JP2007105360A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a satisfactory picture by removing an influence of the movement of a patient between transmission and reception in an ultrasonic diagnostic apparatus performing synthetic aperture. <P>SOLUTION: Transmission and reception are performed three times at the center position of the same aperture. Based on received signals obtained by selecting the same vibrator at the first and second times, phase shifting due to the movement of the patient is calculated. When a received signal obtained by selecting a different vibrator at the third time and the received signal at the second time are added after phase correction, data of twice transmission and reception by the same aperture are used, so that precise phase correction is possible. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus that performs transmission and reception using an array transducer.

  An ultrasound imaging apparatus that performs synthetic aperture scanning is known. This ultrasonic imaging apparatus is known, for example, from (Non-Patent Document 1), and the operation principle will be described below with reference to a schematic block diagram shown in FIG.

  In FIG. 4, the ultrasonic probe 1 includes transducers T1 to T8. The transducer Tn generates an ultrasonic pulse, and the ultrasonic pulse reflected in the subject is received by the transducer Tn as an echo ultrasonic wave. The received signal received by the transducer Tn passes through the multiplexer (MUX) 100, is amplified by the amplifier 102, is converted into digital data by the A / D 103, and is written in the memory 104. When the writing of the reception signal from the transducer Tn to the memory 104 is completed, the MUX 100 next selects a transducer Tn ′ different from the transducer Tn, and writes the reception signal to the memory 104 as in the case of the transducer Tn. . The reception signals obtained by the transducers T1 to T8 as described above are written in the memory 104. Next, in the adder 105, each reception signal obtained by the transducers T1 to T8 stored in the memory 104 is added with a predetermined time difference.

  In this way, the transmission / reception sequence by the transducers T1 to T8 is performed one by one and the signals are integrated, thereby obtaining the same effect as that received simultaneously by the eight transducers.

  If it is assumed that the subject is stationary during the reception period by the transducers T1 to T8, reception directivity such as convergence and deflection in the subject can be given to the ultrasonic probe 1. The received signal added by the adder 105 as described above is subjected to signal processing such as detection by the signal processor 106 and displayed on the display unit 107.

  However, the ultrasonic diagnostic apparatus having the conventional synthetic aperture has a problem that an accurate synthetic aperture cannot be performed when the subject moves during the reception period of the transducers T1 to T8.

  An improvement method when the subject exercises will be described with reference to FIG.

  In FIG. 8, the probe 1 is composed of transducers T1 to T16. The switches 109 to 112 are 4: 1 switches, and the drive pulse signal of the transmission circuit 108 is selected by the switches 109 to 112 and sent to the four vibrators. For example, if the switches 109 to 112 are all connected to a, the transducers T1 to T4 are selected. In this state, when the switch 109 is switched to b, the vibrators T2 to T5 are selected. In this way, the switches 109 to 112 are sequentially switched to change the opening position and repeat transmission / reception to perform two-dimensional scanning.

  Ultrasound radiated from the selected transducer and reflected in the subject (not shown) is converted to an electrical signal by the same transducer, and converted to a digital signal by the A / D converters 113 to 116 via the switches 109 to 112. After being delayed and added by the beam synthesizer 117, the signal is detected by the detector 121 through the aperture synthesizer 2, scan-converted by the digital scan converter (DSC) 122, and displayed on the display unit 107.

  The operation at the time of the synthetic aperture will be described with reference to FIG.

  FIG. 9 shows an example of transmission and reception when the opening center is located between T6 and T7.

  A transmission / reception sequence is performed twice with respect to the center of the opening. Transmission is performed using the transducers T5 to T8 for the first time and the second time. In FIG. 8, the switches 109 to 112 are all connected to b.

  For the first reception, transducers T5 to T8 are used (this is called an inner opening). All the switches 109 to 112 remain connected to b. Immediately after the second transmission, the connections of switches 109 and 110 are changed to c, and switches 111 and 112 are changed to a. Thereby, in the second reception, the transducers T3, T4, T9, and T10 are used (this is called an outer opening).

  In this way, aperture synthesis is realized by performing transmission and reception twice at the same aperture center and switching the reception aperture between inside and outside.

  In FIG. 8, the signal obtained by delay-adding the first received signal is stored in the memory 3 of the aperture adder 2 and output from the memory 3 at the time of the second reception, The adder 12 adds the values.

