JP2012080994A - Ultrasonic diagnosis apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately suppress unnecessary wave components included in signals after phasing and adding, and to prevent excessive suppression particularly, in an ultrasonic diagnosis apparatus.SOLUTION: A spectrum operation part 34 samples a signal level along an element array direction for a reception signal column after phasing processing (after delay processing) and before adding processing, obtains a waveform composed of a plurality of sampling values, and acquires an azimuth spectrum by frequency analysis to it. An azimuth characteristic processing part 36 generates an azimuth spectrum after weighting by applying weighting processing using the azimuth characteristics of a vibration element column generated by the phasing processing and the adding processing to the azimuth spectrum. A coefficient operation part 38 computes a coefficient for unnecessary wave component suppression on the basis of the azimuth spectrum after weighting. A multiplier 40 suppresses the unnecessary wave components by multiplying a coefficient with respect to the output signals of an addition part 28. Instead of multiplication, subtraction can be utilized as well.

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to suppression of unwanted wave components contained in a received signal.

  In an ultrasonic diagnostic apparatus, an ultrasonic pulse is transmitted from an array transducer to a living body, and a reflected wave from the living body is received by the array transducer. At the time of transmission, a plurality of transmission signals having a predetermined delay relationship for forming a transmission beam are supplied to the array transducer, and at the time of reception, phasing is performed on the plurality of reception signals from the array transducer. Processing (delay processing) and addition processing (both phased addition processing) are applied, whereby a reception beam is formed electronically. The signal component from the reception beam azimuth (or reception focal point) is enhanced by the phasing addition processing, and the signal component from the other azimuth (or out-of-focus point) is removed and reduced. Examples of unnecessary wave components include grating lobes, side lobes, sneak components from other directions during multi-directional simultaneous transmission, and noise. In order to enhance the ultrasonic image, it is desired to effectively exclude unnecessary wave components included in the received signal.

  Non-Patent Document 1 discloses a technique for suppressing unnecessary wave components using a coefficient called GCF (Generalized Coherence Factor). This increases the spatial resolution and contrast resolution. A method using GCF will be described below.

  The plurality of vibration elements are aligned in the element arrangement direction, and a plurality of reception signals (reception signal trains) are output from them. A phasing addition process is applied to the received signal sequence in order to form a reception beam or a reception focus. As described above, it consists of phasing processing (delay processing) and addition processing. Data sampling is performed along the transverse direction, that is, the element arrangement direction, with respect to the received signal sequence after the phasing process, and the sampled data sequence is subjected to frequency analysis. Thereby, an orientation spectrum is obtained. If the component is from the focal point, the phase is aligned by the phasing process, so the level of the sampled data string should be uniform, and it appears as a DC component when viewed in terms of spatial frequency. Outside the focus, the level of the sampled data string fluctuates periodically, which appears as a frequency component. Here, it is known that the frequency on the horizontal axis in the azimuth spectrum corresponds to the azimuth (angle) at which the unwanted wave appears.

  The ratio of the area corresponding to the main beam in the above azimuth spectrum for the received signal sequence and the area of the other (whole unwanted wave component) represents the amount of unwanted wave components mixed in. The ratio is the GCF. If the received signal after phasing addition is multiplied by GCF, the signal suppression level can be adaptively suppressed according to the magnitude of the unwanted wave component.

Pai-Chi Li, "Adaptive Imaging Using the Generalized Coherence Factor", IEEE Transactions Ultrasonics, Vol.50, No.2, 2003.

  In the above conventional method, there is a problem that suppression of the received signal becomes excessively large depending on circumstances. That is, in the above-described conventional method, since the information after the delay processing is used, spatial irregularities are referred to, but the reduction of unnecessary signal components in the addition processing after the phasing processing is not taken into consideration. . The frequency distribution that is the basis for calculating the GCF is at a stage before the phasing addition process is applied, and in fact, the unnecessary wave component is canceled to some extent at the stage of the phasing addition process.

  An object of the present invention is to realize appropriate suppression of unnecessary signal components contained in a received signal, and in particular, processes received signals in consideration of suppression of unnecessary wave signal components in phasing addition processing. There is.

