Doppler ultrasonic diagnostic apparatus

A Doppler ultrasonic diagnostic apparatus for measuring or displaying the velocity information of moving members within an organism by transmitting and receiving ultrasonic waves is used for ultrasonic diagnosis in the medical field and the like. The apparatus is composed of a transmission circuitry for producing two ultrasonic waves having different repetition periods and outputting an ultrasonic wave after change-over between them; a velocity calculating means for calculating the velocities of moving reflective members on the basis of the received Doppler signals from the two ultrasonic waves, for example, a velocity calculator or an autocorrelator for obtaining the autocorrelation of a received signal after converting it to a complex signal; a memory for storing the velocity information signals obtained by the velocity calculating means; and other calculating means. The velocity of the moving reflective members is obtained by calculating the difference between or the sum of the two kinds of velocity signals, or calculating the conjugate product or the complex product of the two kinds of velocity signals. The present invention makes it easy to obtain accurate velocity information by an apparatus having a simple structure.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a Doppler ultrasonic diagnostic apparatus 
and, more particularly, to a Doppler ultrasonic diagnostic apparatus which 
is capable of detecting and measuring the velocity of moving reflective 
members and accurately displaying the movement within an organism to be 
examined. 
2. Description of the Prior Art 
Doppler pulse devices are widely used wherein an ultrasonic pulse beam is 
transmitted into reflective members at a fixed repetition frequency, the 
reflected waves from the reflective members are received, and the distance 
to the reflective member is measured by comparing the time difference 
between the transmitted signals and the received signals and at the same 
time the velocity of movement of the reflective members is detected and 
measured by detecting changes in the frequency of the received signal. 
Generally, the repetition frequency of the pulse beam is selected in 
accordance with the distance to the reflective member. In the case of 
measuring reflective members within an organism which is distantly 
located, however, if the frequency selected is high as compared with the 
repetition frequency determined on the basis of the distance to the 
reflective members, an aliasing echo is produced which indicates that the 
reflective members are situated closer than the actual position, as is 
well known, and this makes discrimination of the distance difficult. 
A similar phenomenon is seen in the case of measuring the velocity of 
moving reflective members. If the repetition frequency selected is low as 
compared with the Doppler frequency arising from the velocity of the 
reflective members, an aliasing echo results in a low frequency, thereby 
making discrimination of the velocity difficult. 
In order to measure both distance and velocity without production of 
aliasing echo, it is known that the relationship between a maximum Doppler 
frequency f.sub.dmax and pulse repetition frequency f.sub.r must conform 
to f.sub.dmax =f.sub.r /2 in the case of a device which is capable of 
detecting not only absolute velocity but also whether it is positive or 
negative, and f.sub.dmax =f.sub.r in the case of a device which detects 
and measures only the absolute velocity. 
In a device which is capable of determining whether velocity is positive or 
negative, the following relationship holds: 
EQU f.sub.dmax =(2V.sub.max /c).multidot.f.sub.0 =f.sub.r /2 
(f.sub.0 : ultrasonic pulse beam frequency, V.sub.max maximum velocity, c: 
sound velocity). 
From this formula, the maximum measurable velocity V.sub.max is V.sub.max 
=(f.sub.r /2).multidot.c/(2f.sub.0). 
The maximum distance to the reflective member R.sub.max which can 
unambiguously be determined is given by: 
EQU R.sub.max =c T/2=c/(2f.sub.r) 
where, T=1/f.sub.r is the pulse repetition interval. 
However, as is obvious from the above formulas, such a device suffers from 
the problem that if the pulse repetition frequency f.sub.r is increased in 
order to increase the maximum measurable velocity V.sub.max, there is a 
decrease in the maximum distance R.sub.max at which the moving reflective 
members can be measured without the production of aliasing echo, thereby 
making it impossible to measure rapidly moving reflective members from a 
long distance. 
Combining V.sub.max and R.sub.max gives the following relationship: 
EQU V.sub.max R.sub.max =c.sup.2 /(8.multidot.f.sub.0) 
As is obvious from the above formula, another problem is that if a low 
ultrasonic beam frequency f.sub.o is selected, not only is it difficult to 
produce a transmission wave with a narrow pulse width but also it is 
impossible to form a finely focussed beam, resulting in a decrease in the 
distance resolution and the directional resolution, thus rendering it 
impossible to simultaneously establish the distance to and the velocity of 
a distantly located rapidly moving reflective members. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to eliminate the 
above-described problems in the prior art and to provide a Doppler 
ultrasonic diagnostic apparatus which enables the velocity of reflective 
members in a wide range of from a low speed to a high speed, in 
particular, the velocity of rapidly moving reflective members which are 
located at a long distance to be obtained with good accuracy. 
To achieve this aim, the present invention provides in one aspect a Doppler 
ultrasonic diagnostic apparatus which is composed of: a transmission 
circuitry for producing two ultrasonic waves having different repetition 
periods in the same direction and outputting an ultrasonic wave after 
change-over between them; a velocity calculator for calculating the 
velocities of moving reflective members from the respective received 
Doppler signals of the two ultrasonic waves; a memory for storing a first 
velocity signal obtained by the velocity calculator on the basis of the 
ultrasonic wave which has been transmitted first in that direction; and an 
adder-subtracter for calculating the sum of or the difference between a 
second velocity signal obtained by the velocity calculator on the basis of 
the ultrasonic wave transmitted later in that direction and the first 
velocity signal. 
According to the above-described structure, two ultrasonic waves having 
different repetition periods are first output from the same probe, and 
these two ultrasonic waves are successively transmitted in the same 
direction into an organism to be examined. The respective velocities of 
the ultrasonic waves are calculated by the velocity calculator on the 
basis of the received Doppler signals of the reflected echoes, and the 
first velocity signal obtained from the ultrasonic wave which has been 
transmitted first is stored in the memory. 
The second velocity signal obtained from the ultrasonic wave which is 
transmitted later is directly input to the adder-subtracter, wherein the 
difference between or the sum of the first and second velocity signals is 
calculated. 
The velocity signal includes a deviation of the repetition frequency from 
the carrier frequency, namely, changes in velocity, and it is possible to 
accurately obtain the velocity of rapidly moving reflective members from a 
difference velocity signal and the velocity of slowly moving reflective 
members from a sum velocity signal. 
In another aspect of the present invention, a Doppler ultrasonic diagnostic 
apparatus is provided which is composed of: a transmission circuitry for 
producing ultrasonic waves having two different repetition periods in the 
same direction and outputting an ultrasonic wave after change-over between 
them; a complex signal converter for mixing and detecting a Doppler signal 
obtained from an organism to be examined and a complex reference wave and 
converting them to a complex signal; an autocorrelator for calculating the 
autocorrelation of the complex signal by providing a delay time which is 
an integer multiple of a repetition period; a memory for storing a first 
autocorrelation signal obtained by the autocorrelator on the basis of the 
ultrasonic wave which has been transmitted first in that direction; and a 
velocity processor for obtaining the velocity of moving reflective members 
by calculating the conjugate product or the complex product of a second 
autocorrelation signal obtained by the autocorrelator on the basis of the 
ultrasonic wave transmitted later in that direction and the first 
autocorrelation signal, thereby accurately obtaining the velocity of the 
moving reflective members. 
According to the second aspect of the present invention, two ultrasonic 
waves are successively transmitted in the same direction into the 
organism, in the same way as in the first aspect of the invention, but the 
received Doppler signal of the reflected echo obtained from the organism 
is converted to a complex signal and is thereafter supplied to the 
autocorrelator. The autocorrelator produces two autocorrelation signals; a 
first autocorrelation signal being obtained from the ultrasonic wave which 
has been transmitted first of the two ultrasonic waves having repetition 
periods, while a second autocorrelation signal is obtained from the 
ultrasonic wave transmitted later. 
On the basis of these autocorrelation signals, the complex signals are 
converted to Doppler signals which are substantially obtained from 
ultrasonic waves of a short or long repetition period. That is, the first 
autocorrelation signal is stored in the memory and when the second 
correlation signal is output, the conjugate product or the complex product 
of the first and second autocorrelation signals is obtained, thereby the 
velocity being calculated. 
The argument of the conjugate product is the shift of a frequency of a 
Doppler signal substantially obtained when an ultrasonic having a short 
period (the repetition frequency f.sub.r is high) is transmitted to the 
organism, and the argument of the complex product is the shift of a 
frequency of a Doppler signal obtained when an ultrasonic wave having a 
long repetition period (the repetition frequency f.sub.r is low) is 
transmitted. Therefore, as is clear from the above-described formula: the 
maximum velocity V=f.sub.r /(2f.sub.0 .multidot.K), it is possible to 
accurately obtain the velocity of rapidly moving reflective members from 
the conjugate product and that of slowly moving reflective members from 
the complex product. 
The above and other objects, features and advantages of the present 
invention will become clear from the following description of the 
preferred embodiments thereof, taken in conjunction with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
A first embodiment of the present invention will be explained hereinunder 
with reference to FIG. 1. 
FIG. 1 shows the structure of the circuit of a Doppler ultrasonic 
diagnostic apparatus, which is provided with a transmitter 1 for 
transmitting pulses of a fixed repetition frequency, and the output of the 
transmitter 1 is supplied to an electronic scanner 2. 
The present invention is characterized in that two ultrasonic waves having 
different repetition periods are transmitted to the same direction. For 
this purpose, a transmission period switch 13 is provided in order to 
supply two transmission signals having different repetition periods to the 
electronic scanner 2. The electronic scanner 2, if it performs sector 
scanning, controls the deflection angle of the beam. Control of the 
electronic scanner 2 excites a probe 18, thereby producing two ultrasonic 
pulse beams having different cycles in a given direction. Thus, the 
transmitter 1, the transmission period switch 13, the electronic scanner 2 
and the probe 18 in combination constitute a transmission circuitry. 
The probe 18 is brought into contact with the surface of an organism, and 
ultrasonic waves are transmitted into the organism. The reflected echoes 
from the reflective members are received by the same probe 18 and are 
supplied to a receiver 3 through the electronic scanner 2. The receiver 3 
amplifies the received ultrasonic signal and outputs it to a detector 4. 
The detector 4 mixes and detects the received signal and the reference 
wave which has a frequency of an integer multiple of the repetition 
frequency and is output from the transmitter 1. 
The output of the detector 4 is supplied to a velocity calculator 5, in 
which the received signal which is an analog signal is converted to a 
digital signal, and thereafter the velocity is calculated. 
The velocity can be obtained in various methods. For example, a received 
Doppler signal is converted to a complex signal and from the argument of 
the complex signal the velocity is obtained. 
That is, if a complex signal Z is represented by the formula Z=x+iy, the 
argument .theta. is obtained from the following formula: 
EQU .theta.=tan .sup.-1 (y/x) (1) 
The argument represents the shift of a frequency of the carrier, namely, a 
Doppler frequency, and if the Doppler frequency is fd and the repetition 
period is T, the following relationship holds: 
EQU f.sub.d =.theta./2.pi.T (2) 
and thus, the velocity of moving reflective members is obtained from the 
argument .theta. of the complex signal. 
In the present invention, two ultrasonic waves having different repetition 
periods are transmitted in the same direction into an organism, and the 
velocity of moving reflective member in the range of a low speed to a high 
speed is obtained on the basis of the two ultrasonic waves, as described 
above. In the first embodiment, the accurate velocity of moving reflective 
members is obtained from the two velocity values obtained by the velocity 
calculator 5. 
For this purpose, this embodiment is provided with a memory for storing all 
the first velocity signals on the ultrasonic beam axis obtained from the 
ultrasonic waves which have been first transmitted, a line memory 6 in 
this embodiment, and an adder-subtracter 7 for successively calculating 
the sum of or the difference between a second velocity signal obtained 
from the ultrasonic wave which is transmitted later and the first velocity 
signal. The velocity of the moving reflective members obtained by the 
adder-subtracter 7 is displayed on a CRT display 30. The CRT display 30 
displays the mode of the organism as M-mode or B-mode, and velocity 
information is displayed together therewith. 
The operation of the first embodiment having the above-described structure 
will now be explained. 
Of the two velocity signals obtained by transmitting the two ultrasonic 
waves having different repetition periods in the same direction, the first 
velocity signal which is output first is supplied to and stored in the 
line memory 6, and the second velocity signal which is output later is 
supplied to the adder-subtracter 7. The adder-subtracter 7 reads out the 
first velocity signal from the line memory 6 and calculates the difference 
between the two velocity signals. 
If it is assumed that .theta. obtained by the formula (1) is a velocity 
signal and the first velocity signal obtained from the ultrasonic wave 
which has been first transmitted is .theta..sub.1, the second velocity 
signal obtained from the ultrasonic wave which is transmitted later being 
.theta..sub.2, .theta..sub.1 -.theta..sub.2 is calculated in the following 
formula: 
EQU .theta..sub.1 -.theta..sub.2 =2.pi.f.sub.d (T.sub.1 -T.sub.2)=2.pi.f.sub.d 
.DELTA.T (3) 
wherein T.sub.1 represents the repetition period of the ultrasonic wave 
which has been transmitted first and T.sub.2 the repetition period of the 
ultrasonic wave which is transmitted later. The argument .theta..sub.1 
-.theta..sub.2 obtained from the formula (3) is a velocity signal obtained 
when the ultrasonic wave having the repetition period .DELTA.T is 
transmitted. Since the repetition period .DELTA.T is T.sub.1 -T.sub.2, the 
argument .theta..sub.1 -.theta..sub.2 turns out to be the same as a 
Doppler signal obtained when the ultrasonic wave having a short repetition 
period (high repetition frequency f.sub.r) is transmitted. 
Accordingly, for example, if the repetition period T.sub.1 =250 .mu.s (the 
repetition frequency f.sub.r 1=4 KHz) and the repetition period T.sub.2 
=200 .mu.s (the repetition frequency f.sub.r 2=5 KHz), .DELTA.T equals 50 
.mu.s (the repetition frequency f.sub.r =20 KHz). As a result, the maximum 
measurable Doppler frequency in this case is 20 KHz.div.2=10 KHz, which is 
four times the maximum Doppler frequency 2.5 KHz (=5 KHz.div.2) obtained 
when the repetition period is T.sub.2. 
In this manner, high-speed measurement is enabled by calculating the 
velocity signals obtained from the two ultrasonic waves having different 
frequency periods, and it is possible to convert a Doppler signal to a 
desired signal without almost any change in the maximum measuring depth by 
selecting appropriate values for the repetition periods T.sub.1 and 
T.sub.2. 
In the first embodiment, it is also possible to accurately obtain the 
velocity in a low-speed range by actuating the adder-subtracter 7 as an 
adder. 
The formula (3) is represented in this case as follows: 
EQU .theta..sub.1 +.theta..sub.2 =2.pi.fd (T.sub.1 +T.sub.2)=2.pi.fd.DELTA.T 
(4) 
The argument is equivalent to a Doppler signal obtained when the ultrasonic 
wave having a long repetition period (low repetition frequency f.sub.r), 
and since the velocity value is enlarged in a predetermined speed range 
when the Doppler frequency f.sub.d is low, the low speed of the moving 
reflective member is detected with high accuracy. 
As has been explained, according to the first embodiment, since two 
ultrasonic waves having different repetition periods are transmitted in 
the same direction into an organism so that the sum of or the difference 
between the two velocity signals obtained from the respective ultrasonic 
waves is obtained, it is possible to convert the sum or the difference 
into a signal which corresponds to a Doppler signal containing a velocity 
signal in a wide range of from a high speed to a low speed, thereby making 
it easy to obtain the accurate velocity of a moving reflective member. 
Second Embodiment 
A second embodiment of the present invention in which the velocity of a 
moving reflective member is obtained by an autocorrelation method will 
here be explained. 
FIGS. 2 and 3 show the structure of the circuit of a Doppler ultrasonic 
diagnostic apparatus. Calculation of autocorrelation signals will first be 
explained with reference to FIG. 3. 
Calculation of Autocorrelation Signals 
Referring to FIG. 3, the output of a crystal oscillator 10 is supplied to a 
frequency divider and sync generator 12, from which various output signals 
of a desired frequency are obtained. 
The second embodiment in which two ultrasonic waves having different 
repetition periods are also transmitted is provided with the transmission 
period switch 13, and the transmission circuitry is composed of the 
crystal oscillator 10, the frequency divider and sync generator 12, the 
transmission period switch 13, a driver 14, a duplexer 16 and the probe 
18. The output signal of the frequency divider and sync generator 12 
outputs two transmission repetition frequency signals 100, 101 for 
transmitting ultrasonic pulse waves and outputs, in addition, complex 
reference signals 102, 104 for complex conversion, a sweep synchronizing 
signal 106 for use in displaying the results of the ultrasonic diagnosis, 
and a clock signal 108 for synchronizing various sections of the 
apparatus. 
In the second embodiment, the complex reference signals 102, 104 have 
frequencies which are integer multiples of the transmission repetition 
frequency signals 101, 102, respectively, and are phase-shifted from one 
another, by 90 degrees, in this embodiment, so as to be in a complex 
relationship. 
The transmission signals 100, 101 are supplied to the probe 18 through the 
driver 14 and the duplexer 16, and excite the probe 18 so as to transmit 
two ultrasonic pulse beams having different repetition periods into a 
specimen 20. 
The echoes reflected from the specimen 20 are converted into electrical 
signals by the probe 18 and are forwarded through the duplexer 16 to a 
high frequency amplifier 22 by which they are amplified to a prescribed 
degree, and one of the outputs is supplied to the display section as an 
ordinary B-mode or M-mode display signal. 
The output signal for carrying out an ordinary B-mode or M-mode display is 
supplied from a detector 24 and a video amplifier 26 to the CRT display 30 
through a switch 28, thereby modulating the brightness of the screen. 
The probe 18 is provided with a scanning controller 32 for angularly 
deflecting the ultrasonic pulse beam either mechanically or electrically, 
so as to periodically scan the specimen 20, or for halting the scanning 
operation at a desired deflection angle. The scanning position signal from 
the scanning controller 32 and the sweep synchronizing signal 106 obtained 
from the frequency divider and sync generator 12 are supplied to a sweep 
trigger pulse generator 34 in order to sweep-control the CRT display 30. 
