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DESCRIPTION JP2002034983

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DESCRIPTION JP2002034983
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates
generally to an ultrasonic transmission / reception method and an ultrasonic transmission /
reception apparatus using the same, and more particularly to subharmonic echo intensity using a
microbubble contrast agent. The present invention relates to an ultrasonic transmission /
reception method for detecting Further, the present invention relates to an ultrasonic processing
apparatus and a recording medium recording an ultrasonic processing program for processing a
reception signal obtained by detecting the ultrasonic wave in transmission and reception of such
ultrasonic waves.
[0002]
2. Description of the Related Art In recent years, ultrasonic diagnosis has remarkably advanced in
the diagnosis of chest and abdominal regions because it has a feature that blood flow information
can be obtained. In particular, as ultrasound imaging technology using a contrast agent has been
developed, more accurate blood flow information has come to be obtained. In such ultrasound
imaging, a microbubble contrast agent in which a large number of microbubbles having a
diameter of 1 to several μm are mixed in a liquid is mainly used by injecting it into a vein. The
microbubbles are obtained by sealing a gas (air, fluorocarbon or the like) harmless to the living
body in a shell made of a substance (lecithin or the like) harmless to the living body.
[0003]
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1
In Japanese Patent Application Laid-Open No. 9-164138, an ultrasonic contrast agent of
microbubbles is injected into the blood stream, and an ultrasonic pulse for breaking
microbubbles in tissue is emitted. An ultrasonic diagnostic imaging method has been published,
which measures by ultrasound the extent to which microbubbles have been reperfused into the
tissue during a certain time interval after the destruction of the microbubbles.
[0004]
Further, in ultrasonic transmission / reception technology, use of Doppler signals and harmonic
signals has progressed, and blood flow information can be acquired in more tissues.
In particular, the combination with ultrasound imaging has allowed more accurate assessment of
hemodynamics.
[0005]
Japanese Patent Application Laid-Open No. 11-178824 discloses a transmitting step of
transmitting a sequence of modulated ultrasonic waves into the body and causing a phase
difference to an ultrasonic echo obtained as a response, and responding to the transmitting
sequence. A pulse inversion Doppler ultrasound diagnostic imaging method is described which
comprises the steps of receiving a set of ultrasound echo signals and analyzing the set to
separate phase shift information of linear and non-linear signal components. However, in
detection of such Doppler signals, it is not possible to detect only microbubbles in blood vessels,
since strong signals from large moving tissue such as the myocardium and harmonic signals
generated from the tissue itself are mixed. .
[0006]
Further, US Pat. No. 5,706,819 suppresses the harmonic components of the transmission signal
and scatters by receiving the influence of the harmonic contrast agent while alternately inverting
the polarity (phase). An ultrasonic diagnostic imaging method is disclosed to remove the and to
detect the effects of harmonic contrast agents. However, in order to perform such harmonic
image processing, it is necessary to transmit a plurality of ultrasonic waves of different polarities
(phases), and it takes time for measurement, so if the object moves during that time, the space of
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the image There is a problem that the resolution is lowered.
[0007]
On the other hand, so-called subharmonic imaging in which an image is generated based on
subharmonic (subharmonic) echoes generated only from microbubbles in blood vessels by
irradiating ultrasonic waves having a plurality of continuous waves. Is beginning to be
considered. Since subharmonic components are generated only by the chaotic vibration and
bifurcation of microbubbles, subharmonic imaging is considered to provide contrast
enhancement higher than harmonic imaging.
[0008]
As for sub-harmonic echoes of microbubbles, see P. M. Shankar et al. Acoust. Soc. Am. , 106
(4), 2104 (1999), it is known to be generated by continuous ultrasound, and in order to perform
sub-harmonic imaging, a plurality of continuous burst waves are known. Ultrasonic waves
containing waves are used. However, when a plurality of continuous waves such as burst waves
are used for a long time, one set of waves becomes long, and the spatial resolution of the image is
also degraded.
[0009]
Japanese Patent Application Laid-Open No. 2000-5167 discloses that when transmitting
ultrasonic waves having a plurality of continuous waves, at least one of the waves having an
instantaneous sound pressure which does not destroy the microballoon (microbubbles). An
ultrasonic wave transmission method is disclosed that transmits an ultrasonic wave in which
waves having instantaneous sound pressure that destroys the microballoon are present before
and after, respectively, to reliably generate a subharmonic echo. However, in order to detect a
subharmonic containing a large amount of long wavelength components with respect to the
transmission wave, further improvement is desired including processing of the received signal.