  The present invention is composed of a plurality of vibration elements aligned in the element arrangement direction, and a vibration element array that outputs a reception signal string, and a phasing process and an addition process that are applied in stages to the reception signal string. An adder, a frequency analyzer that performs frequency analysis in the element array direction on the received signal sequence after the phasing process and before the addition process, and obtains an azimuth spectrum; and A weighting processing unit that generates a weighted azimuth spectrum by applying weighting processing using the azimuth characteristics of the vibration element array generated by phase processing and addition processing; and an unnecessary wave component based on the weighted azimuth spectrum A generation unit that generates a suppression signal, and a suppression processing unit that executes unnecessary wave component suppression processing on the output signal of the phasing addition unit using the unnecessary wave component suppression signal. And wherein the Mukoto.

  According to the above configuration, the azimuth spectrum is obtained by performing frequency analysis in the element arrangement direction on the received signal sequence after the phasing process and before the addition process. The azimuth spectrum is also obtained by the method of Non-Patent Document 1, but the method of Non-Patent Document 1 does not take into account suppression of unnecessary signal components by phasing addition processing, so excessive suppression occurs. . According to the above configuration, excessive suppression is prevented by applying a weighting process using the azimuth characteristics of the vibration element array to the azimuth spectrum, that is, by performing a process corresponding to the suppression action of the phasing adder. it can. In other words, it is possible to perform the suppression process after the action of the receiving unit. The orientation characteristic of the vibration element array is a characteristic that reflects the physical characteristics of the vibration element array and the effect of the phasing addition processing. It can be obtained in advance or in real time by experiment or numerical calculation such as simulation. When electron beam scanning of an electronic sector or the like is performed, the azimuth characteristics are obtained for each main beam deflection angle, and the azimuth characteristics to be used are switched according to the main beam deflection angle. In the case of electronic linear scanning, it is possible to maintain the azimuth characteristics when scanning with the main beam. When the transmission aperture, the reception aperture, and other transmission / reception conditions are changed, it is desirable to use the azimuth characteristics suitable for them. At the time of ultrasonic diagnosis, the azimuth spectrum is calculated in real time at each time, and at the same time, weighting processing using appropriate azimuth characteristics is executed in real time.

  Preferably, the generation unit generates the unnecessary wave component suppression signal by specifying at least one of a main beam equivalent portion and an unnecessary wave equivalent portion in the weighted azimuth spectrum. The unnecessary wave component suppression signal may be a coefficient representing the degree of suppression or gain, or may represent the signal power itself. Preferably, the unnecessary wave component suppression signal is subtracted from the output signal of the phasing adder. Preferably, the output signal of the phasing adder is multiplied by the unnecessary wave component suppression signal.

  Preferably, a detection processing unit that performs detection processing on an output signal of the phasing addition unit, and the suppression processing unit performs the unnecessary wave component suppression processing on the signal after the detection processing. When the unnecessary wave suppression signal does not have a positive or negative sign, a multiplication process or a subtraction process is applied to the detected signal.

  ADVANTAGE OF THE INVENTION According to this invention, the moderate suppression of the unnecessary signal component contained in a received signal is realizable. In particular, the received signal can be processed in consideration of suppression of unnecessary wave signal components in the phasing addition processing.

It is a figure which shows the received signal sequence after the delay process corresponded to a main beam component. It is a figure which shows the azimuth | direction spectrum about a main beam component. It is a figure which shows the received signal sequence after the delay process corresponding to the unnecessary wave component which arrives from the direction of (theta) 1. It is a figure which shows the azimuth | direction spectrum of an unnecessary wave component. It is a figure which shows the azimuth | direction spectrum containing both a main beam component and an unnecessary wave component. It is a figure which shows the azimuth | direction characteristic (azimuth profile) of a vibration element row | line | column. It is a figure which shows the azimuth | direction spectrum after applying a weighting process with respect to the azimuth | direction spectrum shown in FIG. 5 using the azimuth | direction characteristic shown in FIG. 1 is a diagram showing a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention.

