JP4070339B2 - Ultrasonic imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic imaging method and apparatus, and more particularly, to an ultrasonic imaging method and apparatus using a microballoon as a contrast agent.
[0002]
[Prior art]
A microballoon is used as a contrast agent for ultrasonic imaging. The microballoon is a microcapsule made of a substance that is harmless to a living body, in which gas is sealed. This is injected into the subject, the microscopic balloon is broken by irradiating the collection site with ultrasonic waves, and imaging is performed using the released gas bubble. For this reason, in imaging, an ultrasonic wave for destroying the microballoon is irradiated on the imaging range, and then the imaging range is scanned with the ultrasonic wave to receive an echo, and an image is generated based on the echo reception signal.
[0003]
[Problems to be solved by the invention]
As described above, in the method of first irradiating the imaging range with ultrasonic waves for destroying the microballoon and then scanning the imaging range with ultrasound again to receive echoes, until the imaging is performed after the microballoon is destroyed In this case, there is a problem that it is impossible to image a very short-lived gas bubble that disappears within a few μs after generation.
[0004]
The present invention has been made to solve the above-described problems, and an object thereof is to realize an ultrasonic imaging method and apparatus for imaging a gas bubble having a short lifetime.
[0005]
[Means for Solving the Problems]
(1) According to a first invention for solving the above problem, the imaging range in the subject into which the microballoon has been injected is irradiated with a continuous first ultrasonic wave that does not destroy the microballoon, A first pulse-like ultrasonic wave that destroys the microballoon is transmitted along a sound ray that passes through the first ultrasonic wave, and the first ultrasonic wave is returned from a reflection point on the sound ray after the second ultrasonic wave has passed. An ultrasonic imaging method is characterized in that an image is generated based on an echo to an ultrasonic wave.
[0006]
(2) A second invention that solves the above-described problem is an ultrasonic irradiation unit that irradiates a continuous first ultrasonic wave that does not destroy the microballoon into an imaging range in a subject into which the microballoon is injected. Ultrasonic transmitting means for transmitting a pulsed second ultrasonic wave for breaking the microballoon along a sound ray passing through the imaging range; and the sound after the second ultrasonic wave has passed. An echo receiving means for receiving an echo for the first ultrasonic wave returned from a reflection point on a line, and an image generating means for generating an image based on the echo received by the echo receiving means It is an ultrasonic imaging apparatus.
[0007]
(3) A third invention for solving the above-mentioned problem is the ultrasonic imaging apparatus according to (2), wherein the frequency of the second ultrasonic wave is different from that of the first ultrasonic wave. .
[0008]
(Function)
In the present invention, since continuous ultrasonic waves are constantly applied to the imaging range, an echo is immediately generated from a gas bubble generated after the ultrasonic pulse has passed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the ultrasonic imaging apparatus. This apparatus is an example of an embodiment of the present invention. An example of an embodiment relating to the apparatus of the present invention is shown by the configuration of the apparatus. An example of an embodiment related to the method of the present invention is shown by the operation of the apparatus.
[0010]
As shown in the figure, this apparatus has ultrasonic transducers 22, 24 and 26. The ultrasonic transducers 22, 24, and 26 are supported by support means (not shown) while maintaining the mutual relationship described later, and constitute an ultrasonic probe (probe) 2.
[0011]
The ultrasonic transducer 22 is driven by a pulse driving unit 62 and transmits an ultrasonic pulse into the subject 4. The ultrasonic pulse is an example of an embodiment of the second ultrasonic wave in the present invention. The ultrasonic transducer 22 and the pulse driving unit 62 are an example of an embodiment of the ultrasonic wave transmission means in the present invention. A microballoon contrast medium is injected into the subject 4 in advance to form a microballoon assembly site 40. The ultrasonic pulse has an intensity capable of breaking the microballoon at the microballoon assembly site 40.
[0012]
The ultrasonic transducer 24 is driven by a CW (continuous wave) driving unit 64 and irradiates the subject 4 with CW ultrasonic waves. CW ultrasound is an example of an embodiment of the first ultrasound in the present invention. The ultrasonic transducer 24 and the CW driving unit 64 are an example of an embodiment of ultrasonic irradiation means in the present invention. The CW ultrasonic wave has an intensity that does not destroy the microballoons at the microballoon assembly site 40.
