Abstract:
Embodiments forming an ultrasound image by adjusting a steering angle of scan lines using virtual transducer elements in an ultrasound system are disclosed herein. In one embodiment, a processing unit forms a first ultrasound image by using the ultrasound data, which may be acquired based on first scan lines steered at a first steering angle. The processing unit determines a center of the target object on the first ultrasound image. A control unit defines virtual transducer elements associated with an array transducer, defines second scan lines and computes a second steering angle of the second scan lines based on the virtual transducer elements and the center of the target object. An ultrasound data acquisition unit forms second ultrasound data based on the second scan lines steered at the second steering angle. The processing unit forms a second ultrasound image by using the second ultrasound data.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from Korean Patent Application No. 10-2009-0081265 filed on Aug. 31, 2009, the entire subject matter of which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    Embodiments described herein generally relate to an ultrasound system, and more particularly to steering angle adjustment of scan lines using virtual transducer elements in an ultrasound system. 
       BACKGROUND 
       [0003]    An ultrasound system has been extensively used in the medical field due to its non-invasive and non-destructive nature. Modern high-performance ultrasound imaging diagnostic systems and techniques are commonly used to produce two-dimensional or three-dimensional ultrasound images of internal features of patients. 
         [0004]    The ultrasound system employs an ultrasound probe containing a transducer array for transmission and reception of ultrasound signals. The ultrasound signals are transmitted along scan lines aligned with the direction of a scan head of the ultrasound probe. The ultrasound system forms ultrasound images based on the received ultrasound signals. Recently, the technique of transmitting the ultrasound signals by steering the scan lines has been used to obtain an ultrasound image having a wider view angle. In this case, however, since the length of the transducer array is fixed, the maximum steering angle may be limited. 
       SUMMARY 
       [0005]    Embodiments for forming an ultrasound image by adjusting a steering angle of scan lines using virtual transducer elements in an ultrasound system are disclosed herein. In one embodiment, by way of non-limiting example, an ultrasound system comprises: an ultrasound data acquisition unit configured to transmit ultrasound signals to a target object along first scan lines steered at a first steering angle and receive echo signals reflected from the target object to form first ultrasound data, the ultrasound data acquisition unit including an array transducer containing a plurality of transducer elements; a processing unit configured to form a first ultrasound image by using the first ultrasound data and determine a center of the target object on the first ultrasound image; and a control unit configured to define virtual transducer elements associated with the array transducer, define second scan lines and compute a second steering angle of second scan lines based on the virtual transducer elements and the center of the target object, wherein the ultrasound data acquisition unit is further configured to transmit ultrasound signals to the target object along the second scan lines steered at the second steering angle and receive echo signals reflected from the target object to form second ultrasound data, and wherein the processing unit is further configured to form a second ultrasound image by using the second ultrasound data. 
         [0006]    In another embodiment, there is provided a method of forming an ultrasound image by adjusting a steering angle of scan lines using virtual transducer elements in an ultrasound system having an array transducer containing a plurality of transducer elements, comprising: a) transmitting ultrasound signals to a target object along first scan lines originating from a first aperture including predetermined transducer elements and steered at a first steering angle, and receiving echo signals reflected from the target object to form first ultrasound data; b) forming a first ultrasound image by using the first ultrasound data and determining a center of the target object on the first ultrasound image; c) defining virtual transducer elements associated with the array transducer, defining second scan lines and computing a second steering angle of the second scan lines based on the virtual transducer elements and the center of the target object; d) transmitting ultrasound signals along the second scan lines originating from a second aperture including the predetermined transducer elements and the virtual transducer elements and steered at the second steering angle into the target object, and receiving echo signals reflected from the target object to form second ultrasound data; and e) forming a second ultrasound image by using the second ultrasound data. 
         [0007]    The Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in determining the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a block diagram showing an illustrative embodiment of an ultrasound system. 
           [0009]      FIG. 2 . is a block diagram showing an illustrative embodiment of an ultrasound data acquisition unit. 
           [0010]      FIG. 3  is a block diagram showing an illustrative embodiment of a process of forming an ultrasound image by adjusting a steering angle using virtual transducer elements. 
