JP3222648B2 - Medical ultrasonic dispersion compression transmission / reception method and medical ultrasonic dispersion compression transmission / reception device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medical ultrasonic dispersion compression transmission / reception method and an improvement of a medical ultrasonic dispersion compression transmission / reception apparatus, and more particularly to a medical ultrasonic dispersion transmission / reception method and a medical ultrasonic dispersion resistant to nonlinear propagation of a medium. The present invention relates to a compression transmitting / receiving apparatus.

[0002]

2. Description of the Related Art A medical ultrasonic device is a kind of ultra-short distance sonar, and has a large lossy dispersive acoustic property of a target (observation target: in this case, the abdominal cavity of a subject) and a diagnostic property. According to the requirements for the spatial resolution of the video system according to the requirements,
The relative bandwidth of the acoustic signal system is very large (that is, the impulse response is very important), and the demand for the dynamic range of the system is always at a limit.

[0003] In addition, the characteristics of the target as an echo source of the soft tissue of the living body are such that the whole of the point target is an echo source like clutter, and the speckle property is fundamental. There is no other than.

[0004] Rather, it is possible to distinguish a slightly different portion in the speckle echo area where the parenchyma of the tissue is scattered, or whether the contents of a luminal organ filled with liquid are really transparent or not. A very important issue is whether there is a foreign substance that emits an echo. Therefore, I extremely dislike all ghosts and spurious responses. That is, it is an essential condition that it is essentially hi-fi and clean.

[0005] Such a demand for the observation system or the signal system is as follows.
It is similar to the situation in audio systems and synthetic aperture radars for resource exploration, but there are some significant differences. That is, real-time properties and security are required. The real-time property means that real-time observation of a moving object, that is, observation of a moving organ without delay (including Doppler shift observation) is required. Ensuring the safety of living tissues is essentially an important issue for medical instruments.

That is, in order to improve the search capability of the apparatus while securing both security and transmission power, a time-bandwidth product is used in place of a large-amplitude single-pulse pulse echo system or a single-frequency CW system. Distributed compression transmission / reception using a spread spectrum system in which (TB product) is much larger than 1 is effective.

[0007]

DISCLOSURE OF THE INVENTION In the echo search of a medical ultrasonic apparatus, there are roughly two types of dispersed signals that can be employed in accordance with the above circumstances: an FM chirp signal and a phase modulation signal based on a complementary sequence. There is. In general, even if the sharpness and shape of the main lobe depend on the circumstances, it is generally necessary that the time side lobe of the transmitted signal on its own principle is at most about -60 dB or less. . This is derived from the level distribution of the echo source in the living tissue, and is the distribution range itself.

When a complementary sequence such as a Golay code is used in a time-division manner as a code signal for phase modulation, the time side lobe is completely eliminated by linearly combining the results after the reception correlation processing of each code. Almost ideal results are obtained for stationary targets. However, this method is inherently vulnerable to targets with a Doppler shift, and has limited applicability.

There is also a system which exhibits complementarity only with respect to a specific value of the bin shift number. However, the system is not a synchronous system but has a strong speckle characteristic in which echo sources are distributed everywhere. Therefore, any undesired response other than the main lobe is literally a ghost source.

The biggest problem is the effect of nonlinear propagation of a medium. In particular, there is a case where a transmitted signal greatly changes its waveform during propagation, and the signal design is based on this.

An acoustic signal in air or water is essentially different from an electromagnetic wave signal in that propagation in a medium is essentially nonlinear. This is a phenomenon in which the sound wave is a longitudinal wave, and a portion having a high instantaneous sound pressure and a large instantaneous particle velocity runs ahead and catches up with a preceding low pressure and slow speed portion. This is hardly noticeable in short-range propagation of low-level sound waves, but when a certain limit depending on the level or frequency is exceeded, the wave front uniformly rises and becomes noticeable.

