Abstract:
A plurality of signal transmitters are respectively configured to produce a pulse current by repeatedly switching the connection state of a switching element. A plurality of ultrasonic transducers are respectively configured to transmit an ultrasonic pulse to a subject to be examined upon receiving said pulse current, and to produce a receiving current upon receiving the reflected wave. A signal receiver is configured to receive said receiving current. A test signal generator is configured to produce a test signal and to output said test signal to a connection point of said signal transmitter, said ultrasonic transducer, and said signal receiver by switching said connection state of said switching element to a state through which said test signal is conducted.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an ultrasonic imaging apparatus comprising a transmitting circuit and a receiving circuit of ultrasonic signals in an ultrasound probe. More specifically, the present invention relates to an ultrasonic imaging apparatus comprising test circuits of the transmitting circuit and the receiving circuit of ultrasonic signals. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventionally, for an ultrasonic imaging apparatus that generates an ultrasonic tomographic image by sending out an ultrasound beam to a subject to be examined and receiving the reflected ultrasonic echo, a 1-dimension array probe on which reed-shaped piezoelectric elements are arranged in an array form is used. 
         [0005]    Electronic scanning using a 1-dimension array probe allows electronic focusing and scanning of ultrasound beams within a surface in the direction of the arrangement of the piezoelectric elements. However, in the direction perpendicular to the direction of arrangement (i.e., the normal line direction of the ultrasonic scanning surface described above), it allows only focusing by using only an acoustic lens, so changes of the focal point are limited to within a narrow range. Therefore, it is difficult to focus various points on a two-dimensional plane. In addition, it is possible only to two-dimensionally scan an ultrasound beam because the arrangement of array elements is a one-dimensional arrangement. 
         [0006]    Therefore, in order to realize omni-directional focusing and high-speed three-dimensional scanning, and to facilitate understanding of the structures within living bodies, a 2-dimension array probe in which ultrasonic transducers are arranged two-dimensionally and that allows delay-controlling in each of the two directions in which ultrasonic transducers are arranged has been proposed in recent years. (For example, see Japanese Unexamined Patent Application Publication 2005-319199.) 
         [0007]    Subsequently, three-dimensional scanning has been conducted and stereoscopic images have been displayed by employing the 2-dimension array probe as described. 
         [0008]    In addition, for 2-dimension array probes such as those with a 32×32 configuration, the number of transducers required is 1,024. In the 2-dimension array probe having the number of transducers as described, it is necessary to transmit/receive ultrasonic waves by using all transducers. In this case, 1,024 transducers are housed in a probe head to be placed in contact with a subject to be examined, so if they are connected to an ultrasonic imaging apparatus without change, 1,000 or more cables will be needed. The structure of such an ultrasound probe is impractical. 
         [0009]    Furthermore, for the 2-dimension array probe, transducer impedance will increase because the shape of transducers is smaller than that of a conventional 1-dimension array probe. As a result, degradation of received echo becomes greater for the 2-dimension array probe. This lowers the amount of information used for forming images and makes proper diagnosis difficult. 
         [0010]    Therefore, in order to efficiently supply a pulse for transmission and to minimize the degradation of received echoes, an ultrasonic imaging apparatus including a probe head with a configuration as shown in  FIG. 1  has conventionally been proposed for the 2-dimension array probe.  FIG. 1  is a diagram of a configuration of an ultrasonic imaging apparatus including a conventional 2-dimension array probe. This ultrasonic imaging apparatus, as shown in  FIG. 1 , incorporates in the probe head  110 , a group of pulsers  112  for supplying a transmitted pulse to the proximity of a transducer  111  in a probe head  110 , a transmission controller  113  for controlling the group of pulsers  112 , a group of receiving electronic circuits  114  for amplifying the received echo, a receiving control circuit  115  for controlling the group of receiving electronic circuits  114 , and a high-pressure prevention circuit  116  for protecting the group of receiving electronic circuits  114  from a high-voltage pulse outputted from the group of pulsers  112 . Herein, the group of pulsers  112  is an aggregation of a plurality of pulsers, and hereinafter, when explaining one pulser, it is simply referred to as a pulser  112 . In addition, hereinafter, an aggregation of a plurality of transducers  111  is referred to as a group of transducers  111 . 
         [0011]    Upon receiving a control signal such as a pulse production command from a body control circuit  015  that is housed in an ultrasonic imaging apparatus body  010 , a probe control circuit  122  conducts a relocation of the data necessary to transmit a control signal or the like. Then, the probe control circuit  122  transmits the control signal to the transmission controller  113 . Upon receiving the control signal, the transmission controller  113  transmits a timing signal for a pulse signal to the group of pulsers  112 . Upon receiving the timing signal from the transmission controller  113 , the group of pulsers  112  generates a pulse signal. The produced pulse signal causes the group of transducers  111  to oscillate and to send out an ultrasound beam to a subject to be examined  030 , and then is received as the received echo that is a reflected wave through the group of transducers  111 . A received echo signal that is based on the received echo received through the group of transducers  111  is sent to the group of receiving electronic circuits  114 . The group of receiving electronic circuits  114  groups a plurality of channels as channels corresponding to the group of transducers  111  and performs local beamforming. This makes it possible to reduce the number of cables for the probe. For example, in the case of the 2-dimension array probe with the 32×32 configuration, assuming that there are 8 channels per group, the group of receiving electronic circuits  114  has 1,024 channels that correspond to the group of pulsers  112 , which are reduced to 1,024/8 groups. 
         [0012]    The received echo signal to which the local beamforming has been performed, is processed such as buffering in the group of signal-processing circuits  121  housed in a probe connecter  120 , and then is entered into the ultrasonic imaging apparatus body  010 . Herein, the probe control circuit  122  conducts setting of the group of signal-processing circuits  121  upon receiving a signal from the body control circuit  015 . A beamforming is performed for the entire received echo signal in a group of receiving electronic circuits of the body  011 . From the received echoes, all of which the received beamforming has been performed upon in the group of receiving electronic circuits of the body  011 , an envelope signal corresponding to information in a living body or the like is extracted by a signal-processing circuit of the body  012 . Furthermore, the received echo is converted to a desired display coordinate in an image-processing circuit  013  and is displayed on the displaying part  014 . 
         [0013]    In addition, the body control circuit  015  that is installed in the ultrasonic imaging apparatus body  010  controls each part of the ultrasonic imaging apparatus body  010  in accordance with parameter information entered from an inputting part  020 , such as operation mode, scan mode, or display mode. 
         [0014]      FIG. 2  is a diagram that represents the skeletal framework of a transmitting/receiving circuit with one channel when employing a pulser that transmits a unipolar pulse.  FIG. 3  is a diagram that represents the skeletal framework of a transmitting/receiving circuit with one channel when employing a pulser that transmits a bipolar pulse. 
         [0015]    Next, operations in the case of the unipolar pulser will be explained. As shown in  FIG. 2 , the pulser  112  has a level shifter  141 , a pulse production FET  142 , and a shunt field-effect transistor (FET)  143 . 
         [0016]    The transmission controller  113  transmits a timing signal to the pulser  112 . The transmission controller  113  has a circuit that produces a timing signal for instructing the transducer  111  to generate an ultrasonic pulse and a timing signal for receiving a signal based on the ultrasonic echo from the transducer  111 . Then, to instruct the transducer I  11  to generate an ultrasonic pulse, the transmission controller  113  repeatedly switches the pulse production FET  142  on and off at a constant timing by means of a timing pulse signal, and turns on the shunt FET  143  when the pulse production FET  142  is off. In addition, when receiving from the transducer  111  a received echo signal that is based on the ultrasonic echo, the transmission controller  113  sends a signal for turning off both the pulse production FET  142  and the shunt FET  143 . 
         [0017]    The level shifter  141  converts the timing pulse entered from the transmission controller  113  into a voltage of several tens of volts and sends a pulse corresponding to the pulse production FET  142  and the shunt FET  143 . 
         [0018]    The pulse production FET  142  is a switching element for producing a pulse and the shunt FET  143  is a switching element for returning the voltage that has risen to ground the pulse. 
         [0019]    When instructing the transducer  111  to generate an ultrasonic pulse (i.e., when sending out an ultrasound beam to the subject to be examined  030 ), the pulse production FET  142  and the shunt FET  143  output a pulse signal by repeating on/off operations at a constant timing upon receiving a command from the transmission controller  113 . At this time, the shunt FET  143  is off when the pulse production FET  142  is on, and the shunt FET  143  becomes on when the pulse production FET  142  turns off. As a result of this, voltage that is increased once by the pulse production FET  142  is grounded instantly. The transducer  111  receives the pulse produced here, and then an ultrasound beam is sent to the subject to be examined  030 . Herein, the high-pressure prevention circuit  116  is a diode; a high-voltage pulse sent from the pulser  112  is blocked and not sent to the receiving electronic circuit  114 . 
         [0020]    When receiving a received echo from the subject to be examined  030 , the ultrasound beam is reflected from the subject to be examined  030  and received in the transducer  111  as a received echo. The transducer  111  converts the received echo into a signal and sends the same to the receiving electronic circuit  114 . This signal passes through the high-pressure prevention circuit  116  because the voltage thereof is weak. At this time, a transmission/reception controller  113  turns off both the pulse production FET  142  and the shunt FET  143  so that the received echo signal will not flow to the group of pulsers  112 . Herein, ‘turning off’ refers to generating a state of high impedance. 
         [0021]    Next, operations of the bipolar pulser  112  will be explained. As shown in  FIG. 3 , the pulser  112  comprises a level shifter  141 , a positive pole pulse production FET  142   a,  a negative pole pulse production FET  142   b,  a shunt FET  143   a  for grounding the voltage of the positive pole pulse production FET  142   a,  and a shunt FET  143   b  for grounding the voltage of the negative pole pulse production FET  142   b.    
         [0022]    Also, in the case of the bipolar pulser  112 , as is the case with the unipolar pulser  112 , a timing signal for transmission is received from the transmission controller  113 , and the level shifter  141  turns the positive pole pulse production FET  142   a,  the negative pole pulse production FET  142   b,  the shunt FET  143   a,  and the shunt FET  143   b  on and off to produce a bipolar pulse. The transducer  111  receives this pulse and sends out an ultrasound beam to the subject to be examined  030 . 
         [0023]    Conventionally, for an ultrasonic imaging apparatus having a 1-dimension array probe, an electronic circuit for transmitting/receiving ultrasonic waves (transmitting/receiving circuit) is housed in the ultrasonic imaging apparatus body. This made it possible to conduct an operation test of the transmitting/receiving circuit independently from the ultrasound probe by running a test program in the ultrasonic imaging apparatus body when using the ultrasonic imaging apparatus having a 1-dimension array probe. However, for the ultrasonic imaging apparatus having a 2-dimension array probe as described above, a transmitting/receiving circuit is housed in a probe head. As a result, it became difficult to conduct the operation test of the transmitting/receiving circuit independently from the ultrasound probe by means of the ultrasonic imaging apparatus having a 2-dimension array probe as described above. 
         [0024]    In addition, for the abovementioned ultrasonic imaging apparatus, 1,000 or more sets of electronic circuits for performing transmission/reception are housed in the probe head. In other words, the apparatus has 1,000 or more sets of structures in which transducers for actually transmitting/receiving ultrasonic waves, a transmitting circuit for applying a high-pressure pulse to each transducer, and a receiving circuit for amplifying a weak ultrasonic echo received by those transducers are directly connected. Therefore, when there is a local abnormality in those electronic circuits for performing transmissions/receptions, the signal goes missing, likely resulting in an artifact or causing unusual heat generation. However, it is difficult to electrically check whether an enormous electronic circuit is operating properly. Thus, an operation check, for example of an ultrasonic imaging apparatus as described, has been acoustically conducted by transmitting a pulse and receiving an echo for channels of all transducers by means of an external target in which a reflecting plate is placed in a water tank. However, the conventional test method always requires a water tank, and a large amount of labor is necessary to conduct the test. Furthermore, in the conventional test method, the angle setting of the 2-dimension array probe against the external target involves errors for each test, and thus the amplitude of the received echo becomes misaligned for each channel. Therefore, it was difficult to achieve high-integrity test results using the conventional test method. 
       SUMMARY OF THE INVENTION 
       [0025]    As described above, the present invention is intended to provide an ultrasonic imaging apparatus that is capable of conducting a test of an electronic circuit that transmits/receives to each corresponding channel by means of a signal to be tested that has been produced in a probe. 
