JP7025886B2 - Oscillator drive circuit and ultrasonic diagnostic equipment - Google Patents

Description

The present invention relates to an oscillator drive circuit, and more particularly to an oscillator drive circuit for generating ultrasonic waves containing a plurality of fundamental frequency components in the oscillator. The present invention also relates to an ultrasonic diagnostic apparatus using an oscillator drive circuit.

The ultrasonic diagnostic device is a device that transmits ultrasonic waves from the body surface toward the inside of the body and measures the reflected waves to observe the tissues in the body and measure the blood flow velocity and the like. It is also known that there is a trade-off relationship that a high ultrasonic frequency is advantageous for distance resolution, while a low ultrasonic frequency is advantageous for deep reach (penetration). There is.

A method (THI: Tissue Harmonics Imaging) for improving the distance resolution in a deep part by using the harmonics of low-frequency ultrasonic waves is known. Further, in order to improve the image quality of THI, an ultrasonic wave containing fundamental wave components having different frequencies (frequency f1, f2 (f2> f1)) is transmitted, and a high frequency component twice as high as the fundamental wave component contained in the reflected wave (frequency f1 and f2 (f2> f1)). It is known to use a frequency 2f1) and a difference sound component (frequency f2-f1) (Patent Document 1).

Japanese Unexamined Patent Publication No. 2004-298620 JP-A-2005-319177 (Fig. 5)

When transmitting ultrasonic waves having fundamental wave components having different frequencies, for example, when using amplitude modulation as described in Patent Document 2, driving of a complicated configuration including a plurality of power supplies having different absolute values. It is not suitable for miniaturization because it requires a circuit.

The present invention has been made in view of such problems of the prior art, and a main object thereof is to provide an oscillator drive circuit having a simple configuration for generating ultrasonic waves having fundamental wave components having different frequencies. To do.

The above-mentioned purpose is an oscillator drive circuit that drives an oscillator to generate an ultrasonic wave, and is a binary or ternary pulse obtained by approximating a modulated signal obtained by frequency-modulating a modulated wave with a carrier. It is achieved by an oscillator drive circuit characterized in that the oscillator is driven by a waveform-based voltage pulse.

With such a configuration, according to the present invention, it is possible to provide an oscillator drive circuit having a simple configuration for generating ultrasonic waves having fundamental wave components having different frequencies.

It is a schematic functional block diagram of the ultrasonic diagnostic apparatus using the drive circuit which concerns on embodiment of this invention. It is a figure which shows the example of the waveform of the voltage pulse output by the drive circuit which concerns on embodiment, and the frequency modulation signal which is the basis | common. It is a figure which shows another example of the waveform of the voltage pulse output by the drive circuit which concerns on embodiment, and the waveform of the frequency modulation signal which is | base | movement thereof. It is a figure which shows the example of the frequency spectrum, the waveform of the reflected wave, and the frequency spectrum of the ultrasonic wave generated by the voltage pulse output by the drive circuit which concerns on embodiment.

Hereinafter, the present invention will be described in detail with reference to the drawings based on an exemplary embodiment.
FIG. 1 is a block diagram showing a configuration example of the ultrasonic diagnostic apparatus according to the present invention. The ultrasonic diagnostic apparatus 100 includes a main body 120 and an ultrasonic probe 130 that can be attached to and detached from the main body 120. The function of the ultrasonic diagnostic apparatus 100 is realized by the control unit 101 controlling the operation of each unit. The control unit 101 has, for example, a programmable processor, reads a program stored in the non-volatile memory 102 into the system memory 103, executes the program, and controls the operation of each unit of the ultrasonic diagnostic apparatus 100. The control unit 101 may use a hardware circuit such as an ASIC or an ASSP as a part of the processing.

For example, the rewritable non-volatile memory 102 stores a program for execution by the control unit 101, GUI data, various setting values of the ultrasonic diagnostic apparatus 100, and the like. Data representing a waveform pattern for generating a pulsed voltage used by the drive circuit 104 to drive the vibrator 105 of the ultrasonic probe 130 (drive waveform pattern data) is also stored in the non-volatile memory 102. ..

The system memory 103 is a memory used by the control unit 101 to read and execute a program, or as a buffer for a received signal.

The drive circuit 104 (oscillator drive circuit) reads out the drive waveform pattern data selected by the control unit 101 from the non-volatile memory 102 among the plurality of drive waveform pattern data stored in the non-volatile memory 102. Then, the drive circuit 104 drives the oscillator 105 by generating a pulsed drive voltage based on the read drive waveform pattern data and applying it to the oscillator 105 in the probe.

