JP4782639B2 - Ultrasonic diagnostic equipment - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to control of a transmission signal supplied to a transducer.

  An array type ultrasonic transducer (array transducer) having a transducer array composed of a plurality of transducers is known. By using an array transducer, an ultrasonic transmission beam is generated by supplying a transmission signal that has been subjected to a delay process or the like corresponding to each transducer element to a plurality of transducer elements included in the array transducer. It is possible to form and further scan the ultrasonic transmission beam electronically.

  With respect to the array transducer, for the purpose of suppressing the transmission side lobe, the transmission signal supplied to the plurality of transducer elements of the array transducer is weighted by a symmetrical transmission voltage distribution function such as a Gaussian function or a cosine function. Techniques for performing are also known.

  Incidentally, Patent Document 1 discloses a technique that uses asymmetric weighting to correct a difference in signal amplitude due to a difference in path length from each vibration element to the focal point when the sound ray direction is inclined. Has been.

JP 2005-253699 A

  If transmission signals supplied to multiple transducer elements of an array transducer are weighted by a symmetrical transmission voltage distribution function such as a Gaussian function or cosine function, the transmission energy is concentrated near the center of the transducer array. For this reason, the thermal energy tends to concentrate at the center of the opening of the array transducer.

  With the strengthening of safety standards for ultrasonic diagnostic apparatuses (for example, IEC60601-2-37), it is necessary to suppress the temperature rise of the ultrasonic probe surface more than before. From such a background, it is not preferable that the thermal energy is concentrated at the center of the aperture of the array transducer.

  Further, as a measure for suppressing the temperature rise of the ultrasonic probe, it is conceivable to reduce the transmission energy by lowering the voltage of the transmission signal supplied to each vibration element. However, if the transmission voltage is lowered, a side-effect problem that echo detection sensitivity is lowered occurs.

  In order to solve these problems, an approach to improve the electroacoustic conversion efficiency of the probe and an approach to improve the S / N of the receiving circuit system of the ultrasonic diagnostic apparatus main body can be considered, but both are technically difficult. The situation was high and it was difficult to make significant improvements.

  In such a situation, the inventors of the present application distribute the thermal energy concentrated near the center of the aperture of the array transducer to keep the transmission voltage and transmission sound pressure high while suppressing the temperature rise of the ultrasonic probe. We have been researching and developing technology to do this.

  The present invention has been made in such a background, and an object thereof is to provide a technique for dispersing thermal energy concentrated in the vicinity of the opening center of an array transducer.

  In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred aspect of the present invention includes an array transducer including a plurality of vibration elements, and a transmission unit that supplies a transmission signal to each of the plurality of vibration elements. And a reception unit that acquires a reception signal from each of the plurality of vibration elements, and the transmission unit has a left-right direction magnitude with respect to a transmission signal supplied to the plurality of vibration elements arranged in the left-right direction. The distribution is subjected to weighting processing that is asymmetrical to the left and right, and is further subjected to weighting processing by inverting the left and right of the distribution that is asymmetrical left and right at predetermined intervals.

  In a preferred aspect, the transmission unit inverts a transmission voltage distribution function whose left and right size distribution is asymmetric left and right at predetermined time intervals, and weights a voltage on a transmission signal based on the transmission voltage distribution function. It is characterized by processing.

  In a preferred aspect, the transmission unit uses a beta density function as a transmission voltage distribution function, and controls a parameter related to a strain direction of the beta density function to invert the beta density function left and right at predetermined time intervals. And

  According to the present invention, it is possible to disperse the thermal energy concentrated near the opening center of the array transducer.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 shows a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 1 is a functional block diagram showing the overall configuration thereof.

  The ultrasonic diagnostic apparatus shown in FIG. 1 includes an array transducer composed of a plurality of vibration elements 10. The plurality of vibration elements 10 are arranged in the left-right direction. In the present embodiment, for example, a sector scanning probe is formed by the plurality of vibration elements 10. Of course, a linear probe or a convex probe may be formed.