         [0026]    A first aspect of this invention is an ultrasound probe, comprising: a plurality of signal transmitters respectively configured to produce a pulse current by repeatedly switching the connection state of a switching element; a plurality of ultrasonic transducers respectively configured to transmit an ultrasonic pulse to a subject to be examined upon receiving said pulse current, and to produce a receiving current upon receiving the reflected wave; a signal receiver configured to receive said receiving current; and a test signal generator configured to produce a test signal and to output said test signal to a connection point of said signal transmitter, said ultrasonic transducer, and said signal receiver by switching said connection state of said switching element to a state through which said test signal is conducted. 
         [0027]    According to this first aspect, when the switching element is fixed to the ground side, a test signal will be sent from the test signal generator that is located in the ultrasound probe. Thus, it is possible to transmit a test signal only when conducting a test and to conduct a test of the ultrasound probe using the test signal generator that is disposed in the ultrasound probe. 
         [0028]    A second aspect of this invention is an ultrasound probe, comprising: a transducer, disposed at a predetermined connection point, configured to receive a pulse signal and to send out an ultrasound beam to a subject to be examined; a signal transmitter configured to produce an ultrasonic pulse from said connection point; and a signal receiver configured to receive a signal that is based on an ultrasonic echo from said connection point, wherein the ultrasound probe comprises: a switching part configured to switch two operation modes consisting of an image-forming mode and a test mode; a transmission controller configured to supply said pulse signal from said signal transmitter to said connection point when instructing said transducer to produce said ultrasonic pulse in said image-forming mode, wherein the transmission controller is configured to turn off said signal transmitter in a high output impedance state when instructing said transducer to receive the ultrasonic echo reflected by the subject to be examined in said image-forming mode, and is configured to turn off said signal transmitter in a high output impedance state in said test mode; a test signal outputting part configured to output a test signal to said connection point; and a test controller configured to turn off the output of said test signal from said test signal outputting part in said image mode, wherein the test controller is configured to instruct said test signal outputting part to output said test signal in said test mode. 
         [0029]    A third aspect of this invention is an ultrasound probe, comprising: a transducer, disposed at a predetermined connection point, configured to receive a pulse signal and to send out an ultrasonic beam to a subject to be examined; a signal transmitter having a first switching element and a second switching element that are connected to said connection point in parallel, the signal transmitter being configured to pulse-drive both said first switching element and said second switching element when instructing said transducer to produce an ultrasonic pulse and configured to turn off said first switching element and said second switching element when instructing said transducer to receive the ultrasonic echo reflected by the subject to be examined; and a signal receiver configured to receive a signal that is based on said ultrasonic echo from said connection point, wherein the ultrasound probe further comprises: a switching part configured to switch between two operation modes consisting of an image-forming mode and a test mode; a test signal outputting part that is connected between said second switching element and said ground in series, wherein the test signal outputting part is configured to output a test signal; a limiter that is connected to said test signal outputting part in parallel, configured to pass a signal outputted from said test signal outputting part through said second switching element; a transmission controller configured to turn off said first switching element and to turn on said second switching element in said test mode; and a test controller configured to operate said test signal outputting part to send out said test signal to said signal receiver in said test mode. 
         [0030]    With the ultrasound probe in the first, second, or third aspect, it is possible to transmit a test signal by cutting off the pulser in the test and by connecting the test signal generator that is located in the ultrasound probe. This makes it possible to transmit a test signal to a test apparatus of the ultrasound probe by using a test signal generator that is located in the ultrasound probe only when conducting a test. In addition, a limiter is provided in the third aspect, so it is possible to avoid entering signals other than the test signal into the signal receiver. 
         [0031]    A fourth aspect of this invention is an ultrasonic imaging apparatus, comprising an ultrasound probe comprising: a transducer, disposed at a predetermined connection point, configured to receive a pulse signal and to send out an ultrasound beam to a subject to be examined; a signal transmitter having a first switching element and a second switching element that are connected to said connection point in parallel, the second switching element being configured to pulse-drive both said first switching element and said second switching element when instructing said transducer to produce an ultrasonic pulse and configured to turn off said first switching element and said second switching element when instructing said transducer to receive the ultrasonic echo reflected by said subject to be examined; and a signal receiver configured to receive a signal that is based on said ultrasonic echo from said connection point, and an image-generating part configured to generate an ultrasonic image based on the signal received from said ultrasound probe and to display the same on a displaying part, wherein said ultrasound probe further comprises: a switching part configured to switch between two operation modes consisting of an image-forming mode and a test mode; a test signal outputting part, connected between said second switching element and said ground in series, configured to output a test signal, a limiter, connected to said test signal outputting part in parallel, configured to obtain a signal outputted from said test signal generator through said second switching element; a transmission controller configured to turn off said first switching element and to turn on said second switching element in said test mode; and a test controller configured to operate said test signal outputting part to send out said test signal to said signal receiver in said test mode, and wherein said image-forming part is configured to compare said test signal received from said signal receiver with a threshold stored in advance and to instruct said displaying part to display a warning in test mode when exceeding said threshold. 
         [0032]    With the ultrasonic imaging apparatus of this fourth aspect, it is possible to determine in the image-forming part, by using the test signal entered from the test signal generator that is located in the ultrasound probe in the test mode, whether there are any abnormalities in the ultrasound probe. This makes it possible to conduct a test of the ultrasound probe by using the test signal outputted from the test signal generator that is located in the ultrasound probe. 
         [0033]    A fifth aspect of this invention is an ultrasound probe, comprising: a transducer, disposed at a predetermined connection point, configured to receive a pulse signal having a polarity of positive and negative and to send out an ultrasound beam to a subject to be examined; a signal transmitter having two first switching elements and two second switching elements, the two first switching elements being connected to said connection point in parallel and respectively having polarity of positive and negative, two second switching elements pairing with said first switching elements, wherein the signal transmitter is configured to pulse-drive both said two first switching elements and said two second switching elements when instructing said transducer to produce an ultrasonic pulse, wherein the signal transmitter is configured to turn off said two first switching elements and said two second switching elements when instructing said transducer to receive the ultrasonic echo reflected by the subject to be examined; and a signal receiver configured to receive a signal that is based on said ultrasonic echo from said connection point, wherein said ultrasound probe further comprises: a switching part configured to switch between two operation modes consisting of an image-forming mode and a test mode; a test signal outputting part that is connected between said second switching element and said ground in series, configured to output a test signal; a limiter that is connected to said test signal outputting part in parallel, configured to obtain a signal sent from said test signal generator through said second switching element; a transmission controller configured to turn off both said two first switching elements and to turn on any one or both of said two second switching elements in said test mode; and a test controller configured to operate said test signal outputting part to send out said test signal to said signal receiver in said test mode. 
         [0034]    With the ultrasonic imaging apparatus of this fifth aspect, it is possible to transmit a test signal to a test apparatus of the ultrasound probe using the test signal generator that is located in the ultrasound probe only when conducting a test for the ultrasound probe that uses a bipolar pulser. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]      FIG. 1  is a configuration diagram that represents a conventional ultrasonic imaging apparatus. 
           [0036]      FIG. 2  is the block diagram of a transmitting/receiving circuit when using a conventional unipolar pulser. 
           [0037]      FIG. 3  is the block diagram of a transmitting/receiving circuit when using a conventional bipolar pulser. 
           [0038]      FIG. 4  is a configuration diagram that represents an example of the ultrasonic imaging apparatus according to the present invention. 
           [0039]      FIG. 5  is a block diagram of the ultrasonic imaging apparatus according to the first embodiment. 
           [0040]      FIG. 6  is a diagram of a flow chart of the test mode in the ultrasonic imaging apparatus according to the first embodiment. 
           [0041]      FIG. 7  is a block diagram of the ultrasonic imaging apparatus according to the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
       [0042]      FIG. 4  is a configuration diagram that represents an example of the ultrasonic imaging apparatus according to the present invention.  FIG. 5  is a block diagram that represents the functions of the ultrasonic imaging apparatus according to the present embodiment. In addition,  FIG. 5  is a diagram that shows the configuration of a circuit that transmits/receives an ultrasonic wave for one channel corresponding to one transducer  111 . 
         [0043]    The ultrasonic imaging apparatus according to the present embodiment has two operational modes: an image-forming mode and a test mode. Operations in the image-forming mode are similar to those of the conventional ultrasonic imaging apparatus that has been explained in the background art. In other words, in  FIG. 5 , a block indicated by the same symbol as in  FIG. 2  has the same functions. Now, hereinafter, an ultrasonic imaging apparatus according to the first embodiment in the test mode will be explained. 
