JPS624976B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic pulsed Doppler apparatus used for observing and measuring blood flow dynamics in a living body, and in particular to an ultrasonic pulsed Doppler apparatus that obtains real-time tomographic images of a living body by scanning an ultrasound beam. At the same time, there is provided an ultrasonic pulsed Doppler device that displays a real-time pulsed Doppler signal of a region designated on the tomographic image.

For information on how to use an ultrasonic pulsed Doppler device in combination with a real-time ultrasonic tomography device to clarify the measurement site of blood flow during blood flow measurement, please refer to
Already published in ``Hirohide Matsuo: Development of a comprehensive ultrasound system for real-time intracardiac local blood flow measurement,'' Proceedings of the 34th Japanese Society of Ultrasound in Medicine (1978) 7-8.
Reported in literature such as ``Kazuhiro Iinuma et al.: Simultaneous display of real-time tomographic images and Doppler signals using sector electronic scanning method, Proceedings of the 35th Japanese Society of Ultrasound in Medicine (1979) pp. 91-92''. has been done.

The above method is effective for observing and measuring complex blood flow such as intracardiac blood flow because the blood flow measurement site can be clearly identified on a real-time tomographic image, and these methods usually obtain pulsed Doppler signals. They are classified into the following two types depending on whether or not the probe for obtaining the tomographic image signal and the probe for obtaining the tomographic image signal are the same.

One-probe method: The probe that obtains the pulsed Doppler signal and the probe that obtains the tomographic image signal are the same.

Two-probe method: The probe that obtains the pulsed Doppler signal and the probe that obtains the tomographic image signal are separate, and each has its own dedicated probe.

The characteristics of the one-probe method are that the probe is small and easy to operate, and the position at which the pulsed Doppler signal is sampled corresponds precisely to the display position on the tomographic image. The feature is that since the probe that obtains the pulsed Doppler signal and the probe that obtains the tomographic image signal are separate, there is a high degree of freedom in selecting the probe in terms of frequency, aperture, etc.

In addition, the above methods are classified into mechanical scanning and electronic scanning depending on the scanning means used to obtain a real-time tomographic image, and into linear scanning, sector scanning, compound scanning, etc. depending on the scanning method.

The present invention relates to a one-probe method among the above-described methods, in which the probe for obtaining tomographic image signals and the probe for obtaining pulsed Doppler signals are the same.

The two-probe method, in which separate probes are used to obtain tomographic image signals and pulsed Doppler signals, has the problem that detection accuracy of the measurement site decreases due to differences in sound wave propagation paths. The secondary method has the advantage that the probe that obtains the tomographic image signal and the pulsed Doppler signal is the same, and the region displayed on the tomographic image corresponds precisely to the region where the pulsed Doppler signal is actually detected.

However, the one-probe method has a problem in that the tomographic image signal mixes into the pulsed Doppler signal, lowering the signal-to-noise ratio (hereinafter abbreviated as SN ratio) of the pulsed Doppler signal. The problems of the prior art will be explained in more detail below.

The first problem with the method of using a pulsed Doppler device and a real-time tomography device in combination is that when the probe drive signal level is the same, the SN of the tomographic image signal
The problem is that the signal-to-noise ratio of pulsed Doppler signals is about 20 to 30 decibels worse than that of pulsed Doppler signals.

This is because tomographic signals see strong reflected signals of sound waves due to differences in acoustic impedance of living tissues, whereas pulsed Doppler signals are caused by the Doppler effect of weak reflected signals of sound waves from blood cells (mainly red blood cells) within blood vessels. This is because we are looking at frequency deviation.

A second problem is that when obtaining tomographic image signals and pulsed Doppler signals in real time, tomographic image signals with high signal levels may mix into the pulsed Doppler signals and interfere with accurate reception of the pulsed Doppler signals. .

This second problem will be explained in more detail using the drawings.

Figure 1 shows an example of application to a living body of a system that obtains tomographic images and pulsed Doppler signals in real time by electronic sector scanning using the one-probe method. 102 is a subject, 103 is an object to be measured from which a pulsed Doppler signal is obtained, such as blood flow, 104 is an organ whose acoustic impedance is significantly different from other parts of the subject and generates a strong reflected signal at the interface, and 105 is a sector-shaped object. The field of view of the sector scan is shown enclosed by .

Fig. 2 shows a timing chart of the system, where a is the rate pulse of the system, and b is a mode switching signal for switching between the tomographic image mode and the pulsed Doppler mode (the high level in the figure is the tomographic image mode). mode, low level indicates pulsed Doppler mode). c is a transmission timing pulse for obtaining a tomographic image signal, d is a transmission timing pulse for obtaining a pulsed Doppler signal, e is a gate pulse used when sampling the pulsed Doppler signal, f is a reflected signal from the direction in which the tomographic image signal is received,
g represents a reflected signal from the pulsed Doppler signal receiving direction.

In Fig. 1, L ₁ , L ₂ , L ₃ , . _. . _{LM ,} . A scanning line for obtaining signals, 106 is a scanning line L _M
The position at which the pulsed Doppler signal is gated is shown above.