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

  First, the principle of unnecessary wave component suppression processing will be described with reference to FIGS. FIG. 1 shows an array transducer 10. The array transducer 10 is constituted by a plurality of vibrating elements 12 arranged in a straight line, for example. Reference numeral 100 denotes a main beam. In the example shown in FIG. 1, only the main beam component is observed. The delay unit (phasing unit) 20 includes a plurality of delay units 22, and delay processing is executed on a plurality of received signals from the plurality of vibration elements 12 according to a delay amount distribution (delay curve). Reference numeral 101 denotes a received signal sequence after delay processing (before addition processing). It consists of a plurality of received signals 102. When a plurality of received signals 102 are sampled in the element arrangement direction at each timing 104, a one-dimensional waveform including a plurality of sampling values is obtained. When frequency analysis processing is applied to the waveform, the orientation spectrum shown in FIG. 2 is obtained. In FIG. 2, the horizontal axis indicates the azimuth θ, which corresponds to the spatial frequency. The vertical axis represents power P. The center of the horizontal axis is an azimuth angle of zero degree, and the main beam exists there. The power of the orientation spectrum 106 is concentrated there. This is a result of an almost ideal phasing process. When the phases of the signals are aligned, the spatial frequency becomes zero and energy concentrates in the vicinity of the azimuth angle of zero degrees on the azimuth spectrum 106.

  On the other hand, in the example shown in FIG. 3, an unwanted wave has arrived from the direction θ1. The main beam component does not appear. When the received signal sequence is sampled at each timing 104, a one-dimensional waveform is obtained in the same manner as described above, and the result of frequency analysis of the waveform is the azimuth spectrum 108 shown in FIG. In the azimuth spectrum 108, an unnecessary wave component arriving from the azimuth θ1 appears remarkably. Actually, unwanted wave components of various sizes come from each direction.

  FIG. 5 shows an azimuth spectrum 110a including both the main beam component and the unwanted wave component. A spectral portion corresponding to the main beam is indicated by 110b, and spectral portions corresponding to unnecessary wave components are indicated by 110c and 110d on both sides thereof. The area Sa of the entire azimuth spectrum 110a is the total area (Sb + Sc + Sd) of the individual spectral portions. For example, the unnecessary wave suppression coefficient k is calculated as the ratio of the area Sb of the portion corresponding to the main beam component to the entire area Sa. However, according to this method, although the unnecessary wave component is actually reduced by the phasing addition process, all of the unnecessary wave components in the azimuth spectrum are evaluated faithfully. Component suppression may be excessive.

  Therefore, in this embodiment, a weighting process for multiplying the orientation spectrum shown in FIG. 5 by the orientation characteristic 112 shown in FIG. 6 is applied. The azimuth characteristics reflect both the physical characteristics of the vibration element array and the electronic action of the phasing adder, and other transmission / reception conditions (transmission aperture, reception aperture, transmission focus) as necessary. Depth, reception depth of focus, etc.). FIG. 7 shows the orientation spectrum 114a after the weighting process. In the azimuth spectrum 114a, unnecessary wave components included in the azimuth spectrum 110a shown in FIG. 5 are significantly reduced. On the other hand, the main beam component existing near the azimuth zero degree is stored as it is. A coefficient or signal for suppressing unnecessary wave components is generated based on the azimuth spectrum after such weighting processing. For example, the area Sb of the spectrum portion 114b corresponding to the main beam and the areas Sc and Sd of the spectrum portions 114c and 114d corresponding to unnecessary wave components existing on both sides thereof are specified, and the coefficient k is calculated as Sb / Sa. This focuses on the main beam component, but it is also possible to calculate a coefficient or signal for suppressing the unwanted wave component by focusing on the unwanted wave component. Coefficients or signals for suppressing unnecessary wave components can be calculated without using the entire area. There are various methods for specifying the main beam component. For example, a half-value width may be used, or a point that falls a predetermined level from the peak to both sides may be determined as the boundary point. It is also possible to use a gradient.

