Patent Publication Number: US-2013231569-A1

Title: Medical ultrasound 2-d transducer array using fresnel lens approach

Description:
Embodiments described herein relate generally to an ultrasound probe and method of operating the same. 
     BACKGROUND 
     As illustrated in  FIG. 20 , a conventional ultrasound imaging system includes a processing unit  1 , a display unit  2 , a cable  3  and a transducer unit or ultrasound probe  4 . The probe  4  is connected to the processing unit  1  via the cable  3 . The processing unit  1  generally controls the transducer unit  4  for transmitting ultrasound pulses towards a region of interest in a patient and receiving the ultrasound echoes reflected from the patient. The processing unit  1  concurrently receives in real time the reflected ultrasound signals for further processing so as to display on the display unit  2  an image of the region of the interest. 
     In detail, the probe  4  further includes a predetermined number of transducer elements, which are grouped into channels for transmitting and receiving the ultrasound signals. For 2-dimensional (2D) imaging data, a number of elements ranges from 64 to 256. On the other hand, for 3-dimensional (3D) imaging data, a number of required channels often exceeds 1000&#39;s. In the above described conventional ultrasound imaging system, the probe  4  also houses a large number of electric components such as circuits and other components for controlling the transmission and reception of the ultrasound signals. In further detail, a transducer array of the probe includes the transducer array elements and the associated control circuitry to perform the generation of ultrasound pulses and the reception of the ultrasound echoes. 
     In general, the above described transducer array elements are shared transmit and receive elements that perform both transmit and receive functions within the same element. Because of the complex circuitries, the transducer arrays having the shared transmit and receive elements undesirably incur high costs and large power consumption among other things. To improve these disadvantages, prior art has attempted to separate the two functions in the transducer array elements. Although certain advantages have been gained by the dedicated transmit array elements and dedicated receive array elements, there remain some additional improvements to be made. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a first embodiment of the two-dimensional array in the probe according to the current invention. 
         FIG. 2  is a diagram illustrating a second embodiment of the two-dimensional array in the probe according to the current invention. 
         FIG. 3  is a diagram illustrating a third embodiment of the two-dimensional array in the probe according to the current invention. 
         FIG. 4  is a diagram illustrating a fourth embodiment of the two-dimensional array in the probe according to the current invention. 
         FIG. 5  is a diagram illustrating a fifth embodiment of the two-dimensional array in the probe according to the current invention. 
         FIG. 6  is a diagram illustrating a sixth embodiment of the two-dimensional array in the probe according to the current invention. 
         FIG. 7  is a diagram illustrating a seventh embodiment of the two-dimensional array in the probe according to the current invention. 
         FIG. 8  is a diagram illustrating an eighth embodiment of the two-dimensional array in the probe according to the current invention. 
         FIG. 9A  is a diagram illustrating an embodiment of the array that is substantially the same as the first embodiment as illustrated in  FIG. 1  and also illustrating a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
         FIG. 9B  is a diagram illustrating an embodiment of the array that is substantially the same as the second embodiment as illustrated in  FIG. 2  and also illustrating a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
         FIG. 9C  is a diagram illustrating an embodiment of the array that is substantially the same as the third embodiment as illustrated in  FIG. 3  and also illustrating a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
         FIG. 10A  is a diagram illustrating an embodiment of the array that is substantially the same as the fourth embodiment as illustrated in  FIG. 4  and also illustrating a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
         FIG. 10B  is a diagram illustrating an embodiment of the array that is substantially the same as the fifth embodiment as illustrated in  FIG. 5  and also illustrating a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
         FIG. 10C  is a diagram illustrating an embodiment of the array that is substantially the same as the sixth embodiment as illustrated in  FIG. 6  and also illustrating a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
         FIG. 11A  is a diagram illustrating an embodiment of the array that is substantially the same as the fourth embodiment as illustrated in  FIG. 4  and also illustrating another certain activation pattern or sequence of the dedicated receive elements and Spot of Arago and Spot of Arago in detecting the ultrasound echoes during the receiving operation. 
         FIG. 11B  is a diagram illustrating an embodiment of the array that is substantially the same as the fifth embodiment as illustrated in  FIG. 5  and also illustrating another certain activation pattern or sequence of the dedicated receive elements and Spot of Arago in detecting the ultrasound echoes during the receiving operation. 
         FIG. 11C  is a diagram illustrating an embodiment of the array that is substantially the same as the sixth embodiment as illustrated in  FIG. 6  and also illustrating another certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
         FIG. 12A  is a diagram illustrating an embodiment of the array that is substantially the same as a combination of the embodiments as illustrated in  FIGS. 10A and 11A  and also illustrates a certain first activation pattern or sequence of the dedicated receive elements and Spot of Arago in detecting the ultrasound echoes during the receiving operation. 
         FIG. 12B  is a diagram illustrating a certain activation pattern or sequence of the dedicated receive elements of the same embodiment as described with respect to  FIG. 12A  in detecting the ultrasound echoes during the receiving operation and also illustrates a certain second activation pattern or sequence of the dedicated receive elements and Spot of Arago in detecting the ultrasound echoes during the receiving operation. 
         FIG. 12C  is a diagram illustrating a certain activation pattern or sequence of the dedicated receive elements of the same embodiment as described with respect to  FIG. 12A  in detecting the ultrasound echoes during the receiving operation and also illustrates a certain third activation pattern or sequence of the dedicated receive elements and Spot of Arago in detecting the ultrasound echoes during the receiving operation. 
         FIG. 13  is a diagram illustrating an embodiment of the array in the probe that is substantially the same as the seventh embodiment as illustrated in  FIG. 7  and also illustrates a certain activation pattern or sequence of the dedicated receive elements and Spot of Arago in detecting the ultrasound echoes during the receiving operation. 
         FIG. 14  is a diagram illustrating an embodiment of the array in the probe that is substantially the same as the eighth embodiment as illustrated in  FIG. 8  and also illustrates a certain activation pattern or sequence of the dedicated receive elements and Spot of Arago in detecting the ultrasound echoes during the receiving operation. 
         FIGS. 15A ,  15 B and  15 C are diagrams illustrating a spatial compounding aperture technique using an embodiment having the array in an elliptical arrangement. 
         FIGS. 16A ,  16 B and  16 C are diagrams illustrating a synthetic aperture technique using an embodiment having the array in an elliptical arrangement. 
         FIGS. 17A and 17B  are diagrams illustrating an asymmetric aperture technique using an embodiment having the array in an elliptical arrangement. 
         FIGS. 18A ,  18 B and  18 C are diagrams illustrating another example of the asymmetric aperture technique using an embodiment having the array in an elliptical arrangement. 
         FIG. 19  is a diagram illustrating a ninth embodiment having non-overlapping annular-like areas according to the current invention. 
         FIG. 20  is a diagram illustrating one exemplary prior art ultrasound imaging system. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the ultrasound transducer array according to the current invention include transducer elements that generate and transmit the ultrasound pulses towards a region of interest in a subject patient and receive the echoes reflected from the structures in the region of interest in the patient. The embodiments of the ultrasound transducer array according the current invention are two-dimensional arrays and generally include dedicated transmit elements and dedicated receive elements without shared transmit/receive elements. The embodiments of the ultrasound transducer array according the current invention are either sparsely or fully populated with the dedicated transmit elements and the dedicated receive elements. These transducer elements optionally include piezoelectric transducers, capacitive micromachined ultrasonic transducers (CMUTs), Piezoelectric micromachined ultrasonic transducers (pMUTs), or any other suitable type of transducers. 
     The dedicated transmit and receive elements are strictly separated and placed in a predetermined set of annular-like areas such as circular, elliptical and polygonal rings in the embodiments of the array according to the current invention. These embodiments of the array have several advantageous features according to the current invention. For example, the advantageous features include improvement in reduced electronic components associated with switching and electronic focusing, near field imaging performance due to large aperture, separation of transducer array element stackups for optimization of center frequency and bandwidth, and enhanced harmonic signal frequencies. Among the above advantages, the less electronic components also lead to desirable reduction in costs, power consumption and overall size. The separation of transducer array element stackups for transmit and receive may optimizes center frequency and bandwidth for each portion of the array through matching layer and/or PZT changes for the respective annular-like areas. 
     Referring now to the drawings, wherein like reference numerals designate corresponding structures throughout the views, and referring in particular to  FIG. 1 , a diagram illustrates an embodiment of the array in the probe according to the current invention. In general, the embodiment is a two-dimensional array  10  of transducer elements that includes dedicated transmit elements that perforin only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention excludes any shared transmit/receive elements that perform both transmit and receive functions within the same element. The dedicated transmit elements and the dedicated receive elements are placed in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like circular areas including a first annular-like area  11  and a second annular-like area  12 . As indicated by different shades, the first annular-like area  11  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  12  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  11  and the second annular-like area  12  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas. For example, if the first annular-like area  11  exclusively includes the dedicated transmit elements, the second annular-like area  12  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  12  is immediately juxtaposed around the first annular-like area  11  and has a substantially concentric center with the first annular-like area  11 . 
     As illustrated in the diagram, the first annular-like area  11  and the second annular-like area  12  are optionally repeated over a predetermined transducer surface of the two-dimensional array  10 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  11 A,  12 A and  11 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  12  is larger than the first annular-like area  11  and is immediately juxtaposed around the first annular-like area  11 , the additionally repeated annular-like areas  11 A,  12 A and  11 B also have substantially the same spatial relationship among them. 
     The term, “annular-like area” is intended to mean in the current patent application that each of the areas is delimited by a pair of substantially parallel outer and inner lines and or curves to form a contiguous strip of area surrounding a predetermined central portion or a donut-hole. Alternatively, the annular-like areas are also intended to mean in the current patent application that each of the areas is substantially concentric with each other while one of a pair of the annular-like areas is surrounded by the other adjacent larger one of the pair of the annular-like areas. Although the annular-like areas include circular and ecliptic rings, the annular-like areas are not limited to these specific shapes of rings and also include an optional combination of different shapes of the rings. For example, in case of polygonal rings, a pair of substantially concentric polygon edges defines each polygonal ring. The above examples do not limit the annular-like areas as used in the current patent application to particular shapes or sizes. Furthermore, the definition is for the spatial relation of the array elements and does not necessarily limit activation patterns or sequences of the dedicated transmit elements in transmitting the ultrasound pulses during the transmission operation. By the same token, the definition also does not necessarily limit activation patterns or sequences of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
     Still referring to  FIG. 1 , the exemplary embodiment additionally includes a third area  13  and a fourth area  14 . The third area  13  is located inside the first annular-like area  11  and at least over the concentric center. The third area  13  is optionally juxtaposed to the first annular-like area  11  or alternatively contained in the first annular-like area  11  with a gap between the third area  13  and the first annular-like area  11 . In this embodiment, as the third area  13  is indicated by the same shade as the second annular-like area  12 , the third area  13  exclusively includes the same one of the dedicated transmit elements and the dedicated dedicated receive elements as the second annular-like area  12 . 
     The above discussed repeated annular-like areas  11 ,  12   11 A,  12 A and  11 B have a certain spatial relationship among them. To have a desired effect, these repeated annular-like areas  11 ,  12   11 A,  12 A and  11 B switch from the dedicated transmit elements to the dedicated receive elements and vice versa at radii Rn as defined in the following equation: 
     