The vibrator 105 included in the ultrasonic probe 130 is an electromechanical conversion element such as a piezoelectric element, and generates (transmits) ultrasonic waves by a voltage applied from a drive circuit 104. Further, the oscillator 105 converts the received vibration into an electric signal (observation signal) and outputs the signal. Although the details of the oscillator 105 are omitted here for the sake of ease of explanation and understanding, usually, a plurality of oscillators are arranged one-dimensionally or two-dimensionally in the probe, and the drive circuit 104 is used. Drives multiple oscillators separately at the timing according to the measurement type, setting, scanning method, etc.

The receiving circuit 106 executes processing such as noise reduction, amplification, A / D conversion, and addition on the observation signal output by the vibrator 105 of the ultrasonic probe 130, and stores it in the system memory 103 as reflected wave data. By controlling and adding the delay time of the received signal of each oscillator, the focus of the received signal can be increased.

The Doppler processing unit 107 is a signal corresponding to, for example, a continuous wave Doppler method, a pulse Doppler method, a color Doppler method (also called CFM (Color Flow Mapping)), a power Doppler method, or the like with respect to the reflected wave data stored in the system memory 103. Processing can be performed. Of the reflected wave data stored in the system memory 103, the address where the reflected wave data of the scanning line to be displayed based on the Doppler method is stored is given to the Doppler processing unit 107 by, for example, the control unit 101. The Doppler processing unit 107 generates an image (a waveform diagram or an image showing the blood flow velocity) representing the blood flow velocity for the target scanning line, and stores the image in the coordinate conversion memory 108.

The B mode processing unit 109 can perform signal processing corresponding to the B mode (mode in which the intensity of the reflected wave is represented by the luminance) for the reflected wave data stored in the system memory 103. Of the reflected wave data stored in the system memory, the address where the reflected wave data of the scanning line to be displayed in the B mode is stored is given to the B mode processing unit 109 by, for example, the control unit 101. The B-mode processing unit 109 generates an image showing the relationship between the depth and the intensity of the reflected wave for each target scanning line, and stores the image in the coordinate conversion memory 110.

The coordinate conversion memories 108 and 110 are for displaying a one-dimensional image in the depth direction generated by the Doppler processing unit 107 and the B mode processing unit 109 in units of scanning lines as a two-dimensional image on the display unit 112 of the raster scan method. Used for coordinate transformation. Although the coordinate conversion memories 108 and 110 are described as separate blocks, they may be implemented as different address blocks in one memory space.

The image composition unit 111 reads out the images stored in the coordinate conversion memories 108 and 110, generates a display image having a format according to the setting, and outputs the display image to the display unit 121. For example, in the case of performing CFM display, a display image is generated by synthesizing the CFM image read from the coordinate conversion memory 108 with the B mode image read from the coordinate conversion memory 110. Further, when the display is performed by the pulse Doppler method, a display image in which the B mode image read from the coordinate conversion memory 110 and the FFT waveform image read from the coordinate conversion memory 108 are arranged is generated. The format of the display image is determined according to the measurement mode and user settings.

The display unit 112 is, for example, a touch display. The display unit 112 may be an external device.

The operation unit 113 is a group of input devices such as buttons, switches, and dials for the user to input an instruction to the ultrasonic diagnostic apparatus 100. When the display unit 112 is a touch display, the touch panel portion is included in the operation unit 113.

Next, the drive voltage used by the drive circuit 104 of the present embodiment to drive the oscillator 105 will be described. Since the drive circuit 104 transmits an ultrasonic wave containing a plurality of fundamental wave components having different frequencies from the vibrator 105, a pulsed voltage having a voltage value pattern based on the waveform of the signal obtained by synthesizing the plurality of fundamental wave signals is used. Drives the oscillator 105.

Here, the drive circuit 104 utilizes frequency modulation in order to realize a voltage value pattern based on the waveform of a signal obtained by synthesizing a plurality of fundamental wave signals with one type of power supply. Specifically, the drive circuit 104 drives the vibrator 105 with a voltage having a binary or ternary pulse waveform obtained by approximating a modulated signal obtained by frequency-modulating a modulated wave with a carrier wave.

Here, when the frequency of the carrier wave is fc, the frequency of the modulated wave is fm, the modulation index is a, and the initial phase angle is θ [deg], the modulated signal Tx (fm) is expressed by the following equation (1). ..
Tx (fm) = cos (2π * fc * t + a * sin (2π * fm * t-π * θ / 180)) ... (1)

FIG. 2A shows the waveform (after normalization) norm_Tx of the modulated signal represented by the equation (1) when fc = 5.0 MHz, fm = 2.8 MHz, a = 1.6, and θ = 135 °. (Fm) and a ternary pulse signal PLS (fm) that approximates the normalized modulated signal are shown.

Here, a pulse signal that approximates the modulated signal can be obtained, for example, as follows.
First, the maximum absolute value of the modulated signal is obtained. Then, by dividing the value of the modulated signal by the maximum absolute value, the modulated signal norm_Tx (fm) normalized to the range of −1.0 to +1.0 is generated.

