JP4627675B2 - Ultrasonic diagnostic equipment - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus that observes harmonic components generated by nonlinearity of a living tissue.

  When the ultrasonic wave propagates in the living body, the ultrasonic wave is distorted due to the non-linearity of the living tissue. Harmonic components (particularly second-order harmonic components) generated thereby are extracted from received signals, and nonlinearity of biological tissues is evaluated and biological tissues are imaged using them. It is known that a tomographic image with good resolution can be formed by using the second harmonic component. Looking at the spectrum of the received signal, there is an overlap between the fundamental wave component and the second harmonic component. In the method of extracting the second harmonic component using HPF, it is difficult to sufficiently exclude the fundamental wave component even when using one having a steep filter characteristic due to the above-described overlap.

  In the PI method (pulse inversion method, phase inversion method), as described in Patent Documents 1 and 2, the first transmission signal and the second transmission signal with the polarity reversed are sequentially transmitted, and each transmission is performed. The first received signal and the second received signal obtained corresponding to the signal are added. By the addition, the fundamental wave component is canceled and the second harmonic component is added twice. This utilizes the fact that the second harmonic component appears in the same polarity regardless of the polarity at the time of transmission. As a method of solving the developed form of the PI method or the problem, there is a method described in Patent Document 3. In this method, a first transmission signal obtained by combining a signal having a frequency f0 and a signal having a frequency 2f0 and a second transmission signal having its polarity inverted are sequentially transmitted, and the first reception signal obtained thereby and A sum signal and a difference signal are generated from the second received signal, and a signal representing the non-linearity of the living tissue is generated by a division operation thereof. In Patent Document 4, it is described that a pulse compression technique is used for detecting harmonic components. Patent Document 5 describes the use of a pulse compression filter.

US Pat. No. 5,706,819 JP 2004-113818 A JP 2001-299964 A JP-T 2002-539881 JP 2003-190157 A

  In the received signal spectrum, the second harmonic component is weak with respect to the fundamental component. Therefore, lack of sensitivity becomes a problem in imaging and measurement using the second harmonic component. In particular, when applying the method described in Patent Document 3, it is required to improve sensitivity.

  An object of the present invention is to provide an ultrasonic diagnostic apparatus capable of obtaining sufficient sensitivity for imaging with harmonic components.

The present invention provides a transmission means for outputting a first transmission signal obtained by combining a first modulation signal and a second modulation signal having a multiplication relationship, and a second transmission signal obtained by inverting the polarity of the first transmission signal. Receiving means for outputting a first reception signal corresponding to the first transmission signal and a second reception signal corresponding to the second transmission signal; and an addition process of the first reception signal and the second reception signal Sum signal generating means for generating a sum signal, difference signal generating means for generating a difference signal by subtracting the first received signal and the second received signal, and pulses for the sum signal and the difference signal, respectively. seen containing a pulse compression means for performing compression processing, means for generating a signal for forming an image from the sum signal and the difference signal after the pulse compression processing, the said pulse compression means, the real part input terminal and an imaginary part Has input terminals and inputs to them A conversion means for converting the sum signal and the difference signal as two signals on the time axis into two signals on the frequency axis, and a pulse compression process on the two signals on the frequency axis Means, and a real part output terminal and an imaginary part output terminal, and two signals on the frequency axis after the pulse compression processing are inversely converted into two signals on the real time after the pulse compression processing, And an inverse transform unit that outputs the sum signal and the difference signal after the pulse compression processing from the real part output terminal and the imaginary part output terminal .

  According to the above configuration, the first reception signal is obtained by ultrasonic transmission based on the first transmission signal, and the second reception signal is obtained by ultrasonic transmission based on the second transmission signal. Desirably, the ultrasonic wave based on the first transmission signal and the ultrasonic wave based on the second transmission signal are sequentially transmitted in each beam direction. A sum signal is obtained by adding the first received signal and the second received signal, and a difference signal is obtained by subtracting the first received signal and the second received signal. An image forming signal is generated from the ratio and the like. In the present invention, the first transmission signal and the second transmission signal are in an anti-phase (inverted) relationship, and each transmission signal is configured as a combination of the first modulation signal and the second modulation signal. Is in a multiplication relationship (or an integer multiple relationship). Since modulation processing can be performed at the time of transmission and pulse compression processing can be performed at the time of reception, the signal level can be raised by convolving energy developed on the time axis at the time of transmission at the time of reception. In particular, since the harmonic component is weak compared to the fundamental wave, the sensitivity becomes a problem during image formation, but the image quality can be improved by increasing the sensitivity.

