JP5396242B2 - Ultrasonic diagnostic equipment - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to a technique for reducing unnecessary signals (side lobes, grating lobes, noise, etc.).

  In order to improve the image quality of an ultrasonic image, it is desirable to reduce unnecessary signals (unnecessary components) such as side lobes, grating lobes, and noises in the reception beamformer. Such an unnecessary component reduction technique is described in Non-Patent Document 1.

  First, a general technique will be described. In the receive beamformer, a plurality of received signals from a plurality of signal elements are subjected to phasing processing (delay processing) and then added for focusing. After the addition, beam data as an RF signal is obtained. The beam data is used for forming an ultrasonic image. In the case of the reflected wave from the focus point, the phase (time phase) is uniform among the plurality of received signals after the delay processing, so that an RF signal having a large amplitude after addition is obtained. On the other hand, in the case of a reflected wave from a place other than the focus point, an RF signal with a low amplitude is observed because the phases do not match among the plurality of received signals. In other words, more unnecessary signals (side lobe components) are observed.

  The technique described in Non-Patent Document 1 focuses on the above phase relationship and reduces unnecessary components. FIG. 1 shows the configuration described in FIG. 7 of Non-Patent Document 1. A plurality of received signals are input to a plurality of delay devices 10 in order to match the phases, and are delayed there. The plurality of received signals after the delay processing are added in the adder 12. The output is beam data as an RF signal. Apart from this signal processing flow, the code adder 14 adds a plurality of sign-bit data included in a plurality of received signals. In this example, the sign has only 1 (positive) or -1 (negative). Code data for the number of channels (N) is added, and this added value SB is input to the SCF table 16, and an evaluation coefficient SCF (Sign Coherence Factor) is output from the SCF table. The SCF is multiplied by the RF signal (beam data), thereby adjusting the gain. SCF is calculated as follows. P is a predetermined index.

SCF has a value between 0 and 1. If the phases of all channels are aligned (in the case of the focus point), SB ² = N ² and SCF has a maximum value of 1. Since the polarity is random if it is noise, the SCF approaches zero. As described above, the SCF of the unnecessary component is relatively smaller than the SCF of the true component. The SCF is also reduced in the case of unnecessary components called side lobes and grating lobes. Therefore, by multiplying the received signal by the SCF, it is possible to adjust the gain and suppress the unnecessary component while preserving the true component.

J. Camacho, et al, "Phase Coherence Imaging", IEEE trans. UFFC, vol. 56, No. 5, 2009.

  By the way, in an ultrasonic diagnostic apparatus, weighting processing (abdization) for a plurality of received signals is generally performed. This is also a technique for reducing side lobes and the like. According to the technique of Non-Patent Document 1, it can be said that this weighting process is not necessary. However, since the technique of Non-Patent Document 1 is a method based on probabilistic or statistical, while the weighting process is a method based on theory, both methods have different properties. Non-Patent Document 1 does not describe a combination with a weighting process. It is expected to realize a configuration in which the method described in Non-Patent Document 1 (sign addition method) and weighting processing are combined or a synergistic effect of both can be expected.

  An object of the present invention is to increase the effect of reducing unnecessary signals as compared with the conventional method.

  An object of the present invention is to realize a new unnecessary signal processing method by combining and further developing a plurality of unnecessary signal reduction methods while taking advantage of each advantage.

  An ultrasonic diagnostic apparatus according to the present invention includes a weighting processing unit that performs weighting processing on a plurality of received signals in accordance with a weighting function that changes with movement of a reception focus point in a depth direction, and a plurality of weighted processing units. A phasing addition processing unit for performing phasing addition processing on the received signal, a plurality of index data representing a state of the plurality of reception signals before or after the weighting processing, and a plurality of weights given to the plurality of reception signals And an evaluation coefficient calculation unit that obtains an evaluation coefficient based on the value, and a gain variable unit that changes the gain of the reception signal after the phasing addition based on the evaluation coefficient. And

  According to the above configuration, the evaluation coefficient is obtained from the plurality of index signals indicating the states of the plurality of reception signals and the plurality of weight values, and the gain of the reception signal is changed based on the evaluation coefficient. In other words, since multiple weight values given to multiple received signals represent the individual contribution, influence, and importance of each received signal, the evaluation coefficient for suppressing unnecessary signals by taking them into consideration Can be determined appropriately. Preferably, the index data is code data indicating whether the amplitude value is positive or negative. However, the index data may be a value indicating whether the received signal level is equal to or higher than a threshold value. If the weight value can be negative as well as positive, it is desirable to refer to the sign of the received signal before the weighting process. The reception focus point is dynamically changed according to the reception dynamic focus method.