  A driver amplifier 20, a weighting circuit 30, and a delay circuit 40 are provided corresponding to each of the plurality of vibration elements 10. The transmission waveform (transmission signal) output from the transmission waveform generator 50 is subjected to various processes by the delay circuit 40, the weighting circuit 30, and the driver amplifier 20, and the transmission signal is supplied to each vibration element 10. Is done.

  The delay circuit 40 is a circuit that performs a delay process according to the vibration element 10 corresponding thereto. That is, the transmission waveform is output from the transmission waveform generator 50 to the plurality of delay circuits 40, and the delay processing corresponding to the vibration element 10 is performed on the transmission waveforms in each delay circuit 40.

  The weighting circuit 30 is a circuit that performs weighting processing according to the vibration element 10 corresponding thereto. That is, the weighting circuit 30 performs voltage weighting processing on the transmission waveform (transmission signal) subjected to delay processing in the delay circuit 40. The weighting process is performed based on the transmission voltage distribution function stored in the distribution function memory 60. This suppresses concentration of transmission energy near the center of the vibrating element array. The weighting process will be described in detail later.

  The transmission signal weighted by the weighting circuit 30 is supplied to the driver amplifier 20. The driver amplifier 20 supplies a drive signal corresponding to the transmission signal to the corresponding vibration element 10. And the vibration element 10 vibrates according to a drive signal, for example, an ultrasonic wave is transmitted in the living body.

  The control unit 70 controls the output timing of the transmission waveform output from the transmission waveform generator 50, the delay amount in each delay circuit 40, and the like. Thus, transmission beam forming is realized, and the ultrasonic transmission beam is electronically scanned.

  The receiving unit 80 acquires a reception signal from each of the plurality of vibration elements 10. The receiving unit 80 performs, for example, phasing addition processing on a plurality of reception signals obtained from the plurality of vibration elements 10 to realize reception beam forming.

  The signal processing unit 90 performs signal processing such as detection and logarithmic compression on the received signal after the phasing addition processing. The signal processing unit 90 may execute Doppler information extraction processing or the like. The signal processed in the signal processing unit 90 is supplied to the display image forming unit 100. The display image forming unit 100 performs coordinate conversion, interpolation processing, or the like on the input signal to form a B-mode image or the like. Further, a Doppler waveform, a color Doppler image, or the like may be formed based on the Doppler information.

  The overall configuration of the present embodiment is as described above. Next, the weighting process in this embodiment will be described in detail. In the following description, the reference numerals shown in FIG. 1 are used for the portions (configurations) shown in FIG.

  In this embodiment, the weighting circuit 30 performs weighting processing on the transmission signals supplied to the plurality of vibration elements 10 arranged in the left-right direction in order to suppress the temperature rise of the probe surface due to the application of the transmission voltage. ing. The weighting circuit 30 performs weighting processing based on the transmission voltage distribution function stored in the distribution function memory 60.

  The transmission voltage distribution function is a function that indicates the distribution of the voltage of the transmission signal, and indicates a distribution in the horizontal direction in which the vibration elements 10 are arranged. The transmission voltage distribution function is an asymmetrical function, and the transmission voltage distribution function is inverted to the left and right every predetermined time to weight the transmission signal. Accordingly, it is possible to keep the transmission voltage and the transmission sound pressure high while dispersing the thermal energy concentrated near the center of the opening, that is, near the center of the vibration element array arranged in the left-right direction, and suppressing the temperature rise.

  A preferred example of the transmission voltage distribution function is a beta density function. The beta density function y (x) is expressed as follows:

  In Equation 1, x is a coordinate in the array (opening) direction. That is, the position in the left-right direction of the vibration elements 10 arranged in the left-right direction is shown. In Equation 1, x is standardized in the range of 0-1. That is, the left end position of the vibration elements 10 arranged in the left-right direction corresponds to 0, and the right end position corresponds to 1. In Equation 1, a is a normalization coefficient for setting the maximum value of y (x) (when x = b / (b + c)) to 1. In addition, b and c are parameters for controlling the | distortion | yield of y (x) (the absolute value of the skewness), the right and left distortion directions, and the area.