Next, the normalized modulation signal norm_Tx (fm) is converted into a ternary pulse signal PLS (fm) by a threshold value.
For example, if the threshold is ± 0.4
PLS (fm) = +0.7 (+0.4≤norm_Tx (fm) ≤ +1.0)
PLS (fm) = 0 (-0.4 ≤ norm_Tx (fm) <+0.4)
PLS (fm) = -0.7 (-1.0 ≤ norm_Tx (fm) <-0.4)
Can be. Note that 0.7 is a convenient value and may be another value. The threshold value can be appropriately determined according to the frequency band.

FIG. 2B shows a frequency spectrum of a normalized modulation signal norm_Tx (fm) and a pulse signal PLS (fm) that approximates the normalized modulation signal norm_Tx (fm). In each case, the components of the carrier frequency fc (second fundamental wave), the difference between the carrier and modulated wave frequencies fc-fm (first fundamental wave), and the sum of the carriers and modulated wave frequencies fc + fm (third fundamental wave) are used. Includes. In addition, it can be seen that the frequency spectrum does not change significantly due to the approximation.

By frequency modulation, a modulated signal including three fundamental wave components of carrier frequency fc and carrier frequency ± modulated wave frequency (fc ± fm) can be obtained. Therefore, the carrier frequency fc and the modulated wave frequency fm are determined so that the output frequency band of the vibrator 105 includes two or more fundamental wave components. The output frequency band of the vibrator is a band determined by the low frequency and the high frequency which are 3 dB lower than the power of the center frequency of the vibrator.

Further, by adjusting the modulation index a, the amplitude ratio of the first to third fundamental waves can be adjusted. For example, the modulation index a can be set so that the difference in the amplitudes of the fundamental waves included in the band of the oscillator becomes small. Further, by adjusting the initial phase angle θ, the distribution of the waveform on the time axis can be adjusted. For example, the initial phase angle θ can be set so that the frequency near the center on the time axis of each transmission waveform becomes low.

The optimum values of the modulation index a and the initial phase angle θ differ depending on the organ to be observed and the depth. Further, the frequency band of the oscillator 105 differs depending on the type of probe. Therefore, for each of the plurality of combinations of fc and fm corresponding to the assumed frequency band of the transducer 105, the pattern of the approximate pulse signal PLS (fm) corresponding to the plurality of combinations of the modulation index a and the initial phase angle θ ( A sequence of values of +0.7, 0, and −0.7) is obtained, and data representing the pattern is stored in the non-volatile memory 102.

The control unit 101 selects one of the PLS (fm) data stored in the non-volatile memory 102 according to the measurement mode and the setting based on the instruction by the user, and the information for specifying the selected data (for example, start). The address) is notified to the drive circuit 104.

The drive circuit 104 reads the PLS (fm) data from the non-volatile memory 102 according to the notified information. Then, the oscillator 105 is driven with a voltage corresponding to the pattern represented by the PLS (fm) data. Here, the drive circuit 104 associates +0.7 of the data with a positive voltage, 0 with a ground potential, and −0.7 with a negative voltage having the same absolute value as the positive voltage, and sets a voltage pulse for driving the vibrator 105. Can be generated. In this case, only two power supplies are required to drive the oscillator 105. Further, since the absolute values of the voltages may be the same only with different polarities, it is possible to suppress the complexity of the power supply circuit.

In the above example, the normalized modulation signal norm_Tx (fm) is converted into a ternary pulse signal, but it may be converted into a binary pulse signal PLS (fm).
For example, when the threshold value is 0,
PLS (fm) = +1.4 (0 <norm_Tx (fm) ≤ +1.0)
PLS (fm) = 0 (-1.0 ≤ norm_Tx (fm) ≤ 0)
Can be. Note that 1.4 is a convenient value for showing the relationship with +0.7 and −0.7 in the example close to the three values, and may be another value. In this case, since one positive voltage power supply is sufficient, the drive circuit 104 can be configured more easily than in the case of approximating the three values.

FIGS. 3A and 3B are approximated to the normalized modulation signal norm_Tx (fm) when fc = 5.0 MHz, fm = 2.8 MHz, a = 1.6, and θ = 135 °. The waveform and frequency spectrum of the binary pulse signal PLS (fm) are shown. The reproducibility of the frequency spectrum is slightly inferior as compared with the case of approximating the three values, but sufficiently good reproducibility is obtained in the output frequency band of the oscillator.

When an image is generated using the difference between the fundamental wave components contained in the reflected wave and the high frequency component as described in Patent Document 1, the drive circuit 104 uses the PLS (fm) data for positive and negative (polarity). ) Is inverted-to further generate a voltage pulse based on the PLS (fm) data. For example, the drive circuit 104 drives the oscillator 105 while switching between two voltage pulses whose polarities are inverted.

