Ultrasonic pulse Doppler blood flow meter with provision to create ultrasonic test waves which, when reflected from a stationary object, result in echoes similar to those produced by a moving object

An ultrasonic pulse Doppler blood flow meter which has: PA0 a rate pulse generator for outputting a rate pulse, PA0 a pulser receiving the rate pulse for outputting a drive pulse, PA0 a transducer excited by the drive pulse for transmitting an ultrasonic wave into an object to be detected and receiving the echoes thereof for converting the echoes into an electrical signal, PA0 a range gate circuit for outputting a sampling pulse after a predetermined time from the output of the rate pulse, PA0 a sample and hold circuit for sampling and holding the echo signals from the transducer in accordance with the sampling pulse, PA0 a converter for Fourier-converting the sampled echo signals, and PA0 a monitor for indicating in a intensity the converted echo signals PA0 advantageously further comprising: PA0 shifting circuit for shifting said predetermined time between the rate pulse and the range gate pulse at the individual periods of the rate pulse, and PA0 a switch circuit for selectively connecting the rate pulse generator and the shifting circuit to the drive pulse generator.

BACKGROUND OF THE INVENTION 
The present invention relates to an ultrasonic pulse Doppler blood flow 
meter which is associated with an operation checking mechanism. 
An ultrasonic pulse Doppler blood flow meter serves to transmit by an 
ultrasonic transducer an ultrasonic wave into the body, receive its 
echoes, extract only echoes from a blood flow corpuscle or cell at the 
position to be measured of the received echoes, obtain a Doppler frequency 
shift from the extracted echoes, and perform a spectrum analysis on the 
echoes, thereby obtaining the blood flow velocity. More specifically, the 
Doppler frequency shift fd can be expressed by the following equation: 
EQU fd=[(2V.multidot.cos .theta.)/C].multidot.fc (1) 
where 
V: the flow velocity of corpuscle (i.e., blood flow velocity), 
.theta.: the angle between the direction of the ultrasonic beam and the 
direction of the blood flow, 
C: velocity of sound in tissue 
fc: the central frequency of the ultrasonic wave transmitted. 
From the equation (1), it is understood that the flow velocity V of the 
blood is proportional to the Doppler frequency shift fd. The Doppler blood 
flow meter obtains the blood flow velocity V in view of this relation by 
obtaining the Doppler frequency shift of the echoes of the blood 
corpuscle. 
An example of a conventional such flow meter is shown in FIG. 1. FIGS. 2A 
to 2D are time charts of the waveforms of the signals in the respective 
sections of the flow meter shown in FIG. 1. A clock pulse a (FIG. 2A) of a 
predetermined frequency is produced from a clock pulse generator 1. A rate 
pulse generator 2 receives the clock pulse a from the clock pulse 
generator 1 and produces a rate pulse b (FIG. 2B) of the period 
corresponding to the period of the ultrasonic wave (the driven period of 
an ultrasonic transducer 4). The rate pulse b is applied to a pulser 3 and 
a range gate circuit 12. The pulser 3 drives the transducer 4 in 
synchronization with the fall of the rate pulse b. When the transducer 4 
is driven, the transducer 4 transmits an ultrasonic wave into a living 
body 5. The ultrasonic wave propagates in the living body 5 and is 
reflected on a vascular wall 6 or blood corpuscles or cells (in FIG. 1, 
only the blood corpulscle designated) by reference numeral 7 is indicated 
by a thick black point, and other blood corpuscles are indicated by small 
points). The echoes d are received by the transducer 4, which converts the 
echoes into an electric signal of the magnitude corresponding to the 
intensity of the echoes. The converted echo signals are inputted to a 
preamplifier AMP 9, and are amplified to the suitable amplitude. The 
amplified echo signals are then inputted to a mixer MIX 10. To the MIX 10 
is inputted a reference signal of the frequency corresponding to the 
central frequency of the ultrasonic wave transmitted from the transducer 
4, from the clock pulse generator 1. The echo signals are mixed by th MIX 
10 with the reference signal from the generator 1. The mixed signal is in 
turn inputted to a low pass filter LPF 11, which removes the harmonic 
component of the mixed signal. The echo signals thus fed through the low 
pass filter LPF 11 are in turn inputted to a sample & hold (S/H) circuit 
13, which samples only the echo signals from the position to be measured 
in accordance with the range gate pulse from the range gate circuit 12 as 
a sampling signal. The echo signals sampled are held at the S/H circuit 13 
until the S/H circuit 13 receives the next range gate pulse. The echo 
signals sampled are in turn inputted to a band pass filter BPF 14, which 
removes the harmonic wave components produced by sampling, echo from a 
stationary reflector such as a vascular wall, and Doppler frequency shift 
signals from a moving article moving relatively slowly to thus sample only 
the Doppler frequency shift signals due to the blood flow. The echo 
signals from the band pass filter BPF 14 are then inputted to a frequency 
analyzer 15, which is composed, for example, of an FFT (fast fourier 
transformer), and which frequency-analyzes the echo signals to produce a 
frequency spectrum corresponding to a blood flow signal. The frequency 
spectrum from the band pass filter BPE 14 is in turn inputted to a monitor 
16, which then indicates as an intensity a blood flow signal. 
Blood flow information is obtained by the conventional blood flow meter 
shown in FIG. 1 by the above-described operation. 
Since the conventional ultrasonic pulse Doppler blood flow meter however 
produces the blood flow information in the format of frequency (Doppler 
frequency shift) as described above, its circuit arrangement is 
complicated, and checks for the operation of the flow meter is accordingly 
complicated. As a conventional operation checking device, there is known 
"The Doppler Signal Simulator for Ultrasonic Pulsed Doppler System" 
described on Japan Ultrasonic Medical Society, Bulletin, 38-C-24 issued in 
April, 1981. This simulator employs as an echo signal obtained from a 
moving article an electric sinusoidal burst signal and obtains a Doppler 
frequency shift by varying the phase of the burst signal. 
Since the burst signal thus obtained is not however an actual echo, this 
device cannot generally check together with the characteristics of the 
ultrasound field and the transmitting & receiving circuits according to a 
transducer. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an ultrasonic pulse 
Doppler blood flow meter which is capable of readily performing the 
operation check thereof in view of the aforementioned drawbacks of the 
conventional flow meter. 
According to the invention, these is provided an ultrasonic pulse Doppler 
blood flow meter comprising: 
rate pulse generating means for producing a rate pulse of a predetermined 
repetition period, 
drive pulse generating means responsive to the rate pulse for producing a 
drive pulse, 
transducer means responsive to the drive pulse for transmitting an 
ultrasonic wave into an object to be detected and responsive to the echoes 
thereof for converting the received echoes into an electrical signal, 
range gate circuit means for producing a range gate pulse after a 
predetermined time from the rate pulse, 
sampling means responsive to the range gate pulse for sampling only echo 
signals from a predetermined depth of the received echo signals, 
frequency analyzing means for performing the frequency analyzation of the 
sampled echo signals, 
display means for indicating in an intensity the analyzed signals, 
shifting circuit means for shifting a predetermined time between the rate 
pulse and the range gate pulse by a predetermined time at every individual 
period of the rate pulse, and 
switching means for selectively connecting said rate pulse generating means 
and said shifting circuit means to said drive pulse generating means. 
According to the invention, there is further provided an ultrasonic pulse 
Doppler blood flow meter comprising: 
rate pulse generating means for producing a rate pulse of a predetermined 
repetition period, 
drive pulse generating means responsive to the rate pulse for producing a 
drive pulse, 
transducer means responsive to the drive pulse for transmitting an 
ultrasonic wave into an object to be detected and responsive to the echoes 
thereof for converting the received echoes into an electrical signal, 
range gate circuit means for producing a range gate pulse after a 
predetermined time from the rate pulse, 
sampling means responsive to the range gate pulse for sampling only echo 
signals from a predetermined depth of the received echo signals, 
frequency analyzing means for performing the frequency analyzation of the 
sampled echo signals, 
display means for indicating in an intensity the analyzed signals, 
shifting circuit means for shifting the rate pulse by a predetermined time 
at every individual period, thereby shifting said predetermined time 
between the rate pulse and the range gate pulse by a predetermined time at 
every individual period of the rate pulse, and 
switching means for selectively connecting said rate pulse generating means 
and said shifting circuit means to said drive pulse generating means. 
