cables increase, which is not practical. For this reason, in a conventional apparatus, a configuration is adopted in which the number of transceiver circuits used corresponds to no more than the transmission/reception wave size and these transceiver circuits and transducers are connected to each other through switches (Patent Document 1). 
     The switch used in such a configuration turns on and off a high-voltage pulse signal at the time of signal transmission. At the same time, it is necessary to turn on and off an analog signal with a low level at the time of signal reception. Therefore, a high voltage characteristic, a function of switching a pulse signal with a large peak current value at high speed, and a low noise characteristic of low ON resistance are simultaneously required for the switching element. In addition, as a transceiver device, it is common to use a transmission and reception separating circuit for protecting a received signal amplifier from the high voltage at the time of signal transmission. As a result, there have been problems regarding the power consumption of each amplifier circuit and the transmission and reception separating circuit, an increase in the number of components, and heat emission and the mounting area. 
     On the other hand, Patent Document 2 realizes the miniaturization by forming a transmitted signal amplifier circuit with a switch configuration or the like. In addition, Patent Document 3 discloses adding received signals from plural transducers by a matrix switch type current adding circuit after voltage-current conversion of the received signals from the transducers. In addition, Patent Document 4 proposes an ultrasonic apparatus which has a circuit configuration suitable for variable control of a required aperture, control of scanning, and the like for plural transducers arrayed, which does not require a special device for protection against a high voltage, and which has a circuit configuration suitable for integration. 
     Citation List 
     Patent Documents 
     [Patent Document 1] JP-UM-A-56-73809 
     [Patent Document 2] U.S. Pat. No. 5,997,479 
     [Patent Document 3] JP-A-2007-185529 
     [Patent Document 4] JP-B-8-3528 
     SUMMARY OF INVENTION 
     Problem to be Solved by the Invention 
     In a transceiver circuit of the ultrasonic diagnostic apparatus in each of the conventional examples described above, the circuit configuration including an amplifier circuit or the like is separately set. Therefore, since there are a large number of components, miniaturization is not realized. 
     In addition, when using an ultrasonic probe including plural transducers, a current addition matrix circuit for adding received signals from plural arbitrary transducers is necessary. In the related art, however, a received signal amplifier circuit and an adding circuit are separately provided. Accordingly, a configuration, such as a voltage-current conversion circuit, is required before the current adding circuit. 
     It is an object of the invention to provide a transceiver circuit which can be built in an ultrasonic probe head that has a small number of components and is suitable for miniaturization, an ultrasonic diagnostic apparatus using it, and its ultrasonic probe. 
     Solution to Problem 
     In order to achieve the above-described object, an ultrasonic diagnostic apparatus of the invention is configured to include: an ultrasonic probe having plural transducers; an apparatus body for reception processing of received signals from the plural transducers; a transmitted and received signal amplifier circuit which amplifies signals transmitted to the plural transducers and amplifies received signals from the plural transducers; and a current adding circuit which adds currents of the received signals amplified by the transmitted and received signal amplifier circuit. 
     In addition, a current adding switch which connects the transmitted and received signal amplifier circuit and the current adding circuit to each other is provided. 
     In addition, the transmitted and received signal amplifier circuit, the current adding circuit, and the current adding switch are built in the ultrasonic probe. 
     In addition, the current adding switch is formed by one FET element corresponding to each of the transducers. 
     In addition, an ultrasonic diagnostic apparatus is configured to include: an ultrasonic probe having plural transducers; an apparatus body for reception processing of received signals from the plural transducers; and a transmitted and received signal amplifier circuit which amplifies signals transmitted to the plural transducers and amplifies received signals from the plural transducers. The transmitted and received signal amplifier circuit includes an FET element operating as a source follower circuit at the time of signal transmission and operating as a gate-grounded circuit at the time of signal reception. 