As described above, in this method, since the synthetic aperture transmission / reception sequence is performed twice, the influence of the movement of the subject is less than that of the conventional first synthetic aperture example.
PDCorl, et al. "A digital synthetic imaging system for NDE", Proc IEEE Ultrasonics Symp., Sept. 1978

  However, even in the second method of the conventional example, when the movement speed of the subject is large enough to cause the signal phases to be different between the first transmission / reception and the second transmission / reception and cancel each other, the image quality is affected by the movement. There is a problem of deterioration.

  An object of the present invention is to solve these problems and to provide a good image quality even when the movement of a subject is fast.

  The present invention realizes an ultrasonic diagnostic apparatus with excellent image quality by eliminating a signal difference due to movement of a subject between a plurality of transmissions and receptions of a synthetic aperture.

  According to the first aspect of the present invention, a plurality of arranged transducers, a switch for selecting a signal to be input to a beam former from signals received by the transducer, and beam formation by a signal selected by the switch. A beamformer to be performed, a memory for temporarily storing the output of the beamformer, and an adder for adding the outputs of the memory and the beamformer, and a plurality of transmission / reception sequences to the subject using the same aperture A synthetic aperture method in which one beam is formed by a plurality of transmission / reception sequences including a signal, and a phase shift due to body movement of the subject between the transmission / reception sequences is detected from signals obtained by the plurality of transmission / reception sequences using the same aperture Phase difference is eliminated by providing means and means for aligning the phases of received signals obtained in transmission and reception sequences at different apertures. It is possible to prevent the deterioration of quality.

  In the second aspect of the invention, as means for detecting the phase difference between the two signals, the phase difference can be easily corrected by detecting the timing at which the signal amplitude crosses zero and changes from positive to negative or from negative to positive. Can be done.

  In the invention of claim 3, by using a correlator as means for detecting the phase difference between the two signals, the phase difference can be easily and accurately corrected.

  According to the fourth aspect of the present invention, the transmission / reception sequence in the same opening for detecting the phase shift is not performed every time, so that the phase difference can be corrected while suppressing the decrease in the frame rate.

  According to the ultrasonic diagnostic apparatus of the present invention, when performing synthetic aperture, the phase of the received signal by each transmission / reception is detected and aligned to prevent signal cancellation due to the phase difference generated when the subject moves. An image with good image quality can be obtained.

  Hereinafter, the implementation of the present invention will be described with reference to FIGS.

(Embodiment 1)
FIG. 1 is an example of a schematic block diagram of an ultrasonic diagnostic apparatus that performs the synthetic aperture method in the first embodiment of the present invention. The contents of the present invention will be described below with reference to FIG.

  In the present invention, whether the aperture addition unit 2 uses the outputs of the memories 3 and 4 and the beam combiner 117 that store signals from the first and second transmission / reception, or uses the data stored in the memories 3 and 4. Switches 5, 6 for selecting the zero cross detectors 6, 7, 2 for detecting the timing at which the amplitude of the signal received in the first and second transmission / reception signals changes from zero to positive or negative or from negative to positive A delay amount calculator 8 that calculates how much delay is applied to which signal from the output of the zero cross detector, a memory 9 that temporarily stores the delay amount calculated by the delay amount calculator 8, and a delay amount calculator 8 Based on the delay amount calculated in step 1, the delay units 10 and 11 that delay each signal and the adder 12 that adds the two signals delayed by the delay units 10 and 11 are configured.

  The following operation is performed with the above configuration. Transmission / reception is performed three times, and reception is performed with the same opening for the first two times and with another opening for the last one time.

  First, transmission / reception is performed for the first time, and the received signal is stored in the memory 4. Next, a second transmission / reception is performed to obtain a reception signal. At this time, the signal is stored in the memory 3. At the same time, the switch 5 is connected to a, and this received signal detects the timing at which the received signal changes from positive to negative or from negative to positive by the zero cross detector 7. At the same time, the received signal by the first transmission / reception is read from the memory 4 and the timing at which the received signal changes from positive to negative or from negative to positive is detected by the zero cross detector 8. The information detected by these two zero-cross detectors 7 and 8 is calculated by a delay amount calculator 9 which is advanced (or delayed) and stored in the delay amount memory 10.

  The signal obtained in the third transmission / reception is input to the delay unit 10 without switching to the memory 4 by switching the switch 6 to a. At the same time, the switch 5 is connected to b, and the signal of the second transmission / reception sequence stored in the memory 3 is read and input to the delay device 9.

  The signals input to the delay units 11 and 13 are delayed by controlling the output of the delay memory 10, the phase shift due to the movement of the subject is corrected, added by the adder 12, and output as one signal. Thus, it is possible to prevent the image quality from being deteriorated due to the movement of the subject.

