JPS6122576B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic Doppler blood flow meter that can measure blood flow with high precision.

In recent years, so-called ultrasonic pulse Doppler blood flow meters have been developed that measure blood flow information in blood vessels and the heart using the Doppler frequency shift of ultrasonic pulses. This ultrasonic pulse Doppler blood flow meter can obtain blood flow information in a specific blood vessel by utilizing excellent distance resolution, and is basically configured as shown in FIG. 1. That is, a reference sine wave signal generated by a reference oscillator 1 is divided by a frequency divider (rate pulse generator) 2 to generate a rate pulse signal having a predetermined repetition period, and the pulse width of this rate pulse signal is It is determined by the burst width setting device 3. Based on this rate pulse signal, the burst generator 4 extracts several periods of the reference sine wave signal, and sends this burst signal to the ultrasonic probe 6 as a transmission pulse signal via the pulser 5.
It supplies and energizes the Thereby, the ultrasonic probe 6 transmits an ultrasonic pulse into the living body 7, and the ultrasonic pulse is transmitted to the blood vessel wall 8a and blood (red blood cells).
8b is received.

At this time, the Doppler shift frequency _d of the reflected wave signal with respect to the blood flow is expressed as _d = 2υ cos θ/C _c where _c is the frequency of the ultrasonic pulse and _c > _d . Where, υ: blood flow velocity θ: angle between the direction of movement of the ultrasound pulse and the direction of blood flow C: the propagation velocity of the ultrasound pulse in the living body (approximately 1530 m/sec).

On the other hand, the reflected ultrasonic signal received by the ultrasonic probe 6 is amplified by the preamplifier 9, and then multiplied by the reference sine wave signal by the mixer 10 and mixed. Thereafter, harmonic components are removed by a low pass filter (LPF) 11 and detected as a Doppler signal. The sampling hold circuit shown at 12 in the figure is connected to the sampling pulse generator 1.
According to the sampling pulse signal generated in step 3, a signal component at a specific depth, that is, a component corresponding to the blood flow, is extracted from the Doppler signal. Here, the sampling pulse generator 13 delays the rate pulse signal from the frequency divider 2 by a predetermined period of time to generate a sampling pulse signal, and this delay time L is determined by the ultrasonic probe 6.
Letting d be the distance between the inside of the blood vessel and the inside of the blood vessel, it is determined by L=2d/C. In this way, the extracted Doppler signal is filtered by a bandpass filter (BPF) 14 to remove Doppler shifts caused by harmonic signals and relatively slow movements of blood vessel walls, etc., and then processed by a spectrum analyzer (not shown) or a zero cross The frequency is converted by a counter or the like and then used for observation. In this way, blood flow information is detected.

By the way, in such a blood flow meter, since the sampling position of the Doppler signal in the sampling and hold circuit 12 is fixed, it is difficult to obtain blood flow information in tissues with rapid pulsation, such as the heart wall or arteries. If you try. It was not possible to stably extract the Doppler signal components of the same region of interest.

Therefore, a method has been proposed in which the sampling position of the Doppler signal is moved according to the pulsation of the tissue, that is, the depth change with respect to the ultrasound probe (Proceedings of the Japanese Society of Ultrasonics in Medicine 34-31978). According to this method, since the sampling position follows the detection site, Doppler signals from the site of interest can be extracted continuously without departing from the pulsation position of the tissue. However, since blood flows through the circulatory tissue, the blood flow drop signal obtained by this method includes deviations due to the pulsation of the circulatory tissue, etc., in addition to deviations due to the original blood flow. . Therefore, the blood flow Doppler signal obtained by the above method does not represent true blood flow information in the tissue, and processing the above blood flow Doppler signal as blood flow information causes many errors. The content was undesirable. In other words,
The blood flow Doppler signal obtained by the above method is information for the ultrasound probe, and is not information for the original circulatory tissue, such as blood vessels.

The present invention has been made in view of the above circumstances, and its purpose is to realize and provide an ultrasonic Doppler blood flow meter that can perform highly accurate blood flow measurement with few errors.

That is, the present invention constantly controls the phase of the reference signal with respect to the reflected signal from the blood by controlling the phase of the reference signal according to the depth change of the ultrasound probe of the circulatory tissue such as the blood vessel wall or the heart wall. This eliminates the influence of frequency shifts caused by the circulatory tissue on blood flow information, and detects blood flow information for the circulatory tissue rather than information for the ultrasound probe. be.

First, the principle of this invention will be explained. As mentioned earlier, if the frequency of the ultrasound pulse is _e and the ultrasound Doppler shift frequency with respect to blood flow is _d , then
The reflected ultrasound signal from circulatory tissues such as the heart wall and blood vessel wall is A(t) cos (2π _c

Claims (1)

[Claims] 1. An ultrasonic probe that transmits and receives ultrasonic waves to blood in circulatory tissue at a predetermined repetition period;
means for obtaining a blood flow Doppler signal by mixing at least a blood reflected signal component with a reference signal among the reflected ultrasound signals obtained by the ultrasound probe;
A means for detecting a change in the depth of the circulatory tissue with respect to the ultrasound probe; and a variable phase shifter for controlling the phase of a reference signal to be mixed with the reflected ultrasound signal based on the depth change. An ultrasonic Doppler blood flow meter characterized by: