1. Field of the Invention
The present invention relates to an ultrasound probe and an ultrasound apparatus.
2. Description of the Related Art
As an ultrasound probe for transmitting and receiving an ultrasound wave, a piezoelectric element, such as lead zirconate titanate (PZT), has normally been used. Recently an ultrasound probe using a capacitive micro-machined ultrasonic transducer (CMUT), which is a capacitance type ultrasound converting element, is under research.
A CMUT has a structure that is created using the micro electro mechanical systems (MEMS) process to which a semiconductor process is applied. The CMUT transmits and receives an ultrasound wave using a light vibrating film, and exhibits excellent wide-band characteristics even in liquid or gas. A CMUT is attracting attention since higher precision ultrasound diagnosis than conventional medical image diagnostic modalities can be implemented.
The CMUT is constituted by a combination of a capacitance type ultrasound converting element in the preceding stage and an electric circuit in the subsequent stage, so as to convert a received ultrasound wave into an electric signal (that is, a receiving signal) and output the signal. Here the current of an output signal of the previously mentioned ultrasound converting element is output based on the time variation of the capacitance, therefore a current-voltage conversion amplifying circuit is normally used for the electric circuit in the subsequent stage (see Japanese Patent Application Laid-Open No. 2011-98071).
On the other hand, in the case of an ultrasound diagnostic apparatus that transmits an ultrasound wave to a test object, such as a bio-sample, and images characteristic information of the test object based on a receiving signal acquired by the reflected wave thereof, different scan type probes are used depending on the purpose of diagnosis. Examples of the scan types are: convex, linear, sector and 2-D array. In the same way, using a different ultrasound probe having different transmitting/receiving characteristics, such as PZT and CMUT, is also considered depending on the diagnostic purpose.
Patent Literature 1: Japanese Patent Application Laid-Open No. 2011-98071
Patent Literature 2: Japanese Patent Application Laid-Open No. 2009-297326
The structure normally used for an ultrasound diagnostic apparatus using a probe for PZT is mixing a transmitting signal and a receiving signal for each single element in a connecting unit for connecting the probe, so as to reduce the number of probe cables by half.
If a probe for CMUT is connected to this connector unit, a protection circuit must be installed for input/output of the current-voltage conversion amplifying circuit which is installed on the receiving side, since voltage higher than the input voltage of the receiving circuit is used for the driving signal on the transmission side. In other words, as the prior art disclosed in Japanese Patent Application Laid-Open No. 2009-297326, the amplifying circuit is protected from overvoltage by using a switch inside the probe in response to a switching control signal at a timing to switch transmission and reception.
However in the case of an apparatus that must change the switching timing for each element individually, the same number of control signals as the number of elements is required, which increases a number of probe cables. Another problem is that the connector unit, constructed for PZT of the ultrasonic diagnostic apparatus, does not include a switching control signal to switch transmission and reception, which means that a dedicated connector unit must be provided separately to connect a probe for CMUT.
With the foregoing in view, it is an object of the present invention to provide a technique to operate an ultrasound probe for a piezoelectric element and an ultrasound probe for CMUT using a common cable.
The present invention provides an ultrasound probe comprising:
a transmitting unit configured to transmit an ultrasound wave in response to an input of a transmitting signal which is an electric signal;
a receiving unit configured to generate a receiving signal by converting a reflected wave of the transmitted ultrasound wave into an electric signal;
an amplifying unit configured to amplify the receiving signal; and
a signal switching unit configured to interrupt the amplifying unit from a path through which the transmitting signal passes, while the transmitting signal is being transmitted.
According to the present invention, a technique to operate an ultrasound probe for a piezoelectric element and an ultrasound probe for CMUT using a common cable can be provided.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will now be described with reference to the drawings. Dimensions, materials and shapes of composing elements and relative positions thereof described below should be appropriately changed according to the configuration and various conditions of the apparatus to which the invention is applied, and are not intended to limit the scope of the invention.
