JP2009011363A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic diagnostic apparatus capable of removing linear signal components and nonlinear signal components due to tissue from received echo signals and extracting only signal components practically due to an ultrasonic contrast medium. <P>SOLUTION: By transmitting ultrasonic waves having an up-chirp waveform and ultrasonic waves having a down-chirp waveform and executing subtraction processing using the echo signals due to them, the nonlinear components due to only the ultrasonic contrast medium are extracted. Thus, in a contrast echo method for injecting the contrast medium and detecting a contrasted image of and by the ultrasonic contrast medium at a low sound pressure so as not to destroy the ultrasonic contrast medium, echoes from the tissue are substantially reduced compared to the conventional one. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus used for acquiring an ultrasonic image related to a subject into which an ultrasonic contrast agent has been injected.

  An ultrasonic diagnostic apparatus is a diagnostic apparatus that displays an image of in-subject information, and is inexpensive, non-explosive, and non-invasive compared to other diagnostic imaging apparatuses such as an X-ray diagnostic apparatus and an X-ray computed tomography apparatus. It is used as a useful device for real-time observation. Due to such characteristics, the application range of the ultrasonic diagnostic apparatus is wide, and it is used for the diagnosis of circulatory organs such as the heart, abdomen such as the liver and kidney, peripheral blood vessels, obstetrics and gynecology, and cerebral blood vessels.

  In recent years, a contrast-enhanced echocardiogram that makes a diagnosis based on the difference in staining between normal tissue and abnormal tissue such as cancer when an ultrasound contrast agent (bubble) is injected into a subject has been launched. It is spreading with. The ultrasound contrast agent used in this technique is composed of a minute ultrasound contrast agent called a micro ultrasound contrast agent, thereby enhancing the reflection intensity of the ultrasound.

  In contrast, the imaging method using the contrast echo method uses a so-called pseudo Doppler effect that uses the disappearance or phase change of the ultrasound contrast agent between pulses, and the nonlinearity of the signal from the ultrasound contrast agent. It can be classified into methods.

  Since the method using the pseudo Doppler effect does not display an echo from a stationary tissue, only the signal from the contrast agent can be imaged. However, this method needs to disintegrate the ultrasonic contrast agent with a high sound pressure, and it is difficult to observe in real time continuously.

  On the other hand, in the imaging method using the nonlinearity of the signal from the ultrasonic contrast agent, a pulse having different amplitude and phase (or amplitude or phase) is transmitted a plurality of times in the same direction, and a linear signal is generated with respect to the echo signal. This is realized by multiplying by a coefficient that cancels. There are two methods in this method depending on the sound pressure used. One is a harmonic signal (a signal having a frequency that is an integral multiple of the fundamental wave) or a sub-harmonic signal (a signal having a frequency that is half that of the fundamental wave) generated by disrupting the ultrasound contrast agent with a high sound pressure. It uses an ultra-harmonic signal (a signal having a frequency that is a fraction of the fundamental wave). This method is not suitable for real-time observation because it destroys the ultrasound contrast agent. The other is a method that does not disrupt the ultrasound contrast agent with a low sound pressure. This method can be observed continuously in real time. As the signal, a harmonic signal or a nonlinear signal generated in the fundamental band is used.

In addition, as a well-known document relevant to this application, there exist the following, for example.
JP 2002-224111 A

  By the way, in the above-described imaging method using a low sound pressure that does not collapse, it is a problem to increase the contrast ratio between the ultrasonic contrast agent and the tissue. This is because it may be difficult to distinguish the signal from the ultrasound contrast agent and the signal from the tissue because nonlinear signals are also generated from the tissue. Particularly in the harmonic imaging method using the second harmonic, the problem is serious because the generation of nonlinear echo signals from the tissue is large. When the sound pressure is lowered, the proportion of the nonlinear signal from the tissue becomes smaller, but it still cannot be zero, so the problem cannot be avoided. By using the nonlinear signal in the fundamental band, the nonlinear signal from the tissue can be reduced as compared with the case where the second harmonic band is used, but it cannot be completely removed.

