JP3052332B2 - Ultrasonic signal processing method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic signal processing method and an apparatus suitable for detecting or inspecting an object by ultrasonic waves, and particularly to an object for measurement in which an object to be measured moves. The present invention relates to an ultrasonic signal processing method and an apparatus therefor that are effective when the ultrasonic signal is processed.

[Conventional technology]

2. Description of the Related Art In an ultrasonic imaging apparatus for medical diagnosis, that is, an apparatus that visualizes the inside of a human body using ultrasonic waves and performs diagnosis based on the image, there is a great need to obtain information from a moving target part. For example, highly accurate information cannot be obtained for various types of diagnostic information related to the heart unless the influence of the movement of the heart is considered. For this reason, a method has been widely used in which an electrocardiographic waveform is used as a synchronization signal and measurement is performed using the periodicity of the motion of the heart. Further, when periodicity cannot be used, a method of obtaining instantaneous information from an object by a measuring means sufficiently faster than the movement of the object is widely used.

Separately, JP-A-61-176326 discloses that
An ultrasonic diagnostic apparatus has been disclosed which controls the relative relationship between the measurement device and the measurement target within a predetermined range by accurately following the movement of the measurement target.

[Problems to be solved by the invention]

By the way, in a conventional ultrasonic diagnostic apparatus, for example, as described in “Handbook of Medical Ultrasonic Equipment” (Corona, 1960), edited by the Japan Electronic Machinery Manufacturers Association, usually, reception is performed every transmission. It was configured to process and signal the signal and display it.

However, in order to cope with high performance requirements such as high accuracy and high resolution of the ultrasonic diagnostic apparatus, it is necessary to extract a weaker measurement signal, and as described above, the reception signal is processed for each transmission. However, there is a problem that the S / N ratio is inevitably reduced in the method of visualizing the image. On the other hand, as in an ultrasonic blood flow meter, that is, an apparatus that measures the velocity of blood flow by applying ultrasonic waves, it is possible to perform measurement by adding the results of multiple transmissions and receptions. It is conceivable that, when the object to be measured is a moving object, the simple addition process has a problem that the measurement signal, particularly a weak measurement signal, is erased like noise.

The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above-described problems in the related art and to enable signal detection with less noise, particularly when an object to be measured moves. It is an object of the present invention to provide an ultrasonic signal processing method and a device therefor that are effective in the case of the above.

[Means for solving the problem]

An object of the present invention is to provide an ultrasonic signal processing method for transmitting an ultrasonic wave to a target object, receiving a reflected or transmitted signal from the target object and processing the signal, and Detecting a change in a signal to measure the motion of the target object; and (2) correcting a change in the plurality of received signals due to the motion to obtain a measurement signal for imaging the target object. And (3) an ultrasonic signal processing method, comprising: a step of adding the measurement signal obtained in the step (2); and transmitting an ultrasonic wave to a target object, and In the ultrasonic signal processing device that receives a reflected signal or a transmitted signal as a received signal, processes the received signal, and visualizes the received signal, detects a phase of a plurality of the received signals to detect a motion of the target object. Means,
An ultrasonic signal processing device comprising: means for correcting a change in the phase of the plurality of reception signals due to the movement; and means for adding the reception signals having the corrected phases. Transmits sound waves to a target object, receives a reflection signal or a transmission signal from the target object as a reception signal, and in the ultrasonic signal processing device that processes and visualizes the reception signal, stores a plurality of the reception signals. A first storage unit that detects a phase of the plurality of received signals stored in the first storage unit to detect a motion of the target object, and a process that is performed by the first unit. Second storage means for storing the plurality of received signals obtained, and based on the movement of the phases of the plurality of received signals based on the plurality of received signals stored in the first and second storage means. Second to compensate for changes A third storage means for storing a unit, the plurality of reception signals processed by means of the second,
A third means for adding the plurality of received signals stored in the third storage means; and a fourth storage means for storing a signal processed by the third means. This is achieved by an ultrasonic signal processor.