       
         
           
             
               r 
               n 
             
             = 
             
               
                 
                   n 
                    
                   
                       
                   
                    
                   λ 
                    
                   
                       
                   
                    
                   f 
                 
                 + 
                 
                   
                     
                       n 
                       2 
                     
                      
                     
                       λ 
                       2 
                     
                   
                   4 
                 
               
             
           
         
       
     
     Where n is an integer while λ is the wavelength of the ultrasound wave the array is meant to focus and f is the distance from the center of the array to the focus. When the array is small compared to the focal length, this can be approximated by the following equation: 
     
       
      
       r 
       n 
       ≅√{square root over (nλf)} 
      
     
     For the arrays with many zones, the distance to the focus may be calculated if the radius of the outermost zone, r N  and its width Δ,r N   
     
       
         
           
             f 
             = 
             
               
                 
                   2 
                    
                   
                     r 
                     N 
                   
                    
                   Δ 
                    
                   
                       
                   
                    
                   
                     r 
                     N 
                   
                 
                 λ 
               
             
           
         
       
     
     In contrast, the fourth area  14  is located outside the largest annular-like area  11 B on the two-dimensional array surface. The fourth area  14  is optionally void of any functional transducer element and/or disabled. Alternatively, the fourth area  14  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     In one exemplary array, the embodiment includes a total of ten thousand (10,000) array elements with 100 Azimuth elements and 100 Elevation elements. Among the 10,000 array elements, assuming that predetermined numbers M and N respectively indicate a number of dedicated transmit elements and dedicated receive elements while a third number O indicates a number of array elements that is optionally unused, the sum of M+N+O is 10,000. For example, the first predetermined number M and the second predetermined number N are respectively 3750 dedicated transmit elements and 3750 dedicated receive elements while the third predetermined number O is 2500 unused array elements. Furthermore, based upon the above example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  11 ,  11 A and  11 B whose area sizes are equal in one embodiment. In another embodiment, based upon the same example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  11 ,  11 A and  11 B whose area sizes are not equal. By the same token, based upon the same example, the 3750 dedicated receive elements are optionally divided among the second annular-like areas  12  and  12 A whose area sizes may or may not be equal. In an alternative embodiment, the third area  13  is optionally included in the second annular-like areas  12  and  12 A for the purpose of populating the array elements. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
       FIG. 2  is a diagram illustrating a second embodiment of the array in the probe according to the current invention. In general, the embodiment is a two-dimensional array  20  of transducer elements that includes dedicated transmit elements that perform only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention excludes any shared transmit/receive elements that perform both transmit and receive functions within the same element. The dedicated transmit elements and the dedicated receive elements are placed in a certain in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like elliptical areas including a first annular-like area  21  and a second annular-like area  22 . As indicated by different shades, the first annular-like area  21  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  22  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  21  and the second annular-like area  22  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like elliptical areas. For example, if the first annular-like area  21  exclusively includes the dedicated transmit elements, the second annular-like area  22  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  22  is immediately juxtaposed around the first annular-like area  21  and has a substantially concentric center with the first annular-like area  21 . 
     As illustrated in the diagram, the first annular-like area  21  and the second annular-like area  22  are optionally repeated over a predetermined transducer surface of the two-dimensional array  20 . As indicated by the shaded elliptical rings in the diagram, the additionally repeated annular-like areas  21 A,  22 A and  21 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  22  is larger than the first annular-like area  21  and is immediately juxtaposed around the first annular-like area  21 , the additionally repeated annular-like areas  21 A,  22 A and  21 B also have substantially the same spatial relationship among them. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 2 , the exemplary embodiment additionally includes a third area  23  and a fourth area  24 . The third area  23  is located inside the first annular-like area  21  and at least over the concentric center. The third area  23  is optionally juxtaposed to the first annular-like area  21  or alternatively contained in the first annular-like area  21  with a gap between the third area  23  and the first annular-like area  21 . In this embodiment, as the third area  23  is indicated by the same shade as the second annular-like area  22 , the third area  23  exclusively includes the same one of the dedicated transmit elements and the dedicated receive elements as the second annular-like area  22 . In contrast, the fourth area  24  is located outside the largest annular-like area  21 B on the two-dimensional array surface. The fourth area  24  is optionally void of any functional transducer element and/or disabled. Alternatively, the fourth area  24  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     In one exemplary array, the embodiment includes a total of ten thousand (10,000) array elements with 100 Azimuth elements and 100 Elevation elements. Among the 10,000 array elements, assuming that predetermined numbers M and N respectively indicate a number of dedicated transmit elements and dedicated receive elements while a third number O indicates a number of array elements that is optionally unused, the sum of M+N+O is 10,000. For example, the first predetermined number M and the second predetermined number N are respectively 3750 dedicated transmit elements and 3750 dedicated receive elements while the third predetermined number O is 2500 unused array elements. Furthermore, based upon the above example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  21 ,  21 A and  21 B whose area sizes are equal in one embodiment. In another embodiment, based upon the same example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  21 ,  21 A and  21 B whose area sizes are not equal. By the same token, based upon the same example, the 3750 dedicated receive elements are optionally divided among the second annular-like areas  22  and  22 A whose area sizes may or may not be equal. In an alternative embodiment, the third area  23  is optionally included in the second annular-like areas  22  and  22 A for the purpose of populating the array elements. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
       FIG. 3  is a diagram illustrating a third embodiment of the array in the probe according to the current invention. In general, the embodiment is a two-dimensional array  30  of transducer elements that includes dedicated transmit elements that perform only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention excludes any shared transmit/receive elements that perform both transmit and receive functions within the same element. The dedicated transmit elements and the dedicated receive elements are placed in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like polygonal areas including a first annular-like area  31  and a second annular-like area  32 . As indicated by different shades, the first annular-like area  31  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  32  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  31  and the second annular-like area  32  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like polygonal areas. For example, if the first annular-like area  31  exclusively includes the dedicated transmit elements, the second annular-like area  32  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  32  is immediately juxtaposed around the first annular-like area  31  and has a substantially concentric center with the first annular-like area  31 . 
     As illustrated in the diagram, the first annular-like area  31  and the second annular-annular-like area  32  are optionally repeated over a predetermined transducer surface of the two-dimensional array  30 . As indicated by the shaded polygonal rings in the diagram, the additionally repeated annular-like areas  31 A,  32 A and  31 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  32  is larger than the first annular-like area  31  and is immediately juxtaposed around the first annular-like area  31 , the additionally repeated annular-like areas  31 A,  32 A and  31 B also have substantially the same spatial relationship among them. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 3 , the exemplary embodiment additionally includes a third area  33  and a fourth area  34 . The third area  33  is located inside the first annular-like area  31  and at least over the concentric center. The third area  33  is optionally juxtaposed to the first annular-like area  31  or alternatively contained in the first annular-like area  31  with a gap between the third area  33  and the first annular-like area  31 . In this embodiment, as the third area  33  is indicated by the same shade as the second annular-like area  32 , the third area  33  exclusively includes the same one of the dedicated transmit elements and the dedicated receive elements as the second annular-like area  32 . 
     In contrast, the fourth area  34  is located outside the largest annular-like area  31 B on the two-dimensional array surface. The fourth area  34  is optionally void of any functional transducer element or disabled. Alternatively, the fourth area  34  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     In one exemplary array, the embodiment includes a total of ten thousand (10,000) array elements with 100 Azimuth elements and 100 Elevation elements. Among the 10,000 array elements, assuming that predetermined numbers M and N respectively indicate a number of dedicated transmit elements and dedicated receive elements while a third number third number O indicates a number of array elements that is optionally unused, the sum of M+N+O is 10,000. For example, the first predetermined number M and the second predetermined number N are respectively 3750 dedicated transmit elements and 3750 dedicated receive elements while the third predetermined number O is 2500 unused array elements. Furthermore, based upon the above example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  31 ,  31 A and  31 B whose area sizes are equal in one embodiment. In another embodiment, based upon the same example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  31 ,  31 A and  31 B whose area sizes are not equal. By the same token, based upon the same example, the 3750 dedicated receive elements are optionally divided among the second annular-like areas  32  and  32 A whose area sizes may or may not be equal. In an alternative embodiment, the third area  33  is optionally included in the second annular-like areas  32  and  32 A for the purpose of populating the array elements. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
       FIG. 4  is a diagram illustrating a fourth embodiment of the array in the probe according to the current invention. In general, the embodiment is a two-dimensional array  40  of transducer elements that includes dedicated transmit elements that perform only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention excludes any shared transmit/receive elements that perform both transmit and receive functions within the same element. The dedicated transmit elements and the dedicated receive elements are placed in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like circular areas including a first annular-like area  41  and a second annular-like area  42 . As indicated by different shades, the first annular-like area  41  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  42  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  41  and the second annular-like area  42  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas. For example, if the first annular-like area  41  exclusively includes the dedicated transmit elements, the second annular-like area  42  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  42  is immediately juxtaposed around the first annular-like area  41  and has a substantially concentric center with the first annular-like area  41 . 
     As illustrated in the diagram, the first annular-like area  41  and the second annular-like area  42  are optionally repeated over a predetermined transducer surface of the two-dimensional array  40 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  41 A,  42 A,  41 B and  42 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  42  is larger than the first annular-like area  41  and is immediately juxtaposed around the first annular-like area  41 , the additionally repeated annular-like areas  41 A,  42 A,  41 B and  42 B also have substantially the same spatial relationship among them. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 4 , the exemplary embodiment additionally includes a third area  43  and/or a fourth area  44 . The third area  43  is a circle and is located inside the first annular-like area  41  and at least over the concentric center. The third area  43  is optionally juxtaposed to the first annular-like area  41  or alternatively contained in the first annular-like area  41  with a gap between the third area  43  and the first annular-like area  41 . In this embodiment, the third area  43  is indicated in white that the third area  43  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  43  optionally further reduces the number of array elements and ultimately improves the electronic circuitry cost, the power consumption and the size. The third area  43  also results in improved beam width thereby enhancing near-field lateral resolution in improving imaging quality. Since the third area  43  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  43  is also called Spot of Arago in the =Tent application. 
     The above discussed repeated annular-like areas  41 ,  42   41 A,  42 A,  41 B and  42 B have a certain spatial relationship among them. To have a desired effect, these repeated annular-like areas  41 ,  42   41 A,  42 A,  41 B and  42 B switch from the dedicated transmit elements to the dedicated receive elements and vice versa at radii Rn as defined in the following equation: 
     
