JPH0414020B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a data processing method for an ultrasonic pulsed Doppler blood flow meter.

(b) Background of the technology Ultrasonic pulsed Doppler blood flow meters transmit pulsed ultrasound waves with a predetermined beam width toward a subject that includes a specific region and a specific range of blood flow to be measured. This method receives reflected ultrasound waves, converts them into electrical signals, and measures the blood flow velocity from the electrical signals using the Doppler effect. Therefore, in general, an ultrasonic Doppler blood flow meter has a main oscillator, which generates reference waves (sine waves and cosine waves) for repeatedly synchronizing the transmission of pulsed ultrasonic waves and for obtaining Doppler signals. (is there to distinguish between the front and rear directions of blood flow from the blood flow meter as the base point), the range gates that set the blood flow area and measurement range are synchronized, and the blood flow velocity distribution is extracted from the Doppler signal. A display device is required to display the spectrum analysis.

However, ultrasound devices that transmit and receive pulsed ultrasound waves generally receive smaller signals from farther away from the subject.
It has the characteristic of having a poor signal-to-noise ratio. In ultrasonic pulsed Doppler blood flow meters, it is difficult to extract signals from deeper parts, and complex data processing as described above is required to determine blood flow velocity, making it difficult to accurately determine blood flow velocity in deep parts. Measurement was considered difficult, and improvements were strongly desired.

(c) Prior art and problems Figure 1 shows a system diagram of an ultrasonic pulse Doppler blood flow meter according to the prior art.

In Figure 1, TR is an ultrasonic transducer in which the transmitting amplifier DA amplifies the driving pulse DT output from the main oscillator MC and the ultrasonic transducer
Drives TR. By this driving, the ultrasonic transducer TR bursts at a predetermined frequency ( _c ) using the end of the drive pulse DT as a synchronization point, and transmits pulsed ultrasonic waves with a predetermined beam width toward the subject.
The reflected ultrasound from the subject is similarly received by the ultrasound transducer TR, converted into an electrical signal, and output, and the received electrical signal is amplified by the reception amplifier RA.

The main oscillator MC has a synchronization point at the end of the drive pulse DT, and the frequency at _which the occupation rate is 1/2 is approximately equal to _c1
The pulse is generated by the reference wave generator RW.
-1. The reference wave generator RW-1 outputs a sine wave S ₁ with a frequency _c1 ( ₁ = _c1 ) synchronized with the input pulse and a cosine wave C ₁ with a phase difference of 90 degrees, each of which is sent to the phase detector PD-1. and input it to PD-2.

The output of the receiving amplifier RA mentioned above is also connected to this phase detector.
The phase difference between the received electrical signal and the reference wave is detected by inputting it to PD-1 and PD-2. That is, if there is a moving object such as blood flow within the subject, a change in phase difference occurs in the received electrical signal due to the Doppler effect. Distinguishing between the movement of the object approaching and moving away from the ultrasonic transducer TR is made by the sine wave and cosine wave of the reference wave described above.

The outputs of the phase detectors PD-1 and PD-2 are sent to the range gates RG-1 and RG-2, respectively. The phase detector PD-1 and
This device samples and holds the output of the PD-2, and the predetermined position is, for example, selecting a specific blood flow point within the subject, and the predetermined width is a relatively short width of the blood flow point. These settings are made in the range gate signal setting unit RGT, depending on whether the blood flow velocity in a range is to be measured or the macroscopic average flow velocity in a relatively long range is to be measured. Therefore, the outputs of the range gate units RG-1 and RG-2 are Doppler signals extracted from blood flow velocity information in a specific range of a specific region of the subject.

When measuring blood flow velocity, the Doppler signal contains mixed signals of movement of blood vessel walls and heart walls, so it is passed through high-pass filters HPF1 and HPF2 in order to remove these signals and measure only the velocity of blood flow. . In other words, since the movements of the blood vessel walls and heart walls described above are sufficiently slow compared to blood flow, the low frequency components can be cut and removed.

The outputs of the HPF1 and HPF2 are sent to the spectrum analysis unit SA-1, and the frequency components of the Doppler signal caused only by the blood flow described above are output, so the velocity of the blood flow can be determined by observing the distribution of the frequency components on the display unit ID. Distribution can be measured and blood flow analysis information can be provided.

However, ultrasound equipment that transmits and receives pulsed ultrasound waves generally has the characteristic that the received signal from the farther part of the subject is smaller and the signal-to-noise ratio is worse. The problem is that it cannot be measured with high precision.

(d) Purpose of the Invention The purpose of the present invention is to measure blood flow velocity distribution deep within a subject with high accuracy using an ultrasonic pulse Doppler blood flow meter.

(e) Structure of the Invention The present invention uses only a single frequency of the reference wave that is approximately equal to the frequency of the transmitted ultrasound, unlike the prior art, as the frequency of the reference wave necessary for detecting the phase difference between the received signal and the received signal to obtain the Doppler signal. Instead, a plurality of reference waves having frequencies close to the single frequency are also used, and for this purpose, a phase difference detection section, a range gate section,
By providing multiple spectrum analysis units corresponding to the reference wave and combining the results, it is possible to extract Doppler signals from a wide frequency band in accordance with the expanded frequency band exhibited by the received signal. The speed can also be measured with high precision and the above purpose can be achieved.