           [0011]      FIG. 4  is a schematic diagram showing scan lines extending from an aperture of an array transducer and steered at a predetermined steering angle. 
           [0012]      FIG. 5  is a schematic diagram showing an embodiment of determining a center of a target object by defining a region of interest on an ultrasound image. 
           [0013]      FIG. 6  is a schematic diagram showing an embodiment of determining a center of a target object by using a seed point on an ultrasound image. 
           [0014]      FIG. 7  is a schematic diagram showing an embodiment of determining a steering angle of scan lines by using virtual transducer elements. 
           [0015]      FIG. 8  is a schematic diagram showing an embodiment of performing receive focusing upon receive signals. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    A detailed description may be provided with reference to the accompanying drawings. One of ordinary skill in the art may realize that the following description is illustrative only and is not in any way limiting. Other embodiments of the present invention may readily suggest themselves to such skilled persons having the benefit of this disclosure. 
         [0017]    Referring to  FIG. 1 , an ultrasound system  100  constructed in accordance with one embodiment is shown. The ultrasound system  100  may include a user input unit  110  configured to receive user instructions. The user instructions may include a first user instruction to define a region of interest (ROI) and a second user instruction to select a seed point. The user input unit  110  may be a mouse, a keyboard, a track ball, a touch screen and the like. The ultrasound system  100  may further include a storage unit  120  for storing templates for use to detect an image of a target object (e.g., vessel) in an ultrasound image. 
         [0018]    The ultrasound system  100  may further include an ultrasound data acquisition unit  130 . The ultrasound data acquisition unit  130  may be configured to transmit ultrasound beams to a target object and receive ultrasound echoes reflected from the target object to thereby form ultrasound data representative of the target object. 
         [0019]    Referring to  FIGS. 2 and 4 , the ultrasound data acquisition unit  130  may include an ultrasound probe  132  having an array transducer  132 A. The array transducer  132 A contains a plurality of transducer elements that may be operable to transmit ultrasound beams along scan lines, which may be aligned from a scan head of the ultrasound probe  132  to the target object. The scan lines may be steered at one of multiple angles relative to the scan head of the ultrasound probe  132 . The ultrasound probe  132  may include any one of a linear probe, a convex probe and the like. 
         [0020]    In one embodiment, the transmission of the ultrasound beams may be controlled by a transmission (Tx) pulse generating section  134 , which is coupled to the ultrasound probe  132 . The Tx pulse generating section  134  may include a plurality of pulsers to generate Tx pulses, which are delivered to the transducer elements of the array transducer  132 A for actuation thereof. The Tx pulse generating section  134  may be further operable to apply delays to the Tx pulses to form a Tx pattern, with which to control the actuation of the transducer elements. In one embodiment, the delays applied to the Tx pulses may be determined by considering virtual transducer elements, which may be virtually formed and extended from one of the edges of the array transducer  132 A in a longitudinal direction of the array transducer  132 A. In this way, the ultrasound beam may be transmitted at a predetermined steering angle. The transducer elements of the ultrasound probe  132  may receive ultrasound echoes reflected from the target object and then output electrical receive signals, which may be analog signals. 
         [0021]    The ultrasound data acquisition unit  130  may further include a beam forming section  136 , which is coupled to the ultrasound probe  132 . The beam forming section  136  may be operable to digitize the electrical receive signals to obtain digital signals. The beam forming section  136  may be further operable to apply delays to the digital signals in consideration of distances between the elements of the ultrasound probe  132  and focal points and the steering angles of the scan lines. The beam forming section  136  may be further operable to sum the delayed digital signals to form receive-focused beams. The beam forming section  136  may be also operable to perform compensation processing upon the receive-focused beams by considering virtual transducer elements. In one embodiment, the compensation processing may include scan line gain compensation and time gain compensation. 
         [0022]    The ultrasound data acquisition unit  130  may further include an ultrasound data forming section  138 , which is coupled to the beam forming section  136 . The ultrasound data forming section  138  may be operable to form ultrasound data based on the receive-focused beams. The ultrasound data may include radio frequency data, In-phase/Quadrature data and the like. 
