Abstract:
An ultrasound diagnostic apparatus including an ultrasound probe configured to transmit toward and receive from a three-dimensional region of a subject, a transmitting and receiving unit configured to acquire ultrasound data by a plurality of executions of multibeam forming, comprising forming a plurality of sets of ultrasound data along a plurality of directions by a one-time transmitting and receiving operation of the ultrasound probe, a data synthesizing unit configured to synthesize a plurality of sets of data relating to the ultrasound data acquired during each of said executions, the sets being acquired along a respective plurality of different receiving directions with respect to a transmitting direction, to generate synthesized ultrasound data, and an image data generation unit configured to generate image data on the basis of the synthesized ultrasound data.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-252570, filed on Sep. 19, 2006, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     An ultrasonic diagnostic apparatus transmits ultrasonic waves generated by array transducers in an ultrasonic probe to a subject and displays images based on ultrasonic waves reflected from boundary surfaces of acoustic impedance. An ultrasonic diagnostic apparatus is extensively used in function diagnosis and conformation diagnosis of organs because it is easy to acquire diagnostic images. 
     By the most popular scan manner of the ultrasonic diagnostic apparatus, array transducers arranged in a row are driven electrically and ultrasonic images are acquired. Lately, 3-dimensional image data can be acquired by a 2-dimensional array probe or a mechanical oscillation 1-dimension array probe. Volume rendering images or MPR (multi plane reconstruction) images can be obtained by reconstruction of the 3 dimensional image data. 
     However, because the many scan lines in the above-mentioned acquisition of the 3-dimensional image data require much more time than 2-dimensional image data because of many scan lines. Therefore, it is very difficult to balance time resolution and space resolution. 
     One solution for this problem, the multibeam forming method. has been invented and used. With the multibeam forming method, a plurality of scan lines can be simultaneously acquired along a plurality of directions. In this method, delay calculations for signals acquired by one transmitting and receiving are executed more than once and each delay calculation corresponds to a distinctive direction of the scan line. The multibeam forming method is a very effective method for generating a 3-dimensional image data. 
     However, the multibeam forming method has a defect. By this method, because center axis of the transmitting ultrasonic beam and the receiving ultrasound beam are ordinarily different, not only reduction of transmitting and receiving sensitivity but also strain of ultrasonic beam occurs. In addition, when the distance between the transmitting beam axis and each receiving beam axis is different, transmitting and receiving sensitivity is different in accordance with the directions of the receiving beam. In other words, 3-dimensional image data acquired by the multibeam forming method includes considerable artifacts. This defect is also described in Japanese patent disclosure (kokai) No. 11-118063. 
       FIGS. 17( a ) and ( b )  are frame formats showing a transmitting beam (continuous line) and receiving beams (dashed line) in the multibeam forming method. The transmitting beam is focused at a predetermined depth. On the other hand, focusing of the receiving beam can be kept narrow along the depth direction by dynamic focus. 
     In this case, the receiving sensitivity of ultrasound is expressed by multiplication of a transmitting acoustic field and a receiving acoustic field. Then in the focused area of the transmitting beam, the transmitting acoustic field affects the receiving acoustic field. Accordingly, as shown by Btr- 1  in  FIG. 17( b ) , beam bending to the center direction is generated. Strain of the image occurs by image generation from transmitting and receiving beams having such beam bending. 
       FIG. 18  is a view showing a frame format of an acoustic field of transmitting and receiving by multibeam forming. The acoustic pressure at end of a transmitting field is less than the acoustic pressure at center of the field. This phenomenon makes the receiving sensitivity uneven and causes stripe patterns in the ultrasonic image acquired by the uneven field. In addition, the reduction of sensitivity causes deterioration of sharpness of the ultrasound image. 
     Furthermore, time phase difference is affected by the stripe pattern. Between receiving beams in one multibeam forming, the signal of the receiving beams is received simultaneously. However, between a receiving beam in one multibeam forming and a receiving beam in another multibeam forming, the sets of signals of the receiving beams are received at different times. With such time phase difference, the subject and ultrasound probe cannot be kept completely static. Then, in boundary lines between sets of multibeam forming, the signal is discontinuous. Because such discontinuity appears in every predetermined number of receiving beams, the discontinuity is easy to recognize. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided an ultrasound diagnostic apparatus including an ultrasound probe configured to transmit toward and receive from a three-dimensional region of a subject, a transmitting and receiving unit configured to acquire ultrasound data by a plurality of executions of multibeam forming, comprising forming a plurality of sets of ultrasound data along a plurality of directions by a one-time transmitting and receiving operation of the ultrasound probe, a data synthesizing unit configured to synthesize a plurality of sets of data relating to the ultrasound data acquired during each of said executions, the sets being acquired along a respective plurality of different receiving directions with respect to a transmitting direction, to generate synthesized ultrasound data, and an image data generation unit configured to generate image data on the basis of the synthesized ultrasound data. 
     According to another aspect of the present invention there is provided a method of acquiring ultrasound data including transmitting and receiving an ultrasonic signal toward and from a three-dimensional region of a subject, acquiring ultrasound data by a plurality of executions of multibeam forming, comprising forming a plurality of sets of ultrasound data along a plurality of directions by a one-time transmitting and receiving operation, synthesizing a plurality of sets of data relating to the ultrasound data acquired during said operations, the sets being acquired along a respective plurality of different receiving directions with respect to a transmitting direction, to generate synthesized ultrasound data, and generating image data on the basis of the synthesized ultrasound data. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a block diagram showing whole components of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 2  is a block diagram showing components of a transmitting and receiving unit of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 3  is a frame format showing transmitting and receiving directions for multibeam forming of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 4  is a block diagram showing components of an ultrasound data processing unit of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 5  is a frame format showing the components of an array transducers movement mechanical section of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIGS. 6( a ) and 6( b )  are frame formats showing the positional relationship of ultrasound data acquisition of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 7  is a frame format showing generation of ultrasound data of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 8  is a chart showing the character of ultrasound data of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 9  is a frame format showing synthesizing processing of ultrasound data of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 10  is a flow chart showing steps of generation of ultrasound data of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 11  is a frame format showing another synthesizing processing of ultrasound data of a first exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 12  is a frame format showing synthesizing processing of ultrasound data of a second exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 13  is a frame format showing another synthesizing processing of ultrasound data of a second exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 14  is a frame format showing synthesizing processing of ultrasound data of a third exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 15  is a block diagram showing whole components of a fourth exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIG. 16  is a frame format showing synthesizing processing of ultrasound data of a fifth exemplary embodiment of the ultrasound diagnostic apparatus of the invention. 