         [0044]    While only one transducer  111  is displayed in  FIG. 5 , the ultrasound probe  100  of the present embodiment actually has the same number of transducers  111  as contained in a 2-dimension array probe, that is, several thousands (represented as n×m in  FIG. 1 ). The pulser  112  is a signal transmitter. The pulser  112  and the transducer  111  are connected to each other at the connection point  200 . In addition, the signal receiver  130  is also connected to the connection point  200  through the high-pressure prevention circuit  116 . 
         [0045]    The switching part  170  is connected to the transmission controller  113  and the test controller  150 . Then, upon receiving from the body control circuit  015  a switching command for the test mode that an operator has entered from the inputting part  020 , the switching part  170  switches the transmission controller  113  and the test controller  150  to the test mode. Incidentally, the ultrasonic diagnostic apparatus according to the present embodiment is normally set in the image-forming mode, and operations to be performed in this case are similar to the operations in  FIG. 2  that have been explained in the related art. 
         [0046]    The pulser  112  has a level shifter  141 , a pulse production FET  142 , and a shunt FET  143 . The pulse production FET  142  is the first switching element. The shunt FET  143  is the second switching element. Herein, only one pulser  112  is described in  FIG. 4 , but actually the same number of pulsers  112  as are in the transducers  111  are disposed for each channel thereof. 
         [0047]    Upon receiving the command to switch to test mode from the switching part  170 , the transmission controller  113  enters into the pulser  112  a signal for controlling the test mode. Due to this signal, a high-voltage power supply  190  for transmission VTX is blocked and the pulse production FET  142  is switched off. Furthermore, due to this signal, the shunt FET  143  is switched on and an output point of the test signal outputting part  153  is connected to an output point of the pulser  112 , that is, the connection point  200 . Meanwhile, when the pulse production FET  142  is off, the impedance on the side of the level shifter  141  viewed from the connection point  200  is high. 
         [0048]    The test controller  150  has a test signal generator  151  and an operation signal input circuit  152 . Herein, only one test controller  150  is disposed in the present embodiment in order to reduce the occupation rate of the volume of the ultrasound probe  100 , but a plurality of test controllers  150  may also be disposed. 
         [0049]    Upon receiving the command to switch to test mode from the switching part  170 , the test controller  150  instructs the test signal generator  151  to produce a test signal. Herein, the test signal is preferably a signal equivalent to the signal level of an ultrasonic echo. The signal level of the ultrasonic echo is a low-amplitude signal. Therefore, the test signal generator  151  produces, for example, a 2.5 MHz and 10 mVpp sine wave as a test signal. 
         [0050]    In addition, upon receiving the command to switch to test mode from the switching part  170 , the test controller  150  instructs the operation signal input circuit  152  to enter an operation signal into the test signal outputting part  153 . 
         [0051]    Upon receiving the operation signal from the operation signal input circuit  152 , the test signal outputting part  153  switches into operating state. Then, the test signal outputting part  153  outputs the received test signal at low impedance. Only one test signal outputting part  153  is displayed in  FIG. 4 , but actually the number of such parts disposed for each channel is equivalent to the number of transducers  111 . 
         [0052]    The limiter  160  has two diodes located opposite to each other. These diodes become conductive when the input voltage is equal to or greater than the forward voltage drop of diodes, 1 V. Therefore, signals having a voltage of 1 V or more are grounded so as not to be sent to the shunt FET  143 . As a result, test signals equal to or less than 1 V head for the shunt FET  143 . In addition, a high-voltage pulse outputted from the pulser  112  in the image-forming mode has a voltage greater than 1 V. Thus, that high-voltage pulse is grounded through the limiter  160 . As a result, the shunt FET  143  in the image-forming mode operates normally and the test signal outputting part  153  that is not used in the image-forming mode is protected from that high-voltage pulse. Herein, in the present embodiment, a limit value of the limiter  160  is configured to be 1 V because a signal of 1 V or less is used as a test signal equivalent to the signal level of the ultrasonic echo. In this regard, however, it is preferable to be set depending on the signal to be used and the degree of protection of the test signal outputting part  153 . Herein, only one limiter  160  is displayed in  FIG. 4 , but actually the number of such parts disposed for each channel is equivalent to the number of transducers  111 . 
         [0053]    The high-pressure prevention circuit  116  is composed of a diode. The high-pressure prevention circuit  116  does not conduct the high-voltage pulse outputted from the pulser  112  when transmitting an ultrasound beam in the image-forming mode. On the other hand, the high-pressure prevention circuit  116  conducts a low-amplitude ultrasonic echo and a test signal when receiving an ultrasound beam in the image-forming mode. Herein,  FIG. 4  shows displaying only one high-pressure prevention circuit  116 , but such parts as many as the part for transducers  111  are actually disposed for each channel. 
