Patent Publication Number: US-2013237828-A1

Title: Method and apparatus for obtaining movement velocity and direction of tissue

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2012-0024112, filed on Mar. 8, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to method and apparatus for obtaining a movement direction and velocity of a tissue included in a target by using the vector Doppler effect. 
     2. Description of the Related Art 
     Ultrasound diagnosis apparatuses transmit ultrasound signals from a surface of a human body to be diagnosed toward a predetermined part in the inside of the human body and obtain images related to a cross-section of soft tissue or blood flow by using information regarding ultrasound signals reflected from the predetermined portion. 
     Ultrasound diagnosis apparatuses have various advantages, including a compact size, low cost, and real-time display. Also, ultrasound diagnosis apparatuses have excellent stability because there is no fear of X-ray exposure, and thus, the ultrasound diagnosis apparatuses are commonly used together with other diagnosis apparatuses, such as computerized tomography (CT) scanners, magnetic resonance imaging (MRI) apparatuses, nuclear medicine diagnosis apparatuses, or the like. 
     General ultrasound diagnosis apparatuses may detect a velocity of blood flow by using the Doppler effect. However, the velocity of blood flow cannot be precisely measured due to the limitation of angle dependency. 
       FIG. 1  is a diagram for describing angle dependency of a general ultrasound diagnosis apparatus. 
     Referring to  FIG. 1 , a transducer may transmit (a direction {circle around (0)}) an ultrasound signal, and receive (a direction {circle around (2)}) an ultrasound response signal reflected from a target. In this regard, in a case where a movement direction of blood flow is a direction {circle around (3)}, the general ultrasound diagnosis apparatus may not detect that the blood flow precisely moves in the direction {circle around (3)} due to the limitation of angle dependency. However, the general ultrasound diagnosis apparatus may merely detect that the blood flow moves far away or closer from the transducer. That is, the transducer may recognize only a direction {circle around (4)} that is an orthogonal component from among movement directions of the blood flow to detect only that the blood flow moves far away from the transducer. 
     Meanwhile, the general ultrasound diagnosis apparatus may not detect a movement of a cardiac muscle that moves left and right with respect to the transducer due to the angle dependency, and thus the general ultrasound diagnosis apparatus may detect instead a movement of a cardiac valve that moves up and down. 
     Therefore, an ultrasound diagnosis apparatus for intuitively obtaining a movement direction and velocity of a cardiac muscle without the limitation of angle dependency is needed. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for obtaining a movement direction and velocity of a tissue included in a target by using the vector Doppler effect. 
     According to an aspect of the present invention, there is provided a method of obtaining a movement velocity and direction of a tissue, the method including: 
     obtaining vector Doppler data from a target by transmitting and receiving an ultrasound signal; and detecting the movement velocity and direction of the tissue included in the target based on the obtained vector Doppler data. 
     The detecting of the movement velocity and direction of the tissue may include: generating frequency spectrum information regarding the obtained vector Doppler data; extracting a clutter signal generated by the tissue based on the generated frequency spectrum information; and detecting the movement velocity and direction of the tissue by using the extracted clutter signal. 
     The detecting of the movement velocity and direction of the tissue may include: displaying the detected movement velocity and direction of the tissue. 
     The detecting of the movement velocity and direction of the tissue may further include: calculating the movement velocity and direction of the tissue by using frequencies of at least two clutter signals included in the vector Doppler data. 
     The extracting of the clutter signal may include: setting a cutoff frequency used to separate a frequency of a blood signal and a frequency of the clutter signal based on the generated frequency spectrum information; and extracting the clutter signal from the vector Doppler data by using a low band filter having the set cutoff frequency. 
     The extracting of the clutter signal may further include: calculating a gain value based on the frequency spectrum information in such a way that the maximum power of the blood signal has a predetermined value; and extracting the clutter signal by applying the calculated gain value to the vector Doppler data. 
     The calculated gain value may be greater than 0 and smaller than 1. 
     The method may further include: compensating for the extracted clutter signal by using a reciprocal of the calculated gain value. 
     The displaying may include: displaying the movement velocity and direction of the tissue as a two-dimensional (2D) image or a tree-dimensional (3D) image. 
     The displaying may include: displaying the movement velocity and direction of the tissue in at least one form of colors, particles, and arrows. 
     The transmission and reception of the ultrasound signal may include at least one of plane wave transmission and reception, focused transmission and reception, scan line transmission and reception, broad beam transmission and reception, and zone based transmission and reception. 