  According to the above configuration, when evaluating the uniformity or randomness of the index data, the weight value can be taken into account, that is, for a more important received signal, it can be more taken into account in the evaluation coefficient calculation. It is possible to obtain a significant unnecessary component reduction effect that cannot be realized by the individual unnecessary component reduction method. In other words, the image quality of the ultrasonic image can be improved by using the synergistic relationship or interpolation relationship of the two unnecessary component reduction methods. Experiments have confirmed that a significant improvement in image quality can be obtained depending on conditions.

  Preferably, the evaluation coefficient calculation unit applies an addition process or a subtraction process to a weight value given to the received signal based on code data of the received signal for each received signal in order to calculate the evaluation coefficient. To do. The addition process is a process of adding the current weight value to the value obtained so far, and the subtraction process is a process of subtracting the current weight value from the value obtained so far. Preferably, the evaluation coefficient calculation unit includes: means for obtaining an addition / subtraction process result value by addition / subtraction processing for the plurality of weight values; means for obtaining an addition process result value by addition processing for the plurality of weight values; Means for normalizing the addition / subtraction processing result using the processing result value, and means for determining the evaluation coefficient from the normalized value. If standardization is performed, a natural unnecessary component reduction effect can be expected regardless of the signal size. The addition processing result value is desirably a value obtained by accumulating the absolute value of each weight value.

  Preferably, the evaluation coefficient calculation unit determines whether or not it is necessary to add code data of the received signal based on a weight value for the received signal for each received signal in order to calculate the evaluation coefficient. Preferably, the evaluation coefficient calculation unit includes means for determining whether or not the weight value satisfies a predetermined condition, means for cumulatively adding the code data when the weight value satisfies a predetermined condition, and the weight value Means for accumulatively adding the absolute value of the code data when the predetermined condition is satisfied, means for normalizing the accumulative addition result of the code data using the accumulative addition result of the absolute value of the code data, and the normalization And a means for determining the evaluation coefficient from a later value.

  Preferably, the gain variable unit determines the gain using a non-linear conversion function that determines the gain from the standardized evaluation coefficient. Preferably, the weighting function is a function that increases the reception aperture as the reception focus point becomes deeper. Preferably, the gain variable section includes means for smoothing the evaluation coefficient, and the gain of the reception signal after the phasing addition is adjusted based on the evaluation coefficient after the smoothing. If smoothing is performed, a smooth unnecessary component suppression action can be expected.

  According to the present invention, the effect of reducing unnecessary signals can be enhanced as compared with the conventional method. Alternatively, a new unnecessary signal processing method can be realized by combining and further developing a plurality of unnecessary signal reduction methods while taking advantage of each advantage.

It is a block diagram which shows the structure of the conventional receiving part. It is a block diagram which shows the structure of the receiving part of the ultrasonic diagnosing device which concerns on this invention. It is a figure which shows the change to the depth direction of a weighting function. It is a figure which shows the 2nd example of a receiving part. It is a figure which shows the 3rd example of a receiving part.

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

  FIG. 2 shows the configuration of the receiving unit of the ultrasonic diagnostic apparatus. Reference numeral 20 denotes a reception beam former that performs reception dynamic focus. The plurality of received signals are input to the plurality of A / D converters 22. As a result, the analog reception signal is converted into a digital reception signal. Here, the first bit corresponds to a sign bit. A plurality of received signals after digital processing are input to a plurality of delay devices 24, where they are delayed. A plurality of received signals after the delay processing are added in an adder 30 via a plurality of multipliers 26. By this addition, the received signal (beam data) after the phasing addition is output as an RF signal. The plurality of multipliers 26 are circuits for weighting processing, and each multiplier 26 multiplies the received signal by the weight value. It is a weighting function that determines a plurality of weight values, and the function is output from the function generator 28.