  The azimuth spectrum is calculated in real time at each time. The weighting azimuth characteristics are dynamically changed in accordance with the beam azimuth in the electronic sector scanning, and preferably a fixed one is fixedly used in the electronic linear scanning. It is desirable to prepare the optimum azimuth characteristics for each transmission / reception condition and selectively use them. The orientation characteristics may be changed according to the probe used.

  FIG. 8 shows a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 1 is a block diagram showing the overall configuration thereof. This ultrasonic diagnostic apparatus is used in the medical field, and is an apparatus that forms an ultrasonic image based on a reception signal obtained by transmitting and receiving ultrasonic waves to and from a living body. In this embodiment, a B-mode tomographic image is formed as an ultrasound image, but a Doppler image or the like may be formed as a matter of course. This ultrasonic diagnostic apparatus has the above-described unnecessary wave component suppression function.

  In FIG. 8, the array transducer 10 includes a plurality of vibration elements 12. The plurality of vibration elements 12 are arranged in a straight line. Of course, they may be arranged in an arc. An ultrasonic beam (transmission beam, reception beam) is formed using the plurality of vibration elements 12 and is electronically scanned. As electronic scanning methods, electronic sector scanning, electronic linear scanning, and the like are known. Of course, a 2D array transducer can be used instead of the 1D array transducer.

  The transmission unit 14 is a transmission beam former. That is, the transmission unit 14 supplies a plurality of transmission signals having a predetermined delay relationship to the plurality of vibration elements 12 during transmission. As a result, a transmission beam is formed. At the time of reception, the reflected wave from each point in the living body is received by the array transducer 10. As a result, a plurality of received signals are generated and output to the amplifying unit 16. Incidentally, the amplification unit 16, the delay unit 20, the apodization processing unit 24, and the addition unit 28 constitute a reception unit, which is a reception beamformer.

  The amplification unit 16 includes a plurality of amplifiers 18. A delay unit 20 is provided at the subsequent stage, and the delay unit 20 includes a plurality of delay units 22. Delay processing (phasing processing) is executed by these delay devices 22. The delay time given to each delay unit 22, that is, the delay data is supplied from the control unit 50. An apodization processing unit 24 is provided after the delay unit 20, and is constituted by a plurality of gain adjusters, that is, amplifiers 26. The apodization processing unit 24 is a known circuit that performs weighting along the element arrangement direction in the transmission / reception aperture. Each received signal after the delay process and after the weight process is output to the adder 28. The plurality of received signals are added by the adder 28, thereby forming a reception beam electronically. The received signal after phasing addition is output to the detector 32. The detection unit 32 is a known circuit that performs detection processing.

  In the present embodiment, an unnecessary wave component suppression unit 30 is provided to suppress unnecessary wave components. Specifically, it is constituted by a spectrum calculation unit 34, an azimuth characteristic processing unit 36, a coefficient calculation unit 38, and a multiplier 40.

  The spectrum calculation unit 34 samples the received signal sequence after the delay process at each time, and acquires a waveform composed of sampling data along the element arrangement direction at each time. And the spectrum calculating part 34 performs a frequency analysis with respect to the waveform of each time, and produces | generates a spectrum, ie, an azimuth | direction spectrum, by this. This azimuth spectrum represents received energy in each azimuth, that is, a spectrum in which a main beam component and an unnecessary wave component appear. The azimuth characteristic processing unit 36 performs the above-described weighting process. Specifically, the azimuth characteristic processing unit 36 is a circuit that multiplies the azimuth spectrum by an azimuth characteristic as a weighting function, that is, an azimuth profile. The azimuth characteristics are dynamically switched according to the beam change angle under the control of the control unit 50, and are also switched by changing the transmission / reception conditions. In this embodiment, electronic sector scanning is executed. However, when electronic linear scanning is selected, the azimuth characteristics may be maintained in beam scanning. That is, it is possible to switch the content of the weighting process according to the operation mode. The coefficient calculation unit 38 calculates a coefficient for suppressing unnecessary wave components based on the azimuth spectrum after the weighting process. There are various methods for calculating the coefficient. In any case, at least one of the main beam component and the unwanted wave component is used, thereby changing the gain for the received signal after phasing addition. The coefficient is calculated. These coefficients are sent to the multiplier 40 and multiplied by the received signal output from the detector 32 after detection. This adjusts the gain of the signal. When the unnecessary wave component is large, the suppression is further increased, thereby reducing the unnecessary wave component generated on the image. However, in the present embodiment, since the coefficient is calculated in consideration of unnecessary wave suppression processing in the phasing adder, that is, in consideration of the azimuth characteristics, there is an effect that excessive suppression occurs as in the prior art. Can be prevented.