     According to another aspect of the present invention, there is provided an apparatus for obtaining a movement velocity and direction of a tissue, the apparatus including: a data obtaining unit for obtaining vector Doppler data from a target by transmitting and receiving an ultrasound signal; a detecting unit for detecting the movement velocity and direction of the tissue included in the target based on the obtained vector Doppler data; and a control unit for controlling the data obtaining unit and the detecting unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a diagram for describing angle dependency of a general ultrasound diagnosis apparatus; 
         FIG. 2  is a block diagram of an apparatus for obtaining a movement velocity and direction of a tissue according to an embodiment of the present invention; 
         FIG. 3  is a flowchart of a method of detecting a movement velocity and direction of a tissue, according to an embodiment of the present invention; 
         FIG. 4  is a flowchart of a method of detecting a movement velocity and direction of a tissue, according to another embodiment of the present invention; 
         FIG. 5  is a graph for describing a method of extracting a clutter signal generated by a tissue by using a low band filter, according to an embodiment of the present invention; 
         FIG. 6  is a graph for describing a method of extracting a clutter signal generated by a tissue by using a gain value, according to an embodiment of the present invention; 
         FIG. 7  is a diagram for describing a method of obtaining a vector component of a tissue, according to an embodiment of the present invention; 
         FIG. 8  is a diagram for describing a method of obtaining a vector component of a tissue, according to an embodiment of the present invention; and 
         FIG. 9  is a diagram for describing a method of a movement velocity and direction of a cardiac muscle, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Most of the terms used herein are general terms that have been widely used in the technical art to which the present invention pertains. However, some of the terms used herein may be created reflecting intentions of technicians in this art, precedents, or new technologies. Also, some of the terms used herein may be arbitrarily chosen by the present applicant. In this case, these terms are defined in detail below. Accordingly, the specific terms used herein should be understood based on the unique meanings thereof and the whole context of the present invention. 
     In the present specification, it should be understood that the terms, such as ‘including’ or ‘having,’ etc., are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof disclosed in the specification, and are not intended to preclude the possibility that one or more other features, numbers, steps, actions, components, parts, or combinations thereof may exist or may be added. Also, the terms, such as ‘unit’ or ‘module’, etc., should be understood as a unit that processes at least one function or operation and that may be embodied in a hardware manner, a software manner, or a combination of the hardware manner and the software manner. 
     Throughout the specification, the ‘target’ may be understood to be part of a human body. For example, the target may be the liver, the heart, the womb, a brain, the breast, or the abdomen, or a fetus. 
     Throughout the specification, the term ‘user’ may be a medical professional, e.g., a doctor, a nurse, a clinical pathologist, or a medical imaging professional, but is not limited thereto. 
     Throughout the specification, a difference between a frequency of an ultrasound signal transmitted to the target and a frequency of an echo signal is referred to as a “Doppler frequency”. Further, a signal having the Doppler frequency is referred to as a “Doppler signal”. 
     In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. 
     As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
       FIG. 2  is a block diagram of an apparatus  100  for obtaining a movement velocity and direction of a tissue according to an embodiment of the present invention. 
     The apparatus  100  for obtaining the movement velocity and direction of the tissue (hereinafter referred to as the “obtaining apparatus  100 ”) according to an embodiment of the present invention may mean a device capable of obtaining an ultrasound image or a vector Doppler image from a target by using ultrasound waves, and displaying the obtained ultrasound image or vector Doppler image to a user. 
     The obtaining apparatus  100  according to an embodiment of the present invention may be implemented in various ways. For example, the obtaining apparatus  100  described in the present specification may be implemented in a mobile terminal as well as a fixable terminal. Examples of the mobile terminal may include a laptop computer, a PDA, a table PC, and the like. 
     The obtaining apparatus  100  according to an embodiment of the present invention may include a data obtaining unit  110 , a frequency converting unit  120 , a detecting unit  130 , a display unit  140 , and a control unit  150 . However, the elements of  FIG. 2  are not indispensable elements. The obtaining apparatus  100  may include a greater number of elements or a lesser number of elements. 
     The data obtaining unit  110  may transmit an ultrasound signal to the target. Also, the data obtaining unit  110  may receive an ultrasound response signal from the target. That is, the data obtaining unit  110  according to an embodiment of the present invention may include a transmitting and receiving unit that transmits and receives the ultrasound signal. An example of the data obtaining unit  110  according to an embodiment of the present invention may include a transducer. 
     Transmission and reception of the ultrasound signal according to an embodiment of the present invention may include plane wave transmission and reception, focused transmission and reception, scan line transmission and reception, broad beam transmission and reception, and zone based transmission and reception. However, the transmission and reception of the ultrasound signal according to an embodiment of the present invention is not limited thereto. 
