JP4653709B2 - Ultrasonic diagnostic equipment - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus that transmits a plurality of ultrasonic waves having different center frequencies.

  In an ultrasonic diagnostic apparatus, in order to increase a frame rate (or volume rate), a plurality of reception beams are simultaneously formed. For the same reason, it has also been proposed to form a plurality of transmission beams simultaneously (or substantially simultaneously) (see Patent Documents 1-3). The latter is executed particularly when simultaneous transmission multistage focusing is performed. In other words, multiple transmission focuses are formed at different positions in the depth direction to improve the azimuth resolution imbalance in the depth direction, thereby improving the image quality of ultrasonic images (two-dimensional images, three-dimensional images, etc.). It is intended.

JP 61-48344 A JP-A-4-108439 JP-A-6-1114056

  When the above-described simultaneous transmission technique is applied, processing of the received signal becomes complicated. That is, it is necessary to discriminate the signal component corresponding to each ultrasonic wave from the received signal. For this reason, the problem that the circuit scale increases is pointed out. On the other hand, usually, a plurality of discriminated signal components are finally combined, but prior to that, there are many cases where adjustment of the size of each signal component is required. There is a need for a simple method for this purpose.

  An object of the present invention is to enable simplification of a received signal processing circuit in applying a simultaneous transmission technique.

  Another object of the present invention is to make it possible to easily adjust the size of each signal component when applying the simultaneous transmission technique.

  The present invention provides a transmission / reception means for transmitting a plurality of ultrasonic waves having different center frequencies simultaneously or successively into a living body, receiving a reflected wave from the living body and outputting a reception signal; Applying a plurality of quadrature detection processing corresponding to the plurality of ultrasonic waves to the received signal, outputting a plurality of complex signals corresponding to the plurality of ultrasonic waves, and output from the quadrature detection unit Real number component adding means for adding a plurality of real number components in a plurality of complex signals and generating a real number component after addition, and adding a plurality of imaginary number components in the plurality of complex signals output from the quadrature detection unit, and adding the imaginary number after addition Imaginary component addition means for generating components, a filter for real number components that applies low-pass processing to the real components after addition, and a filter for imaginary components that applies low-pass processing to the imaginary components after addition And said A luminance signal generation unit that generates a luminance signal for image formation based on the real component after addition output from the filter for several components and the imaginary component after addition output from the imaginary part component filter; The present invention relates to an ultrasonic diagnostic apparatus.

  According to the above configuration, since the quadrature detection unit performs addition for each complex component on a plurality of complex signals corresponding to a plurality of ultrasonic waves, low-pass processing can be applied to each complex component after addition. As a result, the number of low-pass filters can be reduced. Desirably, the number of low-pass filters can be halved as compared with the conventional method. Since the filter is generally composed of many parts, according to the above configuration, the circuit scale can be greatly reduced.

  Preferably, the plurality of ultrasonic waves includes a first ultrasonic wave having a first frequency bandwidth centered on a first center frequency and a second supersonic wave having a second frequency bandwidth centered on a second center frequency. The first frequency bandwidth and the second frequency bandwidth are substantially the same. By aligning the width of the frequency band of each ultrasonic wave, the cutoff frequency in the low-pass process for each complex component after addition can be made uniform. That is, in order to perform addition for each complex component and pass it to a common low-pass filter (or bandpass filter), a plurality of complex components to be added are the same as each other (in the baseband region after quadrature detection). It is desirable to have such a band, that is, it is assumed that the cutoff frequency of the filter can be made uniform. However, it is not always necessary to strictly match the frequency bandwidths of the ultrasonic waves, and the frequency bandwidth condition may be determined in consideration of the signal processing accuracy.

  Preferably, the quadrature detection unit includes a plurality of mixers arranged and arranged corresponding to the plurality of ultrasonic waves, and provided with a reference signal supply unit that supplies a plurality of reference signals to the plurality of mixers. The reference signal supply means has a function of varying the amplitudes of the plurality of reference signals. Preferably, the reference signal supply means weights and varies the amplitudes of the plurality of reference signals according to the depth of the received sample point. According to this configuration, weighting can be performed simultaneously with quadrature detection. The circuit scale can be reduced as compared with the case where weighting is performed after conversion to a complex signal. Therefore, combining the low-pass processing after addition for each complex component described above and this reference signal weighting processing can simplify the overall configuration of the device and reduce the device cost, thus increasing the practical value. It is done.

