JP2000254122A - Method and device for forming reception signal and method and device for picking-up ultrasonic wave image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use bit stream signals which are obtained by means of a simple way by converting the reception signals of an ultrasonic transducer into the bit stream signals by means of a quantizing method except ΔΣ modulation, imparting a previously fixed delay time to add them and filtering the added signals. SOLUTION: Bit stream converting circuits 611-615 provided by a wave reception beam former 610 are arranged at every ultrasonic transducer of a reception aperture and convert the respectively received echo signals into the bit stream signals. The output signals of the circuits 611-615 are respectively inputted to a shift register and delays corresponding to the direction of echo reception sound rays and to the focus distances of echo reception are imparted to the inputted signals. The output signal of the shift register is inputted to an adding circuit 630 and the circuit 630 adds the whole input signals. The output signal of the circuit 630 is filtered by a deformation filter 640 and the echo reception signal for the portion of one sound ray is created.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for forming a received signal and an ultrasonic imaging method and apparatus, and more particularly, to an ultrasonic transducer array (transducc).
and a plurality of signals received by the ER array are converted into bit stream signals, and the converted signals are used to perform reception beamforming, and a reception signal forming method and apparatus, and the like. The present invention relates to an ultrasonic imaging method and apparatus using a reception signal subjected to reception beamforming.

[0002]

2. Description of the Related Art As one method of digitally performing ultrasonic receiving beam forming,
There is a method of performing reception beamforming using a signal converted into a bit stream signal by ΔΣ modulation. In this method, as described in, for example, JP-A-3-114449, a plurality of signals received by an ultrasonic transducer array are ΔΣ-modulated by a plurality of ΔΣ modulators, and a 1-bit quantized signal (bit stream signal) is obtained. )age,
Each of the plurality of signals after Δ を modulation is time-shifted (shi
ft), and the result is added, and the addition result is filtered by a decimation filter (decimation filter).

The output signal of the decimation filter forms a received signal for one sound ray. The azimuth and focus of the received beam are determined by the amount of time shift applied to each of the plurality of signals. By changing the time shift amount, the azimuth of the reception beam is changed, and scanning in the order of sound rays is performed.

[0004]

In the above-mentioned ΔΣ modulator used for the reception beam forming, a loop filter (loop filter) is required to obtain a desired operation characteristic.
There is a problem that many restrictions are imposed on the design of the device.
Further, a ΔΣ modulator designed under such a large number of restrictions has a large number of parts, and this is used for each of about 64 to 128 ultrasonic transducers constituting an ultrasonic transducer array. Has a problem that the number of parts is enormously increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to realize a reception signal forming method and apparatus and an ultrasonic imaging method and apparatus using a bit stream signal obtained by a simple method. It is to be.

It is another object of the present invention to realize a method and apparatus for forming a received signal using a stable bit stream signal and an ultrasonic imaging method and apparatus.

[0007]

Means for Solving the Problems (1) A first aspect of the present invention for solving the above-mentioned problems is that a plurality of ultrasonic transducers constituting an array receive ultrasonic waves, and the plurality of ultrasonic transducers receive the ultrasonic waves. Are converted into bit stream signals by a quantization method other than ΔΣ modulation, and a predetermined delay time is added to the plurality of converted signals,
A method of forming a received signal, comprising adding a plurality of signals to which the delay time has been added, and filtering the added signal.

(2) In the second invention for solving the above-mentioned problem, a dither signal is added to each of the plurality of signals before being converted into the bit stream signal. This is a signal forming method.

(3) A third aspect of the present invention for solving the above-mentioned problems is a plurality of ultrasonic transducers that form an array and receive ultrasonic waves, and a plurality of signals received by the plural ultrasonic transducers are ΔΣ modulated. Signal conversion means for converting to a bit stream signal by a quantization method other than
The system includes: a delay providing unit that adds a predetermined delay time to the plurality of converted signals; an adding unit that adds the plurality of signals to which the delay time is added; and a filtering unit that filters the added signal. A reception signal forming apparatus characterized in that:

(4) A fourth aspect of the present invention for solving the above-mentioned problem is characterized by comprising dithering means for applying a dither signal to each of the plurality of signals before being converted into the bit stream signal. 3) A reception signal forming apparatus according to 3).