     The data obtaining unit  110  may transmit the ultrasound signal and vector Doppler data from the target. The target according to an embodiment of the present invention may include blood flow and a tissue. 
     The vector Doppler data according to an embodiment of the present invention may mean Doppler data including a movement direction component of the target. That is, vector Doppler data according to an embodiment of the present invention may include data regarding Doppler signals received from at least two Doppler angles. 
     The vector Doppler data according to an embodiment of the present invention may include a blood signal generated by the blood flow and a clutter signal generated by the tissue. In this case, according to an embodiment of the present invention, the vector Doppler data may include a plurality of blood signals and a plurality of clutter signals. 
     The frequency converting unit  120  may generate frequency spectrum information regarding the received vector Doppler data. According to an embodiment of the present invention, the frequency converting unit  120  may generate the frequency spectrum information regarding the received vector Doppler data by using the Fourier transformation. 
     The frequency spectrum information according to an embodiment of the present invention may include power values (intensity of signals) with respect to frequencies of the blood signal and the clutter signal. 
     A velocity of the blood flow is relatively faster than that of the tissue, and thus the blood signal generated by the blood flow is located in a high frequency band, and the clutter signal generated by the tissue is located in a low frequency band. 
     Also, reflectivity of the blood flow is generally quite smaller than that of tissues around the blood flow, and thus the intensity of the clutter signal generated by the tissue is higher than that of the blood signal generated by the blood flow. 
     The detecting unit  130  may detect a movement velocity and direction of the tissue based on the vector Doppler data. The movement velocity of the tissue according to an embodiment of the present invention may mean the size of a velocity generated by the movement of the tissue. The movement direction of the tissue according to an embodiment of the present invention may mean the direction of the velocity generated by the movement of the tissue. 
     The detecting unit  130  may extract the clutter signal generated by the tissue based on the generated frequency spectrum information, and detect the movement velocity and direction of the tissue by using the extracted clutter signal. For example, the detecting unit  130  may classify the blood signal and the clutter signal by using the frequency spectrum information of the vector Doppler frequency. 
     According to an embodiment of the present invention, the detecting unit  130  may classify the blood signal and the clutter signal by using a low band filter. The low band filter may have a cutoff frequency set based on the frequency spectrum information. 
     The blood signal generated by the blood flow is located in the high frequency band, and the clutter signal generated by the tissue is located in the low frequency band, and thus the detecting unit  130  may extract the clutter signal generated by the tissue by using the low band filter. 
     According to another embodiment of the present invention, the detecting unit  130  may classify the blood signal and the clutter signal by using a gain value of the vector Doppler data. For example, the detecting unit  130  may calculate the gain value in such a way that the maximum power of the blood signal generated by the blood flow has a predetermined value. According to an embodiment of the present invention, the predetermined value may be “0”. 
     In general, power of the clutter signal generated by the tissue is greater than that of the blood signal generated by the blood flow, and thus the detecting unit  130  may extract the clutter signal generated by the tissue by using the calculated gain value after the power of the blood signal generated by the blood flow is closer to “0”. 
     The detecting unit  130  may obtain the movement velocity and direction of the tissue by using the detected clutter signal generated by the tissue. As described above, the vector Doppler data may include a plurality of clutter signals received from different directions. 
     Therefore, the detecting unit  130  may calculate the movement velocity and direction of the tissue based on frequencies of at least two clutter signals. A method of calculating the movement velocity and direction of the tissue will be described in detail with reference to  FIG. 7 . 
     The display unit  140  may display and output information processed by the obtaining apparatus  100 . For example, the display unit  140  may display the movement velocity and direction of the tissue. In this case, the display unit  140  may overlay and display the movement velocity and direction of the tissue on an ultrasound image of the target. 
     The ultrasound image according to an embodiment of the present invention may be an image generated through at least one of a brightness (B) mode, a color (C) mode, a motion (M) mode, a pulse-wave (PW) mode, a continuous wave (CW) mode, a two-dimensional (2D) mode, and a three-dimensional (3D) mode. 
     Meanwhile, the display unit  140  may display the movement velocity and direction of the tissue as a 2D image or a 3D image. The display unit  140  may display the movement velocity and direction of the tissue in at least one form of colors, particles, and arrows. 
     In a case where the display unit  140  and a touch pad form a mutual layer structure and thus are configured as a touch screen, the display unit  140  may be used as an input device other than an output device. The display unit  140  may include at least one of a liquid crystal display (LCD), a thin film transistor-liquid crystal display (TFT-LCD), an organic light-emitting diode (OLED), a flexible display, and a 3D display. 