  An example of the internal configuration of the zero-cross detectors 7 and 8 and an operation explanatory diagram thereof are shown in FIG. As shown in FIG. 2A, the inside of the zero-cross detector is composed of a comparator 20, a signal delay device 21 for one data rate, a NOT gate 22, and an AND gate 23. When the input signal IN1 of the comparator 20 becomes larger than the threshold value IN2 (here, zero), the output OUT changes from 0 to 1. An output signal is generated by the delay device 21, the NOT gate 22, and the AND gate 23.

  The operation is as shown in FIG. 2B, and the output signal becomes 1 for one clock after the input signal is switched from negative to positive.

  This operation is performed on the first received signal and the second received signal to obtain output signals 1 and 2 in FIG.

  Using a clock signal as shown in the figure, the amount of delay is calculated by counting the time when the delay time count signal becomes 1 with a counter (not shown).

  The delay amount data is stored in the delay amount memory 10 of FIG. 1, and the delay units 11 and 13 are controlled to synchronize the timings of the two signals.

  The delay units 11 and 13 are, for example, FIFO memories, which write input signals at a constant timing and delay the timing of output signals by controlling the delay amount memory 10.

  In the present embodiment, the phase shift due to the movement of the subject is calculated using the received signals obtained from the same aperture. According to this method, for example, in the method of calculating the phase shift from the received signal obtained by using the opening on the middle side at the first time and the outer side at the second time, the path to the transducer of the signal reflected in the subject is There is no influence due to the difference, and the accuracy can be improved.

  A transmission / reception sequence for obtaining a two-dimensional image by sequentially changing acoustic lines will be described with reference to FIG. 2 and (Table 1).

  As shown in FIG. 3, the acoustic lines are gradually changed with respect to the arrayed transducers 1 such as a, b, c... To form a two-dimensional image. This principle is the same as that of a known ultrasonic diagnostic apparatus. In this embodiment, the transmission / reception sequence is performed three times for each acoustic line. Table 1 shows how the transmission / reception sequence from the first time to the twelfth time is performed. In the first to third times, transmission / reception is performed with the opening center position being a. The reception aperture is the first and second times, and the third time is outside. The first and second transmission / reception sequences are used for phase detection, and the second and third transmission / reception sequences are used for aperture synthesis.

  Thereafter, the aperture synthesis is performed for the aperture positions b, c, and d at the 4th to 6th times, the 7th to 9th times, and the 10th to 12th times.

  Table 2 shows another example of the transmission / reception sequence in this embodiment. In this example, the movement of the subject is detected only when the transmission / reception positions are a, c, and e, the phase change is not detected at the openings b and d, and the data on the phase change at the adjacent openings is used. . For example, the phase change data at the opening position a is used at the opening position b. Thereby, the number of transmission / reception sequences for obtaining one image can be reduced, and a high frame rate can be obtained.

(Embodiment 2)
FIG. 4 is an example of a schematic block diagram of an ultrasonic diagnostic apparatus that performs the synthetic aperture method according to the second embodiment of the present invention. The contents of the present invention will be described below with reference to FIG.

  Similar to the first embodiment, the probe 1 performs transmission / reception three times at the same opening position to detect the movement of the subject and synthesize the inner opening and the outer opening.

  In the present embodiment, the movement of the subject is detected by a correlator.

  First, transmission / reception is performed for the first time, and the received signal is stored in the memory 4. Next, a second transmission / reception is performed to obtain a reception signal. At this time, the signal is stored in the memory 3. At the same time, the switch 5 is connected to a and this received signal is input to the correlator 14. At the same time, the received signal by the first transmission / reception is read from the memory 4 and input to the correlator 14. The correlator 14 correlates these two received signals, finds the phase difference, and stores it in the phase memory 15.

  The signal obtained by the third transmission / reception is input to the adder 12 without passing through the memory 4 by switching the switch 6 to a. At the same time, the switch 5 is connected to b, and the signal of the second transmission / reception sequence stored in the memory 3 is read and input to the phase shifter 15.

  The phase shifter 15 corrects the phase shift due to the movement of the subject based on the data in the phase memory 15 and controls the phase of the input signal so that the phase is the same as that of the third received signal. Thus, it is possible to prevent the image quality from being deteriorated due to the movement of the subject.

  The internal configuration of the correlator in the present embodiment will be described with reference to FIG. The correlator is composed of a quadrature detector and a cross correlator.