[0013]
The ultrasonic transducer 26 receives an ultrasonic echo returned from within the subject 4 and inputs an echo reception signal to the echo receiving unit 66. The ultrasonic transducer 26 and the echo receiver 66 are an example of an embodiment of the echo receiving means in the present invention.
[0014]
FIG. 2 shows a schematic configuration of the ultrasonic transducers 22, 24, and 26. In FIG. 2, when three directions perpendicular to each other are x, y, z and the z direction is the depth direction of the subject 4, the ultrasonic transducer 22 is a plurality of transducer elements 22i arranged in the x direction. Have The transducer element 22i is made of a piezoelectric material such as PZT (titanium (Ti) zirconate (Zr) lead acid (Pb)) ceramics. Similarly, the ultrasonic transducers 24 and 26 have a plurality of transducer elements 24i and 26i arranged in the x direction, respectively.
[0015]
The ultrasonic transducers 24 and 26 are arranged adjacent to each other in the y direction. The ultrasonic transducers 22 are arranged adjacent to them in the x direction. The ultrasonic transducers 22, 24, and 26 are supported by support means (not shown) while maintaining such a mutual relationship.
[0016]
The individual transducer elements 24 i of the ultrasonic transducer 24 are simultaneously driven by the CW driving unit 64 to generate CW ultrasonic waves having the same phase. The imaging range 30 is irradiated with plane wave CW ultrasonic waves by wavefront synthesis of these CW ultrasonic waves. The frequency of the CW ultrasonic wave is preferably matched with the resonance frequency of a gas bubble to be described later emitted from the microballoon from the viewpoint of imaging only the gas bubble using the second harmonic echo.
[0017]
Regardless of the coincidence or mismatch with the resonance frequency, it is possible to image using the fundamental wave echo. Further, the CW ultrasonic wave is not necessarily a complete CW, and may be an ultrasonic wave having a long continuous generation period such as a long burst wave. Hereinafter, although an example of CW ultrasonic waves will be described, the same applies when a long burst wave or the like is used.
[0018]
Each transducer element 26 i of the ultrasonic transducer 26 receives an echo returned from the imaging range 30 and inputs an echo reception signal to the echo receiver 66. The imaging range 30 includes a microballoon assembly site 40. The echo receiving unit 66 is provided with a second harmonic filter as necessary.
[0019]
Each transducer element 22i of the ultrasonic transducer 22 is driven by a pulse driving unit 62 to generate an ultrasonic pulse. An ultrasonic beam (beam) 32 is transmitted to the imaging range 30 by wavefront synthesis of these ultrasonic pulses. The direction of the ultrasonic beam (sound ray) 32 is set by a time difference for driving each transducer element. Further, by sequentially switching the orientation, acoustic beam sequential ultrasonic beam scanning is performed within the imaging range 30, and the microballoons at the microballoon assembly site 40 are destroyed. It is preferable that the frequency of the ultrasonic pulse is different from the frequency of the CW ultrasonic wave in terms of blocking the echo of the ultrasonic pulse with a filter. The blocking filter is provided in the echo receiving unit 66, for example.
[0020]
As an ultrasonic wave for breaking the microballoon, for example, as shown in FIG. 3A, an ultrasonic wave having a negative pressure in the first half cycle (cycle) is transmitted. Such an ultrasonic wave can be generated, for example, by a drive signal having the first half cycle as a negative electrode. When such an ultrasonic wave is applied to the microballoon, it is easily broken by a cavitation effect caused by a negative pressure. The higher the hardness of the microballoon, the easier it is to break by negative pressure.
[0021]
Due to the nonlinearity of the ultrasonic wave propagation within the subject 4, for example, as shown in FIG. 3B, the instantaneous sound pressure waveform tends to have a negative period extending as it progresses. The extension of the negative period lengthens the application time of the negative pressure, which has an advantageous effect on the destruction of the microballoon. For this reason, the microballoon can be destroyed even with a relatively low instantaneous sound pressure. In addition, it is advantageous in that the positive portion of the instantaneous sound pressure waveform is steep in that the destruction is accelerated.