  Preferably, the plurality of ultrasonic waves includes a first ultrasonic wave having a first center frequency and a second ultrasonic wave having a second center frequency, and the plurality of complex signals are converted into the first ultrasonic wave. A first complex signal corresponding to the second ultrasonic signal and a second complex signal corresponding to the second ultrasonic wave, wherein the reference signal supply unit gives a large weight to the first complex signal in the first range in the depth direction. And reversing the weight relationship for the first complex signal and the second complex signal within a second range deeper than the first range, and in a third range deeper than the second range. A large weight is given to the second complex signal. According to this configuration, it is possible to improve image quality by preventing a drop in sensitivity of two ultrasonic waves and preventing or reducing the occurrence of joints that cause a sense of incongruity on the image.

  As described above, it is desirable to combine the technique of variable weighting of a plurality of reference signals with the technique of reducing the number of low-pass filters by performing low-pass processing after addition for each complex component in transmission multistage focus. However, it can be used in other combinations.

  As described above, according to the present invention, it is possible to simplify the received signal processing circuit when applying the simultaneous transmission technique. Alternatively, according to the present invention, the size of each signal component can be easily adjusted in applying the simultaneous transmission technique.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the overall configuration of an ultrasonic diagnostic apparatus according to the present invention. This ultrasonic diagnostic apparatus has a simultaneous transmission multistage focus function.

  The transducer 10 is provided in an ultrasonic probe (not shown), and the transducer 10 is an array transducer composed of a plurality of transducer elements in the present embodiment. An ultrasonic beam is formed by the vibrator 10, and the ultrasonic beam is electronically scanned. As an electronic scanning method, electronic sector scanning, electronic linear scanning, and the like are known. A 1D array transducer can be provided, or a 2D array transducer can be provided.

  The transmission unit 12 functions as a transmission beam former. That is, it has a function of supplying a plurality of transmission signals to a plurality of vibrators. In the present embodiment, two types of transmission signals are simultaneously supplied to each transducer in order to realize simultaneous transmission multistage focusing. Alternatively, a synthesized signal obtained by synthesizing two types of transmission signals is supplied. Specific examples of the two types of transmission signals will be described later with reference to FIGS. 3 and 4. However, the center frequencies of the transmission signals are different from each other, and the widths of the frequency bands of the transmission signals are substantially different from each other. Identical. By transmitting ultrasonic waves using two types of frequencies and processing the received signals obtained thereby, it is possible to discriminate two types of received signals corresponding to the two types of transmission frequencies. Incidentally, one of the two types of transmission signals is generated for transmission / reception for short distance, and the other is generated for transmission / reception for long distance. This will be described later with reference to FIG.

  The reception unit 14 functions as a reception beam former. That is, a plurality of reception signals output from a plurality of transducers constituting the transducer 10 are subjected to phasing addition processing in the reception unit 14. A reception beam is electronically formed by this phasing addition processing, and a reception signal after phasing addition corresponding thereto is output to the quadrature detection unit 16.

  The quadrature detection unit 16 has a characteristic configuration in the present embodiment, which will be described below. The quadrature detection unit 16 includes two mixer pairs (corresponding to quadrature detectors) 18 and 20, two adders 30 and 32, and two low-pass filters (LPF) 34 and 36. The mixer pair 18 is composed of two mixers 20 and 22, and a pair of reference signals different in phase by 90 degrees are supplied to the mixers 20 and 22, respectively. When the center frequencies of the two types of transmission signals described above are f1 and f2, respectively, the frequency of the pair of reference signals supplied to the mixer pair 18 is f1. Similarly, the mixer pair 20 includes two mixers 24 and 26, and the pair of reference signals supplied to them are 90 degrees out of phase with each other, and the frequency thereof is f2. That is, in this embodiment, two quadrature detectors are provided corresponding to the two transmission frequencies.