(5) According to a fifth aspect of the present invention, an ultrasonic wave is transmitted, an echo of the ultrasonic wave is received, and a received signal is formed along a predetermined sound ray based on the received signal. An ultrasonic imaging method for generating an image based on the formed reception signal, wherein the reception signal is formed by the method according to (1) or (2).

(6) According to a sixth aspect of the present invention, there is provided an ultrasonic transmitting means for transmitting an ultrasonic wave, a receiving signal forming means for forming a received signal relating to the transmitted ultrasonic wave, An ultrasonic imaging apparatus having image generation means for generating an image based on a signal, wherein the reception signal forming apparatus according to (3) or (4) is used as the reception signal forming means. It is an ultrasonic imaging device.

[0013] In any one of the first to sixth inventions, it is preferable that the bit stream signal is a clocked signal from the viewpoint of appropriately forming a received signal.

In the second invention or the fourth invention, it is preferable that the dither signal is a blue dither signal in order to obtain a bit stream signal having excellent stability. (Operation) In the present invention, the signal conversion is simplified by converting the signal received by the ultrasonic transducer into a bit stream signal by a method other than ΔΣ modulation. Also, by adding a dither signal to the signal before conversion,
Stabilizes signal conversion.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the ultrasonic imaging apparatus. This apparatus is an example of an embodiment of the ultrasonic imaging apparatus of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention. An example of an embodiment of the method of the present invention is shown by the operation of the present apparatus.

The configuration of the present apparatus will be described. As shown in the figure, the present apparatus has an ultrasonic probe (probe) 2. The ultrasonic probe 2 is used for transmitting and receiving ultrasonic waves while being in contact with the subject 100. The ultrasonic probe 2 has an ultrasonic transducer array (not shown). The ultrasonic transducer array is composed of a plurality of ultrasonic transducers. Each ultrasonic transducer is made of a piezoelectric material such as PZT (lead zirconate titanate (Zr) (Pb)) ceramics.

The ultrasonic probe 2 is connected to a transmitting / receiving unit 6. The transmitting / receiving unit 6 drives the ultrasonic transducer array of the ultrasonic probe 2 to transmit an ultrasonic beam,
Further, the ultrasonic transducer array receives an echo received by the ultrasonic transducer array. FIG. 2 is a block diagram of the transmitting / receiving unit 6.
Shown in As shown in the figure, the transmission / reception unit 6 has a signal generation circuit 602. The signal generation circuit 602 outputs a pulse (pu)
1se) A signal is repeatedly generated at a predetermined cycle and input to the transmission beamformer 606. Transmission beamformer 60
6 generates a transmission beamforming signal based on the input signal. The transmission beam forming signal is a plurality of drive signals applied to a plurality of ultrasound transducers constituting a transmission aperture in the ultrasound transducer array, and each drive signal has a delay time corresponding to the azimuth and focus of the ultrasound beam. Granted. Hereinafter, the transmission aperture is referred to as a transmission aperture.

The transmission beam forming signal is supplied to a plurality of ultrasonic transducers constituting a transmission aperture through a transmission / reception switching circuit 608. Each of the plurality of ultrasonic transducers to which the drive signal is applied generates an ultrasonic wave, and a transmitted ultrasonic beam in a predetermined direction is formed by wavefront synthesis of the ultrasonic waves. The transmitted ultrasonic beam converges on a focal point set at a predetermined distance. Signal generation circuit 6
02, transmission beamformer 606, transmission / reception switching circuit 608
The portion including the ultrasonic probe 2 is an example of the embodiment of the ultrasonic transmitting means in the present invention.

