Correction of detecting depth and calculation of speed of moving objects based on time of flight of ultrasound pulses

Abstract

During transmission, speed of ultrasound pulses gradually reduces due to their energy loss from acoustic impedance. So, calculating a detecting depth with fixed speed of the ultrasound pulses will distort ultrasound images. Correction of the detecting depth will rectify a depth registration and improve the imaging quality. The thickness and density of piezoelectric elements (PZT) decide a quantity of the ultrasound pulses, which affect their detecting depth. The density and sound speed in PZT elements decide the frequency of the ultrasound pulses, which can be used to increase the detecting depth for a high frequency ultrasound. Moving objects can change speed of reflected ultrasound pulses, which change their TOF and TOF shift. Therefore the TOF shift can be used to calculate the velocity of the moving objects in a continuous and a pulsed wave and a color ultrasound, and correct aliasing of the pulsed wave and the color ultrasound.

What is claimed is: 
     
         1 . A method for rectifying errors of registration of a detecting depth due to speed reduction of ultrasound pulses during a transmission, the method comprising:
 obtaining a calculated detecting depth from a general speed of the ultrasound pulses and a traveling time between emitting and receiving ultrasound pulses, wherein the calculated detecting depth is a half value of a multiplication result of the general speed of the ultrasound pulses in a transmitting medium and the traveling time between the emitting and the receiving ultrasound pulses;   calculating a speed reducing coefficient of the ultrasound pulses, wherein the speed reducing coefficient of the ultrasound pulses equals to a multiplication result of acoustic impedance and attenuation coefficient;   obtaining a depth shift of the ultrasound pulses, wherein the depth shift of the ultrasound pulses equals to a half value of a multiplication result of the speed reducing coefficient and the traveling time; and   determining a corrected detecting depth, wherein the corrected detecting depth is a difference between the calculated detecting depth and the depth shift.   
     
     
         2 . The method of  claim 1 , further comprising: changing one or more of thickness and density of piezoelectric elements (PZT) to regulate quantity and density of the ultrasound pulses, wherein the quantity of the ultrasound pulses is directly proportional to the thickness and the density of the PZT elements, which comprising:
   Quantity of ultrasound pulses=PZT thickness×PZT density.
   
     
     
         3 . The method of  claim 2 , further comprising: changing the quantity of the ultrasound pulses to regulate their detecting depth wherein increasing the quantity of the ultrasound pulses increases the detecting depth. 
     
     
         4 . The method of  claim 2 , further comprising: changing the density of the PZT elements to regulate the density of the PZT and a speed of sound in the PZT elements wherein increasing the density of the PZT increases the density of the ultrasound pulses and the speed of sound in the PZT elements. 
     
     
         5 . The method of  claim 4 , further comprising: creating a transducer with greater density of the PZT elements and a faster speed of sound in the PZT elements to generate the ultrasound pulses with larger quantity and higher frequency wherein the transducer with high frequency has a deeper detecting depth. 
     
     
         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 of TOF wherein the baseline is a traveling time of the ultrasound pulses emitted from a transducer and reflected from motionless objects at the same depth as from the moving objects, and a TOF shift equals to zero at the baseline, the baseline is decided by a ultrasound system;   obtaining a detected TOF wherein the detected TOF is the time that ultrasound system interprets from the emitting and receiving ultrasound pulses, the detected TOF is decided by the speed of the moving objects and an angle of the moving objects with a ultrasound beam, and the quantity of the ultrasound pulses;   calculating a TOF shift wherein the TOF shift is a difference between the baseline and the detected TOF; and   calculating the speed of the moving objects based on an equation wherein θ is the angle of a ultrasound beam made with the moving objects, a pulse propagation speed is determined by a transmitting medium for the ultrasound pulses, and the TOF shift is the TOF shift for the continuous wave, the pulsed wave and the color ultrasound, the equation is:   
       
         
           
             
               
                 TOF 
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                 shift 
               
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                         moving 
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                         objects 
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                         transducer 
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                         frequency 
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                         θ 
                       
                     
                   
                 
                 
                   pulse 
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                   propagation 
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                   speed 
                 
               
             
           
         
       
     
     
         7 . The method of  claim 6 , further comprising: changing the angle of the ultrasound pulses with the moving objects to regulate a rebounding force wherein the changes of the rebounding force alter the TOF and the TOF shift of the ultrasound pulses. 
     
     
         8 . The method of  claim 6 , further comprising: changing the quantity 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: changing the density of the PZT elements and the sound speed in the PZT elements to regulate the TOF shift of the ultrasound pulses. 
     
     
         10 . 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, the time of the emitted period is decided by ultrasound system;   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 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; and   using the TOF shift to calculate the speed of the moving objects based on the equation.   
     
     
         11 . 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 general 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 a 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; and 
 using the TOF shift to calculate the speed of the moving objects based on the equation. 
 
     
     
         12 . The method of  claim 11 , further comprising a method to correctly calculate the speed of the moving objects after a aliasing for the pulsed wave and color ultrasound comprising:
 identifying an aliasing of the ultrasound pulses, wherein as the actual TOF excesses its aliasing limit, the detected TOF is misinterpreted by ultrasound system to generate a aliasing TOF, the aliasing TOF shift is on opposite site of the baseline and disrupts continuity of the profile of the TOF shift, and the tip of the 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; and   using the corrected TOF shift to calculate the speed of the moving objects based on an equation:   
       
         
           
             
               
                 corrected 
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                 TOF 
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                         objects 
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                   propagation 
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         13 . The method of  claim 12 , 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 a aliasing limit for the actual TOF is less than the 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 opposite site of the baseline, and the tip of the profile of the aliasing TOF shift is toward the baseline; and the aliasing TOF disrupts the continuation of the profile of the TOF shift;   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; and   using the corrected TOF shift to calculate the speed of the forward moving objects based on the equation.   
     
     
         14 . The method of  claim 12 , 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 a 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 the aliasing TOF; the value of the aliasing TOF is smaller than the value of the baseline and the aliasing TOF shift is located on opposite site of the baseline, the tip of the profile of the aliasing TOF shift is toward the baseline; and the aliasing TOF shift disrupts the continuation of the profile of the TOF shift;   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; and   using the corrected TOF shift to calculate the speed of the reversely moving objects based on the equation.   
     
     
         15 . The method of  claim 12 , further comprising a method to differentiating a color of aliasing from a color of disturbed flow and rectifying the color of aliasing for color ultrasound comprising:
 identifying the aliasing TOF shift for the color of aliasing wherein from a flow within one color to a flow on edge of another color, the value of the TOF shift is gradually increased until close to the value of half calculated TOF; 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; the profile of no-aliasing TOF shift is more closer to the baseline, and the tip of the no-aliasing TOF shift is away from the baseline, the no-aliasing flow is a flow before its TOF excesses the aliasing limit;   identifying the TOF shift for the color of disturbed flow wherein from a flow within one color to a flow on 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 colors is away from the baseline; and   rectifying the color of aliasing wherein the aliasing TOF shift is corrected according to the direction of a no-aliasing flow, and the color of aliasing is corrected based on the value of the corrected TOF shift.   
     
     
         16 . The method of  claim 2 , further comprising: changing the quantity of the ultrasound pulses to regulate a rate of speed changes for the reflected pulses wherein increasing the quantity of the ultrasound pulses improves the aliasing. 
     
     
         17 . The method of  claim 6 , further comprising: selecting the moving objects that are closer to the transducer to reduce the systematic errors and to improve the aliasing.