[0022]
On the other hand, as shown in FIG. 4 (a), when a positive ultrasonic wave is used in the first half cycle, even if there is a nonlinearity of propagation, it is positive as shown in FIG. 4 (b). Although the portion becomes steep, the interval between them does not change. Therefore, the period of the negative pressure does not increase, so that the destruction effect of the microballoon is inferior to the case of FIG. Therefore, when the first half cycle uses a positive ultrasonic wave, the instantaneous sound pressure level of the transmitted ultrasonic wave is set high so that a sufficient destruction effect can be obtained.
[0023]
Such ultrasonic waves travel on the sound ray 32 while destroying the microballoons. As the microballoon is broken, gas bubbles are sequentially released on the sound ray 32. The gas bubble generates an echo immediately after it is generated because the CW ultrasonic wave is continuously irradiated from the ultrasonic transducer 24.
[0024]
A schematic diagram of such echo generation is shown in FIG. As shown in the figure, when the ultrasonic pulse 34 passes on the sound ray 32, echoes are generated from the gas bubbles 42, 44, 46 sequentially generated on the sound ray 32, respectively. Circles 42 ', 44' and 46 'represent the wavefront positions of the respective echoes. The figure shows the moment when the wavefront 42 ′ of the echo generated from the gas bubble 42 reaches the transducer element 26 j having the shortest distance in the ultrasonic transducer 26. At this time, the echo generated from the gas bubble 44 is in the middle of propagation, and the echo is just generated in the gas bubble 46.
[0025]
The echo wavefront 42 'sequentially reaches the other transducer elements 26i as it progresses. The arrival time of the wavefront corresponds to the distance from the gas bubble 42 to each transducer element 26i. The echo wavefronts 44 ′ and 46 ′ also sequentially reach the ultrasonic transducer 26 as they travel. The arrival times of these wavefronts correspond to the distances from the gas bubbles 44 and 46 to the transducer elements 26i and the generation time differences of the gas bubbles. Each transducer element 26i of the ultrasonic transducer 26 receives such echoes in time series.
[0026]
The echo receiving unit 6 is connected to a data processing unit 8. An echo reception signal as an RF (radio frequency) signal is input from the echo reception unit 6 to the data processing unit 8 as digital data. The data processing unit 8 processes the input echo data to generate an image. The data processing unit 8 is an example of an embodiment of the image generation means in the present invention.
[0027]
As shown in FIG. 6, the data processing unit 8 includes a data processing processor 80, an echo memory 82, a data memory 84, and an image memory 86. These are connected by a bus 88. Time-series echo data for each transducer element 26 i (hereinafter simply referred to as “element”) input from the echo receiver 6 is stored in the echo memory 82.
[0028]
The data processor 80 generates a B mode image based on the echo data. In order to generate a B-mode image, the echo intensity at each point on the sound ray 32 is obtained one by one and used as a pixel value. As described above, the echo generated at each point on the sound ray 32 reaches the element after a distance corresponding to the distance from the echo generation point to the element of the ultrasonic transducer 26 and a time corresponding to the difference in echo generation time. The data of the corresponding part on the time axis is extracted for each element from the time-series echo data stored in, and the total intensity of these is added to obtain the echo intensity at the echo occurrence point.
[0029]
For example, in order to obtain the echo intensity of the gas bubble 42 shown in FIG. 5, the echo at the position on the time axis corresponding to the arrival time of the wavefront 42 ′ from the gas bubble 42 to each element of the ultrasonic transducer 26 and the echo generation time. Data is extracted element by element and added together. Thereby, the intensity | strength of only the echo with respect to a CW ultrasonic wave is acquired, without including the echo of the ultrasonic pulse which destroyed the microballoon. If the echo of the ultrasonic pulse is removed by a filter in advance, it becomes more perfect.
[0030]
The echo intensity of the gas bubbles 44 and 46 is obtained in the same manner. Similarly, a B-mode image is generated by obtaining echo intensities on a plurality of sound rays having different azimuths and using them as pixel values. The gas bubble image in the B-mode image shows the gas bubble that has just been emitted from the mile balloon. Therefore, an extremely short-lived gas bubble having a lifetime of, for example, about several μs can be accurately imaged. The generated B-mode image is stored in the image memory 86.