         [0054]    The signal receiver  130  has a receiving electronic circuit  114  and a receiving control circuit  115 . A group of receiving electronic circuits  114  receives a test signal outputted from the test controller  150  and coming through the connection point  200 , amplifies the entered test signal, and adjusts gain or the like. Then, the group of receiving electronic circuits  114  transmits the test signal to an image-forming part  180 . The receiving control circuit  115  controls each operation, such as the amplification and gain adjustment, in the receiving electronic circuit  114 . Herein,  FIG. 4  shows displaying only one receiving electronic circuit  114 , but such parts as many as the part for transducers  111  are actually disposed for each channel. 
         [0055]    The image-forming part  180  is housed in the ultrasonic imaging apparatus body  010  shown in  FIG. 4 . Furthermore, the image-forming part  180  has a group of receiving electronic circuits of the body  011 , a signal-processing circuit of the body  012 , an image-processing circuit  013 , and so forth. In addition, the image-processing circuit  013  has a DSP (Digital Signal Prossesor). 
         [0056]    In the DSP included in the image-forming part  180  according to the present embodiment, regarding signal amplitude, wave frequency, and wave distortion, threshold values are stored in advance. For example, a threshold such as 30 mV±10% for amplitude is stored therein. In addition, for the threshold of the frequency or distortion, a threshold such as 10 dB, compared to the test signal from which a secondary or tertiary harmonic component has been outputted at the test signal outputting part  153 , is stored. This allows the image-forming part  180  to determine it to be abnormal when it is a waveform of above or below a predetermined amplitude or when there are many higher harmonic waves other than a predetermined frequency component. 
         [0057]    Upon receiving a test signal, the image-forming part  180  uses the DSP included in the image-processing circuit  013  for a frequency analysis. Then, the image-forming part  180  determines whether the amplitude or the distortion of frequency in the analysis results exceeds the stored threshold. When it exceeds the threshold, the image-forming part  180  instructs the displaying part  014  to display a notification of an abnormal detection and a waveform of the test signal received from the channel in which the abnormality has occurred. Herein, in the present embodiment, a waveform only from the channel in which the abnormality occurs is displayed so that it is easy to see the notification of the abnormal detection. In this regard, however, this may be displayed using another method, and it is also possible to display all waveforms or to display waveforms from a plurality of channels, for example. 
         [0058]    As described above, a test signal is outputted in the test signal outputting part  153 , passes through the shunt FET  143  because the shunt FET  143  is switched on, passes through the high-voltage-prevention circuit  116 , runs through the signal receiver  130 , and is analyzed in the image-forming part  180 . 
         [0059]    The image-forming part  180  comprises a test program in the DSP for performing image processing and conducts a test by executing this test program. This test includes two kinds of tests. One is a test for calibrating the image-forming part  180  itself and the other is a test of portions other than each functional part included in the ultrasonic imaging apparatus body  010  through which a test signal according to the present invention is passed. 
         [0060]    Herein, the image-forming part  180  is housed in the ultrasonic imaging apparatus body  010 , so the test for calibrating the image-forming part  180  itself can be conducted by using the test program of the ultrasonic imaging apparatus body  010 . Therefore, the ultrasonic imaging apparatus body  010  including the image-forming part  180  can be maintained in a normal state independently from the ultrasound probe  100 . 
         [0061]    Thus, firstly the image-forming part  180  is set to its normal state and then the ultrasound probe  100  is operated according to the present invention in test mode. Accordingly, it is possible to conduct tests of portions other than each functional part included in the ultrasonic imaging apparatus body  010  through which a test signal has passed. In other words, by using the test described above, it is possible to check, for each channel thereof, the switching and driving of the pulse production FET  142 , the switching and driving of the shunt FET  143 , control of the pulse production FET  142  and the shunt FET  143  through the transmission controller  113 , and the operations of the signal receiver  130 . 
         [0062]    Next, operations of the ultrasonic imaging apparatus according to the present embodiment in test mode will be explained with reference to  FIG. 6 .  FIG. 6  is a diagram of a flow chart of the test mode in the ultrasonic imaging apparatus according to the present embodiment. 
