CALCULATION OF DEPTH AND SPEED OF OBJECTS WITH CODED PULSES BASED ON SPEED CHANGES OF ULTRASOUND/SOUND

Abstract

During transmission, a speed of ultrasound pulses gradually reduces due to acoustic impedance. A length and a density and a sound speed of the ultrasound pulses decide their average speed in the transmitting medium, frequencies, sound intensity and detecting depth. Time of flight (TOF) and TOF shift can be used to calculate the depth and moving speed of detecting objects. Calculating a speed of moving objects by simultaneously detecting TOFs at one detecting site from two separated piezoelectric (PZT) elements improves the testing results with accuracy, simplification and reproducibility. Coding ultrasound pulses to obtained the TOF and the TOF shift can be used to simultaneously calculate the depth and the moving speed of the objects, which also avoids a problem of an aliasing for highly moving speed of the objects. Coding ultrasound pulses also improves the quality of the imaging.

Description

FIELD OF THE DISCLOSURE

The present disclosure generally relates to the field of sound/ultrasound technology and, more particularly, relates to a method for calculation of detecting depth and speed of moving objects based on speed changes of sound/ultrasound.

BACKGROUND

Transmission of ultrasound pulses is actually energy traveling of acoustic pulses in transmitting medium. If there is acoustic impedance during the transmission of the ultrasound pulses, the acoustic impedance will resist the movement of the ultrasound pulses. Currently, it is supposed that speed of the ultrasound pulses is identical in the same medium during the transmission. But, in the invention, the speed of the ultrasound pulses is considered as gradually reduced during the transmission due to the acoustic impedance of the transmitting medium, which gradually depletes the energy of the ultrasound pulses. According direct relationship between the acoustic impedance and the speed of the ultrasound pulses in the transmitting medium, higher speed of the ultrasound pulses will meet higher acoustic impedance and consume more its energy during the transmission. So, the question is if the speed of the ultrasound pulses can still keep the same as currently supposed when its energy is gradually reduced until exhausted? If the speed of the ultrasound pulses is gradually reduced during transmission, the detecting depth may be wrong based on calculating the detecting depth with fixed ultrasound speed for the ultrasound pulses with different frequencies.

Current ultrasound theory connects frequencies of the ultrasound pulses with their detecting depth, with lower frequency of the ultrasound pulses having deeper detecting depth. But, a thin piezoelectric (PZT) element can make the ultrasound pulses with a high frequency as well as a low frequency, which means the ultrasound pulses with both frequencies sending from the same PZT element have the same level of energy. So, the question is what are main factors that affect the detecting depth of the ultrasound pulses?

Ultrasound pulses can be reflected by motionless or moving objects, and according Doppler theory, it is currently considered that forward moving objects can compress the frequency of the ultrasound pulses and reversely moving objects decompress the frequency of the ultrasound pulses. So, Doppler mechanism has been widely used to measure the velocity of the moving objects based on frequency shift, such as medical ultrasound machine and Doppler radar. For the pulsed wave ultrasound, aliasing is explained with insufficient Doppler sampling rate of the frequency domain analysis. But, the theory of the frequency domain can not completely solve the aliasing problem of the pulsed wave ultrasound and the color ultrasound.

Thus, there is a need to overcome above problems to provide methods for more accurately calculating the detecting depth of ultrasound pulses, increasing the detecting depth of high frequency ultrasound, correctly calculating the speed of the moving objects and correcting the aliasing for the pulsed wave and the color ultrasound.

BRIEF SUMMARY OF THE DISCLOSURE

One aspect of the invention, correcting the transmitting distance of ultrasound pulses can rectify the registration of the detecting depth, which improves the quality of ultrasound images. Current sound/ultrasound theories and applications are based on the identical average speed in the same transmitting medium with various frequencies of the ultrasound pulses. But, the invention is based the speed reduction of sound/ultrasound during the transmission in the medium due to the loss of their energy caused by acoustic impedance. For ultrasound, calculating of the detecting depth of ultrasound pulses based on the identical average speed of the ultrasound pulses will cause miscalculation of the detecting depth due to different average speeds for the ultrasound pulses with different frequencies. Because a length and a density of the ultrasound pulses can affect the average speed of the ultrasound pulses, they can be used to calculate the ultrasound speed reducing coefficient and correct the registration of detecting depth of ultrasound pulses, which improve the quality of images.

In another aspect of the invention, changing thickness and density of piezoelectric (PZT) elements and sound speed in the PZT elements can regulate intensity of the ultrasound pulses, which affect their detecting depth. The detecting depth of the ultrasound pulses is not directly related to their frequencies, but related to the intensity of the ultrasound pulses. The thickness and the density of PZT elements decide the length and density of the ultrasound pulses, and the sound speed in the PZT elements decides the maximal speed of the ultrasound pulses in the transmitting medium. So, selecting the PZT with greater density and higher speed of ultrasound pulses in the PZT elements will increase the detecting depth for high frequency ultrasound.

Another aspect of the invention is detecting the speed of moving objects based on time of flight (TOF) shift of time domain analysis for a continuous wave, a pulsed wave and a color ultrasound. It is based on the speed changes of reflected ultrasound pulses by the moving objects, which change the TOF and the TOF shift of the ultrasound pulses. No matter in the continuous wave or the pulsed wave or the color ultrasound, when checking the speed of blood flow, the ultrasound system always detects the reflected ultrasound pulses from certain locations where ultrasound beam cross with blood vessels to calculate the TOF shift. So, the speed of the moving objects can be calculated based on the TOF shift. A angle between ultrasound beams and a direction of moving objects decides the value of the TOF shift. Calculating the speed of moving objects by simultaneously detecting TOF from two separated PZT elements from same gate avoids the effect of tortuous blood vessels and variant performances of sonographers, which improves the testing results with accuracy, simplification and reproducibility.

In the invention, the theory of above TOF and TOF shift can be used to completely correct an aliasing for the pulsed wave and the color ultrasound no matter how fast the speed of the moving objects will be. A calculated TOF is based on the average speed of ultrasound pulses in the transmitting medium and distance between transducer and the gate. A detected TOF is the time that the ultrasound system interprets from emitted ultrasound pulses and reflected ultrasound pulses. An actual TOF, which is an actual traveling time of the ultrasound pulses between transducer and the detecting objects. If the speed of the moving objects is too fast, which makes the actual TOF excesses its aliasing limit, the ultrasound system will misinterpret the reflected ultrasound pulses and generate the aliasing TOF. For the forward moving objects, the aliasing limit for the actual TOF is less than the value of half calculated TOF. If the actual TOF is smaller than the aliasing limit, the ultrasound system will misinterpret the reflected ultrasound pulse and add a value of calculated TOF into the actual TOF, which generates the aliasing TOF. Then the aliasing TOF is greater than the calculated TOF. So, the aliasing TOF shift is below the baseline, which represents the moving objects toward opposite direction. For reversely moving objects, their TOF aliasing limit is that the actual TOF is greater than the value of one and half calculated TOF. If the actual TOF is greater than its aliasing limit, the ultrasound system will misinterpret the detected TOF and subtract a value of calculated TOF from the actual TOF. Then the aliasing TOF is smaller than the calculated TOF. So, the aliasing TOF shift is above the baseline, which represents the moving objects as forward direction. So, in the invention, a computer program is designed to identify and correct the aliasing TOF shift no matter how fast the speed of the moving objects will be. Identifying and correcting the aliasing TOF shift can also be used to differentiate the colors of aliasing from the colors of the turbulent flow, which benefits clinical judgment and diagnosis.

