JP2018007952A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of Doppler measurement when a sample gate is set at a position deeper than a reference depth.SOLUTION: A region called a sub-gate is generated at a position of a depth obtained by subtracting a reference depth (a depth at which an ultrasound pulse reciprocates in one repetition cycle) from a depth of a sample gate. A pulsed Doppler apparatus forms an ultrasonic beam for attenuating unnecessary ultrasonic waves generated by reflection at the sub-gate, while receiving observation target ultrasonic waves generated by reflection at the sample gate. That is, by processing executed by a phasing weighting unit 24, a reception focus of a received beam is set to the sample gate, and a reception attenuation point of the received beam is set to the sub-gate. The phasing weighing unit 24 outputs a synthesized signal obtained by synthesizing detected wave signals based on the ultrasonic waves reflected at the reception focus so as to strengthen each other and synthesizing detected wave signals based on the ultrasonic waves reflected at the reception attenuation point so as to weaken each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an apparatus that performs Doppler measurement on a subject.

  A pulse Doppler apparatus is widely used as an ultrasonic diagnostic apparatus that measures a blood flow velocity of a subject using the Doppler method. The pulse Doppler device transmits pulse-modulated ultrasonic waves toward a subject at a predetermined pulse repetition frequency (PRF: Pulse Repetition Frequency). A sample gate is set as an area to be measured, and the pulse Doppler apparatus displays a Doppler waveform (speed vs. time waveform) based on the Doppler shift frequency component of the ultrasonic wave received at a timing corresponding to the sample gate.

  In the pulse Doppler device, the measurable Doppler shift frequency, that is, the measurable speed is limited according to the repetition frequency of the ultrasonic pulse. Increasing the repetition frequency increases the upper limit of the measurable speed, and decreasing the repetition frequency decreases the upper limit of the measurable speed. When the velocity of the measurement target such as the blood flow velocity exceeds the measurable velocity range, a so-called folding phenomenon occurs and a measurement error occurs. Therefore, in principle, blood flow velocity and the like are measured within a range defined by the repetition frequency.

  Patent Documents 1 and 2 below describe pulse Doppler devices. Patent Document 3 describes a beam forming process for ultrasonic waves transmitted and received by an ultrasonic diagnostic apparatus as a process related to the present invention.

Japanese Patent Laid-Open No. 11-169374 JP 02-36852 A JP-A-2015-19862

  In order to increase the upper limit of the measurable speed, an HPRF measurement method in which the repetition frequency is increased is considered. In the HPRF measurement method, the sample gate is set at a position deeper than the reference depth where the ultrasonic pulse reciprocates in one cycle of the repetition cycle (reciprocal of the repetition frequency). Therefore, the previously transmitted ultrasonic pulse is reflected by the sample gate, and the next ultrasonic pulse is transmitted before the observation target ultrasonic wave due to this reflection is received.

  In the HPRF measurement method, when unnecessary ultrasonic waves generated by reflecting some of the subsequent ultrasonic pulses at a position shallower than the reference depth are sufficiently small, or when unnecessary ultrasonic waves are not received by overlapping the observation target ultrasonic wave with the time zone Therefore, sufficient measurement accuracy can be obtained. However, depending on the subject, this condition is not necessarily satisfied, and the measurement accuracy may be reduced.

  An object of the present invention is to improve the accuracy of Doppler measurement when a sample gate is set at a position deeper than a reference depth.

  The present invention includes a transmitter that transmits ultrasonic pulses to a subject at a predetermined repetition frequency from a probe that includes a plurality of vibration elements, and a receiver that receives ultrasonic waves reflected within the subject via the probe. A weighting processing unit that performs weighting processing on each reception signal based on the ultrasonic wave received by each of the vibration elements, a synthesis processing unit that synthesizes each reception signal subjected to the weighting processing, and the synthesis processing unit. A Doppler measurement unit that performs Doppler measurement on the subject based on the generated synthesized signal, and the weighting processing unit weights a reception attenuation point in a reception beam of ultrasonic waves received through the probe Processing is performed on each of the received signals.

  According to the weighting process in the present invention, a reception attenuation point is generated in the reception beam of the ultrasonic wave received through the probe. Therefore, a component based on unnecessary ultrasonic waves generated by reflection at the position of the reception attenuation point is reduced in the reception signal.

  Preferably, the weighting processing unit performs a weighting process for generating a reception focus on the reception beam for each received signal, and determines the position of the reception attenuation point based on the position of the reception focus and the repetition frequency. .