  Therefore, there is a need for an imaging method that displays an echo signal only from the ultrasound contrast agent by reducing the echo signal from the tissue as much as possible with a contrast method that does not destroy the ultrasound contrast agent with a low sound pressure.

  The present invention has been made in view of the above circumstances, and removes a linear signal component and a nonlinear signal component caused by tissue from a received echo signal, and extracts only a signal component substantially caused by an ultrasound contrast agent. An object of the present invention is to provide an ultrasonic diagnostic apparatus capable of performing the above.

  In order to achieve the above object, the present invention takes the following measures.

  A first aspect of the present invention is an ultrasonic diagnostic apparatus used for acquiring an ultrasonic image related to a subject into which a contrast medium has been injected, and the first ultrasonic wave whose frequency changes with time and the first Transmitting means for transmitting a second ultrasonic wave having a waveform obtained by reversing the waveform of the ultrasonic wave in the time direction at a predetermined time interval for each beam direction, and a first corresponding to the first ultrasonic wave And the second echo signal corresponding to the second ultrasonic wave, receiving means for pulse-compressing each of the echo signal, the compressed first echo signal, and the compressed second signal An ultrasonic diagnostic apparatus comprising: extraction means for extracting a signal caused by an ultrasonic contrast agent by executing a subtraction process using an echo signal.

  According to a second aspect of the present invention, there is provided an ultrasonic diagnostic apparatus used for acquiring an ultrasonic image related to a subject into which a contrast agent has been injected, the first ultrasonic wave having a temporally changing frequency, A second ultrasonic wave obtained by reversing the polarity of the first ultrasonic wave, a third ultrasonic wave having a waveform obtained by reversing the waveform of the first ultrasonic wave in the time direction, and the polarity of the third ultrasonic wave Transmitting means for transmitting the fourth ultrasonic wave having the inverted frequency at predetermined time intervals for each beam direction, the first echo signal corresponding to the first ultrasonic wave, and the second ultrasonic wave The second echo signal corresponding to the third ultrasonic signal, the third echo signal corresponding to the third ultrasonic wave, and the fourth echo signal corresponding to the fourth ultrasonic wave are received and pulse-compressed respectively. A receiving means; a sum of the first echo signal after compression and the fourth echo signal after compression; Extracting means for extracting a signal caused by the ultrasound contrast agent by executing a subtraction process using the sum of the second echo signal after compression and the third echo signal after compression; An ultrasonic diagnostic apparatus comprising:

  As described above, according to the present invention, an ultrasonic diagnosis that can remove only a signal component caused by an ultrasound contrast agent by removing a linear signal component and a nonlinear signal component caused by tissue from a received echo signal. An apparatus can be realized.

  Hereinafter, first and second embodiments of the present invention will be described with reference to the drawings. In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

(First embodiment)
FIG. 1 shows a block diagram of an ultrasonic diagnostic apparatus 1 according to this embodiment. As shown in the figure, the ultrasonic diagnostic apparatus 1 includes an apparatus main body 2 and an ultrasonic probe 3. The apparatus main body 2 includes an ultrasonic transmission unit 11, an ultrasonic reception unit 13, a signal processing unit 15, an image. A memory 17, a storage unit 19, an image generation unit 23, an image composition unit 25, a monitor 27, a control processor (CPU) 29, an interface unit 31, and an input unit 33 are provided.

  The ultrasonic probe 3 generates ultrasonic waves based on a drive signal from the apparatus body 2 and converts a reflected wave from the subject into an electric signal, a matching layer provided in the piezoelectric vibrator, It has a backing material that prevents the propagation of ultrasonic waves from the piezoelectric vibrator to the rear. When ultrasonic waves are transmitted from the ultrasonic probe 3 to the subject P, the transmitted ultrasonic waves are successively reflected by the discontinuous surface of the acoustic impedance of the body tissue and received by the ultrasonic probe 3 as an echo signal. . The amplitude of this echo signal depends on the difference in acoustic impedance at the discontinuous surface that is supposed to be reflected. In addition, the echo when the transmitted ultrasonic pulse is reflected by the moving blood flow or the surface of the heart wall depends on the velocity component in the ultrasonic transmission direction of the moving object due to the Doppler effect, and the frequency Receive a shift.

