JPH1014921A - Ultrasonic imaging method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method and apparatus which enables accurate detection of harmonic components contained in an echo signal from an interest part traced by an ultrasonic contrast medium having a non-linear ultrasonic reflection characteristic. SOLUTION: This ultrasonic imaging apparatus drives an ultrasonic vibrator to transmit an ultrasonic wave into a specimen and detects a second harmonic component of an echo signal from the specimen. This apparatus is provided with an adjustment means 27 to adjust the generation of waveforms so that none of the second harmonic component exists in the echo signal detected, feedback means 24, 25 and 26 in which the waveform of the detected echo signal undergoes a frequency analysis to compare the second harmonic component with a fundamental wave for feeding back the results of the comparison to the adjustment means and a transmitting means 22 to generate an ultrasonic wave of the waveform adjusted after a contrast tracing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultrasonic imaging method and an ultrasonic imaging apparatus, and more particularly to an ultrasonic imaging method suitable for detecting a propagation path having a non-linear ultrasonic reflection characteristic and an echo from a region of interest. And an ultrasonic imaging apparatus.

[0002]

2. Description of the Related Art In a medical ultrasonic imaging apparatus (ultrasonic imaging apparatus), an ultrasonic wave is transmitted into a subject and an internal structure of the subject is imaged based on an echo signal. Done.

Some ultrasonic contrast agents (foaming agents or contrast agents) return echoes of, for example, second harmonic components of transmitted ultrasonic waves due to the non-linearity of the reflection characteristics. In the present specification, such a reflection characteristic is referred to as a non-linear ultrasonic reflection characteristic.

[0004] When an ultrasonic contrast agent having such properties is injected into a region of interest of a subject to perform imaging,
The inside of the subject is imaged based on the second harmonic component of the echo signal.

[0005]

As described above, when obtaining an ultrasonic image based on the second harmonic component of the echo signal, the following problems occur.

An ultrasonic transducer for generating an ultrasonic wave transmitted into a subject is often driven by a rectangular wave voltage in order to increase the power efficiency of a drive circuit. Due to the included harmonic components, the ultrasonic waves transmitted into the subject also include the harmonic components.

[0007] The second characteristic is also caused by the non-linearity of the medium located between the ultrasonic transducer and the site of interest (propagation path).
Harmonic components may occur. In other words, there is a disadvantage that the second harmonic component generated in the region of interest into which the ultrasound contrast agent has been injected cannot be distinguished from the second harmonic component in the above cases.

For this reason, the second harmonic component is also contained in the echo signal from the echo source having no non-linearity, and the echo between the region of interest and the non-contrast region imaged by the ultrasonic contrast agent is generated. There is a problem that signals cannot be distinguished.

For the above-described measures, it is necessary to provide a low-pass (high-cut) filter for transmitting only the fundamental wave component on the transmission circuit side. In addition, it is necessary to provide a high-pass (low-cut) filter for passing only the second harmonic component and removing the fundamental component on the receiving circuit side.

However, if a filter having a steep cutoff characteristic is used to obtain a desired characteristic, the phase shift becomes large near the cutoff frequency, the attenuation becomes uneven, and the signal passes through the cutoff frequency region. There may be various problems, such as the occurrence of parts that are lost. Also,
When a time filter is used to obtain a steep cutoff characteristic, there is also a problem that the spatial resolution is reduced.

As described above, a new problem as shown in the following also occurs depending on the characteristics of the filter provided to solve the above problem. The present invention has been made in order to solve the above problems, and an object of the present invention is to correctly detect a harmonic component included in an echo signal from a site of interest imaged by an ultrasonic contrast agent having a non-linear ultrasonic reflection characteristic. A method and an apparatus are provided.

[0012]

Accordingly, the present invention, which is a means for solving the problems, is configured as described below.

(1) A first invention is an ultrasonic imaging method for driving an ultrasonic transducer to transmit an ultrasonic wave into a subject and detecting a second harmonic component of an echo signal from the subject. An ultrasonic imaging method characterized in that the ultrasonic wave is transmitted by adjusting the waveform so that the second harmonic component is eliminated from the detected echo signal.

In the ultrasonic imaging method according to the first aspect of the invention, first, the ultrasonic transducer is driven to transmit an ultrasonic wave into the subject, and adjustment is performed so that the second harmonic component of the echo signal is eliminated. Obtain the transmission waveform of the ultrasonic wave.