[0031]
A display unit 10 is connected to the data processing unit 8. The display unit 10 is configured using, for example, a graphic display or the like, and displays a visible image based on image data input from the image memory 86 of the data processing unit 8.
[0032]
The pulse driving unit 62, CW driving unit 64, echo receiving unit 66, data processing unit 8, and display unit 10 are connected to the control unit 12. The control unit 12 gives control signals to these units to control their operation. A status notification signal, a response signal, and the like are transmitted from each part to be controlled to the control unit 12. Ultrasonic imaging is executed under the control of the control unit 12.
[0033]
An operation unit 14 is connected to the control unit 12. The operation unit 14 is operated by an operator and inputs a desired command and information to the control unit 12. For example, the operation unit 14 includes an operation panel including a keyboard and other operation tools.
[0034]
The operation of this apparatus will be described. The operator brings the ultrasonic probe 2 into contact with a desired portion of the subject 4 and operates the operation unit 14 to perform imaging. Imaging is performed under the control of the control unit 12. As a result, the ultrasonic transducer 24 irradiates the imaging range 30 with the CW ultrasonic wave, and the ultrasonic transducer 22 transmits an ultrasonic pulse that destroys the microballoon along the sound ray 32 to the imaging range 30. By changing the direction of the sound ray 32, the imaging range is sequentially scanned by the sound ray.
[0035]
Echoes from the imaging range 30 are received by the ultrasonic transducer 26, and time-series echo reception signals for each element are stored in the echo memory 82. The data processor 80 generates a B-mode image from the data in the echo memory 82 as described above and displays it on the display unit 10. As a result, a B-mode image obtained by imaging the gas bubble just emitted from the microballoon is obtained as a visible image.
[0036]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to realize an ultrasonic imaging method and apparatus for imaging a gas bubble having a short lifetime.
[Brief description of the drawings]
FIG. 1 is a block diagram of an exemplary apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic view showing ultrasonic imaging by the apparatus shown in FIG.
3 is a waveform diagram of an instantaneous sound pressure of an ultrasonic wave transmitted by the apparatus shown in FIG. 1. FIG.
4 is a waveform diagram of instantaneous sound pressure of ultrasonic waves transmitted by the apparatus shown in FIG.
5 is a schematic diagram showing ultrasonic imaging by the apparatus shown in FIG. 1. FIG.
6 is a block diagram of a data processing unit in the apparatus shown in FIG.
[Explanation of symbols]
2 Ultrasonic probes 22, 24, 26 Ultrasonic transducers 22i, 24i, 26i Transducer element 30 Imaging range 32 Ultrasonic beam 4 Subject 40 Micro balloon assembly 62 Pulse drive unit 64 CW drive unit 66 Echo reception unit 8 Data processing unit DESCRIPTION OF SYMBOLS 10 Display part 12 Control part 14 Operation part

Claims (3)

An ultrasonic irradiation means for irradiating a first ultrasonic wave which is a CW ultrasonic wave that does not destroy the microballoon into an imaging range in a subject into which the microballoon has been injected;
An ultrasonic wave transmitting means for transmitting a pulsed second ultrasonic wave that destroys the microballoon along a sound ray passing through the imaging range;
Echo receiving means for receiving an echo for the first ultrasonic wave returned from a reflection point on the sound ray after the second ultrasonic wave has passed;
An ultrasonic imaging apparatus comprising: an image generation unit configured to generate an image based on an echo received by the echo reception unit. The ultrasonic imaging apparatus according to claim 1,
The frequency of the second ultrasonic wave transmitted by the ultrasonic wave transmission means is different from the frequency of the first ultrasonic wave emitted by the ultrasonic wave irradiation means,
The ultrasonic imaging apparatus, wherein the echo receiving means blocks the echo of the second ultrasonic wave with a filter. The ultrasonic imaging apparatus according to claim 1 or 2,
The ultrasonic imaging apparatus characterized in that the second ultrasonic pulse transmitted by the ultrasonic wave transmission means has a negative polarity in the first half cycle and a positive waveform in the next half cycle.

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