JP4418491B2 - Ultrasonic imaging device - Google Patents

Description

  The present invention relates to an ultrasonic imaging method and apparatus, and more particularly to an ultrasonic imaging method and apparatus for simultaneously transmitting ultrasonic beams in a plurality of directions in a subject and generating an image based on the echoes.

Ultrasonic imaging in which an ultrasonic beam is simultaneously transmitted to a plurality of directions in a subject and an image is generated based on an echo is referred to as multi-beam ultrasonic imaging. Multi-beam ultrasound imaging is efficient because it can acquire echo signals of multiple sound rays at a time with a single ultrasound transmission and reception, and the frame rate (frame) of the imaging.
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  The plurality of ultrasonic beams are respectively formed by corresponding beamformers. FIG. 8 shows an example of an ultrasonic beam profile formed by a beam former. As shown in the figure, the beam profile consists of a main lobe m that occurs in the front of the azimuth (angle 0 °), side lobes that occur on both sides of the main lobe, and pedestals that occur on both sides ( pedestal) p. The pedestal p has a signal strength of about −30 dB even at an angle of ± 20 °.

  In the case of multi-beams, it is necessary to sufficiently separate the directions of the individual beams in order to avoid crosstalk due to side lobes and pedestals. For example, in the case of the beam profile of FIG. The azimuths of the individual beams must be at least 50 ° apart.

  For this reason, for example, when a 64-channel ultrasonic transducer array is used, the number of multi-beams that can be practically used is about 2, and there is a problem that a sufficient number of multi-beams cannot always be obtained. It was.

  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 having a large number of multi-beams that can be simultaneously transmitted and received.

  Prior to describing the means for solving the problem, the nature of the parametric component of ultrasound will be described in a preliminary manner. The waveform of the ultrasonic wave is distorted due to the nonlinearity of the ultrasonic wave propagation in the subject, and second-order, third-order or higher-order harmonics are generated based on the distortion. Further, when two ultrasonic waves having different frequencies are transmitted simultaneously, ultrasonic waves having the sum and difference frequencies of those frequencies are respectively generated. Such ultrasonic waves are referred to as parametric components in this document.

  Due to the second-order or higher-order effects of nonlinearity, the waveform distortion is proportional to the n (> 2) power of the instantaneous sound pressure of the ultrasonic wave, so the signal intensity of the parametric component is the instantaneous sound pressure of the transmitted ultrasonic wave. Is proportional to the power of n.

  Therefore, for example, when focusing on the second-order parametric component, the beam profile is obtained by squaring the signal intensity of the beam profile of the fundamental wave. For example, as shown in FIG. 9, the side lobe s and the pedestal p are greatly reduced. And the directivity is improved. The present invention utilizes its echo based on this property of the parametric component of ultrasound. In this document, the echo of the parametric component is referred to as a parametric echo.

  (1) A first invention for solving the above-described problem is an ultrasonic imaging method for simultaneously transmitting ultrasonic beams in a plurality of directions in a subject and generating an image based on the echoes. An ultrasonic imaging method characterized in that an image is generated based on parametric echoes of waved ultrasonic waves.

  (2) A second invention for solving the above-described problem is an ultrasonic imaging apparatus that simultaneously transmits ultrasonic beams in a plurality of directions in a subject and generates an image based on the echoes. An ultrasonic imaging apparatus comprising image generation means for generating an image based on the parametric echo of the ultrasonic wave.

  In the first invention or the second invention, the parametric echo is preferably a second harmonic echo from the viewpoint of obtaining a relatively high level parametric echo.

  (Operation) In the present invention, the directivity of the parametric component of the ultrasonic wave is utilized, and the number of multi-beams is increased by reducing the distance between the plural ultrasonic beams.

  ADVANTAGE OF THE INVENTION According to this invention, the ultrasonic imaging method and apparatus with many multibeams which can be transmitted / received simultaneously are realizable.

  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.

