JP2003000596A - Ultrasonic diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove a fundamental frequency component without lowering a frame rate in an ultrasonic diagnostic device. SOLUTION: Between an ultrasonic receiving part and a digital scan converter in the ultrasonic diagnostic device, an A/D converter for converting an echo signal to a digital signal, a delay circuit 1 for applying arbitrary delay time to the output of this A/D converter, a phase control circuit 6 for variably controlling the phase of the output of this delay circuit, an arithmetic circuit 2 for operating delay data to be applied to the delay circuit 1 and the phase control circuit 6 from the echo signal and a signal synthesizing means 3 for synthesizing the echo signal and the output signal of the phase control circuit, removing the basic wave component from the echo signal and extracting/ emphasizing a higher harmonic component are provided.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an echo generated by an ultrasonic wave (fundamental wave) transmitted from a ultrasonic probe to a living body. The present invention relates to an ultrasonic diagnostic apparatus capable of imaging harmonic components in a signal. 2. Description of the Related Art An ultrasonic diagnostic apparatus irradiates an object with an ultrasonic beam, receives an echo signal, converts the received signal into an image, and displays the image. The higher the frequency of the ultrasonic wave used, the better the resolution (distance resolution) in the depth direction of the ultrasonic image is better. However, if the frequency of the ultrasonic wave to be transmitted is increased, the deep part becomes difficult to see due to the attenuation of the ultrasonic wave.
To solve this, the frequency of the transmitted ultrasonic wave is 2MHz
So-called harmonic imaging, in which the frequency is set to a low level and a harmonic component of an echo signal obtained from a living body is imaged, has become widespread. For this harmonic imaging, a technique of removing most of the frequency band (fundamental wave component) of the ultrasonic wave transmitted from the probe into the living body from the echo signal and extracting a high-frequency component is used. US Pat. No. 5,706,819 discloses a technique for removing the fundamental frequency component from an echo signal and extracting a harmonic component.
And USP, 5,632,277. These transmit the ultrasonic pulse having the opposite polarity or the ultrasonic pulse having a phase difference of 180 degrees twice in one beam direction, and remove the fundamental frequency component by adding the received ultrasonic reception signals. ,
This is for extracting harmonic components. According to both techniques, the fundamental frequency component can be removed without using a high-order filter. However, in the case of these conventional systems, it is necessary to transmit two ultrasonic transmission pulses in order to obtain image data in one ultrasonic scanning line. Therefore, when transmitting an ultrasonic transmission pulse at a constant interval, a measurement time twice as long as a normal B-mode scan is required. For this reason, when compared in the same scanning area, these prior arts have a frame rate of の of the B mode, and therefore, in the case of an organ having motion such as the heart, a good image cannot be obtained. An object of the present invention is to provide an ultrasonic diagnostic apparatus capable of removing a fundamental frequency component from an echo signal without lowering a frame rate, extracting a harmonic component, and forming an image thereof. It is to provide. [0006] In order to achieve the above object, the present invention provides an ultrasonic transmitting unit for transmitting ultrasonic waves into a subject, and receiving an echo signal reflected from the subject. An ultrasonic receiving unit, a phasing and adding unit for performing phasing and addition processing of the reflected echo signal, a signal processing unit for performing pre-imaging processing on a signal output from the phasing and adding unit, and the reflected echo signal A digital scan converter unit for converting the image into an image, and detects blood flow and organ movement from the echo signal,
In an ultrasonic diagnostic apparatus having a color Doppler operation unit that performs an operation process for displaying them in color and a display unit that displays an image, the echo signal is digitally interposed between the ultrasonic reception unit and a digital scan converter. A / D converter for converting to a signal, a delay circuit for giving an arbitrary delay time to the output of the A / D converter, a phase control circuit for variably controlling the phase of the output of the delay circuit, and the delay circuit An arithmetic circuit for calculating the delay data to be applied to the phase control circuit from the echo signal; synthesizing the echo signal and the output signal of the phase control circuit to remove a fundamental component from the echo signal and extract a harmonic component; -It is characterized by having a signal synthesizing means