JPH04164440A - Ultrasonic measuring method of vibration at different parts of heart - Google Patents

Abstract

PURPOSE:To measure time-series signals of vibration speeds in various parts of a heart, which serve effectively diagnosis of cardio-disorder, by sampling the vibration speed of the object to be inspected with uneven intervals of the time at which reflected wave returns for each transmission pulse, and resampling the time-series data of this vibration speed at regular intervals. CONSTITUTION:When A/D conversion is made with sampling frequency several times as great as the sine frequency of transmission pulse wave, a memory capacity of 10M pieces (=10<7>) is needed in order to continuously obtain data corresponding to one heart beat, and this is rather difficult. According to the present invention, the output signals of an orthogonal intersect detector circuit including low frequency components is A/D converted with a sampling frequency fs several hundred times as large as the repeating frequency of the transmission pulses, and digital signals xr(n), xi(n) are obtained. To make A/D conversion for one sec continuously in case fs=1 MHz, it is enough with provision of a memory capacity of 1M pieces approximately, which is practicable. Thereby vibration signals of various parts of heart in pulsation with large amplitudecan be measured with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for non-invasively measuring time-series signals of vibration velocities of various parts of the heart, which is effective in diagnosing heart diseases.

[Conventional technology]

Ultrasonic diagnostic equipment has been used as a non-invasive method of measuring the heart. In order to measure the vibrations of various parts of the heart from above the chest wall, an ultrasound Doppler as shown in Fig. 1 is used.

In FIG. 1, a pulse mode transmitter (1) generates a burst pulse wave having a constant pulse width and a constant repetition frequency as shown in (10). After amplifying this waveform, the elastic waves converted by the ultrasonic transducer (2) in contact with the human chest and the reflected waves from various parts of the heart have the waveform shown in (11). The reflected wave after each transmitted pulse undergoes a Doppler frequency shift depending on the vibration velocity of the target region. This waveform is amplified in (3), and then only the Doppler frequency shift component is extracted as shown in (12) using a quadrature detection circuit (4) and a low-pass filter (5). Sample this waveform/
Hold (6) samples/holds at a certain delay timing from the transmission pulse, (13
) or (14) is generated. Furthermore, after smoothing the step-like waveform with a low-pass filter (7),
Obtain the waveform (15). After that, this waveform is converted into a digital signal by the A/D conversion circuit (8), and the calculator (8) converts this waveform into a digital signal.
In 9), calculate and find the instantaneous frequency and vibration speed.

In addition, as shown in Figure 2, after transmitting an elastic wave, the trigger point is the point at which a large amplitude reflected wave returns from the heart wall in front of the heart, and the Doppler frequency shift after a certain delay time from that point. It is also possible to obtain this and output the vibration velocity waveform of the heart wall in front of the heart, where the amplitude of the reflected wave is large in the heart that beats with a large amplitude. (1) (2) in Figure 2
(3), (4), and (5) are the same as those in Figure 1, but in the circuit (10) in Figure 2, (3)
) detects the point in time at which the reflected wave after the transmitted pulse has a large amplitude above a certain threshold at the output of the circuit, and generates a trigger signal. The circuit (6) performs sampling/holding at the timing of this trigger signal. From the resulting waveform, the vibration velocity is determined by performing the processes in (7), (8), and (9) in the same manner as in FIG.

[Problem that the invention seeks to solve]

Since the heart wall beats with a large amplitude of approximately 8 to 15 mm in one beat, in the configuration shown in Figure 1, the time it takes for the reflected wave to return varies within a range of several μS%IQμs. do. Therefore, the analog circuit sample (6) in Figure 1/
There is a problem in that the hold timing deviates from the time when the reflected wave returns from a certain part on the heart, making it impossible to determine the vibration velocity at a certain part on the heart.

Furthermore, in the trigger detection of (lO) in the configuration shown in FIG. 2, it is only possible to set the heart wall surface in front of which the reflected wave returns with a large amplitude as the reference point for analysis. Therefore, there is a problem in that it is very difficult to detect the vibration of the opposite heart wall whose distance from the front heart wall changes as the heart beats, for example.