         FIGS. 17( a ) and 17( b )  are frame formats showing beam bending of ultrasound data of the ultrasound diagnostic apparatus of the prior art. 
         FIG. 18  is a frame format showing sensitivity unevenness of ultrasound data of the ultrasound diagnostic apparatus of the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. 
     First Exemplary Embodiment 
     In a first exemplary embodiment of the present invention, multibeam forming is executed with controlling delay time for received signals acquired by 1-dimension array vibrator elements in an ultrasonic probe. Two-dimension ultrasonic images along a slice direction intersecting with a scan direction are acquired by oscillating the vibrator elements along the slice direction. Three-dimensional ultrasonic image data is acquired as above. 
     In addition, in the following explanation of the first exemplary embodiment, 3-dimensional data is acquired by mechanically oscillating the sector scan probe. However, the 3-dimensional data may be acquired in a linear or convex scan manner. Also, 3-dimensional data may be acquired by a 2-dimensional array probe having 2-dimensionally arrayed array transducers. 
     (Components) 
       FIG. 1  is a block diagram showing the components of the first exemplary embodiment of the invention.  FIG. 2  and  FIG. 4  are block diagrams showing components included in a transmitting and receiving unit and an ultrasound data processing unit of the exemplary embodiment. 
     An ultrasonic diagnostic apparatus shown in  FIG. 1  includes an ultrasonic probe  1 , a transmitting and receiving unit  2 , an ultrasonic data processing unit  3 , a probe movement mechanical section  4  and an array transducers detection unit  5 . The ultrasonic probe  1  has 1-dimensionally arrayed vibrator elements for sector scan and transmit and receive to/from a subject. The transmitting and receiving unit  2  delivers a driving signal to the ultrasonic probe  1 , delays the received signal and adds the delayed signal. The ultrasonic data processing unit  3  generates B mode data or color Doppler data by processing the received signal acquired from the transmitting and receiving unit  2 . The probe movement mechanism section  4  oscillates the array transducers along a slice direction crossing with a scan direction mentioned below. The array transducers detection unit  5  detects a position of the oscillated vibrator elements. 
     The ultrasonic diagnostic apparatus also includes a transmitting and receiving direction control unit  6 , a data synthesizing unit  7  and a volume data generation unit  8 . The transmitting and receiving direction control unit  6  controls beam directions along the scan direction and the slice direction in the 3-dimensional region of the subject. The data synthesizing unit  7  synthesizes acquired ultrasound data in accordance with positions along the scan direction and the slice direction. The volume data generation unit  8  generates volume data from the synthesized ultrasound data. 
     Furthermore, the ultrasonic diagnostic apparatus includes an image data generation unit  9 , a display unit  10 , a reference signal generation unit  11 , an input unit  12  and a system control unit  13 . The image data generation unit  9  generates 2-dimensional or 3-dimensional images modified in accordance with a desired format. The display unit  10  displays the generated image. The reference signal generation unit  11  generates pulse waves or continuous waves having the same frequency as the center frequency of transmitting ultrasound waves for the transmitting and receiving unit  2 . Information of the subject or initial settings of apparatus or command signal are inputted by the input unit  12 . The system control unit  13  controls the above mentioned various units. 
     A surface of the ultrasonic probe  1  is contacted to the subject and executes transmitting and receiving ultrasonic waves. For example, the array transducers are provided in probe case containing coupling liquid. The array transducers are electric-sound transducers. When the ultrasound wave is transmitted, the array transducers convert an electrical drive signal to a transmit ultrasonic wave and when the reflected ultrasound wave is received, the array transducers convert the received reflected wave to an electric signal. 
     The transmitting and receiving unit  2  includes a transmitting unit  21  supplying drive signals to the array transducers and a receiving unit  22  executing the multibeam forming by delaying and adding signals received by the array transducers 
     Furthermore, as shown in  FIG. 2 , transmitting unit  21  includes a rate pulse generation unit  211 , a delay circuit  212  and a drive circuit  213 . The rate pulse generation unit  211  generates a rate pulse setting the rate cycle of the transmitted ultrasound waves by dividing a continuous wave supplied from the reference signal generation unit  11 . The delay circuit  212  consists of the same number of independent delay lines as the array transducers. The delay circuit  212  delays the rate pulse so that the transmitted wave is focused in accordance with a predetermined depth and direction supplied from the transmitting and receiving direction control unit  6 . The drive circuit  213  has the same number of independent drive circuits as the array transducers and generates drive pulses for driving the array transducers on the basis of the above mentioned delayed rate pulses. 
     The receiving unit  22  includes an A/D converter  221 , beam formers  222  and a quadrature phase detector  223 . The received signal from the ultrasound probe  1  is delivered to the beam formers  222  after digital conversion by the A/D converter  221 . Each of the beam formers  222  has a receiving delay circuit and an adding circuit. The receiving delay circuit delays the digital converted signal so that the added signal has directivity and is focused at a predetermined depth on the basis of a scan control signal from the transmitting and receiving direction control unit  6 . 