The continuous ultrasound doesn't contain information of depth and the pulsed wave ultrasound may generate a problem of aliasing. In the invention, a method of coding ultrasound pulses is used to take advantages of the continuous wave ultrasound and the pulsed wave ultrasound, which can obtain information of depth and speed of the detecting objects at the same time, and avoid the aliasing. Within each pulse duration, different numbers of ultrasound pulses are sent, which is assigned a pulse character. Coded pulse characters are emitted with a same rest period, which is between each pulse duration. Coding pulse characters endow each pulse character with information of a sending time. The TOF of the pulse characters can be obtained between the time of sending the pulse characters and receiving the same pulse characters, and TOF shift can be obtained from the difference of sending rest period and receiving period of the pulse characters. Therefore, the depth and the speed of the detecting objects can be obtained from the TOF and the TOF shift.

Based on the speed reduction of the ultrasound/sound during the transmission, the intensity of the ultrasound pulses, the TOF, and the TOF shift can more accurately present the relationship between the ultrasound pulses with the depth and the speed of the detecting objects than the results from the identical ultrasound speed and the Doppler shift. Other aspects or embodiments of the present disclosure can be understood by those skilled in the art in light of the description, the claims, and the drawings of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are merely examples for illustrative purposes according to various disclosed embodiments and are not intended to limit the scope of the present disclosure.

FIG. 1 is a schematic illustration of rebound force of forward flow to ultrasound pulse;

FIG. 2 is a schematic illustration of rebound force of reversed flow to ultrasound pulse;

FIG. 3 a is a schematic illustration of spectrum for TOF shift of continuous wave ultrasound;

FIG. 3 b is a schematic illustration of TOF shift and the profile of TOF shift for forward moving objects of pulsed wave ultrasound;

FIG. 3 c is a schematic illustration of TOF shift and profile of TOF shift for reversely moving objects of pulsed wave ultrasound;

FIG. 4 is a schematic illustration of aliasing TOF and aliasing TOF shift

FIG. 5 a is a schematic illustration of profile of aliasing TOF shift for forward flow of pulsed wave ultrasound;

FIG. 5 b is a schematic illustration of profile of corrected TOF shift for forward flow of pulsed wave ultrasound;

FIG. 6 a is a schematic illustration of profile of aliasing TOF shift for reversed flow of pulsed wave ultrasound;

FIG. 6 b is a schematic illustration of profile of corrected TOF shift for reversed flow of pulsed wave ultrasound;

FIG. 7 is a schematic illustration of computer program to calculate TOF shift of continuous wave ultrasound;

FIG. 8 is a schematic illustration of computer program to identify and correct aliasing TOF shift, and calculate the speed of moving objects for pulsed wave and color ultrasound;

FIG. 9 is a schematic illustration of the color of aliasing in color ultrasound;

FIG. 10 is a schematic illustration of the colors of turbulent flow in color ultrasound;

FIG. 11 is a schematic illustration of computer program to differentiate the color of turbulent flow from the color of aliasing and correct color of aliasing based on TOF shift; and

FIG. 12 is a schematic illustration of calculation of detecting depth and moving speed of objects with coded ultrasound pulses; and

FIG. 13 is a schematic illustration of calculation of speed of moving objects with two separated PZT elements.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of the disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Speed of Ultrasound Pulses Gradually Reduces During Transmission

Transmitting in a medium, a sound pulse contains its energy, which decides its sound intensity. A pulse of the sound intensity includes its length, density and speed. The length and density of the sound pulse is related to thickness and density of materials that create the sound. The thicker material gives a longer sound pulse, which is like different sounds from different chords of a violin or a piano. The density of the sound is related to density of materials that create the sound. The higher density of the materials is, the greater density of the sound will be, such as the sound difference launched from wood or metal. The sound speed is also related to the speed sent from the material, such as different sound strength when hitting a key of a piano with different forces. Hitting the key more strongly will bring louder sound, which is related to faster sound speed. So, the intensity of the sound pulse is the multiplication value of its length, density and speed. A sound pulse with greater intensity will travel further, and the speed of the sound pulse will gradually reduce due to the acoustic impedance of transmitting medium, which gradually depletes the energy of the sound.

Sound intensity(kg/MS)=sound length(M)×sound density(Kg/M³)×sound speed(M/S)

M=meter; Kg=kilogram; S=second

Piezoelectric elements (PZT) in a transducer of ultrasound machine emit ultrasound pulses with their intensity, which is related to the length, density, and speed of the ultrasound pulses. Nowadays, the speed of the ultrasound pulses with different frequencies is considered as identical in the same medium. But, actually the speed of the ultrasound pulses is not fixed at the same speed as supposed during the transmission, and it will gradually reduce due to an acoustic impedance of the transmitting medium. As bullets shooting from a machine gun, their speed is gradually reduced due to loss of their energy caused by resistance of air. But, frequency of the bullets at any sites of trajectory may be kept the same. The transmission of the ultrasound pulses has the similar mechanism. The acoustic impedance is decided by density of the transmitting medium and the average speed of the ultrasound pulses in the transmitting medium. During the transmission, the speed of the ultrasound pulses gradually reduces due to the loss of their energy caused by the acoustic impedance, which will finally exhausts the energy of the ultrasound pulses. But, Ultrasound pulses keep the same frequency during the transmission, including their reflected frequency. A rate of the speed change of the ultrasound pulses is related to the density of the transmitting medium, sound speed in the transmitting medium, and the length and density of the ultrasound pulses. So, a speed reducing coefficient can be used to express their relationship with the speed changes.