  The configuration of this apparatus will be described. As shown in FIG. 1, the present apparatus has an ultrasonic probe 2. The ultrasonic probe 2 has an ultrasonic transducer array (not shown). The ultrasonic transducer array is configured by arranging a plurality of ultrasonic transducers in an appropriate array such as a one-dimensional array. Each ultrasonic transducer is made of a piezoelectric material such as PZT (titanium (Ti) zirconate (Zr) acid) ceramics. The ultrasonic probe 2 is used in contact with the subject 4.

  The ultrasonic probe 2 is connected to the transmission / reception unit 6. The transmission / reception unit 6 sends a drive signal to the ultrasonic probe 2 to transmit ultrasonic waves. The transmission / reception unit 6 also receives an echo signal received by the ultrasonic probe 2.

  A block diagram of the transceiver 6 is shown in FIG. As shown in the figure, the transmission / reception unit 6 includes a transmission timing generation circuit 602. The transmission timing generation circuit 602 is connected to the transmission beam former 604. The transmission timing generation circuit 602 periodically generates a transmission timing signal and inputs it to the transmission beam former 604.

  The transmission beam former 604 is connected to the transmission / reception switching circuit 606. The transmission beamformer 604 generates a transmission beamforming signal based on the transmission timing signal and inputs it to the transmission / reception switching circuit 606.

  The transmission beamformer 604 performs multi-beamforming, and has, for example, eight beamforming units (not shown), thereby forming eight ultrasonic beams having different directions. Produces 8 sets of drive signals, ie 8 sets of beamforming signals. Each set of beam forming signals includes a plurality of drive signals to which time differences corresponding to directions are given.

  The transmission / reception switching circuit 606 inputs eight sets of beamforming signals to the ultrasonic transducer array. In the ultrasonic transducer array, a plurality of ultrasonic transducers constituting a transmission aperture each generate an ultrasonic wave having a phase difference corresponding to a time difference of drive signals. By the wavefront synthesis of these ultrasonic waves, an ultrasonic beam, that is, a multi-beam, is formed along eight sound rays having different directions.

  In this apparatus, as will be described later, an image is formed on the basis of echoes (harmonic echoes) based on harmonics of transmitted ultrasonic waves. The harmonic echo is an example of an embodiment of the parametric echo in the present invention.

  As shown in FIG. 9, the beam profile of the harmonic wave of the transmitted ultrasonic wave is greatly reduced in the side lobe s and pedestal p, and the directivity is extremely improved. For example, the angle at which the signal intensity is reduced to −40 dB is It narrows to about ± 10 ° from the front of the beam. For this reason, the separation angle between the beams in the multi-beam can be set small, and the number of multi-beams can be set to 8, for example. Note that the number of multi-beams is not limited to eight.

  A reception beam former 610 is connected to the transmission / reception switching circuit 606. The transmission / reception switching circuit 606 inputs a plurality of echo signals received by the reception aperture in the ultrasonic transducer array to the reception beam former 610. The reception beam former 610 performs reception multi-beam forming corresponding to the transmission sound ray. The reception beam former 610 includes, for example, eight beam forming units (not shown), thereby forming eight transmission sound rays having different directions. The echo reception signal along the line is formed. Specifically, each beam forming unit gives a time difference to a plurality of received echoes, adjusts the phase, and then adds them to form an echo reception signal along the sound ray.

  Transmission of the ultrasonic beam is repeatedly performed at predetermined time intervals by a transmission timing signal generated by the transmission timing generation circuit 602. Each time, the transmitting beamformer 604 and the receiving beamformer 610 change the directions of the eight sound rays simultaneously by a predetermined amount. As a result, the inside of the subject 4 is sequentially scanned by sound rays in which eight lines form a set. The transmission timing generation circuit 602 or the reception beam former 610 described above is controlled by the control unit 18 described later.