  The ultrasonic probe 3 is not limited to a one-dimensional array probe in which a plurality of piezoelectric vibrators are arranged in one direction, and may be capable of ultrasonic scanning, for example, a three-dimensional region of a subject. In such a case, the ultrasonic probe 3 has a configuration in which the transducer is mechanically swung along the direction orthogonal to the arrangement direction thereof and ultrasonically scans a three-dimensional region, or a two-dimensionally arranged two-dimensional vibrating element. And a structure for ultrasonically scanning a three-dimensional region by electrical control. When the former configuration is adopted, since the three-dimensional scanning of the subject is performed by the oscillation circuit, the examiner automatically acquires a plurality of two-dimensional tomographic images only by bringing the probe body into contact with the subject. can do. The exact distance between the sections can also be detected from the controlled rocking speed. When the latter configuration is adopted, in principle, a three-dimensional region can be ultrasonically scanned in the same time as acquiring a conventional two-dimensional tomographic image.

  The ultrasonic transmission unit 11 includes a trigger generation circuit, a delay circuit, a pulsar circuit, and the like (not shown). In the pulsar circuit, a rate pulse for forming a transmission ultrasonic wave is repeatedly generated at a predetermined rate frequency fr Hz (period: 1 / fr second). Further, in the delay circuit, a delay time necessary for focusing the ultrasonic wave into a beam shape for each channel and determining the transmission directivity is given to each rate pulse. The trigger generation circuit applies a drive pulse to the probe 3 at a timing based on this rate pulse.

  In addition, under the control of the control processor 29, the ultrasonic transmission unit 11 generates drive pulses for generating signals for canceling tissue nonlinear components (that is, an up-chirp waveform and a down-chirp waveform described later). , Applied to the probe 3.

  The ultrasonic receiving unit 13 performs amplification and phasing addition using the echo signal obtained from the ultrasonic probe 3, and performs quadrature detection to obtain an IQ signal. The IQ signal is assumed to be obtained as a digital signal. Further, when acquiring the IQ signal, the ultrasonic receiving unit 13 sets the center frequency to a fundamental wave band, a second harmonic band, or the like.

  As illustrated in FIG. 2, the signal processing unit 15 includes a pulse compression unit 150, a line buffer 151, an interline calculation unit 152, an envelope detection unit 153, and a logarithmic amplification unit 154.

  The pulse compression unit 150 performs pulse compression on the IQ signal received from the ultrasonic reception unit 13. The pulse compression circuit 150 is composed of, for example, a normal FIR type digital filter.

  The line buffer 151 includes a signal U (or U1, U2) obtained by pulse-compressing an echo signal obtained by up-chirp transmission and a signal D (or D1, D2) obtained by pulse-compressing an echo signal obtained by down-chirp transmission. ) Is temporarily stored.

  The inter-line operation unit 152 performs a subtraction operation UD on the signals on the same scanning line. Further, the inter-line operation unit 152 performs a subtraction operation (U1 + U2) − (D1 + D2) on the signals on the same scanning line.

  The envelope detection unit 153 performs envelope detection using the signal calculated by the interline calculation unit 152.

  The logarithmic amplification unit 154 logarithmically amplifies the signal after envelope detection.

  The image memory 17 temporarily stores various data received from the signal processing unit 15.

  The storage unit 19 is a recording medium such as a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), optical disk (CD-ROM, DVD, etc.), semiconductor memory, etc., and a device that reads information recorded on these media. . The storage unit 19 includes transmission / reception conditions, a predetermined scan sequence, a program for realizing a contrast agent-derived signal extraction function described later, a control program for executing image generation and display processing, and diagnostic information (patient ID, doctor ), Diagnostic protocol, body mark generation program, various signal data and image data, and other data groups. Data in the storage unit 19 can be transferred to an external peripheral device via the interface unit 31.

  The image generation unit 23 generates an ultrasound diagnostic image as a display image based on various data received from the signal processing unit 15 and the storage unit 19. The data before entering the image generation unit 23 may be referred to as “raw data”.

  The image synthesizing unit 25 synthesizes the image received from the image generating unit 23 together with character information of various parameters, scales, etc., and outputs it as a video signal to the monitor 27.