The echo of the transmitted ultrasonic wave is transmitted to the ultrasonic probe 2.
Are received by a plurality of ultrasonic transducers constituting the receiving aperture of the second. Hereinafter, the reception aperture is referred to as a reception aperture. A plurality of echo reception signals received by the plurality of ultrasonic transducers are transmitted and received by a transmission / reception switching circuit 608.
Is input to the receiving beamformer 610 through The reception beamformer 610 adds a delay corresponding to the azimuth of the echo reception sound ray and the focal length of the echo reception to each of the echo reception signals and adds them, thereby obtaining an echo reception signal matching the predetermined sound ray and focus. Form.

The portion including the ultrasonic probe 2, the transmission / reception switching circuit 608, and the reception beam former 610 is an example of the embodiment of the reception signal forming apparatus of the present invention. The configuration of this portion shows an example of an embodiment relating to the device of the present invention. The operation of this part shows an example of an embodiment relating to the method of the present invention. Ultrasonic probe 2, transmission / reception switching circuit 608, and reception beam former 61
The portion consisting of zero is also an example of the embodiment of the received signal forming means in the present invention. Receive beamformer 6
10 will be described later.

The transmission beam former 606 performs sound ray sequential scanning by sequentially switching the direction of the transmission ultrasonic beam. The receiving beamformer 610 sequentially scans the received sound ray by sequentially switching the direction of the received sound ray. Thereby, the transmission / reception unit 6 performs a scan as shown in FIG. 3, for example. That is, the ultrasonic beam 202 extending in the z direction from the radiation point 200 divides the fan-shaped two-dimensional region 206 by θ.
Scan in the direction, so-called sector scan (sector).
scan).

When the transmitting and receiving apertures are formed by using a part of the ultrasonic transducer array, the apertures are sequentially moved along the array to perform scanning as shown in FIG. 4, for example. Can be.
That is, as the ultrasonic beam 202 emitted from the radiation point 200 in the z direction moves on the linear trajectory 204, the rectangular two-dimensional area 206 is scanned in the x direction, and a so-called linear scan is performed. Will be

The ultrasonic transducer array is
A so-called convex array (convex array) formed along an arc extending in the ultrasonic wave transmission direction.
In the case of y), the radiation point 200 of the ultrasonic beam 202 moves on an arc-shaped trajectory 204 as shown in FIG. 5, for example, as shown in FIG. Is scanned in the θ direction, so that a so-called convex scan can be performed.

The transmitting / receiving unit 6 includes a data (data) processing unit 8
It is connected to the. In the data processing unit 8, the echo reception signal from the transmission / reception unit 6 is converted into digital data (digital
ldata). The data processing unit 8 processes the input echo data to generate an image. The data processing unit 8 is an example of an embodiment of an image generating unit according to the present invention.

As shown in FIG. 6, the data processing section 8 includes a data processor (processor) 80, an echo memory (echo memory) 82, a data memory 84, and an image memory 86. These are connected by a bus (bus) 88. Transceiver 6
Is input to the echo memory 82. The data processor 80 generates an image based on the echo data.

A display unit 10 is connected to the data processing unit 8. The display unit 10 includes, for example, a graphic display, and the like.
A visible image is displayed based on the image data input from the image memory 86 of the data processing unit 8.

The transmission / reception unit 6, data processing unit 8 and display unit 10 are connected to a control unit 12. Control unit 12
Supplies a control signal to each of these sections to control the operation thereof. Further, a state notification signal, a response signal, and the like are transmitted from the controlled units to the control unit 12. Ultrasonic imaging is performed under the control of the control unit 12.

An operation unit 14 is connected to the control unit 12. The operation unit 14 is operated by an operator, and the control unit 12
A desired command or information is input to the device. The operation unit 14 includes, for example, an operation panel (panel) including a keyboard and other operation tools.

FIG. 7 is a block diagram showing an example of the receiving beam former 610. As shown in the figure, the reception beamformer 610 includes bit stream conversion circuits 611 to 61.
5 Bit stream conversion circuits 611 to 615
Is an example of an embodiment of a signal conversion unit according to the present invention. The bit stream conversion circuits 611 to 615 are provided for each ultrasonic transducer of the reception aperture. Here, for convenience of explanation, an example in which the receiving aperture is constituted by five ultrasonic transducers is shown. However, in an actual apparatus, it is usual to constitute about 64 to 128 ultrasonic transducers. The bit stream conversion circuits 611 to 615 convert echo signals received by the respective ultrasonic transducers into bit stream signals. The bit stream conversion circuits 611 to 615 will be described later.