Calculation of Detecting Depth of Ultrasound Pulses Based on Speed Change of the Ultrasound Pulses

One aspect of the invention is calculation of detecting depth of the ultrasound pulses based on the speed reduction of the ultrasound pulses during the transmission. Nowadays, calculating the detecting depth is based on an average speed of the ultrasound pulses in the transmitting medium, and the average speed of the ultrasound pulses is considered as identical for the ultrasound pulses with different frequencies in a transmitting medium, which may miscalculate the detecting depth due to a variation of the average speed of the ultrasound pulses with the different frequencies. As the ultrasound pulses leave the PZT elements and enter the transmitting medium, the speed of the ultrasound pulses is at their maximal speed. Then, under effect of the acoustic impedance, the speed of the ultrasound pulses will gradually reduce during the transmitting process. The longer the ultrasound pulses travel, the slower the speed of the ultrasound pulses will be. So, the speed reducing coefficient of the ultrasound pulses can be used to calculate a distance shift. The speed reducing coefficient is directly proportional to the density of the transmitting medium and the sound speed in the PZT elements, and inversely proportional to the length and density of the ultrasound pulses. The sound speed in the PZT elements is directly correlated to the maximal speed of the ultrasound pulses in the transmitting medium as they enter the transmitting medium. The depth shift is caused by speed reduction of the ultrasound pulses during the transmission. The depth shift of the ultrasound pulses is a half value of multiplication result of the speed reducing coefficient and maximal speed in the transmitting medium and traveling time of the ultrasound pulses. V_m is a maximal speed of the ultrasound pulses as they just enter a transmitting medium. t is the traveling time from emitting to receiving the ultrasound pulses. V_avg is a average speed of the ultrasound pulses in the transmitting medium. The detecting depth is a half value of multiplication result of the average speed and the traveling time.

$\mathrm{Speed}\mathrm{reducing}\mathrm{coefficient}=\frac{\mathrm{medium}\mathrm{density}\times \mathrm{sound}\mathrm{speed}\mathrm{in}\mathrm{PZT}}{\mathrm{PZT}\mathrm{density}\times \mathrm{PZT}\mathrm{thickness}}$ Depth shift=speed reducing coefficient×V_m×t/2

$\begin{array}{c}\mathrm{Detecting}\mathrm{depth}=V_m\times t/2-\mathrm{Depth}\mathrm{shift}\\ =V_m\times \left(1-\mathrm{speed}\mathrm{reducing}\mathrm{coefficient}\right)\times t/2\end{array}$ V _avg =V _m×(1−speed reducing coefficient)

Detecting depth=V_avg×t/2

Currently there is just one average speed of the ultrasound pulses in each transmitting medium. For instance, the speed of the ultrasound pulses in the soft tissue is about 1540 meter/second. But a change of the length or density of the ultrasound pulses affects their average speed in the transmitting medium. Such as there may be a difference of the speed reducing coefficient between the ultrasound pulses with 4 MHz and the ultrasound pulses with 8 MHz because of the difference of the length of the ultrasound pulses. So, their average speed in the soft tissue may be different, and their detecting depth may be also different at the same traveling time. Calculating the detecting depth with a fixed average speed may cause an error in their actual traveling depth. Because multiple factors affect the energy and the speed of the ultrasound pulses, such as reflection, absorption and scattering, the mathematic equation of the average speed of the ultrasound pulses just mainly reflects a relationship of the average speed with the length of the ultrasound pulses, which represents different length of the ultrasound pulses with different average speed. Therefore, it is necessary to more accurately calculate the detecting depth based on the different average speed of the ultrasound pulses in the transmitting medium according to the change of the length of the ultrasound pulses.

The Intensity of the Ultrasound Pulses Affect Their Detecting Depth

In another aspect of the invention, increasing the intensity of the ultrasound pulses increases their detecting depth. As the power transferred per unit area, the intensity of the ultrasound pulses equals the multiplication value of the length, density and speed of the ultrasound pulses. Increasing one or more of the thickness and the density of PZT elements and sound speed in the PZT elements increases the intensity of the ultrasound pulses, which increase their detecting depth.

In current ultrasound theory, the attenuation coefficient is directly proportional to the frequency of the ultrasound pulses. The lower the frequency of the ultrasound pulses is, the smaller the attenuation coefficient will be. As the frequency of the ultrasound pulses is inversely proportional to the thickness of the PZT elements, the more thickness of PZT has lower frequency of the ultrasound pulses.

Frequency=sound speed in PZT/2×PZT thickness

attenuation coefficient(dB/cm)=frequency (MHz)/2

Actually, the thickness and the density of the PZT elements are directly related to the length and density of the ultrasound pulses, which affect the intensity of the ultrasound pulses. The more thickness and the density of the PZT elements are, the greater length and density of the ultrasound pulses will be, which increase the intensity of the ultrasound pulses. As a heavier ball has ability of further traveling distance, the ultrasound pulses with greater intensity will have greater penetrating depth. The speed of the ultrasound pulses in the PZT elements is directly correlated to a characteristics of the PZT elements and a of electric output on the PZT element. So, changing the thickness and the density of the PZT elements and the sound speed in the PZT elements can regulate the intensity of the ultrasound pulses and their detecting depth.

Sound intensity=sound length×sound density×sound speed

Sound intensity=acoustic impedance×traveling distance of ultrasound pulses

Increasing Detecting Depth for High Frequency Ultrasound by Increasing the Density of PZT Elements and Sound Speed in the PZT Elements

Currently, in order to increase the frequency of the ultrasound pulses, the thickness of the PZT elements is reduced, which decreases the length of the ultrasound pulses and their detecting depth. But, in the invention, selecting the PZT materials with higher sound transmitting speed and increasing electric output on the PZT elements will increase a frequency of the ultrasound pulses. At the same time, increasing the density of the PZT elements increases the density of the ultrasound pulses, but not just decreasing the thickness of the PZT elements, it will increase the frequency as well as the intensity of the ultrasound pulses. As the result, it increases the detecting depth for high frequency ultrasound.

Frequency=sound speed in PZT/2×PZT thickness

Improving Axial Resoultion of the Ultrasound Pulses by Decreasing Thickness of the PZT Elements

Currently increasing frequency of the ultrasound pulses is used to increase axial resolution. Actually, the axial resolution is decided by length of the ultrasound pulses, which is related to the thickness of the PZT elements. But, the frequency of the ultrasound pulses is not directly related to the axial resolution of the ultrasound pulses, because thin PZT elements can generate high frequency as well as low frequency of the ultrasound pulses. Less thickness of the PZT elements generates shorter ultrasound pulses and smaller numerical values of spatial pulse length, which improve the axial resolution.

At the same time, the thickness of the PZT elements also limits the highest frequency a ultrasound system can reach, which is less than a value of sound speed in PZT elements divided by a length of the ultrasound pulses.

Highest frequency<sound speed in PZT/PZT thickness

Moving Objects Change TOF and TOF ShiftIof the Ultrasound Pulses

Nowadays, Doppler mechanism is widely used to detect the speed of moving objects. According Doppler mechanism, a distance of sound resources, such as a coming or leaving motorcycle, is changing. Therefore, a frequency of sound pulses emitted from an engine of the motorcycle is relatively compress or decompressed due to the movement, which can be used to calculate to its speed.