  Based on the video signal from the image synthesizing unit 25, the monitor 27 performs morphological information (B-mode image) in the subject, blood flow information (average velocity image, dispersion image, power image, etc.), and resolution optimization described later. Various map images obtained in the conversion process are displayed in a predetermined form.

  The control processor (CPU) 29 has a function as an information processing apparatus (computer) and controls the operation of the entire ultrasonic diagnostic apparatus. Further, the control processor 29 reads out a dedicated program for realizing the contrast agent-derived signal extraction function from the storage unit 35, a predetermined scan sequence, a control program for executing image generation / display, and the like on its own memory. And execute operations and controls related to various processes.

  The interface unit 31 is an interface related to the input unit 33, a network, and a new external storage device (not shown). Data such as ultrasonic images and analysis results obtained by the apparatus can be transferred by the interface unit 31 to another apparatus via a network.

  The input unit 33 includes various switches, buttons, a trackball, a mouse, and various switches for taking various instructions, conditions, a region of interest (ROI) setting instruction, various image quality condition setting instructions, and the like from the operator into the ultrasonic diagnostic apparatus 1. Has a keyboard. For example, when the operator operates the end button or the FREEZE button of the input unit 33, the transmission / reception of the ultrasonic wave is ended, and the ultrasonic diagnostic apparatus is temporarily stopped.

  The input unit 33 includes a switch for setting / changing various parameters used in the contrast agent-derived signal extraction function.

(Contrast agent-derived signal extraction function)
Next, the contrast agent-derived signal extraction function of the ultrasonic diagnostic apparatus 1 will be described. This function is an imaging method that does not destroy the ultrasound contrast agent with a low sound pressure, reduces the echo signal from the tissue as much as possible, and visualizes the image using the echo signal only from the ultrasound contrast agent.

  Hereinafter, an outline of the contrast agent-derived signal extraction function will be described with reference to FIGS. The waveforms and spectrum distributions shown in FIGS. 3 to 6 are shown in K. Morgan, J. Allen, P. Dayton, J. Chomas, A. Klibanov, K. Ferrara, “Experimental and Theoretical Evaluation of Microbubble Behavior: Effect. of Transmitted Phase and Bubble Size ”, IEEE Transactions on Ultrasonics, Ferroelectronics, and Frequency Control, Vol.47, No.6, pp.1494-1509, November 2000 Based on simulation.

  When the fundamental wave component from the tissue is reduced using the contrast agent-derived signal extraction function and only the fundamental wave component is extracted from the ultrasound contrast agent, for example, 2 for each beam direction (each scanning line). 1 times of ultrasonic transmission. In the first transmission, an ultrasonic wave having a waveform whose frequency increases with time as shown in FIG. 3A (referred to as an up-chirp waveform or an up-chirp signal) is used. In the second transmission, an ultrasonic wave having a waveform whose frequency decreases with time as shown in FIG. 3B (referred to as a down chirp waveform or a down chirp signal) is used. Note that the up-chirp waveform and the down-chirp waveform have the same amplitude and frequency only by the difference in which the time axis is inverted. Moreover, there is no limitation about the transmission order of an up chirp signal and a down chirp signal. For example, for one scanning line, the down chirp waveform may be transmitted in the first transmission, and the up chirp waveform may be transmitted in the second transmission.

  The received signal (echo signal) corresponding to each of the transmitted up-chirp waveform and down-chirp waveform is compressed by the pulse compression unit 110. Among the echo signals that have been pulse-compressed, the echo signal from the tissue has the same waveform for both the linear component (fundamental wave component) and the non-linear component including the second harmonic component. Of course, the linear fundamental wave components are the same. Further, the nonlinear component from the tissue is approximated by time differentiation of a signal obtained by squaring a transmission pulse (transmission waveform). If it does so, what compressed each echo signal corresponding to two chirp signals with which the time axis was reversed will become the same waveform. That is, for the non-linear component from the tissue, the same waveform as shown in FIG. 4B is obtained with the compressed echo signal corresponding to the up-chirp waveform and the compressed echo signal corresponding to the down-chirp waveform. It is done. Therefore, if both are subtracted, the nonlinear component from the tissue is cancelled.