  FIG. 2 is a diagram for explaining the beta density function, and FIG. 2 shows the waveform of the beta density function y (x) of Equation 1 with x on the horizontal axis and y on the vertical axis. . FIG. 2 shows three waveforms corresponding to the values of b and c in Equation 1. That is, a waveform 1 when b = 0.5, c = 1.54, a waveform 2 when b = c = 1.43, and a waveform 3 when b = 1.54, c = 0.5 are shown.

  As a feature of the beta density function y (x), when b = c, y (x) is symmetrical (waveform 2), and when b> c, y (x) is right-left asymmetric (waveform 3). When b <c, y (x) is left / right asymmetric (waveform 1). Further, by changing the values of b and c (see waveform 1 and waveform 3), the distortion direction of y (x) is changed. However, even if the values of b and c are interchanged, the | distortion | and the area remain unchanged.

  In the present embodiment, using the feature of the beta density function, the right distortion and the left distortion y (x) are alternately switched and used as a transmission voltage distribution function at a predetermined time interval, for example, every 10 seconds. That is, for example, the weighting circuit 30 performs weighting processing using the waveform 1 of FIG. 2 only for the first 10 seconds from the start of transmission, uses the waveform 3 for the next 10 seconds, and further uses the waveform 3 for the next 10 seconds. 1 is used. In this way, by alternately switching between waveform 1 and waveform 3, the thermal energy concentrated near the aperture center of the array transducer is dispersed.

  In general, the sound pressure at the transmission focus is proportional to the area B of the beta density function y (x). The area B (beta function) of the beta density function y (x) is given by the following equation.

  Even if the values of b and c of the beta density function y (x) are exchanged, the area B (beta function) remains unchanged, so that the sound pressure can be kept constant even if the waveform 1 and the waveform 3 are alternately switched. For the waveform 2 in FIG. 2, the parameters b and c are set so that the area is equal to that of the waveforms 1 and 3, so that the sound pressure at the transmission focus based on the waveforms 1 to 3 has the same value.

The temperature associated with the transmission signal is proportional to the square of the transmission voltage (power, strength). The beta density function y (x) is uniquely determined by b and c. In the present embodiment, when the barycentric position of the square y ² (x) of the beta density function is left distortion, x = 1 / 3. The values of b and c are set so that x = 2/3 in the case of right distortion.

FIG. 3 is a diagram showing a waveform obtained by squaring the beta density function. FIG. 3 shows a waveform of the square of the beta density function y ² (x) where x is the horizontal axis and y is the vertical axis. It is shown. FIG. 3 shows three waveforms y ² (x) corresponding to each of the three waveforms y (x) shown in FIG. That, b = 0.5, the waveform 1 y ² (x) in the case of c = 1.54, and the waveform 2 y ² (x) in the case of b = c = 1.43, b = 1.54, in the case of c = 0.5 Waveform 3 of y ² (x) is shown.

  In FIG. 3, the values of b and c are set so that the centroid positions of waveform 1 and waveform 3 are the positions of x = 1/3 and x = 2/3, respectively. Waveform 2 corresponds to the square of a symmetrical beta density function (waveform 2 in FIG. 2). And the waveform 4 shows (waveform 1 + waveform 3) / 2, and this waveform 4 corresponds to the time average when the waveform 1 and the waveform 3 are used alternately. In comparison with the symmetrical waveform 2, the waveform 4 becomes flatter near the center of x (for example, x = 1/3 to x = 2/3), and heat energy can be dispersed.

An example of a specific method for setting the values of b and c is as follows. When the center of gravity of the y ² (x) and x _g, y ² (x) and x _g, respectively expressed as follows.

Then, when x _g = 1/3, the following relational expression regarding b and c is obtained.

This relational expression (6) is substituted into expression (4). Then, y ² (x) of the left distortion is written as y ² (x) _L, and similarly y ² (x) of the right distortion is written as y ² (x) _R. When x = 1/2, y ² (1/2) _L = y ² (1/2) _R. Therefore, b is calculated by numerical calculation so as to satisfy the following equation.