     The quadrature phase detector  223  includes a π/2 phase shifter  224 , mixers  225  and low pass filters  226 . The quadrature phase detector  223  executes orthogonal detection to the added received signals delivered from the beam formers  222  and generates complex receiving signals. 
     Next, transmitting and receiving direction control of multibeam-forming set by delay control of the transmitting delay circuits  212  and the beam formers  222  is explained with reference to  FIG. 3 . As an example, a case that the number of multibeam forming is 4 directions is explained, but this number can be changed arbitrarily.  FIG. 3  shows the directions of receiving and transmitting in the case that number of multibeam forming is 4 and a scan type is the sector scan. However, the present invention is not limited to this case. An X direction of  FIG. 3  corresponds to an array direction of the array transducers of the ultrasound probe  1  and a Y direction of  FIG. 3  corresponds to a direction that is perpendicular to the array direction. 
     The array transducers are supplied with the delay signal from the driving circuit  213  of the transmitting unit  21  and sequentially transmit ultrasound waves along directions indicated by θ 4  and θ 12 , further θ 20 , θ 28 , θ 36  (not shown) on a predetermined cycle. Also, the array transducers simultaneously receive reflected ultrasound waves caused by transmitting wave θ 4  along directions indicated by θ 1 , θ 3 , θ 5  and θ 7  in accordance with the multibeam forming manner. By the same manner, 4-direction multibeam forming is executed in the cases of θ 12 , θ 20  and so on. 
     Ultrasound data q 1 , q 3 , q 5  . . . is generated from the reception signal acquired from directions θ 1 , θ 3 , θ 5  . . . . Furthermore, volume data or image data is generated from this ultrasound data. Therefore, because only one time transition is required for acquiring ultrasound data of directions θ 1 , θ 3 , θ 5  and θ 7 , the time required for acquiring ultrasound data is cut to a quarter and time resolution of volume images is improved. 
       FIG. 4  is a block diagram showing detailed component of the ultrasound data processing unit  3 . The ultrasound data processing unit  3  includes a B mode data generation unit  31  and a color Doppler data generation unit  32 . 
     The B mode data generation unit  31  includes an envelope detector  311  which calculates envelope curve of the complex received signals supplied from the quadrature phase detector  223  and a logarithm converter  312  which converts the detected envelope curve to B mode data. 
     The Doppler data generation unit  32  includes a Doppler signal memory  321  which stores the complex receiving signal, an MTI filter  322  which removes clatter signal caused from whole movement of the subject and an autocorrelation calculator  323  which calculates autocorrelation between sets of the filtered received signals stored in the Doppler signal memory  321  and generates color Doppler data indicating the velocity of blood. 
       FIG. 5  is a frame format showing a concrete example of the probe movement mechanical section  4  shown in  FIG. 1 . The probe movement mechanical section  4  has a function for oscillating array transducers  40  provided near the top of a probe case  41  along a slice direction that is perpendicular to the scan direction. Coupling fluid fills the probe case  41 . The probe movement mechanical section  4  includes an arm  42  to which the vibrator elements  40  are fixed at one end thereof, a rotating disc  43  which is fixed in the other end of the arm  42 , a belt  44 , and a motor  45  which is coupled to the rotation disc  43  by the belt  44 . Furthermore, motor  45  rotates along the direction shown by the arrows in  FIG. 5  in accordance with a probe movement control signal supplied from the transmitting and receiving direction control unit  6 . The rotation movement of the motor  45  is transmitted to the rotation disk  43 , the belt  44  and the array transducers  40  fixed at the end of the arm  42  and oscillating along the slice direction. 
       FIG. 6( a )  and  FIG. 6( b )  are frame formats showing the method of acquiring volume data. Two-dimension data s 1  is acquired by above mentioned scan manner. In  FIG. 6( b ) , q (N,M) indicates nth ultrasound data of θ(M) shown in  FIG. 3 . Two-dimensional data in the X-Z plane is acquired as above. Then  FIG. 6( b )  shows ultrasound beam directions along the slice direction that the array transducers oscillate along. By the oscillation, a plurality of set of 2-dimensional data S(n) can be acquired in accordance with the slice direction which is perpendicular to the 2-dimensional data S(n) at a predetermined interval. By such manner, 3-dimensional data (volume data) can be obtained. 
     Returning to  FIG. 1 , the array transducers detection unit  5  detects position information (information relating position and angle) of array transducers  40  oscillated by the probe movement mechanical section  4  by a not shown an encoder included in the array transducers detection unit  5 . For example, the encoder is provided on the rotation axis of the motor  45  of the probe movement mechanical section  4 , and the position information is detected on the basis of rotation angle of the rotation axis detected by the encoder. Then the system control unit  13  delivers the detected position information to the data synthesizing unit  7 . 
     The transmitting and receiving direction control unit  6  sets directions of transmitting and multibeam forming by controlling the delay time the beam formers  222  in the receiving unit  22  and the delay circuits  212 . Furthermore the transmitting and receiving direction control unit  6  controls the array transducers  40  to scan along the slice direction by controlling of the probe movement mechanical section. 
       FIG. 7  is a frame format showing method of generating ultrasound data by controlling the transmitting and receiving direction control unit  6 . The horizontal axis corresponds to the scan direction and the longitudinal axis corresponds to the slice direction. Two-dimensional data s 1  is constructed from ultrasound data q (1,1), q (1,3), q (1,5) and q (1,7) acquired by transmitting along θ 4  and multibeam forming of θ 1 , θ 3 , θ 5  and θ 7  and from ultrasound data q (1,9), q (1,11), q (1,13) and q (1,15) acquired by transmitting along θ 12  and multibeam forming of θ 9 , θ 11 , θ 13  and θ 15  and so on. 