  However, as shown in FIG. 1, for the two complex signals output from the two mixer pairs 18, 20, two real components and two imaginary components are added by adders 30, 32 for each component. The added real number component is output from the adder 30, and the added imaginary number component is output from the adder 32. Each signal is input to the LPFs 34 and 36. The LPFs 34 and 36 perform low-pass processing on each signal dropped into the baseband region by the above-described quadrature detection processing, that is, remove signal components other than the baseband region.

  The absolute value calculator 38 performs an absolute value calculation on each signal after low-pass processing output from the LPFs 34 and 36. Specifically, after adding the square of each signal, A luminance signal is generated by performing a square root operation on the addition result. The luminance signal is input to a logarithmic converter 40 and subjected to logarithmic conversion processing, and then input to a digital scan converter (DSC) 42.

  The DSC 42 has a coordinate conversion function, an interpolation function, and the like, and executes a process of mapping an input luminance signal onto display coordinates. Thereby, an in-vivo tomographic image is constructed. The image data is sent to the display unit 44.

  The reference signal generator 28 is a circuit that generates two pairs of reference signals to be provided to the quadrature detector 16. Each reference signal may be stored on a memory such as a RAM. Alternatively, each time the reference signal is generated by operating the signal generator. The reference signal generator 28 has a function of performing weighting processing on each pair of complex signals by weighting each reference signal. This will be described later with reference to FIGS.

  The control unit 46 performs operation control of each component shown in FIG. The operation panel 48 includes a keyboard, a track bowl, and the like, and the user can set operating conditions using the operation panel 48.

  FIG. 2 is a schematic diagram showing the concept of simultaneous transmission multistage focus. In this example, the vibrator 10 includes a plurality of vibration elements arranged linearly. In the present embodiment, two ultrasonic beams 50 and 52 are simultaneously formed, and the ultrasonic beam 50 is formed using the opening D1 with the transmission focus point F1 as a focal point. The depth of the transmission focus point F1 is d1. The ultrasonic beam 52 is generated with the opening D2 with the transmission focus point F2 as a focal point, and the depth of the transmission focus point F2 is d2. In the present embodiment, the transmission beam 50 is generated by an ultrasonic wave having a center frequency f1, and the ultrasonic beam 52 is formed by an ultrasonic wave having a center frequency f2. The ultrasonic beams 50 and 52 are transmission beams, and the reception beam is not shown in FIG. By using multiple ultrasonic waves with different center frequencies, the received signal components corresponding to each transmitted ultrasonic wave are discriminated and extracted even if they are transmitted at the same time. Is possible. This is a known technique. Incidentally, although two types of transmission frequencies are used in the present embodiment, of course, three or more types of transmission frequencies may be used. In addition, a plurality of ultrasonic waves may be transmitted at the same time, but a plurality of ultrasonic waves may be transmitted with a time shift.

  FIG. 3 shows the frequency spectrum of the transmitted ultrasonic wave. The horizontal axis is frequency and the vertical axis is power. Reference numeral 100 indicates a frequency characteristic (band) of the vibrator. In the present embodiment, two frequency spectra 102 and 104 are set in the band 100, the frequency spectrum 102 corresponds to the first ultrasonic wave, the center fraction is f1, and the width of the band is This is indicated by reference numeral 102A. The frequency spectrum 104 corresponds to the second ultrasonic wave, the center frequency is f2, and the width of the band is indicated by reference numeral 104A. Here, the bandwidths 102A and 104A of the two spectra are substantially the same in this embodiment. Incidentally, the widths 102A and 104A are, for example, half widths. As will be described later, by aligning the bandwidth of two transmission ultrasonic waves, it is possible to align the cutoff frequency in the low-pass processing for the received signals corresponding to those ultrasonic waves. As shown in FIG. 1, it is possible to perform low-pass processing after performing addition for each complex component after complex signal conversion.

  Incidentally, in FIG. 3, reference numerals 200 and 202 denote baseband shifts by quadrature detection, and actually, baseband shifts are generated by the quadrature detection processing for the reception spectra corresponding to the frequency spectra 102 and 104 described above. become.