That is, the state in which the second harmonic component is not detected in the transmission and reception of the ultrasonic wave when the contrast agent is not injected means that the second harmonic component (distortion component) generated by the medium has an opposite phase. Second harmonic component (reverse distortion component)
By transmitting an ultrasonic wave having a waveform including the above, it means that as a result of the cancellation of the distortion components, the state is equivalent to a state where no distortion component of the ultrasonic waves is generated by the medium.

After the ultrasonic contrast agent is injected, the ultrasonic wave having the waveform adjusted as described above is transmitted, whereby the influence of the second harmonic generated in the medium is eliminated, and the second harmonic from the site of interest is eliminated. Only components can be detected. Therefore,
It is possible to correctly detect a harmonic component included in an echo signal from a site of interest imaged with an ultrasonic contrast agent having a non-linear ultrasonic reflection characteristic.

(2) A second invention is an ultrasonic imaging apparatus for driving an ultrasonic transducer to transmit an ultrasonic wave into a subject and detecting a second harmonic component of an echo signal from the subject. And adjusting means for adjusting the waveform generation so that the detected echo signal has no second harmonic component, and comparing the fundamental wave with the second harmonic by performing frequency analysis on the detected echo signal waveform, An ultrasonic imaging apparatus comprising: a feedback unit that returns a comparison result to the adjustment unit; and a transmission unit that generates an ultrasonic wave having an adjusted waveform after imaging.

In the ultrasonic imaging apparatus according to the second aspect of the present invention, first, the ultrasonic transducer is driven to transmit an ultrasonic wave to a site of interest in the subject, and the echo signal is transmitted using the feedback means and the adjustment means. A transmission waveform of the ultrasonic wave adjusted so as to eliminate the second harmonic component is obtained.

That is, the state where the second harmonic component is not detected in the transmission and reception of the ultrasonic wave when the contrast agent is not injected is defined as the phase opposite to the second harmonic component (distortion component) generated by the medium. Second harmonic component (reverse distortion component)
By transmitting an ultrasonic wave having a waveform including the above, it means that as a result of the cancellation of the distortion components, the state is equivalent to a state where no distortion component of the ultrasonic waves is generated by the medium.

Then, after the ultrasonic contrast agent is injected, the ultrasonic wave having the waveform adjusted as described above is transmitted from the transmitting means, so that the effect of the second harmonic generated in the medium is eliminated, and the ultrasonic wave from the site of interest is eliminated. Only two harmonic components can be detected. Therefore, it is possible to correctly detect a harmonic component included in an echo signal from a site of interest imaged with an ultrasonic contrast agent having a nonlinear ultrasonic reflection characteristic.

(3) A third invention is an ultrasonic imaging method for transmitting an ultrasonic wave into a subject by driving an ultrasonic transducer and detecting a second harmonic component of an echo signal from the subject. Detecting a fundamental component of the echo signal in a state where the second harmonic component of the echo signal is attenuated by the filter;
A first image signal is generated based on the fundamental wave component of the echo signal, and a second harmonic component of the echo signal is detected while the fundamental wave component of the echo signal is attenuated by a filter. Generating a second image signal from the wave component, subtracting a component of the first image signal from the second image signal at a predetermined ratio, and removing a fundamental wave component included in the echo signal. This is an acoustic imaging method.

In the ultrasonic imaging method according to the third aspect, the first image signal is generated from the fundamental wave component of the echo signal detected in a state where the second harmonic component of the echo signal is attenuated by the filter, and Of the echo signal detected with the fundamental wave component of the echo signal attenuated by the
A second image signal is generated from the harmonic component, and a component of the first image signal is subtracted from the second image signal at a predetermined ratio, thereby removing a fundamental wave component included in the echo signal.

Therefore, it is possible to generate an image signal equivalent to that obtained by detecting only the second harmonic component without using a filter having a sharp cutoff characteristic for the echo signal. As a result, the adverse effects of the filter having steep characteristics (phase shift and decrease in spatial resolution) are eliminated, and harmonics included in the echo signal from the site of interest imaged with the ultrasonic contrast agent having the nonlinear ultrasonic reflection characteristics are eliminated. The components can be detected correctly.

