JP2008167876A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimally generate a wave transmission beam shape by changing the weighting in the time axis direction of the drive signals of a plurality of vibrators constituting an aperture. <P>SOLUTION: The ultrasonic diagnostic apparatus is provided with a plurality of drive signal generation parts respectively corresponding to the plurality of vibrators constituting the aperture of an ultrasonic probe for transmitting ultrasonic waves to an object. Each drive signal generation part comprises: a delay part 11 operated in response to transmission start signals; a waveform generation part 12 for generating the drive signals of a variably set waveform in response to the drive start signals outputted from the delay part; and a weighting part 13 for weighting the amplitude of the drive signals outputted from the waveform generation part and outputting them to the corresponding vibrator. The weighting part is formed so as to variably set the weighting of the amplitude of the drive signals differently in the time axis direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to a technique for generating an ultrasonic transmission beam suitable for generating an image having a resolution corresponding to a measurement mode such as a tomographic imaging mode or a blood flow measurement mode. .

  An ultrasonic diagnostic apparatus transmits and receives ultrasonic waves into a subject using a probe in which a plurality of ultrasonic transducers are arranged, and signals reflected echo signals received from the plurality of ultrasonic transducers from within the subject. The image is processed to generate image information such as tomographic images and blood flow information, which contributes to diagnosis. As the image information, the reflected echo signal is subjected to predetermined signal processing to extract a Doppler signal, and a blood flow velocity and direction are obtained and imaged. Generally, in the blood flow measurement mode, blood flow information is measured by locating the blood vessel observation site while viewing the tomographic image, so the same probe is used in the tomographic imaging mode and the blood flow measurement mode. ing.

  Further, in the tomographic imaging mode, it is required to make the ultrasonic transmission beam as thin as possible in order to increase the resolution of the image for easy observation. However, if the transmitted beam is made narrower, side lobes are generated, causing artifacts and reducing the S / N of tomographic images, leading to image quality degradation. On the other hand, in the blood flow measurement mode, the intensity of the reflected echo signal from the blood cell that obtains the Doppler signal is extremely weak, and it becomes difficult to obtain the Doppler signal if artifacts are mixed in the reflected echo signal from the blood cell. There is a need to reduce wall artifacts.

  Therefore, in Patent Document 1, a weighting function for changing the amplitudes of a plurality of drive signals that respectively drive a plurality of ultrasonic transducers is set for each imaging mode and measurement mode, and transmission suitable for each measurement mode is set. It has been proposed to generate a wave beam. That is, a plurality of ultrasonic transducers called apertures are driven at the same time, and a single transmission beam is generated by synthesizing the ultrasonic waves radiated from these ultrasonic transducers. At this time, it is proposed that the drive signal for driving the ultrasonic transducer has a time difference (delay time) to control the focal position of the transmitted beam and to control the amplitude of each drive signal with a weighting function. Yes. According to this, by switching the weighting function, an ultrasonic transmission beam shape suitable for each measurement mode can be obtained, and the image quality in each mode can be improved.

Japanese Patent Laid-Open No. 10-155794

  However, the conventional technique described in Patent Document 1 uses a measurement method by changing the weighting of the amplitude for each drive signal of each ultrasonic transducer along the arrangement direction of a plurality of ultrasonic transducers constituting a so-called aperture. Although an ultrasonic transmission beam shape suitable for the mode is obtained, adjustment of the transmission beam shape according to the depth is not considered.

  The problem to be solved by the present invention is to enable optimal generation of a transmission beam shape according to the depth.

  In order to solve the above-described problems, the present invention includes a transmission unit that generates a drive signal of an ultrasonic probe that transmits an ultrasonic wave to a subject, and the transmission unit is provided for each of a plurality of transducers that form a bore A plurality of corresponding drive signal generators, each of the drive signal generators being variably set in response to a delay unit that operates in response to a transmission start signal and a drive start signal output from the delay unit Apparatus for generating a waveform drive signal, and a weighting unit for weighting the amplitude of the drive signal output from the waveform generation unit and outputting the weight to a corresponding transducer The weighting unit is formed so that the weighting of the amplitude of the drive signal can be variably set in the time axis direction.

