JP2006320596A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform improvement to reduce an artifact by the grating lobe of a transmission ultrasonic wave beam in an ultrasonic diagnostic apparatus. <P>SOLUTION: When an ultrasonic wave frequency, a focal distance, and the depth of field, etc., are input by an input device 18 in the apparatus, a control circuit 17 determines the number of vibrators to be driven by referring to a driven vibrator number table 21 and a driving voltage table 22, fixes the driving voltage, and controls a transmission/reception beam former (a transmission wave beam former being the transmission wave part) 12. The transmission part (the transmission wave beam former) of the transmission/reception beam former 12 drives the fixed number of vibrators by ultrasonic wave with the fixed driving voltage. The tables 21, 22 hold vales which are previously obtained in experiments, etc., and are held in the inner or outer storage area of the control circuit 17. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus for acquiring data relating to ultrasonic reflection at various parts of a living body by entering ultrasonic waves into a living body and receiving the reflected waves, and more particularly, an ultrasonic wave comprising an ultrasonic transducer array. The present invention relates to an ultrasonic diagnostic apparatus using a probe.

  The ultrasonic diagnostic apparatus receives ultrasonic waves into the living body and receives the reflected waves to receive data relating to ultrasonic reflection at each part of the living body, for example, data representing a reflection coefficient, blood flow velocity, etc. Data is acquired. According to this ultrasonic diagnostic apparatus, for example, a B-mode image (ultrasonic tomographic image) can be obtained by scanning a predetermined section in a living body with an ultrasonic beam and obtaining a reflection coefficient distribution in the section. .

  In order to transmit ultrasonic waves into the living body and receive the reflected waves, the ultrasonic probe is brought into close contact with the patient body surface or the like. This ultrasonic probe is usually composed of an ultrasonic transducer array in which a large number of ultrasonic transducers such as piezoelectric elements are arranged in a strip shape. By driving each transducer in a pulse shape, ultrasonic waves are generated from each transducer, and by delaying the drive timing for each transducer, the ultrasonic waves generated from each transducer and synthesized in space are focused. Electronic focus control is performed. Similarly, with respect to the received ultrasonic wave, electronic focus control is performed by adding each of the received signals generated from each transducer receiving the ultrasonic wave with an appropriate delay.

  The spatial resolution (azimuth resolution and distance resolution) and the depth of field (the range in the depth direction that is the focal point) of the acquired ultrasound data are important factors that determine the quality of the B-mode image, the quality of the data, etc. Is a factor. Usually, the azimuth / distance resolution is increased by increasing the driving frequency. In addition, the depth of field is improved by lowering the drive frequency or increasing the drive voltage.

  On the other hand, recent ultrasonic diagnostic apparatuses have a lineup of ultrasonic probes having various shapes and frequency characteristics according to the application to be used. A user usually uses a high frequency probe when observing a shallow part and a low frequency probe when observing a deep part. In addition, there are many ultrasonic diagnostic apparatuses having a frequency switching function, and different frequencies can be used without exchanging the ultrasonic probe.

Furthermore, in order to improve the resolution in the region of interest, an ultrasonic diagnostic apparatus having a function of changing the focal length of the transmitted ultrasonic wave is also widespread. In accordance with the change of the focal length, the drive number of the transducer in the ultrasonic probe changes, and the aperture length of the ultrasonic output also changes. When the focal length is F and the aperture length of the ultrasonic output is D, the focus number #F is defined as follows.
# F = F / D
In many ultrasonic diagnostic apparatuses, an ultrasonic beam is formed by controlling the aperture length, that is, the number of driven vibrators so that the focus number always becomes a constant value. In the actual ultrasonic diagnostic apparatus, since the number of vibrators that can be driven simultaneously is limited, a constant focus number cannot be maintained when the focal length is longer than a certain length.

  By the way, with an ultrasonic probe using an ultrasonic transducer array, noise and artifacts (false images) due to grating lobes are problematic. The ultrasonic beam formed by the ultrasonic transducer array is formed not only in a desired direction but also in other directions, which is called a grating lobe. This grating lobe is also described in, for example, the following non-patent documents.