[0010]
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As a method of detecting the subharmonic intensity, a method of performing fast Fourier
transform (FFT) on the received waveform is used, but the problem is that it is not suitable for
real-time image display because the operation time is long according to FFT. There is. In addition,
according to the method of circuit-like filtering to extract subharmonic frequency components,
subharmonic harmonic components are extracted between fundamental waves and harmonics
and exist at multiple frequencies, so only subharmonics should be extracted. It is difficult.
[0011]
SUMMARY OF THE INVENTION In view of the above, it is therefore an object of the present
invention to ensure that subharmonic echoes are generated with high reliability and to display
subharmonic information at a speed close to real time. Abstract: An ultrasonic transmitting and
receiving method and an ultrasonic transmitting and receiving apparatus are provided.
Furthermore, an object of the present invention is to provide an ultrasonic processing apparatus
used in such ultrasonic transmission and reception and a recording medium recording an
ultrasonic processing program.
[0012]
SUMMARY OF THE INVENTION In order to solve the above problems, the ultrasonic transmission
and reception method according to the present invention comprises the steps of: transmitting
ultrasonic waves of four or more consecutive cycles to a subject; Detecting an echo generated by
reflection of the sound wave on the tissue of the subject to obtain a reception signal; and
delaying the reception signal by a time corresponding to one period of the transmitted
ultrasound to obtain a delayed reception signal. Extracting the sub-harmonic component of the
echo based on the difference between the received signal and the delayed received signal.
[0013]
Also, the ultrasonic transmitting and receiving apparatus according to the present invention
transmits ultrasonic waves of four or more consecutive cycles to the subject, and detects and
receives echoes produced by reflection of the transmitted ultrasonic waves on the tissue of the
subject. A subharmonic component of echo based on a means for obtaining a signal, a means for
obtaining a delayed received signal by delaying the received signal by a time corresponding to
one period of the transmitted ultrasonic wave, and a difference between the received signal and
the delayed received signal And means for extracting
[0014]
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Further, in the ultrasonic processing apparatus according to the present invention, processing of
a received signal obtained by detecting an echo generated by transmitting ultrasonic waves of
four or more consecutive cycles to the subject and reflecting the tissue of the subject is obtained.
Means for obtaining a delayed reception signal by delaying the reception signal by a time
corresponding to one period of the transmitted ultrasonic wave, and an echo based on the
difference between the reception signal and the delayed reception signal. And means for
extracting the subharmonic component of
[0015]
In addition, the recording medium recording the ultrasonic processing program according to the
present invention is obtained by detecting an echo that is generated when ultrasonic waves of
four or more consecutive cycles are transmitted to the subject and reflected by the tissue of the
subject. A recording medium readable by the CPU to process the received signal, and delaying
the received signal by a time corresponding to one period of the transmitted ultrasonic wave to
obtain a delayed received signal; And causing the CPU to execute a procedure of extracting a
subharmonic component of the echo based on the difference between the signal and the delayed
reception signal.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described in detail below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of an ultrasonic transmitting and receiving
apparatus according to an embodiment of the present invention.
[0017]
As shown in FIG. 1, the ultrasonic transmitting and receiving apparatus has an ultrasonic probe
20 including an ultrasonic transducer array constituted by a plurality of ultrasonic transducers.
The ultrasonic probe 20 is used by being in contact with the subject 10 by the operator.
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The micro bubble contrast agent is previously injected into the subject 10, and the micro bubble
100 is contained.
[0018]
The ultrasonic probe 20 is connected to the transmitting and receiving unit 30.
In the transmission / reception unit 30, the transmission timing generation circuit 322
periodically generates a transmission timing signal and supplies the transmission timing signal to
the transmission beam former 321. The transmission beam former 321 generates a plurality of
drive signals (transmission beam forming signals) for driving the plurality of ultrasonic
transducers of the ultrasonic probe 20 with a time difference based on the transmission timing
signal, and the transmission / reception switching circuit 311 To the ultrasonic probe 20 via The
waveforms of these drive signals are selected such that the sound pressure waveform of the
transmitted ultrasonic wave has a waveform described later. The plurality of ultrasonic
transducers that constitute the transmission aperture of the ultrasonic probe 20 respectively
transmit, to the subject 10, a plurality of ultrasonic waves having a phase difference
corresponding to the time difference of these drive signals. An ultrasonic beam is formed by such
wavefront synthesis of a plurality of ultrasonic waves.