  According to the present invention, the weighting coefficient to be multiplied to the drive signal is changed in the time axis direction, and the weighting coefficient to be multiplied to the drive signal of the vibrator constituting the aperture is increased at the center of the aperture and decreased with increasing distance from the center. Distribution can be given. Further, when the focus is shallow, the distribution of the weighting factor can be made steep, and when the focus is deep, the distribution of the weighting factor can be made flat. As a result, the transmitted beam shape can be freely generated according to the depth of focus, so that the optimum transmitted beam shape can be generated in accordance with the measurement mode.

  In addition, combining the setting of the frequency of the drive signal of the transducer constituting the aperture with a high value at the center of the aperture and a lower setting as the distance from the center increases, the position of the transmission wavefront of the ultrasonic wave radiated from each transducer Every time, the frequency component can be accurately adjusted according to the depth. For example, in a transducer farther than the transducer at the center of the wavefront that does not contribute much to the imaging of the shallow area near the probe 1, a weighting factor that increases the low frequency component over time contributes to improved sensitivity in the depth portion. To do. On the other hand, the vibrator near the center of the aperture can keep the frequency band of the synthesized transmission beam constant by allocating the low frequency components in the reverse direction, preventing the image quality from deteriorating as the depth increases. it can.

  For example, when there is a strong reflector at a specific depth, the conventional technique has no ingenuity to transmit the transmission beam deeper than the reflector, and thus there is a problem that the deep portion cannot be drawn well. In this regard, according to the present embodiment, it is possible to reduce the low-frequency component ratio of the inner vibrator having the aperture corresponding to the depth and increase the low-frequency component ratio of the outer vibrator corresponding to the depth. Therefore, the ultrasonic transmission signal can reach a position deeper than the reflector, and the image quality and sensitivity can be improved.

  According to the present invention, the transmission beam shape can be optimally generated according to the depth by changing the weighting in the time axis direction of the drive signals of the plurality of transducers constituting the aperture.

Hereinafter, the present invention will be described in detail based on embodiments. FIG. 1 is a block diagram illustrating an overall configuration of an ultrasonic diagnostic apparatus according to an embodiment. As shown in FIG. 1, an ultrasonic probe 1 is connected to a digital / analog (D / A) conversion unit 3 and an analog / digital (A / D) conversion unit 4 via a transmission / reception separating unit 2. The D / A conversion unit 3 converts digital drive signals output from the transmission circuit 5 to a plurality of transducers constituting the aperture of the probe 1 to analog, and a plurality of corresponding vibrations via the transmission / reception separating unit 2. Output to the child. The A / D converter 4 converts reflected echo signals received by a plurality of transducers constituting the aperture of the probe 1 into digital signals and outputs them to the receiving circuit 6. The receiving circuit 6 generates a received beam by delaying a preset time, phasing and adding the reflected echo signals from a plurality of input transducers. The generated reflected echo signal of the received beam is input to the signal processing unit 7 where image information is generated by processing of tomographic images and blood flow information. Image information generated by the signal processing unit 7 is converted into image data by a digital scan converter (DSC) 8 and an image is displayed on the display unit 9. The memory 10 stores various waveform data corresponding to the wave number of the drive signal, the number of sampling points, and data such as delay time.
That is, according to the measurement conditions such as the measurement mode, the transmission beam is changed by changing the aperture (number of transducers to be driven), the frequency, waveform and wave number of the drive signal, and the delay time for delaying the drive start time of each transducer. Is set to transmit data to control to the optimal shape. Therefore, in the memory 10, for example, the aperture, the optimal frequency, waveform, and wave number of the drive signal are determined for each measurement mode such as the tomographic imaging mode or the blood flow measurement mode, and each transducer constituting the aperture is further configured. Transmission data such as delay time is defined and stored. The delay time of each transducer gives a time difference to the drive timing of each transducer so that the wavefront of the ultrasonic wave radiated from each transducer constituting the aperture is converged to the focal position.