  FIG. 4 shows two transmission signals, (A) shows a transmission signal 106 corresponding to the first ultrasonic wave, and (B) shows a transmission signal 108 corresponding to the second ultrasonic wave. Has been. The band and amplitude (envelope) of each transmission signal are substantially the same.

  FIG. 5 shows a specific configuration example of the LPFs 34 and 36 shown in FIG. The LPF is constituted by a delay train 54, a multiplier train 56 and an adder 58 as shown in the figure. The delay train 54 is constituted by a plurality of delay devices 54A connected in series, and the multiplier train 54 is arranged in parallel. The plurality of multipliers 56A. Each delay unit 54A delays the input signal by a predetermined time unit, and each multiplier 56A multiplies the input signal by a coefficient. The configuration shown in FIG. 5 is known.

  FIG. 6 shows a comparative example of the quadrature detection unit. In addition, the same code | symbol is attached | subjected to the same structure shown in FIG. 1, and the description is abbreviate | omitted. In the quadrature detection unit 16 shown in FIG. 6, a pair of LPFs 62 and 64 are provided in the subsequent stage of each mixer pair 18, and their outputs are input to the absolute value calculator 70. Similarly, the output of the mixer pair 20 is input to a pair of LPFs 66 and 68, and their outputs are input to the absolute value calculator 72. The adder 73 adds the signals output from the absolute value calculators 70 and 72. Even with such a configuration, it is possible to obtain the same processing result as that of the quadrature detection unit 16 shown in FIG. 1, but as is clear from the comparison between FIG. 1 and FIG. Is increasing in the comparative example. In other words, the configuration of FIG. 1 has an advantage that the number of LPFs can be reduced. That is, in the present embodiment, the bandwidths of the two transmission signals are made uniform so that the cut-off frequencies of the LPFs 62, 64, 66, and 68 shown in FIG. It is possible to perform addition processing in the preceding stage, and the number of LFPs can be reduced. Of course, it suffices to determine the degree of matching of the bands between a plurality of transmission signals from the relationship with the required image quality, and it is not always necessary to completely match the respective bands.

  FIG. 7 shows two reception (luminance) profiles corresponding to two transmission beams. They represent reception sensitivity. In the reception profile 74, the sensitivity is highest at the short-distance focal point F1, while in the reception profile 76, the sensitivity is highest at the long-distance focal point F2. M represents the boundary area. As described above, since the luminance changes in the respective reception profiles 74 and 76 along the depth direction, in order to form a uniform image, the depth with respect to the reception signals corresponding to the respective transmission frequencies. It is necessary to perform weighting along the direction (weighted addition processing).

  In this case, in the circuit configuration shown in FIG. 1, it is possible to weight each of the two signals input to the adders 30 and 32, but in order to further reduce the circuit scale, the present embodiment is implemented. In the embodiment, the reference signals supplied to the mixers 20, 22, 24, and 26 are weighted in advance.

The weighting function in that case is shown in FIG. 8. Reference numeral 78 indicates the weighting function for the two reference signals supplied to the mixer pair 18 shown in FIG. 1, and similarly, reference numeral 80 is shown in FIG. 2 shows a weighting function for a pair of reference signals supplied to the mixer pair 20. For convenience, three sections can be defined along the depth direction. The first section is a period in which the weighting function 78 is dominant, and the second period is a period in which the two weighting functions 78 and 80 cross each other. The third interval is an interval in which the weighting function 80 is dominant. That is, as is clear from the contents shown in the drawing, in the first section, the weight value of the weighting function 78 is 1 (the weight value of the weighting function 80 is 0) throughout the first section, and in the second section, As the depth increases, the weight value of the weighting function 78 decreases from 1 to 0 and at the same time the weight value of the weighting function 80 increases from 0 to 1 (both functions cross on the way). The weight value of the weighting function 80 is 1 (the weight value of the weighting function 78 is 0).