The present invention is related to an ultrasound probe for transmitting/receiving an ultrasound wave, and an ultrasound diagnostic apparatus for imaging characteristic information on a test object using a receiving signal acquired by transmitting an ultrasound wave onto a bio-sample.
To be more specific, the apparatus of the present invention uses an ultrasound echo technique that transmits an ultrasound wave from an ultrasound probe to a test object, receives a reflected wave (echo wave) reflected inside the test object, and acquires characteristic information on the inside of the test object as image data. The characteristic information on the inside of the test object acquired here is information reflecting the difference of the acoustic impedance among tissues inside the test object.
The ultrasound wave referred to in this invention is a kind of elastic wave, and includes waves referred to as a sound wave, an ultrasound wave and an acoustic wave.
Typically the ultrasound apparatus according to the present invention is implemented as an ultrasound diagnostic apparatus that acquires characteristic information on a test object, that is a bio-sample, and uses the information for diagnosis. In the following description, the ultrasound apparatus will be explained using such an ultrasound diagnostic apparatus. Also PZT is used as an example of a piezoelectric element that is used for a probe, but a type of piezoelectric element is not limited to PZT. In the following description, “CMUT” refers to a capacitance type ultrasound converting element.
Basic operation for imaging using an ultrasound wave will be described. If an electric signal is transmitted from the transmitting unit 3 in a state of contacting the ultrasound probe 5 to a test object, such as a bio-sample, an ultrasound wave is generated. The ultrasound wave propagates in the object for a very short time, and returns as a reflective echo if the wave contacts something hard. Then the reflective echo is converted into an electric signal by the ultrasound probe 5, and is detected by the receiving unit 4. The detected electric signal becomes a receiving signal. Then the distance from the ultrasound probe to the point where the ultrasound is reflected is calculated on the basis of time from a moment of transmitting the ultrasound wave to a moment of returning the reflective echo, and the image processing unit 7 generates image data on the internal state. Then an image based on the image data is displayed on the display 9 using the display control unit 8, whereby a functional image representing the substance distribution of the bio-tissue can be visualized.
A driving signal (transmitting signal) 100 outputted from the transmitting unit 3 becomes a high voltage (e.g. normally about ±100V) electric signal, which is much higher than an allowable voltage value of a receiving signal 101 which is inputted to the receiving unit. Therefore a limiter 22 must be disposed on the side of input to the receiving circuit. The limiter 22 is normally constituted by a circuit integrating a diode bridge, an inductor and a resistor as discrete components, and has a function to limit the input voltage to the receiving circuit 23 to be within the allowable value.
In the signal transmitting cable 6, a transmitting/receiving signal from the ultrasound probe 5 is connected with a coaxial cable 61, and a GND line 102 which leads to a base of a vibrating element is connected as a separate system. In other words, one coaxial cable corresponds to each vibrating element of PZT, therefore the number of lines of coaxial cables to be used is the same as the number of elements of the probe.
A switching control signal (SWITCH) 103 for controlling the ON/OFF of SW1 to SW3 is a signal that is outputted from the transmission/reception control unit 2 which controls beam forming. The receiving timing and the transmitting timing are repeated at a reversed timing, so SW1 and SW2 have a configuration the reverse of the configuration of SW3. This switch circuit is normally constructed by an analog switch when operation speed is considered, but the configuration is not limited to this if the device can switch at high-speed.
If the probe for CMUT is used, a bias power supply (BIAS) 104 must be provided from the outside, therefore a high voltage power supply, about 100 V, is connected as BIAS and operated.
The signal line when the probe for CMUT is connected as shown in
The transmission/reception control signal is now considered. In the actual ultrasound wave measurement, the transmitting beam forming is often performed, hence a delay is caused to the output timing of the transmitting signal from each element. This means that a timing when high voltage is applied shifts in each element. In this case, the switching control signal must be changed for each element in order to cancel the shift of the timing. In other words, the coaxial cable 61 requires two signal lines for each element.