[Action]

In the ultrasonic signal processing method according to the present invention, the phase change of the received signal due to the movement of the target object is detected, and the detected signal is corrected and added. Thus, there is an effect that the enhancement can be performed.

Further, in the ultrasonic signal processing device according to the present invention,
Since the measurement signal enhanced based on the above-described ultrasonic signal processing method is visualized, it is possible to realize an ultrasonic signal processing device capable of obtaining an image with a good S / N.
In relation to the processing time,
It is practical to visualize the entire target object with a low-frequency signal and use a high-frequency signal for performing high-precision imaging only on a part of the target object.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of signal processing in an ultrasonic imaging apparatus according to a first embodiment of the present invention. In the figure, T is a signal source, TR is a transducer, X is a measurement target, and M1 to
M4 is a memory, MD is a motion detection processor, MC is a motion correction processor, and ADD is a signal adder.

The outline of signal processing in the ultrasonic imaging apparatus according to the present embodiment is as follows. That is, in the present embodiment, the transducer TR is driven by the signal S from the signal source T,
Ordinarily, the object to be measured X is irradiated with a beam-shaped ultrasonic wave, and the reflected signal R is received and sequentially stored in the memory M1.
This storage content fluctuates with time due to the movement of the measurement object X as shown in the figure. This fluctuation situation is measured by the motion detection processing unit MD, and the result is stored in the memory M2.
Using the motion information obtained in this manner, the motion correction processing unit MC corrects the change due to the motion of the content of the memory M1 by a method such as coordinate conversion, and stores the result in the memory M3. The received signal whose motion has been corrected in this way is added to the signal adder.
Addition is performed at each time by ADD, and the addition result is stored in the memory M4.

When the above-described processing is performed, all received signals are added in phase, and noise is canceled because the phase is irregular. The function of the motion detection processing unit MD will be described later in detail.

FIG. 2 is a block diagram of signal processing in an ultrasonic imaging apparatus according to a second embodiment of the present invention. In the present embodiment, spatial resolution in the distance direction is given by the depth of focus, and continuous waves are transmitted to perform imaging. In this case, the content of the memory M1 is a phase change, and the motion can be detected by measuring the phase change by the motion detection processing unit MD. When a motion correction process is performed using this information, a sine wave of a single frequency is obtained. The addition process in the signal adder ADD in this case is performed by Fourier transform or the like. By performing this processing while changing the convergence position, imaging becomes possible.

FIG. 3 is a block diagram of signal processing in an ultrasonic imaging apparatus according to a third embodiment of the present invention. In the present embodiment, the transmitter TR1 and the receiver TR2 face each other, and the same processing is performed on the transmitted signal. In this case, phase processing similar to that of the embodiment shown in FIG. 2 is performed.

In the above embodiment, for the sake of simplicity, an example has been described in which all received signals are temporarily stored and then the motion correction process is performed. However, as shown in FIG. Can be corrected sequentially. In the present embodiment, the output of the motion detection processing unit MD is applied to the motion correction processing unit MC to perform motion compensation of the received signal R, and the output of the motion correction processing unit MC is added. .

Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 5 shows an example in which an ultrasonic signal (part a) for measuring the motion of an object having a lower frequency than the original measurement signal (part b) is used as the signal S described above. . Here, the high frequency component of the reflected reception signal R is stored in the memory M1 in FIG. On the other hand, low frequency components are stored in memory.
Store in M5. Since the low frequency component has low attenuation, according to the present embodiment, motion measurement can be performed at a high S / N.

FIG. 6 shows another configuration example of the above-described ultrasonic signal for measuring the low-frequency object motion. The waveform shown in FIG. 6 (a) is the sum of the waveforms shown in FIGS. 6 (b) and (c), and includes high-frequency and low-frequency signal components. When the waveform shown in FIG. 6 (d) is transmitted due to the nonlinearity of the propagation medium, the waveform becomes distorted as shown in FIG. 6 (e). This waveform is shown in FIG.
And the waveform shown in FIG. 5 (g), which contains a high-frequency component and a low-frequency component as in the case of the signal S shown in FIG. By performing such processing, exercise measurement can be performed with a high S / N.