[0019]
On the other hand, the ultrasonic probe 20 receives the ultrasonic wave (echo) reflected from the
object 10, converts it to an electric signal, and outputs it to the reception beam former 331
through the transmission / reception switching circuit 311. Do. As described above, a plurality of
echo signals received by the plurality of ultrasonic transducers constituting the reception
aperture of the ultrasonic probe 20 are input to the reception beam former 331. The receive
beamformer 331 applies a time difference to a plurality of receive echoes to adjust the phase,
and then adds them to form an echo receive signal along the acoustic ray, that is, performs
beamforming of the receive wave. It is supposed to be. The receiving beam former 331 scans the
sound ray of the receiving wave according to the transmission.
[0020]
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The ultrasonic beam transmitted by the ultrasonic probe 20 is set so as to generate a continuous
wave which forms, for example, the sound pressure waveform shown in FIG. As shown in FIG. 2,
this sound pressure waveform is a continuous wave for n periods (wavelengths) (n is an integer
of 4 or more). The subharmonic is a sound wave having a wavelength of n / m times the
transmission wavelength λ (m is a natural number and n and m are independent), and in
particular, a sound wave having a wavelength of m = 2 tends to appear strongly is there.
[0021]
In the above, preferably, 4 ≦ n ≦ 5 × 10 4, and the continuous waves include waves of 4 cycles
or more and 50,000 cycles or less. Here, the reason why the number of cycles is four or more is
to facilitate generation of the subharmonics. Moreover, the reason for setting the period to
50,000 cycles or less is to prevent waves reflected back from the object from becoming
interference. In the case of using an ultrasonic wave of 1 MHz, 50,000 cycles correspond to 1/20
second. Further, the upper limit of the number of periods of continuous waves is more preferably
10,000 wavelengths or less, and further preferably 1,000 wavelengths or less. FIG. 3A shows an
example of the waveform of such a transmission wave. Further, FIG. 3 (b) shows an example of an
echo waveform of a micro bubble generated by this transmission wave.
[0022]
The transmission of the ultrasonic beam is repeated at predetermined time intervals by the
transmission timing signal generated by the transmission timing generation circuit 322 shown in
FIG. The direction of the ultrasonic beam is sequentially changed by the transmission beam
former 321. Thereby, the inside of the subject 10 is scanned by the sound rays formed by the
ultrasonic beam. That is, in the inside of the subject 10, the direction of the sound ray changes
sequentially. The transmission / reception unit 30 having such a configuration performs, for
example, a scan as shown in FIG. In FIG. 4, an ultrasonic beam (sound ray 202) extending from
the radiation point 200 in the z-direction scans the fan-shaped two-dimensional area 206 in the
θ-direction to perform a so-called sector scan.
[0023]
On the other hand, when transmitting and receiving apertures are formed using a part of the
ultrasonic transducer array, the apertures are moved sequentially along the ultrasonic transducer
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array, as shown in FIG. 5, for example. It is possible to do such a scan. In FIG. 5, the rectangular
two-dimensional area 206 is scanned in the x direction by translating the sound rays 202
extending in the z direction from the radiation point 200 along the straight locus 204, and socalled linear scanning is performed. .
[0024]
When the ultrasonic transducer array is a so-called convex array formed along a circular arc
extending in the ultrasonic wave transmission direction, as shown in FIG. Scan can be performed.
In FIG. 6, the radiation point 200 of the sound ray 202 is moved along an arc-shaped locus 204
centered on the diverging point 208, and the fan-shaped two-dimensional area 206 is scanned in
the θ direction, so-called convex scan I do.
[0025]
Referring again to FIG. 1, the reception beam former 331 is connected to the fundamental wave
processing unit 401 and the subharmonic processing unit 402 of the signal processing unit 40.