     The obtaining apparatus  100  may also include two or more display units  140 . The touch screen may be configured to detect a touch input pressure as well as a touch input location and a touched area. The touch screen may also be configured to detect a proximity touch as well as a real touch. 
     The control unit  150  may generally control the data obtaining unit  110 , the frequency converting unit  120 , the detecting unit  130 , and the display unit  140 . 
     According to an embodiment of the present invention, the control unit  150  may set the cutoff frequency used to separate the frequency of the blood signal and the frequency of the clutter signal based on the frequency spectrum information generated by the frequency converting unit  120 . 
     The control unit  150  may calculate the gain value in such a way that the maximum power of the blood signal generated by the blood flow has the predetermined value based on the frequency spectrum information generated by the frequency converting unit  120 . 
     Meanwhile, the control unit  150  may compensate for the clutter signal extracted by applying the calculated gain value. In this regard, the control unit  150  compensates for the extracted clutter signal by using a reciprocal number of the calculated gain value. 
     The obtaining apparatus  100  according to an embodiment of the present invention may transmit and receive unfocused beam. In a case where focused beam is generally used, the obtaining apparatus  100  needs to transmit the focused beam for each scan line, which increases an amount of calculation. However, the obtaining apparatus  100  according to an embodiment of the present invention uses the unfocused beam, which reduces the amount of calculation, thereby detecting the movement velocity and direction of the tissue in real time. 
     A method of detecting the movement velocity and direction of the tissue by using each element of the obtaining apparatus  100  will be described in detail with reference to  FIG. 3 . 
       FIG. 3  is a flowchart of a method of detecting a movement velocity and direction of a tissue, according to an embodiment of the present invention. 
     Referring to  FIG. 3 , the method of detecting the movement velocity and direction of the tissue according to an embodiment of the present invention includes operations that are time-serially processed by the obtaining apparatus  100  shown in  FIG. 2 . Therefore, although omitted, the above description of the obtaining apparatus  100  shown in  FIG. 2  also applies to the method shown in  FIG. 3 . 
     The obtaining apparatus  100  may transmit and receive an ultrasound signal and obtain vector Doppler data from a target (S 310 ). The target according to an embodiment of the present invention may include blood flow and a tissue. Thus, the vector Doppler data according to an embodiment of the present invention may include a blood signal generated by the blood flow and a clutter signal generated by the tissue. 
     The obtaining apparatus  100  may detect a movement velocity and direction of the tissue based on the obtained vector Doppler data (S 320 ). The movement velocity and direction of the tissue according to an embodiment of the present invention is information regarding a movement of the target. For example, if the target is a heart, the movement velocity and direction of the tissue may be the size of a velocity of the heart that contracts and relaxes and a direction thereof. 
     This will be described in more detail with reference to  FIG. 4 . 
       FIG. 4  is a flowchart of a method of detecting a movement velocity and direction of a tissue, according to another embodiment of the present invention. 
     Referring to  FIG. 4 , the method of detecting the movement velocity and direction of the tissue according to an embodiment of the present invention includes operations that are time-serially processed by the obtaining apparatus  100  shown in  FIG. 2 . Therefore, although omitted, the above description of the obtaining apparatus  100  shown in  FIG. 2  also applies to the method shown in  FIG. 4 . 
     The obtaining apparatus  100  may transmit an ultrasound signal to a target including blood flow and a tissue (S 410 ). In this case, the obtaining apparatus  100  obtains vector Doppler data generated by the target (S 420 ). The vector Doppler data according to an embodiment of the present invention may include a blood signal generated by the blood flow and a clutter signal generated by the tissue. 
     According to an embodiment of the present invention, the obtaining apparatus  100  may transmit a plurality of ultrasound signals having different transmission angles to the target and receive a plurality of echo signals having different receiving angles from the target. According to another embodiment of the present invention, the obtaining apparatus  100  may transmit one ultrasound signal to the target and receive a plurality of echo signals having different receiving angles from the target. 
     The obtaining apparatus  100  may generate frequency spectrum information regarding the vector Doppler data (S 430 ). The frequency spectrum information according to an embodiment of the present invention may indicate correlations between frequencies of the “blood signal and the clutter signal” and intensities thereof. 
     The frequency spectrum information according to an embodiment of the present invention may be expressed as shown in  FIG. 5 . Referring to  FIG. 5 , an X axial direction may indicate frequency components of a clutter signal  510  and a blood signal  520 , and a Y axial direction may indicate power value (intensities of signals) component of the clutter signal  510  and the blood signal  520 . 
     The obtaining apparatus  100  may extract the clutter signal generated by the tissue by classifying the clutter signal and the blood signal based on the frequency spectrum information (S 440 ). 