     Two-dimensional data s 2  neighboring to s 1  is constructed from ultrasound data q (2,5), q (2,7), q (2,9) and q (2,11) acquired by transmitting along 08 and multibeam forming of θ 5 , θ 7 , θ 9  and θ 11  and from ultrasound data q (2,13), q (2,15), q (2,17) and q (2,19) acquired by transmitting along θ 12  and multibeam forming of θ 13 , θ 15 , θ 17  and θ 19  and so on. Two-dimensional data s 3  neighboring to s 2  is constructed from ultrasound data q (3,1), q (3,3), q (3,5) and q (3,7) acquired by transmitting along θ 4  and multibeam forming of θ 1 , θ 3 , θ 5  and θ 7  and from ultrasound data q (3,9), q (3,11), q (3,13) and q (3,15) acquired by transmitting along θ 12  and multibeam forming of θ 9 , θ 11 , θ 13  and θ 15  and so on. 
     The transmitting direction is shifted at predetermined intervals along the scan direction. For example, in an odd number slice, ultrasound data begins from acquiring data by transmitting along direction θ 4  and receiving along directions θ 1 , θ 3 , θ 5  and θ 7 . In an even number slice, ultrasound data begins from acquiring data by transmitting along direction θ 8  and receiving along directions θ 5 , θ 7 , θ 9  and θ 11 . 
     Returning to  FIG. 1  again, the data synthesizing unit  7  includes a data storage unit  71  and a calculation unit  72 . The data storage unit  71  stores at least a plurality of sets of ultrasound data of the 2-dimensional data neighboring each other. Each set of ultrasound data of the 2-dimensional data is related to position information of the 2-dimensional data supplied from array transducers detection unit  5  and information of receiving directions supplied from transmitting and receiving direction control unit  6  as attendant information. 
     The calculation unit  72  reads out the ultrasound data and the attendant information of a predetermined region from 3-dimensional ultrasound data stored in the data storage unit  71 . Then the calculation unit  72  synthesizes the read out ultrasound data along the scan direction and the slice direction and calculates position information of the synthesized ultrasound data on the basis of the position information of the unsynthesized ultrasound data. The calculation unit  72  supplies the synthesized ultrasound data and its position information to the volume data generation unit  8 . 
     The volume data generation unit  8  includes a memory and stores the synthesized ultrasound data supplied from the calculation unit  72  in the memory in accordance with the position information added to the ultrasound data. In this manner, the volume data generation unit  8  generates volume data. 
     Next, synthesizing of the ultrasound data generated by the ultrasound data processing unit  3  executed by the data synthesizing unit  7  is explained with reference to  FIG. 8  and  FIG. 9 .  FIG. 8  is a frame format showing the character of 2-dimension data s 1 , s 2  and s 3  stored in the data storage unit  71  of the data synthesizing unit  7 . Each of q (1,1), q (1,3), q (1,5), . . . composing 2-dimensional data s 1 ; q (2,5), q (2,7), q (2,9), . . . composing 2-dimensional data s 2 ; and q (3,1), q (3,3), q (3,5), . . . composing 2-dimensional data s 3  has uneven receiving sensitivity and beam bending as explained with reference to  FIG. 16  and  FIG. 17 . In  FIG. 8 , receiving sensitivity A 2  indicates receiving sensitivity of an inner receiving direction near to a transmitting direction and receiving sensitivity A 1  indicates receiving sensitivity of outer an receiving direction far from a transmitting direction. Normally A 1  is smaller than A 2 . 
     Beam bending B+ and B− indicate beam bending of the inner receiving direction near to a transmitting direction and beam bending B 2 + and B 2 − indicate beam bending of the outer receiving direction far from a transmitting direction. Normally, the absolute value of B+ equals the absolute value of B−, the absolute value of B 2 + equals the absolute value of B 2 − and the absolute values of B+, B− are smaller than the absolute values of B 2 +, B 2 − respectively. 
     In addition,  FIG. 9  is a frame format showing synthesizing performed by the calculation unit  72  in the data synthesizing unit  7 . The data storage unit  71  stores ultrasound data q (1,1), q (1,3), q (1,5), . . . composing 2-dimensional data s 1 , q (2,5), q (2,7), q (2,9), . . . composing 2-dimensional data s 2  and q (3,1), q (3,3), q (3,5), composing 2-dimensional data s 3 . The calculation unit  72 , for example, generates Q (1,5) by reading out and synthesizing sets of ultrasound data of q (1,5), q (1,7), q (2,5) and q (2,7). Furthermore, the calculation unit  72  calculates a center position between q (1,5), q (1,7), q (2,5) and q (2,7) on the basis of position information attendant to the ultrasound data q (1,5), q (1,7), q (2,5) and q (2,7). The ultrasound data Q (1,5) is related to its position information and stored in the memory of volume data generation unit  8 . 
     The synthesizing is simply averaging or adding when the synthesized ultrasound data is treated as data for a center direction of the receive directions in this exemplary embodiment. In addition, a format of the volume data is the orthogonal coordinate system (U, V, W) of a 3-dimensional space where values are set at intervals (δu, δu, δu). Normally, the synthesized ultrasound data generated along polar coordinates is 3-dimensional scan converted and the volume data along the orthogonal coordinate system is generated. 
     In this manner, the calculation unit  72  also generates ultrasound data Q (1,7) by synthesizing q (1,7), q (1,9), q (2,7) and q (2,9), ultrasound data Q (1,9) by synthesizing q (1,9), q (1,11), q (2,9) and q (2,11), ultrasound data Q (2,5) by synthesizing q (2,5), q (2,7), q (3,5) and q (2,7) which are in neighboring 2-dimension data s 2  and s 3 , ultrasound data Q (2,7) by synthesizing q (2,7), q (2,9), q (3,7) and q (2,9) . . . etc. Furthermore, this synthesizing executed between 2-dimensional data s 3  and s 4 , between s 4  and s 5  . . . etc. The memory of volume data generation unit stores ultrasound data acquired by synthesizing q (1,5), q (1,7), q (1,9), q (1,11) . . . q (2,5), q (2,7), q (2,9), q (2,11) . . . q (3,5), q (3,7), q (3,9), q (3,11) . . . in accordance with the position information and volume data is generated. 