As containing the energy, the ultrasound pulses can be reflected by motionless or moving objects. No matter in the continuous wave or the pulsed wave or the color ultrasound, when checking speed of blood flow, the ultrasound system always detects the reflected ultrasound pulses from fixed locations where the ultrasound beam cross with blood vessels to calculate TOF shift of the reflected ultrasound pulses. So, distances from the reflecting sites are fixed. It is more like playing table tennis, a racket hits a ball at a fixed location and changes a speed of the reflected ball, which changes its TOF. Comparing to motionless objects, moving objects will change the rebounding force to the ultrasound pulses. As in the FIG. 1, forward moving objects will generate the forward rebound force shift against the ultrasound pulses. The forward rebounding force shift is decided by a speed and an angle θ of the moving objects with the ultrasound beam. The faster speed of the moving objects and smaller angle θ will generate greater forward rebounding force shift, which increases the speed of the reflected ultrasound pulses. The smallest angle θ is zero. So, its TOF is decreased and smaller than the TOF from motionless objects (baseline). As the result, the TOF shift is increased and above the baseline. On the contrary, as in the FIG. 2, reversely moving objects will generate reversed rebounding force shift with the same direction of emitted ultrasound pulses, which reduces the rebounding force. The faster speed of the moving objects and greater angle θ will create greater reversed rebounding force shift, which decreases the reflected speed of the ultrasound pulses. The greatest angle θ is 180 degree. So, its TOF is increased and greater than the baseline. As the result, the TOF shift is below baseline.

As the length and density of the ultrasound pulses is directly correlated to the thickness and density of the PZT elements, changing the length and density of the ultrasound pulses also affects their TOF and TOF shift. For the forward moving objects, increasing the length and density of the ultrasound pulses will have smaller rate of increased speed of the reflected pulses. It elongates their TOF and reduces their TOF shift. Decreasing the length and density of the ultrasound pulses have greater rate of increased speed of the reflected ultrasound pulses, which will shorten their TOF and increase their TOF shift. For reversely moving objects, increasing the length and density of the ultrasound pulses will have smaller rate of decreased speed of the reflected ultrasound pulses. It shortens its TOF and decreases their TOF shift. Decreasing the length and density of the ultrasound pulses have greater rate of decreased speed of the reflected ultrasound pulses, which elongates their TOF and increase their TOF shift.

So, one aspect of the invention is calculating the speed of the moving objects based on the TOF shift for the continuous wave or the pulsed wave or the color ultrasound. As mentioned above, the speed of the ultrasound pulses will gradually reduce, and the moving objects will generate the rebounding force shift, which changes the speed of the reflected ultrasound pulses, their TOF and TOF shift. Therefore, the TOF shift can more accurately present relationship between the speed of the moving objects and characters of the ultrasound pulses.

Caluclating Speed of Moving Objects Based on TOF Shift for Continuous Wave Ultrasound

Currently, it is considered that speed of the ultrasound pulses is fixed in the same medium during the transmission. The moving objects will change the frequency of the reflected ultrasound pulses. The forward moving objects will compress the reflected frequency, which is higher than the emitted frequency. Its Doppler shift is above the baseline. The reversely moving objects will decompress the reflected frequency, which is lower than the emitted frequency. Its Doppler shift is below the baseline. So, calculating Doppler shift of the continuous wave (CW) ultrasound is based on difference between the reflected frequency and the emitted frequency. V_objects is a speed of the moving objects, f is a frequency of a transducer, and V is a speed of the ultrasound pulses in a transmitting medium.

Doppler shift=reflected frequency−emitted frequency

$\mathrm{Doppler}\mathrm{shift}=\frac{2\times V_{\mathrm{objects}}\times f\times \cos \left(\theta \right)}{V}$

The invention discloses that a TOF shift of the CW ultrasound is used to calculate the speed of the moving objects. The TOF shift of the CW ultrasound is difference between a time of emitting period and a time of reflected period. There are two PZT parts in CW ultrasound transducer. As in the FIG. 7, the emitting PZT part emits the continuous ultrasound pulses with identical emitted period between previous and following emitted ultrasound pulses (105), which is decided by the ultrasound system. The receiving PZT part receives the reflected ultrasound pulses and detects the reflected period between previously and following reflected ultrasound pulses (106). The reflected period is decided by the speed of the moving objects and the angle of the moving objects with a beam of the ultrasound pulses. If the ultrasound pulses are reflected from motionless objects, the reflected period equals to the emitted period and their TOF shift is zero. So, the emitted period is set as a baseline, and the TOF shift equals zero at the baseline. Then, the ultrasound system obtains the TOF shift from difference between the emitted period and the reflected period, and calculates speed of the moving objects according to the equation of the TOF shift (108).

emitted period=the time between previous and following emitted pulses

reflected period=the time between previously and following reflected pulses

TOF shift=emitted period−reflected period

$\mathrm{TOF}\mathrm{shift}=\frac{2\times V_{\mathrm{objects}}\times f\times \cos \left(\theta \right)}{V_{\mathrm{avg}}}$

As 101 in FIG. 3, the emitted period is the time between the previously and following emitted pulses, which forms the baseline. The reflected period is the time between previously and following reflected ultrasound pulses. If the ultrasound pulses are reflected from the moving objects that are vertical to the ultrasound beam (flow N), the emitted period equals to its reflected period, and the TOF shift is zero. But, if the ultrasound pulses are reflected from the forward moving objects (flow M), the speed of the reflected ultrasound pulses will be accelerated due to the increasing rebounding force, which shorten the TOF M′. So, the reflected period will be less than the time of the emitted period, which generates TOF shift M′ and is above the baseline. On the contrary, for the reversely moving object (flow O), the TOF O′ will be elongated due to the reduced rebounding force and the speed of the reflected ultrasound pulses. So, the reflected period will be greater than the time of the emitted period, which generates the TOF shift O′ and is below the baseline.

As 100 in FIG. 3, for the CW ultrasound, a transducer receives all of the reflected ultrasound pulses from an area under the transducer. If there are several moving objects with different velocities toward the transducer, they will rebound the ultrasound pulses with different reflected speeds and TOFs, which generate different TOF shifts related to these moving objects. Then the ultrasound system will trace and compare a list of these reflected pulses and respectively present their TOF shifts on TOF shift spectrum. For CW ultrasound, because there are usually multiple moving objects under the transducer with different velocities, such as multiple blood vessels, its TOF shift spectrum often presents as spectral broadening as 102 in FIG. 3a. So, a computer program can be used to calculate the speed of the moving objects based on the values of the TOF shift as in FIG. 7.