The transmission circuit 5 reads the transmission data for each measurement mode stored in the memory 10, generates a different drive signal for each transducer constituting the aperture, converts it to an analog signal by the D / A converter 3, and transmits it. A drive signal is output via the wave separation unit 2 to drive each vibrator constituting the aperture. Ultrasonic waves having different transmission data are radiated from the respective transducers into the subject, and the ultrasonic waves are synthesized to generate a transmission beam having a desired shape. In other words, the transmission circuit 5 includes a plurality of drive signal generation units respectively corresponding to the plurality of vibrators constituting the aperture. As is well known, each drive signal generation unit generates a delay unit that operates in response to a transmission start signal, and a drive signal having a waveform that is variably set in response to the drive start signal output from the delay unit. And a waveform generation unit that performs the configuration. The drive signal generation unit includes a weighting unit that is a feature of the present embodiment, and the weighting unit weights the amplitude of the drive signal output from the waveform generation unit and outputs the weight to the corresponding transducer. FIG. 2 shows a detailed configuration for realizing the aperture weighting function according to the characteristic configuration of the present embodiment of the transmission circuit 5 of FIG. As illustrated, the aperture weight coefficient generation circuit 18 includes weight coefficient generators 20-1 to 20-n provided corresponding to the plurality of vibrators 1 to n constituting the aperture. Each of the weight coefficient generation units 20-1 to 20-n has the same hardware configuration, and includes a control unit 21, an address generation circuit 22, a data buffer 23, a weight memory 24, an address switch 25, and an address buffer 26. The address counter 27 and the control signal / clock generation circuit 28 are provided. Each of the weighting factor generators 20-1 to 20-n generates aperture weighting factors A1 to An and outputs them to multipliers (not shown) that multiply the drive signals for driving the vibrators 1 to n.

  Each of the weight coefficient generation units 20-1 to 20-n operates based on the weight control clock signal 29 output from the drive signal generation control unit 14. The weight control clock signal 29 is applied to each transducer by multiplying the amplitude of the drive signal output from the waveform generation unit by the weighting factors A1 to An and changing the weighting factor in the time axis direction (temporally). It has become.

  In other words, the weight coefficient data is stored in the weight memory 24 via the data buffer 23. The address where the weight coefficient data is stored is generated by the address generation circuit 22 and is given to the address switch 25 via the address buffer 26. The address switch 25 switches the write and read addresses. When writing the weight coefficient data into the weight memory 24, the address switch 25 is switched to the write address. Further, write control is performed by the control signal / clock generation circuit 28. The operation of writing the weight coefficient data in the weight memory 24 is performed every time the drive signal is transmitted. Alternatively, a plurality of weight coefficient data is stored in advance corresponding to the measurement mode, and the weight coefficient data corresponding to the measurement mode to be executed is read from the weight memory 24 and multiplied by the drive signal. Can be output to the instrument. The weight memory 24 is a memory having a general single data input / output terminal, but a FIFO memory or the like can be used instead.

  Further, the control signal / clock generation circuit 28 connects the address switch 25 to the address counter 27 and switches to read in response to a command from the control unit 21, reads the weight coefficient data stored in the weight memory 24, and A different weighting factor is output for each clock to multiply the drive signal.

  As a result, as shown in FIG. 3, the weighting factor generators 20-1 to 20-n output weighting factors A1 to An (n = 5 in the illustrated example) that change in the time axis direction (temporal). . Then, the multipliers 13-1 to 13-n multiply the drive signals by weighting factors A1 to An that change with time, and output the result to each transducer. In the graph shown in FIG. 3, the vertical axis represents the value of the weighting coefficient, and the horizontal axis represents the time from the start of transmission. The weighting factor A1 is a weighting factor of the vibrator at the center of the aperture, and the weighting factor An is a weighting factor of the transducers at both ends of the aperture, and is set to a symmetric weighting factor with respect to the center of the aperture.

  The weight memory 24 has an address corresponding to the transmission time width, but it is also possible to change the weight value in a time shorter than the data change time width of the waveform generation unit. Thereby, it is also possible to control the bandwidth of the transmission frequency. That is, when different frequency components f1 to fn are recorded for each transducer 1 to n in the waveform generation unit and the weighting factors A1 to An have different function forms, the waveform generation unit radiates from a plurality of transducers constituting the aperture. By synthesizing the ultrasonic waves of the frequency components f1 to fn to form a transmission beam, the ratio of the frequency components of the synthesized transmission beam can be slightly changed.

  As described above, according to the present embodiment, since the weighting factors A1 to An added to the amplitude of the drive signal are changed with time for each vibrator, the following effects can be obtained.