     Next, the image data generation unit  9  of  FIG. 1 , for example, includes a not shown opacity and tone adjustment unit and a rendering unit. The opacity and tone adjustment unit reads out volume data stored in the volume data generation unit  8  and sets opacity and tone of voxels of the read out volume data. On the other hand, the rendering unit renders the volume data on the basis of opacity and tone set by the opacity and tone adjustment unit and generates volume rendering images. 
     The display unit  10  includes a not shown display data generation unit, conversion unit and monitor. The display data generation unit generates data for display from 3-dimension image data or 2-dimension image data generated by image data generation unit  9 . The generations of the data for display is executed by scan conversion in accordance with predetermined format of display. The conversion unit executing an A/D conversion to the supplied data for display and TV format conversion. The monitor displays the data converted by the conversion unit. 
     The input unit  12  includes an operation panel which has a display panel, a key board, a track ball, a mouse, a selection button, input button and so on provided thereon. An operator inputs information of the subject, acquiring conditions for volume data, display conditions or some kind of command signal. 
     Furthermore, the system control unit  13  includes a not shown CPU and a memory. The information inputted from the input unit  12  by the operator is stored in the memory. The CPU wholly controls each unit mentioned above on the basis of the stored information. 
     Next, the effect of the synthesizing performed in the synthesizing unit  7  is explained with reference to  FIG. 8  and  FIG. 9 . For example in a case that q (1,5), q (1,7) of the 2-dimensional data s 1  and q (2,5), q (2,7) of data s 2  is synthesized to Q (1,5), sensitivity A(1,5) and beam bending B(1,5) of the ultrasound data Q (1.5) is expressed by expression (1) qualitatively. 
     
       
         
           
             
               
                 
                   
                     
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     On the other hand, in a case where q (1,7), q (1,9) of the 2-dimensional data s 1  and q (2,7), q (2,9) of data s 2  is synthesized to Q (1,7), sensitivity A(1,7) and beam bending B(1,7) of the ultrasound data Q (1.7) is also expressed by expression (1). 
     In addition, with reference to  FIG. 8 , no synthesized ultrasound data is synthesized from ultrasound data that is acquired only in the same time phase. This means that all boundary lines of scan lines are affected from time phase difference. This is the same condition as normal single-beam forming. 
     Thus, the formally known sensitivity unevenness, beam bending, and time phase difference occurring in the multibeam forming method is eliminated. 
     (Steps of Generating Image Data) 
     Next, steps of generating image data in present exemplary embodiment are explained with reference to  FIG. 10 . In this explanation, volume data is generated on the basis of B mode data acquired from a 3-dimensional region of the subject and volume rendering image data is generated on the basis of the volume data. However, volume data may be generated from color doppler data and surface rendering images, MIP image data or MPR image data may be generated. 
     Before generating image data of the subject, the operator of the ultrasound diagnostic apparatus  100  inputs information of the subject using input unit  12  and sets the generation conditions of the volume data or image data (step S 1  of  FIG. 10 ). 
     Next, the operator sets a top of the probe case  41  on the surface of the subject and inputs a command for starting the generation of image data (step S 2  of  FIG. 10 ). Supplying the command signal by the system control unit  13  starts the generation of image data. 
     When image data is generated, rate pulse generation unit  211  of the transmitting unit  21  supplies a rate pulse determining the frequency of the transmitting wave to the delay circuit  212 . On the basis of the control signal supplied from transmitting and receiving direction control unit  6 , the delay circuit  212  delays the rate pulse for focusing and directing to direction θ 4 . The delay circuit delivers the delayed signals to the driving circuits. The driving circuit generates driving signals and supplies the driving signal to the array transducers  40 . Then ultrasound waves are transmitted in direction θ 4 . 
     A part of the transmitted ultrasound waves are reflected from a boundary surface having a difference of acoustic impedance and are received by the array transducers  40 . After the A/D converter converts this received signal to a digital signal, the beam former adds the received signal with the delay for focusing and directing to directions θ 1 , θ 3 , θ 5 , θ 7 . 
     Next the ultrasound data processing unit  3  generates and stores ultrasound data q (1,1), q (1,3), q (1,5) and q (1,7). In this time, the ultrasound generation unit stores first position data along the slice direction supplied from array transducers detection unit  5  and receives direction information of ultrasound data (θ 1 , θ 3 , θ 5  and θ 7 ) as the attendant information related to the ultrasound data. When generation and storage of ultrasound data of θ 1 , θ 3 , θ 5  and θ 7  of the first slice is finished, ultrasound data q (1,9), q (1,11), q (1,13) and q (1,15) is generated and stored as in the above-mentioned multibeam forming of transmitting to direction θ 12 . This data is stored as 2-dimensional data s 1  in the data storage unit  71 . 
     When generation and storage of ultrasound data of the 2-dimension data s 1  of first slice is finished, the transmitting and receiving direction control unit  6  derivers a probe movement control signal to the probe movement mechanical section  4  on the basis of the instructing signal from the system control unit  13 . Then the probe movement mechanical section  4  moves the array transducers  40  to a position of the second slice. Next, system control unit  13  controls the operation so as to transmit ultrasound to directions θ 8 , θ 16  . . . and ultrasound data q (2,5), q (2,7), q (2,9), q (2,11) is generated and stored . . . as in the above-mentioned multibeam forming. The data is stored with its attendant data to data storage unit  71  as 2-dimensional data s 2 . 
     Next, in the same manner, ultrasound data q (3,1), q (3,3), q (3,5) . . . of the third slice and ultrasound data q (4,5), q (4,7), q (4,9) . . . is generated sequentially and the data is stored as 2-dimensional data s 3 , s 4 , s 5  . . . (step S 3  of  FIG. 10 ). 