         [0063]    Step S 001 : An operator enters switching to test mode by means of the inputting part  020 . Upon receiving the input of switching, the body control circuit  015  instructs the switching part  170  to switch to test mode. The switching part  170  instructs the transmission controller  113  and the test controller  150  to switch to test mode. 
         [0064]    Step S 002 : The transmission controller  113  turns off the pulse production FET  142  and turns on the shunt FET  143 . 
         [0065]    Step S 003 : The test controller  150  instructs the operation signal input circuit  152  to transmit an operation signal to the test signal outputting part  153 . The test signal outputting part  153  switches into the operating state. 
         [0066]    Step S 004 : The test controller  150  instructs the test signal generator  151  to produce a test signal at a level equivalent to an ultrasonic echo and transmits the test signal to the test signal outputting part  153 . 
         [0067]    Step S 005 : The test signal outputting part  153  outputs the test signal at low impedance. 
         [0068]    Step S 006 : The test signal passes through the shunt FET  143 , the high-voltage-prevention circuit  116 , and the signal receiver  130  in each channel and is sent to the image-forming part  180 . 
         [0069]    Step S 007 : The image-forming part  180  performs a frequency analysis of the received test signal using the DSP. 
         [0070]    Step S 008 : The DSP determines whether the analyzed test signal exceeds any of the threshold values. Go to Step S 009  when there is a channel that exceeds its threshold, or end the test if none of the channels exceed their threshold. 
         [0071]    Step S 009 : The image-forming part  180  instructs the displaying part  014  to display a notification of an abnormal detection and information on the channel in which the abnormality has been detected. 
         [0072]    As described above, in the ultrasonic imaging apparatus according to the present embodiment, a test signal is produced from the ultrasound probe, so it is possible to conduct a test of the pathway in the signal transmitter, the signal receiver, and each channel without using a water tank, target, etc. for the test. Therefore, it is possible to readily conduct the test and thus contribute to reductions of erroneous diagnoses and medical malpractice due to failures of ultrasound probes comprising a transmitter/receiver. 
       Second Embodiment 
       [0073]    For the second embodiment, a configuration for the ultrasonic imaging apparatus of the first embodiment is also applied, and further a bipolar pulser is used. The present embodiment is similar to the first embodiment for operations of portions other than the bipolar pulser, so the bipolar pulser in test mode will be explained below.  FIG. 7  is a block diagram that represents the functions of the ultrasonic imaging apparatus according to the second embodiment. 
         [0074]    The transmission controller  113  sends, to the pulser  112 , a signal for turning off the pulse production FET  142  and turning off the shunt FET  143  upon receiving a command to switch to test mode from the switching part  170 . 
         [0075]    The pulser  112  has a level shifter  141 , a positive pole pulse generator  142   a  for producing a positive pole pulse, a negative pole pulse generator  142   b  for producing a negative pole pulse, a shunt FET  143   a  corresponding to the positive pole pulse production FET  142   a,  and a shunt FET  143   b  corresponding to the negative pole pulse production FET  142   b.    
         [0076]    Upon receiving a command from the transmission controller  113 , the pulser  112  turns off the positive pole pulse production FET  142   a  and the negative pole pulse production FET  142   b;  that is, it puts them into high impedance. Furthermore, the pulser  112  turns on both shunt FET  143   a  and shunt FET  143   b.  Herein, in the present embodiment, both the shunt FET  143   a  and the shunt FET  143   b  are turned on; that is, a test signal from the test controller  150  is sent to the connection point  200 . However, this means that it switches to test mode when the output point of the test signal outputting part  153  is connected to the output point of the pulser  112 , so it may also be configured to turn on either one of shunt FET  143   a  or the shunt FET  143   b.    
         [0077]    When the pulser  112  is operating as described, a test signal outputted from the test signal outputting part  153  passes through the shunt FET  143   a  or the shunt FET  143   b,  the high-pressure prevention circuit  116 , and the signal receiver  130 , and is then sent to the image-forming part  180 . 
         [0078]    As described above, the operations of the ultrasonic imaging apparatus according to the present embodiment as described make it possible to, even when using a bipolar pulser, conduct a test of each channel by using a test signal outputted from the test signal outputting part without using a water tank, target, etc. for conducting the test. This makes it possible to readily test also the ultrasonic imaging apparatus using the bipolar pulser.