Note that the predetermined ratio at the time of subtraction is a ratio at which the fundamental wave component contained in the echo signal is eliminated. For example, the first image signal and the second image signal before the contrast are generated. The ratio at which the cross-correlation with the image signal is minimized. That is, a coefficient that minimizes the cross-correlation between the first image signal and the second image signal is obtained before the imaging, and the first image signal and the second image signal are multiplied by the first image signal after the imaging. By subtracting the component of the image signal, the fundamental component contained in the echo signal can be removed.

(4) A fourth invention is an ultrasonic imaging apparatus for driving an ultrasonic transducer to transmit an ultrasonic wave into a subject and detecting a second harmonic component of an echo signal from the subject. Detecting a fundamental component of the echo signal in a state where the second harmonic component of the echo signal is attenuated by the filter;
A fundamental wave image signal generating means for generating a first image signal from the fundamental wave component of the echo signal, and detecting a second harmonic component of the echo signal in a state where the fundamental wave component of the echo signal is attenuated by a filter; A second harmonic image signal generating means for generating a second image signal from the second harmonic component of the echo signal; and subtracting a component of the first image signal from the second image signal according to a predetermined ratio. An ultrasonic imaging apparatus comprising: a subtraction unit that removes a fundamental component included in a signal.

In the ultrasonic imaging apparatus according to the fourth aspect of the present invention, the first image signal is generated from the fundamental wave component of the echo signal detected in a state where the second harmonic component of the echo signal is attenuated by the filter. Of the echo signal detected with the fundamental wave component of the echo signal attenuated by the
A second image signal is generated from the harmonic component, and a component of the first image signal is subtracted from the second image signal at a predetermined ratio, thereby removing a fundamental wave component included in the echo signal.

Therefore, it is possible to generate an image signal equivalent to that obtained by detecting only the second harmonic component without using a filter having a sharp cutoff characteristic for the echo signal. As a result, the adverse effects (such as phase shift and deterioration of spatial resolution) of the filter having steep characteristics are eliminated, and harmonics included in an echo signal from a site of interest imaged with an ultrasonic contrast agent having nonlinear ultrasonic reflection characteristics are eliminated. Wave components can be detected correctly.

The predetermined ratio at the time of subtraction is a ratio at which the fundamental wave component contained in the echo signal is eliminated, and, for example, the first image signal and the second image signal before the contrast are obtained. The ratio at which the cross-correlation with the image signal is minimized.

Therefore, it is preferable that the subtraction means performs the subtraction by obtaining such a predetermined ratio. That is, a coefficient that minimizes the cross-correlation between the first image signal and the second image signal is obtained before the imaging, and the first image signal and the second image signal are multiplied by the first image signal after the imaging. By subtracting the component of the image signal, the fundamental component contained in the echo signal can be removed.

[0030]

Embodiments of the present invention will be described below in detail with reference to the drawings. Here, FIG. 1 is a flowchart showing a processing procedure of an ultrasonic imaging method as one embodiment of the present invention, and FIG. 2 is a flowchart showing a main part of an ultrasonic imaging apparatus as one embodiment of the present invention. It is a block diagram which shows a schematic structure. FIG. 3 is a configuration diagram showing an ultrasonic imaging apparatus which is the entire configuration of the ultrasonic imaging apparatus shown in FIG.

First, an overall configuration of an ultrasonic imaging apparatus using the ultrasonic imaging apparatus according to the embodiment will be described. The ultrasonic imaging apparatus described below is not limited to medical equipment.

In FIG. 3, reference numeral 1 denotes a probe as an ultrasonic probe, 11 denotes a cable for electrically connecting the probe 11 to the main body of the ultrasonic imaging apparatus, and 2 denotes a cable and an ultrasonic probe. This is a cable connector for mechanically connecting the ultrasonic imaging apparatus main body.

20 is a transmitting / receiving circuit, 30 is a logarithmic amplifier, 4
Reference numeral 0 denotes an envelope detection unit, 50 denotes a digital scan converter (DSC), 60 denotes a display unit, 70 denotes a control unit, and 80 denotes an operation unit.

The probe 1 is connected to a transmitting / receiving circuit 20 by a cable connector 2. The probe 1 is in contact with an object (not shown), transmits an ultrasonic wave into the object according to a transmission signal given from the transmission / reception circuit 20, and detects an echo signal returned from the object as a reception signal. It is.