Calculationg Speed of Moving Objects by TOF Shift for Pulsed Wave and Color Ultrasound

There is only one part of PZT elements in a transducer of the pulsed wave ultrasound, which sends and receives ultrasound pulses. So, the transducer has to receive previously reflected pulses before sending next emitted pulses. In order to detect speed of the moving objects, a gate is set with a certain distance. So, based on the average speed of the ultrasound pulses and the distance between the transducer and the gate, a calculated TOF can be obtained as A in FIG. 3b, which is set as the baseline, and the TOF shift at the baseline equals to zero. The detected TOF is that the ultrasound system interprets TOF from the emitted and reflected ultrasound pulses, which can be affected by the moving objects. The actual TOF is the time the ultrasound pulses actually travel between the transducer and the gate. As the ultrasound pulses leave a transducer and enter the transmitting medium, their speed is at maximal and will gradually reduce during the transmitting process. The moving objects will rebound the ultrasound pulses and change the detected TOF, which generates the TOF shift between the calculated TOF and detected TOF. The calculated TOF is based on the average speed of ultrasound pulses in the transmitting medium. So, when the actual TOF excesses its aliasing limit and the value of TOF shift is smaller than the value of a half calculated TOF, ultrasound system will misinterpret the detected TOF, which generates the aliasing. Before the aliasing, the detected TOF is the actual TOF, and after the aliasing, the detected TOF is the aliasing TOF. The TOF shift is difference between the calculated TOF and the detected TOF. For a forward moving object, it accelerates the speed of the reflected pulses, which shorten its actual TOF as B in FIG. 3b. So, the actual TOF is smaller than the calculated TOF, and the TOF shift is above the baseline. As increasing the speed of the moving objects, the value of the detected TOF decreases and the value of the TOF shift increases, tip of the profile of the TOF shift is away from the baseline (80 in FIG. 3b). On the contrary, reversely moving objects elongate their actual TOF, which is greater than the baseline, and the TOF shift is below the baseline. As the speed of the moving objects increases, the value of the detected TOF and the value of the TOF shift both increase, and the tip of the profile of the TOF shift is away from the baseline (82 in FIG. 3c). Then the speed of the moving objects can be calculated according the value of the TOF shift.

TOF shift=calculated TOF−detected TOF

$\mathrm{TOF}\mathrm{shift}=\frac{2\times V_{\mathrm{objects}}\times f\times \cos \left(\theta \right)}{V_{\mathrm{avg}}}$

Identifying and Correcting Aliasing for Pulsed Wave Ultrasound

For the pulsed wave ultrasound, there is the aliasing, which is caused by the ultrasound system misinterpreting the detected TOF from the reflected ultrasound pulses. If the speed of the moving objects is too fast, and makes the actual TOF excesses its aliasing limit, the ultrasound system will misinterpret it and the detected TOF becomes an aliasing TOF. Then the aliasing TOF shift is located on opposite side of the baseline, which presents the moving objects as toward opposite direction. The aliasing TOF shift also disrupts continuation of the profile of the TOF shift.

For forward moving objects, the aliasing limit of the actual TOF is less than the value of half calculated TOF. if the actual TOF is smaller than its aliasing limit, the ultrasound system will misinterpret the reflected pulses, and the aliasing TOF is a value of a actual TOF adding a calculated TOF, which is larger than the calculated TOF (104 in FIG. 4). So, the aliasing TOF shift becomes below baseline, which misrepresents the moving objects moving toward opposite direction. As the result, before the actual TOF excesses its aliasing limit, the value of the TOF shift is above the baseline(from E to F in FIG. 5). But, after the actual TOF excesses its aliasing limit, the value of the aliasing TOF shift is below the baseline(G and H in FIG. 5a); As the speed of the moving objects increases, both the value of the aliasing TOF and the value of the aliasing TOF shift decrease; and the tip of the profile of the aliasing TOF shift is toward the baseline (81 in FIG. 5a), which discontinues the profile of the TOF shift.

Aliasing TOF=actual TOF+calculated TOF

Aliasing TOF shift=calculated TOF−aliasing TOF

Aliasing TOF shift=−actual TOF

So, in the invention, a computer program is designed to identify and correct the aliasing TOF shift. For the forward moving objects, the actual TOF is smaller than calculated TOF, and its TOF shift is above the baseline. As the speed of moving objects is increased, its actual TOF keeps decrease and smaller than the calculated TOF, and the TOF shift keeps increase and above baseline. But, after the actual TOF excesses its aliasing limit, the aliasing TOF becomes greater than the calculated TOF, and the aliasing TOF shift becomes below the baseline. The computer program will trace and compare the value of the following TOF and TOF shift with the value of the previous TOF and TOF shift. If the value of the TOF and the TOF shift approaches the value of half calculated TOF, and the value of following TOF shift is below the baseline, which discontinues the profile of the TOF shift. It is the aliasing TOF shift. After identifying the aliasing TOF shift, the ultrasound system will register the corrected TOF shift by subtracting the value of the aliasing TOF shift from one calculated TOF (116 in FIG. 8).

TOF shift=calculated TOF−actual TOF

Aliasing TOF shift=−actual TOF

corrected TOF shift=calculated TOF−|aliasing TOF shift|

After rectifying the registering errors of TOF shift, the value of the corrected TOF shift will keep increase as increase of the speed of the moving objects, and the tip of the profile of the TOF shift is away from the baseline (84 in FIG. 5b), which reestablish the continuation of the profile of the TOF shift (FIG. 5b), and the value of the correct TOF shift can be used to calculated the speed of the moving objects.

For the reversely moving objects, the rebounding force is reduced, which decreases the reflected speed of the ultrasound pulses and increases their TOF, which is greater than the value of the calculated TOF. So, the value of the TOF shift is below the baseline. For the reversely moving objects, the aliasing limit of the actual TOF is larger than the value of one and half calculated TOF. If the value of the actual TOF excesses its aliasing limit, the ultrasound system will misinterpret the reflected ultrasound pulses and the aliasing TOF is the value of the actual TOF subtracting a calculated TOF, which is smaller than the calculated TOF. So, the aliasing TOF shift will be above the baseline; as the speed of the reversely moving objects keeps increase, the aliasing TOF is increased but the aliasing TOF shift is decreased, which make the tip of the profile of TOF shift is toward baseline (83 in FIG. 6a). As a result, the continuity of the profile of TOF shift is disrupted (FIG. 6a). In the invention, the computer program is used to identify the aliasing. As the value of actual TOF is close to the value of one and half calculated TOF and TOF shift approaches the value of half calculated TOF, if following TOF shift is above the baseline, the aliasing TOF shift is identified.

Aliasing TOF=actual TOF−calculated TOF

Aliasing TOF shift=calculated TOF−aliasing TOF

Aliasing TOF shift=2×calculated TOF−actual TOF

After identifying the aliasing TOF shift, the computer program will rectify the aliasing TOF shift by subtract the value of a calculated TOF from the value of the aliasing TOF shift, which is based on following equations:

TOF shift=calculated TOF−actual TOF

aliasing TOF shift=2×calculated TOF−actual TOF

correct TOF shift=aliasing TOF shift−calculated TOF

After correcting the aliasing TOF shift, the corrected TOF shift will increase as the speed of the moving objects keeps increase, which makes the tip of the profile of the corrected TOF shift away from the baseline. The corrected TOF shift will reestablish the continuation of the profile of the TOF shift (FIG. 6b), and it can be used to calculate the speed of the moving objects.