     That is, in the ultrasonic diagnostic apparatus according to a first aspect of the invention, amplifier circuits used for both transmission and reception are provided in the ultrasonic probe in the relationship of 1:1 with the number of transducers so that driving of all elements is realized without using matrix switches with different amplitude characteristics for transmission and reception of signals even if the number of elements used for sound field formation like a matrix array is larger than the number of phasing channels of the ultrasonic diagnostic apparatus body. 
     More specifically, the transmitted and received signal amplifier circuit is shared by using a transmitter circuit, which is formed by a source follower circuit, as a gate-grounded amplifier during a signal receiving period. A transmitter circuit is formed only by a MOS field effect transistor (FET), for example, and has a simple configuration which can be formed by an existing semiconductor manufacturing process. As a result, a size capable of being built in a general ultrasonic probe head is realized. 
     In addition, according to a second aspect of the invention, a received signal amplifier circuit for each transducer can amplify the current of a received signal from the transducer. 
     In addition, according to a third aspect, a current switch is connected to the received signal amplifier circuit so that the currents can be added by grouping the received signals. The current switch group has a matrix form, and switches the number of which corresponds to the number of elements can be connected to each receiving circuit output terminal. This switch is formed by a MOSFET. One MOSFET may be provided at each connection point of the matrix, and may have a small size for switching only a received wave current. 
     Advantageous Effects of Invention 
     As described above, according to the invention, a configuration of an amplifier circuit used for both transmission and reception which can be built in an ultrasonic probe and which has a function of adding currents of received signals from plural elements becomes possible in the ultrasonic diagnostic apparatus. According to this configuration, since the same transistor element can be used for both transmission and reception, a transmission and reception separating circuit which is grounded for protection of a receiver circuit in the related art can be eliminated. As a result, it is possible to realize a reduction in the area and an improvement in the S/N ratio. 
     In addition, since the gate potential of a transistor element is fixed at the time of signal reception, the input impedance is low. Accordingly, noise of the gate-grounded amplifier can be suppressed to be low. 
     In addition, the current-amplified received signals from each element can be added for each group of arbitrary elements by a matrix current switch. 
     The number of switching elements, such as MOSFETs, at each connection point of the matrix may be 1, and the switching element may have a small size for switching only a received signal current. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of an ultrasonic diagnostic apparatus according to a first embodiment. 
         FIG. 2  is a view showing an example of an amplifier circuit used for both transmission and reception according to the first embodiment. 
         FIG. 3  is a view showing a specific example of an amplifier circuit used for both transmission and reception according to the first embodiment. 
         FIG. 4  is a view showing a received current adding switch according to a second embodiment. 
         FIG. 5  is a view showing a received current adding switch according to the second embodiment. 
         FIG. 6  is a block diagram of an ultrasonic diagnostic apparatus according to a third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, various kinds of embodiments of the invention will be described with reference to the drawings. In addition, it is needless to say that this does not limit the invention. 
     First Embodiment 
       FIG. 1  shows an ultrasonic diagnostic apparatus according to a first embodiment. 
     The apparatus of the present embodiment is configured to include an ultrasonic probe  31 , a transmitted signal phasing circuit  02 , and a transmitted signal generating section  14 , a transmitted and received signal amplifier circuit  400  with a transmission and reception separating function, a transducer  05 , an ultrasonic probe cable  06 , a received signal amplifier circuit  401 , a received signal phasing circuit  08 , a signal processing circuit  09 , an image processing circuit  10 , and a display monitor  11 . 
     The ultrasonic probe  31  is characterized in that the transducer  05 , the transmitted signal phasing circuit  02 , the transmitted and received signal amplifier circuit  400 , the transmitted signal generating section  14 , a current adding switch  402 , and a current adding circuit  403  are provided therein. 
     Electric signals after pulse signals or carrier signals of continuous waves are determined by the transmitted signal generating section  14  and amplified by the transmitted and received signal amplifier circuit  400  is applied to the transducer  05 . The transducer  05  is formed to have a function of converting the signal into an ultrasonic wave and transmitting it to the subject and a function of receiving an ultrasonic wave reflected from the inside of the subject and converting the wave into an electric signal and outputting it. 