The appearance angle θ of the grating lobe is calculated by the following equation.
d × sin θ = λ = c / f
Where d: element spacing of the strip-shaped transducer of the ultrasonic probe λ: wavelength in the propagation medium c: speed of sound in the propagation medium f: ultrasonic frequency in the propagation medium
θ = sin-1 (c / df)
In order to obtain a high-quality image that is not affected by artifacts, it is necessary to increase θ as much as possible.

The level of the grating lobe depends on the frequency and the number of driving elements, and the level increases as the frequency increases and the number of driving elements increases.
Japan Electronic Machinery Manufacturers Association, “Medical Ultrasound Equipment Handbook” Corona, 1985, 65 pages.

  The conventional ultrasonic diagnostic apparatus only controls the number of vibrators to be driven in relation to the focus number as described above, and is incapable of artifacts due to grating lobes.

  An object of the present invention is to provide an ultrasonic diagnostic apparatus improved so as to reduce artifacts due to grating lobes.

  In order to achieve the above object, in the ultrasonic diagnostic apparatus according to the present invention, an ultrasonic probe composed of an ultrasonic transducer array and each transducer of the ultrasonic probe are synthesized in a propagation medium by pulse driving. A transmission beam former for transmitting the ultrasonic beam, an input means for inputting the ultrasonic frequency for driving the transducer and the focal length of the synthetic ultrasonic beam, and an ultrasonic frequency for each focal length of the synthetic ultrasonic beam. The higher the is, the smaller the number of drive vibrators, the means for holding a table of focal length, frequency and drive vibrator number data, and the table is accessed according to the above input information, and the read drive vibrator number data It is characterized by having a control means for controlling the transmission beamformer so as to determine the vibrator to be driven on the basis of which the vibrator is driven.

  In the ultrasonic diagnostic apparatus, a table of focal length, frequency, and drive transducer number data is held. In this table, drive vibrator number data is determined for each focal length and ultrasonic frequency. The number of drive vibrators is determined so as to decrease as the frequency increases. Therefore, when the ultrasonic frequency and the focal length are input by the input means, the control means accesses the above table, reads out the drive vibrator number data corresponding to the ultrasonic frequency and the focal distance, By controlling the transmit beamformer to drive the transducer to generate an ultrasonic beam, the optimal number of transducers are driven to form a synthesized ultrasonic beam so that artifacts due to grating gloves are reduced. be able to.

  Next, an ultrasonic diagnostic apparatus embodying the present invention will be described with reference to the drawings.

  In the ultrasonic diagnostic apparatus according to one embodiment of the present invention, an ultrasonic probe 11 is connected to a transmission / reception beam former 12 as shown in FIG. The ultrasonic probe 11 is in close contact with the surface of a subject such as a patient's body, and is composed of a transducer array in which a large number of ultrasonic transducers (piezoelectric elements) are arranged. Are ultrasonically driven in pulses. The pulsed drive timing of each transducer is controlled, and ultrasonic waves generated from these transducers are radiated into the subject, synthesized in the propagation medium, and focused. The focal length is determined by delay control of the drive timing.

  The incident ultrasonic wave is reflected in the subject, and the reflected wave returns to the ultrasonic probe 11 to vibrate each transducer, and a reception signal is generated from each transducer. The reception signals from the transducers are delayed in the transmission / reception beam former 12 and added to obtain a reception signal of the synthesized ultrasonic beam having a predetermined focal point for the received ultrasonic waves. The received signal thus obtained is sent to the signal processing circuit 13 and subjected to gain adjustment processing, quadrature detection processing, filter processing, log compression processing, dynamic range adjustment processing, enhancement processing, and the like, and then sent to the image processing circuit 14. For example, a B-mode image that is a tomographic image of a specific section of the patient's body is formed, and further sent to the image monitor device 16 via the display circuit 15, and the B-mode image or the like is displayed on the display screen of the image monitor device 16. Will be.

  An input device 18 such as a keyboard is connected to the control circuit 17 so that ultrasonic scanning conditions and the like can be input. The control circuit 17 controls the transmission / reception beamformer 12, the signal processing circuit 13, the image processing circuit 14, the display circuit 15 and the like according to the input conditions. The input conditions are an ultrasonic frequency, a focal length, a depth of field, and the like. The focal length and the visual field depth are determined according to the position / size of the region of interest within the subject. The ultrasonic frequency is set according to the desired azimuth / distance resolution by selecting a high frequency if high resolution is to be obtained and a low frequency if not so much.