Now, suppose that an ultrasound beam for obtaining a tomographic image signal and an ultrasound beam for obtaining a pulsed Doppler signal are alternately emitted as shown in FIGS. 2b, c, and d. That is, assume that the directivity of transmitting and receiving the ultrasonic beam is switched in the order of L ₁ →L _M →L ₂ →L _M →L ₃ →L _M . . . To explain using Fig. 2, an ultrasonic beam is emitted in the _L1 direction at time _t1 , then in the _LM direction at time _t2 , in the L2 direction at time _t3 , and in the _L2 direction at time _t4 .
It is assumed that an ultrasonic beam is emitted in _{the M} direction, at time t ₅ in the L ₃ direction, and at time t ₆ in the L _M direction (the same applies hereinafter).

In this example, since the electronic sector scanning method is used, the deflection of the ultrasonic beam is determined by electronically controlling the transmission/reception delay time given to each element making up the electronic sector probe. conduct.

As shown in FIG. 1, when a strong ultrasound reflector 104 exists outside the field of view of the subject, the reflected signal from this reflector is mixed into the reflected signal for obtaining the pulsed Doppler signal. This situation is shown in Fig. 2 f and g. In the figure, the arrow indicates the position where the reflected signal for obtaining a tomographic image is mixed with the reflected signal for obtaining a pulsed Doppler signal. If this position coincides with the gate position for sampling the pulsed Doppler signal as shown in FIGS. 2e and 2f, the reflected signal from the direction in which the tomographic image signal is received acts as noise on the pulsed Doppler signal.

Moreover, in the case of FIG. 1, when the scanning direction of the ultrasonic beam changes, the transmission point and the reflector 10 change accordingly.
4 changes, and therefore the time from transmission to the return of the reflected signal, ie, T ₁ , T ₂ , T ₃ in FIG. 2 changes. Therefore, the reflected signal from the reflector 104 acts as if it were a signal that has undergone a Doppler shift, becomes a pseudo Doppler signal, and interferes with detection of the Doppler signal from the true blood flow.

Above, we have discussed the mixing of tomographic image signals into pulsed Doppler signals due to reflections from outside the visual field.
A similar phenomenon is also caused by multiple reflections.

The present invention has been made in view of the problems of the prior art described above, particularly the mixing of tomographic image signals into pulsed Doppler signals, and its purpose is to improve pulsed Doppler signals.
The purpose is to improve the signal-to-noise ratio.

The present invention further relates to an ultrasonic pulsed Doppler apparatus that obtains and displays tomographic image signals and pulsed Doppler signals in real time using a single probe method.

As mentioned above, in conventional devices, the ultrasound frequency for obtaining tomographic image signals and the ultrasound frequency for obtaining pulsed Doppler signals are the same, and it is difficult to prevent mixing of tomographic image signals and pulsed Doppler signals in the frequency domain. It was impossible.

On the other hand, using probe construction technology that has rapidly advanced in recent years, it is possible to construct a probe with a broadband frequency response.
J, H, GO11, “The design of broadband
f1uid−1oaded u1trasonic transducers”, IEEE
Trans.Sonics and U1trasonics, vo1, SU−
26, pp. 385-393, November, 1979, or G. Kossoff, “The effects of backing and
matching on the performance of pjezoelectric
ceramic transducers”, IEEE Trans, Sonics
and U1trasonics, vo1, SU−13, pp, 20−30,
It is described in detail in documents such as March 1966.

The present invention uses such a broadband probe to
By selecting different ultrasound frequencies for obtaining tomographic image signals and pulsed Doppler signals, the tomographic image signal can be mixed into the pulsed Doppler signal, or the tomographic image of the pulsed Doppler signal, which is vice versa. This method greatly reduces contamination of the signal by limiting it in the frequency domain, thereby obtaining pulsed Doppler signals and tomographic image signals with a good signal-to-noise ratio.

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

FIG. 3 shows the principle of the present invention,
In the figure, 301 is the frequency response curve of the probe;
302 is a frequency response curve necessary to obtain a pulsed Doppler signal, and 303 is a frequency response curve necessary to obtain a tomographic image signal. ₁ is the ultrasound center frequency for obtaining pulsed Doppler signals, ±Δ
₁ represents the band used, ₂ represents the ultrasound center frequency for obtaining the tomographic image signal, and ± _Δ2 represents the band used.

FIG. 3a shows a preferred embodiment of the invention, in which two signals with bands can be separated using a band-limiting filter without crosstalk. The conditions that do not cause the above crosstalk and the conditions that do not cause cross-modulation during detection can be expressed mathematically as shown in the following equation, Satisfying the formula is a preferred implementation condition of the present invention.

Next, in the embodiment shown in FIG. 3b, two curves 302 and 303 indicating the band overlap,
Although the effect of preventing mixing of the pulsed Doppler signal and the tomographic image signal is reduced compared to the case shown in FIG.