  When n transducers are driven by the drive signal formed according to this embodiment, the frequency component can be accurately adjusted according to the depth for each position of the transmission wavefront of the ultrasonic wave radiated from each transducer. For example, in a transducer farther than the transducer at the center of the wavefront that does not contribute much to the imaging of the shallow area near the probe 1, a weighting factor that increases the low frequency component over time contributes to improved sensitivity in the depth portion. To do. On the other hand, the vibrator near the center of the aperture can keep the frequency band of the synthesized transmission beam constant by allocating the low frequency component in the reverse direction. By keeping the frequency band of the transmission beam constant, it is possible to prevent the image quality from deteriorating due to the deep depth.

  For example, when there is a strong reflector at a specific depth, the conventional technique has no ingenuity to transmit the transmission beam deeper than the reflector, and thus there is a problem that the deep portion cannot be drawn well. In this regard, according to the present embodiment, it is possible to reduce the low-frequency component ratio of the inner vibrator having the aperture corresponding to the depth and increase the low-frequency component ratio of the outer vibrator corresponding to the depth. Therefore, the ultrasonic transmission signal can reach a position deeper than the reflector, and the image quality and sensitivity can be improved.

  In addition, changing the frequency component mixing ratio with respect to the depth for each transducer is effective in improving the image quality. However, the frequency component mixing ratio is changed to that shown in FIG. It is preferable to adjust the distribution of the weighting factors shown. It is also possible to change the weighting coefficient in real time so as to optimize the captured image. In this case, it is possible to prepare a plurality of data groups in which the aperture pair and the frequency mixing ratio are changed for each depth, and to switch the data groups while observing the images to obtain an image most suitable for observation. The switching of the data group can be structured such that it can be continuously changed by a dial, a key switch, or other manual input means installed on a panel or the like. As a result, the retry can be easily performed, and the optimum weight data can be selected very efficiently by sending and returning the dial. As a result, the diagnostic efficiency is improved and the diagnostic cost is reduced.

  Furthermore, a method of automatically determining the optimum image by automating this is also possible. In this case, a method of comparing an image obtained from each data with a teacher image stored in advance and determining a combination most suitable for diagnosis is possible.

  As described above, according to the present embodiment, it is possible to generate a highly accurate and high S / N transmission beam for all the focal points for one transmission.

  In the embodiment of FIG. 2, the control signal / clock generation circuit 28 can switch the address of the weight memory 24 with a clock different from the transmission waveform memories 12-1 to 12-n. Furthermore, the clock frequency can be made variable according to the transmission state of the drive signal. Further, for example, it is possible to share the write address of the weight memory 24 and perform the write control at the same timing. Furthermore, although an example in which addresses are common to each memory has been described, it is also possible to individually control addresses and change clock speeds. In this case, more detailed weight control is possible. In addition, the weight function recorded in the weight memory 24 can be rewritten for each transmission, or a plurality of coefficients can be stored in advance and can be switched and output for each transmission by a method such as controlling the upper address of the memory. .

1 is an overall configuration diagram of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. FIG. 2 is a detailed configuration diagram of an aperture weight coefficient generation circuit of the transmission circuit of FIG. 1. It is a graph which shows an example of an aperture weighting coefficient.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Probe 5 Transmission circuit 6 Reception circuit 14 Drive signal generation control part 18 Aperture weight coefficient generation circuit 20 Weight coefficient generation part

Claims (2)

A transmission unit that generates a drive signal for an ultrasound probe that transmits an ultrasonic wave to a subject is included, and the transmission unit includes a plurality of drive signal generation units respectively corresponding to a plurality of transducers that form the aperture. Each of the drive signal generation units generates a delay unit that operates in response to a transmission start signal, and generates a drive signal having a waveform that is variably set in response to the drive start signal output from the delay unit. And a weighting unit that weights the amplitude of the drive signal output from the waveform generation unit and outputs the weight to the corresponding transducer.
The ultrasonic diagnostic apparatus, wherein the weighting unit is formed so that the weighting of the amplitude of the drive signal can be variably set in the time axis direction. In claim 1,
The transmission unit includes a drive signal generation control unit that controls the delay units, the waveform generation units, and the weighting units of the plurality of drive signal generation units, and the drive signal generation control unit An ultrasonic diagnosis characterized by individually controlling the delay time of each drive signal of the signal generation unit, the wave number and frequency components of the waveform, and the weighting coefficient of the amplitude variably set in the time axis direction. apparatus.

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