     The transmitted signal phasing circuit  02  is for adjusting an application timing of a transmitted signal to each driven transducer when forming a transmitted beam on the subject. Generally, a timing is controlled such that a voltage is applied early to a driven transducer in proportion to the distance of the transducer from the focusing position. 
     A transmitted signal amplifier section in the transmitted and received signal amplifier circuit  400  is for amplifying a transmitted signal waveform, which is formed by the transmitted signal generating section  14 , up to the sufficient size by driving the transducer  05  in order to generate an ultrasonic signal. 
     The transmitted signal generating section  14  determines a carrier wave shape. For example, the transmitted signal generating section  14  includes a memory and stores one or plural carrier waveforms. The stored waveforms can be selected by a control circuit  12  in an ultrasonic diagnostic apparatus body  100 . Alternatively, the waveform may be transmitted from the ultrasonic diagnostic apparatus body  100  through the ultrasonic probe cable  06  and stored whenever a transmitted signal is generated. 
     The current adding switch  402  is connected to a transducer in the relationship of 1:1, and the output destination is the current adding circuit  403 . The current adding circuit  403  adds received signals of plural arbitrary elements as will be described in detail later, and the maximum number of output signals is the number of channels, in which phasing processing is possible, of the received signal phasing circuit  08  of the apparatus body  100 . 
     Next, the received signal amplifier circuit  401  of the apparatus body  100  amplifies an ultrasonic signal acquired from the subject, and also has a function of changing the gain every time. When a gain sufficient to form a diagnostic image can be secured, the amplification function is not necessary in the transmitted and received signal amplifier circuit  400 . In this case, the transmitted and received signal amplifier circuit  400  outputs a 1X signal or has only a function of changing the gain according to the depth. 
     The received signal phasing circuit  08  has a function of forming a beam similarly to the transmitted signal phasing circuit  02 . The received signal phasing circuit  08  is for adjusting an addition timing of signals from all transducers, at which a signal from the subject is acquired, for each transducer when forming a received beam. A delay time is increased in proportion to the distance of a transducer from the focusing position for matching of addition timing of received signals of transducers far from the focusing position. 
     The signal processing circuit  09  and the image processing circuit  10  are for performing coordinate transformation processing according to the type of ultrasonic probe by performing signal processing for converting phased and added signals into brightness information by detection processing or the like and performing image signal processing represented by gamma (γ) processing or the like. Here, the processed signal is displayed as a diagnostic image on the display monitor  11 . 
     In addition, each of the constituent circuits described above receives a basic clock signal from the control circuit  12 , so that timing control of each section and the like are performed. Specifically, switching control of transmission and reception or switching of a diagnostic mode is performed. In addition, a power supply  13  is controlled by the control circuit  12  so as to output various electric power values. The electric power with various values generated herein is supplied to each circuit section (not shown). 
       FIG. 2  shows a detailed circuit block diagram of an example of the transmitted and received signal amplifier circuit  400  which has both a transmission and reception separating function and a transmitted and received signal amplifying function associated with the present embodiment. In addition, (a) and (b) in  FIG. 2  show states of the transmitted and received signal amplifier circuit  400  at the time of signal transmission and reception, respectively. 
       501 ,  502 ,  503 ,  504 ,  508 , and  05  denote a driver element M 1 , a Zener diode Dz, a resistor Rd, a constant current source, a carrier signal generating circuit, and a transducer, respectively. The carrier signal generating circuit  508  is a block corresponding to the transmitted signal generating section  14  and the transmitted signal phasing circuit  02  shown in  FIG. 1 . 