  According to the present invention, the position of the reception attenuation point is determined based on the position of the reception focus and the repetition frequency, and a reception beam having the reception attenuation point at an appropriate position with respect to the position of the reception focus and the repetition frequency is formed. .

  Preferably, the weighting processing unit includes a coefficient operation unit that applies a weighting coefficient to each of the received signals, and each of the weighting coefficients includes a predetermined value of the synthesized signal based on the ultrasound reflected at the reception attenuation point. It is determined based on the condition that it is less than or minimum.

  In the present invention, the weighting coefficient is determined based on the condition that the combined signal based on the ultrasonic wave reflected at the reception attenuation point is less than or equal to the predetermined value, and this weighting coefficient is applied to each received signal. In the process of determining the weighting coefficient, for example, a numerical analysis method such as an MV method (Minimum Variance method), a minimum norm method, a linear prediction method, or a MUSIC method (Multiple Signal Classification method) can be used. In this case, processing by numerical calculation becomes possible.

  Preferably, a delay unit is provided in a signal path from the reception unit to the synthesis processing unit, and forms the reception beam by individually delaying each reception signal.

  In the present invention, it is sufficient if a delay unit is provided in the signal path from the receiving unit to the synthesis processing unit, and there is a degree of freedom in design.

  According to the present invention, it is possible to improve the accuracy of Doppler measurement when the sample gate is set at a position deeper than the reference depth.

It is a figure which shows the structure of a pulse Doppler apparatus. It is a figure which shows notionally a receiving beam, a sample gate, a subgate, a receiving focus, and a receiving attenuation point with a tomographic image. It is a timing chart explaining the fall of measurement accuracy arises in the conventional pulse Doppler apparatus. It is a figure which shows the structure of a phasing weighting part. It is a figure which shows a simulation result. It is a figure which shows a simulation result. It is a figure explaining a multiple gate measuring method. It is a figure which shows the modification of a phasing weighting part.

(1) Configuration of Pulse Doppler Device FIG. 1 shows the configuration of a pulse Doppler device according to an embodiment of the present invention. The pulse Doppler device includes a transmission unit 18, a probe 10, a reception unit 22, a phasing weighting unit 24, a Doppler measurement unit 26, and a display unit 28. The pulse Doppler device transmits pulse-modulated ultrasonic waves from the probe 10 toward the subject 14 at a predetermined repetition frequency (PRF), and receives the ultrasonic waves reflected in the subject 14. The sample gate is set as a measurement target region by a user operation, and the pulse Doppler device generates a Doppler waveform image based on the Doppler shift frequency component of the ultrasonic wave received at a timing corresponding to the sample gate, and displays it on the display unit 28. To do.

  A specific configuration of the pulse Doppler device will be described. When diagnosing the subject 14, the probe 10 is in contact with the surface of the subject 14. The probe 10 includes a plurality of vibration elements 12. The transmission unit 18 outputs a transmission signal to each vibration element 12 of the probe 10 based on the control by the control unit 20. This transmission signal is, for example, a sine wave signal that is turned on / off in response to a pulse signal having a rectangular time waveform, that is, a pulse-modulated electric signal. Each vibration element 12 generates an ultrasonic wave according to the transmission signal, so that the ultrasonic wave is transmitted from the probe 10.

  When transmitting the ultrasonic wave, the transmission unit 18 adjusts the delay time or level of the transmission signal output to each vibration element 12 according to the control by the control unit 20, and forms a transmission beam by the ultrasonic wave transmitted from the probe 10. That is, the control unit 20 forms a transmission beam in the probe 10 by controlling the transmission unit 18.

  The transmission unit 18 may adjust the delay time or level of the transmission signal output to each vibration element 12 according to control by the control unit 20 and adjust the direction or radiation position of the transmission beam. That is, the control unit 20 may adjust the direction or radiation position of the transmission beam formed in the probe 10 by controlling the transmission unit 18.

  When the ultrasonic wave reflected in the subject 14 is received by each vibration element 12 of the probe 10, each vibration element 12 outputs an electrical signal corresponding to the received ultrasonic wave to the receiving unit 22. Under the control of the control unit 20, the reception unit 22 amplifies the reception signal output from each vibration element 12 and outputs a plurality of channels of reception signals corresponding to the plurality of vibration elements 12 to the phasing weighting unit 24.

  The transmission unit 18 outputs a local signal L having the same frequency as the transmission signal to the phasing weighting unit 24. Further, the control unit 20 outputs various information for executing processing on each received signal to the phasing weighting unit 24.