       
         
           
             
               r 
               n 
             
             = 
             
               
                 
                   n 
                    
                   
                       
                   
                    
                   λ 
                    
                   
                       
                   
                    
                   f 
                 
                 + 
                 
                   
                     
                       n 
                       2 
                     
                      
                     
                       λ 
                       2 
                     
                   
                   4 
                 
               
             
           
         
       
     
     Where n is an integer while λ is the wavelength of the ultrasound wave the array is meant to focus and f is the distance from the center of the array to the focus. When the array is small compared to the focal length, this can be approximated by the following equation: 
     
       
      
       r 
       n 
       ≅√{square root over (nλf)} 
      
     
     For the arrays with many zones, the distance to the focus may be calculated if the radius of the outermost zone, r N  and its width Δ,r N   
     
       
         
           
             f 
             = 
             
               
                 
                   2 
                    
                   
                     r 
                     N 
                   
                    
                   Δ 
                    
                   
                       
                   
                    
                   
                     r 
                     N 
                   
                 
                 λ 
               
             
           
         
       
     
     In contrast, the fourth area  44  is located outside the largest annular-like area  42 B on the two-dimensional array surface. The fourth area  44  is optionally disabled or devoid of any functional transducer element. Alternatively, the fourth area  44  is optionally populated by the dedicated transmit elements for maximum power and/or the dedicated receive elements for maximum sensitivity. 
     In one exemplary array, the embodiment includes a total of ten thousand (10,000) array elements with 100 Azimuth elements and 100 Elevation elements. Among the 10,000 array elements, assuming that predetermined numbers M and N respectively indicate a number of dedicated transmit elements and dedicated receive elements while a third number O indicates a number of array elements that is unused, the sum of M+N+O is 10,000. For example, the first predetermined number M and the second predetermined number N are respectively 3750 dedicated transmit elements and 3750 dedicated receive elements while the third predetermined number O is 2500 unused array elements. Furthermore, based upon the above example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  41 ,  41 A and  41 B whose area sizes are equal in one embodiment. In another embodiment, based upon the same example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  41 ,  41 A and  41 B whose area sizes are not equal. By the same token, based upon the same example, the 3750 dedicated receive elements are optionally divided among the second annular-like areas  42 ,  42 A and  42 B whose area sizes may or may not be equal. In an alternative embodiment, the third area  43  is included in the number N if the third area  43  is equipped with array elements and unused. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
       FIG. 5  is a diagram illustrating a fifth embodiment of the array in the probe according to the current invention. In general, the embodiment is a two-dimensional array  50  of transducer elements that includes dedicated transmit elements that perform only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention excludes any shared transmit/receive elements that perform both transmit and receive functions within the same element. The dedicated transmit elements and the dedicated receive elements are placed in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like elliptical areas including a first annular-like area  51  and a second annular-like area  52 . As indicated by different shades, the first annular-like area  51  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  52  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  51  and the second annular-like area  52  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like elliptical areas. For example, if the first annular-like area  51  exclusively includes the dedicated transmit elements, the second annular-like area  52  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  52  is immediately juxtaposed around the first annular-like area  51  and has a substantially concentric center with the first annular-like area  51 . 
     As illustrated in the diagram, the first annular-like area  51  and the second annular-like area  52  are optionally repeated over a predetermined transducer surface of the two-dimensional array  50 . As indicated by the shaded elliptical rings in the diagram, the additionally repeated annular-like areas  51 A,  52 A,  51 B and  52 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  52  is larger than the first annular-like area  51  and is immediately juxtaposed around the first annular-like area  51 , the additionally repeated annular-like areas  51 A,  52 A,  51 B and  52 B also have substantially the same spatial relationship among them. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 5 , the exemplary embodiment additionally includes a third area  53  and/or a fourth area  54 . The third area  53  is an ellipse and is located inside the first annular-like area  51  and at least over the concentric center. The third area  53  is optionally juxtaposed to the first annular-like area  51  or alternatively contained in the first annular-like area  51  with a gap between the third area  53  and the first annular-like area  51 . In this embodiment, the third area  53  is indicated in white that the third area  53  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  53  optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  53  also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  53  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  53  is also called Spot of Arago in the current application. 
     In contrast, the fourth area  54  is located outside the largest annular-like area  52 B on the two-dimensional array surface. The fourth area  54  is optionally disabled or devoid of any functional transducer element. Alternatively, the fourth area  54  is optionally populated by the dedicated transmit elements for maximum power and/or the dedicated receive elements for maximum sensitivity. 
     In one exemplary array, the embodiment includes a total of ten thousand (10,000) array elements with 100 Azimuth elements and 100 Elevation elements. Among the 10,000 array elements, assuming that predetermined numbers M and N respectively indicate a indicate a number of dedicated transmit elements and dedicated receive elements while a third number O indicates a number of array elements that is unused, the sum of M+N+O is 10,000. For example, the first predetermined number M and the second predetermined number N are respectively 3750 dedicated transmit elements and 3750 dedicated receive elements while the third predetermined number O is 2500 unused array elements. Furthermore, based upon the above example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  51 ,  51 A and  51 B whose area sizes are equal in one embodiment. In another embodiment, based upon the same example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  51 ,  51 A and  51 B whose area sizes are not equal. By the same token, based upon the same example, the 3750 dedicated receive elements are optionally divided among the second annular-like areas  52 ,  52 A and  52 B whose area sizes may or may not be equal. In an alternative embodiment, the third area  53  is included in the number N if the third area  53  is equipped with array elements and unused. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
       FIG. 6  is a diagram illustrating a sixth embodiment of the array in the probe according to the current invention. In general, the embodiment is a two-dimensional array  60  of transducer elements that includes dedicated transmit elements that perform only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention excludes any shared transmit/receive elements that perform both transmit and receive functions within the same element. The dedicated transmit elements and the dedicated receive elements are placed in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like polygonal areas including a first annular-like area  61  and a second annular-like area  62 . As indicated by different shades, the first annular-like area  61  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  62  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  61  and the second annular-like area  62  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like polygonal areas. For example, if the first annular-like area  61  exclusively includes the dedicated transmit elements, the second annular-like area  62  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  62  is immediately juxtaposed around the first annular-like area  61  and has a substantially concentric center with the first annular-like area  61 . 
     As illustrated in the diagram, the first annular-like area  61  and the second annular-like area  62  are optionally repeated over a predetermined transducer surface of the two-dimensional array  60 . As indicated by the shaded polygonal rings in the diagram, the additionally repeated annular-like areas  61 A,  62 A,  61 B and  62 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  62  is larger than the first annular-like area  61  and is immediately juxtaposed around the first annular-like area  61 , the additionally repeated annular-like areas  61 A,  62 A,  61 B and  62 B also have substantially the same spatial relationship among them. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 6 , the exemplary embodiment additionally includes a third area  63  and/or a fourth area  64 . The third area  63  is a polygon and is located inside the first annular-like area  61  and at least over the concentric center. The third area  63  is optionally juxtaposed to the first annular-like area  61  or alternatively contained in the first annular-like area  61  with a gap between the third area  63  and the first annular-like area  61 . In this embodiment, the third area  63  is indicated in white that the third area  63  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  63  optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  63  also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  63  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  63  is also called Spot of Arago in the current application. 
     In contrast, the fourth area  64  is located outside the largest annular-like area  62 B on the two-dimensional array surface. The fourth area  64  is optionally disabled and/or devoid of any functional transducer element. Alternatively, the fourth area  64  is optionally populated by the dedicated transmit elements for maximum power and/or the dedicated receive elements for maximum sensitivity. 
     In one exemplary array, the embodiment includes a total of ten thousand (10,000) array elements with 100 Azimuth elements and 100 Elevation elements. Among the 10,000 array elements, assuming that predetermined numbers M and N respectively indicate a number of dedicated transmit elements and dedicated receive elements while a third number O indicates a number of array elements that is unused, the sum of M+N+O is 10,000. For example, the first predetermined number M and the second predetermined number N are respectively 3750 dedicated transmit elements and 3750 dedicated receive elements while the third predetermined number O is 2500 unused array elements. Furthermore, based upon the above example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  61 ,  61 A and  61 B whose area sizes are equal in one embodiment. In another embodiment, based upon the same example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  61 ,  61 A and  61 B whose area sizes are not equal. By the same token, based upon the same example, the 3750 dedicated receive elements are optionally divided among the second annular-like areas  62 ,  62 A and  62 B whose area sizes may or may not be equal. In an alternative embodiment, the third area  63  alternative embodiment, the third area  63  is included in the number N if the third area  63  is equipped with array elements and unused. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
       FIG. 7  is a diagram illustrating a seventh embodiment of the array in the probe according to the current invention. In general, the embodiment is a two-dimensional array  70  of transducer elements that includes dedicated transmit elements that perform only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention excludes any shared transmit/receive elements that perform both transmit and receive functions within the same element. The dedicated transmit elements and the dedicated receive elements are placed in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like circular areas including a first annular-like area  71  and a second annular-like area  72 . As indicated by different shades, the first annular-like area  71  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  72  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  71  and the second annular-like area  72  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas. For example, if the first annular-like area  71  exclusively includes the dedicated transmit elements, the second annular-like area  72  exclusively includes the dedicated receive elements. Although the second annular-like area  72  is not immediately juxtaposed around the first annular-like area  71 , the second annular-like area  72  has a substantially concentric substantially concentric center with the first annular-like area  71 . 
     In the seventh embodiment of the array in the probe, there is an optional annular-like area  75  between the first annular-like area  71  and the second annular-like area  72 . The optional annular-like area  75  is optionally populated with either one of the dedicated transmit elements or the dedicated receive elements, and these elements may be also optionally used or disabled. Alternatively, the optional annular-like area  75  is optionally populated with neither one of the dedicated transmit elements or the dedicated receive elements. Furthermore, an additional optional annular-like area  75 ′ surrounds the second annular-like area  72 , and the additional optional annular-like area  75 ′ may be implemented in a similar manner as the optional annular-like area  75 . 