Another method of avoiding the happening of aliasing is modifying the computer program in the ultrasound system to prevent adding or subtracting the value of a calculated TOF into the detected TOF after the actual TOF excesses its aliasing limit.

Differentiating Color of Aliasing from Color of Turbulent Flows for Color Ultrasound

For the color ultrasound, ultrasound system automatically sets different baselines at regular distance along the ultrasound beam. The TOF from reflected ultrasound pulses is compared with their respective baseline and get their TOF shift. Then colors are assigned according to a value of the TOF shift to represent a velocity of the moving objects. But, there are similar color patterns between color of the aliasing and color of turbulent flows. For the aliasing pattern, the color of the aliasing mistakenly presents as the moving objects toward opposite side after the actual TOF excesses its aliasing limit. For the turbulent flows, the color of the turbulent flows truly presents their moving direction. So, this will make the difficulties for clinical judgment and diagnosis for pathological situations. In the invention, differentiating the color of the aliasing from the color of the turbulent flows is based on the characters of the TOF shift of different colors.

For the color of the aliasing in FIG. 9, when a forward flow (S) passes a narrow part of vessel, the speed of a flow will be accelerated within the narrow part. If its actual TOF excesses its aliasing limit, the aliasing TOF shift marks the flow with a color of the aliasing (T) at the narrow part, which represents the flow as toward opposite direction. Color of U represents the flow between the color of the no-aliasing S and the color of the aliasing T, and the value of TOF shift for the color U is close to the value of half calculated TOF because the actual TOF for the color U is closing to its aliasing limit. From the color T to the color U, or from the color S to the color U, their TOF shift is gradually increased until close to the value of half calculated TOF. For the color of the aliasing, the profile of the aliasing TOF shift will be more close to the value of half calculated TOF with its tip of the profile of the aliasing TOF shift toward baseline. But for the color of the no-aliasing (color S), the profile of the no-aliasing TOF shift will be more close to the baseline with the tip of the profile of the no-aliasing TOF shift away from the baseline. Correcting the aliasing TOF shift is based on the direction of no-aliasing flow as forward or reversely moving direction. Then the color of the aliasing can be corrected based on the corrected TOF shift. The designed computer program in FIG. 11 will trace and identify the characters of the profile of the TOF shift for theses colors, and correct the color of the aliasing by rectifying their aliasing TOF shift.

But, for the color of the turbulent flows in FIG. 10, the color of X represents a forward flow that enters in an enlarged part of a blood vessel. The flow will become turbulent at the enlarged part of the vessel, and the color of Y represents a reversed blood flow. The color of Z represents the edge between the flow X and the flow Y. The TOF shift for the color Z will be close to zero because its actual TOF is close to its baseline. Because the speed of the flow is gradually decreased to the edge Z, the TOF shift from one color to the edge of another color is gradually reduced until close to the zero. The tip of the profile of the TOF shift for both colors is away from the baseline and the profile of their TOF shift keeps its continuity. The colors of flows are assigned based on their TOF shift.

So, differentiating and correcting the aliasing TOF shift for the color of aliasing from the TOF shift for the color of turbulent flows will benefit the clinical judgment and diagnosis for truly pathological conditions.

Calculation of Speed of Moving Objects with Two Separated PZT Elements Without Need to Adjust the Angle of the Ultrasound Beam

The speed value of the moving objects is important in judging some pathological conditions, such as stenosis of blood vessels. The angle of the ultrasound beam with the direction of the moving objects decides the value of TOF shift, which affects the calculation of the speed of the moving objects. Currently in order to get accurate speed of the moving objects, it is important to adjust the angle of the ultrasound beam with the direction of the moving objects within 45 to 60 degree. But, the tortuous blood vessels and variant performances of sonographers often derive different speed values of the moving objects from a same testing site, which increases the difficulties in the clinical diagnosis. In the invention, by simultaneously checking the TOF shifts at one detecting site from two separated PZT elements, the speed value of the moving objects can be accurately calculated without the need to adjust the angle of the ultrasound beams with the direction of the moving objects, which simplifies the operating procedures and avoids the variation of detection.

As in the FIG. 13, after selecting a detecting site, two TOF shifts are simultaneously detected from PZT A and PZT B, and an angle μ is between two ultrasound beams from the PZT A and the PZT B, and an angle θ is between ultrasound beam from the ultrasound beam A with the direction of the moving objects. Therefore, their individual TOF shifts will be obtained, and the speed of the moving (V_objects) can be calculated based on the values of the TOF shifts, the transducer frequency (f), the angle μ and the average speed of the ultrasound pulses in the transmitting medium (V_avg).

$\mathrm{TOF}\mathrm{shift}A=\frac{2\times V_{\mathrm{objects}}\times f\times \cos \left(\theta \right)}{V_{\mathrm{avg}}}$ $\mathrm{TOF}\mathrm{shift}B=\frac{2\times V_{\mathrm{objects}}\times f\times \cos \left(\theta +\mu \right)}{V_{\mathrm{avg}}}$ $V_{\mathrm{objects}}=\frac{V_{\mathrm{avg}}\times \sqrt{\begin{array}{c}{\left(\mathrm{TOF}\mathrm{shiftA}\right)}^2-2\times \mathrm{TOF}\mathrm{shiftA}\times \\ \mathrm{TOF}\mathrm{shiftB}\times \cos \left(\mu \right)+{\left(\mathrm{TOF}\mathrm{shiftB}\right)}^2\end{array}}}{2\times f\times \sin \left(\mu \right)}$

Calculation of Detecting Depth and Moving Speed of Objects with Coded Ultrasound Pulses