(f) Embodiment of the Invention Figure 2a shows the frequency spectrum of the received signal reflected from the deep part of the ultrasonic pulsed Doppler blood flow meter and the spectrum when three reference waves are used as an embodiment of the invention. The status of frequency allocation of the reference wave is shown. 4 is the frequency spectrum of the received signal reflected from the deep part of the subject and input to the ultrasonic pulse Doppler blood flow meter.

Normally, the spectrum of ultrasonic waves reflected from a subject has a relatively wide frequency band centered around _c , as shown in Figure 2 a, 4. On the other hand, in an ultrasonic pulsed Doppler blood flow meter, the frequency of the reference wave is set at _c. approximately equal to
The signal band actually used when performing Doppler measurement with setting _c1 and extracting blood flow information in a certain region using a range gate is relatively narrow as shown at 1 in FIG. 2a. Particularly when dealing with received signals from deep within the subject, the signal-to-noise ratio is poor and the reference wave _c1 alone is insufficient, making it impossible to obtain highly accurate blood flow information. Therefore, in the embodiment of the present invention, in addition to _c1 , reference waves _c2 having a lower frequency than _c1 and _c3 having a higher frequency are provided, and the reference wave _c2 has a phase difference due to the Doppler effect in the frequency range of curve 2 shown by the dotted line. Detect reference wave _C3
detects the phase difference due to the Doppler effect in the frequency range of curve 3 shown by the dotted line.

In other words, in this embodiment, in addition to the conventional frequency _c1 , _c2
and _c3 to detect the phase difference from the three-wave reference wave to obtain a Doppler signal with more blood flow information than before.

The three reference waves mentioned above are the ultrasonic transmission drive pulses DT generated by the main oscillator MC as shown in Figure 2b.
The frequency is ₁ with the occupancy rate 1/2 and the synchronization point is the terminal of
The rectangular waves ₂ and ₃ are input to the reference wave generators RW-1, RW-2 and RW-3 as shown in Fig. 3, and RW-1, RW-2 and RW-3 are sine waves and cosine waves, respectively. Outputs the reference wave of

The sine wave and cosine wave of the reference wave are each 2 compared to the conventional one.
Since the wave is increasing, the phase detection section as shown in Figure 3
PD, range gate RG, high pass filter
Increase HPF and spectrum analysis section SA and synthesis section
The AV combines these analysis results and displays them as a blood flow velocity distribution on the display ID. In addition, the reference wave is _c1 ,
Three waves, _c2 and _c3, are used, but as shown in Figure 2a, the blood flow velocity distribution in band 1, which includes the center frequency of the received signal spectrum, is dominant. In order to make it easier to see, the signal amplification is weighted shallowly for _c1 and deeply for _c2 and _c3 .

(g) Effects of the Invention According to the present invention, the frequency band of the received signal reflected from the deep part of the subject of the ultrasonic pulsed Doppler blood flow meter can be effectively used, and the velocity distribution of blood flow in the deep part can be achieved with high precision. This can have a great effect on expanding the medical applications of blood flow meters.

[Brief explanation of drawings]

Figure 1 shows a system diagram of an ultrasonic pulse Doppler blood flow meter according to the prior art, and Figure 2 a shows the frequency spectrum of the received signal due to ultrasound reflection from the subject by the ultrasonic pulse Doppler blood flow meter, and the positioning of the reference wave frequency. , shows the frequency drift band due to the Doppler effect of blood flow that can be detected by the reference wave, and FIG.
(b) shows the rectangular wave output of the main oscillator for forming the reference wave in the embodiment of the present invention, and FIG. 3 shows a system diagram of the embodiment of the present invention. The same symbols throughout the figure indicate the same objects, MC is the main oscillation unit, DA is the transmission amplifier, TR is the ultrasonic transducer, RA is the reception amplifier, PD is the phase detection unit, RW is the reference wave generation unit,
RG is the range gate section, RGT is the range gate signal setting section, HPF is the high-pass filter, SA is the spectrum analysis section, AV is the synthesis section, and ID is the display section. In addition, DT is the drive pulse, _c is the frequency of the transmitted ultrasound, ₁ , ₂ , and ₃ are the frequencies of the fundamental rectangular waves forming the reference wave, S is the sine wave of the reference wave, and C is the cosine of the reference wave. wave, _c1 , _c2 and _c3 indicate the frequency of the reference wave.

Claims (1)

[Claims] 1 Transmit pulsed ultrasound to the subject in synchronization with the output from the main oscillator, receive the pulsed ultrasound reflection from the subject, convert it into a received electrical signal, and combine the received electrical signal with the output of the main oscillator. The phase difference between a sine wave and a cosine wave having a frequency almost equal to the frequency of the transmitted ultrasound wave is detected in synchronization with the reference wave, and the phase difference detection signal is used as a signal of a specific part of the subject and a specific range using a range gate. In an ultrasonic pulse Doppler blood flow meter that sample-holds and spectrally analyzes and displays the range gate output, the reference wave used for phase difference detection is divided into multiple groups having a frequency approximately equal to that of the transmitted ultrasonic wave and a frequency close to the frequency. sine waves and cosine waves, the phase difference between the received electrical signal and each of the plurality of sets of sine waves and cosine waves is simultaneously detected by a plurality of phase difference detection means, and the phase difference detection results are each sampled by a range gate. An ultrasonic pulse Doppler blood flow meter characterized by hold, spectrum analysis, synthesis, and display.