Bit stream conversion circuits 611 to 615
Are input to the shift registers 651 to 655, respectively. The shift registers 651 to 655 give the input signal a delay corresponding to the azimuth of the echo reception sound ray and the focal length of the echo reception. Shift register 651-
Reference numeral 655 is an example of an embodiment of a delay time providing unit according to the present invention. Adjustment of the delay time is performed by the shift register 65.
This is performed by switching the output extraction digits in 1 to 655.

The output signals of the shift registers 651 to 655 are input to the adding circuit 630. The addition circuit 630 is an example of an embodiment of the addition means in the present invention. The adder circuit 630 adds all the input signals. The addition circuit 630 is constituted by, for example, a digital addition circuit adapted to the bit stream signal. The output signal of the adding circuit 630 is filtered by the decimation filter 640 to form an echo reception signal for one sound ray.

The decimation filter 640 is an example of the embodiment of the filtering means in the present invention. As the decimation filter 640, a digital decimation filter or an analog (anal)
og) decimation filter is used. When a digital decimation filter is used, an echo reception signal is obtained as digital data. When an analog decimation filter is used, an echo reception signal is obtained as an analog signal.

FIG. 8 shows a bit stream conversion circuit 61i.
FIG. 2 shows a block diagram of an example of (i: 1 to 5). As shown in the figure, the bit stream conversion circuit 61i is composed of a comparator 11i. The input signal ei to be converted is input to one input terminal of the comparator 11i, and the reference signal ref having a constant period is input to the other input terminal. The reference signal ref is, for example, a sawtooth signal, and its amplitude is set to be larger than the maximum amplitude of the input signal ei, and the frequency is set to be several times higher than the frequency of the input signal ei.

The comparator 11i has a logical value of 1 or 0 according to the magnitude of the input signal ei with respect to the reference signal ref.
, Ie, a bit stream signal. Bit stream signal eo
Is proportional to the input signal ei. That is, the input signal ei is converted into a pulse width signal. When the comparator 11i is a single-input type, as shown in FIG. 9, a signal obtained by adding the input signal ei and the reference signal ref by the adder 12i is input.

The pulse width modulation signal can be given a time shift by a shift register, and can be returned to the original signal by a decimation filter. Therefore, the processing performed on the ΔΣ modulated signal can be similarly performed on the pulse width modulated signal, and beamforming can be performed.

The pulse width conversion circuit may have a configuration as shown in FIG. That is, the OP amplifier (op
A feedback circuit including a resistor 14i and a capacitor 15i is provided in the
The input signal ei is input to the non-inverting input terminal, and the clock signal CLK is input to the inverting input terminal through the capacitor 16i. With such a circuit, the input signal ei is converted into a pulse width signal whose cycle is defined by the clock signal CLK. The frequency of the clock signal CLK is set to be several times higher than the frequency of the input signal ei.

The pulse width conversion circuit may have a configuration as shown in FIG. That is, a feedback circuit including the resistor 18i and the capacitor 19i and a feedback circuit including the resistor 21i are provided in the OP amplifier 17i, and the input signal ei is input to the non-inverting input terminal through the resistor 22i. With such a circuit, the input signal ei is connected to the resistor 18i
Is converted into a pulse width signal whose period is determined by the time constant of the feedback circuit composed of

The input signal ei may be input to the inverting input terminal through the resistor 19i 'as shown in FIG. In that case, the other end of the resistor 22i connected to the non-inverting input terminal is connected to a common.

The pulse width conversion circuit may have a configuration as shown in FIG. That is, a feedback circuit including resistors 24i and 25i, a capacitor 26i and diodes 27i and 28i is provided in the OP amplifier 23i.
The input signal ei is input to the non-inverting input terminal. With such a circuit, the input signal ei is converted into a pulse width signal whose period is determined by the time constant of the feedback circuit including the resistors 24i and 25i and the capacitor 26i. Further, in this circuit, a dither signal due to thermal noise generated by the diodes 27i and 28i is added, so that the input signal e
It is possible to convert i to near 0 level with high accuracy, and to prevent abnormal oscillation of the circuit.