The other output of the high frequency amplifier 22 is subjected to the 
calculation of autocorrelation in accordance with the present invention. 
The received Doppler receiving signal which is output from the high 
frequency amplifier 22 is first supplied to a complex signal converter 36 
to be converted to a complex signal. 
In this embodiment, the complex signal converter 36 is provided with a pair 
of mixers 38a, 38b, each of which includes a phase detector. The received 
signal is mixed with the complex reference signals 102, 104 in the 
respective mixers 38. Since the complex reference signals 102, 104 are in 
a complex relationship, namely, since they are 90 degree out of phase, as 
described above, it is possible to output the complex signals which 
correspond to the high frequency signal from the mixers 38. More 
precisely, as a result of mixing and detecting operation of the received 
signal and the respective complex reference signals, each of the mixers 38 
outputs two signals, one having a frequency equal to the sum of the 
frequencies of the input received signal and the complex reference signal, 
an the other having a frequency equal to the difference between their 
frequencies. Both signals are supplied to low pass filters 40a, 40b, which 
pass only the respective difference frequency component. 
In the mixing and detecting operation carried out by the mixers 38, the 
complex reference signals 102, 104 are single-frequency continuous waves, 
whereas the other input signal, namely, the received signal is a pulse 
wave including Doppler information. As a result, the outputs from the low 
pass filters 40 include a large number of spectral components. The complex 
conversion will now be explained through the use of conversion formulas. 
The complex reference signal 102 has a frequency f0 which is an integer 
multiple of the transmission repetition frequency f.sub.r, and if the 
amplitude of this complex frequency signal 102 is taken as 1, the complex 
reference signal 102 is represented as the following sine wave voltage 
signal: 
EQU sin 2.pi.f.sub.0 t (5) 
On the other hand, if the transmission frequency is taken as f.sub.0, the 
signal received by the probe 18 is expressed as 
EQU sin (2.pi.f.sub.0 t+2.pi.f.sub.d t) (6) 
wherein fd is the Doppler shift frequency. 
Although this received signal generally includes the spectrum 
EQU sin {2.pi.(f.sub.0 .+-..sup.n f.sub.r) t+2.pi.f.sub.d 
.multidot.(1.+-.nf.sub.r /f.sub.0)t} 
(wherein f.sub.r is the transmission repetition frequency and n is a 
natural number such as 0, 1, 2 . . . ), only the spectrum shown in the 
case in which n=0, namely, the spectrum represented by formula (2) will be 
explained hereinunder for the purpose of simplifying the explanation. 
Since the product of the complex reference signal 102 and the received 
signal is obtained in the mixer 38a, the output expressed by the following 
formula is derived which is equal to twice the product of formulas (5) and 
(6): 
EQU cos 2.pi.f.sub.d t-cos (4.pi.f.sub.0 t+2.pi.f.sub.d t) 
Since the frequency of 2f.sub.0 +f.sub.d is eliminated from this output by 
the low pass filter 40a, the output signal is expressed as 
EQU cos 2.pi.f.sub.d t (7) 
On the other hand, the other complex reference signal 104 is out of phase 
by 90 degrees with respect to the signal 102, it is expressed as the 
following cosine voltage signal: 
EQU cos 2.pi.f.sub.0 t (8) 
and is converted into the following signal after being mixed and detected 
in the mixer 38b and by the filtering operation of the low pass filter 
40b: 
EQU sin 2.pi.f.sub.d t (9) 
thus producing a complex signal having a real component represented by 
formula (7) and an imaginary component represented by formula (9). These 
signals are represented by the following formula: 
EQU Z.sub.1 =cos 2.pi.f.sub.d t+jsin2.pi.fdt (10) 
The signals Z.sub.1 thus obtained by complex conversion are then converted 
to digital signals by A/D converters 42a, 42b, and thereafter they are 
forwarded to a complex delay-line canceller 44. The clock signal 108 is 
supplied to the A/D converters 42 for sampling. 
Since the second embodiment is provided with the complex delay-line 
canceller 44, it is possible to eliminate the portions of the signal 
received from the stationary or slow moving members within the organism 
and to obtain velocity signals of only the moving portions, thereby 
greatly improving the quality of the video signal. 
The complex delay-line canceller 44 has a pair of delay lines 46a, 46b each 
of which has a delay time equal to one period (T) of the repetition 
signal. These delay lines 46a, 46b may be constituted, for example, by a 
memory or a shift register which consists of the same number of memory 
elements as the number of clock pulses contained in one period. 