         [0023]    The ultrasound system  100  may further include an ultrasound image forming unit  140 , which may be coupled to the ultrasound data forming section  138 , for example, via a control unit  160 . The ultrasound image forming unit  140  may be operable to form ultrasound images based on the ultrasound data. In one embodiment, the ultrasound images may include a brightness-mode (B-mode) image, although they are not limited thereto. 
         [0024]    The ultrasound system  100  may further include an image processing unit  150 , which may be coupled to the ultrasound image forming unit  140 , for example, via the control unit  160 . The image processing unit  150  may be operable to detect a center of the target object (e.g., vessel), which constitutes the main part of the ultrasound image. The center detection may be achieved by using the vessel template stored in the storage unit  120  or based on the user instruction. 
         [0025]    The ultrasound system  100  may further include a control unit  160 , which is coupled to elements of the ultrasound system  100  such as the user input unit  110 , the storage unit  120 , the ultrasound acquisition unit  130 , the image forming unit  140  and the image processing unit  150 . The control unit  160  may be responsive to the user instruction to issue first control signals to control the operations of elements of the ultrasound system  100 . The control unit  160  may be further operable to issue second control signals to form the virtual transducer elements, detect the vessel center and define a steering angle of scan lines. 
         [0026]    In the embodiment explained above, it has been described that the ultrasound image forming unit  140 , the image processing unit  150  and the control unit  160  are configured with separate elements in the ultrasound system  100 . However, these components may be embodied with a single processor such as a central processing unit, a microprocessor, a graphic processing unit, application-specific integrated circuit and the like. 
         [0027]    The ultrasound system may further include a display unit  170  for displaying the ultrasound images such as the elastic images, the B-mode images, the compound images and the like. In one embodiment, the display unit  170  may include at least one of a cathode ray tube (CRT) display, a liquid crystal display (LCD), an organic light emitting diode (OLED) display and the like. 
         [0028]    Hereinafter, a process of forming an ultrasound image by adjusting a steering angle of scan lines based on the virtual transducer elements will be explained by referring to the figures. Referring to  FIG. 3 , the ultrasound data acquisition unit  130  may be operable to transmit ultrasound signals to a target object and receive echo signals, thereby acquiring first ultrasound data at A 102 . More particularly, the Tx signal generating section  134  may be operable to apply Tx signals by considering transducer elements included in a predetermined aperture (“first aperture AP 1 ”) and predetermined focal points to thereby output first Tx signals, as shown in  FIG. 4 . The aperture may represent a range of transducer elements, which may substantially participate in transmission and reception of the ultrasound signals. In  FIG. 4 , a symbol “V” may represent a target object image, i.e., a vessel image in the ultrasound image and symbols S 1 -S N  may represent scan lines originating from the first aperture AP 1 . 
         [0029]    The ultrasound probe  132  may be operable to transmit ultrasound signals to the target object in response to the first Tx signals. It may then receive echo signals to thereby form first receive signals. The beam forming section  136  may be operable to focus the first receive signals in consideration of the transducer elements within the first aperture AP 1  and the predetermined focal points to form first receive-focused beams. The ultrasound data forming section  138  may be operable to form first ultrasound data by using the first receive-focused beams. 
         [0030]    The image forming unit  140  may be operable to form a first ultrasound image based on the first receive-focused beams at A 104 . The first ultrasound image may be displayed on a screen of the display unit  170 . The image processing unit  150  may be operable to detect the vessel in the first ultrasound image at A 106  and then detect a center of the vessel at A 108 . 
         [0031]    In one embodiment, the image processing unit  150  may be operable to extract a vessel template from the storage unit  120 . The image processing unit  150  may be operable to position the extracted vessel template on the first ultrasound image and move the vessel template to detect the vessel in the first ultrasound image. The vessel detection may be carried out by using a well-known method such as pattern patting (matching), sum of absolute difference and the like. The image processing unit  150  may be operable to detect a maximum diameter from the detected vessel and define a center of the maximum diameter as a center of the vessel. 