As a typical example for practical use, results obtained by computer simulation will be described with reference to FIG. First, a cosine-square-amplitude-modified linear chirp signal having a total frequency of about 50 wavelengths with an upper / lower frequency ratio of about 2: 1 is generated in the computer (FIG. 8). When the waveform is broken by simulating the nonlinear propagation in the computer, a wall starts to rise from a belly having a large amplitude and thorns appear as shown in FIG. Suppose the echo source just sent it back at a low level without changing the waveform. Attention is paid to the correlation between this waveform and the original transmission waveform. Here, when the waveform of FIG. 9 is band-limited to the original signal bandwidth (removing the second harmonic and higher) in consideration of the circumstances of the receiver,
As shown in FIG. 10, the waveform becomes thin and flat, as if the apodization were out of order. When this is correlated with the original transmission waveform, the time side lobe does not deteriorate so much even if a considerably distant distortion occurs. However, as shown in FIG. 11, a large bump is generated on one side. This knot is a result of the distortion of the lower frequency band of the chirp waveform (second harmonic) having a correlation with the component at the wider end of the replica, and assuming a broadband chirp signal accordingly That is natural. However, since the signal actually desired has such a wide band, this problem cannot be avoided. If the upper / lower frequency ratio is significantly narrower than 2: 1 and is suppressed to, for example, about 1.4: 1, the bump can be easily removed by a filter. However, in such a case, a spatial resolution equivalent to the current device cannot be obtained.

Next, a complementary sequence phase modulated wave will be considered. The code A and the code B whose waveforms are shown in FIG. 12 are transmitted and received separately in time, correlated, and the results are added. The system bandwidth and code length are assumed to be substantially the same as in the case of the above-described chirp signal. The code length is 16 bits (A
= 8D82, B = 414E), and therefore has a unique process gain 32, and the sidelobes after addition of the unique autocorrelation should exactly cancel within the calculation error. As shown in FIG. 14, the state after the addition of the correlation matches at the digit of -150 dB.

In this case, this property is maintained relatively well up to the point where some propagation non-linearity exists, but worsens in other cases. That is, in the vicinity of the shock wave limit, the waveforms shown in FIGS.
It looks like 6. The waveforms of FIGS. 15 and 16 are correlated with the waveforms of FIGS. 12 and 13, respectively, and when the results are added, -30 dB to -40 dB as shown in FIG.
Worse to the extent. Thus, the side lobe is -30d
When it becomes as large as B, it becomes unsuitable for practical use.

The present invention has been made in view of the above points, and an object of the present invention is to realize a medical ultrasonic dispersion compression transmission / reception method and a medical ultrasonic dispersion compression transmission / reception apparatus which are resistant to nonlinear propagation of a medium. .

[0016]

The object of the present invention is to provide a transmission signal generating means for generating a first transmission signal and a second transmission signal having the opposite polarity to the first transmission signal by spread modulation. A transmitting and receiving means for irradiating a target with a transmitted signal as an ultrasonic wave, receiving a reflected wave and outputting it as a received signal, and a reception result of the first transmitted signal and a signal waveform of the first transmitted signal. The cross-correlation is determined as a first correlation result, the cross-correlation between the reception result of the second transmission signal and the signal waveform of the second transmission signal is determined as a second correlation result, and the first correlation result and This is solved by a medical ultrasonic dispersion compression transmission / reception device including a reception signal processing unit that obtains a compressed demodulation output by adding the second correlation result with the time axis aligned.

[0017]

In this medical ultrasonic dispersion compression transmitting and receiving apparatus,
After the first transmission signal generated by the spread modulation and the second transmission signal having the opposite polarity to the first transmission signal are transmitted, the reception result of the first transmission signal and the first transmission signal are transmitted. The first correlation result obtained from the cross-correlation with the signal waveform of the wave signal, and the second correlation result obtained from the cross-correlation between the reception result of the second transmission signal and the signal waveform of the second transmission signal By adding the correlation result in a state where the time axes are matched, a compressed demodulation output is obtained in which distortion generated by nonlinear propagation of the medium is canceled.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a medical ultrasonic dispersion compression transmission / reception apparatus for realizing a medical ultrasonic dispersion compression transmission / reception method according to an embodiment of the present invention, mainly showing a part for performing distributed compression transmission / reception, and FIG. FIG. 3 is a configuration diagram showing details of a reception signal processing device of the medical ultrasonic device shown in FIG. FIG. 3 is a flowchart showing a procedure in the case of performing distributed compression transmission / reception using a chirp signal, and FIG. 4 is a characteristic diagram showing a result of addition of cross correlation. FIG. 5 is a flowchart showing a procedure in the case of performing distributed compression transmission / reception using a phase modulation signal based on a complementary sequence, and FIG. 6 is a characteristic diagram showing a result of cross-correlation addition.