     As a next step, calculation unit  72  of the data synthesizing unit  7  reads out sets of ultrasound data neighboring each other from the data storage unit  71  and synthesizes the sets of the ultrasound data along slice direction and scan direction on the basis of the respective attendant data (step S 4  of  FIG. 10 ). 
     Furthermore, calculation unit  72  calculates positions of synthesized ultrasound data from position information of the sets of the ultrasound data and delivers the calculated position information to the volume data generation unit  8  with relation to the synthesized ultrasound data (step S 5  of  FIG. 10 ). The foregoing synthesizing operation and calculating the position of the synthesized ultrasound data is repeated for all or a part of the stored ultrasound data. The synthesized ultrasound data and its position information is delivered to the volume data generation unit  8 . The volume data generation unit  8  arrays and stores in a memory the synthesized ultrasound data delivered from the calculation unit  72  on the basis of the position data which is attendant data of the synthesized ultrasound data. In this manner, the volume data generation unit  8  generates volume data (step S 6  of  FIG. 10 ) 
     Image generating unit  9  includes an opacity and tone adjustment unit for the read out volume data stored in the memory of the volume data generation unit  8  and sets opacity and tone on the basis of the voxel value of the volume data. Image data generation unit  9  also includes a rendering unit to render the volume data 3 dimensional image data on the basis of the opacity and tone set by opacity and tone adjustment unit. The rendering unit generates the volume rendering image data and delivers it to the display unit  10  (step S 7  of  FIG. 10 ). 
     The display unit generates data for display from the volume rendering image data by scan conversion on the basis of the predetermined manner of display. The display unit displays the volume rendering image data (step S 8  of  FIG. 10 ). 
     The case where the number of beams in the multibeam forming is an odd number is explained above. However, this manner can be adapted to a case where the number of beams in the multibeam forming is an even number. Hereinafter, a case where the number is an even number is explained with reference to  FIG. 11 . 
     Two-dimensional data s 1  is constructed from ultrasound data q (1,1), q (1,3) and q (1,5) acquired by transmitting along θ 3  and from ultrasound data q (1,7), q (1,9) and q (1,11) acquired by transmitting along θ 9  . . . . 2-dimensional data s 2  neighboring to s 1  is constructed from ultrasound data q (2,4), q (2,6) and q (2,8) acquired by transmitting along θ 6  and from ultrasound data q (2,10), q (2,12) and q (2,14) acquired by transmitting along θ 12  . . . 2-dimensional data s 3  neighboring to s 2  is constructed from ultrasound data q (3,1), q (3,3) and q (3,5) acquired by transmitting along θ 3  . . . s 4 , s 5 , s 6  are constructed by above mentioned manner. 
     Calculation unit  72 , for example, generates Q (1,4) by reading out and synthesizing sets of ultrasound data of q (1,3), q (1,5) and q (2,4). The ultrasound data Q (2,4) and its&#39; position information is related each other and stored in the memory of volume data generation unit  8 . In this manner, the calculation unit  72  also generates ultrasound data Q (2,6) by a synthesizing operation on q (1,5), q (1,7) and q (2,6). Furthermore, in synthesizing data between s 2 , s 3 , the position relationship of data is synthesized. Ultrasound data Q (2,4) is generated by a synthesizing operation on q (2,4), q (3,3) and q (3,5), ultrasound data Q (2,6) is generated by a synthesizing operation on q (2,6), q (3,5) and q (3,7) . . . etc. Furthermore, this synthesizing operation is executed between 2-dimensional data s 3  and s 4 , between s 4  and s 5  . . . etc. 
     In addition portions of synthesized data of this manner are not equally spaced along the slice direction. If necessary, interpolating may be performed between neighboring sets of ultrasound data so that ultrasound data is equally spaced. In this case, this interpolating may be performed in processing of the 3-dimensional scan conversion along orthogonal coordinate system (U, V, W) of the 3-dimensional space where values are set at intervals (δu, δu, δu). 
     In this manner, sensitivity and beam bending of the synthesized ultrasound data are also expressed by summation between ultrasound data as mentioned above. This means that the formerly known sensitivity unevenness and beam bending in the multibeam forming method is eliminated. Also no ultrasound data is synthesized from ultrasound data that is acquired only in the same time phase. This is the same condition as normal single-beam forming. This means that formerly known sensitivity unevenness, beam bending, and time phase difference in the multibeam forming method is eliminated. 
     Second Exemplary Embodiment 
     Hereinafter, other manners of a synthesizing operation executed by the data synthesizing unit  7  are described with reference to  FIG. 12  and  FIG. 13 .  FIG. 12  is a frame format showing a second exemplary embodiment. In this figure, 2-dimensional data s 1 , which is a first slice, composed from ultrasound data q (1,1), q (1,3), q (1,5) and q (1,7) which is acquired by multibeam forming transmitting in direction θ 4  and reception from θ 1 , θ 3 , θ 5  and θ 7  and ultrasound data q (1,9), q (1,11), q (1,13) and q (1,15) which is acquired by multibeam forming transmitting in direction θ 12  and reception from θ 9 , θ 11 , θ 13  and θ 15  . . . . 
     2-dimensional data s 2 , which is a second slice, is composed from ultrasound data q (2,3), q (2,5), q (2,7) and q (2,9) which is acquired by multibeam forming transmitting in direction θ 6  and reception from θ 3 , θ 5 , θ 7  and θ 9  and ultrasound data q (2,11), q (2,13), q (2,15) and q (2,17) which is acquired by multibeam forming of a transmitting to direction θ 14  and reception from θ 11 , θ 13 , θ 15  and θ 17  . . . . 