  Preferably, the first modulation signal is a first chirp signal whose frequency changes in a first frequency band, and the second modulation signal has a frequency in a second frequency band as a harmonic band with respect to the first frequency band. Is a second chirp signal that changes.

In the above configuration, for example, the first chirp signal is a signal whose frequency changes linearly from the frequency f0 to the frequency f1 (center frequency _f01 ), and the second chirp signal is linear in frequency from the frequency 2f0 to the frequency 2f1. (Center frequency 2f ₀₁ ). Note that it is desirable that the second frequency band has a double relationship when viewed from the first frequency band. Both bands in which frequency modulation is performed are separated or partially overlapped.

  In a desirable mode of the present invention, in the “addition process” of the reception signal, the fundamental wave component (frequency: f0−f1) derived from the first modulation signal in the first transmission signal and the first modulation signal in the second transmission signal. And the fundamental wave component (frequency: 2f0-2f1) derived from the second modulated signal in the first transmission signal and the second wave in the second transmission signal. The fundamental wave component (frequency: 2f0-2f1) derived from the two modulated signals is canceled out, and the harmonic component (frequency: 2f0-2f1) derived from the first modulated signal in the first transmission signal and the second transmission A sum signal obtained by adding the harmonic component (frequency: 2f0-2f1) derived from the first modulated signal in the signal can be obtained. On the other hand, in the “subtraction process” of the received signal, the fundamental wave component (frequency: f0−f1) derived from the first modulated signal in the first transmission signal and the fundamental wave derived from the first modulated signal in the second transmission signal. The component (frequency: f0-f1) is added, and the fundamental wave component (frequency: 2f0-2f1) derived from the second modulated signal in the first transmission signal and derived from the second modulated signal in the second transmission signal The fundamental wave component (frequency: 2f0-2f1) to be added is added, while the harmonic component (frequency: 2f0-2f1) derived from the first modulated signal in the first transmission signal and the first modulation in the second transmission signal The harmonic component (frequency: 2f0-2f1) derived from the signal is canceled and a difference signal is obtained. The residual fundamental wave component can be removed by applying BPF processing to the sum signal. If BPF processing is applied to the difference signal, the fundamental wave component in the first frequency band can be removed and the fundamental wave component in the second frequency band can be extracted.

  Preferably, the pulse compression means performs pulse compression on the sum signal and a signal component in the second frequency band included in the sum signal. Preferably, the pulse compression means simultaneously performs a pulse compression process and a filter process for extracting a signal component in the second frequency band. This configuration is advantageous because two processes can be realized at once.

  Preferably, the pulse compression means includes means for converting an input signal on the time axis into a signal on the frequency axis, means for executing a pulse compression process on the signal on the frequency axis, and the pulse compression. Means for inversely converting a signal on the subsequent frequency axis into a signal on the time axis. According to this configuration, the configuration can be simplified compared to pulse compression on the time axis (time domain).

  Preferably, detection means for detecting the sum signal and difference signal after pulse compression is provided at the subsequent stage of the pulse compression means, and the sum signal and difference signal before detection are input to the pulse compression means. Desirably, a detection means for detecting the sum signal and the difference signal is provided between the sum signal generation means and the difference signal generation means and the pulse compression means, and the pulse compression means has a sum signal after detection. And a difference signal are input.

  As described above, according to the present invention, it is possible to provide an ultrasonic diagnostic apparatus that can compensate for a lack of sensitivity in imaging with harmonic components.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

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

  The array transducer 10 is disposed in an ultrasonic probe (not shown). The array transducer 10 includes a plurality of transducer elements, and an ultrasonic beam is formed by the array transducer 10, and the ultrasonic beam is electronically scanned. It is also possible to use a so-called 2D array transducer as the array transducer 10. In the present embodiment, transmission / reception is repeatedly executed twice for each beam direction.