First, distributed compression transmission / reception using a chirp signal will be described with reference to FIGS. The selection unit 11 is selected to a desired state by an instruction from the system control unit 10, and the transmission signal generator 12 generates a transmission signal having a predetermined code and polarity in accordance with the selected state. Here, a pair of transmission signals (A, -A) with inverted polarities is generated (step (1) in FIG. 3). The transmission signals A and -A are D
The signal is converted into a digital signal by the / A converter 13 and transmitted from the transducer 14 toward the subject (step in FIG. 3).
(2)). Then, the reflected wave from the subject is received by the transducer 14 (step (3) in FIG. 3), amplified by the amplifier 15, and
The digital signal is converted by the / D converter 16. And
The received signal processing device 17 performs a cross-correlation process between the transmitted signal and the received signal for each of A and -A,
The respective correlation results are obtained (step (4) in FIG. 3). The correlation result for A and the correlation result for -A obtained in this way are added (step (5) in FIG. 3), and after performing various processes, display is performed on the display device 18.

The cross-correlation processing will be described in more detail with reference to FIG. The reception waveform digitally converted by the A / D converter 16 is temporarily stored in a reception waveform temporary storage unit 17a and supplied to one input of a correlator 17c. Further, the sample waveform generation unit 17b is notified of the code and polarity selection state of the selection unit 11, and generates a sample waveform having the same waveform as the transmission signal, and supplies the same to the other input of the correlator 17c. The correlator 17c performs a cross-correlation process between the received waveform and the sample waveform. Further, an integration process is performed in the integrator 17d. Here, the result of the characteristic shown in FIG. 11 is obtained for the transmission signal A. In the present embodiment, the cross-correlation processing (dechirp processing) is similarly performed on the transmission signal A and the transmission signal -A having the opposite polarity, and the correlation results are added with their time axes aligned, and the display temporary storage unit is added. 17e. As a result, the result of the characteristic shown in FIG. 4 can be obtained. The one shown in FIG.
As compared with the characteristic of No. 1, the bump-shaped portion is canceled or eliminated. Therefore, it has sufficient resistance to non-linear propagation of the medium, and clears -60 dB.

Next, the case of complementary sequence phase modulation will be described. In addition to the phase modulated waves of the conventional code A and code B, the code (code-A,-
B) is also used to transmit and receive these separately in time, correlate them, and then add the results.

That is, the selection section 11 is selected to a desired state by an instruction from the system control section 10, and the transmission signal generator 12 generates a transmission signal having a predetermined code and polarity in accordance with the selected state. Here, two pairs of transmission signals (A, -A, B, -B) with inverted polarities are generated (step (1) in FIG. 5). The transmission signals A, -A, B, and -B are D
The signal is converted into a digital signal by the / A converter 13 and transmitted from the transducer 14 toward the subject a total of four times (FIG. 5).
Step (2)). The reflected wave from the subject is received by the transducer 14 (step (3) in FIG. 3), amplified by the amplifier 15, and converted to a digital signal by the A / D converter 16. Then, in the reception signal processing device 17, A,-
The cross-correlation processing between the transmission signal and the reception signal is performed for each of A, B, and -B, and the respective correlation results are obtained (step (4) in FIG. 3). Finally, the four types of correlation results for A, -A, B, and -B thus obtained are added (step (5) in FIG. 3). As a result, the result of the characteristic shown in FIG. 6 can be obtained. 6, the time side lobe is reduced to about -45 dB as compared with the characteristic shown in FIG. Therefore, it has sufficient resistance to nonlinear propagation of a medium.

As described above in detail, in the present embodiment, two types of chirp signal and complementary sequence phase modulation are used.
By transmitting and receiving the waveform whose polarity is inverted and adding the correlation result, the influence of nonlinear propagation can be considerably reduced.