According to the invention, there is further provided an ultrasonic pulse 
Doppler blood flow meter comprising: 
rate pulse generating means for producing a rate pulse of a predetermined 
repetition period, 
drive pulse generating means responsive to the rate pulse for producing a 
drive pulse, 
transducer means responsive to the drive pulse for transmitting an 
ultrasonic wave into an object to be detected and responsive to the echoes 
thereof for converting the received echoes into an electrical signal, 
range gate circuit means for producing a range gate pulse after a 
predetermined time from the rate pulse, 
sampling means responsive to the range gate pulse for sampling only echo 
signals from a predetermined depth of the received echo signals, 
frequency analyzing means for performing the frequency analyzation of the 
sampled echo signals, 
display means for indicating in an intensity the analyzed signals, 
shifting circuit means for shifting the range gate pulse by a predetermined 
time at every individual period, thereby shifting said predetermined time 
between the rate pulse and the range gate pulse by a predetermined time at 
every individual period of the rate pulse, and 
switching means for selectively connecting said rate pulse generating means 
and said shifting circuit means to said drive pulse generating means. 
According to the invention, there is still further provided a quasi Doppler 
signal generating apparatus comprising: 
rate pulse generating means for producing a rate pulse of a predetermined 
repetition period, 
range gate circuit means for producing a range gate pulse by delaying in a 
predetermined time from the rate pulse, 
shifting circuit means for shifting a predetermined time between the rate 
pulse and the range gate pulse by a predetermined time at individual 
period of the rated pulse, 
drive pulse generating means responsive to the output pulse from said 
shifting means for producing a drive signal, 
transducer means responsive to the drive pulse for transmitting an 
ultrasonic wave into an object to be detected and responsive to the echoes 
thereof for converting the echoes into an electrical signal, 
sampling means for sampling only the echo signals from a predetermined 
depth of the received echo signals in accordance with the range gate 
pulse, 
frequency analyzing means for performing the frequency analyzation of the 
sampled echo signals, and 
display means for indicating in an intensity the analyzed signals. 
According to the invention, there is further provided a quasi Doppler 
signal generating apparatus comprising: 
rate pulse generating means for producing a rate pulse of a predetermined 
repetition period, 
range gate circuit means for producing a range gate pulse by delaying in a 
predetermined time from the rate pulse, 
shifting circuit means for shifting the rate pulse by a predetermined time 
at every individual period, thereby shifting said predetermined time 
between the rate pulse and the range gate pulse by a predetermined time at 
individual period of the rated pulse, 
drive pulse generating means responsive to the output pulse from said 
shifting means for producing a drive signal, 
transducer means responsive to the drive pulse for transmitting an 
ultrasonic wave into an object to be detected and responsive to the echoes 
thereof for converting the echoes into an electrical signal, 
sampling means for sampling only the echo signals from a predetermined 
depth of the received echo signals in accordance with the range gate 
pulse, 
frequency analyzing means for performing the frequency analyzation of the 
sampled echo signals, and 
display means for indicating in an intensity the analyzed signals. 
According to the invention, there is still further provided a quasi Doppler 
signal generating apparatus comprising: 
rate pulse generating means for producing a rate pulse of a predetermined 
repetition period, 
range gate circuit means for producing a range gate pulse by delaying in a 
predetermined time from the rate pulse, 
shifting circuit means for shifting the range gate pulse by a predetermined 
time at every individual period, thereby shifting said predetermined time 
between the rate pulse and the range gate pulse by a predetermined time at 
individual period of the rated pulse, 
drive pulse generating means responsive to the output pulse from said 
shifting means for producing a drive signal, 
transducer means responsive to the drive pulse for transmitting an 
ultrasonic wave into an object to be detected and responsive to the echoes 
thereof for converting the echoes into an electrical signal, 
sampling means for sampling only the echo signals from a predetermined 
depth of the received echo signals in accordance with the range gate 
pulse, 
frequency analyzing means for performing the frequency analyzation of the 
sampled echo signals, and 
display means for indicating in an intensity the analyzed signals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The principle of the present invention will be first described. When an 
ultrasonic wave is transmitted from a transducer through a body to a blood 
corpuscle moving at a velocity V in the direction of the beam of the 
ultrasonic wave in a period Tr in a repeated manner, the time required 
from the transmission of the ultrasonic wave through the arrival of the 
wave at the blood corpuscle to the reception of the wave by the transducer 
sequentially becomes different for the respective waves transmitted 
successively. 
