JP2004113694A - Ultrasonic imaging apparatus and ultrasonic imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic imaging apparatus that reduces a crosstalk between ultrasonic echoes reflected from a plurality of directions while employing a multi-beam system simultaneously sending and receiving a plurality of ultrasonic beams to obtain an ultrasonic image at a high sampling rate. <P>SOLUTION: The ultrasonic imaging apparatus has an ultrasonic search unit 13 forming ultrasonic beams in accordance with a plurality of drive signals and sending them to a subject and receiving ultrasonic echoes reflected from the subject, sending side circuits 10 to 12 adjusting the amount of delay of the plurality of drive signals and supplying to the ultrasonic search unit to parallelly scan the subject by the plurality of ultrasonic beams having different phases, and a receiving side circuits 16 to 25 acquiring image information concerning the subject by processing a plurality of detection signals generated by the reception of the ultrasonic search unit of ultrasonic echoes on the basis of the phase information of ultrasonic echoes. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic imaging apparatus and an ultrasonic imaging method used for performing diagnosis and non-destructive inspection of an in vivo organ by transmitting and receiving ultrasonic waves.
[0002]
[Prior art]
In an ultrasonic imaging apparatus used as a medical ultrasonic diagnostic apparatus or industrial flaw detection apparatus, an ultrasonic probe (probe) including a plurality of ultrasonic transducers having an ultrasonic transmission / reception function is usually used. It is done. By using such an ultrasonic probe, the subject is scanned with an ultrasonic beam formed by combining ultrasonic waves transmitted from a plurality of ultrasonic transducers, thereby obtaining image information about the subject. It is done. Furthermore, an ultrasonic image in a two-dimensional or three-dimensional region of the subject is reproduced based on this image information. As one of scanning methods using such an ultrasonic beam, so-called sector scanning is known in which a fan-shaped two-dimensional region of a subject is scanned in an angular direction.
[0003]
Sector scanning was originally developed as a technique for observing the heart from the intercostal space of the human body. In general, in sector scanning, an ultrasonic beam extending in the depth direction of a subject from a transmission point is sequentially transmitted in a fan shape into the subject, and the fan-shaped two-dimensional region of the subject is equalized by this ultrasonic beam. Scanned at an interval angle. Here, at each angle, image information relating to a plurality of sampling points distributed at equal intervals along the ultrasonic beam along the ultrasonic beam is sampled at regular time intervals. A two-dimensional or three-dimensional ultrasound image obtained based on sampled image information is called a tomographic echocardiogram for the heart.
[0004]
On the other hand, in harmonic imaging using the harmonic component of the fundamental wave contained in ultrasound, the echo signal from the bloodstream is enhanced by destroying bubbles of the ultrasound contrast agent with high sound pressure. Yes. Patent Document 1 below discloses that the frame rate in harmonic imaging is improved by shifting the phase of an ultrasonic beam transmitted in time series by 180 °. Patent Document 2 below discloses that the phase of an ultrasonic beam transmitted in time series is shifted by 180 °.
[0005]
Incidentally, in recent years, it has been studied to obtain an ultrasonic image at a higher sampling rate. In Patent Document 3 below, an ultrasonic imaging system that uses a two-dimensional transducer array to form a three-dimensional ultrasonic image in real time and simultaneously transmits and receives a plurality of ultrasonic beams is used. Several techniques for removing talk have been disclosed. As a technique for removing the crosstalk, the ultrasonic beam is encoded and transmitted, the main beam is transmitted in a direction in which the side lobe of the adjacent beam becomes zero, the transmission direction of the ultrasonic beam is separated, or a plurality of The use of different center frequencies between the ultrasound beams is mentioned.
[0006]
However, even if the ultrasonic beam is coded, if the number of ultrasonic beams simultaneously transmitted and received increases, it becomes difficult to identify the ultrasonic beam by the code. Further, even if the main beam is transmitted in a direction in which the side lobe of the adjacent beam becomes zero, the side lobe of the adjacent beam is not completely zero in the living body. On the other hand, when separating the transmission direction of the ultrasonic beam, it is difficult to simultaneously transmit and receive many ultrasonic beams. In addition, when using different center frequencies among a plurality of ultrasonic beams, the frequency band of the ultrasonic transducer is limited, and thus the number of ultrasonic beams that are simultaneously transmitted and received is limited.