Because the pulsed wave ultrasound causes the aliasing and the continuous wave ultrasound loses information of distance, a method of coding ultrasound pulses can combine advantages of the pulsed wave ultrasound and the continuous wave ultrasound as well as avoid their disadvantages. This method is more like coding genomic sequence of deoxyribonucleic acid (DNA). A pulse duration is a time that ultrasound pulses are sent. During each pulse duration, different numbers of ultrasound pulses are sent, which is assigned a pulse character. For instance, just one pulse within the pulse duration is assigned as a pulse character A, two pulses as a pulse character C, three pulses as a pulse character G, and four pulses as a pulse character T. A resting period is a time between each adjacent pulse duration, and the resting period for the emitted ultrasound pulses keeps identical. A transducer of the ultrasound system contains one pair or more of sending PZT elements and receiving PZT elements. The sending PZT elements send ultrasound pulses with specific coded pulse characters, such as ATC GCG . . . , which is like codes of a DNA sequence. By this way, it actually endows information of emitting time for each pulse character. The receiving PZT elements receive reflected ultrasound pulses, which contain the same codes of pulse characters, such as A′T′C′ G′C′G′ . . . , which contains information of receiving time for each pulse character. Therefore, TOF can be obtained from the time between the emitting time and the receiving time of the related pulse characters. At the same time, TOF shift can also obtained from the time difference of emitting resting time and receiving resting time of the related pulse characters. For instance, TOF of pulse character A can be obtained from a time between the emitted pulse character A and the reflected pulse character A′, and TOF shift can be obtained from a time difference between the emitted resting period of the pulse character A and the receiving resting period of the pulse character A′. If reflections of the ultrasound pulses from one point keep identical TOF and their TOF shift is zero, it means the reflections coming from motionless objects. So, the TOF can be used to calculate the depth or distance of the motionless objects. If the TOF and the TOF shift keep variable, it means the reflections coming from moving objects. So, the TOF shift can be used to calculate the speed of the moving object. Because the moving objects change the TOF, which can not be used to calculate its actual location. By adding the TOF shift into the TOF, the TOF shift will compensate the changed part of TOF. For the forward moving objects, the TOF shift is positive, which will compensate shortened TOF. For the reversely moving object, the TOF shift is negative, which will offset extended TOF. So, a sum of the TOF shift with the TOF can be used to calculate the depth or distance of the moving objects. The depth or distance of the moving objects is a half multiplication value of the sum of TOF shift and TOF with the average speed of ultrasound in the transmitting medium. Both the speed and location of the moving objects can be used in imaging the color ultrasound. So, the method of the coded ultrasound pulses combines the advantages of the pulsed wave ultrasound and the continuous wave ultrasound in the ultrasound system, which can obtain the information of distance and speed of the detecting objects at the same time (FIG. 12). It also avoids aliasing for detecting moving objects with high velocity.

Improving Imaging Quality with Coded Ultrasound Pulses

Because each PZT element may not only receive the reflected ultrasound pulses emitted by itself but also receive the reflected ultrasound pulses emitted from other PZT elements, which cause noise and artifacts, such as mirror image or refraction. The noise and artifacts will affect quality of ultrasound images. With each PZT element emits its specific codes of the pulse characters, after receiving reflected ultrasound pulses, the ultrasound system will compare the received codes of the pulse characters with the emitted ones, and register locations of the reflections that have the same received codes of the pulse characters with the emitted codes of the pulse characters to an area belonging to the PZT element that emits the codes of the pulse characters. By this way, it may improve the noise and the artifacts.

Detecting Depth and Speed of Moving Objects in Other Applications of Sound

Ultrasound just occupies sound wave with frequencies of more than 20 kilohertz. Actually sound pulses with any frequencies have the same mechanisms mentioned as above. So, the applications in detecting depth and calculating a speed of moving objects as mentioned above can be used in the sound pulses with any other sound frequencies, such as radar and sonar.

Other applications, advantages, alternations, modifications, or equivalents to the disclosed embodiments are obvious to those skilled in the art and are intended to be encompassed within the scope of the present disclosure.

Claims

1. A method for calculating a detecting depth as speed reduction of ultrasound pulses during a transmission, the method comprising: calculating a speed reducing coefficient of the ultrasound pulses in a transmitting medium, wherein the speed reducing coefficient of the ultrasound pulses is directly proportional to the density of the transmitting medium and the sound speed in the PZT elements, and inversely proportional to a density and a thickness of the PZT elements, which comprising:

2. A method of claim 1, further comprising increasing a intensity of the ultrasound pulses by increasing one or more of a thickness of the PZT elements and a density of the PZT elements and a sound speed in the PZT elements, wherein the thickness of the PZT elements decides a length of the ultrasound pulses, and the density of the PZT elements decides a density of the ultrasound pulses, and the sound speed in the PZT elements decides the maximal speed of the ultrasound pulses in the transmitting medium, a multiplication value of the length of the ultrasound pulses and the density of the ultrasound pulses and the speed of the sound pulses decides the intensity of the ultrasound pulses, which comprising: Sound intensity(kg/MS)=sound length(M)×sound density(Kg/M3)×sound speed(M/S)M=meter; Kg=kilogram; S=second.

3. The method of claim 2, further comprising increasing the intensity of the ultrasound pulses to increase a detecting depth of the ultrasound pulses in the transmitting medium.

4. The method of claim 3, further comprising increasing detecting depth for high frequency ultrasound by increasing the density of the PZT elements and the sound speed in the PZT elements wherein increasing the sound speed in the PZT elements and the density of the PZT increases the frequency of the ultrasound pulses as well as their intensity.

5. The method of claim 2, further comprising improving axial resolution by decreasing the length of the ultrasound pulses wherein the thickness of the PZT elements decides the length of the ultrasound pulses as well as limits the highest frequency a ultrasound system can reach.

6. A method of using time of flight (TOF) shift of the ultrasound pulses to calculate a speed of moving objects in a continuous wave, a pulsed wave and a color ultrasound, the method comprising: setting a baseline wherein the baseline is a span of traveling time of the ultrasound pulses reflected from motionless objects at the same depth as from the moving objects, and a TOF shift equals to zero at the baseline;obtaining a detected TOF wherein the detected TOF is a traveling time that a ultrasound system interprets from the reflected ultrasound pulses, the detected TOF is related to the speed of the moving objects and the angle of the moving objects with a ultrasound beam, and the intensity of the ultrasound pulses;calculating the TOF shift wherein the TOF shift is a time difference between the baseline and the detected TOF; andcalculating the speed of the moving objects (Vobjects) based on an equation of TOF shift including the angle θ of the ultrasound beam made with the moving objects, an average speed (Vavg) of the ultrasound pulses in the transmitting medium, the transducer frequency (f), wherein the TOF shift is the TOF shift for the continuous wave, the pulsed wave and the color ultrasound, the equation of the TOF shift is:

7. The method of claim 6, further comprising calculating the speed of the moving objects by simultaneously detecting TOF shifts at one site from two separated PZT elements, wherein the speed of the moving objects can be calculated based on the values of the TOF shifts, the transducer frequency, the angle μ between two ultrasound beams from the PZT elements and the average speed of the ultrasound pulses in the transmitting medium as the following equation:

8. The method of claim 6, further comprising changing the intensity and the angle of the ultrasound pulses to regulate the speed of the reflected ultrasound pulses wherein the changes of the speed of the reflected ultrasound pulses alter the TOF and the TOF shift of the ultrasound pulses.

9. The method of claim 6, further comprising a method of calculating the speed of the moving objects for the continuous wave ultrasound comprising: setting a time of a emitted period as the baseline wherein the time of the emitted period is the time between previously and following emitted pulses;obtaining a time of a reflected period as the detected TOF wherein the time of the reflected period is the time between previously and following reflected ultrasound pulses;calculating a TOF shift wherein the TOF shift is a difference between the time of the emitted period and the time of the reflected period; andusing the TOF shift to calculate the speed of the moving objects based on the equation of TOF shift.