  As will be described later, the phasing weighting unit 24 delays each of the reception signals of a plurality of channels by an appropriate delay time, and further generates a composite signal by applying a weighting coefficient to output to the Doppler measurement unit 26. The synthesized signal is synthesized so that the received signals based on the ultrasonic waves reflected at the reception focal point set on the reception beam 16 are intensified, and the ultrasonic waves reflected at the reception attenuation point set on the reception beam 16 are combined. This is a signal obtained by synthesizing the received signals based on each other so as to weaken each other.

  The Doppler measurement unit 26 performs frequency analysis processing on the synthesized signal, and generates image data representing the Doppler waveform. The Doppler waveform is a time waveform in which time is taken on the horizontal axis and speed, Doppler shift frequency, or values corresponding to these are taken on the vertical axis. The Doppler measurement unit 26 outputs the Doppler waveform image data to the display unit 28. The display unit 28 displays the Doppler waveform based on the Doppler waveform image data. Note that the Doppler measurement unit 26 may generate data representing the Doppler waveform by a numerical value. This numerical data is, for example, data in which speed, Doppler shift frequency, or values corresponding to these are associated with time. The Doppler measurement unit 26 generates image data for displaying the Doppler waveform numerically and outputs the image data to the display unit 28. The display unit 28 displays the Doppler waveform as a numerical value based on the image data.

(2) Processing executed by the phasing weighting unit The technical significance of the processing executed by the phasing weighting unit 24 will be described. FIG. 2 conceptually shows the reception beam 30, the sample gate 32, the sub-gate 34, the reception focal point 36, and the reception attenuation point 38 together with the tomographic image 40. Sample gate 32 is set on the circulator 42 in a position deeper than the reference depth D _0. Reference depth _{D 0} is the distance the ultrasound in 1 repetition period T (= 1 / PRF) reciprocates.

As described above, when the sample gate 32 is set at a position deeper than the reference depth D _{0 and} a moving object such as blood is in the sample gate 32, the ultrasonic pulse transmitted earlier is reflected by the sample gate 32, and this reflection is performed. The next ultrasonic pulse is transmitted before the ultrasonic wave is received by the probe.

The time until the ultrasonic wave transmitted from the probe is reflected and returned to the probe is made to coincide with the time obtained by subtracting the repetition period T from the sample gate depth time (the time for the ultrasonic wave to reciprocate between the probe and the sample gate). A region called a sub-gate is generated at a special position. In another expression, a region called a sub-gate occurs at a position where the depth from the probe is a depth corresponding to the distance from the reference depth D ₀ to the sample gate 32.

  When there is a tissue that reflects ultrasonic waves in the sub-gate 34, the conventional pulse Doppler apparatus has the following problems. That is, an unnecessary ultrasonic wave generated by reflecting a part of a subsequent ultrasonic pulse by the sub-gate 34 is received by overlapping the observation target ultrasonic wave with a time zone, and the unnecessary ultrasonic wave interferes with the observation target ultrasonic wave. There was a problem that the measurement accuracy was lowered.

  FIG. 3 shows a timing chart for explaining that the measurement accuracy is lowered in the conventional pulse Doppler apparatus. FIG. 3A shows an ultrasonic pulse transmitted by the pulse Doppler device. The pulse Doppler device repeatedly transmits ultrasonic pulses at a repetition period T. The sample gate is set at a position deeper than the reference depth. Sample gate time zones S0, S1, S2,... Corresponding to the position of the sample gate are set to a time delayed by the sample gate depth time DPT after the transmission pulse is transmitted. That is, the sample gate time zone S1 is set at the time when the sample gate depth time DPT has elapsed since the transmission pulse P1 was transmitted. Also, the sample gate time zone S2 is set at the time when the sample gate depth time DPT has elapsed since the transmission pulse P2 was transmitted, and the sample gate time at the time when the sample gate depth time DPT has elapsed since the transmission pulse P3 was transmitted. A band S3 is set.

  FIG. 3B shows ultrasonic waves received by a conventional pulse Doppler device. This figure shows a case where a part of a later ultrasonic pulse is reflected by a sub-gate to generate an unnecessary ultrasonic wave and is received by superimposing an ultrasonic wave to be observed and a time zone. FIG. 3C shows the ultrasonic waves to be observed and unnecessary ultrasonic waves separately. The ultrasonic wave to be observed is indicated by a solid line, and the unnecessary ultrasonic wave is indicated by a broken line. This diagram is a conceptual diagram in which the ultrasonic wave to be observed and the unnecessary ultrasonic wave are distinguished for convenience of explanation, and it is difficult to actually distinguish these ultrasonic waves.

