JPH0228971B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a Doppler ultrasonic diagnostic apparatus, and particularly to a reference frequency oscillator used in its frequency mixer.

Background of the technology Ultrasonic diagnostic equipment that uses the Doppler effect For example, ultrasound Doppler blood statistics transmits ultrasound waves of a certain frequency, and in this example, receives the ultrasound waves reflected from the bloodstream of the target object and uses it as a reference. frequency, and the flow velocity of the object is measured from the mixed output of the difference between both frequencies. FIG. 1 shows an example, in which 10 is an original oscillator that generates a high frequency F ₀ , 12 and 14 are M, which generates a high frequency F ₀ ,
A frequency divider 16 that divides the frequency by N receives the rate frequency F _R =F ₀ /MN from the frequency divider 14 and transmits it to the ultrasonic transducer 20.
18 is a circuit that amplifies the reflected wave reception output of the vibrator 20. 22 is a mixer that combines the output of the reception amplification circuit 18 and the reference frequency F _M from the frequency divider 12.
= F ₀ /M is mixed. The mixer output includes a reflected wave and a beat component (Doppler shift component) of the reference frequency, and the low-pass filter 24 extracts only the beat component. 28 is a delay circuit, and the frequency divider 14
, or the rate frequency signal (which becomes the drive timing signal), is delayed by a time corresponding to the depth of the object to be measured. In addition to the monostable multivibrator 30, this delayed drive timing signal is converted into a pulse having a width corresponding to the depth range desired for Doppler measurement (a pulse that specifies the so-called sample position or sample volume), and controls the opening and closing of the range gate 26. . This gate 26 extracts only the portion desired for Doppler measurement from the output of the filter 24, and by passing this through the band pass filter 32, a Doppler shift signal of the portion desired to be measured is obtained. In actual equipment, another mixer 22 is provided in order to determine the flow direction, and mixing is often performed by adding the output of the receiving amplifier circuit 18 and a reference frequency phase-shifted by 90 degrees to this mixer 22. For details, please refer to Japanese Patent Application No. 53-129386 (Japanese Patent Application No. 55-54941)
No. 129387 (Japanese Unexamined Patent Publication No. 55-54942). An example of frequency etc. is F ₀ = 5MHz, M
=2 Therefore, F _M =2.5MHz, which is chosen to be approximately the same as the center frequency of the ultrasonic reflected wave. _FR is 10, 20,
For example, 30KHz. Figure 2 shows the output waveforms of each part in Figure 1, where (a) is the output of the original oscillator 10, (b)
shows the waveforms of the output of the frequency divider 14, (c) the output of the monostable multi 30, and (d) the output of the frequency divider 12. T ₀
is the period of the original frequency F ₀ , T _R is the period of the rate frequency F _R , τ is the delay time of the delay circuit 28, T _M is the period of the reference frequency F _M , M and N are both integers, and N>
1, M1.

Prior Art and Problems In conventional ultrasonic Doppler blood flow, the output of the original oscillator 10, which is equipped with a crystal oscillator or the like as the reference frequency F _M and oscillates an accurate frequency, is divided by an integer M in Fig. 1. A frequency obtained by dividing the reference frequency by an integer N is used for the repeated transmission period, that is, the rate period, of the ultrasonic waves. In this way, the reference frequency F _M or its period T _M and the rate frequency F _R or its period T _R are in an integer ratio relationship with the output frequency F ₀ or its period T ₀ of the original oscillator, and are synchronized. Doppler shift components can be extracted accurately. However, when the reference frequency or period and the rate frequency or period are in an integer ratio relationship, a television receiver is used as a display, and tomographic images and Doppler analysis outputs are stored in a frame memory and read out from the memory. When displaying images or Doppler analysis output on a television receiver, there may be problems.

In other words, in a television receiver, a predetermined synchronization signal, for example a horizontal synchronization signal, has a frequency of 15.748KHz and a period of 63.5μS.
The original frequency F ₀
It must be possible to create such a periodic signal for television, and also to create the timing for writing and reading data into the frame memory. The original frequency F ₀ is set to 12MHz, for example, taking into account reading and writing to the frame memory and the TV synchronization signal,
By dividing this, for example, the reference frequency F _M is 3MHz.
and divide the F _M to obtain the rate frequency F _R (F _R is
(Usually, it can be changed arbitrarily to 3KHz, 4KHz, etc.)
, it is difficult for the ratio of F _M and F _R or T _M and T _R to be an integer, and in order to make the ratio an integer while maintaining the synchronization and timing described above, the original frequency F ₀ must be made very high. It is necessary to set the frequency to a common multiple of the above frequencies, which poses a major constraint on device design.

Purpose of the Invention The present invention makes it possible to avoid raising the original frequency F ₀ unnecessarily above the highest frequency actually required in an ultrasonic diagnostic apparatus even when a television receiver is used as a display. With the goal.