The fundamental wave processing unit 401 and the subharmonic processing unit 402 process
the received echo reception signal for each sound ray, and output the processed reception signal
to the image processing unit 403. The image processing unit 403 generates a B-mode image
obtained by performing luminance modulation with the strength of the received wave based on
the processed received signal. Here, the subharmonic processing unit 402 extracts a
subharmonic signal from the reception signal input from the reception beam former 331, using a
method described later.
[0026]
FIG. 7 shows a part of the configuration of the subharmonic processing unit 402. As shown in
FIG. In FIG. 7, the delay circuit 1 delays the reception signal by the transmission basic period τ.
The difference circuit 2 extracts and outputs the subharmonic signal by obtaining the difference
between the received signal and the delayed received signal. Each of the fundamental wave
processing unit 401 to the image processing unit 403 shown in FIG. 1 may be configured by an
analog circuit or may be configured by a digital circuit. Alternatively, it may be configured by
software and a CPU. In that case, the control unit 60 including the CPU processes the received
signal based on the ultrasonic processing program recorded in the recording medium 70. As the
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recording medium 70, a floppy disk, a hard disk, an MO, an MT, a RAM, a CDROM, a DVDROM, or
the like corresponds.
[0027]
Next, a method of extracting a subharmonic signal in the present embodiment will be described
with reference to FIG. FIG. 8 is a waveform diagram for explaining processing of a received wave
in the fundamental wave processing unit. The echo of the micro bubble is as shown by a
waveform R1 shown in FIG. This waveform R1 is delayed by the basic period τ of the
transmission wave to create a waveform R2. Next, the difference between the waveform R1 and
the waveform R2 is obtained to obtain the waveform RSUB of the sub-harmonic signal. The echo
of the transmission ultrasonic wave is formed by the sum of the fundamental wave, the
harmonics and the subharmonic signal. Here, since the fundamental wave and the harmonics
have a waveform in which the basic period τ of the transmission wave is a repeating unit, they
are removed by the above-described signal processing. As a result, only the subharmonic signal
remains.
[0028]
The fundamental wave processing unit 401 shown in FIG. 1 detects a fundamental wave echo
(received wave having the same frequency as the fundamental frequency of the transmitted
wave) obtained from the received wave, and amplifies the detected signal using logarithmic
amplification and envelope detection. By doing this, a signal representing the intensity of the
echo at each reflection point on the sound line, that is, an A-scope signal is obtained. The
fundamental wave processing unit 401 forms B-mode image data by using the instantaneous
amplitude at each time point of the A scope signal as the respective luminance value.
[0029]
A subharmonic processing unit 402 shown in FIG. 1 performs logarithmic amplification and
envelope detection on the subharmonic echo obtained from the received wave, thereby
representing a signal representing the intensity of the echo at each reflection point on the sound
line, ie, A Get scope signal. The subharmonic processing unit 402 forms B-mode image data with
the instantaneous amplitude at each time point of the A-scope signal as the respective luminance
value.
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[0030]
The fundamental wave processing unit 401 and the subharmonic processing unit 402 are
connected to the image processing unit 403. The image processing unit 403 generates a plurality
of B mode images based on the B mode image data input from the fundamental wave processing
unit 401 and the sub harmonic processing unit 402, respectively. This operation will be
described in detail below.
[0031]
The B-mode image data by the fundamental wave echo and the subharmonic echo inputted from
the fundamental wave processing unit 401 and the subharmonic processing unit 402 for each
sound ray are stored in the sound ray data memory in the image processing unit 403. Ru. Each
sound ray data space is formed in the sound ray data memory. The sound ray data space in the
sound ray data memory is converted from data in the sound ray data space to data in the
physical space by scan conversion of a digital scan converter (DSC) 404. The image data
converted by the DSC 404 is stored in the image memory 405. An image memory 405 stores
image data of the physical space. The data of the sound ray data memory and the image memory
405 are subjected to predetermined data processing by the image processing processor.
[0032]
A display unit 50 is connected to the image memory 405. The display unit 50 displays an image
based on the image data of the physical space stored in the image memory 405. The display unit
50 is desirably capable of displaying a color image.
[0033]
The transceiver unit 30 and the signal processing unit 40 shown in FIG. 1 are connected to the
control unit 60. The control unit 60 supplies control signals to these units to control their
operation. Further, various notification signals are input to the control unit 60 from these units.