Subtracters 48a, 48b are connected to the delay lines 46. The subtracters 
48 successively compare the inputs of the delay lines 46 (i.e. the signals 
during the current period) with the outputs thereof (i.e. the signals 
during the preceding period) at the same depth and calculate the 
difference between the signals during one period. Therefore, the echo 
signals from the stationary or slowly moving member exhibit little or no 
difference between one period, so that the output of the subtracters 48 
approaches zero, while the output of a rapidly moving member, for example, 
blood flow signals are detected as a large value, so that it is possible 
to suppress the reflected signal from the stationary or slowly moving 
object, namely, clutter. 
The operation of the complex delay-line canceller 44 will be explained in 
the following with reference to the following formulas. Although digital 
signals are input to the delay-line canceller 44 in FIG. 3, the following 
explanation will be made on the basis of the analog signals represented by 
formula (10) for the purpose of simplifying the explanation. If the inputs 
Z.sub.1 of the delay-line canceller 44 are represented by formula (10), 
the output Z.sub.2 delayed by one period is represented by the following 
formula: 
EQU Z.sub.2 =cos 2.pi.f.sub.d (t-T)+jsin 2.pi.f.sub.d (t-T) (11) 
As a result, the difference outputs of the subtracters 48 are 
EQU Z.sub.3 =Z.sub.1 -Z.sub.2 =-2 sin 2.pi.f.sub.d (T/2).multidot.sin 
2.pi.f.sub.d {t-(T/2}+j2 sin 2.pi.f.sub.d (T/2).multidot.cos 2.pi.f.sub.d 
{t-(T/2)} 
If the difference output Z.sub.3 is expressed by 
EQU Z.sub.3 =x.sub.3 +jy.sub.3 
x.sub.3, y.sub.3 are expressed by the following formulas; 
EQU x.sub.3 =-2 sin 2.pi.f.sub.d (T/2).multidot.sin 2.pi.f.sub.d {t-(T/2)}(12) 
EQU y.sub.3 =2 sin 2.pi.f.sub.d (T/2).multidot.cos 2.pi.f.sub.d {t-(T/2)}(13) 
Thus, x.sub.3, y.sub.3 are output from the subtracters 48a, 48b, 
respectively. 
The complex signals from which the low velocity signal components have been 
eliminated in the above-described way are then processed by an 
autocorrelator 50 in order to obtain the autocorrelation of the signals 
Z.sub.3 having a delay of T. 
The input signals Z.sub.3 are delayed by one period by delay-lines 52a, 52b 
to produce signals Z.sub.4. The output Z.sub.4 is represented by the 
following formula: 
EQU Z.sub.4 =x.sub.4 +jy.sub.4 
EQU x.sub.4 =-2 sin 2.pi.f.sub.d (T/2).multidot.sin 2.pi.f.sub.d {t-(3T/2)}(14) 
EQU y.sub.4 =2 sin 2.pi.f.sub.d (T/2).multidot.cos 2.pi.f.sub.d {-(3T/2)}(15) 
The conjugate signal Z.sub.4 * of the signal Z.sub.4 is represented by 
Z.sub.4 *=x.sub.4 -jy.sub.4, and the conjugate product of Z.sub.3 and 
Z.sub.4 * is obtained by the following formula, thereby calculating the 
autocorrelation: 
EQU Z.sub.3 Z.sub.4 *=(x.sub.3 +iy.sub.3) (x.sub.4 -jy.sub.4)=x.sub.3 x.sub.4 
+y.sub.3 y.sub.4 +j (x.sub.4 y.sub.3 -x.sub.3 y.sub.4) 
In order to obtain this autocorrelation, the autocorrelator 50 is provided 
with four multipliers 54a, 54b, 55a and 56b, and two adder-subtracters 
58a, 58b. 
If the output of the adder-subtracter 58b is R, the following formula is 
obtained from formulas (12), (13), (14) and (15): 
EQU R=x.sub.3 x.sub.4 +y.sub.3 y.sub.4 =4 sin.sup.2 2.pi.f.sub.d 
.multidot.(T/2)cos 2.pi.f.sub.d T (16) 
If the output of the adder-subtracter 58b is I, the following formula is 
obtained in the same way: 
EQU I=x.sub.4 y.sub.3 -x.sub.3 y.sub.4 =4 sin.sup.2 2.pi.f.sub.d 
.multidot.(T/2)sin 2.pi.f.sub.d T (17) 
By combining the outputs from both adder-subtracters 58, the 
autocorrelation signal is expressed as follows: 
EQU S=R+jI (18) 
Since this output S includes the variable signal components and the noise 
component produced from the apparatus, it is averaged by an averaging 
circuit in order to eliminate such noise component. The average is 
expressed by S=R+jI, whereby the autocorrelation is calculated. 