Assume that the above-described required time for a certain arbitrary 
transmission of the ultrasonic wave is t and that the distance of the 
transducer to the blood corpuscle at the time when the ultrasonic wave 
transmitted from the transducer arrives at the blood corpuscle is x. 
Because a velocity of the blood flow (blood corpuscle etc.) is generally 
lower than a propagation velocity, S of the ultrasonic wave, the required 
time t can be obtained from the following equation: 
EQU t.apprxeq.2x/S (2) 
The required time t' of the next transmitted ultrasonic wave (the 
transmitted wave after a period Tr from the previously transmitted wave) 
can be obtained from the following equation, since the blood corpuscle has 
moved in the distance of .DELTA.x (=V.multidot.Tr) during one period Tr: 
EQU t'.apprxeq.2(x+.DELTA.x)/S (3) 
Assume that t'-t=.DELTA.t is set, 
##EQU1## 
can be obtained. 
Let us now relate this teaching concerning blood corpuscles flowing through 
the body to a testing situation in which a stationary target is employed. 
The equation (4) is substituted for the equation (1), and .theta.=0 is set 
(which is reasonable in a testing situation with a transducer aimed at a 
stationary target), and the equation (1) can be transformed as follows: 
EQU fd.apprxeq..DELTA.t.multidot.fc/Tr (5) 
As evident from the equation (5), the .DELTA.t becomes a factor for 
determining the Doppler frequency shift fd. In view of the relationship 
between the fd and .DELTA.t, it is understood that a quasi Doppler 
frequency shift fd can be obtained by shifting by .DELTA.t the time 
interval between the rate pulse and the range gate pulse for each 
transmitted wave (i.e., for each transmission period). Thus, Doppler shift 
can be created in vitro, using reflections from a stationary target by the 
.DELTA.t shifting as well as in vivo using reflections from moving 
corpuscles. This effect is used in the present invention to simulate 
dopper shift caused by blood flow using a stationary target in vitro. 
An embodiment of the blood flow meter according to the present invention 
will now be described in more detail with reference to the accompanying 
drawings and particularly to FIG. 3. 
A clock pulse generator 1 generates a clock pulse a (e.g., 19.2 MHz) (FIG. 
2A) of a predetermined period. The clock pulse generator 1 is connected to 
rate pulse generator 2. The rate pulse generator 2 frequency-divides the 
clock pulse thus received from the generator 1 and produces a rat pule b 
(FIG. 2B) of a suitable frequency. The frequency of the rate pulse 
corresponds to the frequency for driving the ultrasonic transducer. The 
rate pulse generator 2 is connected to a shifting circuit 21, and the rate 
pulse from the generator 2 is inputted to the shifting circuit 21. The 
shifting circuit 21 also receives a clock pulse from the clock pulse 
generator 2 in addition to the rate pulse from the rate pulse generator 2. 
Thus, the shifting circuit 21 produces pulses b(1), b(2), . . . , b(n) 
(FIGS. 4A and 4B) having increased pulse width sequentially in the amount 
of the time .DELTA.t for each rate pulse b in accordance with the rate 
pulse b and the clock pulse a. The shifting circuit 21 is connected to a 
switch circuit 22. The switch circuit 22 has two stationary contacts CS1, 
CS2 and a movable contact Cm. The circuit 21 is connected to the 
stationary contact CS1. The rate pulse generator 2 is connected to the 
stationary contact CS2. A pulser 3 is connected to the movable contact Cm. 
The switch circuit 22 serves to select the device as the operation of the 
circuit for the original blood flow sensing or as the circuit for 
detecting the quasi Doppler frequency shift for the check. When the device 
is set to the blood flow sensing mode, the movable contact Cm is connected 
to the stationary contact CS2 side, while when the device is set to the 
check mode, the movable contact Cm is connected to the stationary contact 
CS1 side. The operation of the circuit in the case of the sensing mode is 
substantially similar to that of the conventional blood flow meter 
described previously with reference to FIG. 1. 