The transmission / reception circuit 20 supplies a transmission signal to the probe 1 under the control of the control unit 70, and receives and amplifies the detected echo signal. In addition,
In outputting the transmission signal and receiving the ultrasonic detection signal, phase difference addition for each transmission signal and phasing addition of each reception signal are performed, and beam forming (beam forming) for determining directivity of ultrasonic transmission and reception is performed. beam steering and beam steering for ultrasonic beam scanning
g) is performed.

The logarithmic amplifier 30 is for amplifying the output signal of the transmission / reception circuit 20 logarithmically. The envelope detection unit 40
The output signal of the logarithmic amplifier 30 is subjected to envelope detection to obtain a B-mode image signal.

The digital scan converter 50 includes:
Under the control of the control unit 70, the image signal output from the envelope detection unit 40 is converted into a digital signal and stored in an image memory (not shown), and the stored image data is synchronized with the display operation of the display unit 60. Output.
The display unit 60 displays image data provided from the digital scan converter 50 as an image under the control of the control unit 70.

The control unit 70 controls the operation of the transmission / reception circuit 20, the digital scan converter 50, and the display unit 60 by supplying control signals to the display unit 60. The operation unit 80 is operated by an operator and gives commands and data to the control unit 70.

<Configuration of Ultrasound Imaging Apparatus (1)>
FIG. 2 shows details of the transmission circuit 21 and the reception circuit 28 in the transmission / reception circuit 20. In FIG. 2, reference numeral 22 denotes a waveform generator that generates a waveform of an ultrasonic wave to be transmitted, and 23 denotes a transmission amplifier that amplifies a waveform generated by the waveform generator for transmission.

Reference numeral 24 denotes a receiving amplifier as a preamplifier for amplifying the received ultrasonic signal received by the probe 1;
A / D converter converts the output signal of the reception amplifier 24 into digital data (digital reception data) by A / D conversion, and 26 performs a frequency analysis of the digital reception data to remove a distortion component. A digital signal processor (DSP) 27 is an inverse filter creating unit that receives the processing result from the DSP 26 and forms an inverse equalizer when generating a waveform.

Here, what is called an inverse equalizer and an inverse filter is based on the fact that control is performed in a process reverse to that of an equalizer and a filter in ordinary ultrasonic imaging.

Here, the transmitting circuit 20 constitutes transmitting means. Further, a receiving amplifier 24, an A / D converter 25
And the DSP 26 constitute feedback means for performing feedback to the waveform generator 22. In addition, the waveform generator 22 and the inverse filter creating unit 27 constitute an adjusting unit that adjusts the waveform.

<Operation of Ultrasound Imaging Apparatus (1)>
Here, the operation of the ultrasonic imaging apparatus will be described with reference to the flowchart of FIG.

First, in the state where the ultrasonic contrast agent (contrast agent) is not injected into the site of interest, the following calibration processing (determination of transmission / reception and transmission waveform of ultrasonic wave)
I do.

That is, under the control of the control unit 70,
The probe 1 and the transmission / reception circuit 20 transmit an ultrasonic wave (frequency f0) to the subject and receive an echo signal (S1 in FIG. 1).

At this stage, the echo signal obtained by the probe 1 is amplified by the receiving amplifier 24, converted into digital data by the A / D converter 25, and then processed by the DSP 26.

That is, the DSP 26 analyzes the frequency of the echo signal by FFT or multiplication by software, compares the level of the fundamental wave component and the level of the second harmonic component included in the echo signal, and creates an inverse filter for the level comparison result. Output to the unit 27.

The inverse filter generator 27 generates a control signal for generating a waveform such that the level of the second harmonic component included in the echo signal is reduced by referring to the level comparison result, and generates the waveform. Output to the container 22.

The waveform generator 22 that has received the control signal for generating a waveform generates an ultrasonic waveform in which the second harmonic component is canceled out and becomes small by including the second harmonic component having the opposite phase. (S2 in FIG. 1).

By repeating the above feedback loop (S1, S2, S3 in FIG. 1), the distortion of the medium existing between the probe 1 and the region of interest under the condition that the ultrasonic contrast agent is not injected is obtained. As a result, the waveform generation unit 22 can generate a waveform that cancels out the second harmonic component generated by the above operation and prevents the second harmonic component from being detected.