  FIG. 5A shows the configuration of the quadrature detector. It comprises multipliers 24 and 25 and low-pass filters 26 and 27. A reference signal having a frequency substantially equal to the center frequency of the transmission pulse is input to the multipliers 24 and 25, and the phases of the reference signals differ by 90 degrees in the multipliers 24 and 25.

  The multipliers 24 and 25 multiply the input signal by the reference signal, and the low-pass filters 26 and 27 remove harmonic components. The output signals are I and Q.

  Orthogonal detection outputs I1n and Q1n of depth n in the first transmission / reception and quadrature detection outputs I2n and Q2n of the same depth in the second transmission / reception are input to the correlator 28 as shown in FIG. 5B.

  The correlator 28 calculates and outputs the phase difference θn between the first and second signals by vector calculation as shown in FIG.

  FIG. 6 shows an internal configuration of the phase shifter in the present embodiment. The phase shifter includes an all-pass filter 29 that rotates the phase by 90 degrees, variable gain amplifiers 30 and 31, and an adder 32.

  The all-pass filter 29 adds a signal having a phase difference of 90 degrees and the original signal at an appropriate amplitude ratio in the variable gain amplifiers 30 and 31. The gains of the variable gain amplifiers 30 and 31 are set so that the amplitude of the phase shift output is equal to the input and an arbitrary phase rotation is obtained. The gain range is −1 to 1.

  As in the first embodiment, in the present embodiment, the phase information at adjacent opening positions can be used for correction without performing phase detection at all opening positions.

  The ultrasonic diagnostic apparatus according to the present invention, when performing synthetic aperture, prevents signal cancellation due to a phase difference that occurs when the subject moves by detecting and aligning the phase of the received signal by each transmission and reception. This is useful as an ultrasonic diagnostic apparatus and the like.

1 is a schematic block diagram of an ultrasonic diagnostic apparatus that performs a synthetic aperture according to a first embodiment of the present invention. Explanatory drawing of the transmission / reception sequence in the 1st Embodiment of this invention Explanatory drawing of zero cross detection and delay in the first embodiment of the present invention Schematic block diagram of an ultrasonic diagnostic apparatus for performing synthetic aperture in the second embodiment of the present invention Explanatory drawing of the phase detection by the correlator in the 2nd Embodiment of this invention Explanatory drawing of the phase shift in the 2nd Embodiment of this invention 1 is a schematic block diagram of an ultrasonic diagnostic apparatus for performing synthetic aperture in the first conventional example of the present invention. Schematic block diagram of a conventional ultrasonic diagnostic apparatus Another schematic block diagram of a conventional ultrasonic diagnostic apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Probe T1-T16 Vibrator 2 Aperture synthetic | combination part 3, 4 Memory 5, 6 Switch 7, 8 Zero cross detector
DESCRIPTION OF SYMBOLS 9 Delay amount calculator 10 Delay amount memory 11, 13 Delay device 12 Adder 14 Correlator 15 Phase memory 16 Phase shifter 20 Comparator 21 Signal delay device 22 NOT
23 AND
24, 25 Multiplier 26, 27 Low pass filter 28 Correlator 29 All pass filter 30, 31 Variable gain amplifier 32 Adder 100 Multiplexer (MUX)
DESCRIPTION OF SYMBOLS 101,108 Transmission circuit 102 Amplifier 103,113-116 A / D converter 104 Memory 105 Adder 106 Signal processor 107 Display part 109-112 Switch 117 Beam former 121 Detector 122 Digital scan converter (DSC)

Claims (4)

A plurality of transducers arranged; a switch for selecting a signal to be input to a beam former from signals received by the transducer; and a beam former and a beam former for performing beam formation by a signal selected by the switch A memory for temporarily storing the output of the memory and an adder for adding the outputs of the memory and the beam former, and a plurality of transmission / reception sequences including a transmission / reception sequence to the subject using a plurality of times the same aperture Means for detecting a phase shift due to body movement of a subject between transmission / reception sequences from signals obtained by a plurality of transmission / reception sequences using the same aperture using a single aperture forming method, and transmission / reception sequences at different apertures An ultrasonic diagnostic apparatus comprising means for aligning the phases of the received signals obtained in step 1. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein the means for detecting the phase is a zero cross detector. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein the means for detecting the phase is a correlator. 4. The ultrasonic diagnostic apparatus according to claim 2, wherein a transmission / reception sequence in the same opening for detecting a phase shift is not performed every time.

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