In other words, the clock pulse signal a (FIG. 2A) of a predetermined 
frequency such as for example, 19.2 MHz is provided by the clock pulse 
generator 1. The rate pulse generator 2 frequency-divides the clock pulse 
a thus received from the generator 1 and produces a rate pulse b (FIG. 2B) 
of the period corresponding to the period of the transmitted ultrasonic 
wave (the driven period of the ultrasonic transducer 4). The rate pulse b 
is in turn supplied to a pulser 3 and a range gate circuit 12. The pulser 
3 drives the transducer 4 in synchronization with the fall of the rate 
pulse b. The transducer 4, thus driven, transmits an ultrasonic wave into 
a living body. The wave thus transmitted propagates in the living body, 
and is reflected on the vascular wall, blood corpuscles. The echoes d 
(FIG. 2D) are received by the transducer 4, which in turn converts the 
received echoes into an electric signal of the magnitude corresponding to 
the intensity of the echoes. The converted echo signals are inputted to 
the pre-amplifier AMP 9, which in turn amplifies the inputted signals to a 
suitable amplitude. The amplified echo signals are then inputted to a 
mixer MIX 10. To the MIX 10 is inputted the reference signal of the 
frequency corresponding to the central frequency of the ultrasonic wave 
transmitted from the transducer 4, from the clock pulse generator 1. The 
MIX 10 then mixes the echo signals with the reference signal. The mixed 
signal is in turn inputted to a low pass filter LPF 11 which then removes 
the harmonic wave components from the mixed signal. The echo signals thus 
fed through the low pass filter LPF 11 are in turn inputted to a sample & 
hold (S/H) circuit 13, which in turn samples only the echo signal from the 
position to be measured in accordance with the range gate pulse from the 
range gate circuit 12 as a sampling signal. The echo signals sampled are 
held at the S/H circuit 13 until the S/H circuit 13 receives the next 
range a gate pulse. The sampled echo signals are then inputted to a band 
pass filter BPF 14, which removes the harmonic wave components produced by 
sampling, echo from a stationary reflector such as vascular wall, and 
Doppler frequency shift signals from a moving article moving relatively 
slowly, and samples only the Doppler frequency shift signals due to the 
blood flow. The signal from the band pass filter is in turn inputted to a 
frequency analyzer 15, which is composed, for example, of an FFT (fast 
fourier transformer), which in turn frequency-analyzes the signal thus 
inputted and produces a frequency spectrum corresponding to a blood flow 
signal. The frequency spectrum from the frequency analyzer 15 is in turn 
inputted to a monitor 16, which indicates as a blood flow signal its 
intensity. 
The blood flow can be detected similarly to the blood flow meter in FIG. 1 
by the operation described above. 
The operation of the blood flow meter in the case of check mode will now be 
described. 
When the blood flow meter is set to the check mode, the pulses b(1), b(2), 
. . . , b(n) from the circuit 21 is inputted to the pulser 3. The pulser 3 
outputs a drive pulse to the transducer 4 in accordance with the pulses 
b(1), b(2), . . . , b(n). The transducer 4 excites and transmits an 
ultrasonic wave at the fall of the drive pulse thus received. The 
transducer 4 is disposed at the water surface of water 19 filled in a 
water tank 17. A ball target 18 which functions as a reflecting article is 
disposed under water. The transducer 4 is excited by the drive pulse from 
the pulser 3 to transmit the ultrasonic wave. The ultrasnoic wave 
propagates in the water 19 to arrive at the target 18. The echoes from the 
target is received by the transducer 4. The echoes thus received are 
converted into an electric signal by the transducer 4. The electrical echo 
signal is then inputted to a pre-amplifier 9, and is amplified to a signal 
having a suitable amplitude. The amplifier 9 is connected to a mixer 10, 
and the amplified echo signals are in turn inputted to the mixer 10. To 
the mixer 10 is also inputted the reference signal from the clock pulse 
generator 1. The mixer 10 mixes the echo signals with the reference 
signal, thereby phase-detecting the echo signals. The mixer 10 is 
connected to a low pass filter 11, and the phase-detected echo signal 
g(1), g(2), . . . , g(n) (FIGS. 4A and 4B) are in turn inputted to a low 
pass filter 11. The harmonic wave components produced by the mixer 10 are 
removed by the low pass filter 11. The low pass filter 11 is connected to 
a sample & hold circuit 13, and the output echo signals from the low pass 
filter are in turn inputted to the sample & hold circuit 13. To the sample 
& hold circuit 13 is connected a range gate circuit 12. The range gate 
circuit 12, thus connected, receives the clock pulse from the clock pulse 
generator 1 and the rate pulse from the rate pulse generator 2, and 
outputs sample signal (range gate pule) c(1), c(2), . . . , c(n) for 
producing only the echo signals from a predetermined depth. The sample & 
hold circuit 13 samples and holds only the echo signals from the target 18 
inputted from the low pass filter 11 in accordance with the sample signal 
from the range gate circuit 12. The sample and hold circuit 13 is 
connected to a band pass filter 14, and the sampled signal h (FIG. 4C) is 
inputted to the band pass filter 14. Only the signal component i (FIG. 4D) 
of the Doppler frequency shift, i.e., quasi Doppler frequency shift is 
produced from the blood flow by the band pass filter 14. The band pass 
filter 14 is connected to a frequency analyzer 15, and the signal from the 
filter 14 is in turn inputted to the frequency analyzer 15. The signal 
from the filter 14 is frequency-analyzed by the frequency analyzer 15. 