[0007]
[Patent Document 1]
US Pat. No. 6,193,663 (abstract)
[Patent Document 2]
US Pat. No. 6,358,210 (abstract)
[Patent Document 3]
US Pat. No. 6,179,780 (abstract, FIGS. 7-10)
[0008]
[Problems to be solved by the invention]
Therefore, in view of the above points, the present invention adopts a multi-beam method in which a plurality of ultrasonic beams are simultaneously transmitted and received in order to obtain an ultrasonic image at a high sampling rate, and an ultrasonic echo reflected from a plurality of directions. An object of the present invention is to provide an ultrasonic imaging apparatus and an ultrasonic imaging method that can reduce crosstalk between the two.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, an ultrasonic imaging apparatus according to the present invention is an ultrasonic imaging apparatus, and forms an ultrasonic beam by a plurality of ultrasonic transducers respectively operating according to a plurality of drive signals to form a subject. A plurality of drive signals are transmitted so as to scan the subject in parallel with a plurality of ultrasonic beams having different phases and an ultrasonic probe that transmits and receives an ultrasonic echo reflected from the subject. The transmission side circuit that adjusts the amount of delay and supplies it to the ultrasonic probe, and the multiple detection signals obtained by the ultrasonic probe receiving the ultrasonic echo are used as the phase information of the ultrasonic echo. And a receiving side circuit that obtains image information related to the subject by performing processing based on the processing.
[0010]
The ultrasonic imaging method according to the present invention also forms an ultrasonic beam by a plurality of ultrasonic transducers that operate according to a plurality of drive signals, transmits the ultrasonic beam to the subject, and transmits an ultrasonic echo reflected from the subject. An ultrasonic imaging method for imaging a subject using a receiving ultrasonic probe, wherein a plurality of drive signals are used so that the subject is scanned in parallel by a plurality of ultrasonic beams having different phases. (A) adjusting the delay amount and supplying the ultrasonic probe to the ultrasonic probe, and a plurality of detection signals obtained by receiving the ultrasonic echo by the ultrasonic probe, the phase of the ultrasonic echo And (b) obtaining image information relating to the subject by processing based on the information.
[0011]
According to the present invention, crosstalk between ultrasonic echoes reflected from a plurality of directions can be reduced by scanning a subject in parallel with a plurality of ultrasonic beams having different phases.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the ultrasonic imaging apparatus according to the first embodiment of the present invention. This ultrasonic imaging apparatus is used as, for example, a medical ultrasonic diagnostic apparatus or an industrial flaw detection apparatus.
[0013]
As shown in FIG. 1, the ultrasonic imaging apparatus includes an ultrasonic probe 13 and transmission-side circuits 10 to 12 that transmit ultrasonic waves by supplying a plurality of drive signals to the ultrasonic probe 13. The ultrasonic probe 13 processes a plurality of detection signals obtained by receiving ultrasonic echoes, and obtains image information relating to the subject, and is output from the reception side circuit. An image display unit 30 that displays an image based on an image signal and a system control unit 40 such as a CPU that controls the circuits of the respective units are included.
[0014]
The ultrasonic probe 13 used in contact with a subject includes a plurality of ultrasonic transducers 14 constituting a two-dimensional transducer array. As the ultrasonic transducer 14, for example, a piezoelectric material made of a ceramic piezoelectric material such as PZT (Pb (lead) zirconate titanate) or a polymeric piezoelectric material such as PVDF (polyvinyl difluoride) is used. An element can be used. In the present embodiment, one ultrasonic transducer is used for both transmission and reception of ultrasonic waves. However, separate ultrasonic transducers may be provided for transmission and reception of ultrasonic waves. Further, instead of the two-dimensional transducer array, a 1.5-dimensional transducer array having a small number of rows or columns or a one-dimensional transducer array may be used.
[0015]
When transmitting ultrasonic waves, the transmission beamformer 10 controls transmission delay so that the subject is scanned in parallel (substantially simultaneously) by N ultrasonic beams (N is an integer of 2 or more) having different phases. N addresses are supplied to the unit 11. The transmission delay control unit 11 has a built-in delay time for ultrasonic waves to be transmitted from the plurality of ultrasonic transducers 14 included in the ultrasonic probe 13 based on the supplied N addresses. Reading from the time storage memory, and generating a plurality of firing signals based on the readout.
[0016]
The plurality of firing signals generated in the transmission delay control unit 11 are supplied to the plurality of pulsar circuits 12, respectively. These pulser circuits 12 output a plurality of drive signals to the ultrasonic probe 13 in accordance with the supplied ignition signal. The plurality of ultrasonic transducers 14 included in the ultrasonic probe 13 generate ultrasonic waves based on the drive signal output from the corresponding pulser circuit 12. Thus, the subject can be scanned by deflecting the ultrasonic beam formed by the combination of the ultrasonic waves generated from the plural ultrasonic transducers in a desired direction.
[0017]
Here, as shown in FIG. 2, when the length of one side of the opening of the two-dimensional transducer is L and the maximum deflection angle is θ _MAX , the delay amount τ _MAX required for the maximum deflection is expressed by the following equation. Is done.
τ _MAX = (L · sin θ _MAX ) / c (1)
However, c is the speed of sound of ultrasonic waves. As shown in FIG. 3, when the time interval between the transmission waves A and B is T, T must satisfy the following condition in order to take advantage of the characteristics of the multi-beam method.
T ≦ 10τ _MAX (2)
Here, τ _MAX is about 10 μs, and 10τ _MAX corresponds to almost half of the path of ultrasonic waves. Furthermore, it is desirable that T satisfies the following conditions in order to prevent the dead zone from becoming a problem.
T ≦ τ _MAX (3)
[0018]
As described above, it is necessary to successively form a plurality of ultrasonic beams extending in different directions within a short time by combining a plurality of transmission waves. Therefore, the pulsar circuit 12 is preferably a high-speed pulsar circuit that can output a drive signal with a high repetition period.
[0019]
In the present embodiment, transmission is performed so that the phase difference between two adjacent ultrasonic beams among N ultrasonic beams is π / 2 + 2nπ (n is an integer, and is 0 in the following). The beam former 10 and the transmission delay control unit 11 adjust the delay amounts of the plurality of drive signals. For example, as shown in FIG. 4, three ultrasonic beams 1 to 3 whose phases are rotated by 90 ° are transmitted in parallel in three directions separated by an angle φ. These ultrasonic beams are steered to move in the same direction. FIG. 5 shows the waveforms of these three ultrasonic beams, and FIG. 6 shows the intensity distribution with respect to the angle of the transmitted wave to be synthesized. In FIG. 6, the intensity distribution of the transmitted wave at a certain distance from the center of the two-dimensional transducer array is shown.
[0020]
On the other hand, at the time of receiving ultrasonic waves, detection signals output from the plurality of ultrasonic transducers 14 are amplified by a plurality of corresponding preamplifiers 16 and then input to the reception delay control unit 17. The reception delay control unit 17 adds a desired delay to the amplified detection signal under the control of the system control unit 40. As a result, reception beam forming based on phase matching is performed on a plurality of detection signals obtained by a plurality of ultrasonic transducers 14 included in the ultrasonic probe 13 receiving an ultrasonic echo.