4 (a) and 4 (b) show the waveforms of + PLS (fm) and -PLS (fm) when fc = 5.0 MHz, fm = 2.8 MHz, a = 1.2, and θ = 65 °, and the waveforms thereof. The frequency characteristics are shown respectively. Both + PLS (fm) and -PLS (fm) are the first fundamental wave (frequency f1 (= fc-fm)), the second fundamental wave (frequency f2 (= fc)), and the third fundamental wave (frequency f3 (= fc + fm)). )) Has the components.

The oscillator is placed in water, and + PLS (fm) and -PLS (fm) are alternately applied to the oscillator four times toward the metal plate target placed at a distance of about 9.2 cm, and the reflected wave of + PLS (fm). Was added to generate the received signal + Rx (fm), and the reflected wave of −PLS (fm) was added to generate the received signal −Rx (fm). The waveform of the addition signal of + Rx (fm), -Rx (fm), and + Rx (fm) and -Rx (fm) and the frequency spectrum of the addition signal are shown in FIG. 4 (c).

Since the third fundamental wave is out of the band of the oscillator, most of it is not actually transmitted. In the added signal obtained by adding + Rx (fm) and -Rx (fm), the fundamental wave component is canceled out, and the difference tone component (frequency f2-f1 (= fm)) and the second harmonic (frequency 2f1 = 2 × (frequency 2f1 = 2 ×). It can be seen that it contains a large amount of fc-fm)). Therefore, the drive circuit 104 according to the present embodiment can be suitably used for carrying out THI.

As described above, according to the oscillator drive circuit according to the present embodiment, a plurality of basics are driven by driving the oscillator with a voltage pulse based on a binary or ternary pulse waveform that approximates a frequency-modulated signal. An ultrasonic wave containing a wave component can be generated at one or two voltages. Therefore, it is advantageous for the miniaturization and cost reduction of the circuit. Further, since it is possible to easily obtain a received signal including a difference tone component and a second harmonic component of a plurality of fundamental waves, it is also suitable for carrying out THI.

100 ... Ultrasonic diagnostic device, 101 ... Control unit, 102 ... Non-volatile memory, 103 ... System memory 103, 104 ... Drive circuit, 121 ... Display unit.

Claims (10)

It is an oscillator drive circuit that drives an oscillator to generate ultrasonic waves.
An oscillator drive circuit, characterized in that the oscillator is driven by a voltage pulse based on a binary or ternary pulse waveform obtained by approximating a modulated signal obtained by frequency-modulating a modulated wave with a carrier wave. The oscillator drive circuit according to claim 1, wherein the frequency of the carrier wave and the difference between the frequency of the carrier wave and the frequency of the modulated wave are included in the frequency band of the ultrasonic wave generated by the oscillator. The oscillator drive circuit according to claim 1 or 2, wherein the oscillator is driven while switching between the voltage pulse and the voltage pulse whose polarity is reversed. The oscillator drive circuit according to any one of claims 1 to 3, wherein when the pulse waveform has three values, it has 0 and two values having different polarities and the same absolute value. The oscillator drive circuit according to any one of claims 1 to 3, wherein when the pulse waveform has two values, it has 0 and a positive value. Further having a storage means for storing data representing the pulse waveform,
The oscillator is driven by reading the data from the storage means and applying a voltage corresponding to the value of the data.
The oscillator drive circuit according to any one of claims 1 to 5. When the modulation signal has the frequency of the carrier wave as fc, the frequency of the modulated wave as fm, the modulation index as a, and the initial phase angle as θ,
Tx (fm) = cos (2π * fc * t + a * sin (2π * fm * t-π * θ / 180))
The oscillator drive circuit according to any one of claims 1 to 6, wherein the oscillator drive circuit is represented by. A storage means for storing data representing pulse waveforms corresponding to each of the plurality of modulation signals having different modulation indices and initial phase angles.
Further having a selection means for selecting one of the data stored in the storage means according to the setting.
The oscillator is driven by reading the data selected by the selection means from the storage means and applying a voltage corresponding to the value of the data.
The oscillator drive circuit according to claim 7. With the oscillator
The oscillator drive circuit according to any one of claims 1 to 8, which drives the oscillator.
An ultrasonic diagnostic apparatus characterized by having. It is a control method of an ultrasonic diagnostic device having an oscillator.
The oscillator is driven by a voltage pulse based on a binary or ternary pulse waveform obtained by approximating a modulated signal obtained by frequency-modulating a modulated wave with a carrier to generate an ultrasonic wave in the oscillator. A control method for an ultrasonic diagnostic apparatus, which comprises a process.

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