     Furthermore, 2-dimensional data s 3 , which is a third slice, is composed from ultrasound data q (3,5), q (3,7), q (3,9) and q (3,11) which is acquired by multibeam forming transmitting in direction θ 8  and reception from θ 5 , θ 7 , θ 9  and θ 11  and ultrasound data q (3,13), q (3,15), q (3,17) and q (3,19) which is acquired by multibeam forming transmitting in direction θ 16  and reception from θ 13 , θ 15 , θ 17  and θ 19  . . . . 
     Two-dimensional data s 4 , which is a fourth slice, is composed from ultrasound data q (4,7), q (4,9), q (4,11) and q (4,13) which is acquired by multibeam forming of a transmitting to direction θ 10  and reception from θ 7 , θ 9 , θ 11  and θ 13  . . . . 
     Furthermore, after the fourth slice, for the fifth to ninth slices and tenth to thirtieth slices . . . , 2-dimensional data s 5  to s 9  and s 10  to s 13  . . . is generated in the same manner as in the case of generating 2-dimension data s 1  to s 4  on the first to fourth slices. 
     Next calculation unit  72  in the data synthesizing unit  7  reads out ultrasound data q (1,7), q (2,7), q (3,7) and q (4,7) which is ultrasound data corresponding to θ 7  of 2-dimensional data s 1 , s 2 , s 3  and s 4 . Then by the synthesizing of this ultrasound data, the calculation unit  72  generates ultrasound data Q (2,7) synthesizes and calculates a center position between q (1,7), q (2,7), q (3,7) and q (4,7) on the basis of position information attended to the ultrasound data q (1,7), q (2,7), q (3,7) and q (4,7). Ultrasound data Q (2,7) is related to its&#39; position information and stored in the memory of volume data generation unit  8 . The synthesizing is also simply averaging or adding in this exemplary embodiment. However, the synthesizing may be weighted mean. For example, q (2,7) and q (3,7) may be more weighted than q (1,7) and q (4,7) for sharpness of acquired image. However simply averaging or adding is more suitable for reduction of the effects of beam bending or sensitivity unevenness. 
     In a same manner, the calculation unit  72  sequentially calculates Q (2,9) from q (1,9), q (2,9), q (3,9) and q (4,9) . . . ; Q (2,11) from q (1,11), q (2,11), q (3,11) and q (4,11); Q (3,7) from q (2,7), q (3,7), q (4,7) and q (5,7) . . . ; Q (3,9) from q (2,9), q (3,9), q (4,9) and q (5,9) . . . ; Q (4,7) from q (3,7), q (4,7), q (5,7) and q (6,7) . . . . 
     In this manner sensitivity and beam bending of the synthesized ultrasound data are also expressed by summation between ultrasound data as mentioned above. This means that formerly known sensitivity unevenness and beam bending by the multibeam forming method are eliminated. Also no ultrasound data is synthesized from ultrasound data that is acquired only in the same time phase. This is the same condition as normal single-beam forming. This means that the formerly known sensitivity unevenness, beam bending, and time phase difference in the multibeam forming method is eliminated. 
     In the where case the number of beams in the multibeam forming is an odd number is explained above. However, the second exemplary embodiment can be adapted to a case where the number of beams in the multibeam forming is an even number. Hereinafter, a case where number of beams is an even number is explained with the reference to  FIG. 13 . 
     Two-dimensional data s 1  is constructed from ultrasound data q (1,1), q (1,3) and q (1,5) acquired by transmitting along θ 3  and from ultrasound data q (1,7), q (1,9) and q (1,11) acquired by transmitting along θ 9  . . . . 2-dimensional data s 2  neighboring to s 1  is constructed from ultrasound data q (2,3), q (2,5) and q (2,7) acquired by transmitting along θ 5  and from ultrasound data q (2,9), q (2,11) and q (2,13) acquired by transmitting along θ 11  . . . . 2-dimensional data s 3  neighboring to s 2  is constructed from ultrasound data q (3,5), q (3,7) and q (3,9) acquired by transmitting along θ 7  . . . s 4 , s 5 , s 6  is constructed by above mentioned manner. 
     Next calculation unit  72  in the data synthesizing unit  7  reads out ultrasound data q (1,5), q (2,5) and q (3,5) which is ultrasound data corresponding to θ 5  of 2-dimensional data s 1 , s 2  and s 3 . Then by the synthesizing of this ultrasound data, calculation unit  72  generates ultrasound data Q (2,5) and calculates a center position on the basis of position information attended to the ultrasound data. Ultrasound data Q (2,5) is related to its&#39; position information and stored in the memory of volume data generation unit  8 . In the same manner, calculation unit  72  sequentially calculates Q (2,7) from q (1,7), q (2,7) and q (3,7) . . . ; Q (2,9) from q (1,9), q (2,9) and q (3,9); Q (3,5) from q (2,5), q (3,5) and q (4,7) . . . ; Q (4,5) from q (4,5), q (3,5) and q (4,5) . . . . 
     In this manner, sensitivity and beam bending of the synthesized ultrasound data are also expressed by the summation between ultrasound data as mentioned above. This means that the formerly known sensitivity unevenness and beam bending in the multibeam forming method is eliminated. Also no ultrasound data is synthesized from ultrasound data that is acquired only in the same time phase. This is the same condition as in normal single-beam forming. This means that the formerly known sensitivity unevenness, beam bending, and time phase difference in the multibeam forming method is eliminated. 
     In addition, compared to the case of 4-beam multibeam forming, there is a number of sets of ultrasound data that are not synthesized. In the manner shown in  FIG. 12 , 12 sets of ultrasound data (q (1,1), q (1,3) q (1,5), q (2,3), q (2,5), q (3,5), q (1,n−4), q (2,n−4), q (2,n−2), q (3,n−4), q (3,n−2) and q (3,n) (n is an end number along the scan direction)) are not synthesized and not used in 2-dimensional data s 1  to s 4 . However, in the manner shown in  FIG. 13 , the number of sets of ultrasound data that are not synthesized and not used in is 6 (q (1,1), q (1,3), q (2,3), q (1,n−2), q (2,n−2) and q (2,n)) in 2-dimensional data s 1  to s 3 . 