  The transmission unit 12 functions as a transmission beam former. In the present embodiment, the transmission unit 12 sequentially outputs a first transmission signal and a second transmission signal. These transmission signals are in a phase-inverted relationship, and each transmission signal is a combined modulation signal obtained by combining two modulation signals as will be described later with reference to FIG. The transmitter 12 will be described in detail. The signal generator 22 has two signal generators 24 and 26 in the example shown in FIG. The first signal generator 24 generates the first modulated signal 100 and the second signal generator 26 generates the second modulated signal 102. The modulation signals 100 and 102 are added by the adder 30 to generate a combined modulation signal. The combined modulation signal is delayed by the delay processor 32. By the phase adjustment at that time, the first transmission signal and the second transmission signal can be generated from the combined modulation signal. Of course, the first signal generator 24 and the second signal generator 26 generate the modulation signals for the first transmission signal and the second transmission signal and the second modulation signals for the first transmission signal and the second transmission signal, respectively. You may make it do. The transmission signal (first transmission signal or second transmission signal) after the delay processing is converted from a digital signal to an analog signal in the D / A converter 34. The transmission signal as an analog signal is linearly amplified by the amplifier 36, and the amplified transmission signal is output to the array transducer 10. In FIG. 1, only one transmission channel is shown in the transmission unit 12, but actually, a plurality of transmission channels (transmitters) are provided in parallel corresponding to the plurality of vibration elements. A transmission beam is formed by setting a predetermined delay relationship between the transmission signals. As described above, the first transmission and the second transmission are sequentially executed per one beam direction.

  In the array transducer 10, a first ultrasonic pulse is generated by supplying the first transmission signal, and a first reflected wave corresponding to the first ultrasonic pulse is received by the array transducer 10. Thereby, the first received signal is obtained. Similarly, when the second transmission signal is supplied to the array transducer 10, the second ultrasound pulse is transmitted from the array transducer 10 into the living body. Then, the reflected wave corresponding to the second ultrasonic pulse is received by the array transducer 10, whereby the second received signal is output from the array transducer 10.

  The receiving unit 14 functions as a receiving beam former. Specifically, a reception beam is electronically formed by performing a phasing addition process on the reception signals (first reception signal and second reception signal) output from the plurality of array transducers 10. The reception signals after the phasing addition (first reception signal and second reception signal) thus obtained are output to the harmonic component processing unit 16. In the harmonic component processing unit 16 shown in FIG. 1, the line memory 38 stores a reception signal obtained first in a certain beam direction. The line memory 38 is a memory that stores an echo data string corresponding to one received beam, for example. When a subsequent received signal is obtained, the previously stored received signal is read from the line memory. Specifically, the received signal 108 is output to the adder 40 and the subtractor 42, while the received signal 110 read from the line memory 38 is output to the adder 40 and the subtractor 42. The adder 40 adds the reception signal 108 and the reception signal 110 and outputs a sum signal 112 thereby. On the other hand, the subtractor 42 performs a subtraction process on the received signal 108 and the received signal 110, thereby outputting a difference signal 114.

  Such addition processing and subtraction processing are also described in detail in the above-mentioned Patent Document 3, but harmonic components due to in-vivo nonlinearity are extracted by the addition processing, and such harmonics are extracted by the subtraction processing. A fundamental wave component that is not a wave component is extracted.

  The pulse compression unit 44 includes pulse compression filters 46 and 48 in the configuration example shown in FIG. As described above, each transmission signal is configured as a modulation signal, and the pulse compression filters 46 and 48 execute a pulse compression process for demodulating the modulation signal. A specific configuration example of the pulse compression filters 46 and 48 will be described with reference to FIG. 4. In this embodiment, the pulse compression filters 46 and 48 execute the pulse compression processing and the band pass filter processing simultaneously. Yes. As a result, it is possible to extract a signal component existing in a frequency band twice the fundamental frequency while performing pulse compression. The remaining fundamental wave component can be removed by the filtering process of the pulse compression filter 46, and the non-linear component can be extracted with high accuracy, and only the fundamental wave existing in the double frequency band can be extracted by the filtering process of the pulse compression filter 48. Is possible.

  Signals 116 and 118 output from the pulse compression filters 46 and 48 are input to the detection circuits 50 and 52, respectively. The signal after the detection processing by the detection circuits 50 and 52 is output to the division circuit 54. The division circuit 54 generates a signal representing nonlinearity in the living body by executing a division operation based on the two input signals. The signal is output to the display processing unit 18 via a high pass filter (HPF) 56. The HPF 56 is a differentiating circuit for acquiring the temporal change rate of the signal output from the dividing circuit 54.