In this circuit, for example, as shown in FIG.
Type flip flop (D-type flip-
flop) circuit 29i and the clock signal CL
By setting the frequency fs of K to several tens to one hundred times the frequency of the input signal ei, it is possible to obtain a bit stream signal that is oversampled or clocked by a high-speed clock signal.

Such clocking is preferable in that a bit stream signal with a fine time resolution is obtained and the delay is precisely given by the shift register. Further, it is preferable in that the filtering by the decimation filter is performed with high accuracy. It is needless to say that a clocking circuit using a similar D-type flip-flop circuit may be provided in the circuits shown in FIGS.

As shown in FIG. 15, for example, as shown in FIG. 15, the dither signal is converted from the signal of the dither signal source 31i to the OP amplifier 2 by using the noise generated by the diode provided in the feedback circuit.
3i may be input to the inverting input terminal. The dither signal source 31i is an example of an embodiment of the dither providing means in the present invention. As the dither signal source 31i,
For example, as shown in FIG.
um) distribution, so-called blue dither (blue)
A device that generates a dither signal is preferable in that dithering is effectively performed.
As shown in the figure, the blue dither signal has a spectrum distribution in which the signal intensity gradually increases from a low frequency to a wide frequency between a frequency fi of the input signal and a quarter of the sampling clock frequency fs.

The dither signal source 31i has a white noise (white noise) such as a thermal noise.
e) It can be obtained by passing the output of the source through an appropriate filter. The dither signal is not limited to the blue dither signal, but may be white dither (white d).
iter) and pink dither (pink dithe)
r) or PN (pseudo random n
oise) and the like.

The bit stream conversion circuit 61i is not limited to the above-described pulse width modulation circuit. For example, as shown in FIG. 17, a dithered input signal ei and a dither signal application signal are input to a comparator 11i. A 1-bit converter may be used, and as shown in FIG. 18, an OP amplifier 32i is fed back by resistors 33i and 34i and a capacitor 35i, and an input signal ei is input to an inverting input terminal through a resistor 36i. Then, it may be configured by a 1-bit converter that uses the internal noise of the OP amplifier 32i itself as a dither signal. In addition,
Of course, a clocking circuit using a D-type flip-flop circuit may be provided on the output side in both converters.

The bit stream conversion circuit 61i constituted by the pulse width modulation circuit or the 1-bit converter as described above can be realized with a configuration which is significantly simpler than that using the ΔΣ modulator. Therefore, even if each of them is provided for each of 64 to 128 ultrasonic transducers constituting the receiving aperture, the number of components can be reduced to a considerably smaller number than in the case of using the ΔΣ modulator.

The operation of the present apparatus will be described. The operator contacts the ultrasonic probe 2 with a desired part of the subject 100 and operates the operation unit 14 to perform ultrasonic imaging. Imaging is performed under the control of the control unit 12 based on an instruction from the operator. The transmission / reception unit 6 performs, for example, the sector scan shown in FIG. 3 to form an echo reception signal along each sound ray. As described above, the formation of the echo reception signal is performed by once converting the analog signal into a bit stream signal, delay-adding the bit stream signal group, and filtering the addition result. Based on the echo data obtained as described above, the data processing unit 8 performs, for example, a B mode (B mod)
e) Generate images and the like. The generated image is displayed on the display unit 10.

[0047]

As described above in detail, according to the present invention, it is possible to realize a reception signal forming method and apparatus and an ultrasonic imaging method and apparatus using a bit stream signal obtained by a simple method.

Further, it is possible to realize a reception signal forming method and apparatus and an ultrasonic imaging method and apparatus using a stable bit stream signal.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to an example of an embodiment of the present invention.

FIG. 2 is a block diagram of a transmission / reception unit in the device shown in FIG.