On the other hand, as shown in Figure 3, the reflected signal is transmitted at the frequency of the transmitted wave (
It is conceivable to perform A/D conversion at a sampling frequency several times higher than several MHz), but in this case, the A/D converter (5
) requires a huge amount of high-speed memory, and it is difficult to continuously collect data for the length of one heart beat.

[Purpose of the invention]

The purpose of the present invention is to solve these problems and provide a method for measuring vibrations of various parts of the heart beating with large amplitude, which is necessary for local abnormal diagnosis based on the elastic characteristics of each part of the heart. It's about doing.

[Means for solving problems]

Therefore, in the present invention, the output signal of a quadrature detection circuit in a diagnostic device using ultrasonic Doppler is A/D converted at a high speed several hundred times the repetition frequency of the transmitted pulse, and the returned reflected wave is calculated from the obtained digital signal. Find the time it takes for each transmitted pulse to arrive.

The vibration velocity of the object is calculated from the Doppler frequency deviation at that time.
First, the return time of the reflected wave for each transmitted pulse is sampled at unequal intervals, and then the time series data of vibration velocity sampled at unequal intervals is resampled at equal intervals. Measures continuous data for one beat of vibrations in each part of the heart, which beats with large amplitude. The vibration measurement method is explained in the fourth section.
This will be explained using the block diagram shown in the figure. Pulse mode oscillator (
1) is obtained by taking the product of a pulse wave with a pulse width of 1 μs (stretched or compressed as necessary) and a repetition frequency of 2 kHz (changed as necessary) and a sine wave of 3.5 MHz (changed as necessary). The generated burst pulse waveform is amplified and output. Ultrasonic transducer (2) in contact with the human chest
) The reflected waves of the elastic waves from various parts of the heart are converted back into electric signals by the ultrasonic transducer, amplified by the preamplifier length gate circuit (3), and then the incident signal is discarded. Here, the gate circuit is used to cut off large amplitude incident signals. Quadrature detection circuit (4
), a 90 degree phase shift converter is used to separate the reflected signal into two components 5r(t) and s;(t), and a multiplier demodulates the original sine wave to obtain xr(t). and xl(t
).

Here, Xr(t), x, (t) is also 5r(t), 5
Similar to l(t), they are in a Hilbert transform relationship with each other.

Putting these signals together, the analytical signal x(t) is expressed as x(t)
”xr(t)+J x,(t)=A(t)exp(φ(
t)) (1), Doppler angular frequency shift ω, (t) is given by the following equation.

In order to obtain the time series ωd(t) of this Doppler frequency shift, the following processing is performed. First, the output signal of the quadrature detection circuit (4) is converted into a digital signal by the LA A/D converter (6) which has passed through the anti-alias filter (5). The sampling frequency at that time is expressed as f,=1/T3, and is set to several hundred times the repetition frequency of the transmission pulse generated by the circuit (1). At this time, the anti-alias filter (5) cuts off frequency components of f, 72 or higher. When the reflected wave from the heart is A/D converted with the configuration shown in Figure 3 at a sampling frequency several times the sine frequency of the transmitted pulse wave, it takes 10M to continuously obtain data for the heart and dregs.
(=107), which was not an easy task. Therefore, in the present invention, the output signal of the quadrature detection circuit containing low frequency components is A/D converted at a sampling frequency f, which is several hundred times the repetition frequency of the transmission pulse, and the digital signal x, (n), x, (n) is obtained.

In the case of f,=IMHz, in order to perform A/D conversion continuously for one second, it is realistic to prepare a storage capacity of about IM. At the same time as the A/D conversion of the output signal of the quadrature detection circuit, the output signal of the pulse mode oscillator, which is input to the ultrasound transducer, and the electrocardiogram waveform are also A/D converted.
Convert and find a reference point for later processing.