  The display processing unit 18 has a function as a digital scan converter (DSC), that is, an image forming function, an interpolation calculation function, and the like. The image data thus formed is output to the display unit 20, and a tomographic image in the living body is displayed on the display unit 20 as a black and white image, for example.

  The pulse compression filters 46 and 48 are preferably configured to perform processing with floating point precision using a general-purpose programmable device such as a DSP (digital signal processor). However, in consideration of processing speed and cost, it is also possible to realize pulse compression using processing with fixed-point precision and dedicated hardware such as an FFT chip.

  FIG. 2 shows the first modulated signal 100 and the second modulated signal 102 described above. These are chirp pulses, and the second modulation signal 102 has a double frequency relationship with respect to the first modulation signal 100.

  FIG. 3 shows a first transmission signal 104 and a second transmission signal 106 generated by combining the first modulated wave signal 100 and the second modulated wave signal 102. The first transmission signal 104 and the second transmission signal 106 have a relationship in which the phases are reversed. The ultrasonic waves having two transmission waveforms as shown in FIG. 3 are sequentially transmitted into the living body. Note that weighting on the time axis may be applied to each transmission signal, and in that case, a Gaussian function or the like can be used.

  FIG. 4 shows a specific configuration example of the pulse compression filters 46 and 48 shown in FIG. In this configuration example, a signal on the time axis is converted into a signal on the frequency axis, and a compression operation is executed on the frequency axis.

  The FFT module 70 has two input terminals, ie, a real part and an imaginary part. In the example shown in FIG. 4, the sum signal 112 or the difference signal 114 is input to the input terminal of the real part. 0 is input to the input terminal of the imaginary part. The FFT module 70 converts the signal on the time axis into a signal on the frequency axis. A coefficient sequence representing the transfer function H ′ (ω) is stored on the memory 74. This transfer function H ′ (ω) is the product of both when the transfer function of the bandpass filter (BPF) is BPF (ω) and the transfer function of the pulse compression filter in the double frequency band is H (ω). expressed. The coefficient sequence output from the memory 74 is given to the complex multiplier 72. The sum signal 112 or the difference signal 114 is input to the complex multiplier 72, and a complex multiplication operation is executed using the input coefficient sequence. This has the advantage that the BPF process and the pulse compression process can be realized simultaneously in a single process, and the processing efficiency can be greatly increased.

  The signal output from the complex multiplier 72 is input to an IFFT module (inverse FFT module) 76, where the signal on the frequency axis is returned to the signal on the time axis. Of the two output terminals of the IFFT module 76, the sum signal 116 or the difference signal 118 after pulse compression appears at the output terminal of the real part, and the output terminal of the imaginary part is not used here.

  Therefore, according to the configuration shown in FIGS. 1 to 4, two transmission signals are configured as a combined modulation signal, and it is possible to perform pulse compression processing on the sum signal and the difference signal at the stage of reception signal processing. There is an advantage that the image quality of the ultrasonic image, particularly the sensitivity can be improved by dealing with the above-mentioned problem of insufficient sensitivity.

  FIG. 5 shows another configuration example of the harmonic component processing unit 16 shown in FIG. In addition, the same code | symbol is attached | subjected to the structure similar to the structure shown in FIG. 1, and the description is abbreviate | omitted.

  In the configuration example shown in FIG. 5, a BPF 62 is inserted between the adder 40 and the detection circuit 50, and similarly, a BPF 64 is inserted between the subtractor 42 and the detection circuit 52. The pulse compression unit 44 is provided in the subsequent stage of the detection circuits 50 and 52. Here, the BPFs 62 and 64 are circuits for extracting a component in the double frequency band in the received signal as the RF signal. The residual signal component is removed from the sum signal 112 and the difference signal 114 is removed. In contrast, signal extraction in the double frequency band is performed. In the configuration example shown in FIG. 1, the pulse compression unit 44 performs pulse compression on the RF signal, but in the configuration example shown in FIG. 5, pulse compression is performed on the signal in the baseband region after detection. .

  FIG. 6 shows still another configuration example of the harmonic component processing unit 16 shown in FIG. In addition, the same code | symbol is attached | subjected to the structure similar to the structure shown in FIG. 1, and the description is abbreviate | omitted.