  The observation target ultrasonic wave A0 shown in FIG. 3 (c) is a transmission pulse transmitted immediately before the transmission pulse P1 and reflected by the sample gate, and the unnecessary ultrasonic wave B1 is The transmission pulse P1 is reflected by the sub-gate and received. The observation target ultrasonic wave A1 is obtained by reflecting the transmission pulse P1 at the sample gate, and the unnecessary ultrasonic wave B2 is obtained by reflecting the transmission pulse P2 by the sub-gate. The observation target ultrasonic wave A2 is obtained by reflecting the transmission pulse P2 at the sample gate, and the unnecessary ultrasonic wave B3 is obtained by reflecting the transmission pulse P3 by the sub-gate. The observation target ultrasonic wave A3 is received by the transmission pulse P3 reflected by the sample gate, and the unnecessary ultrasonic wave B4 is received by the transmission pulse P4 reflected by the sub-gate.

  The reception ultrasonic wave R0 shown in FIG. 3B is obtained by superimposing the observation target ultrasonic wave A0 and the unnecessary ultrasonic wave B1. The reception ultrasonic wave R1 is obtained by superimposing the observation target ultrasonic wave A1 and the unnecessary ultrasonic wave B2. The reception ultrasonic wave R2 is obtained by superimposing the observation target ultrasonic wave A2 and the unnecessary ultrasonic wave B3. The reception ultrasonic wave R3 is obtained by superimposing the observation target ultrasonic wave A3 and the unnecessary ultrasonic wave B4.

  As described above, in the conventional pulse Doppler apparatus, unnecessary ultrasonic waves are received in addition to the observation target ultrasonic waves in the sample gate time zone, and there is a problem that measurement accuracy is lowered due to the influence of the unnecessary ultrasonic waves.

  Therefore, the pulse Doppler device according to the present embodiment forms an ultrasonic beam that attenuates unnecessary ultrasonic waves that are reflected by the sub-gate while receiving the observation target ultrasonic waves that are reflected by the sample gate. That is, an ultrasonic beam that attenuates the received signal component based on the unnecessary ultrasonic waves B1, B2, B3,... Shown in FIG.

  In other words, the reception focus of the reception beam is set in the sample gate and the reception attenuation point of the reception beam is set in the sub-gate by the processing executed by the phasing weighting unit 24 in FIG.

  The phasing weighting unit 24 delays each received signal individually, performs quadrature detection, applies a weighting coefficient to the detection signal obtained by quadrature detection, and adds and sums it to output a combined signal. . The combined signal is combined so that the detection signals based on the ultrasonic waves reflected at the reception focal point set on the reception beam are intensified, and the detection is based on the ultrasonic waves reflected at the reception attenuation point set on the reception beam. The signal is synthesized so that the signals are weakened. The components based on the unnecessary ultrasonic waves B1, B2, B3,... Shown in FIG. The reception beam and the reception focus are formed by delay processing for each reception signal. The reception attenuation point on the reception beam is formed by weighting processing for each received signal (multiplication of a complex conjugate value of a weighting coefficient for each detected signal).

(3) Configuration of Phase Delay Weighting Unit FIG. 4 shows the configuration of the phase delay weighting unit 24. The phasing weighting unit 24 includes delay units 44-1 to 44-n, quadrature detection units 46-1 to 46-n, weighting coefficient determination unit 48, complex multiplication units 50-1 to 50-n, and synthesis processing unit 52. Is provided. Of the quadrature detection units 46-1 to 46-n, the part that performs digital signal processing, the weighting coefficient determination unit 48, the complex multiplication units 50-1 to 50-n, and the synthesis processing unit 52 are configured by, for example, a processor. . These components may be configured by a program executed by a processor, or may be configured individually by an electronic circuit that is hardware.

The delay unit 44-1 to 44-n, the received signal _r 1 ~r _n of n channels are inputted. Delay unit 44-p (p = 1~n), only the delay time tau _p supplied from the control unit delays the received signal _{r p,} and outputs the quadrature detection section 46-p.