  As shown in FIG. 3, the weighting function is a function that increases the reception aperture as the reception focus point becomes deeper. Reference numeral 42 denotes a center line. Reference numeral 40 denotes an array transducer, which is composed of a plurality of transducer elements. Reference numerals 44 to 52 show examples of weighting functions. The deeper the reception focus point, the wider its function form. Such weighting processing is for suppressing unnecessary signals, but it may not be possible to sufficiently improve the quality of an ultrasonic image.

  Returning to FIG. 2, the code | symbol 100 has shown the gain control part. It includes a weight adder / subtractor 32, a weight adder 34, an evaluation coefficient calculator 36, a smoothing circuit 37, and a multiplier 38. In this example, the weight adder / subtractor 32 is input with a plurality of code data (index data) extracted from a plurality of received signals after the weighting process. Also, a plurality of weight values given to a plurality of received signals are input. For each channel (that is, received signal), it is determined whether the code data is +1 or −1. If it is +1, a weight value addition process is executed. Processing is executed. Conventionally, +1 or -1 is added, but according to the present embodiment, the sign value can be positively used using the weight value. Alternatively, it is possible to consider more important received signals. If the phase is uniform among a plurality of received signals, a large positive or negative value is obtained as a result of addition / subtraction. On the contrary, when diversity is recognized in the phase among a plurality of received signals, a small positive or negative value is obtained as a result of addition / subtraction. Since the result of addition / subtraction differs depending on the weight function, it is desirable to divide the result of addition / subtraction by the sum of weight values, that is, to perform normalization processing. The sum of the weight values is calculated in the weight adder 34, and the normalization calculation is executed in the evaluation coefficient calculation unit 36. Specifically, the evaluation coefficient calculation unit 36 performs the following calculation. A indicates an addition / subtraction value which is an output of the weight adder / subtractor 32.

  Here, N indicates the number of channels, b indicates code data (+1 or −1) of each channel received signal, and a indicates a weight value in each channel. The addition / subtraction value A has a value of 0 to 1 by normalization. Then, in order to obtain the evaluation coefficient S, the following nonlinear function (or monotonically increasing function) may be used. S also has a value between 0 and 1.

  Here, n is n ≧ 0 and adjusts the degree of change of S with respect to A. Further, h in the formula (4) can be set between 0 and 1, and gives a base value or an offset value to S. If n = 0 or h = 1, S = 1, which is a state of the conventional method in which unnecessary components are not reduced. That is, by changing the values of n and h, the reduction degree of unnecessary components and the texture of the formed image can be adjusted.

  In FIG. 2, the evaluation coefficient calculation unit 36 calculates the evaluation coefficient S by executing equation (1). However, in the configuration of FIG. 2, a smoothing circuit 37 that smoothes the evaluation coefficient S is provided so that the image quality is smoothly improved. That is, the evaluation coefficient S is smoothed in the depth direction (time), and is multiplied by the phasing-added RF signal. This smoothing can be constituted by an FIR type or IIR type low-pass filter, and can reduce the statistical fluctuation of S.

  Note that the weighting function is normally generated based on a window function such as Gaussian or Hanning. Although the window width (opening length) and the window function change depending on the depth, if such a change does not change for each reception beam, the denominator on the right side in equation (1) can be tabulated.

  The above configuration can be applied to harmonic imaging, Doppler mode, etc. in addition to transmission / reception of fundamental waves. The present invention can also be applied to a multidirectional simultaneous reception system using a two-dimensional array transducer.

  Next, another embodiment will be described with reference to FIGS. 4 and 5. In addition, the same code | symbol is attached | subjected about the structure similar to the structure shown in FIG. 2, and the description is abbreviate | omitted.

  In FIG. 4, a plurality of code data included in a plurality of reception signals before weighting processing are input to the weight adder / subtractor 32. According to this configuration, even if the weighting function partially has a minus sign, the evaluation coefficient can be calculated without being affected by such sign inversion.