In the average circuit, the operation of adding the outputs delayed by one 
period by delay lines 60a, 60b to the inputs for the current period by the 
adders 62a, 62b, and feeding back the outputs obtained to the delay lines 
60 is repeated. If a digital circuit is used for this addition, the 
average value is obtained merely by outputting the zone bits of the added 
output. However, if this operation is simply repeated, the magnitude of 
the output successively increases with an increase in the numbers of 
additions, until at last saturation is reached. To prevent this, this 
embodiment is provided with weighting circuits 64a, 64b for attenuating 
the outputs before adding them to the inputs. More specifically, if the 
amount of attenuation is defined as .alpha., the signal for, for example, 
10 periods earlier than the current period is attenuated by a factor of 
.alpha..sup.10 relative to the signal for the current period before the 
former signal is added to the latter signal. Therefore, the effect on the 
output is made small, so that an averaging effect like that of a low pass 
filter or a running average circuit can be obtained. Moreover, it is 
possible to adjust the degree of averaging by changing the amount of 
weighting by the weighting circuits 64. 
As described above, in the second embodiment, the autocorrelations of the 
complex signals are obtained by obtaining the conjugate product, and it is 
possible to obtain the velocity by obtaining the argument .theta. of the 
autocorrelation outputs S. The argument .theta. is obtained from formulas 
(16) and (17) as follows: 
EQU .theta.=tan.sup.-1 (I/R)=2.pi.f.sub.d T (19) 
As a result, it is very easy to obtain the Doppler shift frequency f.sub.d 
from the argument .theta. as follows: 
EQU f.sub.d =.theta./2.pi.T (20) 
Although the autocorrelations are obtained from the conjugate product of 
the complex signals in the above explanation, it is also possible to 
obtain them from the complex product of the complex signals. According to 
the complex product, it is possible to obtain the velocity of moving 
reflective members at a short distance with high accuracy. 
Velocity Processing in the Second Embodiment 
As described above, the second embodiment is characterized in that two 
ultrasonic waves having different repetition periods are transmitted in 
the same direction into an organism, and the accurate velocity is obtained 
from the conjugate product or the complex product of the autocorrelation 
signal of a Doppler signal thereby obtained. For this purpose, the second 
embodiment is provided with line memories 72a, 72b for storing the first 
autocorrelation signals obtained from the transmitted ultrasonic wave 
which has been transmitted first, and a velocity processor 76 for 
calculating the velocity of moving reflective members from a second 
autocorrelation signal obtained from the ultrasonic wave which is 
transmitted later and the first autocorrelation signal, in addition to the 
above-described structure such as the autocorrelator 50. 
The velocity processor 76 is composed of a complex multiplier 84 consisting 
of multipliers 78, 80 and adder-subtracters 82, and an argument calculator 
86. The line memories 72 are provided for the purpose of delaying the 
first autocorrelation signal by a predetermined time in order to 
simultaneously compare the second autocorrelation signal and the first 
correlation signal. Various delay lines are usable in place of the line 
memories so long as they have the above-described function. 
The second embodiment has the above-described structure. Velocity 
processing based on the conjugate product or the complex product will here 
be explained. 
The outputs R, I of the autocorrelator 50 are expressed by the following 
formulas on the assumption that the absolute value of the autocorrelation 
is .vertline.S.vertline., and they are supplied to the line memories 72a, 
72b, respectively. 
EQU R=.vertline.S.vertline. cos .theta. (21) 
EQU I=.vertline.S.vertline. sin .theta. (22) 
The outputs R and I are the final values of the autocorrelator 50 and the 
average values obtained by transmitting ultrasonic pulses several times in 
a given direction. The argument .theta. is a signal which indicates 
individual item of velocity information obtained from an ultrasonic wave 
having a different period. 
The velocity of moving reflective members is obtained on the basis of two 
autocorrelation signals obtained from two ultrasonic waves having 
different repetition periods. The first autocorrelation signal obtained 
from the ultrasonic wave which has first been transmitted is stored in the 
line memories 72. In the first autocorrelation signal the signal R is 
stored in the line memory 72a, while the signal I is stored in the line 
memory 72b. They are written into or read out of the memories by a memory 
controller 74 to which a clock pulse and a scanning address signal are 
supplied. 
The second autocorrelation signal obtained from the ultrasonic wave which 
is transmitted later is directly supplied to the complex multiplier 84 of 
the velocity processor 76, not through the line memories 72. If the 
adder-subtracter 82a in the complex multiplier 84 is operated as an adder, 
and the adder-subtracter 82b as a subtracter, the conjugate product of the 
first and second autocorrelation signals is calculated. 