That is, the state where the second harmonic component is not detected in the transmission and reception of the ultrasonic wave when the contrast agent is not injected means that the second harmonic component (distortion component) generated by the medium has an opposite phase. Second harmonic component (reverse distortion component)
As a result of transmitting the ultrasonic wave having the waveform including the above, as a result of the distortion component being cancelled, the ultrasonic wave has no distortion component generated by the medium existing between the probe 1 and the site of interest. It means there is.

When the transmission waveform is determined with reference to the level of the second harmonic component, the FF of the reception signal is determined.
In response to the T result, it is also possible to create a spectrum in which only the 2f0 component has an opposite phase, and determine the transmission waveform by performing an inverse FFT on this spectrum.

Further, a part which has been subjected to digital signal processing by the DSP 26 may be replaced with an analog circuit, and equivalent processing may be performed in analog signal processing. When the DSP 26 detects that the second harmonic component has become sufficiently small by the feedback control as described above, the control unit 7
In response to the instruction of 0, the inverse filter creating unit 27 or the waveform generator 22 saves as control data or waveform data of the transmission waveform that does not generate the second harmonic component, and completes the calibration process.

At this point, the control unit 70 notifies the operator via the display unit 60 that the calibration process has been completed. The operator who has received the notification injects a contrast agent (contrast agent) in order to image a site of interest of the subject (S4 in FIG. 1).

Then, after the contrast medium is injected, ultrasonic waves are transmitted and received to execute ultrasonic imaging (S5 in FIG. 1). According to the calibration processing so far, the second harmonic component is not generated depending on the medium (propagation path with distortion). Since no distortion is detected), it is possible to reliably detect only the second harmonic component generated by the site of interest into which the contrast agent has been injected. In this case, it is needless to say that the probe 1 must not be moved before and after the injection of the contrast agent.

<Configuration of Ultrasound Imaging Apparatus (2)>
Next, a configuration of an ultrasonic imaging apparatus according to a second embodiment will be described with reference to FIG. In FIG. 5, the same components as those in FIG. 3 described above are denoted by the same reference numerals.

Reference numeral 1 denotes a probe (prob) as an ultrasonic probe.
e), 20 is a transmission / reception circuit, 22 is a waveform generator that generates an ultrasonic waveform to be transmitted, and 23 is a transmission amplifier that amplifies the waveform generated by the waveform generator for transmission.

Reference numeral 24 denotes a reception amplifier as a preamplifier for amplifying the reception ultrasonic signal received by the probe 1, 29
a is a filter having a band-pass characteristic for passing the same frequency (f0) as the transmission signal at the center, and 29b is a filter having a band-pass characteristic for passing the transmission signal and the second harmonic frequency (2f0) at the center. It is.

Reference numeral 31 denotes a logarithmic amplifier for the received signal of the frequency f0, 32 denotes a logarithmic amplifier for the received signal of the frequency 2f0, 41 denotes an envelope detector for the received signal of the frequency f0, and 42 denotes a frequency of 2f0. Is an envelope detector for the received signal.

Reference numeral 43 denotes an adaptive erasure unit for adaptively erasing two types of B-mode image signals obtained by envelope detection. Reference numeral 50 denotes a digital scan converter (digital s).
canconverter: DSC), 60 is a display unit. Note that the control unit 70 and the operation unit 80 are omitted.

Here, the probe 1 is brought into contact with a subject (not shown), transmits an ultrasonic wave into the subject in accordance with a transmission signal provided from the transmission / reception circuit 20, and receives an echo signal returned from the subject. This is detected as a wave signal.

The transmission / reception circuit 20 supplies a transmission signal to the probe 1 under the control of the control unit 70, and receives and amplifies the detected echo signal. In addition,
In outputting the transmission signal and receiving the ultrasonic detection signal, phase difference addition for each transmission signal and phasing addition of each reception signal are performed, and beam forming (beam forming) for determining directivity of ultrasonic transmission and reception is performed. beam steering and beam steering for ultrasonic beam scanning
g) is performed.