10. The method of claim 6 further comprising a method of calculating the speed of the moving objects for the pulsed wave and the color ultrasound comprising: setting a time of a calculated TOF as the baseline wherein the calculated TOF is the time that ultrasound system calculates according to a distance between a transducer and a gate and the average speed of the ultrasound pulses in the transmitting medium;obtaining the detected TOF wherein the detected TOF is the time that ultrasound system interprets from ultrasound pulses traveling between the transducer and the gate, before an aliasing the detected TOF is an actual TOF, and the actual TOF is a truly traveling time of the ultrasound pulses;calculating a TOF shift wherein the TOF shift is a difference between the value of the calculated TOF and the value of the detected TOF; andusing the TOF shift to calculate the speed of the moving objects based on the equation of TOF shift.

11. The method of claim 10 further comprising a method to correctly calculate the speed of the moving objects after the aliasing for the pulsed wave and the color ultrasound comprising: identifying an aliasing TOF, wherein as the actual TOF excesses its aliasing limit, the detected TOF is misinterpreted by ultrasound system to generate the aliasing TOF, the aliasing TOF shift is on opposite site of the baseline and disrupts continuity of a profile of the TOF shift, and a tip of a profile of the aliasing TOF shift is toward the baseline;obtaining a corrected TOF shift by rectifying the aliasing TOF shift to correct registration of the reflected ultrasound pulses after the actual TOF exceeds the aliasing limit, the tip of the profile of corrected TOF shift is away from the baseline, and the corrected TOF shift reconstructs the continuation of the profile of the TOF shift; andusing the corrected TOF shift to calculate the speed of the moving objects based on an equation of corrected TOF shift:

12. The method of claim 11, wherein for forward moving objects, the speed of the moving objects is correctly calculated after the aliasing by: identifying the aliasing for the forward moving objects wherein the aliasing limit for the actual TOF is less than a value of half calculated TOF; after the actual TOF excesses the aliasing limit, the ultrasound system misinterprets the detected TOF by adding a value of one calculated TOF to a value of the actual TOF to form an aliasing TOF, the value of the aliasing TOF is greater than the value of the baseline and its TOF shift is located on an opposite site of the baseline, and the aliasing TOF shift disrupts the continuation of the profile of the TOF shift, and the tip of the profile of the aliasing TOF shift is toward the baseline;obtaining the corrected TOF shift by subtracting a value of the aliasing TOF shift from a value of the calculated TOF to reestablish the continuation of the profile of the TOF shift; andusing the corrected TOF shift to calculate the speed of the forward moving objects based on the equation of corrected TOF shift.

13. The method of claim 11, wherein for reversely moving objects, the speed of the moving objects is correctly calculated after the aliasing by: identifying the aliasing for the reversely moving objects wherein the aliasing limit for the actual TOF is greater than the value of one and half calculated TOF; after the actual TOF excesses the aliasing limit, the ultrasound system misinterprets the detected TOF by subtracting a value of one calculated TOF from a value of the actual TOF to form an aliasing TOF; the value of the aliasing TOF is smaller than the value of the baseline and the aliasing TOF shift is located on the opposite site of the baseline, and the aliasing TOF shift disrupts the continuation of the profile of the TOF shift, and the tip of the profile of the aliasing TOF shift is toward the baseline;obtaining the corrected TOF shift by subtracting a value of the calculated TOF shift from a value of the aliasing TOF shift to reestablish the continuation of the profile of the TOF shift; andusing the corrected TOF shift to calculate the speed of the reversely moving objects based on the equation of corrected TOF shift.

14. The method of claim 10 further comprising a method of avoiding the aliasing by modifying the computer program in the ultrasound system to prevent adding or subtracting a value of a calculated TOF from the detected TOF after the actual TOF excesses its aliasing limit.

15. The method of claim 11, further comprising a method of differentiating a color of the aliasing from a color of turbulent flows and rectifying the color of the aliasing for the color ultrasound comprising: identifying the aliasing TOF shift for the color of the aliasing wherein from the color of the aliasing to a edge of another color, the value of the TOF shift is gradually increased until close to the value of half calculated TOF, and the profile of the aliasing TOF shift is more close to the value of half calculated TOF, and the tip of the profile of the aliasing TOF shift is toward the baseline; a color of no-aliasing represents a flow before its actual TOF excesses the aliasing limit, the profile of the no-aliasing TOF shift is more closer to the baseline, and the tip of the no-aliasing TOF shift is away from the baseline;identifying the TOF shift for the color of turbulent flows wherein from one color to a edge of another color, the value of the TOF shift is gradually decreased until close to zero, the tip of the profile of the TOF shift for the color of turbulent flows is away from the baseline; andrectifying the color of the aliasing wherein the aliasing TOF shift is corrected according to the direction of the no-aliasing flow, and the color of the aliasing is corrected based on the value of the corrected TOF shift.

16. A method of calculation of the detecting depth and the moving speed of objects with coding ultrasound pulses comprising: a transducer contains one pair or more of emitting PZT elements and receiving PZT elements, assigning different numbers of the ultrasound pulses within each pulse duration to form different pulse characters, a resting period is a time between each adjacent pulse duration;the emitting PZT elements emit specifically coded pulse characters, which endow information of a emitting time for each pulse character, and the resting period for the emitted ultrasound pulses keeps identical;the receiving PZT elements receive reflected ultrasound pulses, and decode received pulse characters to compare with the emitted codes of the pulse characters, TOF is obtained from a time between the emitted pulse character and the same reflected pulse character, and TOF shift is obtained from a time difference between the emitted resting period and the correspondingly received resting period;identifying motionless objects from the reflected ultrasound pulses with identical value of the TOF and zero value of the TOF shift, therein the depth of the motionless objects is calculated from the TOF; andidentifying moving objects from the reflected ultrasound pulses with variable values of the TOF and the TOF shift, therein the speed of the moving objects is calculated with the equation of TOF shift, the depth of the moving objects is a half multiplication value of the sum of the TOF and the TOF shift with the average speed of ultrasound in the transmitting medium, for forward moving objects, the TOF shift is positive value, and for reversely moving objects, the TOF shift is negative value, the equation of calculating the depth of the moving objects comprising: depth of moving objects=Vavg.×(TOF+TOF shift)/2

17. The method of claim 16 further comprising improving noise and artifacts with coding ultrasound pulses wherein by comparing the received codes of the pulse characters with the emitted codes of the pulse characters, the reflections that have the identical received codes of the pulse characters with the emitted codes of the pulse characters will be registered to an area that belongs to the PZT element that emits the codes of the pulse characters.

18. A method of claim 1, further comprising applications in detecting a depth or a distance of objects with sound pulses of any frequencies.

19. A method of claim 6, further comprising applications in calculating a speed of moving objects with sound pulses of any frequencies.

20. A method of claim 16, further comprising applications in detecting depth and distance and moving speed of objects with coded sound pulses with sound pulses of any frequencies.