[0021]
An output signal is extracted from the reception delay control unit 17 for each of N reception beams corresponding to ultrasonic beams transmitted in parallel. These output signals are corrected for attenuation of detection signals in deep detection by an STC (Sensitivity Time Gain Control) circuit 18. The number of synchronous detection circuits 19 corresponding to the N reception beams performs detection detection of the detection signal for each of the N reception beams. These synchronous detection circuits 19 are supplied with a local oscillation signal generated by a local oscillator while rotating the phase by 90 °. Thereby, synchronous detection of the detection signal is performed corresponding to the phase of the transmitted ultrasonic beam, and the intensity of the received wave is obtained. Alternatively, instead of performing synchronous detection, a correlation process may be performed on the detection signal to obtain the intensity of the received wave corresponding to the phase of the transmitted ultrasonic beam.
[0022]
FIG. 7 shows reception characteristics with respect to angle. By multiplying the intensity distribution of the transmission wave shown in FIG. 6 and the reception characteristic shown in FIG. 7, the intensity distribution of the reception wave as shown in FIG. 8 is obtained. In FIG. 8, the broken line indicates the intensity distribution of the received wave when the phases of the plurality of transmission beams are the same in the prior art, and a crosstalk of about −30 dB occurs at the peak position of the adjacent transmission beam. Yes. On the other hand, the solid line shows the intensity distribution of the received wave when the phase of the plurality of transmission beams is rotated by 90 ° in this embodiment, and shows that crosstalk can be reduced by synchronous detection or correlation processing. Yes. The alternate long and short dash line indicates the intensity distribution of the received wave when only one beam is transmitted without using the multi-beam method.
[0023]
The detection signals output from the respective synchronous detection circuits 19 are logarithmically compressed by the Log compression circuit 20, converted into digital signals (detection data) by the A / D converter 21, and temporarily stored in the memory 22. Furthermore, by converting the scanning format in a DSC (Digital Scan Converter) 24, the image data in the scanning space of the ultrasonic beam is converted into image data in the physical space. When displaying a three-dimensional image, a three-dimensional image constructing unit 23 may be incorporated between the memory 22 and the DSC 24. The three-dimensional image construction unit 23 generates voxel data that is data about a certain volume from a plurality of pieces of tomographic data stored in the memory 22. The image data whose scanning format is converted by the DSC 24 is converted into an analog signal by the D / A converter 25, and an ultrasonic image is displayed on the image display unit 30.
[0024]
Next, a second embodiment of the present invention will be described.
In the present embodiment, the transmission beamformer is set so that the phase difference between two adjacent ultrasonic beams among N ultrasonic beams is π + 2nπ (n is an integer, and is 0 in the following). 10 and the transmission delay control unit 11 adjust the delay amounts of the plurality of drive signals. The other points are the same as in the first embodiment. For example, as shown in FIG. 9, four ultrasonic beams 1 to 4 whose phases are rotated by 180 ° are transmitted in parallel in four directions separated by an angle φ ′. These ultrasonic beams are steered to move in the same direction.
[0025]
FIG. 10 shows the waveforms of these four ultrasonic beams, and FIG. 11 shows the intensity distribution with respect to the angle of the transmitted wave to be synthesized. FIG. 11 shows the intensity distribution of the transmission wave at a certain distance from the center of the two-dimensional transducer array. Here, the broken line indicates the intensity distribution of the transmission wave when the phases of the plurality of transmission beams are the same in the prior art. On the other hand, the solid line shows the intensity distribution of the transmission wave when the phase of the plurality of transmission beams is rotated by 180 ° in this embodiment, and at the midpoint of the transmission direction of the adjacent ultrasonic beams, The transmission sound pressure decreases due to cancellation of transmission waves whose phases are shifted by 180 °.
[0026]
FIG. 12 shows reception characteristics with respect to angle. When the transmission wave intensity distribution shown in FIG. 11 is multiplied by the reception characteristic shown in FIG. 12, the reception wave intensity distribution as shown in FIG. 13 is obtained. In FIG. 13, the broken line shows the intensity distribution of the received wave when the phases of the plurality of transmission beams are the same in the conventional technique. On the other hand, the solid line shows the intensity distribution of the received wave when the phases of the plurality of transmission beams are rotated by 180 ° in this embodiment, and shows that crosstalk can be reduced by synchronous detection or correlation processing. Yes. In the present embodiment, although the peak of the adjacent ultrasonic beam remains, the dip can be deepened, so that the contrast in the vicinity of the transmission direction of the ultrasonic beam is increased.