Structure of the Invention The present invention provides that the phase of the reference frequency given to the mixer is
Focusing on the fact that if the phase and frequency are kept constant with respect to the ultrasound transmission timing near the timing corresponding to the so-called sample position, it is not necessarily necessary to keep the phase and frequency constant at other timings. At least in the vicinity of the timing corresponding to the sample position, the original frequency is kept low by using a synchronous oscillator that maintains a constant phase with respect to the ultrasound transmission timing. That is, the present invention transmits ultrasonic waves at a constant rate, receives and amplifies the reflected waves, mixes the amplified signal with the reference frequency of the reference oscillator using a mixer, and outputs the mixed output using a low-pass wave generator. In a Doppler ultrasonic diagnostic device that obtains information about speed by oscillating waves, the reference oscillator is capable of synchronous oscillation, which is initialized for a certain period of time at a specific timing of the rate cycle and starts oscillating at a specific initial phase each time. The device is characterized by having an oscillator, which will be described in detail below with reference to the drawings.

Embodiment of the Invention FIG. 3 shows an embodiment of the invention, in which the same parts as in FIG. 1 are given the same reference numerals. The difference from FIG. 1 is that in FIG. 3, the original frequency F ₀ is directly divided by K to obtain the transmission timing (rate frequency), and 34 is the K frequency divider. Reference frequency F _M
is created by the M frequency divider 12 as in FIG. 1, but the rate frequency F _R is input to this frequency divider to initialize it. That is, frequency divider 12 is a flip-flop or counter that can be cleared or preset, in this example F ₀
It is a counter that counts F R , and by inputting F _R to the clear terminal of the counter, F _R
The counter is cleared for a pulse width of . In this example, M=2 and the frequency divider 12 divides F ₀ by 2.
_FM is output, but it is placed in a clear state during the pulse width period of _FR , and the clearing is released when the pulse disappears.
Output starts from the next pulse of F ₀ . In this way, as is clear from Fig. 4, the reference frequency F _M
The phase of is always relative to the ultrasonic transmission timing F _R ,
Therefore, it is kept constant with respect to the range gate pulse (output of the monostable multi 30) and has no effect on the extraction of the Doppler deviation component. In other words, extraction similar to that shown in FIG. 2 can be performed. Also, the frequency division ratio K, M
are both integers, but K/M need not be an integer.

If the frequency division ratio K/M is not an integer, the relative phase of frequencies F _M and F _R will vary, making it impossible to correctly extract the Doppler shift component. Initialization of the frequency divider 12 by the transmission timing F _R improves this point, and F _M
and _FR are synchronized. Note that this initialization causes the reference frequency F _M to be generated intermittently, and the time τ' from when the initialization of the frequency divider 12 is completed and the output starts until the range gate pulse is applied is It is sufficiently long compared to the time from when the pass filter 24 receives the input until the output becomes stable;
It is necessary to ensure that the influence of the mixer output during the initial stage does not appear during the range gate pulse period.

Instead of using the frequency divider 12 of the original frequency F ₀ to generate the reference frequency F _M , a free-running oscillator such as a CR oscillator may be used. In this case, initialization can be done by short-circuiting capacitor C by F _R , and since it is not frequency division, the frequency of the reference frequency F _M and the original frequency
F ₀ can be set completely independently.

Effects of the Invention According to the present invention described above, there is no longer a restriction that the rate period T _R must include an integer number of reference frequency bases _T Timing matching with the synchronous system becomes extremely easy. Note that the primary oscillator for the ultrasonic transmission system and the primary oscillator for other synchronization systems in the above device are provided independently, and the signal obtained by the ultrasonic transmission system is transmitted to A by using the clock of the ultrasonic transmission signal. /D conversion and writing to a frame memory operated by a frame memory synchronization system clock via a buffer memory such as FIFO (first-in/first-out) memory, the internal clock Although the problem of matching between the systems can be solved, this is not preferable because the amount of hardware in the buffer memory increases and the beats of the clock system signals that are not synchronized with each other may adversely affect the ultrasonic transmission signal.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional example, Fig. 2 is a diagram showing waveforms of each part thereof, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a diagram showing waveforms of each part thereof. . In the drawing, 20 is an ultrasonic transmitter/receiver, _FM is a reference frequency, 22 is a mixer, 24 is a low-pass wave generator, 12
is an oscillator capable of synchronous oscillation.

Claims (1)

[Claims] 1. Ultrasonic waves are transmitted at a constant rate, the reflected waves are received and amplified, the amplified signal is mixed with a reference frequency from a reference oscillator using a mixer, and the mixed output is converted into a low-frequency signal. In a Doppler ultrasonic diagnostic device that obtains information about speed by passing waves through a wave transducer, the reference oscillator is initialized for a certain period of time at a specific timing of the rate cycle and starts oscillating at a specific initial phase each time. An ultrasonic diagnostic device comprising an oscillator capable of synchronous oscillation. 2. The rate period is obtained by dividing the output of an oscillator that continuously oscillates at a constant frequency higher than that of an oscillator capable of synchronous oscillation, and the oscillator capable of synchronous oscillation divides the output of the continuous oscillator and 2. The ultrasonic diagnostic apparatus according to claim 1, wherein the ultrasonic diagnostic apparatus is a frequency divider that is initialized for a certain period of time at a specific timing of a cycle. 3. The ultrasonic diagnostic apparatus according to claim 1, wherein the oscillator capable of synchronous oscillation is a CR free-running oscillator that is initialized for a certain period of time at a specific timing of a rate cycle.