  On the other hand, the echo signal from the ultrasound contrast agent has a different waveform when the compressed echo signal corresponding to the up-chirp waveform is compared with the compressed echo signal corresponding to the down-chirp waveform.

  FIG. 5A shows an echo signal from the ultrasonic contrast agent when an up-chirp waveform is transmitted. FIG. 5B shows the result of pulse compression of the echo signal shown in FIG. 5A with respect to a signal obtained by quadrature detection centering on the fundamental band. FIG.5 (c) has shown the echo signal from an ultrasonic contrast agent at the time of transmitting a down chirp waveform. FIG. 5D shows the result of pulse compression of a signal obtained by orthogonally detecting the echo signal shown in FIG. 5C around the fundamental band. Each of the waveforms shown in FIGS. 5A and 5C is a wideband signal, and includes a fundamental wave band, a second harmonic band, and other wide bands.

  FIG. 5 (e) shows the result of subtracting the signal of FIG. 5 (d) from the signal of FIG. 5 (b). Since the response to the ultrasound contrast agent differs between the up-chirp signal and the down-chirp signal, an echo signal as shown in FIG. 5E remains. There is a concern that the echo signal from such a bubble may not be pulse-compressed. However, when actually performed, it can be seen that pulse compression is performed. On the other hand, as described above, the echo from the tissue is canceled because the signals after compression of the up-chirp signal and the down-chirp signal completely coincide with each other (see FIG. 4).

  In addition, in the case where the second harmonic component from the tissue is reduced by using this contrast agent-derived signal extraction function and only the second harmonic component from the ultrasonic contrast agent is extracted, for example, the polarity is reversed. Two up-chirp waveforms and two down-chirp waveforms with reversed polarities are transmitted at predetermined time intervals for each beam direction (each scanning line).

  FIG. 6A shows echo signals from the respective ultrasonic contrast agents when two up-chirp signals (respectively indicated as up-chirp signal (+) and up-chirp signal (−)) having opposite polarities are transmitted. is there. FIG. 6B shows the second order of the signals of FIG. 6A (in this case, the echo signals corresponding to the up-chirp signal (+) and the up-chirp signal (−) whose polarity is inverted). Pulse compression is performed on each signal detected orthogonally around the harmonic band, and the results are added. As can be seen from the figure, it can be seen that the signal after the addition generates less unnecessary echo signals at the end than the echo signals before the addition.

  FIG. 6C shows echo signals corresponding to the up-chirp signal (+) and the up-chirp signal (−) whose polarity is similarly reversed. FIG. 6D shows the pulse compression result and the addition signal.

  Further, FIG. 6 (e) shows the result of subtracting the signal of FIG. 6 (d) from the signal of FIG. 6 (b). Thus, it can be seen that the ultrasonic contrast agent signal remains in the second harmonic band from the difference between the signals after up-chirp and down-chirp compression. Also in FIG. 6D, it can be seen that the signal after the addition generates less unnecessary echo signals at the end portion than the echo signals before the addition.

  Note that the signals shown in FIGS. 6A and 6C are wideband signals and include a fundamental band, a second harmonic band, and other wide bands.

  On the other hand, the second harmonic signal from the tissue is canceled because the difference between the compressed signal of the up-chirp signal and the down-chirp signal completely matches as described above. Therefore, only the signal from the ultrasound contrast agent remains.

  As described above, by echo compressing the echo signal obtained by transmitting the up-chirp signal and the down-chirp signal and subtracting both, the echo from the tissue can be canceled for both linear and nonlinear signals. Since the signal from the ultrasound contrast agent remains, the contrast ratio between the ultrasound contrast agent and the tissue can be increased.

(First embodiment)
Next, the operation of the ultrasonic diagnostic apparatus 1 when acquiring an ultrasonic image will be described. In the present embodiment, an example of imaging using a fundamental wave component is taken as an example.

  FIG. 7 is a flowchart showing the flow of each process executed when acquiring an ultrasonic image. As shown in the figure, first, the ultrasonic transmission unit 11 generates a drive signal for generating an up-chirp waveform and a down-chirp waveform, and supplies this to the ultrasonic probe 3 (step S1).