     As illustrated in the diagram, the first annular-like area  71  and the second annular-like area  72  are optionally repeated over a predetermined transducer surface of the two-dimensional array  70 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  71 A,  72 A,  71 B and  72 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  72  is larger than the first annular-like area  71  and is not immediately juxtaposed around the first annular-like area  71 , the additionally repeated annular-like areas  71 A,  72 A,  71 B and  72 B also have substantially the same spatial relationship among them. By the same token, the additionally repeated annular-like areas  71 A,  72 A,  71 B and  72 B are interlaced by optional annular-like areas  75 A and  75 B as well as by additional optional annular-like area  75 A′. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 7 , the exemplary embodiment additionally includes a third area  73  and a fourth area  74 . The third area  73  is a circle and is located inside the first annular-like area  71  and at least over the concentric center. The third area  73  is optionally juxtaposed to the first annular-like area  71  or alternatively contained in the first annular-like annular-like area  71  with a gap between the third area  73  and the first annular-like area  71 . In this embodiment, the third area  73  is indicated in white that the third area  73  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  73  optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  73  also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  73  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  73  is also called Spot of Arago in the current application. 
     In contrast, the fourth area  74  is located outside the largest annular-like area  72 B on the two-dimensional array surface. The fourth area  74  is optionally disabled or devoid of any functional transducer element. Alternatively, the fourth area  74  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     In one exemplary array, the embodiment includes a total of ten thousand (10,000) array elements with 100 Azimuth elements and 100 Elevation elements. Among the 10,000 array elements, assuming that predetermined numbers M and N respectively indicate a number of dedicated transmit elements and dedicated receive elements while a third number O indicates a number of array elements that is unused, the sum of M+N+O is 10,000. For example, the first predetermined number M and the second predetermined number N are respectively 3750 dedicated transmit elements and 3750 dedicated receive elements while the third predetermined number O is 2600 unused array elements. Furthermore, based upon the above example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  71 ,  71 A and  71 B whose area sizes are equal in one embodiment. In another embodiment, based upon the same example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  71 ,  71 A and  71 B whose area sizes are not equal. By the same token, based upon the same example, the 3750 dedicated receive elements are optionally divided among the second annular-like areas  72 ,  72 A and  72 B annular-like areas  72 ,  72 A and  72 B whose area sizes may or may not be equal. In an alternative embodiment, the third area  73  is included in the number N if the third area  73  is equipped with array elements and unused. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
     In addition to the above illustrated embodiment, alternative embodiments based upon the seventh embodiment further include an elliptical embodiment and a polygonal embodiment. In the elliptical alternative embodiment, the dedicated transmit elements and the dedicated receive elements are both placed in annular-like elliptical areas including a first annular-like area and a second annular-like area as described with respect to the seventh embodiment. Similarly, the third area, the fourth and the fifth area also exist in the elliptical alternative embodiment in a substantially similar manner as described with respect to the seventh embodiment. By the same token, in the polygonal alternative embodiment, the dedicated transmit elements and the dedicated receive elements are both placed in annular-like polygonal areas including a first annular-like area and a second annular-like area as described with respect to the seventh embodiment. Similarly, the third area, the fourth area and the fifth area also exist in the polygonal alternative embodiment in a substantially similar manner as described with respect to the seventh embodiment. Although the above alternative embodiments are not illustrated in drawings, the alternative embodiments are disclosed by the illustrated seventh embodiment in combination with the above description. 
       FIG. 8  is a diagram illustrating an eighth embodiment of the array in the probe according to the current invention. In general, the embodiment is a two-dimensional array  80  of transducer elements that includes transmit/receive elements that perform both transmit and receive functions, dedicated transmit elements that perform only transmit functions and functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention includes shared transmit/receive elements that perform both transmit and receive functions within the same element in addition to the dedicated transmit elements and the dedicated receive elements. The dedicated transmit elements and the dedicated receive elements are interlaced with the transmit/receive elements in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like circular areas including a first annular-like area  81  and a second annular-like area  82  while the shared transmit/receive elements are placed in a sixth annular-like area  86 . As indicated by different shades, the first annular-like area  81  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  82  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In addition, the sixth annular-like area  86  include the shared transmit/receive elements. In other words, the first annular-like area  81  and the second annular-like area  82  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas while the sixth annular-like area  86  is placed between the first annular-like area  81  and the second annular-like area  82  and includes the shared transmit/receive elements. For example, if the first annular-like area  81  exclusively includes the dedicated transmit elements, the second annular-like area  82  exclusively includes the dedicated receive elements and the sixth annular-like area  86  is placed between the first annular-like area  81  and the second annular-like area  82  and includes the shared transmit/receive elements. In the eighth embodiment, the second annular-like area  82  is immediately juxtaposed around the sixth annular-like area  86 , and the sixth annular-like area  86  is immediately juxtaposed around the first annular-like area  81 . Both the second annular-like area  82  and the sixth annular-like area  86  have a substantially concentric center with the first annular-like area  81 . 
     As illustrated in the diagram, the first annular-like area  81  and the second annular-like area  82  are optionally repeated over a predetermined transducer surface of the two-dimensional array  80 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  81 A,  82 A,  81 B and  82 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements while the sixth annular-like areas  86 ,  86 A and  86 B include the shared transmit/receive elements. In the illustrated embodiment, as the second annular-like area  82  is larger than the first annular-like area  81  and is immediately juxtaposed around the sixth annular-like areas  86 , the additionally repeated annular-like areas  81 A,  82 A,  81 B and  82 B and the sixth annular-like areas  86 ,  86 A and  86 B also have substantially the same spatial relationship among them. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 8 , the exemplary embodiment additionally includes a third area  83  and a fourth area  84 . The third area  83  is a circle and is located inside the first annular-like area  81  and at least over the concentric center. The third area  83  is optionally juxtaposed to the first annular-like area  81  or alternatively contained in the first annular-like area  81  with a gap between the third area  83  and the first annular-like area  81 . In this embodiment, the third area  83  is indicated in white that the third area  83  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  83  optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  83  also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  83  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  83  is also called Spot of Arago in the current application. 
     In contrast, the fourth area  84  is located outside the largest annular-like area  82 B on the two-dimensional array surface. The fourth area  84  is optionally disabled or devoid of any functional transducer element. Alternatively, the fourth area  84  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     In one exemplary array, the embodiment includes a total of ten thousand (10,000) array elements with 100 Azimuth elements and 100 Elevation elements. Among the 10,000 array elements, assuming that predetermined numbers M and N respectively indicate a number of dedicated transmit elements and dedicated receive elements while a third number O indicates a number of array elements that is unused, the sum of M+N+O is 10,000. For example, the first predetermined number M and the second predetermined number N are respectively 3750 dedicated transmit elements and 3750 dedicated receive elements while the third predetermined number O is 2600 unused array elements. Furthermore, based upon the above example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  81 ,  81 A and  81 B whose area sizes are equal in one embodiment. In another embodiment, based upon the same example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  81 ,  81 A and  81 B whose area sizes are not equal. By the same token, based upon the same example, the 3750 dedicated receive elements are optionally divided among the second annular-like areas  82 ,  82 A and  82 B whose area sizes may or may not be equal. In an alternative embodiment, the third area  83  is included in the number N if the third area  83  is equipped with array elements and unused. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
     In addition to the above illustrated embodiment, alternative embodiments based upon the eighth embodiment further include an elliptical embodiment and a polygonal embodiment. In the elliptical alternative embodiment, the shared transmit/receive elements, elements, the dedicated transmit elements and the dedicated receive elements are all placed in annular-like elliptical areas including a first annular-like area, a second annular-like area and a sixth annular-like area as described with respect to the eighth embodiment. Similarly, the third area and the fourth also exist in the elliptical alternative embodiment in a substantially similar manner as described with respect to the eighth embodiment. By the same token, in the polygonal alternative embodiment, the shared transmit/receive elements, the dedicated transmit elements and the dedicated receive elements are all placed in annular-like polygonal areas including a first annular-like area, a second annular-like area and a sixth annular-like area as described with respect to the eighth embodiment. Similarly, the third area and the fourth areas also exist in the polygonal alternative embodiment in a substantially similar manner as described with respect to the eighth embodiment. Although the above alternative embodiments are not illustrated in drawings, the alternative embodiments are disclosed by the illustrated eighth embodiment in combination with the above description. 
     Now referring to  FIGS. 9A ,  9 B and  9 C, a certain optional operation of one of the above described embodiments will be described.  FIG. 9A  illustrates an embodiment of the array in the probe according to the current invention. In general, the embodiment is substantially the same as the first embodiment as illustrated in  FIG. 1 . A two-dimensional array  90  includes a first annular-like area  91  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  92  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  91  and the second annular-like area  92  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas. For example, if the first annular-like area  91  exclusively includes the dedicated transmit elements, the second annular-like area  92  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  92  is immediately juxtaposed around the first annular-like area  91  and has a substantially concentric center with the first annular-like area  91 . 
     As illustrated in the diagram, the first annular-like area  91  and the second annular-like area  92  are optionally repeated over a predetermined transducer surface of the two-dimensional array  90 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  91 A,  92 A and  91 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  92  is larger than the first annular-like area  91  and is immediately juxtaposed around the first annular-like area  91 , the additionally repeated annular-like areas  91 A,  92 A and  91 B also have substantially the same spatial relationship among them. 
     Still referring to  FIG. 9A , the exemplary embodiment additionally includes a third area  93  and a fourth area  94 . The third area  93  is located inside the first annular-like area  91  and at least over the concentric center. The third area  93  is optionally juxtaposed to the first annular-like area  91 . In this embodiment, as the third area  93  is indicated by the same shade as the second annular-like area  92 , the third area  93  exclusively includes the same one of the dedicated transmit elements and the dedicated receive elements as the second annular-like area  92 . In contrast, the fourth area  94  is located outside the largest annular-like area  91 B on the two-dimensional array surface. The fourth area  94  is optionally void of any functional transducer element or disabled. Alternatively, the fourth area  94  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     The term, “annular-like area” is intended to mean the same as defined elsewhere in the current patent application. Since the definition is for the spatial relation of the array elements, it does not necessarily limit activation patterns or sequences of the dedicated transmit elements in transmitting the ultrasound pulses during the transmission operation. By the same token, the definition also does not necessarily limit activation patterns or sequences of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
       FIG. 9A  also illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  91 ,  91 A and  91 B. Alternatively, a combination of the second annular-like area  92 ,  92 A and the third area  93  is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are dynamically activated or steered. In other words, the selected annular-like receive areas have the steering angle of 0 degrees. Thus, the annular-like receive areas substantially maintain their spatial relation of the dedicated receive elements. 
     Now referring to  FIG. 9B , a diagram illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  91 ′,  91 A′ and  91 B′. Alternatively, a combination of the second annular-like area  92 ′,  92 A′ and the third area  93 ′ is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are dynamically activated or steered. In other words, the selected annular-like receive areas have the steering angle of 30 Azimuth degrees or 30 degrees in the X direction. Thus, the annular-like receive areas substantially elongated in their spatial relation of the dedicated receive elements. The annular-like receive areas become more elliptical in the direction of steering in comparison to the circular ring spatial relation of the dedicated receive elements. 