The processing in the computer (7) in FIG. 4 will be described in detail using FIG. Evaluating the deviation, resampling the time series data sampled at irregular intervals to equal intervals, and finding the vibration velocity when the pulsation is large amplitude as continuous data for one beat.

The processing performed by a computer on the waveform obtained by performing A/D conversion in FIG. 4 will be explained using FIG. 5. First, (a) shows the incident wave A/D converted with the sampling period TS, the real part xr(n), and the imaginary part x,(n) of the reflected wave, and shows that the object is pulsating with large amplitude. When there are two waves, the reflected waves are spaced unevenly as shown in this figure. In (b), xr (n)2+ z, (n)2 indicates the squared amplitude of the reflected wave, so using this value, calculate the return of the reflected wave from a certain part of the target for each transmitted pulse. The time of arrival can be identified. Let n be the time at which a reflected wave returns from a certain part with respect to the kth transmitted pulse. X, (nk
) and Xt(nb), the -
By interpolating the data between n k, ``k+I, n, or 2110., we obtain a time series with a sampling period T as shown in (C).In the interpolated data, as shown in (d), Reflected wave Xr at time n and the next time nl+T
(Ilk), xl (nk), and X r (n v,
+Ts)+X i (n 1''Ts) to find the Doppler angular frequency shift ωa(nk). Since equation (2) is an equation for finding the Doppler angular frequency shift from a continuous signal, This equation is replaced with a digital signal as follows.The phase angle φ(n
, ), Xr (n*”Ts) and X I (n , +'r
Using the phase angle φ(nb+Ts) obtained from s), ω
a (n k) can be obtained by the following difference approximation.

Next, ωa(n*) is interpolated at the sampling period T, and as shown in (e), the time series data obtained here is resampled at equal time intervals, and the Doppler angular frequency deviation is The time series ωd(n) of the shift is obtained. From this ω, (n), according to the following formula,
Find the vibration velocity time series v(n).

C is the propagation speed of the sound wave in the medium, and fo is the frequency of the sine wave of the incident wave. The vibration velocity time series obtained in this way is the fifth
It is obtained as shown in (f) of the figure.

In the above interpolation process, from the sampling theorem, 1 (lc
)d(n) l <yr/Te is required. Here, Ts is the repetition period of the transmission pulse. Substituting this into equation (4), it is necessary to satisfy the following condition: ITs·v(n)l<λ/4 (5) where λ is the wavelength.

In addition, the calculation of equation (3), which is the difference approximation of the Doppler shift frequency of equation (2), is not performed at the repetition period of the transmission pulse as shown in FIG. As shown in Figure 5(d), the period T is several hundredths of that.
Approximation accuracy can be improved by performing this on the waveform obtained in s.

From the above processing, the return times of reflected waves included in reflected waves Regarding the state, it is possible to obtain instantaneous frequency and vibration velocity waveforms at equal time intervals, and it is possible to obtain useful clues for diagnosis of each part of the heart.

〔Effect of the invention〕

As described above, the present invention can non-invasively and highly accurately measure vibration signals of various parts of the heart that beat with large amplitude, which is effective in diagnosing heart diseases.

[Example] A basic experiment was conducted using a water tank that corresponds to vibrations on the heart wall that fluctuate with large amplitude, as outlined in FIG. 6. A rubber plate is moving with a large amplitude (width 14+n+n) in a water tank, and the reflected waves from its surface are analyzed. FIG. 7 shows the treatment results obtained in this water tank experiment.

(a) is the A/D converted incident wave, (b) and (c) are the A/D converted reflected waves x, (n), x;
n) and the results of interpolation using those values at the time of the largest amplitude of the reflected wave are shown superimposed. Also (d)
shows the vibration velocity time series v(n) obtained by substituting the instantaneous angular frequency ω, (n) obtained from the interpolation results of (b) and (c) into equation (4). The vertical bar in the figure indicates the amplitude of the vibration velocity at the time the reflected wave returns.