Quadrature detection section 46-p, the transmission is performed with a quadrature detection for the received signal r _p by the local signal L having ultrasonic and same frequency, the level in the time period outside the sample gate hours forcibly 0 In-phase component signal I _p and quadrature component signal Q _p are generated. Then, the complex detection signal v _p = I _p + j · Q _p is output to the complex multiplier 50-p. The in-phase component signal I _p indicates a component having the same phase as the local signal L, and the quadrature component signal Q _p indicates a component whose phase difference from the local signal L is 90 °. j is an imaginary unit, and the in-phase component signal I _p and the quadrature component signal Q _p are Doppler shift frequency components of ultrasonic waves received by the probe. That is, the frequencies of the in-phase component signal I _p and the quadrature component signal Q _p coincide with the Doppler shift frequency of the ultrasonic wave received by the probe.

  The weighting coefficient determination unit 48 and the complex multiplication units 50-1 to 50-n have a function as a weighting processing unit that performs weighting processing on each received signal.

The weighting coefficient determination unit 48 determines weighting coefficients W _{1 to} W _n by a coefficient determination process described later, and outputs them to the complex multiplication units 50-1 to 50 -n, respectively.

  The complex multipliers 50-1 to 50-n function as a coefficient operation unit that applies a weighting coefficient to each detected signal (each received signal). Here, to apply a weighting coefficient means to change the value of a signal to be processed based on the weighting coefficient, and in this embodiment, to multiply the detection signal by a conjugate complex number of the weighting coefficient.

Complex multiplier 50-p (p = 1~n) outputs multiplied by the detection signal _{v p} conjugate weighting factor is a complex conjugate of the weighting factor _{W p} in _W ^{p *} to the synthesis processing unit 52. The synthesis processing unit 52 adds and sums W ₁ ^* · v _{1 to} W _n ^* · v _n to generate a synthesized signal, and outputs the synthesized signal to the Doppler measurement unit 26 in FIG. This composite signal is a signal based on an ultrasonic wave received according to a reception beam in which a reception focus is set in the sample gate and a reception attenuation point is set in the sub-gate. In the synthesized signal, unnecessary ultrasonic waves reflected at the reception attenuation point are suppressed, so that the measurement error included in the Doppler waveform generated by the synthesized signal is reduced.

(4) Coefficient Determination Process The coefficient determination process executed by the weighting coefficient determination unit 48 will be described. The coefficient determination process according to the present embodiment is a process based on the MV method (Minimum Variance method). The weighting coefficient to be calculated is represented by a column vector W like (Equation 1). The superscript T represents the transpose of the vector.

  The filter weighting vector Wχ that sets the reception focus in the sample gate and sets the reception attenuation point in the sub-gate is expressed by (Equation 4) under the condition that (Equation 2) and (Equation 3) hold. Is obtained by searching for a column vector W having an evaluation value P (W) of less than a predetermined value or a minimum value. Superscript H indicates a conjugate transpose matrix.

The column vector a included in (Equation 2) is a reference vector represented by (Equation 3). Reference vector a corresponds to the column vector a detection signal v ₁ to v _n components propagation time from the reception focal point aligned by each delay unit. (Equation 2) has the significance that the weighting coefficient vector W maintains the value of the combined signal with respect to the detection signal arriving from the reception focal point.

  The matrix R included in (Expression 4) is obtained by (Expression 5) and (Expression 6).

Here, u _p corresponds to the ultrasonic wave reflected by the reception attenuation point set in the sub-gate and received by the p-th vibration element. T included in (Expression 6) represents time, and f represents the frequency of ultrasonic waves. t _p ^att is the time for the ultrasonic wave to propagate the distance from the reception attenuation point to the p-th vibration element. t _p ^f is a time during which the ultrasonic wave propagates a distance from the reception focal point to the p-th vibration element. Δt is the time for the ultrasonic wave to propagate through the distance between the reception attenuation point and the reception focal point.

  Of the previously transmitted ultrasound pulse, the ultrasound reflected at the reception focal point and returned to the probe, and the next transmitted ultrasound pulse reflected at the reception attenuation point and returned to the probe is reflected by the probe. Under the condition that they are received at the same time, the ultrasonic wave reflected at the reception focal point is expressed as (Equation 7).

That is, (Equation 6) is received when the ultrasonic wave reflected by the reception focal point is received by the p-th vibration element and at the same time the ultrasonic wave reflected by the reception attenuation point is received by the p-th vibration element. It shows that the ultrasonic wave reflected at the attenuation point is delayed in phase by 2πf (t _p ^att + Δt−t _p ^f ) with respect to the ultrasonic wave reflected at the reception focal point.