  The up-chirp waveform is generated by giving a Gaussian envelope as shown in the following formula (1), for example.

  The corresponding down chirp signal is generated by the following equation (2).

  Next, in response to the drive signal supplied from the ultrasonic transmission unit 11, the ultrasonic probe 3 applies ultrasonic waves having an up-chirp waveform and ultrasonic waves having a down-chirp waveform to each subject. It transmits at predetermined time intervals for each direction, and receives each echo signal (that is, each echo signal caused by each of the up-chirp waveform and down-chirp waveform) due to the transmission ultrasonic wave (step S2).

  Next, the ultrasonic receiving unit 13 generates an IQ signal expressed by the following equation by performing quadrature detection of the reflected echo of the up chirp from the point reflector around f0 (step S3). This IQ signal is assumed to be obtained as a digital signal.

  This signal can be compressed into a Gaussian waveform represented by the following equation (4) by giving an appropriate filter coefficient in the ultrasonic receiving unit 13.

  Note that filter coefficients are omitted for convenience of explanation.

  Similarly, the received IQ signal from the down-chirp point reflector can be expressed by the following equation (5).

  Next, the signal processing unit 15 performs pulse compression processing on each IQ signal corresponding to each of the up-chirp signal and the down-chirp signal (step S4). The pulse-compressed signal can be expressed by the following equation (6).

  Next, the signal processing unit 15 subtracts the down-chirp waveform after the pulse compression from the up-chirp waveform after the pulse compression, thereby canceling the linear component of the tissue component and extracting the signal from the ultrasound contrast agent. (Step S5). That is, the fundamental wave signal (linear component) from the tissue is canceled (cancelled) as shown in the following equation (7) from the equations (4) and (6).

  On the other hand, the signal from the ultrasonic contrast agent is extracted as the signal remains as shown in FIG. 6E in the subtraction process of the down-chirp waveform after the pulse compression from the up-chirp waveform after the pulse compression.

  Next, the image generation unit 23 generates an ultrasound image using the extracted signal from the ultrasound contrast agent (step S6). The generated ultrasonic image is combined with predetermined information in the image combining unit 25 and displayed in a predetermined form on the monitor 27 (step S7).

(Second embodiment)
Next, an operation of the ultrasonic diagnostic apparatus 1 according to the second embodiment when acquiring an ultrasonic image will be described. In the present embodiment, a case will be described in which the signal component from the tissue is reduced and the signal component from the ultrasound contrast agent is extracted and imaged in the second harmonic band.

  FIG. 8 is a flowchart showing the flow of each process executed when acquiring an ultrasonic image. As shown in the figure, first, the ultrasonic transmission unit 11 includes an up chirp waveform (+) having inverted polarities, an up chirp waveform (−), and a down chirp waveform (+) having inverted polarities, A drive signal for generating a down chirp waveform (-) is generated and supplied to the ultrasonic probe 3 (step S11).

  Note that the up-chirp waveform (+) is, for example, according to the equation (1), and the up-chirp waveform (−) is obtained by inverting the amplitude of the equation (1) (or by shifting the phase by 180 °). Can be represented by Similarly, the down chirp waveform (+) is obtained by, for example, equation (2), and the down chirp waveform (−) is obtained by inverting the amplitude of equation (2) (or by shifting the phase by 180 °). ).

  Next, the ultrasonic probe 3 responds to the drive signal supplied from the ultrasonic transmission unit 11 to the subject with an up-chirp waveform (+), an up-chirp waveform (−), and a down-chirp waveform (+). , Ultrasonic waves having respective waveforms of the down chirp waveform (−) are transmitted at predetermined time intervals in each beam direction, and echo signals (that is, up chirp waveform (+), up chirp) caused by the transmitted ultrasonic waves are transmitted. Each echo signal resulting from each of the waveform (−), the down chirp waveform (+), and the down chirp waveform (−) is received (step S12).