     Now referring to  FIG. 9C , a diagram illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  91 ″,  91 A″ and  91 B″. Alternatively, a combination of the second annular-like area  92 ″,  92 A″ and the third area  93 ″ is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are dynamically activated or steered. In other words, the selected annular-like receive areas have the steering angle of 30 Azimuth degrees and 30 Elevation degrees or 30 degrees in the X and Y directions. Thus, the annular-like receive areas substantially elongated in their spatial relation of the dedicated receive elements. The annular-like receive areas become more elliptical in the direction of steering in comparison to the circular ring spatial relation of the dedicated receive elements. 
     Now referring to  FIGS. 10A ,  10 B and  10 C, a certain optional operation of one of the above described embodiments will be described.  FIG. 10A  illustrates an embodiment of the array that is substantially the same as the fourth embodiment as illustrated in  FIG. 4 . A two-dimensional array  100  includes a first annular-like area  101  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  102  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  101  and the second annular-like area  102  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas. For example, if the first annular-like area  101  exclusively includes the dedicated transmit elements, the second annular-like area  102  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  102  is immediately juxtaposed around the first annular-like area  101  and has a substantially concentric center with the first annular-like area  101 . 
     As illustrated in the diagram, the first annular-like area  101  and the second annular-like area  102  are optionally repeated over a predetermined transducer surface of the two-dimensional array  100 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  101 A,  102 A,  101 B and  102 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  102  is larger than the first annular-like area  101  and is immediately juxtaposed around the first annular-like area  101 , area  101 , the additionally repeated annular-like areas  101 A,  102 A,  101 B and  102 B also have substantially the same spatial relationship among them. 
     Still referring to  FIG. 10A , the exemplary embodiment additionally includes a third area  103  and a fourth area  104 . The third area  103  is a circle and is located inside the first annular-like area  101  and at least over the concentric center. The third area  103  is optionally juxtaposed to the first annular-like area  101  or alternatively contained in the first annular-like area  101  with a gap between the third area  103  and the first annular-like area  101 . In this embodiment, the third area  103  is indicated in white that the third area  103  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  103  optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  103  also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  103  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  103  is also called Spot of Arago in the current application. 
     In contrast, the fourth area  104  is located outside the largest annular-like area  102 B on the two-dimensional array surface. The fourth area  104  is optionally void of any functional transducer element or disabled. Alternatively, the fourth area  104  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     The term, “annular-like area” is intended to mean the same as defined elsewhere in the current patent application. Since the definition is for the spatial relation of the array elements, it does not necessarily limit activation patterns or sequences of the dedicated transmit elements in transmitting the ultrasound pulses during the transmission operation. By the same token, the definition also does not necessarily limit activation patterns or sequences of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
       FIG. 10A  also illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  101 ,  101 A and  101 B. Alternatively, a combination of the second annular-like area  102 ,  102 A and  102 B is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are dynamically activated or steered. In other words, the selected annular-like receive areas have the steering angle of 0 degrees. Thus, the annular-like receive areas substantially maintain their spatial relation of the dedicated receive elements. 
     Now referring to  FIG. 10B , a diagram illustrates a certain activation pattern or sequence of the dedicated receive elements of the same embodiment as described with respect to  FIG. 10A  in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  101 ′,  101 A′ and  101 B′. Alternatively, a combination of the second annular-like area  102 ′,  102 A′ and  102 B′ is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are dynamically activated or steered. In other words, the selected annular-like receive areas have the steering angle of 30 Azimuth degrees or 30 degrees in the X direction. Thus, the annular-like receive areas substantially elongated in their spatial relation of the dedicated receive elements. The annular-like receive areas become more elliptical in the direction of steering in comparison to the circular ring spatial relation of the dedicated receive elements. 
     Now referring to  FIG. 10C , a diagram illustrates a certain activation pattern or sequence of the dedicated receive elements of the same embodiment as described with respect to  FIG. 10A  in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  101 ″,  101 A″ and  101 B″. Alternatively, a combination of the second annular-like area  102 ″,  102 A″ and  102 B″ is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are dynamically activated or steered. In other words, the selected annular-like receive areas have the steering angle of 30 Azimuth degrees and 30 Elevation degrees or 30 degrees in the X and Y directions. Thus, the annular-like receive areas substantially elongated in their spatial relation of the dedicated receive elements. The annular-like receive areas become more elliptical in the direction of steering in comparison to the circular ring spatial relation of the dedicated receive elements. 
     Now referring to  FIG. 11A , a diagram illustrates an embodiment that is substantially the same as the fourth embodiment as illustrated in  FIG. 4 . A two-dimensional array  110  includes a first annular-like area  111  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  112  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  111  and the second annular-like area  112  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas. For example, if the first annular-like area  111  exclusively includes the dedicated transmit elements, the second annular-like area  112  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  112  is immediately juxtaposed around the first annular-like area  111  and has a substantially concentric center with the first annular-like area  111 . 
     As illustrated in the diagram, the first annular-like area  111  and the second annular-like area  112  are optionally repeated over a predetermined transducer surface of the two-dimensional array  110 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  111 A,  112 A,  111 B and  112 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  112  is larger than the first the first annular-like area  111  and is immediately juxtaposed around the first annular-like area  111 , the additionally repeated annular-like areas  111 A,  112 A,  111 B and  112 B also have substantially the same spatial relationship among them. 
     Still referring to  FIG. 11A , the exemplary embodiment additionally includes a third area  113  and a fourth area  114 . The third area  113  is a circle and is located inside the first annular-like area  111  and at least over the concentric center. The third area  113  is optionally juxtaposed to the first annular-like area  111  or alternatively contained in the first annular-like area  111  with a gap between the third area  113  and the first annular-like area  111 . In this embodiment, the third area  113  is indicated in white that the third area  113  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  113  optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  113  also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  113  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  113  is also called Spot of Arago in the current application. 
     In contrast, the fourth area  114  is located outside the largest annular-like area  112 B on the two-dimensional array surface. The fourth area  114  is optionally void of any functional transducer element or disabled. Alternatively, the fourth area  114  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     The term, “annular-like area” is intended to mean the same as defined elsewhere in the current patent application. Since the definition is for the spatial relation of the array elements, it does not necessarily limit activation patterns or sequences of the dedicated transmit elements in transmitting the ultrasound pulses during the transmission operation. By the same token, the definition also does not necessarily limit activation patterns or sequences of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
       FIG. 11A  also illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  111 ,  111 A and  111 B. Alternatively, a combination of the second annular-like area  112 ,  112 A and  112 E is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are neither dynamically activated nor steered. Thus, the annular-like receive areas substantially maintain their spatial relation of the dedicated receive elements. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
     On the other hand, the third area or Spot of Arago  113  is dynamic during the receive operation. For example, the size of Spot of Arago  113  dynamically changes from a first size  113 A to a second size  113 B or vice versa during the receive operation. The size change is not limited to the above two sizes and includes an exemplary size sequence of small to large to smaller to none. For example, the size of the dynamic Spot of Arago  113  changes due to the first annular-like areas  111 , which changes its size by activating or deactivating predetermined portions in a certain sequence during the receive operation. Furthermore, the Spot of Arago  113  dynamically changes with respect to image depth or time in a certain embodiment. 
     Now referring to  FIG. 11B , a diagram illustrates an embodiment that is substantially the same as the fifth embodiment as illustrated in  FIG. 5 . A two-dimensional array  110 ′ includes a first annular-like area  111 ′ exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  112 ′ area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  111 ′ and the second annular-like area  112 ′ alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like elliptical areas. For example, if the first annular-like area  111 ′ exclusively includes the dedicated transmit elements, the second annular-like area  112 ′ exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  112 ′ is immediately juxtaposed around the first annular-like area  111 ′ and has a substantially concentric center with the first annular-like area  111 ′. 
     As illustrated in the diagram, the first annular-like area  111 ′ and the second annular-like area  112 ′ are optionally repeated over a predetermined transducer surface of the two-dimensional array  110 ′. As indicated by the shaded elliptical rings in the diagram, the additionally repeated annular-like areas  111 A′,  112 A′,  111 B′ and  112 B′ also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  112 ′ is larger than the first annular-like area  111 ′ and is immediately juxtaposed around the first annular-like area  111 ′, the additionally repeated annular-like areas  111 A′,  112 A′,  111 B′ and  112 B′ also have substantially the same spatial relationship among them. 
     Still referring to  FIG. 11B , the exemplary embodiment additionally includes a third area  113 ′ and a fourth area  114 ′. The third area  113 ′ is a ellipse and is located inside the first annular-like area  111 ′ and at least over the concentric center. The third area  113 ′ is optionally juxtaposed to the first annular-like area  111 ′ or alternatively contained in the first annular-like area  111 ′ with a gap between the third area  113 ′ and the first annular-like area  111 ′. In this embodiment, the third area  113 ′ is indicated in white that the third area  113 ′ is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  113 ′ optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  113 ′ also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  113 ′ having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  113 ′ is also called Spot of Arago in the current application. 
     In contrast, the fourth area  114 ′ is located outside the largest annular-like area  112 B′ on the two-dimensional array surface. The fourth area  114 ′ is optionally void of any functional transducer element or disabled. Alternatively, the fourth area  114 ′ is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     The term, “annular-like area” is intended to mean the same as defined elsewhere in the current patent application. Since the definition is for the spatial relation of the array elements, it does not necessarily limit activation patterns or sequences of the dedicated transmit elements in transmitting the ultrasound pulses during the transmission operation. By the same token, the definition also does not necessarily limit activation patterns or sequences of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
       FIG. 11B  also illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  111 ′,  111 A′ and  111 B′. Alternatively, a combination of the second annular-like area  112 ′,  112 A′ and  112 B′ is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are neither dynamically activated nor steered. Thus, the annular-like receive areas substantially maintain their spatial relation of the dedicated receive elements. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
     On the other hand, the third area or Spot of Arago  113 ′ is dynamic during the receive operation. For example, the size of Spot of Arago  113 ′ dynamically changes from a first size  113 A′ to a second size  113 B′ or vice versa during the receive operation. The size change is not limited to the above two sizes and includes an exemplary size sequence of small to large to smaller to none. For example, the size of the dynamic Spot of Arago  113 ′ changes due to the first annular-like areas  111 ′, which changes its size by activating or deactivating predetermined portions in a certain sequence during the receive operation. Furthermore, the Spot of Arago  113 ′ dynamically changes with respect to image depth or time in a certain embodiment. 
     Now referring to  FIG. 11C , a diagram illustrates an embodiment that is substantially the same as the sixth embodiment as illustrated in  FIG. 6 . A two-dimensional array  110 ″ includes a first annular-like area  111 ″ exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  112 ″ area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  111 ″ and the second annular-like area  112 ″ alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like polygonal areas. For example, if the first annular-like area  111 ″ exclusively includes the dedicated transmit elements, the second annular-like area  112 ″ exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  112 ″ is immediately juxtaposed around the first annular-like area  111 ″ and has a substantially concentric center with the first annular-like area  111 ″. 