  FIG. 9 shows a reference signal generated by applying two weighting functions as shown in FIG. (A) shows a waveform 81 of a reference signal supplied to the short distance, that is, the mixer 22 shown in FIG. (B) shows a waveform 82 of a reference signal supplied to the long-distance mixer 26 shown in FIG. Incidentally, only a sine waveform is shown in FIG. 9, and a cosine waveform is generated in the same manner. As shown, the amplitude of the waveform is varied as a result of the weighting function shown in FIG. 8 being applied to the waveform. By supplying such a reference signal to each mixer, weighting processing can be performed simultaneously with quadrature detection, and with such a configuration, uniformity of reception sensitivity in the depth direction can be ensured, and the circuit scale of the apparatus Can be significantly reduced.

1 is a block diagram showing an overall configuration of an ultrasonic diagnostic apparatus according to the present embodiment. It is a schematic diagram which shows two transmission beam profiles. It is a figure which shows the zone | band of a vibrator | oscillator, and two transmission spectra. It is a figure which shows the waveform of two transmission signals. It is a figure which shows the general structure of a low-pass filter. It is a block diagram which shows a comparative example. It is a figure which shows two reception profiles. It is a figure which shows two weighting functions. It is a figure which shows two reference signals.

Explanation of symbols

  10 transducers, 12 transmitters, 14 receivers, 16 quadrature detectors, 18, 20 mixer pairs, 20, 22, 24, 26 mixers, 30, 32 adders, 34, 36 low-pass filters (LPF), 38 absolute value calculation vessel.

Claims (5)

Transmitting / receiving means for transmitting a plurality of ultrasonic waves having different center frequencies simultaneously or successively into a living body, receiving a reflected wave from the living body and outputting a reception signal;
Applying a plurality of quadrature detection processing corresponding to the plurality of ultrasonic waves to the received signal, and outputting a plurality of complex signals corresponding to the plurality of ultrasonic waves, and a quadrature detection unit,
Real number component addition means for adding a plurality of real number components in a plurality of complex signals output from the quadrature detection unit and generating a real number component after addition;
An imaginary number component adding means for adding a plurality of imaginary components in a plurality of complex signals output from the quadrature detection unit and generating an imaginary number component after the addition;
A real component filter that applies low-pass processing to the added real component;
An imaginary component filter that applies low-pass processing to the imaginary component after addition; and
A luminance signal generation unit that generates a luminance signal for image formation based on the added real number component output from the real number component filter and the added imaginary number component output from the imaginary number component filter;
An ultrasonic diagnostic apparatus comprising: The apparatus of claim 1.
The plurality of ultrasonic waves includes a first ultrasonic wave having a first frequency bandwidth centered on a first center frequency, a second ultrasonic wave having a second frequency bandwidth centered on a second center frequency, and Including
The first frequency bandwidth and the second frequency bandwidth are substantially the same;
An ultrasonic diagnostic apparatus. The apparatus of claim 1.
The quadrature detection unit has a plurality of mixers arranged corresponding to the plurality of ultrasonic waves,
Reference signal supply means for supplying a plurality of reference signals to the plurality of mixers is provided,
The reference signal supply means has a function of varying the amplitude of the plurality of reference signals.
An ultrasonic diagnostic apparatus. The apparatus of claim 3.
The ultrasonic diagnostic apparatus, wherein the reference signal supply means weights and varies the amplitudes of the plurality of reference signals according to the depth of a received sample point. The apparatus of claim 4.
The plurality of ultrasonic waves includes a first ultrasonic wave having a first center frequency and a second ultrasonic wave having a second center frequency;
The plurality of complex signals include a first complex signal corresponding to the first ultrasonic wave and a second complex signal corresponding to the second ultrasonic wave,
In the first range in the depth direction, the reference signal supply means gives a large weight to the second range deeper than the first range by increasing the amplitude of the first complex signal over the entire first range. Within the range, the amplitude of the first complex signal is decreased according to the depth, and at the same time the amplitude of the second complex signal is increased, so that the first complex signal and the second complex signal are in the middle of the second range. Reversing the magnitude relationship of the weights, and in the third range deeper than the second range , a large weight is given by increasing the amplitude of the second complex signal over the entire third range .
An ultrasonic diagnostic apparatus.

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