Thus, the frequency analyzation of the echo from the target 18 as a 
stationary article is performed. The frequency analyzer 15 is connected to 
a monitor 16 as a display device, and the monitor 16 indicates in an 
intensity the frequency-analyzed Doppler frequency shift on its screen. 
The b(1), b(2), . . . , b(n) are repeated at a predetermined period Ta. 
This repetition period TA has a predetermined relation with respect to the 
interval .DELTA.f of the frequency spectrum having the Doppler frequency 
shift, i.e., .DELTA.f=1/Ta. Accordingly, it is preferable to set the 
period Ta so that the interval .DELTA.f becomes a freqency corresponding 
to the frequency resolution of the frequency analyzer 15. 
FIG. 5 shows a block circuit diagram of an example of the shifting pulse 
generator 21. FIGS. 6A to 6F are time charts of the signals of the 
respective sections of the generator 21. 
A selector 31 is connected to a Read Only Memory (ROM) 33 and an UP/DOWN 
Counter 35 to switch the memory 33 and the UP/DOWN mode of the counter 35. 
The selector 31 switches the memory 33 and the counter 35 to the count up 
mode when signals are product to simulate the ball target 18 (reflector) 
moving toward the transducer 4 while switches the memory 33 and the 
counter 35 to the count down mode when signals are produced to simulate 
the target 18 moving away from the transducer 4. A selector 32 is 
connected to the ROM 33 and a multiplexer 41. The selector 32 sets a 
Doppler frequency shift fd to be obtained, and, more concretely, sets the 
Doppler frequency shift by supplying a 2-bit control a signal to the ROM 
33 and the multiplexer 41. A counter 34 receives a rate pulse b (FIG. 6B) 
and outputs signal j when it counts a predetermined pieces of the pulses 
corresponding to the period Ta. A counter 34 is connected to the UP/DOWN 
counter 35, and the signal j is inputted to the UP/DOWN counter 35. A 
2-input AND gate 36 receives at one input terminal a rate pulse b and is 
connected at the other input terminal to the output terminal of the 
UP/DOWN counter 35. The output terminal of the AND gate is connected to 
the input terminal of the UP/DOWN counter 35. The output terminal of the 
UP/DOWN counter 35 is connected to the first input terminal of a 3-input 
AND gate 38. A clock pulse (a) is respectively inputted to a 1/2-frequency 
divider 39 and 3/8-frequency divider 40. The output terminals of the 
dividers 39 and 40 are respectively connected to the multiplexer 41. Thus, 
the pulse signal divided into 1/2-frequency by the divider 39 and the 
pulse signal divided into 3/8-frequency by the divider by the divider 40 
are respectively inputted to the multiplexer 41. A clock pulse a (FIG. 6A) 
is also inputted directly to the multiplexer 41. The output terminal of 
the UP/DOWN counter 35 is respectively connected to the dividers 39 and 
40, and the output signal of the UP/DOWN counter 35 is inputted to the 
dividers 39 and 40. To the multiplexer 41 are inputted 2-bit control 
signal from the selector 32, and the multiplexer 41 selects one of the 
input pulse signals in accordance with the bit content of this control 
signal. The selected pulse signal is inputted to the second input terminal 
of the 3-input AND gate 38. The output terminal of the AND gate 38 is 
connected to the input terminal of a Down Counter 37. To the Down counter 
37 is further inputted a rate pulse b. The output terminal of the Down 
counter 37 is connected as the output terminal of the shifting pulse 
generator 21 to the first stationary contact CS1 of the switching circuit 
32, and is also connected to the input terminal of an inverter 42. The 
output terminal of the inverter 42 is connected to the third input 
terminal of the 3-input AND gate 38. 