     As illustrated in the diagram, the first annular-like area  111 ″ and the second annular-like area  112 ″ are optionally repeated over a predetermined transducer surface of the the two-dimensional array  110 ″. As indicated by the shaded polygonal rings in the diagram, the additionally repeated annular-like areas  111 A″,  112 A″,  111 B″ and  112 B″ also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  112 ″ is larger than the first annular-like area  111 ″ and is immediately juxtaposed around the first annular-like area  111 ″, the additionally repeated annular-like areas  111 A″,  112 A″,  111 B″ and  112 B″ also have substantially the same spatial relationship among them. 
     Still referring to  FIG. 11C , the exemplary embodiment additionally includes a third area  113 ″ and a fourth area  114 ″. The third area  113 ″ is a polygon and is located inside the first annular-like area  111 ″ and at least over the concentric center. The third area  113 ″ is optionally juxtaposed to the first annular-like area  111 ″ or alternatively contained in the first annular-like area  111 ″ with a gap between the third area  113 ″ and the first annular-like area  111 ″. In this embodiment, the third area  113 ″ is indicated in white that the third area  113 ′ is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  113 ″ optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  113 ″ also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  113 ″ having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  113 ″ is also called Spot of Arago in the current application. 
     In contrast, the fourth area  114 ″ is located outside the largest annular-like area  112 B″ on the two-dimensional array surface. The fourth area  114 ″ is optionally void of any functional transducer element or disabled. Alternatively, the fourth area  114 ″ is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     The term, “annular-like area” is intended to mean the same as defined elsewhere in in the current patent application. Since the definition is for the spatial relation of the array elements, it does not necessarily limit activation patterns or sequences of the dedicated transmit elements in transmitting the ultrasound pulses during the transmission operation. By the same token, the definition also does not necessarily limit activation patterns or sequences of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
       FIG. 11C  also illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  111 ″,  111 A″ and  111 B″. Alternatively, a combination of the second annular-like area  112 ″,  112 A″ and  112 B″ is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are neither dynamically activated nor steered. Thus, the annular-like receive areas substantially maintain their spatial relation of the dedicated receive elements. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
     On the other hand, the third area or Spot of Arago  113 ″ is dynamic during the receive operation. For example, the size of Spot of Arago  113 ″ dynamically changes from a first size  113 A″ to a second size  113 B″ or vice versa during the receive operation. The size change is not limited to the above two sizes and includes an exemplary size sequence of small to large to smaller to none. For example, the size of the dynamic Spot of Arago  113 ″ changes due to the first annular-like areas  111 ″, which changes its size by activating or deactivating predetermined portions in a certain sequence during the receive operation. Furthermore, the Spot of Arago  113 ″ dynamically changes with respect to image depth or time in a certain embodiment. 
     Now referring to  FIGS. 12A ,  12 B and  12 C, a certain optional operation of one of the above described embodiments will be described.  FIG. 12A  illustrates an embodiment of the array that is substantially the same as a combination of the embodiments as illustrated in  FIGS. 10A and 11A . A two-dimensional array  120  includes a first annular-like area  121  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  122  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  121  and the second annular-like area  122  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas. For example, if the first annular-like area  121  exclusively includes the dedicated transmit elements, the second annular-like area  122  exclusively includes the dedicated receive elements. Furthermore, the second annular-like area  122  is immediately juxtaposed around the first annular-like area  121  and has a substantially concentric center with the first annular-like area  121 . 
     As illustrated in the diagram, the first annular-like area  121  and the second annular-like area  122  are optionally repeated over a predetermined transducer surface of the two-dimensional array  120 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  121 A,  122 A,  121 B and  122 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  122  is larger than the first annular-like area  121  and is immediately juxtaposed around the first annular-like area  121 , the additionally repeated annular-like areas  121 A,  122 A,  121 B and  122 B also have substantially the same spatial relationship among them. 
     Still referring to  FIG. 12A , the exemplary embodiment additionally includes a third area  123  and a fourth area  124 . The third area  123  is a circle and is located inside the the first annular-like area  121  and at least over the concentric center. The third area  123  is optionally juxtaposed to the first annular-like area  121  or alternatively contained in the first annular-like area  121  with a gap between the third area  123  and the first annular-like area  121 . In this embodiment, the third area  123  is indicated in white that the third area  123  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  123  optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  123  also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  123  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  123  is also called Spot of Arago in the current application. 
     In contrast, the fourth area  124  is located outside the largest annular-like area  122 B on the two-dimensional array surface. The fourth area  124  is optionally void of any functional transducer element or disabled. Alternatively, the fourth area  124  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     The term, “annular-like area” is intended to mean the same as defined elsewhere in the current patent application. Since the definition is for the spatial relation of the array elements, it does not necessarily limit activation patterns or sequences of the dedicated transmit elements in transmitting the ultrasound pulses during the transmission operation. By the same token, the definition also does not necessarily limit activation patterns or sequences of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. 
       FIG. 12A  also illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  121 ,  121 A and  121 B. Alternatively, a combination of the second annular-like area  122 ,  122 A and  122 B is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are dynamically activated or steered. In other words, the selected annular-like receive areas have the steering angle of 0 degrees. Thus, the annular-like receive areas substantially maintain their spatial relation of the dedicated receive elements. 
     At the same time, the third area or Spot of Arago  123  is dynamic during the receive operation. For example, the size of Spot of Arago  123  dynamically changes from a first size  123 A to a second size  123 B or vice versa during the receive operation. For example, the size of the dynamic Spot of Arago  123  changes due to the first annular-like areas  121 , which changes its size by activating or deactivating predetermined portions in a certain sequence during the receive operation. Furthermore, the Spot of Arago  123  dynamically changes with respect to image depth or time in a certain embodiment. 
     Now referring to  FIG. 12B , a diagram illustrates a certain activation pattern or sequence of the dedicated receive elements of the same embodiment as described with respect to  FIG. 12A  in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  121 ′,  121 A′ and  121 B′. Alternatively, a combination of the second annular-like area  122 ′,  122 A′ and  122 B′ is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are dynamically activated or steered. In other words, the selected annular-like receive areas have the steering angle of 30 Azimuth degrees or 30 degrees in the X direction. Thus, the annular-like receive areas substantially elongated in their spatial relation of the dedicated receive elements. The annular-like receive areas become more elliptical in the direction of steering in comparison to the circular ring spatial relation of the dedicated receive elements. 
     At the same time, the third area or Spot of Arago  123 ′ is dynamic during the receive operation. For example, the size of Spot of Arago  123 ′ dynamically changes from a first size  123 A′ to a second size  123 B′ or vice versa during the receive operation. For example, the size of the dynamic Spot of Arago  123 ′ changes due to the first annular-like areas  121 ′, which changes its size by activating or deactivating predetermined portions in a certain sequence during the receive operation. Furthermore, the Spot of Arago  123 ′ dynamically changes with respect to image depth or time in a certain embodiment. 
     Now referring to  FIG. 12C , a diagram illustrates a certain activation pattern or sequence of the dedicated receive elements of the same embodiment as described with respect to  FIG. 12A  in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  121 ″,  121 A″ and  121 B″. Alternatively, a combination of the second annular-like area  122 ″,  122 A″ and  122 B″ is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are dynamically activated or steered. In other words, the selected annular-like receive areas have the steering angle of 30 Azimuth degrees and 30 Elevation degrees or 30 degrees in the X and Y directions. Thus, the annular-like receive areas substantially elongated in their spatial relation of the dedicated receive elements. The annular-like receive areas become more elliptical in the direction of steering in comparison to the circular ring spatial relation of the dedicated receive elements. 
     At the same time, the third area or Spot of Arago  123 ″ is dynamic during the receive operation. For example, the size of Spot of Arago  123 ″ dynamically changes from a first size  123 A″ to a second size  123 B″ or vice versa during the receive operation. For example, the size of the dynamic Spot of Arago  123 ″ changes due to the first annular-like areas  121 ″, which changes its size by activating or deactivating predetermined portions in a certain sequence during the receive operation. Furthermore, the Spot of Arago  123 ″ dynamically changes with respect to image depth or time in a certain embodiment. 
       FIG. 13  is a diagram illustrating an embodiment of the array in the probe according to the current invention. In general, the embodiment is substantially the same as the seventh embodiment as illustrated in  FIG. 7 . In general, the embodiment is a two-dimensional array  130  of transducer elements that includes dedicated transmit elements that perform only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention excludes any shared transmit/receive elements that perform both transmit and receive functions within the same element. The dedicated transmit elements and the dedicated receive elements are placed in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like circular areas including a first annular-like area  131  and a second annular-like area  132 . As indicated by different shades, the first annular-like area  131  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  132  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  131  and the second annular-like area  132  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas. For example, if the first annular-like area  131  exclusively includes the dedicated transmit elements, the second annular-like area  132  exclusively includes the dedicated receive elements. Although the second annular-like area  132  is not immediately juxtaposed around the first annular-like area  131 , the second annular-like area  132  has a substantially concentric center with the first annular-like area  131 . 
     In the embodiment of the array in the probe, there is an optional annular-like area  135  between the first annular-like area  131  and the second annular-like area  132 . The optional annular-like area  135  is optionally populated with either one of the dedicated transmit elements or the dedicated receive elements, and these elements may be also optionally used or disabled. Alternatively, the optional annular-like area  135  is optionally populated with neither one of the dedicated transmit elements or the dedicated receive elements. Furthermore, an additional optional annular-like area  135 ′ surrounds the second annular-like area  132 , and the additional optional annular-like area  135 ′ may be implemented in a similar manner as the optional annular-like area  135 . 
     As illustrated in the diagram, the first annular-like area  131  and the second annular-like area  132  are optionally repeated over a predetermined transducer surface of the two-dimensional array  130 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  131 A,  132 A,  131 B and  132 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  132  is larger than the first annular-like area  131  and is not immediately juxtaposed around the first annular-like area  131 , the additionally repeated annular-like areas  131 A,  132 A,  131 B and  132 B also have substantially the same spatial relationship among them. By the same token, the additionally repeated annular-like areas  131 A,  132 A,  131 B and  132 B are interlaced by optional annular-like areas  135 A and  135 B as well as by additional optional annular-like area  135 A′. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 13 , the exemplary embodiment additionally includes a third area  133  and a fourth area  134 . The third area  133  is a circle and is located inside the first annular-like area  131  and at least over the concentric center. The third area  133  is optionally juxtaposed to the first annular-like area  131  or alternatively contained in the first annular-like area  131  with a gap between the third area  133  and the first annular-like area  131 . In this embodiment, the third area  133  is indicated in white that the third area  133  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  133  optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  133  also results in improved beam width and thereby enhances near-field lateral resolution in improving imaging quality. Since the third area  133  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  133  is also called Spot of Arago in the current application. 
     In contrast, the fourth area  134  is located outside the largest annular-like area  132 B on the two-dimensional array surface. The fourth area  134  is optionally disabled or devoid of any functional transducer element. Alternatively, the fourth area  134  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
       FIG. 13  also illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  131 ,  131 A and  131 B. Alternatively, a combination of the second annular-like area  132 ,  132 A and  132 B is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are neither dynamically activated nor steered. Thus, the annular-like receive areas substantially maintain their spatial relation of the dedicated receive elements. 