     In the present embodiment, an N channel MOS field effect transistor (hereinafter, simply referred to as NMOSFET) is used as the driver element M 1 . The carrier signal generating circuit  508  is connected to a gate terminal of the driver element  501 . The Zener diode  502  and the resistor  503  are connected in parallel between a drain terminal of the driver element  501  and a positive power supply +HV, and a received amplified signal is extracted from the drain terminal of the driver element  501  at the time of signal reception. The constant current circuit  504  is connected between a source terminal of the driver element  501  and a negative power supply −HV, and the source terminal of the driver element  501  is connected to the transducer  05  so that transmitted and received signals can be transmitted through the source terminal. 
     An operation at the time of signal transmission based on the circuit configuration shown in (a) of  FIG. 2  is shown below. At the time of signal transmission, these circuits form a source follower. The voltage applied to the gate terminal of the driver element  501  appears at the source terminal as it is, driving the transducer  05 . When a positive voltage is applied to the transducer  05 , a current flows from the positive power supply +HV to the transducer  05  through the Zener diode  502  and the driver element  501 . In addition, when a negative voltage is applied, a current flows from the transducer  05  to the constant current source  504 . 
     The Zener diode  502  is provided to bypass a current when a large current of a transmitted signal flows, so that a voltage drop does not occur at the resistor  503 . The Zener diode  502  may be replaced, for example, with a switch which becomes conductive at the time of signal transmission and non-conductive at the time of signal reception. 
     An operation at the time of signal reception in the circuit configuration shown in (b) of  FIG. 2  is shown below. An N type high-voltage MOSFET (NMOSFET) forms a gate-grounded circuit at the time of signal reception. By controlling the carrier signal generating circuit  508  to output a constant value (Vdc), the gate potential of the driver element  501  is fixed and the driver element  501  operates as a gate-grounded amplifier. In this case, the gain is determined by a product of the transconductance gm of the field effect transistor and the resistance  503 . 
     Thus, the received signal from the transducer  05  is amplified by the driver element  501  and is extracted as a received signal. 
     In addition, the carrier signal generating circuit  508  is controlled by the control circuit  12 . For example, by the control circuit  12 , the carrier signal generating circuit  508  is controlled to output a carrier signal when a signal with an output of H (high) is input and to output an appropriate DC electric potential (Vdc) when a signal with an output of L (low) is input. It is needless to say that such a circuit configuration can be easily formed by those skilled in the art. 
     The configuration of the present embodiment is advantageous in that the same driver element  501  can be used both for transmission and reception and a transmission and reception separating circuit, which is grounded for protection of the receiver circuit in the related art, can be omitted. As a result, it is possible to realize a reduction in the area and an improvement in the S/N ratio. 
       FIG. 3  shows a more specific example of the circuit configuration of the present embodiment. (a) and (b) of  FIG. 3  show an operation of a circuit at the time of signal transmission and an operation of a circuit at the time of signal reception, respectively. In the present embodiment, since the power consumption is reduced by circuit switching at the time of signal transmission and reception, a configuration using a low-voltage transistor is possible. As a result, a smaller IC can be made. In addition, in  FIGS. 3 ,  505 ,  506 ,  511 ,  512 ,  513 , and  514  serve as driver elements formed by NMOSFETs, and  506  and  513  serve as current sources formed by NMOSFETs. In addition, the current source  513  is a current source using a differentiating circuit, and a current flows only when a signal is input. 
     Hereinafter, an operation at the time of signal transmission will be described. At the time of signal transmission, only the driver elements  511 ,  512 ,  513 , and  514  are made to operate and the other driver elements  505  and  506  are turned OFF, as shown in (a) of  FIG. 3 . By forming the driver elements  511 ,  512 , and  513  in multiple stages as shown in  FIG. 3 , a voltage applied to each transistor can be suppressed to be low. That is, since the driver elements  511 ,  512 , and  513  can be formed by low-voltage transistors, a smaller IC can be made. 