[0024]

As described above in detail, after transmitting the first transmission signal generated by the spread modulation and the second transmission signal having the opposite polarity to the first transmission signal, the first transmission signal is transmitted. The first correlation result obtained from the cross-correlation between the reception result of the transmission signal and the signal waveform of the first transmission signal, the reception result of the second transmission signal, and the signal of the second transmission signal By adding the second correlation result obtained from the cross-correlation with the waveform in a state where the time axis is matched, a compressed demodulation output in which distortion caused by nonlinear propagation is canceled is obtained. Therefore, it is possible to realize a medical ultrasonic dispersion compression transmission / reception method and a medical ultrasonic dispersion compression transmission / reception device that are resistant to nonlinear propagation of a medium.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a configuration related to transmission / reception of a medical ultrasonic dispersion compression / transmission / reception device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a configuration of a main part related to reception signal processing of the medical ultrasonic dispersion compression transmission / reception device according to one embodiment of the present invention;

FIG. 3 is a flowchart illustrating an example of processing contents of a distributed compression transmission / reception method according to an embodiment of the present invention.

FIG. 4 is a characteristic diagram illustrating characteristics of processing results of the distributed compression transmission / reception method according to one embodiment of the present invention;

FIG. 5 is a flowchart illustrating an example of processing contents of a distributed compression transmission / reception method according to an embodiment of the present invention.

FIG. 6 is a characteristic diagram showing characteristics of processing results of the distributed compression transmission / reception method according to one embodiment of the present invention.

FIG. 7 is a waveform diagram showing a waveform of a transmission signal of dispersion compression transmission / reception.

FIG. 8 is a waveform diagram showing an autocorrelation result of a transmission signal of dispersion compression transmission / reception.

FIG. 9 is a waveform diagram showing a state in which a transmission signal of dispersion compression transmission / reception is distorted by nonlinear propagation.

FIG. 10 is a waveform diagram showing a state in which a distorted waveform is band-limited.

FIG. 11 is a waveform chart showing a cross-correlation result.

FIG. 12 is a waveform diagram showing a waveform of a transmission signal of dispersion compression transmission / reception.

FIG. 13 is a waveform diagram showing a waveform of a transmission signal of dispersion compression transmission / reception.

FIG. 14 is a waveform diagram showing an autocorrelation result of a transmission signal of dispersion compression transmission / reception.

FIG. 15 is a waveform diagram showing a state in which a transmission signal of distributed compression transmission / reception is distorted by nonlinear propagation.

FIG. 16 is a waveform diagram showing a state in which a transmission signal of distributed compression transmission / reception is distorted by nonlinear propagation.

FIG. 17 is a waveform chart showing a cross-correlation result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 System control part 11 Selection part 12 Transmitted signal generator 13 D / A converter 14 Transmitter / receiver 15 Amplifier 16 A / D converter 17 Received signal processing device 18 Display device

Claims (2)

(57) [Claims] 1. A medical ultrasonic dispersion compression transmission / reception method, comprising: transmitting a first transmission signal generated by spread modulation and a second transmission signal having a polarity opposite to that of the first transmission signal; The cross-correlation between the reception result of the transmission signal and the signal waveform of the first transmission signal is obtained as a first correlation result, and the reception result of the second transmission signal and the signal waveform of the second transmission signal are obtained. A cross-correlation is obtained as a second correlation result, and a compressed demodulation output is obtained by adding the first correlation result and the second correlation result in a state where the time axes are aligned. Ultrasonic dispersion compression transmission / reception method. 2. A medical ultrasonic dispersion compression transmitting / receiving apparatus, comprising: a transmission signal generating means (spread signal) for generating a first transmission signal and a second transmission signal having a polarity opposite to that of the first transmission signal by spread modulation. 10, 11 and 12), a transmitting / receiving means (14) for irradiating a target with a transmitted signal as an ultrasonic wave, receiving a reflected wave and outputting as a received signal.
And a cross-correlation between the reception result of the first transmission signal and the signal waveform of the first transmission signal is obtained as a first correlation result, and the reception result of the second transmission signal and the second transmission signal A cross-correlation with the signal waveform is obtained as a second correlation result, and the received signal that obtains a compressed demodulation output by adding the first correlation result and the second correlation result in a state where the time axis is matched is obtained. A medical ultrasonic dispersion compression transmission / reception device, comprising: processing means (17).