[0027]
【The invention's effect】
As described above, according to the present invention, crosstalk between ultrasonic echoes reflected from a plurality of directions is reduced by scanning a subject in parallel with a plurality of ultrasonic beams having different phases. be able to.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an ultrasonic imaging apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining a delay amount necessary for deflection of an ultrasonic beam.
FIG. 3 is a diagram for explaining conditions relating to a time interval of transmission waves in the first embodiment of the present invention.
FIG. 4 is a diagram for explaining transmission of a plurality of ultrasonic beams according to the first embodiment of the present invention.
FIG. 5 is a diagram showing waveforms of three ultrasonic beams transmitted in the first embodiment of the present invention.
FIG. 6 is a diagram showing an intensity distribution of a transmission wave in the first embodiment of the present invention.
FIG. 7 is a diagram showing reception characteristics in the first embodiment of the present invention.
FIG. 8 is a diagram showing an intensity distribution of a received wave in the first embodiment of the present invention.
FIG. 9 is a diagram for explaining transmission of a plurality of ultrasonic beams according to the second embodiment of the present invention.
FIG. 10 is a diagram showing waveforms of three ultrasonic beams transmitted in the second embodiment of the present invention.
FIG. 11 is a diagram showing an intensity distribution of a transmission wave in the second embodiment of the present invention.
FIG. 12 is a diagram illustrating reception characteristics according to the second embodiment of the present invention.
FIG. 13 is a diagram showing an intensity distribution of a received wave in the second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Transmission beam former 11 Transmission delay control part 12 Pulsar circuit 13 Ultrasonic probe 14 Ultrasonic transducer 16 Preamplifier 17 Reception delay control part 18 STC circuit 19 Synchronous detection circuit 20 Log compression circuit 21 A / D converter 22 Memory 23 3D image construction unit 24 DSC
25 D / A converter 30 Image display unit 40 System control unit

Claims (5)

An ultrasonic imaging device comprising:
An ultrasonic probe that forms an ultrasonic beam by a plurality of ultrasonic transducers that operate according to a plurality of drive signals, transmits the ultrasonic beam to the subject, and receives an ultrasonic echo reflected from the subject; and
A transmission-side circuit that adjusts delay amounts of a plurality of drive signals and supplies the ultrasound probe to scan the subject in parallel with a plurality of ultrasonic beams having different phases; and
A plurality of detection signals obtained by the ultrasonic probe receiving ultrasonic echoes based on the phase information of the ultrasonic echoes to obtain image information about the subject;
An ultrasonic imaging apparatus comprising: The transmission side circuit sets a delay amount of a plurality of drive signals so that a phase difference between two adjacent ultrasonic beams among the plurality of ultrasonic beams is π / 2 + 2nπ or π + 2nπ (n is an integer). The ultrasonic imaging apparatus according to claim 1, comprising means for adjusting. The ultrasonic imaging apparatus according to claim 1, wherein the reception side circuit includes means for performing synchronous detection or correlation processing on a plurality of detection signals obtained by reception of ultrasonic echoes. Using an ultrasonic probe that forms an ultrasonic beam by a plurality of ultrasonic transducers that operate according to a plurality of drive signals, transmits the ultrasonic beam to the subject, and receives an ultrasonic echo reflected from the subject, An ultrasonic imaging method for imaging a subject,
(A) adjusting the delay amount of the plurality of drive signals and supplying the ultrasonic probe so as to scan the subject in parallel with the plurality of ultrasonic beams having different phases;
(B) obtaining image information on the subject by processing a plurality of detection signals obtained by the ultrasonic probe receiving ultrasonic echoes based on phase information of the ultrasonic echoes; ,
An ultrasonic imaging method comprising: The ultrasonic imaging method according to claim 4, wherein step (b) includes performing synchronous detection or correlation processing on a plurality of detection signals obtained by reception of ultrasonic echoes.

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