そして、（６）の関係式からcを算出する。

Then, c is calculated from the relational expression (6).

Further, the calculated values of b and c are adjusted in consideration of the required sound pressure, that is, the area B of y (x). Thus, the values of b and c in FIGS. 2 and 3 are set so that x _g = 1 / 3.043 and B = 0.6.

  In the present embodiment, the beta density function is used as the transmission voltage distribution function, and the values of parameters b and c relating to the strain direction of the beta density function are controlled, so that the beta density functions of waveform 1 and waveform 3 shown in FIG. For example, switching is performed every 10 seconds. Comparing the time average when the waveform 4 shown in FIG. 3, that is, the waveform 1 and the waveform 3 are alternately used, with the waveform 2 shown in FIG. 3, in this embodiment, that is, the waveform 1 and the waveform 3 are used alternately. In this case, it can be seen that the power near the center of the opening is decreasing. For example, the value of waveform 2 when x = 0.5 is 1, whereas the value of waveform 4 when x = 0.5 is lowered to about 0.57.

  Thus, in this embodiment, the thermal energy concentrated near the opening center of the array transducer is dispersed. This makes it possible to design a probe that keeps the transmission voltage and transmission sound pressure high while suppressing the temperature rise of the ultrasonic probe.

  In this embodiment, as the transmission voltage distribution function, a beta distortion function with a left distortion (waveform 1 in FIG. 2) and a beta density function with a right distortion (waveform 3 in FIG. 2) are alternately used. FIG. 4 is a diagram showing the difference in beam characteristics due to the difference between the left distortion and the right distortion. FIG. 4 is a simulation result showing a transmission beam directivity at a deflection angle of 30 ° and a focus distance of 75 mm based on a transmission voltage distribution of a left distortion and a right distortion of a 2.5 MHz sector probe (aperture length: 19.2 mm) in an attenuation medium. is there.

  FIG. 4 shows two waveforms (beam characteristics) in the case of left distortion and right distortion, but the two waveforms almost overlap. There is little difference in the beam characteristics between them, and the difference in peak sound pressure is 1 dB or less. That is, substantially the same beam characteristics can be maintained even if the left and right of the transmission voltage distribution function are reversed.

As mentioned above, although preferred embodiment of this invention was described, embodiment mentioned above is only a mere illustration in all the points, and does not limit the scope of the present invention. For example, the transmission voltage distribution function is not limited to the beta density function. For example, w (x) may be an arbitrary symmetric density function, and two types of distribution functions x ^b · w (x) and (1-x) ^c · w (x) may be used as a transmission voltage distribution function. . Furthermore, the present invention includes other modifications without departing from the essence thereof.

1 is a functional block diagram showing an overall configuration of an ultrasonic diagnostic apparatus according to the present invention. It is a figure for demonstrating a beta density function. It is a figure which shows the waveform obtained by squaring a beta density function. It is a figure which shows the difference in the beam characteristic accompanying the difference between left distortion and right distortion.

Explanation of symbols

  10 vibrating elements, 30 weighting circuits, 60 distribution function memory.

Claims (3)

An array transducer including a plurality of transducer elements;
A transmission unit for supplying a transmission signal to each of the plurality of vibration elements;
A receiving unit for obtaining a received signal from each of the plurality of vibration elements;
Have
The transmission unit performs weighting processing in which the distribution of the size in the left-right direction is asymmetrical with respect to the transmission signal supplied to the plurality of vibration elements arranged in the left-right direction, and further determines the left and right of the left-right asymmetric distribution Apply weighting by inverting every time,
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The transmission unit inverts a transmission voltage distribution function whose left-right size distribution is asymmetric left and right every predetermined time, and performs voltage weighting processing on a transmission signal based on the transmission voltage distribution function.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
The transmitter uses a beta density function as a transmission voltage distribution function, and controls a parameter related to the strain direction of the beta density function, thereby inverting the beta density function left and right at predetermined time intervals.
An ultrasonic diagnostic apparatus.

Images