Here, as shown in FIG. 1, the arrangement direction of the plurality of vibration elements is the x-axis direction, and the depth direction of the subject 14 is the y-axis positive direction. Further, the x coordinate of the end point of the reception beam 16 is set to 0. The angle θ formed by the y-axis positive direction indicating the depth direction of the subject 14 and the reception beam 16, the x coordinate x _p of the p-th vibration element, the position r _f of the reception focus in the reception beam direction (set to the sample gate) And the position of the reception attenuation point r _att (the position of the reception attenuation point set in the sub-gate) in the direction of the reception beam, t _p ^att and t _p ^f 8) and (Equation 9). Here, c is the propagation speed of the ultrasonic wave.

  The time Δt during which the ultrasonic wave propagates through the distance from the reception attenuation point to the reception focal point is expressed by (Equation 10).

Further, since the reception attenuation point is set to the sub-gate, the position of the reception attenuation point is expressed by (Equation 11). Incidentally, c / (half PRF) included in equation (11) is equal to the reference depth _{D 0.}

Therefore, first, by giving the reception focus position r _f , the ultrasonic wave propagation velocity c, and the repetition frequency PRF that are known to (Equation 11), the position r _{att of the} reception attenuation point set in the sub-gate is obtained. It is done. Next, the position r _{f of the} reception focus, the position r _att of the reception attenuation point and the ultrasonic wave propagation velocity c which are known from (Equation 11) are given to (Equation 10) to reach the reception focus from the reception attenuation point. The time Δt during which the ultrasonic wave propagates the distance up to is obtained. Then, by giving the position r _att of the reception attenuation point, the x-coordinate x _p of the p-th vibration element, the angle θ formed by the depth direction and the reception beam, and the ultrasonic wave propagation velocity c to (Equation 8), A time t _p ^att for the ultrasonic wave to propagate through the distance from the reception attenuation point to the p-th vibration element is obtained. Furthermore, the reception focus position r _f , the x coordinate x _p of the p-th vibration element, the angle θ formed by the depth direction and the reception beam, and the ultrasonic wave propagation velocity c are given to (Equation 9), and reception is performed. the distance from the focal point up to the p-th transducer elements time t _p ^f the ultrasonic waves are propagated is obtained.

Thus, the position _{r f} of the reception focus, repetition frequency PRF, 1 th ~n th x-coordinate _x 1 ~x _n of the vibration elements, the angle between the depth direction with receive beam 16 theta, and ultrasound if the propagation velocity c is known, based on these known values unwanted ultrasonic delay time ^{_{(t p att + Δt-t}} p f) is obtained, and further is required _{u p} represented by equation (6) . By obtaining u _p for each of p = 1 to n, an evaluation value P (W) is obtained for a weighted column vector W based on (Equation 5) and (Equation 4). The filter weighting vector Wχ is obtained by changing each component of the weighting column vector W and searching for the weighting column vector W such that each evaluation value P (W) is less than a predetermined value or the minimum value.

(5) Coefficient Determination Process Performed by Weighting Coefficient Determination Unit The coefficient determination process will be described from the viewpoint of the process performed by the weighting coefficient determination unit 48. The weighting factor determination unit 48, a position r _f of the receive focal point based on the user's _operation, repetition frequency PRF, 1 th ~n th x-coordinate x ₁ ~x n of the vibration _elements, and the depth direction and the reception beam And the ultrasonic wave propagation velocity c are input.

Weighting coefficient determining section 48, based on the equation (6) and (8) through (11), obtains the ultrasonic _{u p} for each p = 1 to n, furthermore, is represented by equation (5) A correlation matrix R is obtained. The weighting coefficient determination unit 48 is a column vector that sets the evaluation value P (W) represented by (Equation 4) to be less than a predetermined value or a minimum value under the condition that (Equation 2) and (Equation 3) hold. By searching W, a filter weight vector Wχ is obtained.

In the coefficient determination process, it is not necessary to execute an adaptive process using the detection signals v _{1 to} v _n, and thus the filter weighting vector Wχ is quickly obtained.

(6) Simulation Results FIG. 5 shows simulation results for the pulse Doppler device according to the present embodiment. In this simulation result, the reception focal point is set at a position with a depth of 80 mm, and the reception attenuation point is set at a position with a depth of 40 mm. FIG. 5A shows the reception level obtained in the depth direction of the reception beam. The horizontal axis indicates the depth in the direction of the azimuth angle θ = 0 °, and the vertical axis indicates the magnitude of the combined signal when the point wave source is arranged at each depth position. FIG. 5B shows the reception level obtained in the azimuth direction of the reception beam. The horizontal axis indicates the azimuth angle for the depth y = 80 mm, and the vertical axis indicates the magnitude of the combined signal when the point wave source is arranged in each azimuth having a depth of 80 mm.