(e) shows the vibration velocity of (d) over a longer period of time. The fine vibrations correspond to mechanical vibrations in the aquarium. (f) is a time-series power spectrum of the vibration velocity.

FIG. 8 shows the results of measuring the vibration velocity of the human heart wall using this measurement method.

[Brief explanation of drawings]

FIG. 1 is an outline of the configuration of the most common conventional vibration measurement method using ultrasonic Doppler. In Figure 2, after transmitting an elastic wave, the point in time when a reflected wave of large amplitude returns from the heart wall in front is used as a trigger point, and the Doppler frequency shift is determined after a certain delay time from that point. This is an overview of a conventional method for measuring the vibrations of the heart wall in front of a heart that beats with large amplitude. Figure 3 shows the reflected signal at the frequency of the transmitted wave (several MH).
A configuration diagram of a measurement method that performs direct A/D conversion at several times z) is shown. FIG. 4 is an overview of the configuration diagram of the vibration measurement method based on the present invention. FIG. 5 is an explanation of the processing performed by a computer on the waveform obtained by performing A/D conversion in FIG. Fig. 3(a) shows a transmitted pulse wave that has been A/D converted with a sampling period T, and reflected waves x, (n), and xr (n), and shows that the object is pulsating with a large amplitude. When Xr
(n)2+x, (n)2 indicates the squared amplitude value of the reflected wave, so from this value it is possible to identify the time when a large reflected wave from the object returns for one transmitted pulse. (
C) is the result of interpolation between reflected waves for each of x, (n), and Xl(n). (d) is based on equation (3) from the values of x, (n) and x, (n) at time n and the time n immediately after that, +'r, in the data obtained by interpolation. , ωa(n*). (e) shows the result of interpolating ωa(n*) with the sampling period TS. By resampling the time series data obtained here at equal time intervals, the instantaneous angular frequency time series ωd
(n) is obtained. (f) is this time series ω, (n) to (5
) is the result of finding the vibration velocity time series v(n). Fig. 6 is a schematic diagram of a basic experiment using a water tank that deals with vibrations on the heart wall that fluctuate with large amplitudes, in which a rubber plate moves with large amplitude (width 14 mm). FIG. 7 shows the processing results of reflected waves obtained in the water tank experiment. (a)
is the A/D converted incident wave, and (b) and (c) are the A/D converted reflected waves Xr(n)+X+(n
) and the results of interpolation from those values at the time of the largest amplitude of the reflected wave are shown superimposed. (d) is (b)
The instantaneous angular frequency ω, (n) obtained from the interpolation results of (c) and
and the vibration velocity time series v(n) obtained by equation (5). (e) shows the vibration velocity of (d) over a longer period of time. (f) is a time-series power spectrum of the vibration velocity. FIG. 8 shows the results of measuring the vibration velocity of the human heart wall using this measurement method. Fig. 1 Last temple station number 1 limb periodic pulse Fig. 2 Drunk jaw temple F FREQUENCY (Hz) Fig. 5 Fig. 6 Fig. 7 FREQUENCY (Hz) Fig. 8

Claims (1)

[Claims] A burst pulse wave with a constant pulse width and a constant repetition frequency is used as a transmitted pulse wave, and after amplification, it is converted into an elastic wave by an ultrasound transducer placed in contact with the human chest and transmitted into the body, and the reflected waves from various parts of the heart are regenerated. After converting it into an electrical signal using an ultrasonic transducer and amplifying it, the output signal is A/D converted at a high speed several hundred times the repetition frequency of the transmitted pulse through a quadrature detection circuit, and the reflected wave is calculated from the obtained digital signal. The return time is determined for each transmitted pulse, and the vibration velocity of the object is sampled from the Doppler frequency shift at that time at unequal intervals of the return time of the reflected wave for each transmitted pulse, and then Second, the time-series data of the vibration velocity sampled at unequal intervals is resampled at equal intervals to measure one beat's worth of continuous data of the vibrations of each part of the heart.