Note that in the above explanation, ₁ and Δ ₁ are used for pulsed Doppler signals, and ₂ and Δ ₂ are used for tomographic image signals, but these can be replaced with each other.
₁ and Δ ₁ for tomographic image signals, ₂ and Δ ₂
It can also be used for pulsed Doppler signals.

Furthermore, as described in the prior art section, the reflected signal from the blood flow is considerably smaller than the reflected signal from the interface between tissues having different acoustic impedances. Therefore, as a way to solve this problem, if the intensity of the sound waves emitted to obtain the pulsed Doppler signal is made larger than the intensity of the sound waves emitted to obtain the tomographic image signal, the SN ratio of the pulsed Doppler signal can be reduced to that of the tomographic image signal. It is possible to get the S/N ratio close to that of

Generally, when the above method is used, the pulsed Doppler signal is mixed into the tomographic image signal, or vice versa, but in the case of the embodiment of the present invention, the two signals are separated in the frequency domain. Therefore, even if the intensity of the emitted sound waves is changed, the signals will not mix with each other.

FIG. 4 is a block diagram showing an embodiment of the present invention in which the principle shown in FIG. 3 is applied to an actual device. In the figure, 401 is a probe;
02 is a transmission/reception switch, 403 is a transmission signal switch,
404 is a received signal distribution switch; 405 is a pulsed Doppler signal transmitter; 406 is a tomographic image signal transmitter; 407 is a pulsed Doppler signal band-limiting filter; 408 is a tomographic image signal band-limiting filter;
09 is a pulsed Doppler signal receiver, 410 is a tomographic image signal receiver, 411 is a mixer, and 412 is a display device.

The transmitter has independent transmitters 405 and 406 for pulsed Doppler signals and tomographic image signals, respectively, and switches the frequency, number of peaks, and amplitude of pulses that drive the probe in each mode. The received signal is subjected to two band-limiting filters 407 and 408 to limit signals outside the frequency band used, and the pulsed Doppler signal and tomographic image signal are subjected to necessary received signal processing in receivers 409 and 410, respectively, and then sent to a mixer. The pulsed Doppler signal and the tomographic image signal are mixed in 411 and displayed on the display 41.
2 displays the results in real time.

By using the ultrasonic pulsed Doppler apparatus having such a configuration, it is possible to greatly reduce the mixing of the pulsed Doppler signal of the tomographic image signal into the tomographic image signal, or vice versa.

As is clear from the above detailed description, the present invention provides an ultrasonic pulsed Doppler apparatus employing a single probe method, in which the ultrasonic frequency for obtaining a pulsed Doppler signal and the ultrasonic frequency for obtaining a tomographic image are made different. The present invention provides an ultrasonic pulsed Doppler device that has a small probe, can clearly detect blood flow measurement sites on real-time tomography, and can obtain pulsed Doppler signals with a good signal-to-noise ratio. It can be realized.

[Brief explanation of the drawing]

Figure 1 is an operational explanatory diagram showing an example of application to a living body of a system that obtains tomographic images and pulsed Doppler signals in real time by electronic sector scanning using the one-probe method, and Figure 2 is an operation diagram of the system shown in Figure 1. 3A and 3B are diagrams of the principle of the present invention, and FIG. 4 is a block diagram of an ultrasonic pulse Doppler apparatus according to an embodiment of the present invention. 301... Frequency response curve of the probe, 302...
...Frequency curve necessary to obtain a pulsed Doppler signal, 303... Frequency curve necessary to obtain a tomographic image signal, 401... Probe, 402... Transmission/reception switch, 403... Transmission signal switch, 404 ……
Received signal distribution switch, 405, 406... Transmitter, 407, 408... Filter, 409, 41
0...Receiver, 411...Mixer, 412...Display device.

Claims (1)

[Scope of Claims] 1. A single probe for obtaining ultrasonic tomographic image signals and ultrasonic pulsed Doppler information, a tomographic image signal transmitter and a pulsed Doppler signal transmitter that generate mutually different frequencies; A transmission signal switch that switches signals from both transmitters, a reception signal distribution switch that switches the reception signal from the probe, and a tomographic image signal receiver and pulsed Doppler that receive the signals from the reception signal distribution switch. It includes a signal receiver, a mixer that mixes the signals from both receivers, and a display that displays the result of the mixer, and the drive frequency band of the probe is set to ₁ (center frequency) ±△ ₁ (band) and ₂ (center frequency) ±△ ₂ (band), one of these two frequency bands is used for Doppler and the other is used for tomographic images, and the two frequency bands are ₁ < _{2 1} + An ultrasonic pulse Doppler apparatus characterized by satisfying the following conditions: _Δ1 < ₂ - Δ ₂ 2 _Δ 1 < ₁ 2 Δ ₂ < ₂ . 2. The ultrasonic pulsed Doppler apparatus according to claim 1, wherein the intensity of the sound waves emitted to obtain the pulsed Doppler signals is greater than the intensity of the sound waves emitted to obtain the tomographic image signals.