  The transceiver unit 6 having such a configuration performs scanning as shown in FIG. 3, for example. That is, the fan-shaped two-dimensional region 206 is scanned in the θ direction with eight sound rays 202 extending in the z direction from the radiation point 200, and so-called sector scan is performed.

  When the transmission and reception apertures are formed by using a part of the ultrasonic transducer array, the apertures are sequentially moved along the array to perform scanning as shown in FIG. 4, for example. That is, by moving the sound ray 202 emitted from the radiation point 200 in the z direction along the linear locus 204, the rectangular two-dimensional region 206 is scanned in the x direction, and so-called linear scan is performed. Done.

  When the ultrasonic transducer array is a so-called convex array formed along an arc extending in the ultrasonic wave transmission direction, for example, as shown in FIG. Thus, it goes without saying that a so-called convex scan can be performed by moving the radiation point 200 of the sound ray 202 along the arc-shaped locus 204 and scanning the fan-shaped two-dimensional region 206 in the θ direction.

  The transmission / reception unit 6 is connected to a B-mode processing unit 10. The transmission / reception unit 6 inputs an echo reception signal for each sound beam of the multi-beam to the B mode processing unit 10. The B mode processing unit 10 forms a B mode image signal based on the echo reception signal.

  The B-mode processing unit 10 includes a filter 102 as shown in FIG. The filter 102 has eight filter units (not shown) corresponding to the echo reception signals of eight sound rays. Each filter unit extracts an echo reception signal having the same frequency as, for example, the second harmonic (second harmonic) of the fundamental frequency of the harmonic echo, that is, the transmitted ultrasonic wave.

  Note that the filter may extract third-order or higher-order harmonics as necessary. Higher order harmonics are preferable in that the beam profile is further improved. However, the second harmonic echo is preferable in that the signal level is the highest among the harmonic echoes. Hereinafter, an example of the second harmonic echo will be described, but the same applies to the case of the third and higher harmonics.

  The filter 102 is connected to the logarithmic amplifier circuit 104. The logarithmic amplification circuit 104 has eight logarithmic amplification units corresponding to the eight filter units, and each logarithmically amplifies the second harmonic echo. The logarithmic amplifier circuit 104 is connected to the envelope detection circuit 106. The envelope detection circuit 106 has eight envelope detection units corresponding to the eight logarithmic amplification units, and each envelope-detects the logarithmically amplified second harmonic echo. As a result, a B-mode image signal representing the intensity of the second harmonic echo at each reflection point on the sound ray is simultaneously obtained for eight sound rays.

  The B mode processing unit 10 is connected to the image processing unit 14. The B-mode processing unit 10 inputs an 8-sound B-mode image signal to the image processing unit 14. The image processing unit 14 generates a B-mode image based on the B-mode image signal input from the B-mode processing unit 10. Since the B-mode image signal is based on the second harmonic echo, the B-mode image is a second harmonic echo image. The B-mode processing unit 10 and the image processing unit 14 are an example of an embodiment of image generation means in the present invention.

  As shown in FIG. 7, the image processing unit 14 includes a sound ray data memory 142, a digital scan converter 144, an image memory 146, and an image processing processor connected by a bus 140. (Processor) 148 is provided.

  The B-mode image signal input for each sound ray from the B-mode processing unit 10 is stored in the sound ray data memory 142 as a digital signal. A sound ray data space is formed in the sound ray data memory 142.

  The digital scan converter 144 converts sound ray data space data into physical space data by scan conversion. The image data converted by the digital scan converter 144 is stored in the image memory 146. The image memory 146 stores physical space image data. The image processor 148 performs predetermined data processing on the data in the sound ray data memory 142 and the image memory 146, respectively.

  A display unit 16 is connected to the image processing unit 14. The display unit 16 receives an image signal from the image processing unit 14 and displays an image based on the image signal. The display unit 16 is configured by, for example, a graphic display.