     According to an embodiment of the present invention, the obtaining apparatus  100  may extract the clutter signal by using a low band filter. This will be described with reference to  FIG. 5 . 
       FIG. 5  is a graph for describing a method of extracting a clutter signal generated by a tissue by using a low band filter, according to an embodiment of the present invention. 
     As shown in  FIG. 5 , a velocity of blood flow is relatively quite faster than that of the tissue, and thus the blood signal  520  generated by the blood flow is located in a high frequency band, and the clutter signal  510  generated by the tissue is located in a low frequency band. In this case, the obtaining apparatus  100  may set a cutoff frequency used to detect the clutter signal based on the frequency spectrum information. That is, the obtaining apparatus  100  may set the cutoff frequency suitable for removing the blood signal  520  generated by the blood flow that is present in the high frequency band. For example, the cutoff frequency may be x in  FIG. 5 . 
     In this case, the obtaining apparatus  100  may detect the clutter signal by applying the low band filter having the set cutoff frequency to the vector Doppler data. 
     According to another embodiment of the present invention, the obtaining apparatus  100  may extract the clutter signal by adjusting a gain value of the vector Doppler data. This will be described with reference to  FIG. 6 . 
       FIG. 6  is a graph for describing a method of extracting a clutter signal generated by a tissue by using a gain value, according to an embodiment of the present invention. 
     In general, reflectivity of blood flow is quite smaller than that of tissues (vessel walls, muscle, etc.) around the blood flow, and thus the intensity of the clutter signal generated by the tissue is mostly higher than that of a blood signal generated by the blood flow. 
     That is, referring to  FIG. 6 , according to frequency spectrum information, power of a clutter signal  610  generated by the tissue is much greater than that of a blood signal  620  generated by the blood flow. 
     Thus, the obtaining apparatus  100  may calculate the gain value in such a way that the maximum power of the blood signal  620  has a predetermined value. According to an embodiment of the present invention, the predetermined value may be closer to “0”. Also, the gain value may be greater than 0 and smaller than 1. 
     That is, the obtaining apparatus  100  may extract the clutter signal  610  by applying the gain value that makes the maximum power of the blood signal  620  closer to “0” to vector Doppler data. 
     For example, in a case where the maximum power of the blood signal  620  has a value “a”, and the maximum power of the clutter signal  610  has a value “b”, the obtaining apparatus  100  may calculate the gain value “0.0001” that makes the value “a” of the maximum power of the blood signal  620  closer to “0”. If the gain value “0.0001” is applied to the vector Doppler data, the maximum power of the blood signal  620  is a×0.0001(L0) closer to “0”, and the maximum power of the clutter signal  610  is b×0.0001(L0) much greater than “0”. Thus, the obtaining apparatus  100  may extract the clutter signal  610  generated by the blood flow. 
     Meanwhile, the obtaining apparatus  100  may compensate for a gain with respect to the clutter signal detected by adjusting the gain value. That is, the obtaining apparatus  100  may compensate for a power value of the clutter signal by using a reciprocal of the calculated gain value. 
     For example, in a case where the calculated gain value is “0.0001”, since the maximum power value of the detected clutter signal is b×0.0001, if the reciprocal “10000(1/0.0001)” of the calculated gain value is applied to the detected clutter signal, the maximum power value of the detected clutter signal is “b”. 
     Referring back to  FIG. 3 , the obtaining apparatus  100  may obtain the movement velocity and direction of the tissue by using the detected clutter signal (S 450 ). The vector Doppler data according to an embodiment of the present invention may include a plurality of clutter signals having different receiving angles. 
     Therefore, the obtaining apparatus  100  may calculate the movement velocity and direction of the tissue based on frequencies of the plurality of clutter signals. This will be described with reference to  FIGS. 7 and 8 . 
       FIG. 7  is a diagram for describing a method of obtaining a vector component of a tissue, according to an embodiment of the present invention. 
     The data obtaining unit  110  transmits a first ultrasound signal S 1  and a second ultrasound signal S 2  to a tissue P of a target. The tissue P moves in a direction A as a velocity vector  . Frequencies of the first ultrasound signal S 1  and the second ultrasound signal S 2  vary according to the tissue P moving in the direction A. Thus, the data obtaining unit  110  receives an echo signal having a changed frequency. 
       FIG. 8  is a diagram for describing a method of obtaining a vector component of the tissue P, according to an embodiment of the present invention. 
     If the velocity vector   of the tissue P is projected in a vertical direction, velocity vectors    1  and    2  may be obtained. The first ultrasound signal S 1  is reflected by the tissue P and is transmitted to the data obtaining unit  110 . A clutter signal generated at this time corresponds to the velocity vector    1 . Also, the second ultrasound signal S 2  is reflected by the tissue P and is transmitted to the data obtaining unit  110 . A clutter signal generated at this time corresponds to the velocity vector    2 . 
     In a case where an angle difference between a y axis and the velocity vector    1  is θ 1 , and an angle difference between the y axis and the velocity vector    2  is θ 2 , equations regarding the velocity vectors    1  and    2  are as follows. 
       Regarding    1 ,  y =tan θ1· x    [Equation 1]
 