In the configuration example shown in FIG. 6, only one pulse compression filter 47 is used in the pulse compression unit 44. A specific configuration example thereof is shown in FIG. 7, and the configuration example shown in FIG. 7 is compared with the configuration example shown in FIG. In the configuration example shown in FIG. 4, the input terminal of the imaginary part in the FFT 70 is not substantially used, and the output terminal of the imaginary part in the IFFT 76 is not used. On the other hand, in the configuration example shown in FIG. 7, in order to effectively use the unused channels, the sum signal 112 is input to the input terminal of the real part and the difference signal 114 is input to the input terminal of the imaginary part. ing. As described above, the FFT 70 has two input terminals to which a signal pair on the time axis is input and two output terminals that output a signal pair on the frequency axis. In the complex multiplier 72, complex multiplication operation is simultaneously executed for both signals, and a sum signal 116 after pulse compression and a difference signal 118 after pulse compression appear at two output terminals of the IFFT 76, respectively. As described above, the IFFT 76 has two input terminals to which a signal pair on the frequency axis is input and two output terminals for outputting a signal pair on the time axis. Thus, focusing on the fact that the real part and the imaginary part in the complex signal can be filtered separately without mutual interference, pulse compression is performed on two signals using a single pulse compression filter. According to this configuration, there is an advantage that the configuration of the pulse compression unit can be saved in half. In the configuration example shown in FIG. 1, the function of the bandpass filter that the pulse compression filters 46 and 48 have may be transferred to the detection circuits 50 and 52. As a detection method in the detection circuits 50 and 52, for example, a quadrature detection method or the like can be used.

1 is a block diagram showing a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention. It is a figure which shows a 1st modulation signal and a 2nd modulation signal. It is a figure which shows two synthetic | combination modulated signals in a phase inversion relationship. It is a figure which shows the structural example of a pulse compression filter. It is a block diagram which shows the other structural example of a harmonic component process part. It is a block diagram which shows the further another structural example of a harmonic component process part. It is a block diagram which shows the structural example of the pulse compression filter shown in FIG.

Explanation of symbols

  10 array transducer, 12 transmitter, 14 receiver, 16 harmonic component processor, 22 signal generator, 24, 26 signal generator, 44 pulse compressor, 46, 48 pulse compression filter.

Claims (5)

Transmitting means for outputting a first transmission signal obtained by combining the first modulation signal and the second modulation signal having a multiplication relationship, and a second transmission signal obtained by inverting the polarity of the first transmission signal;
Receiving means for outputting a first received signal corresponding to the first transmitted signal and a second received signal corresponding to the second transmitted signal;
Sum signal generating means for generating a sum signal by adding the first received signal and the second received signal;
Difference signal generating means for generating a difference signal by subtracting the first received signal and the second received signal;
Pulse compression means for performing a pulse compression process on each of the sum signal and the difference signal;
Means for generating a signal for image formation from the sum signal and the difference signal after the pulse compression processing;
Only including,
The pulse compression means includes
A conversion means that has a real part input terminal and an imaginary part input terminal, and converts the sum signal and the difference signal as two signals on the time axis input to them into two signals on the frequency axis;
Means for performing a pulse compression process on the two signals on the frequency axis;
It has a real part output terminal and an imaginary part output terminal, and inversely converts two signals on the frequency axis after the pulse compression processing into two signals on the real time after the pulse compression processing, and converts them into the pulse compression processing Inverse conversion means for outputting from the real part output terminal and the imaginary part output terminal as a later sum signal and difference signal,
An ultrasonic diagnostic apparatus comprising: The apparatus of claim 1.
The first modulated signal is a first chirp signal whose frequency changes in a first frequency band,
The ultrasonic diagnostic apparatus, wherein the second modulation signal is a second chirp signal whose frequency changes in a second frequency band as a harmonic band with respect to the first frequency band. The apparatus of claim 2 .
The ultrasonic diagnostic apparatus characterized in that the pulse compression means simultaneously performs a pulse compression process and a filter process for extracting a signal component within the second frequency band. The apparatus of claim 1.
Detection means for detecting the sum signal and difference signal after pulse compression is provided at the subsequent stage of the pulse compression means,
2. An ultrasonic diagnostic apparatus according to claim 1, wherein a sum signal and a difference signal before detection are input to the pulse compression means. The apparatus of claim 1.
Detection means for detecting the sum signal and the difference signal is provided between the sum signal generation means and the difference signal generation means and the pulse compression means,
The ultrasonic diagnostic apparatus, wherein a sum signal and a difference signal after detection are input to the pulse compression means.

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