  Thus, when the ultrasonic frequency, the focal length, the depth of field, and the like are input, the control circuit 17 refers to the drive transducer number table 21 and the drive voltage table 22 and determines the number of transducers to be driven. Determine the drive voltage. The tables 21 and 22 are held in a storage area inside or outside the control circuit 17.

  As described above, the number of drive vibrators, that is, the aperture length is generally determined according to the focal length so that the focus number is constant, but it is also a determinant of the grating level. An optimum one is obtained in advance by experiments and held on the table 21. That is, as shown in the figure, the number of drive vibrators is basically determined according to the focal length, but depending on the ultrasonic frequency, it is small when the frequency is high (High) and large when it is low (Low). In the middle (Middle) frequency, the intermediate number is used. As described above, the higher the ultrasonic frequency and the greater the number of drive vibrators, the higher the level of the grating lobe. In order to avoid image quality degradation due to the grating lobe as much as possible, drive vibration occurs when the frequency is high. The number of children is reduced to suppress the level of the grating lobe.

  In addition, the driving voltage for ultrasonically driving each transducer is determined in the table 22 according to the depth of field. In order to improve the depth of field, in general, the drive voltage is increased, but when the drive voltage is increased, the sound pressure amplitude increases, resulting in distortion due to the nonlinear effect in the propagation medium and increasing the harmonic component. Drawback is also a problem. Furthermore, since the higher frequency component of the ultrasonic wave is attenuated in the propagation medium, when the drive voltage is high, the band is narrower than when the drive voltage is low, and the center frequency is observed to be low. Therefore, taking these into consideration, the optimum drive voltage for each depth of field is obtained in advance by experiments or the like and stored as the table 22.

  By accessing the tables 21 and 22 as described above, the control circuit 17 determines the number of drive vibrators and the drive voltage, controls the transmission / reception beam former (the transmission part) 12, and transmits / receives the beam former 12. The transmitting portion (transmitting beamformer) of the ultrasonic wave drives the predetermined number of vibrators with a predetermined driving voltage, and starts scanning with the ultrasonic beam. As a result, in the ultrasonic probe 11, the optimal number of transducers are ultrasonically driven in pulses with the optimal driving voltage, so that the transmitted ultrasonic beam characteristics are improved and artifacts are reduced. B-mode images with high diagnostic ability can be obtained.

  The above description is for one embodiment, and it is needless to say that specific configurations and the like can be variously changed without departing from the gist of the present invention. Although described as having a hardware configuration, there are parts such as the signal processing circuit 13 and the image processing circuit 14 that can be realized by software. It goes without saying that the numerical values in the drive vibrator number table 21 and the drive voltage table 22 are examples.

  According to the ultrasonic diagnostic apparatus of the present invention, it is possible to drive each transducer of the ultrasonic probe by determining the optimum number of drive elements according to the input values of the ultrasonic frequency and the focal length, thereby reducing artifacts. In addition, it is possible to obtain a B-mode image with better image quality that is useful for diagnosis.

1 is a block diagram of an ultrasonic diagnostic apparatus according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Ultrasonic probe 12 ... Transmission / reception wave beam former 13 ... Signal processing circuit 14 ... Image processing circuit 15 ... Display circuit 16 ... Image monitor device 17 ... Control circuit 18 ... Input device 21 ... Drive Number-of-vibrators table 22 …… Drive voltage table

Claims (1)

  An ultrasonic probe comprising an ultrasonic transducer array, a transmission beamformer for transmitting an ultrasonic beam synthesized in a propagation medium by pulse driving each transducer of the ultrasonic probe, and the transducer The input means for inputting the ultrasonic frequency to be driven and the focal length of the synthetic ultrasonic beam, and the higher the ultrasonic frequency is for each focal length of the synthetic ultrasonic beam, the smaller the number of driving vibrators, the focal length, the frequency and the driving vibration. A means for holding a table of child data, and the table for accessing the table according to the input information, determining the vibrator to be driven based on the read drive vibrator number data, and driving the vibrator An ultrasonic diagnostic apparatus comprising: control means for controlling the beam former.

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