When the UP/DOWN counter 35 receives the signal j (FIG. 6C), the counter 35 
latches, for example, 8-bit data of the ROM 33. Then, the counter 35 
up-counts, for example, the data latched by the rate pulse b supplied 
through the gate 36. The counted value of the UP/DOWN counter 35 is 
inputted to the Down counter 37. When the bits forming the latched data 
such as 8 bits become all High level, the UP/DOWN counter 35 produces an 
output signal k (FIG. 6D) of Low level. This output signal k is inputted 
as a signal for closing the gate to the AND gates 36, 38, and the 
frequency dividers 40, 41. When the rate pulse b is inputted to the Down 
counter 37, the Down counter 37 latches, for example, 8 bits of the 
UP/DOWN counter 35. Then, the Down counter 37 downcounts the data selected 
by the multiplexer 41 and latched by the pulse signal inputted. When all 
bits of the latched data become Low level, the Down counter 37 produces a 
signal l of High level. The signal l (FIG. 6F) is inputted through the 
inverter 42 to the gate 38, and is also supplied as the output signal of 
the shifting pulse generator 21 to the pulser 3. 
When the moved distance of the echo is represented by y mm, the number n of 
generated rate pulses during a period Ta has the following relation: 
EQU n.apprxeq.2y/(.DELTA.t.multidot.S) 
Accordingly, the data supplied from the ROM 33 to the UP/DOWN counter 35 
becomes 8 bit data represented by binary number from the numberic value 
(255-n). The counter 35 counts up by n with the rate pulse b, with the 
numeric value (255-n) as an initial value. The Down counter 37 latches the 
8 bit data from the UP/DOWN counter 35 every time the counter 37 receives 
the rate pulse b, down-counts the clock pulse a with the 8 bit data as an 
intial value, and outputs the signal l when becoming zero. Therefore, the 
initial value latched by the down counter 37 increases by "1" every time 
the rate pulse b is renewed such as (255-n) at the first rate pulse, 
(255-n+1) at the second rate pulse and (255-n+2) at the third rate pulse. 
Accordingly, the pulse width of the signal l increases in the amount of a 
period of the clock pulse a every time the rate pulse b is renewed, i.e., 
at every rate pulse period. When this signal l is inputted to the pulser 
3, the timing for driving the transducer 4 can be delayed by a period of 
the clock pulse a. Since the shifting circuit 21 operates as described 
above, the Doppler frequency shift fd becomes 500 Hz from the 
above-described equation (5) when the clock pulse a is 19.2 MHz, the 
central freqency fc of the ultrasonic wave is 2.4 MHz, the repetition 
frequency fr (=1/Tr) of the rate pulse b is 4 KHz and the clock pulse a is 
selected by the multiplexer 41. When the signal selected by the 
multiplexer 41 is a signal frequency-divided by 1/2 from the clock pulse a 
of the 1/2-frequency divider 39 or a signal frequency-divided by 3/8 from 
the clock pulse a of the 3/8-frequency divider 40, the Doppler frequency 
shift fd respectively become 1,000 Hz and 1333 Hz. 
In the embodiment described above, the timing for driving the transducer 4 
is varied by a predetermined time .DELTA.t every time the rate pulse b is 
renewed, but similar effect can also be obtained even if the shifting 
pulse is applied to the range gate pulse and the range gate pulse is 
varied by .DELTA.t at every renewal. 
As described above, according to the present invention, the blood flow 
meter employs a type of detecting the Doppler frequency shift from the 
actual ultrasonic echo. Accordingly, the present invention provides the 
ultrasonic pulse Doppler blood flow meter which can readily generally 
check with the ultrsonic field of the transducer and the receiving 
circuit. 
The present invention is not limited to the particular measurement of the 
blood flow rate described above. For example, the flow meter of the 
present invention can also be applied also for a fluid flow rate measuring 
device of the fluid flowing in a conduit.