for enhancing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 14 is an overall configuration diagram of the ultrasonic diagnostic apparatus of the first embodiment. In FIG. 14, 18 is an ultrasonic transmitter for transmitting ultrasonic waves, 20 is an ultrasonic receiver for receiving ultrasonic waves, and 21 is for removing a fundamental frequency component, which is a characteristic part of the present invention, for detecting a harmonic component. , A phasing and adding unit for performing phasing and addition processing of echo signals, an envelope detecting unit for converting an echo signal into a tomographic image, and an ultrasound echo signal 23 as an image. A digital scan converter unit for conversion, 25 is a color Doppler operation unit for detecting blood flow, body movement, and the like, and performing an arithmetic process for displaying them in color, and 26 is a display means for displaying an image. Next, FIG. 1 shows the internal structure of the harmonic detection unit 21. In FIG. 1, reference numeral 1 denotes a time delay unit including a delay element or the like, 2 denotes a complex multiplier that multiplies two waves together with both a real part and an imaginary part, 3 denotes a signal combining unit that includes an adder, 6
Is a harmonic detection control unit that outputs a control signal for harmonic detection. Next, the operation of the ultrasonic diagnostic apparatus and the higher harmonic wave detecting section having the above-described configurations will be described. First, the ultrasonic transmission unit 18
, An ultrasonic wave is transmitted to the subject. Then, the echo is reflected from the subject. After the reflected echo is received by the ultrasonic wave receiving unit 20, the higher harmonic wave is detected by the harmonic wave detecting unit 21, and the phasing and adding unit 22 performs the phasing and adding process. Thereafter, the image signal is converted into an image signal by the envelope detection unit 23, and then converted into image data for monitor display by the digital scan converter unit 24. At the same time, the echo signal subjected to the phasing addition processing is subjected to processing for displaying a color image of blood flow information and the like in the subject by the color Doppler operation unit 25 and is input to the digital scan converter unit 24.
The two image data input to the digital scan converter section 24 are displayed on the display means 26 alternatively or combined. The operation inside the harmonic detecting section 21 is as follows. In FIG. 1, the echo signal X (t) input to the harmonic detection unit 21 is analyzed by the harmonic detection control unit 6 for the fundamental frequency and the harmonic frequency, and the delay control amount n and the minute phase The control amount e- ^{jw0t '} is output. (A specific example of the inside of the high-frequency detection control unit 6 will be described later with reference to FIG. 10.) The delay control amount n is sent to the time delay unit 1, and X (t) is equal to n × Δt (Δt is a sampling interval). ) Is delayed. Furthermore,
The minute phase control amount e- ^{jw0t '} is sent to the complex multiplier 2 and multiplied by the output result of the time delay means 1. The output result of the complex multiplier 2 is sent to the signal synthesizing means 3 and synthesized with the original echo signal X (t) to become Y (t). [0011] and the delay amount n × Delta] t with time delay means 1, at half wavelength of the fundamental frequency component to be the sum removal of ^'delay amount t by' fine phase control amount ^e -jw0t (T _0/2) If there is, Y
(T) is a signal in which the fundamental frequency component has been removed from X (t). This is represented by the following equations and figures. However, where the echo signal X (t) is the amplitude A ₀ is the initial phase is 0, the fundamental frequency X ₀ of frequency omega ₀ (t), ₁ amplitude A, the initial phase is 0, the frequency is omega ₁ Assuming that it is composed of harmonics X ₁ (t), it is expressed as in equation (1). (Equation 1) 2 (a) shows an echo signal X (t), the two waves shown in FIG. 2 (b) is an echo signal X (t) the fundamental frequency X ₀ (t) and harmonic X ₁ (t) This is shown separately. Next, the echo signal X (t) is
Is delayed by the time of n × Δt, the output X ′ (t) becomes
The following equation (2) is obtained. (Equation 2) FIG. 3A shows an echo signal X (t) and a signal X ′ (t) obtained by delay-shifting the echo signal X (t) by n × Δt, and FIG.
FIG. 3B shows X (t) and X ′ (t) divided into two waves, and the dotted line shows the wave before delay and the solid line shows the wave after delay. . Further, when a signal X '(t) obtained by delay-shifting the echo signal X (t) by n.times..DELTA.t is multiplied by the complex multiplier 2 with the phase control amount e- ^jw0t' , the output X "(t ) Is given by the following equation (3). FIG. 4A shows X ′ (t) and the phase delay control amount e ^{−jw0t ′.}
X ”(t) that is delayed and shifted in FIG. 4 (b), and FIG. 4 (b) shows them as fundamental waves X ₀ ′ (t), X ″ ₀ (t) and harmonics X ₁ ′ (t), X ₁ ″.