In the transmitting / receiving circuit 20, an ultrasonic signal according to the waveform from the waveform generator 22 is amplified by the transmission amplifier 23 and applied to the probe 1. The receiving amplifier 24
The received signal amplified by the filter 29a has the same frequency (f0) component as that of the transmitted signal extracted by the filter 29a.
Then, the transmitted signal and the second harmonic (2f0) component are extracted.

The logarithmic amplifiers 31 and 32 are connected to the transmitting / receiving circuit 2
The output signals of 0 (center frequencies f0 and 2f0) are each logarithmically amplified. The envelope detectors 41 and 42 are:
The output signals of the logarithmic amplifiers 31 and 32 are respectively envelope-detected to obtain a B-mode image signal.

The adaptive erasure section 43 performs adaptive erasure on the B-mode image signal from the envelope detection section 41 and the B-mode image signal from the envelope detection section 42, thereby obtaining mutually overlapping reception signals. The wave signal component is removed to generate a B-mode image signal using only one of the components.

As an example of adaptive erasure, a ratio at which the cross-correlation between two signal components is minimized is obtained, and the two signal components are subtracted in a state of multiplying this coefficient after the contrast. Extracting only one of the components.

The digital scan converter 50 is
Under the control of the control unit 70, the image signal output from the adaptive erasure unit 43 is converted into a digital signal and stored in an image memory (not shown), and the stored image data is adjusted in accordance with the display operation of the display unit 60. Output.

The display unit 60 displays image data provided from the digital scan converter 50 as an image under the control of the control unit 70. In this embodiment, the adaptive erasure unit 43 constitutes a subtraction unit.

<Operation of Ultrasound Imaging Apparatus (2)>
Here, the operation of the ultrasonic imaging apparatus will be described with reference to the flowchart of FIG.

First, the following calibration processing (transmission / reception of ultrasonic waves and determination of coefficients used for subtraction) is performed without injecting an ultrasonic contrast agent (contrast agent) into a site of interest.

That is, under the control of the control unit 70,
The probe 1 and the transmitting / receiving circuit 20 transmit an ultrasonic wave (frequency f0) to the subject and receive an echo signal (S1 in FIG. 4).

At this stage, the echo signal obtained by the probe 1 is amplified by the receiving amplifier 24 and then filtered by the filter 29.
The component of the center frequency f0 is extracted by a, and the component of the center frequency 2f0 is similarly extracted by the filter 29b.

Then, for the received signals of the respective frequency components, B-mode image signals are generated by the logarithmic amplifiers 31 and 32 and the envelope detectors 41 and 42, respectively (S2 in FIG. 4).

Here, the adaptive erasure section 43 performs, as a pre-processing stage of the adaptive erasure, for example, such that when one or both image signals are multiplied by a coefficient, the cross-correlation between the two signals is minimized. The coefficients are obtained in advance (S3, S4 in FIG. 4).
4).

At this point, the control unit 70 notifies the operator via the display unit 60 that the calibration process has been completed. The operator receiving this notification injects a contrast agent (contrast agent) to image a site of interest of the subject (S5 in FIG. 4).

After the contrast agent is injected, ultrasonic waves are transmitted and received to perform ultrasonic imaging (S6 in FIG. 4). After the echo signal received by the probe 1 is amplified by the receiving amplifier 24, the component of the center frequency f0 is extracted by the filter 29a, and the center frequency 2f is similarly extracted by the filter 29b.
Zero components are extracted. Then, for the received signals of the respective frequency components, logarithmic amplifiers 31 and 32,
The envelope detection units 41 and 42 generate B-mode image signals.

Here, adaptive erasure section 43 performs the main processing of adaptive erasure, and extracts only one component.
That is, the image signal having the center frequency f0 and the center frequency 2f
The image signal of 0 is multiplied by the coefficient obtained in the calibration process, and then the image signal of f0 is subtracted for each pixel from the image signal of 2f0 (S7 in FIG. 4).

Before performing such subtraction, it is necessary to perform positioning so that each pixel of the image signal matches. In other words, by subtracting the coefficient that minimizes the cross-correlation between the two image signals before the contrast, by multiplying the coefficient by the two image signals after the contrast, the echo contained in the second harmonic component of the echo signal is reduced. It becomes possible to minimize the component of the fundamental wave component of the signal. It should be noted that subtraction of two image signals in a state in which these coefficients are multiplied means that linear combination is performed on these two image signals.