     A transmission wave which is an. ON signal is applied to gates of the driver elements  511 ,  513 , and  514  as a signal from the control circuit  12  and an OFF signal is applied to gates of the driver elements  505  and  506  as a signal from the control circuit  12  at the time of signal transmission shown in (a) of  FIG. 3 , that is, in a signal transmission section. For example, in the driver element  506 , an electric potential lower than the source potential (−LV) of the driver element  506  is applied from the control circuit  12 , so that the circuit does not operate. 
     At the time of signal reception shown in (b) of  FIG. 3 , that is, in a signal receiving section, an OFF signal is applied to the gates of the driver elements  511 ,  513 , and  514  and, for example, a voltage equal to or higher than 3 V is applied to the gate of the driver element  505  to turn on the driver element. Accordingly, a fixed voltage is applied to the gate of the M 3  by +LV and R 2 , and the M 3  is gate-grounded. An electric potential determined by resistors R 101  and R 102  and −LV is applied to the driver element  506 . Accordingly, the driver element  506  changes to an ON state and a current flows through the element. 
     As shown in (a) of  FIG. 3 , when a positive voltage is applied to the transducer  05 , a current flows from a positive power supply to the transducer  05  through the driver elements  511  and  512 . By outputting a carrier signal from the carrier signal generating circuit  508  to both the driver elements  511  and  514 , the driver elements  511 ,  512 , and  513  are made to operate simultaneously. In addition, when a negative voltage is applied to the transducer  05 , a current is made to flow from the transducer  05  only at the falling edge by controlling the gate terminal of the driver element  513  through the differentiating circuit grounded to the output of the carrier signal generating circuit  508 . 
     At the time of signal reception, only the driver elements  512 ,  505 , and  506  are made to operate, and the driver elements  511 ,  513 , and  514  are turned OFF by controlling the carrier signal generating circuit  508 , as shown in (b) of  FIG. 3 . Thus, by circuit switching at the time of signal transmission and reception, the elements can be made to operate with low voltage supply ±LV at the time of signal reception. In this way, since the receiver circuit can be formed by lower voltage transistors, a smaller IC can be made. 
     In addition, since the gate potential of the driver element  512  is fixed by the driver element  505  at the time of signal reception, the input impedance is low. Accordingly, noise of the gate-grounded amplifier can be suppressed to be low. 
     In addition, in the circuit configuration shown in (a) of  FIG. 3 , an arrow ( ) is given to a transistor to which a control signal from the control circuit  12  is actually output. However, the control method is not limited thereto, but any method may be used as long as it is a mechanism capable of turning a transistor ON and OFF. 
     Second Embodiment 
     Next, as a second embodiment, an embodiment in which an analog matrix for adding a received signal from each cell for every arbitrary group at the time of wave receiving operation is added to the circuit configuration in the first embodiment will be described using  FIGS. 4 and 5 . (a) of  FIG. 4  shows a transducer with a two-dimensional configuration of Am×Bn, and (b) of  FIG. 4  shows a circuit configuration having an analog matrix switch (SW)  402  for reading a signal from an arbitrary element of the transducer Am×Bn. 
     In (a) of  FIG. 4 , a received signal is amplified by the gate-grounded transistor M 3  and the resistor Rd. ADC constant current and a wave receiving AC current id flow through the M 3 , and an id*Rd signal is acquired in an Rd section. 
     In order to add received signals from the transducer (Am×Bn)  05  divided into plural arbitrary groups, a current matrix switch (SW)  402  is connected between the element M 3  and the resistor Rd. Since a received signal can be extracted as a current from Rd, MOSFETs (Qm, n), the number of which is equivalent to the number of transducers, are connected to each output end of the current matrix switch group  402 . However, one MOS may be provided at each connection point of the matrix, and may have a small size for switching only a received signal current. 
     (b) of  FIG. 4  shows a state where received signals from two transducers A 1 B 1  and A 2 B 2  are added and input to P 2  of a received signal phasing channel of the main body. 