(T) is divided into two waves and displayed. Here, n · Δt + t ′ is the fundamental frequency (ω ₀ )
180 °, and 360 ° relative to the harmonic (ω ₁ ). Then, the equation (3) is transformed into the following equation (4). (Equation 4) Finally, the output Y (t) of the signal synthesizing means 3 is synthesized as follows from equations (1) and (4) (FIG. 5). (Equation 5) Here, assuming that t ′ << T ₀ , Therefore, from equation (6), it is possible to remove the fundamental frequency component from the echo signal and extract the harmonic component. Figure 5
Then, the harmonic X ₁ (t) is emphasized and X ₁ (t) + X ₁ ″ (t)
Whereas X originally contained in X (t)
₀ (t) has been removed. Next, the internal structure of the harmonic detection control section 6 will be described with reference to FIG. In FIG. 10, 7 is frequency analysis means such as FFT operation means and wavelet operation means, 8 is basic frequency detection means composed of registers, comparators, etc., and 9 is a delay phase composed of memories 10, 12 and a counter 11. Control means. The operation of the harmonic detection control unit 6 will be described. First, the frequency analysis means 7 outputs a time-response echo signal X (t).
To a frequency response echo signal X (f). The fundamental frequency detecting means 8 compares the reflected echo signal intensities of the respective frequencies and outputs the frequency f0 having the maximum value. Delaying the phase control means 9, to the output f ₀ of the fundamental frequency detecting means 8, the number n of sampling intervals substantially delay interval is a delay amount to become a T _0/2, wherein the sampling interval × n, exactly To T ₀
The correction phase rotation amount (phase control amount) e- ^{jw0t '} is output as the amount not becoming / 2. Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 15 is an overall configuration diagram of an ultrasonic diagnostic apparatus according to the second embodiment. In the second embodiment, the arrangement order of the harmonic detection unit 21 and the phasing addition unit 22 is changed compared to the first embodiment. As a result, the harmonics are detected after the phasing addition, so that only one channel is required for the circuit in the harmonic detector. Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 16 is an overall configuration diagram of an ultrasonic tomographic apparatus according to the third embodiment. In the third embodiment, the harmonic detection unit 21 is provided in the phasing addition unit 22. With this structure, the complex multiplier and the adder can be shared by the phasing addition unit 22 and the harmonic detection unit 2, so that the circuit scale can be reduced. Next, a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 11 shows the internal structure of the harmonic detector 21 according to the fourth embodiment. Reference numeral 4 denotes a newly added complex multiplier. In the present embodiment, the unit vector e ^{−jw0t ′} of the harmonic component is input together with the echo signal X (t), and is multiplied by the complex multiplier 4 by X (t). As a result, the harmonic component of the echo signal X (t) is frequency-shifted to the baseband, and the detection accuracy of the harmonic component is improved. on the other hand,
When the input unit vector is the fundamental frequency (ω ₀ ), the fundamental frequency component is frequency-shifted to the baseband, so that the detection accuracy of the fundamental frequency component is improved. In the case of the fourth embodiment, the internal structure of the harmonic detection control section 6 is as shown in FIG. The case of FIG. 10 is different from the case of FIG. 9 of the first embodiment in that the output f _{0 of the} register 8 is directly input to the memory 12. This is because, in the case of the fourth embodiment, the delay phase control is performed after the frequency shift, and therefore, when performing the delay phase control, the calculation must be made in consideration of f ₀ . On the other hand, since an ordinary ultrasonic reception signal has a pulse waveform having a certain envelope, an actual signal flow in the higher harmonic wave detector is as shown in FIG. 7 (a) shows the echo signal, FIG. 7 (b) shows the reflected echo signal decomposed into two waveforms, FIG. 7 (c) shows the output of the complex multiplier 2, and FIG. 7 (d).