  In FIG. 5, as in the configuration of FIG. 4, a plurality of code data included in a plurality of reception signals before weighting processing is used, but these are input to the comparison circuit 54. The comparison circuit 54 outputs the code data as it is for each channel only when the weight value is not less than the threshold value + H or not more than -H. Specifically, if the weight value is larger than the threshold value + H or smaller than -H, the code data is output as it is, and if the weight value is between the threshold value + H and -H, 0 is output. That is, the output of the comparison circuit 54 takes a ternary value (+1, 0, −1). The output b is added by the adder 56, and the added value is output to the evaluation coefficient calculation unit 36. On the other hand, the absolute value adder 58 cumulatively adds the absolute values output from the comparison circuit 54 and outputs the added value M to the evaluation coefficient calculation unit 36 for normalization. The evaluation coefficient calculation unit 36 performs the following calculation.

  According to the configuration of FIG. 5, when the weight is small, it is excluded from the evaluation target, and in other cases, the difference between uniformity and diversity is reflected in the determination of the gain in consideration of the sign bit. Can do. For example, when the weight value is in the range of 0 to 1.0, if H is set to 0.3, the sign bit can be considered only for a channel within about −10 dB from the peak of the weighting function.

  20 reception beam former, 26 multiplier, 28 function generator, 32 weight adder / subtractor, 34 weight adder, 36 evaluation coefficient calculator, 37 smoothing circuit, 38 multiplier.

Claims (9)

A weighting processing unit that performs weighting processing on a plurality of received signals according to a weighting function that varies with movement of the reception focus point in the depth direction;
A phasing addition processing unit that executes phasing addition processing on the plurality of weighted reception signals;
An evaluation coefficient calculation unit that obtains an evaluation coefficient based on a plurality of index data representing a state of a plurality of reception signals before or after the weighting process and a plurality of weight values given to the plurality of reception signals;
A gain variable section that changes the gain of the received signal after the phasing addition based on the evaluation coefficient;
An ultrasonic diagnostic apparatus comprising: The apparatus of claim 1.
The ultrasonic diagnostic apparatus according to claim 1, wherein the index data is sign data indicating whether an amplitude value is positive or negative. The apparatus of claim 2.
The evaluation coefficient calculation unit applies an addition process or a subtraction process to a weight value given to the reception signal based on code data of the reception signal for each reception signal in order to calculate the evaluation coefficient.
An ultrasonic diagnostic apparatus. The apparatus of claim 3.
The evaluation coefficient calculator is
Means for obtaining an addition / subtraction processing result value by addition / subtraction processing for the plurality of weight values;
Means for obtaining an addition process result value by an addition process for the plurality of weight values;
Means for normalizing the addition / subtraction processing result using the addition processing result value;
Means for determining the evaluation coefficient from the normalized value;
An ultrasonic diagnostic apparatus comprising: The apparatus of claim 2.
The evaluation coefficient calculation unit determines whether or not addition processing of code data of the received signal is necessary based on a weight value for the received signal for each received signal in order to calculate the evaluation coefficient.
An ultrasonic diagnostic apparatus. The apparatus of claim 5.
The evaluation coefficient calculator is
Means for determining whether the weight value satisfies a predetermined condition;
Means for cumulatively adding the code data when the weight value satisfies a predetermined condition;
Means for cumulatively adding the absolute value of the code data when the weight value satisfies a predetermined condition;
Means for normalizing the cumulative addition result of the code data using the cumulative addition result of the absolute value of the code data;
Means for determining the evaluation coefficient from the normalized value;
An ultrasonic diagnostic apparatus comprising: The apparatus of claim 1.
The ultrasonic diagnostic apparatus, wherein the gain variable unit determines a gain using a non-linear conversion function that determines a gain from the standardized evaluation coefficient. The apparatus of claim 1.
The ultrasonic diagnostic apparatus according to claim 1, wherein the weighting function is a function that increases a reception aperture as a reception focus point becomes deeper. The apparatus of claim 1.
Means for smoothing the evaluation coefficient,
The gain of the received signal after the phasing addition is adjusted based on the evaluation coefficient after the smoothing,
An ultrasonic diagnostic apparatus.

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