       FIG. 5  shows a situation of group division in an operation at the time of signal reception of the transmitted and received signal amplifier circuit  400  when the transducer  05  forms an “Am×Bn” matrix array. The transmitted and received signal amplifier circuit  400  is connected to each transducer  05 , and the current adding switch  402  is connected to the output. Switches, the number of which is equivalent to the number of received signal phasing channels of the main body (in the drawing, q channels), are connected to each output of the transmitted and received signal amplifier circuit  400 , and switches corresponding to the number of transducers “Am×Bn” are connected to an output of each current adding switch. 
     A delay device  404  capable of arbitrarily delaying a received signal acquired by each transducer is provided before or behind the transmitted and received signal amplifier circuit  400 . This delay device  404  can set an arbitrary amount of delay by the control circuit  12 . 
     Third Embodiment 
       FIG. 6  shows, as a third embodiment, a case where the transmitted signal phasing circuit  02  and the transmitted and received signal amplifier circuit  400  described above are provided in the ultrasonic diagnostic apparatus body. 
     That is, the transmitted and received signal amplifier circuit  400  built in the ultrasonic probe  01 , the transmitted signal generating section  14  corresponding to the carrier signal generating circuit  508 , and the transmitted signal phasing circuit  02  in the first embodiment described above are mounted in an ultrasonic diagnostic apparatus body  1000 . When the total number of transducers  05  in the ultrasonic probe  01  is different from the total number of transmitted and received signal amplifier circuits in the ultrasonic diagnostic apparatus, one channel of the transmitted and received signal amplifier circuit  400  may be electrically connected to plural different transducers by a change-over switch  200 . In addition, the transmitted signal phasing circuit  02  may be omitted when necessary. 
     When the total number of transducers  05  and the total number of transmitted and received signal amplifier circuits  400  are equal, the change-over switch  200  is not necessarily needed. 
     In addition, the current adding switch  402  and the current adding circuit  403  are assumed to be included in the received signal phasing circuit  08  in  FIG. 6 . The current adding switch  402  and the current adding circuit  403  perform received signal phasing processing, and one object of the current adding switch  402  and the current adding circuit  403  is to prevent an increase in the number of received signals of the ultrasonic probe cable  06  by adding received signals of plural arbitrary elements when the total number of transducers  05  is larger than the total number of transmitted and received signal amplifier circuits  400  in the previous embodiment. However, in the method in which the transmitted and received signal amplifier circuit  400  is included in  FIG. 6 , the number of receiving signal lines used and the total number of transmitted and received signal amplifier circuits  400  are generally equal in the ultrasonic probe cable  06 . Accordingly, previous received signal addition is performed by the received signal phasing circuit  08 . The current adding switch  402  and the current adding circuit  403  may also be used for this phasing method. 
     INDUSTRIAL APPLICABILITY 
     According to the invention, the configuration of an amplifier circuit used for both transmission and reception which has a function of adding currents of received signals from plural elements becomes possible in the ultrasonic diagnostic apparatus. Therefore, since the same transistor element can be used both for transmission and reception, it is very useful in that it is possible to realize a reduction in the area and an improvement in the S/N ratio. 
     Reference Signs List 
     
         
           01 ,  31 : ultrasonic probe 
           02 : transmitted signal phasing circuit 
           03 : transmitted signal amplifier circuit 
           04 : transmission and reception separating circuit 
           05 : transducer 
           06 : ultrasonic probe cable 
           07 : received signal amplifier circuit 
           08 : received signal phasing circuit 
           09 : signal processing circuit 
           10 : image processing circuit 
           11 : display monitor 
           12 : control circuit 
           13 : power supply 
           100 ,  1000 : ultrasonic diagnostic apparatus body 
           200 : change-over switch 
           400 : transmitted and received signal amplifier circuit 
           401 : received signal amplifier circuit 
           402 : current adding switch 
           403 : current adding matrix 
           404 : delay device