For example, the short pulse waveform shown in FIG. 6 (h) has a wide frequency component shown in FIG. 6 (i). Therefore,
It is also possible to perform motion measurement using the low frequency component shown in (j) of the received signal.

Next, still another embodiment of the present invention will be described with reference to FIG. FIG. 7 shows that the signal S for measurement described above (part b) is transmitted alternately as the signal S for high-frequency measurement (part b) and the ultrasonic signal for measurement of object motion at low frequency (part a). This example shows an example in which a received signal based on a motion measurement signal (part a) is selectively stored in a memory M5 by a changeover switch SW in a memory M1. Here, if the signal (part b) to be added is transmitted at a higher frequency, the number of additions increases, which is effective for improving the S / N.

In the case of a living body, exercise due to the pulsation of the heart becomes a problem. Therefore, an ECG (Electro Cardio Graph) signal (electrocardiographic signal) or a UCG (Ultrasonic Cardio Grap
h) Using a signal (ultrasonic echocardiographic signal) and synchronizing the exercise measurement with the heartbeat as described above, a stable signal in diastole can be used.

As shown in FIG. 8, transmitting a wideband long-time signal,
It is also possible to perform a cross-correlation between the received signal and the transmitted waveform and perform the present signal processing on the correlator output. The transmission waveform in this case includes a pseudo random number, an FM wave, an M-sequence waveform,
Various waveforms such as Barker series can be applied.

In a case where a wideband signal is transmitted, the content of M4, which is the result of the improvement in S / N by such addition, is emphasized in the high frequency range to improve the distance resolution. Further, since a signal in a wide band from low frequency to high frequency can be obtained, the frequency characteristic of the attenuation coefficient of the target substance can be measured with high accuracy. Any display that combines this attenuation information with video information or motion information obtained by this method is possible.

In addition, when imaging is performed by an ultrasonic signal processing device that processes and obtains an image obtained by the method described in each of the above-described embodiments, as shown in FIG. By performing the motion-corrected addition process only on a part of the target, a relatively high-speed video device can be configured. Here, an optimal operation is realized by performing the entire imaging with a third signal (for example, 3 to 3.5 MHz) different from that for addition (for example, 20 MHz) or for motion measurement (for example, 1 MHz). it can.

Specifically, the heartbeat cycle of an adult is about 1 second, and the movement of a living body is small within 1 msec, and a phase change of up to 1/4 wavelength does not occur with ultrasonic waves of normal frequency. For this reason, in the device according to the present method, a configuration in which the addition time is 1 msec or more and 1 sec or less is particularly effective in biological measurement. Further, it is effective to select the frequency of the above-described signal for motion measurement from about 1 to 3 MHz from the attenuation amount of the ultrasonic wave in the living body. It is particularly effective to make the ratio of both frequencies 1.5 times or more.

FIG. 10 is a diagram for explaining the contents of a kind of preprocessing in which the phase of a received signal is detected, the received signal is converted into data indicating a phase, and then stored in the memory M1.

The received signal is applied to two multipliers MR and MI, the sine wave signal D is applied to a 90-degree phase difference generator HB, and the generated signals DR and DI are applied.
To obtain a complex signal by extracting low frequency components. When the received signal R and _{R = Acos (ω o t +} θ) DR + jDI = exp (jω d t), the multiplier output _{Acos (ω o t + θ)} exp (jω d t) = (A / 2) [exp {j ( ω _ot + θ)｝ + exp ｛−j (ω
_{o t + θ)}] ·} exp (jω d t) = (A / 2) [exp {j ((ω o + ω d) t + θ)} + exp
{−j ((ω _o −ω _d ) t + θ)}]. Therefore, the output of the low pass filter LPF (A / 2) [exp {-j ((ω o + ω d) t + θ)}] = CR
+ JCI, which makes it possible to save storage capacity or to perform motion correction by phase rotation. In particular, when ω _o = ω _d , the phase information is stored.