  The transmission / reception unit 6, the B-mode processing unit 10, the image processing unit 14, and the display unit 16 are connected to the control unit 18. The control unit 18 gives control signals to these units to control their operation. In addition, various notification signals are input to the control unit 18 from each part to be controlled. The operation of this apparatus proceeds under the control of the control unit 18.

  An operation unit 20 is connected to the control unit 18. The operation unit 20 is used by an operator to input commands and information to the control unit 18. The operation unit 20 includes, for example, an operation panel having a keyboard and other operation tools.

  The operation of this apparatus will be described. The operator contacts the ultrasonic probe 2 with a desired location of the subject 4 and operates the operation unit 20 to perform imaging. Imaging is performed under the control of the control unit 18 based on a command or the like input from the operation unit 20.

  Thereby, for example, a multi-beam sector scan with eight sound rays as shown in FIG. 3 is performed. Since the number of multi-beams is 8, scanning can be performed at a frame rate that is four times faster than the conventional example with two multi-beams. Alternatively, it is possible to scan an area four times wider at the same frame rate. Of course, the same applies to the linear scan and the convex scan shown in FIGS.

  In the subject 4, a second harmonic echo is generated due to nonlinearity of ultrasonic propagation. The B mode processing unit 10 generates a B mode image signal based on the second harmonic echo. These B-mode image signals are stored in the sound ray data memory 142 of the image processing unit 14. The image processor 148 scan-converts the B-mode image data in the sound ray data memory 142 with the digital scan converter 144 and writes it in the image memory 146. The image written in the image memory 146 is displayed on the display unit 16. Thereby, the B-mode image by the second harmonic echo is displayed as a visible image.

  The example in which the parametric echo is a harmonic echo has been described above, but the same effect can be obtained when the echo of the sum or difference frequency in the simultaneous transmission of two frequencies is used.

  Further, although the example in which the ultrasonic transducer array is a one-dimensional array has been described, the array is not limited to a one-dimensional array, and may be an appropriate array such as a two-dimensional array. When a two-dimensional array is used to scan a three-dimensional region of a subject, the frame rate is generally slow or the imaging region tends to be narrow. However, since the number of multi-beams is large, they can be greatly improved.

  In addition, not only in arrays but also in ultrasonic probes using a single ultrasonic transducer, the beam profile can be improved by using parametric echoes. The same effect can be obtained also when performing.

  Further, although an example of B-mode imaging has been described, ultrasonic imaging is not limited thereto, and it goes without saying that dynamic images may be captured using a Doppler shift of parametric echo. Nor.

It is a block diagram of an example of an apparatus of an embodiment of the invention. It is a block diagram of the transmission / reception part in the apparatus shown in FIG. It is a conceptual diagram of the sound ray scanning by the apparatus shown in FIG. It is a conceptual diagram of the sound ray scanning by the apparatus shown in FIG. It is a conceptual diagram of the sound ray scanning by the apparatus shown in FIG. FIG. 2 is a block diagram of a B mode processing unit in the apparatus shown in FIG. 1. FIG. 2 is a block diagram of an image processing unit in the apparatus shown in FIG. 1. It is a figure which shows an example of the beam profile of a beam former. It is a figure which shows an example of the beam profile of a beam former.

Explanation of symbols

2 Ultrasonic probe 4 Subject 6 Transmission / reception unit 10 B mode processing unit 14 Image processing unit 16 Display unit 18 Control unit 20 Operation unit 602 Transmission timing generation circuit 604 Transmission beam former 606 Transmission / reception switching circuit 610 Reception beam former 102 Filter 104 logarithmic amplifier circuit 106 envelope detector circuit

Claims (1)

An ultrasonic wave transmitting means for simultaneously transmitting ultrasonic waves of two frequencies in a plurality of directions in the subject;
An image that receives parametric echoes from the sum or difference of the two frequencies generated by nonlinearity of ultrasonic propagation in the subject simultaneously from a plurality of directions and generates an image based on the received signals. Generating means;
An ultrasonic imaging apparatus comprising:

Images