  Next, the ultrasonic receiving unit 13 receives each echo signal from the up-chirp waveform (+), up-chirp waveform (−), down-chirp waveform (+), and down-chirp waveform (−) from the point reflector. Are orthogonally detected using the center frequency as the second harmonic band, thereby generating IQ signals corresponding to the respective echo signals (step S13). Each IQ signal is obtained as a digital signal.

  Next, the pulse compression unit 150 of the signal processing unit 15 applies each IQ signal corresponding to each of the up-chirp waveform (+), the up-chirp waveform (−), the down-chirp waveform (+), and the down-chirp waveform (−). On the other hand, a pulse compression process is executed (step S14). The line buffer 151 includes a signal U1 obtained by pulse-compressing an IQ signal corresponding to the up-chirp waveform (+), a signal U2 obtained by pulse-compressing an IQ signal corresponding to the up-chirp waveform (−), and an IQ corresponding to the down-chirp waveform (+). The signal D1 obtained by pulse compression of the signal and the signal D2 obtained by pulse compression of the IQ signal corresponding to the down chirp waveform (−) are temporarily stored. The inter-line operation unit 152 performs an operation (U1 + U2) − (D1 + D2) on the same signal on the same scanning line, cancels the non-linear component from the tissue, and extracts the non-linear component from the ultrasound contrast agent. (Step S15).

  Next, the image generation unit 23 generates an ultrasound image using the extracted signal from the ultrasound contrast agent (step S6). The generated ultrasonic image is combined with predetermined information in the image combining unit 25 and displayed in a predetermined form on the monitor 27 (step S7).

  In addition, it is as follows when the process in step S13, S14, S15 described above is demonstrated using numerical formula. That is, the second harmonic from the tissue can be approximated by the time derivative of the square of the transmission pulse waveform. When described by an expression, it is as follows.

  By applying an appropriate pulse compression filter to a signal obtained by orthogonally detecting the echo signal in the second harmonic band, the following waveform is obtained. (Echo signals and filter coefficients in the second harmonic band are omitted because they are fairly long.)

  This is the same for all up-chirp waveforms (+), up-chirp waveforms (-), down-chirp waveforms (+), and down-chirp waveforms (-). The reason why the polarity (+) and the polarity (−) are the same is because it is squared. Also, the up-chirp waveform and the down-chirp waveform are the same because they are waveforms that are simply time-inverted.

  Therefore, the second harmonic signal generated from the tissue due to non-linear propagation is the same after compression with up-chirp and down-chirp. In this embodiment, in order to efficiently remove the fundamental wave signal, two transmissions of polarity (+ and polarity (−) are performed. For this reason, the fundamental wave signal is added by adding the signals whose polarities are inverted. The second harmonic signal from the tissue can be removed by the operation (U1 + U2) − (D1 + D2), while the echo signal from the ultrasound contrast agent is (U1 + U2) Even if the calculation of-(D1 + D2) is performed, the second harmonic component remains (see FIG. 6 (e)), so that only the signal from the ultrasound contrast agent can be detected in the second harmonic band.

  In the present embodiment, a total of four transmissions each having two polarities in the up-chirp waveform and the down-chirp waveform are performed, but the processing may be performed by two transmissions with only one polarity.

(effect)
According to the configuration described above, the following effects can be obtained.

  First, an ultrasonic wave having an up-chirp waveform and an ultrasonic wave having a down-chirp waveform are transmitted, and a subtraction process using an echo signal resulting from these is executed, thereby causing a linear component or non-linearity caused only by the ultrasonic contrast agent. Ingredients can be extracted. Therefore, the contrast echo method that detects the contrast of the ultrasound contrast agent with the ultrasound contrast agent without injecting the contrast agent and destroying the ultrasound contrast agent at a low sound pressure significantly reduces the echo from the tissue compared to the conventional method. Can be reduced. As a result, the accuracy of the echo signal being visualized being a signal from the ultrasound contrast agent is increased, and diagnosis can be facilitated.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Specific examples of modifications are as follows.

  Each function according to the present embodiment can also be realized by installing a program for executing the processing in a computer such as a workstation and developing the program on a memory. At this time, a program capable of causing the computer to execute the technique is stored in a recording medium such as a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), an optical disk (CD-ROM, DVD, etc.), or a semiconductor memory. It can also be distributed.