For example, when transmitting the waveform S of FIG.
11 is shown in FIG. The processing of FIG. 12A is performed on this signal. Here, TGC1 and TGC2 are amplifiers whose amplification degree changes with time, and the waveforms of the respective parts are shown in FIG.
It is as RT _2. By this processing, the range of change in the signal amplitude of the RM is compressed, so that the configuration of the analog-to-digital converter AD of the signal is simplified. Also, as shown in FIG. 12 (b), analog-digital converters AD1 and AD
By arranging the two, it is possible to select the optimum converter for each. In this case, the number of bits of AD1 can be smaller than the number of bits of AD2. Further, the operation speed of AD2 can be made lower than the operation speed of AD1.

Here, the function of the motion detection processing unit MD will be described in detail with reference to an example shown in FIG.

Consider the case of measuring the phase of one the respective times of the reflected signals R ₁ is the contents of the memory M1. The configuration of the main part (first half) of the motion detection processing unit MD shown in FIG. 13 is the same as that of the phase detection unit shown in FIG. 10, and ω _o = ω in FIG.
_This corresponds to the case of _d . Therefore, the signal CR _{figure, P 1 (t) = (} A / 2) having a phase theta ₁ of the received signals _{R 1} at time t becomes _{exp {-jθ 1 (t)}} . This value is stored in the temporary memory MT. Similarly,
Signal CI has phase θ ₁ of received signal R ₁ at time t.

P ₂ (t) = (A / 2) exp {−jθ ₂ (t)}. When this conjugate signal is obtained by the conjugate unit CP, P ₂ ^* (t) = (A / 2) exp {jθ ₂ (t)}. From these two, the complex multiplier DP, when making _P 1 a ^{_{(t) · P 2 * (}} t), P 1 (t) · P 2 * (t) = (A 2/4) exp [j {θ
₁ (t) −θ ₂ (t)｝]. Since this phase angle θ ₁ (t) −θ ₂ (t) is proportional to the moving distance of the reflector, the moving distance can be calculated by the conversion table CT.

Apart from this, a fixed signal that does not move, such as unnecessary reflection inside the transducer, is generated. This signal may be problematic because it grows greatly by the addition process. In this case, it is possible to measure and store the signals due to these unnecessary reflections before the measurement of the actual object, and to subtract these unnecessary signals from the actual signals.

In the above, for the sake of simplicity, only the most important correction of the fluctuation in the distance direction has been described. However, if the addition time is extremely increased, the movement in the azimuth direction also becomes a problem.
In this case, needless to say, it is possible to cope with the problem by adding a motion detection unit in the azimuth direction.

It should be noted that the present method is not limited to the above-described embodiment, and it is apparent that the present method can be applied to most fields that conventionally use ultrasonic signals.

〔The invention's effect〕

As described in detail above, according to the present invention, the phase change of the received signal due to the movement of the target object is detected, and the detected signal is corrected and added, so that the received signal is separated from noise. There is an effect that enhancement by adding a large number becomes possible.

[Brief description of the drawings]

1 to 5, FIG. 7, and FIG. 8 are block diagrams showing an embodiment of the present invention, FIG. 6 is an explanatory diagram of a method of constructing a motion measurement signal of the present system, and FIG. FIG. 10 is an explanatory diagram of a signal processing method, FIG. 10 is an explanatory diagram of a phase detection method, FIG. 11 is a received signal waveform of each unit, FIG. 12 is a diagram showing a configuration example of an analog-digital conversion unit, and FIG. It is a block diagram showing an example of composition of a motion detection processing part. S: Transmit signal, R: Receive signal, T: Signal source, TR: Transceiver, M1
~ M5: memory unit, MD: motion detection processing unit, MC: motion correction processing unit, ADD: signal addition unit, HPF: high-pass filter, LPF: low-pass filter, SW: changeover switch, COR: correlator, MR, MI: multiplier, H
B: 90 degree phase difference generator, MT: temporary memory, CP: conjugator, DP:
Complex multiplier, CT: conversion table.