       Regarding    2 ,  y    32  tan θ2· x    [Equation 2]
 
     In a case where velocities of the velocity vectors    1  and    2  are v 1  and v 2 , respectively, first dimensional vertical lines w 1  and w 2  in perpendicular to the velocity vectors   1  and    2  respectively, are as follows: 
       Regarding  w 1,  y =−(1/tan  74  1) x+v 1/cos θ1   [Equation 3]
 
       Regarding  w 2,  y =−(1/tan θ2) x+v 2/cosθ2   [Equation 4]
 
     The following equation between the velocities v 1  and v 2  and Doppler frequencies regarding the first ultrasound signal S 1  and the second ultrasound signal S 2  transmitted from the data obtaining unit  110  is obtained. 
         vn =(   fn/f )· c    [Equation 5]
 
     In Equation 5 above,  fn denotes a Doppler frequency, f denotes frequencies of the first ultrasound signal S 1  and the second ultrasound signal S 2 , c denotes a sound velocity of the first ultrasound signal S 1  and the second ultrasound signal S 2 , and n denotes an integer. 
     Although the frequencies of the first ultrasound signal S 1  and the second ultrasound signal S 2  transmitted to the tissue P has opposite directions, since the frequencies are transmitted in different directions having the same size angle, the following equations between θ 1  and θ 2  are as follows. 
       θ1=π−θ2   [Equation 6]
 
       cos θ1=−cos θ2   [Equation 7]
 
       tan θ1=−tan θ2   [Equation 8]
 
     If an intersection point of Equations 3 and 4 by using Equations 6, 7, and 8 is calculated, the following equations are obtained. 
     