Also, instead of multiplying both image signals by a coefficient, if one image signal is multiplied by a coefficient such that the two image signals have a similar ratio and then subtraction is performed, the second harmonic of the echo signal is also obtained. It becomes possible to minimize the component of the fundamental wave component of the echo signal included in the wave component.

Therefore, by subtracting the component of the f0 image signal from the 2f0 image signal after the contrast according to a predetermined ratio (the ratio at which the cross-correlation between the two image signals is minimized before the contrast), the echo signal can be obtained. It becomes possible to remove the included fundamental wave component.

As described above, since the mutual influence can be eliminated at the stage when the image signal is generated, the cut-off characteristics of not only the filter 29b that allows the second harmonic component to pass but also the filter 29a that allows the fundamental component to pass. There is no problem even if it is loose.

For this reason, a steep cut-off characteristic has conventionally been required, and various problems (such as phase shift and a decrease in spatial resolution) caused by this need to be reduced to a gentle cut-off characteristic. Can be solved all at once.

The B-mode image signal adaptively erased by the adaptive eraser 43 is input to the digital scan converter 50 and stored as digital image data. The image data stored in the digital scan converter 50 is transmitted to the display unit 6 under the control of the control unit 70.
0 is read out at the display timing of the display unit 60.
Is displayed as an image.

In the above description, a coefficient that minimizes the cross-correlation between two image signals is obtained before the injection of the contrast agent, and the subtraction is performed by multiplying the two image signals by the coefficient after the contrast agent. , Used as an example of adaptive erasure.

However, other than this, when an image signal of the second harmonic is obtained, various adaptive erasures that provide the same effect are executed so that leakage of the fundamental wave component can be suppressed. It is also possible. As this adaptive erasure,
For example, it is conceivable to apply a two-dimensional adaptive inverse filter. It is also conceivable to obtain an estimation formula that can estimate the second harmonic image signal before the injection of the contrast agent from the image signal of the fundamental wave, and subtract the estimated value obtained by this estimation formula.

In any case, before the injection of the contrast agent, measures are taken to suppress the leakage of the fundamental wave component by using the two image signals. Try to keep components from leaking. In this case, it is needless to say that the probe 1 must not be moved before and after the injection of the contrast agent.

[0087]

As described above in detail with the embodiments, according to the inventions described in this specification, the following effects can be obtained.

(1) In the ultrasonic imaging method according to the first aspect of the present invention, the ultrasonic wave is transmitted by adjusting the waveform so that the second harmonic component is eliminated from the detected echo signal. The generated second harmonic component is canceled, and only the second harmonic component from the site of interest can be detected. Therefore, it is possible to correctly detect a harmonic component included in an echo signal from a site of interest imaged with an ultrasonic contrast agent having a nonlinear ultrasonic reflection characteristic.

(2) In the ultrasonic imaging apparatus according to the second invention, an ultrasonic wave is transmitted to a region of interest before the imaging,
A feedback unit and an adjustment unit for detecting a second harmonic component generated from a site of interest and a medium, and generating an ultrasonic wave having a waveform such that the second harmonic component disappears in the echo signal detected at this time after the imaging; First, the ultrasonic transducer is driven to transmit ultrasonic waves to a site of interest in the subject,
The transmission waveform of the ultrasonic wave adjusted so as to eliminate the second harmonic component of the echo signal is obtained, and after the ultrasonic contrast agent is injected, the ultrasonic wave having the waveform adjusted in this manner is transmitted, so that the medium is transmitted. The generated second harmonic component is canceled, and only the second harmonic component from the site of interest can be detected. Therefore, it is possible to correctly detect a harmonic component included in an echo signal from a site of interest imaged with an ultrasonic contrast agent having a nonlinear ultrasonic reflection characteristic.

(3) In the ultrasonic imaging method of the third invention, the first image signal based on the fundamental wave component and the second image signal based on the second harmonic component are used by using a filter having a gradual characteristic.
By subtracting the component of the first image signal from the second image signal after the contrast at a predetermined ratio determined before the contrast, the fundamental wave component included in the echo signal is removed. It becomes possible.