Claims (13)

(57) [Claims] 1. An ultrasonic wave is transmitted to a target object, and a reflection signal or a transmission signal from the target object is received as a reception signal.
In the ultrasonic signal processing method for processing the received signal, (1) a step of detecting a change in a signal between the plurality of received signals and measuring a motion of the target object; Correcting a change in a plurality of received signals to obtain a measurement signal for imaging the target object; and (3) adding the measurement signal obtained in the step (2). Characteristic ultrasonic signal processing method. 2. An ultrasonic signal processing method according to claim 1, further comprising a step of storing said plurality of reception signals prior to said step (1). 3. The ultrasonic signal processing method according to claim 1, wherein in the step (1), a received signal for measuring a movement, which has a lower frequency than the measurement signal and measures the movement, is used. An ultrasonic signal processing method, comprising: 4. The ultrasonic signal processing method according to claim 3, wherein the ratio of the frequency of the received signal for motion measurement to the frequency of the measurement signal is 1: 1.5 or more. Processing method. 5. The ultrasonic signal processing method according to claim 3, wherein the ultrasonic waves include a first ultrasonic wave having a first frequency for obtaining the reception signal for obtaining the measurement signal; An ultrasonic signal having a frequency lower than the frequency of 1 and being transmitted to the target object substantially simultaneously with the second ultrasonic wave for receiving the received signal for motion measurement. Processing method. 6. An ultrasonic signal processing method according to claim 3, wherein said ultrasonic wave has a first frequency having a first frequency for obtaining said reception signal for obtaining said measurement signal, and said first ultrasonic wave having said first frequency. An ultrasonic signal processing method having a lower frequency than the first frequency and transmitting the second ultrasonic wave for receiving the received signal for motion measurement to the target object alternately. . 7. The ultrasonic signal processing method according to claim 6, wherein the frequency of transmission of said first ultrasonic wave is higher than the frequency of transmission of said second ultrasonic wave. Ultrasonic signal processing method. 8. The ultrasonic signal processing method according to claim 1, wherein the ultrasonic waves in a wide band are transmitted to the target object,
An ultrasonic signal processing method characterized by performing the process of the step (1) after performing a cross-correlation process between a transmission waveform and the reception signal. 9. The ultrasonic signal processing method according to claim 8, wherein the transmission waveform of the wide band is an irregular waveform. 10. The ultrasonic signal processing method according to claim 1, wherein the step (1) is performed after detecting the phases of the plurality of received signals. 11. An ultrasonic signal processing apparatus for transmitting an ultrasonic wave to a target object, receiving a reflected signal or a transmitted signal from the target object as a received signal, and processing and imaging the received signal. Means for detecting the movement of the target object by detecting the phase of the received signal, means for correcting a change due to the movement of the phase of the plurality of received signals, and means for correcting the phase of the received signal. An ultrasonic signal processing device having means for performing addition. 12. The ultrasonic signal processing apparatus according to claim 11, wherein the phase change due to the movement of a part of the target object is corrected during the imaging. 13. An ultrasonic signal processing apparatus for transmitting an ultrasonic wave to a target object, receiving a reflected signal or a transmitted signal from the target object as a received signal, and processing and imaging the received signal. First storage means for storing the reception signal of the first object; first means for detecting the phase of the plurality of reception signals stored in the first storage means to detect the motion of the target object; Second storage means for storing the plurality of reception signals processed by the first means; and the plurality of reception signals based on the plurality of reception signals stored in the first and second storage means. A second means for correcting a change in the phase of the movement due to the movement, a third storage means for storing the plurality of received signals processed by the second means, and a third storage means for storing the plurality of received signals. A third method for adding the plurality of reception signals; Stage and ultrasonic signal processing apparatus characterized by having a fourth storage means for storing the processed signals by means of the third.