Abstrict An ultrasonic pulse Doppler blood flow meter which has: a rate
pulse generator for outputting a rate pulse, a pulser receiving
the rate pulse for outputting a drive pulse, 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, a range gate circuit for outputting
a sampling pulse after a predetermined time from the output of the
rate pulse, a sample and hold circuit for sampling and holding the
echo signals from the transducer in accordance with the sampling
pulse, a converter for Fourier-converting the sampled echo signals,
and a monitor for indicating in a intensity the converted echo signals
advantageously further comprising: 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 a switch
circuit for selectively connecting the rate pulse generator and
the shifting circuit to the drive pulse generator.
Claims What is claimed is:
1. An ultrasonic pulse Doppler blood flow analyzer including a
testing circuit comprising:
rate pulse generating means for producing rate pulses of predetermined
periods;
drive pulse generating means responsive to the rate pulses for
producing drive pulses;
transducer means responsive to the drive pulses for transmitting
an ultrasonic waves toward a stationary 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
each of the rate pulses for sampling only echo signals from the
stationary object;
frequency analyzing means for frequency analyzing the sampled echo
signals; and
shifting circuit means for shifting the rate pulses and the range
gate pulses relative to each other by a predetermined time at every
individual period of the rate pulses to change the sampled echo
signals into quasi Doppler-shifted signals.
2. The Doppler blood flow meter according to claim 1 wherein said
shifting circuit means comprises a counter for counting said rate
pulses and producing a repetition signal when a predetermined number
corresponding to a predetermined repetition period is counted, an
UP/DOWN counter set at the initial value thereof with the repetition
signal of said counter for counting said rate pulses and up-counting
and down-counting said rate pulses within a period of said repetition
period, a memory for storing an initial value to be set, a plurality
of frequency dividing means responsive to the said clock signal
for frequency-dividing said clock pulse and setting said predetermined
time, multiplexer means for selecting any of said dividing means
and producing the divided signal, and down counter responsive to
said rate pulse for latching the data from said UP/DOWN counter,
down-counting the data with the output of said selected dividing
means, and producing a signal for driving said drive pulse generating
means when the counted data reaches a predetermined value.
3. An ultrasonic pulse Doppler blood flow analyzer including a
testing circuit comprising:
rate pulse generating means for producing rate pulses of predetermined
repetition periods;
drive pulse generating means responsive to the rate pulses for
producing drive pulses;
transducer means responsive to the drive pulses for transmitting
ultrasonic waves towards a stationary 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
each of the rate pulses;
sampling means responsive to the range gate pulses for sampling
only echo signals from the stationary object;
frequency analyzing means for frequency analyzing the sampled echo
signals;
display means for indicating the intensity of the analyzed signals;
and
shifting circuit means for shifting the rate pulses relative to
the range gate pulses by a predetermined time at every individual
period to change the sampled echo signals into quasi Doppler-shifted
signals.
4. The Doppler blood flow meter according to claim 3 wherein said
shifting circuit means comprises a counter for counting said rate
pulses and producing a repetition signal when a predetermined number
corresponding to a predetermined repetition period is counted, an
UP/DOWN counter set at the initial value thereof with the repetition
signal of said counter for counting said rate pulses and up-counting
and down-counting said rate pulses within a period of said repetition
period, a memory for storing an initial value to be set, a plurality
of frequency dividing means responsive to the said clock signal
for frequency-dividing said clock pulse and setting said predetermined
time, multiplexer means for selecting any of said dividing means
and producing the divided signal, and down counter responsive to
said rate pulse for latching the data from said UP/DOWN counter,
down-counting the data with the output of said selected dividing
means, and producing a signal for driving said drive pulse generating
means when the counted data reaches a predetermined value.
5. An ultrasonic pulse Doppler blood flow analyzer including a
testing circuit comprising:
rate pulse generating means for producing rate pulses of predetermined
repetition periods;
drive pulse generating means responsive to the rate pulses for
producing drive pulses;
transducer means responsive to the drive pulses for transmitting
ultrasonic waves toward a stationary 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
each of the rate pulses;
sampling means responsive to the range gate pulse for sampling
only echo signals from the stationary object;
frequency analyzing means for frequency analyzing the sampled echo
signals; and
shifting circuit means for shifting the range gate pulses by a
predetermined time at every individual period to change the sampled
echo signals into quasi Doppler-shifted signals.
Description 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:
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.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block circuit diagram of an example of a conventional
ultrasonic pulse Doppler blood flow meter;
FIGS. 2A to 2D are timing charts of the signals at the respective
sections of the blood flow meter shown in FIG. 1;
FIG. 3 is a block circuit diagram of an embodiment of an ultrasonic
pulse Doppler blood flow meter according to the present invention;
FIGS. 4A to 4D are timing charts of the signals of the respective
sections of the blood flow meter shown in FIG. 3;
FIG. 5 is a block circuit diagram of an example of the shifting
pulse generator associated with the blood flow meter in FIG. 1;
and
FIGS. 6A to 6G are timing charts of the signals of the respective
sections of the shifting pulse generator in FIG. 5.
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:
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:
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:
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:
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 1000 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. |