FIG. 3 is a conceptual diagram of sound ray scanning by the transmission / reception unit shown in FIG. 2;

FIG. 4 is a conceptual diagram of sound ray scanning by the transmission / reception unit shown in FIG. 2;

FIG. 5 is a conceptual diagram of sound ray scanning by the transmission / reception unit shown in FIG. 2;

FIG. 6 is a block diagram of a data processing unit in the device shown in FIG.

FIG. 7 is a block diagram illustrating an example of a reception beam former in the transmission / reception unit illustrated in FIG. 2;

8 is a block diagram of an example of a bit stream conversion circuit in the receiving beamformer shown in FIG.

FIG. 9 is a block diagram of an example of a bit stream conversion circuit in the receiving beamformer shown in FIG. 7;

FIG. 10 is a block diagram illustrating an example of a bit stream conversion circuit in the receiving beamformer illustrated in FIG. 7;

11 is a block diagram of an example of a bit stream conversion circuit in the receiving beamformer shown in FIG.

FIG. 12 is a block diagram illustrating an example of a bit stream conversion circuit in the receiving beamformer illustrated in FIG. 7;

FIG. 13 is a block diagram illustrating an example of a bit stream conversion circuit in the receiving beamformer illustrated in FIG. 7;

FIG. 14 is a block diagram illustrating an example of a bit stream conversion circuit in the receiving beamformer illustrated in FIG. 7;

FIG. 15 is a block diagram illustrating an example of a bit stream conversion circuit in the receiving beamformer illustrated in FIG. 7;

16 is a graph showing a spectrum of a dither signal generated by the dither signal source shown in FIG.

FIG. 17 is a block diagram illustrating an example of a bit stream conversion circuit in the receiving beamformer illustrated in FIG. 7;

FIG. 18 is a block diagram illustrating an example of a bit stream conversion circuit in the receiving beamformer illustrated in FIG. 7;

[Explanation of symbols]

 2 Ultrasonic probe 6 Transmitter / receiver unit 8 Data processing unit 10 Display unit 12 Control unit 14 Operation unit 100 Subject 606 Transmitting beamformer 610 Receiving beamformer 611-615 Bit stream conversion circuit 651-655 Shift register 630 Addition circuit 640 Decimation Filter 11i Comparator 13i, 17i, 23i, 32i OP amplifier 31i Dither signal source

Claims (6)

[Claims] An ultrasonic wave is received by a plurality of ultrasonic transducers constituting an array, and a plurality of signals received by the plurality of ultrasonic transducers are respectively converted into bit stream signals by a quantization method other than ΔΣ modulation, A reception signal forming method, comprising: adding a predetermined delay time to the plurality of converted signals; adding the plurality of signals to which the delay time is added; and filtering the added signal. 2. The method according to claim 1, wherein a dither signal is added to each of the plurality of signals before being converted into the bit stream signal. 3. A plurality of ultrasonic transducers forming an array and receiving ultrasonic waves, and signals respectively converting a plurality of signals received by the plurality of ultrasonic transducers into bit stream signals by a quantization method other than ΔΣ modulation. Conversion means, delay providing means for providing a predetermined delay time to the plurality of converted signals, adding means for adding the plurality of signals provided with the delay time, and filtering means for filtering the added signals. , A reception signal forming apparatus. 4. The reception signal forming apparatus according to claim 3, further comprising: dither applying means for applying a dither signal to each of the plurality of signals before being converted into the bit stream signal. 5. An ultrasonic wave transmitting and receiving an echo thereof, forming a received signal along a predetermined sound ray based on the received signal, and generating an image based on the formed received signal. An ultrasonic imaging method, wherein the reception signal is formed by the method according to claim 1 or 2. 6. An ultrasonic transmission unit for transmitting an ultrasonic wave, a reception signal forming unit for forming a reception signal related to the transmitted ultrasonic wave, and an image generation unit for generating an image based on the formed reception signal. An ultrasonic imaging apparatus comprising: the receiving signal forming unit;
An ultrasonic imaging apparatus characterized by using the reception signal forming apparatus according to (1).