     On the other hand, the third area or Spot of Arago  133  is dynamic during the receive operation. For example, the size of Spot of Arago  133  dynamically changes from a first size  133 A to a second size  133 B or vice versa during the receive operation. For example, the size of the dynamic Spot of Arago  133  changes due to the first annular-like areas  131 , which changes its size by activating or deactivating predetermined portions in a certain sequence during the receive operation. Furthermore, the Spot of Arago  133  dynamically changes with respect to image depth or time in a certain embodiment. 
     In addition to the above illustrated embodiment, alternative embodiments based upon the above embodiment further include an elliptical embodiment and a polygonal embodiment. In the elliptical alternative embodiment, the dedicated transmit elements and the dedicated receive elements are both placed in annular-like elliptical areas including a first annular-like area and a second annular-like area as described with respect to the seventh embodiment. Similarly, the third area, the fourth and the fifth area also exist in the elliptical alternative embodiment in a substantially similar manner as described with respect to the above embodiment. By the same token, in the polygonal alternative embodiment, the dedicated transmit elements and the dedicated receive elements are both placed in annular-like polygonal areas including a first annular-like area and a second annular-like area as described with respect to the above embodiment. Similarly, the third area, the fourth area and the fifth area also exist in the polygonal alternative embodiment in a substantially similar manner as described with respect to the above illustrated embodiment. Although the above alternative embodiments are not illustrated in drawings, the alternative embodiments are disclosed by the illustrated embodiment in combination with the above description. The operation of these alternative embodiments is also substantially similar to the above described embodiment. 
       FIG. 14  is a diagram illustrating a ninth embodiment of the array in the probe according to the current invention. In general, the embodiment is substantially the same as the eighth embodiment as illustrated in  FIG. 8 . In general, the embodiment is a two-dimensional array  140  of transducer elements that includes transmit/receive elements that perform both transmit and receive functions, dedicated transmit elements that perform only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention includes shared transmit/receive elements that perform both transmit and receive functions within the same element in addition to the dedicated transmit elements and the dedicated receive elements. The  The dedicated transmit elements and the dedicated receive elements are interlaced with the transmit/receive elements in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like circular areas including a first annular-like area  141  and a second annular-like area  142  while the shared transmit/receive elements are placed in a sixth annular-like area  146 . As indicated by different shades, the first annular-like area  141  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  142  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In addition, the sixth annular-like area  146  include the shared transmit/receive elements. In other words, the first annular-like area  141  and the second annular-like area  142  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas while the sixth annular-like area  146  is placed between the first annular-like area  141  and the second annular-like area  142  and includes the shared transmit/receive elements. For example, if the first annular-like area  141  exclusively includes the dedicated transmit elements, the second annular-like area  142  exclusively includes the dedicated receive elements and the sixth annular-like area  146  is placed between the first annular-like area  141  and the second annular-like area  142  and includes the shared transmit/receive elements. In the eighth embodiment, the second annular-like area  142  is immediately juxtaposed around the sixth annular-like area  146 , and the sixth annular-like area  146  is immediately juxtaposed around the first annular-like area  141 . Both the second annular-like area  142  and the sixth annular-like area  146  have a substantially concentric center with the first annular-like area  141 . 
     As illustrated in the diagram, the first annular-like area  141  and the second annular-like area  142  are optionally repeated over a predetermined transducer surface of the two-dimensional array  140 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  141 A,  142 A,  141 B and  142 B also exclusively have have an alternate one of the dedicated transmit elements and the dedicated receive elements while the sixth annular-like areas  146 ,  146 A and  146 B include the shared transmit/receive elements. In the illustrated embodiment, as the second annular-like area  142  is larger than the first annular-like area  141  and is immediately juxtaposed around the sixth annular-like areas  146 , the additionally repeated annular-like areas  141 A,  142 A,  141 B and  142 B and the sixth annular-like areas  146 ,  146 A and  146 B also have substantially the same spatial relationship among them. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 14 , the exemplary embodiment additionally includes a third area  143  and a fourth area  144 . The third area  143  is a circle and is located inside the first annular-like area  141  and at least over the concentric center. The third area  143  is optionally juxtaposed to the first annular-like area  141  or alternatively contained in the first annular-like area  141  with a gap between the third area  143  and the first annular-like area  141 . In this embodiment, the third area  143  is indicated in white that the third area  143  is devoid of the dedicated transmit elements and the dedicated receive elements or is alternatively disabled. The third area  143  optionally further reduces the number of array elements and ultimately improves the cost, the power consumption and the size. The third area  143  also results in improved beam width and thereby enhances near-field lateral resolution in improved imaging quality. Since the third area  143  having non-functioning array elements or lacking array elements correlates with the opaque optical disk in a first Fresnel zone which produces the spot of Arago in optics diffraction theory, the third area  143  is also called Spot of Arago in the current application. 
     In contrast, the fourth area  144  is located outside the largest annular-like area  142 B on the two-dimensional array surface. The fourth area  144  is optionally disabled or devoid of any functional transducer element. Alternatively, the fourth area  144  is optionally populated by the dedicated transmit elements for maximum power or the dedicated receive elements for maximum sensitivity. 
     In one exemplary array, the embodiment includes a total of ten thousand (10,000) array elements with 100 Azimuth elements and 100 Elevation elements. Among the 10,000 array elements, assuming that predetermined numbers M and N respectively indicate a number of dedicated transmit elements and dedicated receive elements while a third number O indicates a number of array elements that is unused, the sum of M+N+O is 10,000. For example, the first predetermined number M and the second predetermined number N are respectively 3750 dedicated transmit elements and 3750 dedicated receive elements while the third predetermined number O is 2600 unused array elements. Furthermore, based upon the above example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  141 ,  141 A and  141 B whose area sizes are equal in one embodiment. In another embodiment, based upon the same example, the 3750 dedicated transmit elements are optionally divided among the first annular-like areas  141 ,  141 A and  141 B whose area sizes are not equal. By the same token, based upon the same example, the 3750 dedicated receive elements are optionally divided among the second annular-like areas  142 ,  142 A and  142 B whose area sizes may or may not be equal. In an alternative embodiment, the third area  143  is included in the number N if the third area  143  is equipped with array elements and unused. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
       FIG. 14  also illustrates a certain activation pattern or sequence of the dedicated receive elements in detecting the ultrasound echoes during the receiving operation. During the receive operation, either one of the annular-like areas is activated to detect the ultrasound echoes. The activated annular-like area is optionally a combination of the first annular-like areas  141 ,  141 A and  141 B. Alternatively, a combination of the second annular-like area  142 ,  142 A and  142 B is activated to detect the ultrasound echoes. In either case, the selected annular-like receive areas are neither dynamically activated nor steered. Thus, the steered. Thus, the annular-like receive areas substantially maintain their spatial relation of the dedicated receive elements. 
     On the other hand, the third area or Spot of Arago  143  is dynamic during the receive operation. For example, the size of Spot of Arago  143  dynamically changes from a first size  143 A to a second size  143 B or vice versa during the receive operation. For example, the size of the dynamic Spot of Arago  143  changes due to the first annular-like areas  141 , which changes its size by activating or deactivating predetermined portions in a certain sequence during the receive operation. Furthermore, the Spot of Arago  143  dynamically changes with respect to image depth or time in a certain embodiment. 
     In addition to the above illustrated embodiment, alternative embodiments based upon the embodiment further include an elliptical embodiment and a polygonal embodiment. In the elliptical alternative embodiment, the shared transmit/receive elements, the dedicated transmit elements and the dedicated receive elements are all placed in annular-like elliptical areas including a first annular-like area, a second annular-like area and a sixth annular-like area as described with respect to the above embodiment. Similarly, the third area and the fourth also exist in the elliptical alternative embodiment in a substantially similar manner as described with respect to the above embodiment. By the same token, in the polygonal alternative embodiment, the shared transmit/receive elements, the dedicated transmit elements and the dedicated receive elements are all placed in annular-like polygonal areas including a first annular-like area, a second annular-like area and a sixth annular-like area as described with respect to the above embodiment. Similarly, the third area and the fourth areas also exist in the polygonal alternative embodiment in a substantially similar manner as described with respect to the above embodiment. Although the alternative embodiments are not illustrated in drawings, the alternative embodiments are disclosed by the illustrated embodiment in combination with the above description. The operation of these alternative embodiments is also substantially similar to the above described embodiment. 
     In addition to the above described operations of the embodiments, there are other operations that can be applied to the embodiments of the array in an independent or combined manner. Now referring to  FIGS. 15A ,  15 B and  15 C, a spatial compounding aperture technique is illustrated using an embodiment having the array in an elliptical arrangement. In general, the detailed description of the array including the elliptical annular-like areas of the diagram in  FIG. 15A  is substantially similar to that for the second embodiment as described with respect to the second embodiment as illustrated in  FIG. 2 . Since the spatial compounding aperture technique is optionally applicable to other embodiments, the technique will be described in its general operational manner. The spatial compounding aperture technique as illustrated in  FIGS. 15A ,  15 B and  15 C is merely exemplary and does not limit any aspect of the spatial compounding aperture technique as applied to this or other embodiments. 
       FIG. 15A  illustrates a predetermined beam direction with respect to its transmit aperture during a transmit operation. The substantially same transmit operation is repeated for a predetermined number of times.  FIG. 15B  illustrates the beam direction with respect to its receive aperture during a first receive operation. The beam direction is steered to +30 degrees in the counter clockwise direction with respect to the transmit beam from the first transmit firing. By the same token,  FIG. 15C  illustrates the beam direction with respect to its receive aperture during a second receive operation. The beam direction is steered to −30 degrees in the clockwise direction with respect to the transmit beam from the second transmit firing. 
     Now referring to  FIGS. 16A ,  16 B and  16 C, a synthetic aperture technique is illustrated using an embodiment having the array in an elliptical arrangement. In general, the detailed description of the array including the elliptical annular-like areas of the diagram in  FIG. 16A  is substantially similar to that for the second embodiment as described with respect to the second embodiment as illustrated in  FIG. 2 . Since the synthetic aperture technique is optionally applicable to other embodiments, the technique will be described in its general operational manner. The synthetic aperture technique as illustrated in  FIGS. 16A ,  16 B and  16 C is merely exemplary and does not limit any aspect of the synthetic aspect of the synthetic aperture technique as applied to this or other embodiments. 
       FIG. 16A  illustrates a transmit aperture during a transmit operation. The substantially same transmit operation is repeated for a predetermined number of times.  FIG. 16B  illustrates the receive aperture during a first receive operation. A left half of the receiving elements are used to detect echoes with respect to the transmit beam from the first transmit firing. By the same token,  FIG. 16C  illustrates the receive aperture during a second receive operation. A right half of the receiving elements are used to detect echoes with respect to the transmit beam from the second transmit firing. 
     As already described, the activation pattern of the transducer elements is not limited to a particular sequence. Although another example of the synthetic aperture techniques is not illustrated in a drawing, the example involves the standard annular-like areas with varied activation patterns both on the transmission and reception as below:
         a. On the first transmit, a first half of the transmit elements (t 1 ) is activated to transmit ultrasound pulses while a first half of the receive elements (r 1 ) is activated to receive echoes.   b. On the second transmit, the same first half of the transmit elements (t 1 ) is activated to transmit ultrasound pulses while a second half of the receive elements (r 2 ) is activated to receive echoes.   c. On the third transmit, a second half of the transmit elements (t 2 ) is activated to transmit ultrasound pulses while the first half of the receive elements (r 1 ) is activated to receive echoes.   d. On the fourth transmit, the second half of the transmit elements (t 2 ) is activated to transmit ultrasound pulses and the second half of the receive elements (r 2 ) is activated to receive echoes.       