Indicates the output of the signal combining means 3. According to this,
Since there is a difference in the shape of the envelope between the fundamental frequency component and the harmonic component, the rejection rate of the fundamental frequency component decreases near the start point and the end point of the pulse. However, there is also a merit that the fundamental wave component cannot be completely removed. That is, when the signal output from the envelope detection unit 23 is imaged by the digital scan converter unit 24 and displayed on the monitor 26, the fundamental wave and the harmonic are combined and displayed. Therefore, a portion that does not generate a harmonic is displayed by a fundamental wave, and a portion that generates a harmonic is displayed on an image with the harmonic being emphasized. Next, a fifth embodiment of the present invention will be described with reference to the drawings. FIG. 8 shows the internal structure of the harmonic detector 21 according to the fifth embodiment. In FIG. 8, reference numeral 5 denotes an adder. In the fifth embodiment, the time delay means 1, the complex multiplier
2. It has n sets of harmonic detection control units 6. In the present embodiment, n sets of waves having different amplitudes and delay times are created and added, so that the influence of the envelope included in the fundamental frequency component and the harmonic component can be removed as shown in FIG. In the case of the fifth embodiment, the internal structure of the harmonic detection control section 6 is as shown in FIG. In FIG. 12, reference numeral 13 denotes a bandwidth detection unit for detecting the bandwidths of the fundamental frequency component and the harmonic component, and reference numeral 14 denotes coefficient calculation means for calculating coefficients (amplitude and delay time) of a waveform created with delay. It is. After detecting the band of each wave, the harmonic detection control unit 6 determines the boundary between the band of the fundamental frequency and the band of the harmonic, determines the coefficient of the delayed wave, and separates each wave, thereby increasing the separation accuracy. FIG. 13 is a diagram schematically showing a procedure for performing optimization for obtaining the coefficient. In FIG. 13, reference numeral 15 denotes a filter including a register, a multiplier, an adder, etc., 16 denotes a subtractor, and 17 denotes a least square error calculating means including a register, a memory, a comparator, and the like. As shown in this schematic diagram, if the signal is synthesized once, the filter is applied again, the subtraction process is performed, and the optimum coefficient value is obtained by the least square method, the removal rate of the fundamental frequency component is increased. According to the present invention, as described above, a delayed signal is created based on an echo signal, and the echo signal and the delayed echo signal are combined to obtain a harmonic component. Is extracted, emphasized, and imaged and displayed, so that it is possible to provide an image that can be easily diagnosed without lowering the frame rate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an internal structure of a harmonic detector according to a first embodiment of the present invention. FIG. 2 is a waveform diagram showing a schematic echo signal X (t) and its decomposition into a fundamental component and a harmonic component. FIG. 3 is a diagram showing a waveform when a fundamental wave component X (t) is delayed and shifted by time delay means. FIG. 4 is a diagram showing a waveform when the signal X ′ (t) shown in FIG. 3 is subjected to phase delay control by a complex multiplier. FIG. 5 is a diagram illustrating an output waveform of a signal combining unit. FIG. 6 is a block diagram showing an internal structure of a harmonic detector according to a fourth embodiment of the present invention. FIG. 7 is a diagram showing a signal waveform in a processing procedure for extracting and enhancing a harmonic component of an actual echo signal. FIG. 8 is a block diagram showing an internal structure of a harmonic detector according to a fifth embodiment of the present invention. FIG. 9 is a diagram showing a waveform from which the influence of an envelope is removed. FIG. 10 is a block diagram showing an internal structure of an ultrasonic detection control unit according to the first embodiment of the present invention. FIG. 11 is a block diagram showing an internal structure of an ultrasonic detection control unit according to a fourth embodiment of the present invention. FIG. 12 is a block diagram showing an internal structure of an ultrasonic detection control unit according to a fifth embodiment of the present invention. FIG. 13 shows a procedure for optimizing a coefficient. FIG. 14 is a block diagram showing an overall configuration diagram of an ultrasonic diagnostic apparatus according to the first embodiment of the present invention. FIG. 15 is a block diagram showing an overall configuration diagram of an ultrasonic diagnostic apparatus according to a second embodiment of the present invention. FIG. 16 is a block diagram showing an overall configuration diagram of an ultrasonic diagnostic apparatus according to a third embodiment of the present invention. [Description of Signs] 1 time delay means 2 complex multiplier 3 signal synthesis means 6 harmonic detection control unit 21 harmonic detection unit

Claims (1)

Claims: 1. An ultrasonic transmitter for transmitting an ultrasonic wave into a subject, an ultrasonic receiver for receiving an echo signal reflected from the subject, and phasing of the echo signal. A phasing addition unit that performs an addition process, a signal processing unit that performs pre-imaging processing on a signal output from the phasing addition unit, and a digital scan converter unit that converts the reflected echo signal into an image. An ultrasonic diagnostic apparatus having a color Doppler operation unit for detecting a blood flow and organ movement from the echo signal and performing an arithmetic process for displaying them in color, and a display unit for displaying an image; An A / D converter for converting the echo signal into a digital signal between the receiving unit and the digital scan converter; a delay circuit for providing an arbitrary delay time to the output of the A / D converter; A phase control circuit that variably controls the phase of the output of the path, a calculation circuit that calculates delay data to be applied to the delay circuit and the phase control circuit from the echo signal, and combines the echo signal and an output signal of the phase control circuit. An ultrasonic diagnostic apparatus comprising a signal synthesizing means for removing a fundamental component from the echo signal and extracting and enhancing a harmonic component.