  FIG. 6 shows a simulation result of the pulse Doppler device in the prior art. This simulation result corresponds to the case where the filter weighting vector W is a Hamming window in the pulse Doppler device according to the present embodiment. FIG. 6A shows the reception level obtained in the depth direction of the reception beam. The horizontal axis indicates the depth in the direction of the azimuth angle θ = 0 °, and the vertical axis indicates the magnitude of the combined signal when the point wave source is arranged at each depth position. FIG. 6B shows the reception level obtained in the azimuth direction of the reception beam. The horizontal axis indicates the azimuth angle for the depth y = 80 mm, and the vertical axis indicates the magnitude of the combined signal when the point wave source is arranged in each azimuth having a depth of 80 mm.

  As apparent from FIGS. 5 and 6, in the pulse Doppler device according to the present embodiment, the reception level of the ultrasonic wave reflected at the reception attenuation point is smaller than the reception level of the ultrasonic wave reflected at the reception focal point. Therefore, by setting the reception focus on the sample gate and setting the reception attenuation point on the sub-gate, the influence of ultrasonic waves reflected by the sub-gate is suppressed, and the measurement accuracy is improved.

(7) Multiple gate measurement method The pulse Doppler device according to the embodiment of the present invention directs a transmission beam and a reception beam in each of a plurality of directions in a time division manner, and a moving object such as blood for a sample gate corresponding to each transmission / reception beam. A multi-gate measurement method may be performed to measure. The multiple gate measurement method is described in Patent Document 2, for example. In this method, since the speed of the moving object is measured with respect to a plurality of sample gates in a time division manner, the speed of the moving object at a plurality of locations is quickly measured.

  FIG. 7 shows transmission beams 54-1 and 54-2 when the direction of the transmission beam is switched between the direction of azimuth angle -θ1 and the direction of azimuth angle θ2 at every switching time Ta. The pulse Doppler device transmits an ultrasonic pulse to the transmission beam 54-2 when the switching time Ta has elapsed after transmitting an ultrasonic pulse to the transmission beam 54-1, and the switching time Ta has elapsed. At times, an ultrasonic pulse is transmitted to the transmission beam 54-1, and an ultrasonic pulse is transmitted to the transmission beam 54-2 when the switching time Ta has elapsed.

  In this case, the reference depth Da is a distance Da = c · Ta / 2 at which the ultrasonic pulse reciprocates during the switching time Ta. If the sample gate 56-1 for the transmit beam 54-1 and the sample gate 56-2 corresponding to the transmit beam 54-2 are at a position deeper than the reference depth Da, a sub-gate is generated for each transmit / receive beam.

  In general, since the directivity of the transmission beam and the reception beam is wide, ultrasonic waves are transmitted and received in directions where the directivity of the transmission beam and the reception beam is not maximum. Therefore, unnecessary ultrasonic waves may be received when the ultrasonic waves are reflected by the sub-gate of each reception beam.

  Therefore, a measurement error is reduced by providing a reception attenuation point in the sub-gate for each reception beam and suppressing unnecessary ultrasonic waves received by the pulse Doppler apparatus. In FIG. 7, the sample gate 56-1 and the sub-gate 58-1 corresponding to the transmission beam 54-1, respectively, are provided with a reception focal point and a reception attenuation point, and the sample gate 56-2 and the sub-gate 58 corresponding to the transmission beam. -2 shows an example in which a reception focal point and a reception attenuation point are provided. Since the positions of the reception focus and the reception attenuation point are different for each transmission / reception beam, different filter weighting vectors Wχ are used for each transmission / reception beam.

(8) Modified Example (8-1) Subgate at a Position Deeper than the Sample Gate In the above, an example in which a reception attenuation point is set at a subgate generated at a position shallower than the sample gate has been described. The sub gate also occurs at a position deeper than the sample gate. In other words, the sub-gate is generated at a position symmetrical to the sub-gate located at a position shallower than the sample gate with the sample gate as the center. If there is a tissue that reflects ultrasonic waves at a subgate deeper than the sample gate, unwanted ultrasonic waves generated by the reflection of the preceding ultrasonic pulse by the subgate are generated by the subsequent ultrasonic pulse being reflected by the sample gate. It is received by superimposing the observation target ultrasonic wave and the time zone. Therefore, a reception attenuation point may be provided in a sub-gate located deeper than the sample gate. The position of the reception attenuation point set in the sub-gate located deeper than the sample gate is obtained by (Equation 12).