     Now referring to  FIGS. 17A and 17B , an asymmetric aperture technique is illustrated using an embodiment having the array in an elliptical arrangement. In general, the detailed description of the array including the elliptical annular-like areas of the diagram diagram in  FIG. 17A  is substantially similar to that for the second embodiment as described with respect to the second embodiment as illustrated in  FIG. 2 . Since the asymmetric aperture technique is optionally applicable to other embodiments, the technique will be described in its general operational manner. The asymmetric aperture technique as illustrated in  FIG. 17B  is merely exemplary and does not limit any aspect of the asymmetric aperture technique as applied to this or other embodiments. 
       FIG. 17A  illustrates one example of symmetric apertures when the beam is not steered and centered using an embodiment having the array in an elliptical arrangement. In contrast,  FIG. 17B  illustrates one example of asymmetric apertures for a larger field of view in virtual apex mode using an embodiment having the array in an elliptical arrangement. In this case, the beam origin intersects the array at different places based on the beam steering angle in 3D acoustic space. In addition,  FIG. 17B  also illustrates one example of asymmetric apertures during both transmit and receive operations. As illustrated, when the beam is off center and steered to the side, an aperture falls off the edge of the array and results in creating an asymmetric aperture. 
     Now referring to  FIGS. 18A ,  18 B and  18 C, another example of the asymmetric aperture technique is illustrated using an embodiment having the array in an elliptical arrangement. In general, the detailed description of the array including the elliptical annular-like areas of the diagram in  FIG. 18A  is substantially similar to that for the second embodiment as described with respect to the second embodiment as illustrated in  FIG. 2 . Since the asymmetric aperture technique is optionally applicable to other embodiments, the technique will be described in its general operational manner. The asymmetric aperture technique as illustrated in  FIGS. 18A ,  18 B and  18 C is merely exemplary and does not limit any aspect of the asymmetric aperture technique as applied to this or other embodiments. 
       FIG. 18A  illustrates one example of symmetric apertures when the beam is steered as indicated by an arrow using an embodiment having the array in an elliptical arrangement. In addition, the center of the elliptical arrangement or beam origin is indicated by a dotted line that is extended to  FIGS. 18B and 18C . In the near field, when the beam is steered, the aperture side closer to the focus location may become larger. In general, as the echoes are received from deeper portions of acoustic space, the apodization function becomes centered on the beam origin as illustrated in  FIGS. 18B and 18C . 
       FIG. 18B  illustrates one example of asymmetric apertures using an embodiment having the array in an elliptical arrangement at a first depth in acoustic space. At this depth, an aperture falls off the center of the beam origin as indicated by the dotted line and results in creating an asymmetric aperture after apodization weighting is applied to each element. In contrast,  FIG. 18C  illustrates at a second depth in acoustic space, an aperture falls more on the center of the beam origin as indicated by the dotted line and results in creating a more symmetric aperture after apodization weighting is applied to each element. Consequently, as the depth changes, the effect is to skew the symmetry of the effective aperture after apodization weighting is applied to each element. 
       FIG. 19  is a diagram illustrating a ninth embodiment having multiple non-overlapping annular-like areas according to the current invention. In general, although the embodiment is similar to the seventh embodiment as illustrated in  FIG. 7 , it lacks a Spot of Arago. In general, the embodiment is a two-dimensional array  190  of transducer elements that includes dedicated transmit elements that perform only transmit functions and dedicated receive elements that perform only receive functions. That is, the embodiment according to the current invention excludes any shared transmit/receive elements that perform both transmit and receive functions within the same element. The dedicated transmit elements and the dedicated receive elements are placed in a certain predetermined spatial arrangement as indicated by different shades of color in the diagram. 
     The dedicated transmit elements and the dedicated receive elements are both placed in annular-like circular areas including a first annular-like area  191  and a second annular-like area  192 . As indicated by different shades, the first annular-like area  191  exclusively includes either one of dedicated transmit elements or dedicated receive elements while the second annular-like area  192  area exclusively includes the other one of the dedicated transmit elements and the dedicated receive elements. In other words, the first annular-like area  191  and the second annular-like area  192  alternate the dedicated transmit elements and the dedicated receive elements in their respective annular-like circular areas. For example, if the first annular-like area  191  exclusively includes the dedicated transmit elements, the second annular-like area  192  exclusively includes the dedicated receive elements. Although the second annular-like area  192  is not immediately juxtaposed around the first annular-like area  191 , the second annular-like area  192  has a substantially concentric center with the first annular-like area  191 . 
     In the embodiment of the array in the probe, there is an optional annular-like area  195  between the first annular-like area  191  and the second annular-like area  192 . The optional annular-like area  195  is optionally populated with either one of the dedicated transmit elements or the dedicated receive elements, and these elements may be also optionally used or disabled. Alternatively, the optional annular-like area  195  is optionally populated with neither one of the dedicated transmit elements or the dedicated receive elements. Furthermore, an additional optional annular-like area  195 ′ surrounds the second annular-like area  192 , and the additional optional annular-like area  195 ′ may be implemented in a similar manner as the optional annular-like area  195 . 
     As illustrated in the diagram, the first annular-like area  191  and the second annular-like area  192  are optionally repeated over a predetermined transducer surface of the two-dimensional array  190 . As indicated by the shaded circular rings in the diagram, the additionally repeated annular-like areas  191 A,  192 A and  191 B also exclusively have an alternate one of the dedicated transmit elements and the dedicated receive elements. In the illustrated embodiment, as the second annular-like area  192  is larger than the first annular-like area  191  and is not immediately juxtaposed around the first annular-like area  191 , the additionally repeated annular-like areas  191 A,  192 A and  191 B also have substantially the same spatial relationship among them. By the same token, the additionally repeated annular-like areas  191 A,  192 A and  191 B are interlaced by optional annular-like areas  195 A and  195 B. The term, “annular-like area” is intended to have the same meaning as already described with respect to  FIG. 1  in the in the current patent application. 
     Still referring to  FIG. 19 , the exemplary embodiment additionally includes a third area  193  and a fourth area  194 . The third area  193  is a circle and is located inside the first annular-like area  191  and at least over the concentric center. The third area  193  is optionally juxtaposed to the first annular-like area  191  or alternatively contained in the first annular-like area  191  with a gap between the third area  193  and the first annular-like area  191 . In this embodiment, the third area  193  contains the same elements as the second annular-like area  192 . 
     In contrast, the fourth area  194  is located outside the largest annular-like area  191 B on the two-dimensional array surface. The fourth area  194  is optionally disabled or devoid of any functional transducer element. Alternatively, the fourth area  194  is optionally populated by the dedicated transmit elements for maximum power and/or the dedicated receive elements for maximum sensitivity. 
     In another exemplary embodiment, the array is optionally fully populated or sparsely populated by the dedicated transmit elements and the dedicated receive elements. In case of semi-sparsely populated rings, a predetermined Apodization function is applied to weight the detected signals for the purpose of shaping a beam profile. 
     According to any and or all of the above described embodiments, at least the following advantages are substantially achieved. The use of dedicated receive elements, dedicated transmit elements and or Spot of Arago lowers implementation costs of the related electronics. 
     Furthermore, with respect to the transmit and or receive operations, beam width is advantageously optimized particularly in the near field, and the optimized beam width results in better resolution of an image. Sidelobes are also advantageously optimized particularly in the near field, and the optimized sidelobes result in reduced noise in an image. 
     While certain embodiments have been described above, these embodiments have been presented by way of example only and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope of the inventions.