  Incidentally, although multiplication of coefficients is performed in the present embodiment, other methods such as signal subtraction may be used to suppress or reduce unnecessary wave components. Since the amount of unnecessary wave components can be quantified in the weighted azimuth spectrum, a signal representing the amount of unnecessary wave components may be generated, and the signal may be subtracted from the received signal.

  The received signal that has undergone the above processing is sent to the signal processing unit 42. The signal processing unit 42 executes various signal processing such as logarithmic conversion, and the processed signal is sent to the image forming unit 44. The image forming unit 44 is configured by a digital scan converter (DSC) in the present embodiment. Thereby, a B-mode tomographic image is constructed. The image data is sent to the display 48 via the display processing unit 46. As described above, the D-mode image is formed in the present embodiment, but a two-dimensional blood flow image or the like may be formed.

  According to the present embodiment, in suppressing unnecessary wave components, it is possible to perform suppression processing of the received signal after phasing addition in consideration of unnecessary wave component suppression action of the reception beamformer. This can be effectively prevented, thereby improving the image quality of the ultrasonic image. In particular, in the past, there was a problem that so-called blackout or the like was likely to occur on an ultrasonic image due to excessive suppression, but according to the configuration of the above embodiment, such blackout is effectively prevented. Thus, there is an advantage that an image useful for disease diagnosis can be formed.

  DESCRIPTION OF SYMBOLS 10 Array transducer | vibrator, 30 Unwanted wave component suppression part, 34 Spectrum calculating part, 36 Direction characteristic processing part, 38 Coefficient calculating part, 40 Multiplier.

Claims (6)

A plurality of vibration elements arranged in the element arrangement direction, a vibration element array that outputs a reception signal string,
A phasing addition unit that applies phasing processing and addition processing in stages to the received signal sequence;
A frequency analysis unit that obtains an orientation spectrum by performing frequency analysis in the element array direction on the received signal sequence after the phasing process and before the addition process;
A weighting processing unit that generates a weighted azimuth spectrum by applying a weighting process using the azimuth characteristics of the vibration element array generated by the phasing process and the addition process to the azimuth spectrum;
A generating unit that generates an unnecessary wave component suppression signal based on the weighted azimuth spectrum;
A suppression processing unit that performs unnecessary wave component suppression processing on the output signal of the phasing addition unit using the unnecessary wave component suppression signal;
An ultrasonic diagnostic apparatus comprising: The apparatus of claim 1.
An ultrasonic diagnostic apparatus, wherein the azimuth characteristics of the vibration element array are changed based on a main beam deflection angle. The apparatus according to claim 1 or 2,
The ultrasonic diagnostic apparatus, wherein the generating unit generates the unnecessary wave component suppression signal by specifying at least one of a main beam equivalent portion and an unnecessary wave equivalent portion in the weighted azimuth spectrum . The apparatus of claim 3.
The ultrasonic diagnostic apparatus, wherein the unnecessary wave component suppression signal is subtracted from an output signal of the phasing adder. The apparatus of claim 3.
The ultrasonic diagnostic apparatus, wherein the output signal of the phasing adder is multiplied by the unnecessary wave component suppression signal. The apparatus of claim 1.
A detection processing unit that performs detection processing on the output signal of the phasing addition unit,
The ultrasonic diagnostic apparatus, wherein the suppression processing unit executes the unnecessary wave component suppression processing on the signal after the detection processing.

Images