     Furthermore, in such a manner, the second exemplary embodiment can be adapted to cases of a number of beams for multibeam forming where the number is more than 1. 
     Third Exemplary Embodiment 
     Hereinafter, another manner of the synthesizing operation executed by the data synthesizing unit  7  is described with reference to  FIG. 14 .  FIG. 14  is a frame format showing a third exemplary embodiment. This exemplary embodiment makes it possible to generate 2-dimensional images that eliminate the effect of beam bending, sensitivity unevenness and time phase difference. 
     In this exemplary embodiment, 2-dimensional data s 1  and s 2  are acquired in same manner as the first exemplary embodiment shown in  FIG. 9 . However, 2-dimensional data s 3 , s 4 , s 5  . . . are not acquired. Then, the synthesized ultrasound data is generated about only one slice. 
     In this manner, formerly known sensitivity unevenness, beam bending, and time phase difference in the multibeam forming method is eliminated. In addition, compared to the formerly known 2-beam multibeam forming, the frame rate is same. Furthermore, 2-beam multibeam forming has no sensitivity unevenness. However, the third exemplary embodiment has an effect of eliminating beam bending and time phase difference by comparison to 2-beam multibeam forming. 
     Fourth Exemplary Embodiment 
     In above mentioned exemplary embodiment, the data synthesizing unit  7  synthesizes data from the ultrasonic data processing unit  3 . However, present invention is not limited in this manner. For example, the data synthesizing unit  7  may execute the above-mentioned synthesizing operation to complex received signals supplied from the transmitting and receiving unit  2  as shown in  FIG. 15 . When the ultrasound data processing unit  3  generates ultrasound data from the complex receiving signal synthesized in the data synthesizing unit  7 , the effect explained above is realized. Furthermore, because the synthesized receiving signal has phase information, more proper adjustment can be executed, especially for beam bending. 
     Fifth Exemplary Embodiment 
     In above mentioned exemplary embodiment, the case where 1-dimensional sector array transducers are oscillated and acquire volume data is mainly explained. However, in a fifth exemplary embodiment, volume data is acquired by a 2-dimensional array probe. In this case, by one transmitting and receiving operation using multibeam forming, ultrasound data can be acquired for a 3-dimensional region. 
       FIG. 16  is a frame format showing a fifth exemplary embodiment. In this figure, 2-dimensional data s 1  and s 2  are composed from ultrasound data q (1,1), q (1,3), q (1,5), q (1,7) q (2,1), q (2,3), q (2,5) and q (2,7) which is acquired by multibeam forming transmitting in direction θ 4  being a center direction between s 1  and s 2  and reception from θ 1 , θ 3 , θ 5  and θ 7  of s 1  and s 2  and ultrasound data q (1,9), q (1,11), q (1,13), q (1,15), q (2,9), q (2,11), q (2,13) and q (2,15) which is acquired by multibeam forming transmitting in direction θ 12  being a center direction between s 1  and s 2  and reception from θ 9 , θ 11 , θ 13  and θ 15  of s 1  and s 2  . . . . 
     On the other hand, 2-dimensional data s 3  and s 4  are composed from ultrasound data q (3,5), q (3,7), q (3,9), q (3,11), q (4,5), q (4,7), q (4,9) and q (4,11) which is acquired by multibeam forming transmitting in direction θ 8  being a center direction between s 3  and s 4  and reception from θ 5 , θ 7 , θ 9  and θ 11  of s 3  and s 4  and ultrasound data q (3,13), q (3,15), q (3,17), q (3,19) q (4,13), q (4,15), q (4,17) and q (4,19) which is acquired by multibeam forming transmitting in direction θ 16  being a center direction between s 3  and s 4  and reception from θ 13 , θ 15 , θ 17  and θ 19  of s 3  and s 4  . . . . 
     Furthermore, 2-dimensional data s 5  to s 9  and s 10  to s 13  . . . is generated in the same manner of the case of generating 2-dimension data s 1  to s 4 . 
     Next, calculation unit  72  in the data synthesizing unit  7  reads out ultrasound data q (1,7), q (2,7), q (3,7), q (4,7) which is ultrasound data corresponding to θ 7  of 2-dimensional data s 1 , s 2 , s 3  and s 4  and q (1,9), q (2,9), q (3,9) and q (4,9) which is ultrasound data corresponding to θ 7  of 2-dimensional data s 1 , s 2 , s 3  and s 4 . Then by the synthesizing this ultrasound data, calculation unit  72  generates ultrasound data Q (2,5) and calculates a center position between q (1,7), q (2,7), q (3,7) q (4,7), q (1,9), q (2,9), q (3,9) and q (4,9) on the basis of position information attended to the ultrasound data. The ultrasound data Q (2,5) and its&#39; position information is related each other and stored in the memory of volume data generation unit  8 . 
     In a same manner, calculation unit  72  sequentially calculates Q (2,7) from q (1,7), q (2,7), q (3,7), q (4,7) q (1,9), q (2,9), q (3,9) and q (4,9) . . . ; Q (3,7) from q (2,7), q (3,7), q (4,7), q (5,7), q (2,9), q (3,9), q (4,9) and q (5,9) . . . . 
     In this manner, sensitivity, beam bending, of the synthesized ultrasound data is also expressed by summation between ultrasound data as mentioned above. This means that formerly known sensitivity unevenness and beam bending in the multibeam forming method is eliminated. Also no ultrasound data is synthesized from ultrasound data that is acquired only in the same time phase. This is the same condition as normal single-beam forming. This means that the formerly known sensitivity unevenness, beam bending, and time phase difference in the multibeam forming method is eliminated. 
     Numerous variations of the present invention are possible in light of the above description. It is therefore to be understood that the invention as claimed can be practiced other than is specifically described herein.