The conjugate product means the product of the conjugate complex of one of 
the two autocorrelation signals and the complex number of the other 
autocorrelation signal. Therefore, the complex multiplier 84 calculates 
the following formula: 
##EQU1## 
R.sub.1, I.sub.1 are first autocorrelation signal components and R.sub.2, 
I.sub.2 are second autocorrelation signal components. They are expressed 
by the following formulas: 
##EQU2## 
The following formula is obtained by substituting formulas (24), (25) into 
formula (23): 
##EQU3## 
The complex signal of the complex product obtained in this way is supplied 
to the argument calculator 86 to obtain the argument from the following 
formula: 
##EQU4## 
Insertion of integrators 88a, 88b consisting of the delay lines 60, the 
adders 62 and the weighting circuits 64 between the complex multiplier 84 
and the argument calculator 86 enables highly accurate measurement free 
from a noise signal. 
The final argument obtained in this way corresponds to a third Doppler 
signal which is obtained from the two Doppler signal having different 
repetition periods, and it is possible to obtain the velocity of moving 
reflective members from this argument. 
In formula (28), the repetition period .DELTA.T=T.sub.1 -T.sub.2, which 
turns out to be the same signal as the Doppler signal obtained when the 
ultrasonic wave having the repetition period .DELTA.T is transmitted into 
the organism to be examined. 
Accordingly, for example, if the repetition period T.sub.1 =250 .mu.s (the 
repetition frequency f.sub.r 1=4 KHz) and the repetition period T.sub.2 
=200 .mu.s (the repetition frequency f.sub.r 2=5 KHz), .DELTA.T equals 50 
.mu.s (the repetition frequency f.sub.r =20 KHz). As a result, the maximum 
measurable Doppler frequency in this case is 20 KHz.div.2=10 KHz, which is 
four times the maximum Doppler frequency 2.5 KHz (=5 KHz.div.2) obtained 
when the repetition period is T.sub.2. 
In this manner, high-speed measurement is enabled by obtaining the 
conjugate product of autocorrelation signals, and it is possible to 
convert a Doppler signal to a desired signal without almost any change in 
the maximum measuring depth by selecting appropriate values for the 
repetition periods T.sub.1 and T.sub.2. 
Calculation of the complex product of autocorrelation signals will now be 
explained. 
The complex product is obtained by operating the adder-subtracters 82a of 
the complex multiplier 84 as a subtracter, and the adder subtracter 82b as 
an adder in the opposite manner to the case of calculating the conjugate 
product. 
The complex product is expressed by the following formula: 
##EQU5## 
The final argument obtained in this way is represented as follows: 
EQU .theta..sub.1 +.theta..sub.2 =2.pi.f.sub.d (T.sub.1 +T.sub.2) (30) 
The argument (.theta..sub.1 +.theta..sub.2) corresponds to a velocity 
signal obtained when the ultrasonic wave having a short repetition period, 
namely, having a low repetition frequency is transmitted. Since the 
velocity value is enlarged in a predetermined speed range when the Doppler 
frequency fd is low, as described above, it is easy to detect a low speed. 
The velocity signal obtained in this manner is converted to an analog 
voltage signal by a D/A converter 68, and the resulting analog signal is 
applied to the CRT display 30 via a switch 70 as a brightness modulation 
signal, whereby the velocity distribution of the movement is displayed as 
a picture on the CRT display 30 in either B-mode or M-mode. 
According to the second embodiment, the CRT display 30 can selectively 
display either the ordinary video signal or the Doppler signal, or can 
display both of these signals simultaneously. That is, either of the 
pictures can be displayed independently or they can be displayed in the 
overlapping state. 
The Doppler ultrasonic diagnostic apparatus according to the first and 
second embodiment are adaptable to display in M-mode, two-dimensional step 
scanning in B-mode, and a moving-target indicator (MTI). In the case of 
B-mode, it is possible to display the Doppler signal over the tomograph of 
an organism to be examined. 
As described above, according to the present invention, it is possible to 
obtain the accurate velocity of moving reflective members by transmitting 
two kinds of ultrasonic waves having different repetition periods into an 
organism to be examined, and calculating the sum of or the difference 
between the two velocity signals obtained therefrom, or calculating the 
conjugate product or the complex product of the two autocorrelation 
signals obtained therefrom. 
Consequently, it is possible to simultaneously display the velocity of 
blood flow and the velocity distribution of blood flow in addition to the 
diagnostic information from a conventional diagnostic apparatus which 
employs the diagnostic echo method. Thus, the present invention provides 
an ultrasonic diagnostic apparatus which is capable of providing a large 
amount of practically useful diagnostic information. 
While there has been described what are at present considered to be 
preferred embodiments of the invention, it will be understood that various 
modifications may be made thereto, and it is intended that the appended 
claims cover all such modifications as fall within the true spirit and 
scope of the invention.