Ultrasonic imaging is performed under the control of the control unit 60. Furthermore, the
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control unit 60 includes an operation unit. The operation unit is operated by the operator to
input desired commands and information to the control unit. The operation unit is configured of,
for example, an operation panel provided with a keyboard and other operation tools.
[0034]
Next, the operation of the ultrasonic transmitting and receiving apparatus according to the
present embodiment will be described. The operator brings the ultrasonic probe 20 into contact
with a desired portion of the subject 10 and operates the operation unit to perform imaging.
Under the control of the control unit 60, ultrasonic waves are transmitted / received while
sequentially scanning sound rays to perform imaging. For example, while sequentially scanning
sound rays by sector scanning as shown in FIG. 4, an ultrasonic beam is transmitted for each
sound ray, its echo is received, and a B-mode image is received based on an echo reception wave.
Generate Of course, the linear scan or the convex scan as shown in FIG. 5 or 6 may be performed.
[0035]
The ultrasonic beam transmitted at this time has, for example, the sound pressure waveform
shown in FIG. 2, and continuously vibrates the microbubbles 100 to surely generate a
subharmonic echo. B-mode image data is formed based on the echo reception wave at each
sound ray. As the B-mode image data, one based on the fundamental wave echo and one based
on the sub-harmonic echo are respectively formed, and are stored in the sound ray data memory
in the image processing unit 403. Sound ray data in the sound ray data memory is scan
converted by the DSC 404 and written in the image memory 405. The operator scans the
operation unit and causes the display unit 50 to display these B mode images. For example, as
shown in FIG. 9, the display 110 of the display unit displays a composite image of the tomogram
111 of the tissue obtained based on the fundamental wave echo and the image 112 obtained
based on the sub-harmonic echo of the microbubbles. Let
[0036]
In the above embodiment, an example in which B-mode imaging is performed using subharmonic echo has been described, but ultrasonic imaging is not limited to B-mode imaging, and
Doppler shift of sub-harmonic echo is used. The dynamic image may be captured.
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[0037]
As described above in detail, according to the present invention, ultrasonic wave transmission
and reception capable of displaying subharmonic information at a speed close to real time with
high reliability of subharmonic echo generation. It can be realized.
[0038]
Brief description of the drawings
[0039]
1 is a block diagram showing an ultrasonic transmitting and receiving apparatus according to an
embodiment of the present invention.
[0040]
2 is a diagram showing the sound pressure waveform of the ultrasonic wave transmitted from
the ultrasonic transmitting and receiving apparatus according to an embodiment of the present
invention.
[0041]
Fig.3 (a) is a figure which shows the example of the waveform of the transmission wave in one
Embodiment of this invention, (b) is a figure which shows the example of the echo waveform of
the micro bubble produced by this transmission wave.
[0042]
4 is a diagram showing an example of sound ray scanning in the ultrasonic transmitting and
receiving apparatus according to an embodiment of the present invention.
[0043]
5 is a diagram showing another example of sound ray scanning in the ultrasonic transmitting and
receiving apparatus according to an embodiment of the present invention.
[0044]
<Figure 6> It is the figure which shows furthermore the other example of sound ray scan in the
ultrasonic transmitting and receiving device which relates to one execution form of this
invention.
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[0045]
7 is a block diagram showing a part of the configuration of the sub-harmonic processing unit of
FIG.
[0046]
8 is a waveform diagram for explaining the processing of the received wave in the sub-harmonic
processing unit of FIG.
[0047]
9 is a view showing an example of a display image in the ultrasonic transmitting and receiving
apparatus according to an embodiment of the present invention.
[0048]
Explanation of sign
[0049]
Reference Signs List 1 delay circuit 2 difference circuit 10 object 20 ultrasonic probe 30
transmitting / receiving unit 40 signal processing unit 50 display unit 60 display unit 70
recording medium 100 micro bubble 110 display 111 display unit 111 tomogram of tissue 112
subharmonic echo of micro bubble Based on the image 200, the radiation point 202, the sound
ray 204, the locus 206, the two-dimensional area 208, the divergence point 311, the
transmission / reception switching circuit 321, the transmission beam former 322, the
transmission timing generator 331, the reception beam former 401, the fundamental wave
processor 402 403 image processing unit 404 digital scan converter (DSC) 405 image memory
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