  In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  As described above, according to the present invention, an ultrasonic wave that can substantially remove only a signal component caused by an ultrasonic contrast agent by removing a linear signal component and a nonlinear new synthetic component caused by tissue from a received echo signal. A diagnostic device can be realized.

FIG. 1 shows a block diagram of an ultrasonic diagnostic apparatus 1 according to this embodiment. FIG. 2 is a block diagram of the signal processing unit 15. 3A shows an up-chirp signal (up-chirp waveform) whose frequency increases with time, and FIG. 3B shows a down-chirp signal (down-chirp waveform) whose frequency decreases with time. Show. FIG. 4A shows an example of the signal waveform of the fundamental wave subjected to pulse compression, and FIG. 4B shows an example of the signal waveform of the second harmonic wave subjected to pulse compression. FIG. 5 is a diagram for explaining extraction processing of a nonlinear component caused by the ultrasound contrast agent in the first embodiment. FIG. 6 is a diagram for explaining the extraction process of the nonlinear component due to the ultrasound contrast agent in the first embodiment. FIG. 7 is a flowchart showing the flow of each process executed when acquiring an ultrasound image according to the first embodiment. FIG. 8 is a flowchart showing the flow of each process executed when acquiring an ultrasonic image according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ultrasonic diagnostic apparatus, 2 ... Apparatus main body, 3 ... Ultrasonic probe, 11 ... Ultrasonic transmission unit, 13 ... Ultrasonic reception unit, 15 ... Signal processing unit, 17 ... Resolution optimization unit, 23 ... Image generation unit DESCRIPTION OF SYMBOLS 23 ... Image composition unit, 27 ... Monitor, 29 ... Control processor (CPU), 31 ... Interface unit, 33 ... Input unit, 35 ... Storage unit, 170 ... Contrast evaluation unit, 172 ... Calculation memory, 174 ... Optimum sound speed determination unit

Claims (4)

An ultrasound diagnostic apparatus used for acquiring an ultrasound image of a subject into which a contrast medium has been injected,
A first ultrasonic wave whose frequency changes with time and a second ultrasonic wave having a waveform obtained by reversing the waveform of the first ultrasonic wave in the time direction are transmitted at predetermined time intervals for each beam direction. Sending means to
Receiving means for receiving a first echo signal corresponding to the first ultrasonic wave and a second echo signal corresponding to the second ultrasonic wave, and pulse-compressing each;
An extraction means for extracting a signal caused by an ultrasound contrast agent by performing a subtraction process using the first echo signal after compression and the second echo signal after compression;
An ultrasonic diagnostic apparatus comprising: The first ultrasonic wave is an up chirp waveform whose frequency increases with time,
The second ultrasonic wave is a down chirp waveform with a frequency decreasing in time;
The ultrasonic diagnostic apparatus according to claim 1. An ultrasound diagnostic apparatus used for acquiring an ultrasound image of a subject into which a contrast medium has been injected,
A first ultrasonic wave whose frequency changes with time, a second ultrasonic wave whose polarity of the first ultrasonic wave is reversed, and a waveform obtained by reversing the waveform of the first ultrasonic wave in the time direction. Transmitting means for transmitting the third ultrasonic wave having the third ultrasonic wave and the fourth ultrasonic wave having the polarity of the third ultrasonic wave inverted at a predetermined time interval for each beam direction;
A first echo signal corresponding to the first ultrasonic wave; a second echo signal corresponding to the second ultrasonic wave; a third echo signal corresponding to the third ultrasonic wave; Receiving means for receiving a fourth echo signal corresponding to four ultrasonic waves, and pulse-compressing each;
The sum of the first echo signal after compression and the fourth echo signal after compression, and the sum of the second echo signal after compression and the third echo signal after compression were used. An extraction means for extracting a signal caused by the ultrasonic contrast agent by executing a subtraction process;
An ultrasonic diagnostic apparatus comprising: The first ultrasonic wave is an up chirp waveform whose frequency increases with time,
The third ultrasonic wave is a down chirp waveform with a frequency decreasing in time;
The ultrasonic diagnostic apparatus according to claim 3.

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