         [0032]    In one embodiment, if a first user instruction for defining a region of interest is inputted through the user input unit  110 , then the image processing unit  150  may be operable to indicate a region of interest  230  on an ultrasound image  210 , as shown in  FIG. 5 . The image processing unit  150  may be operable to determine a center of the region of interest  230  and indicate the determined center of the region of interest  230  as a point  240  on the ultrasound image  210 . The image processing unit  150  may be operable to move the center point  240  in up, down, right and left directions by predetermined distances to detect regions  251 - 254  having maximum brightness differences at the respective directions. The image processing unit  140  may determine the detected regions  251 - 254  as a vessel wall  220 . The image processing unit  150  may be operable to form a rectangle whose sides pass through the regions  251 - 254 . The image processing unit  150  may determine the center of the rectangle as a center of the vessel  220 . 
         [0033]    In one embodiment, if a second user instruction for defining a seed point is inputted through the user input unit  110 , then the image processing unit  150  may be operable to indicate a seed point  270  on the first ultrasound image  210 , as shown in  FIG. 6 . The image processing unit  150  may be operable to move the seed point  270  in up, down, right and left directions by predetermined distances to detect regions  281 - 284  having maximum brightness differences at each of the directions. The detected regions  281 - 284  may be determined as walls of the vessel  220 . The image processing unit  150  may be operable to form a rectangle, of which each side passes through the regions  281 - 284 . The image processing unit  150  may determine a center of the rectangle as the center of the vessel  220 . 
         [0034]    The control unit  160  may be operable to define a plurality of virtual transducer elements  132 B (denoted by dotted lines) from one of the edges of the array transducer  132 A in a longitudinal direction thereof, as show in  FIG. 7 , at A 110 . The virtual transducer elements may be defined manually by inputting a user instruction or automatically according to preset information stored in the ultrasound system  100 . The control unit  160  may be further operable to determine a second aperture AP 2  corresponding to the virtual transducer elements  132 B and a third aperture AP 3  including the first aperture AP 1  and the second aperture AP 2 , at A 112 . 
         [0035]    The control unit  160  may be operable to compute a center AP C  of the third aperture AP 3  at A 114  and define a scan line S C  originating from the center AP C  at A 116 . The control unit  160  may be operable to further compute a steering angle θ of the scan line S C , which passes the vessel center VC, at A 118 . This computed steering angel θ may be set as a maximum steering angle. 
         [0036]    The Tx pulse generating section  134  may be operable to generate Tx pulses. The Tx pulse generating section  134  may be further operable to apply delays to the Tx pulses in consideration of the positions of transducer elements within the third aperture AP 3 , a focal point (i.e., vessel center) and the steering angle θ computed at act A 118  to thereby output second Tx signals at A  120 . 
         [0037]    The ultrasound probe  132  may be operable to output ultrasound signals to the target object in response to the second Tx signals and receive echo signals reflected from the target object to thereby form second receive signals at A 122 . The beam forming section  136  may be operable to apply delays to the second receive signals by considering the positions of transducer elements within the third aperture AP 3 , a focal point and the steering angle θ to thereby form second receive-focused beams at A 124 . In one embodiment, the receive signals may include signals, which are outputted from the real transducer elements  132 A, and signals that are virtually outputted from the virtual transducer elements  132 B, as shown in  FIG. 8 . The beam forming section  136  may be further operable to perform scan line gain compensation upon the second receive-focused beams based on the virtual transducer elements  132 B at A 126 . In this way, a relatively low intensity of the second receive-focused beams due to the virtual transducer elements may be compensated. Further, the beam forming section  136  may be further operable to perform time gain compensation upon the second receive-focused beams for compensating for attenuation of the ultrasound signals. 
         [0038]    The ultrasound data forming section  138  may be operable to form second ultrasound data based on the second receive-focused beams provided from the beam forming section  136  at A 128 . The image forming unit  140  may be operable to form a second ultrasound image by using the second ultrasound data provided from the ultrasound data forming section  138  at A 130 . The display unit  170  may display the second ultrasound image, which may be provided from the image forming unit  140 , at A 132 . 
         [0039]    Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope of the principles of this disclosure. More particularly, numerous variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.