Based on the above description, Example 1 of the present invention will now be described.
In the signal line connecting the receiving CMUT and the I-V conversion amplifying circuit, a signal of weak current outputted from the CMUT flows. Therefore if the SW2 shown in
A bidirectional diode 29 is installed on a transmitting path connected to the transmitting CMUT 27. Since only weak signal components during reception can be cut off because of the characteristics of the diode, the function that allows only transmitting signals to pass can be implemented in the same manner as SW3.
A T/R switch (T/R SW1), on the other hand, is a circuit referred to as a high voltage protection device, which protects the output side of the I-V conversion amplifying circuit. The T/R switch means a transmitting/receiving switch, which corresponds to the signal switching unit of the present invention. Unlike the device that turns ON/OFF by the switching control signal used in
The T/R switch of this example starts to turn OFF if the voltage drop between both terminals exceeds ±2.0V. In the OFF state, this device can withstand ±100V from the terminal, where only a 200 μA micro-current can flow. The voltage threshold is not limited to this value, but can be a predetermined value according to the characteristics of the apparatus. While a high voltage transmitting signal exceeding the predetermined value is transmitted, the T/R switch enters the OFF state to block the I-V conversion amplifying circuit, and while a transmitting signal is not transmitted, such as a period when a low voltage receiving signal flows, the circuit is connected and the electric signal flows through.
In the signal transmitting cable 6, a transmitting/receiving signal from the ultrasound probe is connected to the coaxial cable 61 for each element. In
As described above, according to the ultrasound apparatus having the configuration of this example, if a probe for PZT and a probe for CMUT, in which a transmitting element and a receiving element are separate, are alternatively used, a common connector can be used for connecting either probe while protecting circuits from high voltage during transmitting the ultrasound wave. Further, the amount of wiring of the coaxial cable can be reduced.
In the signal transmitting cable 6, a transmitting/receiving signal from the ultrasound probe is connected with the coaxial cable 61 for each element. The switching control signal (SWITCH) is not used, and the bias power supply BIAS to supply power to CMUT and the driving power supply VCC and GND, to supply power to the I-V conversion amplifying circuit 24, are connected. In comparison with the signal transmitting cable 6 in the case of using the probe for PZT shown in
As described above, according to the ultrasound apparatus having the configuration of this example, a probe for PZT and a probe for CMUT, in which a common element is used for a transmission and reception, are alternatively used, and a common connector can be used for connecting either probe while protecting circuits from high voltage when transmitting the ultrasonic wave. Further, the amount of wiring of the coaxial cable can be reduced.
In this configuration, high voltage (e.g. ±100V) is not applied to the coaxial cable 61 for the transmitting/receiving signal in the signal transmitting cable 6, hence the protection circuit need not be installed on the output side of the I-V conversion amplifying circuit. On the input side however, high voltage transmitting signal 105 is applied, hence the T/R SW2 must be installed.
In the signal transmitting cable 6, a transmitting/receiving signal from the ultrasound probe is connected with the coaxial cable 61 for each element. The switching control signal (SWITCH) is not used, and the bias power supply BIAS to supply power to the CMUT and the amplifier, and the driving power supply VCC and GND to supply power to the I-V conversion amplifying circuit 24, are connected. In comparison with the signal transmitting cable 6 in the case of using the probe for PZT shown in
As described above, according to the ultrasound apparatus having the configuration of this example, if a probe for PZT and a probe for CMUT, in which a common element is used for transmission and reception, are alternatively used, a common connector can be used for connecting either probe while protecting circuits from high voltage when transmitting the ultrasound wave. Further, the amount of wiring of the coaxial cable can be reduced. Furthermore the scale of the protection circuit can be decreased by installing the amplifier.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2012-35159, filed on Feb. 21, 2012, which is hereby incorporated by reference herein its entirety.
Number | Date | Country | Kind |
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2012-035159 | Feb 2012 | JP | national |