       
         
           
             
               
                 
                   x 
                   = 
                   
                     
                       
                         
                           v 
                           1 
                         
                         + 
                         
                           v 
                           2 
                         
                       
                       2 
                     
                      
                     
                       
                         sin 
                          
                         
                             
                         
                          
                         
                           θ 
                           2 
                         
                       
                       
                         
                           cos 
                           2 
                         
                          
                         
                           θ 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     9 
                   
                   ] 
                 
               
             
             
               
                 
                   y 
                   = 
                   
                     
                       
                         v 
                         2 
                       
                       - 
                       
                         v 
                         1 
                       
                     
                     
                       2 
                        
                       cos 
                        
                       
                           
                       
                        
                       
                         θ 
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     10 
                   
                   ] 
                 
               
             
           
         
       
     
     In equations 9 and 10 above, x and y denote coordinates of A. 
     If a velocity v of the velocity vector   and an angle φ of the y axis is calculated by using Equations 9 and 10, the following equations are obtained. 
     
       
         
           
             v 
             = 
             
               
                  
                 
                   v 
                   ⇀ 
                 
                  
               
               = 
               
                 
                   
                     x 
                     2 
                   
                   + 
                   
                     y 
                     2 
                   
                 
               
             
           
         
       
       
         
           
             φ 
             = 
             
               
                 tan 
                 
                   - 
                   1 
                 
               
                
               
                 y 
                 x 
               
             
           
         
       
     
     The obtaining apparatus  100  may obtain a movement velocity and direction of the tissue P by using the calculated velocity v of the velocity vector   and the angle φ. 
     Referring back to  FIG. 3 , the obtaining apparatus  100  may display the movement velocity and direction of the tissue P on an ultrasound image of the target (S 460 ). According to an embodiment of the present invention, the obtaining apparatus  100  may display the movement velocity and direction of the tissue P as a two-dimensional (2D) image or a three-dimensional (3D) image. The obtaining apparatus  100  may display the movement velocity and direction of the tissue P in at least one form of colors, particles, and arrows. 
     Therefore, according to an embodiment of the present invention, the obtaining apparatus  100  may precisely detect sizes of the movement direction of velocity of the tissue P without being influenced by angle dependency, and provide a user with the movement velocity and direction of the tissue P. 
       FIG. 9  is a diagram for describing a method of a movement velocity and direction of a cardiac muscle, according to an embodiment of the present invention. 
     Referring to  FIG. 9 , even if a user sets sample volume including a tissue (for example, a cardiac muscle) and blood flow, the obtaining apparatus  100  may identify only a clutter signal generated by the tissue (for example, the cardiac muscle) by adjusting a low band filter or a gain value. 
     The obtaining apparatus  100  also may calculate a movement velocity and direction of the tissue by using frequencies of a plurality of clutter signals generated by the tissue. 
     Therefore, the obtaining apparatus  100  may display the movement velocity and direction of the tissue on an ultrasound image to the user. That is, according to an embodiment of the present invention, the obtaining apparatus  100  may intuitively present sizes of the movement direction of velocity of the tissue without the limitation of angle dependency. 
     Embodiments of the present invention include a computer-readable recording medium including program commands for executing operations implemented through various computers. The computer-readable recording medium can store program commands, data files, data structures, or combinations thereof. The program commands recorded in the computer-readable recording medium may be specially designed and configured for the present invention or be known to those of ordinary skill in the field of computer software. Examples of a computer-readable recording medium include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, or hardware devices such as ROMs, RAMs, and flash memories, which are specially configured to store and execute program commands. Examples of the program commands include a machine language code created by a compiler and a high-level language code executable by a computer using an interpreter and the like. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.