When providing a receive attenuation point sub-gate in a position deeper than the sample gate, substituting receive attenuation points set in the sub-gate in a position deeper than the sample gate per a u _p obtained according to equation (6) to (5) Then, the evaluation value P (W) may be obtained.

Also, in the case of providing both sub-gate to receive attenuation point of the position and the depth position shallower than the sample gate, and u _ps obtained reception decay point is set to a sub-gate at a position shallower than the sample gate per according (6) , by substituting receive attenuation points set in the sub-gate in a position deeper than the sample gate per a u _{p =} u ps ₊ u _pd obtained by adding the u _pd obtained according (6) to (5), the evaluation value What is necessary is just to obtain P (W).

(8-2) Other Methods for Obtaining Filter Weight Vector Wχ In the above, the coefficient determination process based on the MV method has been described. There are various methods such as a minimum norm method, a linear prediction method, and a MUSIC method (Multiple Signal Classification method) for obtaining a weighting coefficient such that a reception focus and a reception attenuation point are provided on a reception beam.

(8-3) Modified example of phasing weighting unit The delay units 44-1 to 44-n are provided at any position in the signal path from the reception unit 22 to the synthesis processing unit 52, so that the reception beam and the reception are received. A focal point can be formed. FIG. 8 shows a modification in which the position of each delay unit is changed with respect to the phasing weighting unit 24 shown in FIG. In the phasing weighting unit 24 shown in FIG. 4, a delay unit is provided in front of each quadrature detection unit, whereas in the phasing weighting unit 60 shown in FIG. 8, each complex multiplication unit is provided. A delay unit is provided at the subsequent stage.

  In the phasing weighting unit 60, the weighting coefficient determination unit 48 uses the reference vector b expressed by (Equation 13) instead of the reference vector a expressed by (Equation 2) and (Equation 3).

The reference vector b means that a vector in which the phase of each component is advanced with respect to each component of the reference vector a is based on the fact that the delay processing is not performed in each delay unit. By using the reference vector b, the value of the synthesized signal is maintained with respect to the detection signal arriving from the reception focus. Further, t _p ^f does not depend on (9), the coefficient determining process is performed as a constant value 0.

10 probe, 12 vibrating element, 14 subject, 16, 30 reception beam, 18 transmission unit, 20 control unit, 22 reception unit, 24, 60 phasing weighting unit, 26 Doppler measurement unit, 28 display unit, 32, 56- 1,56-2 Sample gate, 34,58-1,58-2 Sub-gate, 36 reception focus, 38 reception attenuation point, 40 tomographic image, 42 circulator, 44-1 to 44-n delay unit, 46-1 46-n orthogonal detection unit, 48 weighting coefficient determination unit, 50-1 to 50-n complex multiplication unit, 52 combining processing unit, 54-1, 54-2 transmission beam.

Claims (4)

A transmitter that transmits ultrasonic pulses at a predetermined repetition frequency from a probe including a plurality of vibration elements to a subject;
A receiving unit that receives the ultrasonic waves reflected in the subject through the probe;
A weighting processing unit for weighting each received signal based on the ultrasonic wave received by each of the vibration elements;
A synthesis processing unit that synthesizes each of the received signals subjected to the weighting process;
A Doppler measurement unit that performs Doppler measurement on the subject based on the synthesized signal generated by the synthesis processing unit,
The weighting processing unit
An ultrasonic diagnostic apparatus, wherein weighting processing for generating a reception attenuation point in a reception beam of ultrasonic waves received through the probe is performed on each reception signal. The ultrasonic diagnostic apparatus according to claim 1,
The weighting processing unit
Performing a weighting process for generating a reception focal point on the reception beam for each reception signal;
An ultrasonic diagnostic apparatus characterized in that the position of the reception attenuation point is determined based on the position of the reception focus and the repetition frequency. The ultrasonic diagnostic apparatus according to claim 1 or 2,
The weighting processing unit
A coefficient operation unit for applying a weighting coefficient to each received signal;
Each said weighting factor is
An ultrasonic diagnostic apparatus, characterized in that the ultrasonic diagnostic apparatus is determined based on a condition that the combined signal based on the ultrasonic wave reflected at the reception attenuation point is less than or equal to a predetermined value. The ultrasonic diagnostic apparatus according to any one of claims 1 to 3,
An ultrasonic diagnostic apparatus, comprising: a delay unit that is provided in a signal path from the reception unit to the synthesis processing unit and that forms the reception beam by individually delaying each reception signal.

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