Therefore, it is possible to generate an image signal equivalent to that obtained by detecting only the second harmonic component without using a filter having a sharp cutoff characteristic for the echo signal. As a result, the adverse effect of the filter having the steep characteristic is eliminated, and it is possible to correctly detect the harmonic component included in the echo signal from the part of interest imaged with the ultrasonic contrast agent having the nonlinear ultrasonic reflection characteristic. .

(4) In the ultrasonic imaging apparatus according to the fourth aspect of the present invention, the first image signal based on the fundamental component and the second image based on the second harmonic component are used by using a filter having a gradual characteristic.
By subtracting the component of the first image signal from the second image signal after the contrast at a predetermined ratio obtained before the contrast by the subtraction means, the fundamental wave component included in the echo signal is generated. Can be removed.

Therefore, it is possible to generate an image signal equivalent to that obtained by detecting only the second harmonic component without using a filter having a sharp cutoff characteristic for the echo signal. As a result, the adverse effect of the filter having the steep characteristic is eliminated, and it is possible to correctly detect the harmonic component included in the echo signal from the part of interest imaged with the ultrasonic contrast agent having the nonlinear ultrasonic reflection characteristic. .

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a processing procedure according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an apparatus according to the first embodiment of the present invention.

FIG. 3 is a block diagram of an ultrasonic imaging apparatus using the apparatus according to the first embodiment of the present invention. It is a block diagram of a device of another embodiment of the present invention.

FIG. 4 is a flowchart illustrating a processing procedure according to a second embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration of an apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 probe 20 transmission / reception circuit 21 transmission circuit 22 waveform generator 23 transmission amplifier 24 reception amplifier 25 A / D converter 26 DSP 27 inverse filter generator 28 reception circuit 29a filter (pass center frequency: f0) 29b filter (pass center) Frequency: 2f0) 31, 32 Logarithmic amplifier 41, 42 Envelope detector 43 Adaptive erasure unit 50 DSC 60 Display unit 70 Control unit 80 Operation unit

Claims (4)

[Claims] An ultrasonic imaging method for driving an ultrasonic transducer to transmit an ultrasonic wave into a subject and detecting a second harmonic component of an echo signal from the subject, comprising: An ultrasonic imaging method, comprising: adjusting a waveform so as to eliminate a second harmonic component in a signal; and transmitting an ultrasonic wave. 2. An ultrasonic imaging apparatus for driving an ultrasonic transducer to transmit an ultrasonic wave into a subject and detecting a second harmonic component of an echo signal from the subject, wherein the detected echo is An adjusting means for adjusting the waveform generation so that the signal has no second harmonic component; a frequency analysis of a detected echo signal waveform to compare a fundamental wave with a second harmonic; and a comparison result to the adjusting means. An ultrasonic imaging apparatus comprising: feedback means for feeding back; and transmission means for generating an ultrasonic wave having an adjusted waveform after imaging. 3. An ultrasonic imaging method for driving an ultrasonic vibrator to transmit an ultrasonic wave into a subject and detecting a second harmonic component of an echo signal from the subject, the method comprising: A fundamental wave component of the echo signal is detected with the second harmonic component of the signal attenuated, a first image signal is generated by the fundamental wave component of the echo signal, and a fundamental wave component of the echo signal is attenuated by the filter. The second harmonic component of the echo signal is detected in the state in which the second image signal is generated, a second image signal is generated by the second harmonic component of the echo signal, and the cross-correlation between the first image signal and the second image signal is detected. An ultrasonic imaging method comprising: subtracting a component of a first image signal from a second image signal in accordance with a predetermined ratio that minimizes, and removing a fundamental wave component included in an echo signal. 4. An ultrasonic imaging apparatus for driving an ultrasonic vibrator to transmit an ultrasonic wave into a subject and detecting a second harmonic component of an echo signal from the subject, wherein the ultrasonic imaging apparatus includes: A fundamental wave image signal generating means for detecting a fundamental wave component of the echo signal in a state where the second harmonic component of the signal is attenuated, and generating a first image signal based on the fundamental wave component of the echo signal; A second harmonic image signal generating means for detecting a second harmonic component of the echo signal in a state where the fundamental component of the signal is attenuated, and generating a second image signal from the second harmonic component of the echo signal; Subtracting the first image signal component from the second image signal according to a predetermined ratio that minimizes the cross-correlation between the first image signal and the second image signal, Subtraction means for removing; An ultrasonic imaging apparatus comprising: