Abstract:
Provided is a technology capable of obtaining at high speed a three-dimensional image having good image quality, without increasing the load on an ultrasonic diagnostic device. A plurality of filter processing having different effects are performed, prior to rendering, on tomographic volume data that has completed coordinate transformation, and volume data is obtained for each. A prescribed weight is added to each voxel for each of the obtained volume data, and a three-dimensional image is generated from the volume data obtained thereby. The filter processing having different effects may be different types of filter processing such as smoothing and sharpening, the same filter processing but having different strengths, or a combination of filter processing and no filter processing.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an ultrasonic diagnostic device that builds an ultrasonic image of a diagnostic region in an object using ultrasound and displays the ultrasonic image, and more particularly, to an ultrasonic diagnostic device that can build three-dimensional ultrasonic images of a tomographic image, a blood flow image, and elasticity image data. 
       BACKGROUND ART 
       [0002]    An ultrasonic diagnostic device transmits ultrasound to an object using an ultrasonic probe, receives a reflected echo signal from the object, and generates a tomographic image of the object using the reflected echo signal. In the ultrasonic diagnostic device, the ultrasonic probe is automatically or manually operated in a minor-axis direction, whereby three-dimensional data is obtained. The obtained three-dimensional data is projected on a two-dimensional projection surface by a method such as volume rendering to display a projected image (a three-dimensional image). For example, blood flow speed and blood flow strength in a blood flow image or information concerning distortion and hardness in an elasticity image are three-dimensionally acquired to generate and display a projected image. 
         [0003]    At present, signal processing (image processing) from the reflected echo signal to the projected image generation is carried out in real time. A technique called real-time 3D or 4D for displaying a three-dimensional image as a moving image is generally adopted. 
         [0004]    However, an ultrasonic image includes a large number of artifacts peculiar to ultrasound such as speckle noise, causing deterioration in image quality of a three-dimensional image. In order to reduce such noise and improve the image quality, three-dimensional filter processing such as smoothing having a relatively light processing load is performed. However, for example, the smoothing reduces the noise of the three-dimensional image and improves the image quality but, on the other hand, sometimes makes a boundary unclear. Since a data amount of three-dimensional data is enormous, it is difficult to perform, in real time, arbitrary image processing for improving the image quality. 
         [0005]    As a technique for solving such a problem, for example, there is a method of determining, for each space, whether voxel data smoothed by a moving average method is amplified and used and improving image quality (see, for example, Patent Literature 1). In this method, it is determined according to a standard deviation of peripheral luminance whether the voxel data is used. 
         [0006]    There is a method of improving image quality of a three-dimensional image by coupling a plurality of pieces of volume data when sufficient three-dimensional volume data is not obtained by one scanning (see, for example, Patent Literature 2). 
         [0007]    Further, there is a technique for improving image quality of a three-dimensional image by combining two images, i.e., a volume rendering image in which a shape of an object can be grasped and a volume rendering image in which structure of the object can be grasped (see, for example, Patent Literature 3). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: JP-A-2007-229283 
         Patent Literature 2: JP-A-2009-61182 
         Patent Literature 3: JP-A-2006-130071 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0011]    When processing is excessive, even if an implementation region of smoothing is switched for each space, a harmful effect of the smoothing that an image becomes unclear cannot be removed. There is no choice but to select smoothing intensity out of smoothing intensities prepared in advance. There is no degree of freedom of the selection. Therefore, it is difficult to apply smoothing at optimum intensity. 
         [0012]    The coupling processing disclosed in Patent Literature 2 is performed by averaged voxel values of the same region acquired at different times. Therefore, although a temporal smoothing effect is obtained, a spatial smoothing effect is not obtained. 
         [0013]    When the combining processing disclosed in Patent Literature 3 is carried out, rendering processing needs to be carried out twice. Since a computational amount of the rendering processing is larger compared with three-dimensional filter processing such as smoothing, a load on a device is large. The rendering processing is not suitable for implementation in real time. 
         [0014]    The present invention has been devised in view of the above and it is an object of the present invention to provide a technique that can acquire a three-dimensional image having satisfactory image quality at high speed without increasing a load on an ultrasonic diagnostic device. 
       Solution to Problem 
       [0015]    The present invention applies, before rendering processing, a plurality of kinds of filter processing having different effects to tomographic volume data and obtains volume data in the respective kinds of filter processing. The present invention generates a three-dimensional image from volume data obtained by giving weight set in advance to the obtained respective volume data and adding up the volume data for each voxel. 
         [0016]    The kinds of filter processing having the different effects may be kinds of processing having different kinds of filters such as smoothing and sharpening or may be the same kinds of filter processing having different intensities. The kinds of filter processing may be filter processing to be performed and filter processing not to be performed. 
         [0017]    Specifically, there is provided an ultrasonic diagnostic device including: an ultrasonic probe; a transmitting unit configured to transmit a driving signal to the ultrasonic probe; a three-dimensional tomographic data generating unit configured to generate, using an ultrasonic signal from a test target measured by the ultrasonic probe, tomographic volume data of the test target; a three-dimensional image processing unit configured to generate a three-dimensional image from the tomographic volume data; and a display unit configured to display the three-dimensional image generated by the three-dimensional image processing unit. The three-dimensional image processing unit includes: a smoothing unit configured to apply spatial smoothing to the tomographic volume data and generate smoothed volume data; a weighted addition unit configured to multiply, when the smoothed volume data is generated, the tomographic volume data and the smoothed volume data with a weight coefficient and add up the volume data to generate combined volume data; and a rendering unit configured to apply, when the combined volume data is generated, rendering processing to the combined volume data and generate the three-dimensional image. 
         [0018]    According to another aspect, there is provided an ultrasonic diagnostic device including: an ultrasonic probe; a transmitting unit configured to transmit a driving signal to the ultrasonic probe; a three-dimensional tomographic data generating unit configured to generate, using an ultrasonic signal from a test target measured by the ultrasonic probe, tomographic volume data of the test target; a three-dimensional image processing unit configured to generate a three-dimensional image from the tomographic volume data; and a display unit configured to display the three-dimensional image generated by the three-dimensional image processing unit. The three-dimensional image processing unit includes: a filter processing unit configured to apply each of a plurality of kinds of three-dimensional filter processing to the tomographic volume data and generate processed volume data in the respective kinds of three-dimensional filter processing; a weighted addition unit configured to multiply, when a plurality of pieces of the processed volume data are generated, the plurality of pieces of processed volume data with a weight coefficient and add up the plurality of pieces of processed volume data to generate combined volume data; and a rendering unit configured to apply, when the combined volume data is generated, rendering processing to the combined volume data and generate the three-dimensional image. 
         [0019]    According to still another aspect, the present invention provides there is provided an ultrasonic diagnostic device including: an ultrasonic probe; a transmitting unit configured to transmit a driving signal to the ultrasonic probe; a three-dimensional tomographic data generating unit configured to generate, using an ultrasonic signal from a test target measured by the ultrasonic probe, tomographic volume data of the test target; a three-dimensional image processing unit configured to generate a three-dimensional image from the tomographic volume data; and a display unit configured to display the three-dimensional image generated by the three-dimensional image processing unit. The three-dimensional image processing unit includes: a filter processing unit configured to apply each of a plurality of kinds of three-dimensional filter processing to the tomographic volume data and generate processed volume data in the respective kinds of three-dimensional filter processing; and a rendering unit configured to apply, when the processed volume data is generated, rendering processing to a plurality of pieces of the generated processed volume data while multiplying the processed volume data with a weight coefficient and adding up the processed volume data for each constituent voxel to generate the three-dimensional image. 
         [0020]    Further, there is provided an image processing method in an ultrasonic diagnostic device for transmitting ultrasound to a test target, applying image processing to tomographic volume data of the test target generated using a received ultrasonic signal, and generating a three-dimensional image. The image processing method includes: a smoothing step for applying spatial smoothing to the tomographic volume data and generating smoothed volume data; a weighted addition step for multiplying the tomographic volume data and the smoothed volume data with a weight coefficient and adding up the volume data to generate combined volume data; and a rendering step for applying rendering processing to the combined volume data and generating the three-dimensional image. 
         [0021]    Further, there is provided a program for an ultrasonic diagnostic device for causing a computer to function as: a three-dimensional tomographic data generating unit configured to transmit ultrasound to a test target and generate tomographic volume data of the test target using a received ultrasonic signal; a smoothing unit configured to apply spatial smoothing to the tomographic volume data and generate smoothed volume data; a weighted addition unit configured to multiply the tomographic volume data and the smoothed volume data with a weight coefficient and add up the volume data to generate combined volume data; and a rendering unit configured to apply rendering processing to the combined volume data and generate the three-dimensional image. 
       Advantageous Effects of Invention 
       [0022]    According to the present invention, it is possible to acquire a three-dimensional image having satisfactory image quality at high speed without increasing a load on an ultrasonic diagnostic device. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0023]      FIG. 1  is a block diagram of an ultrasonic diagnostic device in a first embodiment. 
           [0024]      FIG. 2  is a functional block diagram of a three-dimensional image processing unit in the first embodiment. 
           [0025]      FIG. 3  is a flowchart of three-dimensional image processing in the first embodiment. 
           [0026]      FIGS. 4(   a ) to  4 ( c ) are diagrams for explaining volume data generated by the three-dimensional image processing in the first embodiment. 
           [0027]      FIGS. 5(   a ) to  5 ( c ) are diagrams for explaining a three-dimensional image generated in the first embodiment. 
           [0028]      FIGS. 6(   a ) to  6 ( c ) are diagrams for explaining a weight coefficient setting interface in the first embodiment. 
           [0029]      FIGS. 7(   a ) to  7 ( c ) are diagrams for explaining a smoothing coefficient setting interface in the first embodiment. 
           [0030]      FIG. 8  is a functional block diagram of a three-dimensional image processing unit in a second embodiment. 
           [0031]      FIG. 9  is a flowchart of three-dimensional image processing in the second embodiment. 
           [0032]      FIG. 10  is a functional block diagram of a three-dimensional image processing unit in a third embodiment. 
           [0033]      FIG. 11  is a flowchart of three-dimensional image processing in the third embodiment. 
           [0034]      FIGS. 12(   a ) to  12 ( c ) are diagrams for explaining a smoothing method and sharpening method setting interface in the third embodiment. 
           [0035]      FIG. 13  is a functional block diagram of a three-dimensional image processing unit in a fourth embodiment. 
           [0036]      FIG. 14  is a flowchart of three-dimensional image processing in the fourth embodiment. 
           [0037]      FIG. 15  is a diagram for explaining volume data generated in the fourth embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0038]    An embodiment of the present invention is explained below on the basis of the drawings. In the following explanation, in all the figures for explaining the embodiment of the present invention, components having the same functions are denoted by the same reference numerals and signs and repeated explanation of the components is omitted. In this embodiment, a three-dimensional image is generated from combined volume data generated by giving weight set in advance to tomographic volume data after three-dimensional image conversion and smoothed data of the tomographic volume and adding up the data. An ultrasonic diagnostic device includes an ultrasonic probe, a transmitting unit configured to transmit a driving signal to the ultrasonic probe, a three-dimensional tomographic data generating unit configured to generate, using an ultrasonic signal from a test target measured by the ultrasonic probe, tomographic volume data of the test target, a three-dimensional image processing unit configured to generate a three-dimensional image from the tomographic volume data, and a display unit configured to display the three-dimensional image generated by the three-dimensional image processing unit. 
         [0039]    First, an ultrasonic diagnostic device  0001  in this embodiment is explained using  FIG. 1 . As shown in  FIG. 1 , the ultrasonic diagnostic device  0001  includes an ultrasonic probe  0002  used in contact with an object  0010 , a transmitting unit  0005  configured to repeatedly transmit ultrasound to the object  0010  at a fixed time interval via the ultrasonic probe  0002 , a receiving unit  0006  configured to receive a reflected echo signal reflected from the object  0010 , a transmission and reception control unit  0007  configured to control operations of the transmitting unit  0005  and the receiving unit  0006 , and a phasing addition unit  0008  configured to subject the reflected echo signal received by the receiving unit  0006  to phasing addition. 
         [0040]    The ultrasonic probe  0002  includes a plurality of oscillators. The ultrasonic probe  0002  transmits ultrasound to the object  0010  via the oscillators and receives a reflected echo signal. The plurality of oscillators are arrayed in a rectangular shape or a fan shape. The ultrasonic probe  0002  mechanically swings the oscillators in a direction (a minor-axis direction) orthogonal to a direction of the array to thereby three-dimensionally transmit and receive ultrasound. Note that, as the ultrasonic probe  0002 , an ultrasonic probe may be used in which a plurality of oscillators are two-dimensionally arrayed and that electronically controls transmission and reception of ultrasound to three-dimensionally transmit and receive the ultrasound. 
         [0041]    The transmitting unit  0005  transmits a driving signal to the ultrasonic probe  0002 . The transmitting unit  0005  generates a wave transmission pulse for driving the oscillators of the ultrasonic probe  0002  to generate ultrasound. When generating the wave transmission pulse, the transmitting unit  0005  controls a phase of a wave transmission signal passed to the respective oscillators of the ultrasonic probe  0002  and sets a convergent point of transmitted ultrasound to certain depth. The receiving unit  0006  amplifies, with a predetermined gain, reflected echo signals received by the respective oscillators of the ultrasonic probe  0002  and generates RF signals, i.e., reception signals. The transmission and reception control unit  0007  controls operations of the transmitting unit  0005  and the receiving unit  0006 . The phasing addition unit  0008  adds up, after aligning phases of the RF signals amplified by the receiving unit  0006 , the RF signals to thereby form an ultrasonic beam converging at one point or a plurality of convergent points and generate RF signal frame data (equivalent to RAW data). 
         [0042]    The three-dimensional tomographic data generating unit generates, using an ultrasonic signal from a test target measured by the ultrasonic probe  0002 , tomographic volume data of the test target. The ultrasonic diagnostic device  0001  includes a tomographic information calculating unit  0011 , a three-dimensional tomographic data storing unit  0012 , and a three-dimensional coordinate conversion unit  0013  as components of the three-dimensional tomographic data generating unit configured to generate tomographic volume data, which is three-dimensional data of a diagnostic region, from the RF signal frame data. The ultrasonic diagnostic device  0001  includes a three-dimensional image processing unit  0014  and a display data generating unit  0016  as components configured to generate a three-dimensional image (a two-dimensional projected image of three-dimensional volume data) of a diagnostic region having amplitude of received ultrasound as luminance, from the tomographic volume data. Further, the ultrasonic diagnostic device  0001  may include an arbitrary tomographic image creating unit  0015  as a component configured to create a two-dimensional image of an arbitrary tomographic profile. Details of the respective units are explained below. 
         [0043]    The ultrasonic diagnostic device  0001  includes an operation unit  0004  and a display device (a display unit)  0009  as user interfaces. Further, the ultrasonic diagnostic device  0001  includes a control unit  0003  configured to control operation of the entire ultrasonic diagnostic device  0001 . 
         [0044]    The tomographic information calculating unit  0011  applies signal processing such as gain correction, log compression, detection, edge enhancement, and smoothing to the RF signal frame data generated by the phasing addition unit  0008  and forms secondary tomographic data. In that case, the control unit  0003  controls the tomographic information calculating unit  0011  according to a setting condition received from an operator via the operation unit  0004 . 
         [0045]    The three-dimensional tomographic data storing unit  0012  stores the two-dimensional tomographic data formed by the tomographic information calculating unit  0011  while associating the two-dimensional tomographic data with an acquisition position thereof. The acquisition position is a transmitting and receiving direction. For example, when a coordinate system including a θ direction and a φ direction orthogonal to the θ direction is used, if two-dimensional tomographic data is formed by a measurement result obtained by performing transmission and reception in the θ direction, the three-dimensional tomographic data storing unit  0012  stores, for each position in the φ direction orthogonal to the θ direction, a plurality of pieces of two-dimensional tomographic data using the position as an index. 
         [0046]    The three-dimensional coordinate conversion unit  0013  applies three-dimensional coordinate conversion to the plurality of pieces of two-dimensional tomographic data stored in the three-dimensional tomographic data storing unit  0012  and generates tomographic volume data. 
         [0047]    The three-dimensional image processing unit  0014  applies three-dimensional image processing to the tomographic volume data after the coordinate conversion in the three-dimensional coordinate conversion unit  0013  and generates a three-dimensional image. The three-dimensional image processing unit  0014  executes the three-dimensional image processing every time tomographic volume data is generated and generates a three-dimensional image. Details of the three-dimensional image processing in this embodiment are explained below. A color scale, brightness of which increase mainly according to luminance, such as a gray scale changing from black to white according to luminance or a sepia color having a reddish tinge is given to the generated three-dimensional image. 
         [0048]    The arbitrary tomographic image creating unit  0015  creates, using the two-dimensional tomographic data stored in the three-dimensional tomographic data storing unit  0012 , a two-dimensional image of a tomographic profile designated by the operator. Note that the operator sets a conversion coefficient via the operation unit  0004  to thereby designate a displayed tomographic profile. 
         [0049]    The display data generating unit  0016  generates display data for causing the display device  0009  to display the three-dimensional image generated in the three-dimensional image processing unit  0014 . The display data generating unit  0016  in this embodiment generates display data every time a three-dimensional image is generated and updates display data of the display device  0009 . Note that, when the ultrasonic diagnostic device  0001  includes the arbitrary tomographic image creating unit  0015 , the display data generating unit  0016  generates, as display data, display data for displaying the three-dimensional image together with the two-dimensional image generated in the arbitrary tomographic image creating unit  0015 . For example, the display data generating unit  0016  displays the two-dimensional image and the three-dimensional image in parallel to each other. 
         [0050]    Next, the three-dimensional image processing unit  0014  characteristic in this embodiment is explained using  FIG. 2 .  FIG. 2  is a functional block diagram of the three-dimensional image processing unit  0014  in this embodiment. 
         [0051]    As shown in the figure, the three-dimensional image processing unit  0014  in this embodiment performs three-dimensional image processing for combining, at an arbitrary ratio, tomographic volume data itself generated by the three-dimensional coordinate conversion unit  0013  and data, which is obtained by applying smoothing to the tomographic volume data, and generating a three-dimensional image. The three-dimensional image processing unit  0014  includes a three-dimensional smoothing unit  0201 , a weighted addition unit  0202 , and a gradient calculating unit  0203  for realizing the three-dimensional image processing. Hereinafter, in this embodiment, the tomographic volume data subjected to the smoothing is referred to as smoothed volume data (smooth volume data) and the tomographic volume data itself not subjected to the smoothing is referred to as texture volume data (original volume data). 
         [0052]    The three-dimensional smoothing unit (the filter processing unit)  0201  applies spatial smoothing (three-dimensional smoothing) to the tomographic volume data after the coordinate conversion in the three-dimensional coordinate conversion unit  0013  and generates smoothed volume data. The three-dimensional smoothing unit (the filter processing unit)  0201  may apply each of a plurality of kinds of three-dimensional filter processing to the tomographic volume data and generate processed volume data in the respective kinds of three-dimensional filter processing. In this embodiment, as the smoothing, for example, averaging filter processing for averaging the tomographic volume data using voxel values around the tomographic volume data is used. Intensity of smoothing of the averaging filter processing depends on the number of averaged voxels. The number of averaged voxels is set by the operator as a smoothing coefficient. 
         [0053]    The weighted addition unit  0202  performs weighted addition processing for subjecting a plurality of pieces of volume data generated from the same tomographic volume data to weighted addition using a set weight coefficient and generating volume data. The weighted addition unit  0202  performs the weighted addition for each voxel of volume data. The weighted addition unit  0202  multiplies, every time smoothed volume data is generated, the tomographic volume data and the smoothed volume data with the weight coefficient and adds up the volume data to generate combined volume data. The weighted addition unit  0202  multiplies, every time a plurality of pieces of processed volume data are generated, the plurality of pieces of processed volume data with the weight coefficient and adds up the volume data to generate combined volume data. Hereinafter, in this embodiment, volume data obtained by the weighed addition processing is referred to as combined volume data. In this embodiment, the plurality of pieces of volume data generated from the same tomographic volume data are two volume data, i.e., texture volume data, which is the tomographic volume data itself, and smoothed volume data generated from the tomographic volume data by the three-dimensional smoothing unit  0201 . 
         [0054]    As the weight coefficient, the control unit  0003  notifies the weighted addition unit  0202  of a value set by the operator via the operation unit  0004 . That is, the operation unit (the interface)  0004  receives an input of the weight coefficient. The weight coefficient is set as, for example, a value between 0 and 1. The addition is performed according to the following Equation (1) for each voxel corresponding to both the volume data. Here, the weight coefficient is represented as W, a luminance value of one volume data of a predetermined voxel v is represented as V 1   v , a luminance value of the other volume data is represented as V 2   v , and a luminance value of the combined volume data is represented as Cv. 
         [0000]        Cv=V 1 v·W+V 2 v ·(1 −W )  (1)
 
         [0055]    The gradient calculating unit  0203  generates gradient information of the combined volume data. The gradient information is a gradient (a gradient value) of a luminance value for each voxel calculated from luminance values of respective voxels forming the combined volume data and luminance values of voxels around the respective voxels. 
         [0056]    A rendering unit  0204  applies volume rendering processing to the combined volume data and generates a three-dimensional image. The rendering unit  0204  may apply, every time combined volume data is generated, the rendering processing to the combined volume data and generate the three-dimensional image. The rendering unit  0204  may apply, every time processed volume data is generated, the rendering processing to a plurality of pieces of the generated processed volume data while multiplying the processed volume data with the weight coefficient and adding up the processed volume data for each constituent voxel to generate the three-dimensional image. Note that the generated three-dimensional image is displayed on the display device  0009  via the display data generating unit  0016 . 
         [0057]    The rendering unit  0204  applies the volume rendering processing to the combined volume data using the following Formula (2) and Formula (3) to thereby form a three-dimensional image of a diagnostic region of the object. The control unit  0003  receives a projecting direction (a line of sight direction) from the operator via the operation unit  0004 . 
         [0000]        C   out   =C   out-1 +(1 −A   out-1 )· A   i   ·C   i   ·S   i   (2)
 
         [0000]        A   out   =A   out-1 +(1 −A   out-1 )· A   i   (3)
 
         [0058]    In the above equations, C i  represents a luminance value of an ith voxel present on a line of sight when the combined volume data is viewed from a certain point on a created two-dimensional projection surface. When data of N voxels are arranged on the line of sight, a value C out  obtained by integrating i=0 to N is a final output pixel value. C out-1  indicates an integrated value up to an i−1th voxel. 
         [0059]    In the above equations, A i  represents opacity of the ith voxel present on the line of sight. The opacity A i  takes a value from 0 to 1.0. A relation between voxel values and opacity is set in advance as an opacity table in which a relation between luminance values and opacity is set. The rendering unit  0204  obtains opacity from a luminance value of a voxel referring to the opacity table. 
         [0060]    S i  indicates a gradient value of the ith voxel present on the line of sight. For example, when a normal of a surface specified by a gradient of the luminance value of the ith voxel coincides with the line of sight, for example, 1.0 is given to S i . When the normal is orthogonal to the line of sight, for example, 0 is given to S i . As a gradient with respect to the line of sight is larger, a gradient value decreases and a calculated output pixel value is a smaller value. Note that, in this embodiment, a configuration not including the gradient calculating unit  0203  is also possible. In this case, a fixed value, for example, 1.0 is always given to S i . 
         [0061]    Note that initial values of both C out  and A out  are 0. 
         [0062]    As indicated by Equation (3), A out  is integrated every time the volume rendering processing passes through a voxel and converges to 1.0. Therefore, as indicated by Equation (2), the integrated value A out-1  of the opacity up to the i−1th voxel is ≡1.0, the ith voxel value C i  is not reflected on an output image. According to such volume rendering processing, it is possible to grasp a voxel having high opacity as a surface and stereoscopically display three-dimensional tomographic image data. 
         [0063]    The finally obtained C out  is subjected to color scale conversion, converted into color information such as RGB, and output. 
         [0064]    Note that the rendering unit  0204  may generate a three-dimensional image for each element of the color information such as RGB according to the following Equations (4) to (6): 
         [0000]        CR   out   =CR   out-1 +(1 −A   out-1 )· A   i   ·CR   i   ·S   i   (4)
 
         [0000]        CG   out   =CG   out-1 +(1 −A   out-1 )· A   i   ·CG   i   ·S   i   (5)
 
         [0000]        CB   out   =CB   out-1 +(1 −A   out-1 )· A   i   CB   i   ·S   i   (6)
 
         [0065]    Here, CR i  represents a red component of a luminance value of the ith voxel present on the line of sight when the combined volume data is viewed from a certain point on a created two-dimensional projection surface. CG i  and CB i  respectively represent a green component and a blue component. 
         [0066]    Note that a method in which the rendering unit  0204  in this embodiment generates a three-dimensional image from the combined volume data is not limited to this. For example, the method may be a maximum value projection method (Maximum intensity projection) for making a structure on an inside rather than on a surface transparently visible and displaying only a high-luminance structure in a region of interest, a minimum value projection method (Minimum intensity projection) for rendering only a low-luminance structure, or a method (Ray summation) for displaying a cumulative image of voxel values in the line of sight direction. 
         [0067]    The rendering unit  0204  may be configured to discriminate, in a process of the rendering processing, luminance values of voxels of respective processing targets according to a threshold and select whether data of the voxels is enabled or disabled. The operator sets the threshold via the operation unit  0004 . The control unit  0003  notifies the rendering unit  0204  of the threshold. 
         [0068]    Note that the ultrasonic diagnostic device  0001  in this embodiment includes a CPU, a memory, and a storage device. Further, the ultrasonic diagnostic device  0001  may include a GPU (Graphics Processing Unit). Functions of the control unit  0003  and the respective units (the tomographic information calculating unit  0011 , the three-dimensional coordinate conversion unit  0013 , the three-dimensional image processing unit  0014 , the arbitrary tomographic image creating unit  0015 , and the display data generating unit  0016 ) for generating tomographic volume data from the RF signal frame data and further generating a two-dimensional image and a three-dimensional image are realized by the CPU or the GPU loading a program stored in the storage device in advance to the memory and executing the program. 
         [0069]    Next, a flow of three-dimensional image processing by the three-dimensional image processing unit  0014  in this embodiment and an image generated by the three-dimensional image processing are explained using  FIG. 3  and  FIG. 4 . 
         [0070]      FIG. 3  is a processing flow of the three-dimensional image processing by the three-dimensional image processing unit  0014  in this embodiment.  FIG. 4  is a diagram for explaining volume data obtained by the three-dimensional image processing by the three-dimensional image processing unit  0014  in this embodiment.  FIG. 4(   a ) is tomographic volume data (texture volume data)  0401 , which is output data of the three-dimensional coordinate conversion unit  0013 . 
         [0071]    The three-dimensional smoothing unit (the filter processing unit)  0201  sets a smoothing coefficient (step S 1101 ). The smoothing coefficient is designated by the operator via the operation unit  0004  out of smoothing coefficients set in advance. The three-dimensional smoothing unit  0201  receives the designated smoothing coefficient via the control unit  0003  and sets the smoothing coefficient. Note that, in this embodiment, in order to execute averaging filter processing as the smoothing, the number of averaged voxels is set as the smoothing coefficient as explained above. 
         [0072]    Next, the three-dimensional smoothing unit  0201  applies the smoothing to tomographic volume data, which is output data of the three-dimensional coordinate conversion unit  0013  and generates smoothed volume data (step S 1102 ).  FIG. 4(   b ) is smoothed volume data  0402  after the smoothing by the three-dimensional smoothing unit  0201 . 
         [0073]    The weighted addition unit  0202  receives and sets the weight coefficient (step S 1103 ). 
         [0074]    The weight coefficient is set by the operator via the operation unit  0004 . The weighted addition unit  0202  receives the weight coefficient via the control unit  0003  and sets the weight coefficient. 
         [0075]    The weighted addition unit  0202  performs addition processing indicated by above Equation (1) for each voxel using the set weight coefficient (step S 1104 ), adds up the smoothed volume data and the texture volume data, and generates combined volume data. Combined volume data  0403  generated here is shown in  FIG. 4(   c ). 
         [0076]    For example, as shown in  FIG. 4(   b ), even if the smoothed volume data  0402  is excessively subjected to the smoothing, the smoothed volume data  0402  is subjected to the addition processing by the weighted addition unit  0202 , whereby it is possible to obtain the smoothed combined volume data  0403  intermediate between the smoothed volume data  0402  and the texture volume data  0401 . If the weigh coefficient is changed, it is possible to obtain combined volume data having desired smoothing intensity intermediate between the smoothed volume data  0402  and the texture volume data  0401 . 
         [0077]    The gradient calculating unit  0203  applies a luminance gradient calculation for a voxel to the combined volume data  0403  and generates gradient information (step S 1105 ). Then, the rendering unit  0204  performs the rendering processing using the combined volume data  0403  and a gradient value for each voxel and generates a three-dimensional image (step S 1106 ). The generated three-dimensional image is changed to display data by the display data generating unit  0016  and displayed on the display device  0009 . 
         [0078]    Next, an effect on a three-dimensional image given by a weight coefficient set by the operator is explained using  FIG. 5 . In this embodiment, V 1   v  in Equation (1) is explained as a luminance value of the texture volume data  0401  and V 2   v  is explained as a luminance value of the smoothed volume data  0402 . 
         [0079]    A three-dimensional image  0501  shown in  FIG. 5(   a ) is a three-dimensional image generated when a weight coefficient W is set to 1.0. The three-dimensional image  0501  is generated from combined volume data obtained by weighting the texture volume data  0401  with 1.0 and weighting the smoothed volume data  0402  with 0.0 according to Equation (1). 
         [0080]    When 1.0 is set as the weight coefficient W, as the combined volume data from which the three-dimensional image  0501  is generated, the texture volume data  0401  is directly used. Therefore, the three-dimensional image  0501  is generated from volume data not smoothed at all. Consequently, information such as wrinkles of fingers and a face of a fetus is retained but, on the other hand, unevenness remains on a boundary line of the image. 
         [0081]    A three-dimensional image  0502  shown in  FIG. 5(   b ) is a three-dimensional image generated when the weight coefficient W is set to 0.0. The three-dimensional image  0502  is generated from combined volume data obtained by weighting the texture volume data  0401  with 0.0 and weighting the smoothed volume data  0402  with 1.0 according to Equation (1). 
         [0082]    When 0.0 is set as the weight coefficient W, as the combined volume data from which the three-dimensional image  0502  is generated, the smoothed volume data  0402  is directly used. Therefore, the three-dimensional image  0502  is generated from volume data smoothed by a set smoothing coefficient. Consequently, the boundary line of the image is smooth without unevenness but, on the other hand, information such as the wrinkles of the fingers and the face of the fetus disappears. 
         [0083]    A three-dimensional image  0503  shown in  FIG. 5(   c ) is a three-dimensional image generated when the moderate weight coefficient W, for example, 0.5 is set. The three-dimensional image  0503  is generated from combined volume data obtained by weighting the texture volume data  0401  with 0.5 and weighting the smoothed volume data  0402  with 0.5 according to Equation (1). As shown in the figure, in the obtained three-dimensional image  0503 , unevenness on the boundary line moderately disappears and information such as the wrinkles of the fingers and the face of the fetus is retained. 
         [0084]    As explained above, it is possible to adjust finally obtained image quality by adjusting the weight coefficient. In this embodiment, the operator adjusts the weight coefficient by changing the weight coefficient in real time while looking at an image displayed on the display device  0009 . 
         [0085]    Next, an interface with which the operator sets and adjusts a weight coefficient is explained using  FIG. 6 . 
         [0086]      FIG. 6(   a ) is an example in which the interface for setting and adjusting a weight coefficient is configured by a changing dial  0601 , a coefficient display region  0602 , and a three-dimensional image display region  0600 . The operation unit  0004  includes the changing dial  0601 . The operator changes the weight coefficient between 0.0 and 0.1 by operating the changing dial  0601 . 
         [0087]    The display device  0009  includes the coefficient display region  0602  and the three-dimensional image display region  0600 . Note that the three-dimensional image display region  0600  is a region where a three-dimensional image generated by the three-dimensional image processing unit  0014  is displayed. 
         [0088]    The control unit  0003  displays, every time the operator sets or changes a weight coefficient via the changing dial  0601 , the weight coefficient in the coefficient display region  0602 . The control unit  0003  notifies, every time the operator sets or changes a weight coefficient via the changing dial  0601 , the three-dimensional image processing unit  0014  of the weight coefficient. The three-dimensional image processing unit  0014  receives the notification and repeats the processing from step S 1103  of the flow of the three-dimensional image processing. The generated three-dimensional image is displayed in the three-dimensional image display region  0600 . The operator sets an optimum weight coefficient while checking the three-dimensional image displayed in the three-dimensional image display region  0600 . 
         [0089]      FIG. 6(   b ) is an example in which the interface for setting and adjusting a weight coefficient is configured by a touch panel on the display device  0009 , the coefficient display region  0602 , and the three-dimensional image display region  0600 . The display device  0009  includes a slide bar  0603  for receiving an instruction for increasing and reducing a value of a coefficient. The operator changes a weight coefficient between 0.0 and 0.1 by operating the slide bar  0603  using a finger or an input device such as a mouse, a trackball, or a keyboard included in the operation unit  0004 . Processing performed by the control unit  0003  when the weight coefficient is set or changed by the operator is the same as the processing in the example shown in  FIG. 6(   a ). 
         [0090]      FIG. 6(   c ) is an example in which the interface for setting and adjusting a weight coefficient is configured by the touch panel on the display device  0009 , the coefficient display region  0602 , and the three-dimensional image display region  0600 . The display device  0009  includes an increase instruction region  0604  for receiving an instruction for increasing a value of a coefficient and a reduction instruction region  0605  for receiving an instruction for reducing the value of the coefficient. The operator changes a weight coefficient between 0.0 and 0.1 via the increase instruction region  0604  or the reduction instruction region  0605 . The operator performs an instruction using a finger or the input device such as the mouse or the keyboard included in the operation unit  0004 . Processing performed by the control unit  0003  when the weight coefficient is set or changed by the operator is the same as the processing in the example shown in  FIG. 6(   a ). 
         [0091]    Note that, in the example shown in  FIG. 6(   c ), the increase instruction region  0604  and the reduction instruction region  0605  are included in the coefficient display region  0602 . However, the increase instruction region  0604  and the reduction instruction region  0605  do not always have to be included in the coefficient display region  0602 . 
         [0092]    Note that the interface with which the operator sets and adjusts a weight coefficient is not limited to the above. 
         [0093]    Note that the interface may be configured to enable the operator to change a smoothing coefficient as well in real time between smoothing coefficients prepared in advance while checking a three-dimensional image. In this case, like the weight coefficient, the operator sets an optimum smoothing coefficient by changing the smoothing coefficient in real time while looking at an image displayed on the display device  0009 . In the following explanation, the interface with which the operator sets and changes a smoothing coefficient is explained using  FIG. 7 . 
         [0094]      FIG. 7(   a ) is an example in which the interface for setting and changing a smoothing coefficient is configured by a changing dial  0701 , a coefficient display region  0702 , and the three-dimensional image display region  0600 . The operation unit  0004  includes the changing dial  0701 . The operator selects a smoothing coefficient out of smoothing coefficients set in advance using the changing dial  0701 . For example, the smoothing coefficients set in advance are displayed on the display device  0009  as numbers. The control unit  0003  notifies the three-dimensional image processing unit  0014  of a smoothing coefficient corresponding to a number selected by the operator. 
         [0095]    The display device  0009  includes the coefficient display region  0702 . The three-dimensional image display region  0600  is a region where a three-dimensional image generated by the three-dimensional image processing unit  0014  is displayed. 
         [0096]    The control unit  0003  displays, every time the operator sets or changes a smoothing coefficient via the changing dial  0701 , the smoothing coefficient in the coefficient display region  702 . The control unit  0003  notifies, every time the operator sets or changes a smoothing coefficient via the changing dial  0701 , the three-dimensional image processing unit  0014  of the smoothing coefficient. The three-dimensional image processing unit  0014  receives the notification and repeats the processing from step S 1101  of the flow of the three-dimensional image processing. The generated three-dimensional image is displayed in the three-dimensional image display region  0600 . The operator sets an optimum smoothing coefficient while checking the three-dimensional image displayed in the three-dimensional image display region  0600 . 
         [0097]      FIG. 7(   b ) is an example in which the interface for setting and changing a smoothing coefficient is configured by the touch panel on the display device  0009 , the coefficient display region  0702 , and the three-dimensional image display region  0600 . The display device  0009  includes a slide bar  0703  for receiving an instruction for increasing and reducing a value of a coefficient. The operator selects a smoothing coefficient out of the smoothing coefficients set in advance by operating the slide bar  0703  using a finger or the input device such as the mouse, the trackball, or the keyboard included in the operation unit  0004 . Processing performed by the control unit  0003  when a smoothing coefficient is set or changed by the operator is the same as the processing in the example shown in  FIG. 7(   a ). 
         [0098]      FIG. 7(   c ) is an example in which the interface for setting and changing a smoothing coefficient is configured by the touch panel on the display device  0009 , the coefficient display region  0702 , and the three-dimensional image display region  0600 . The display device  0009  includes an increase instruction region  0704  for receiving an instruction for increasing a value of a coefficient and a reduction instruction region  0705  for receiving an instruction for reducing the value of the coefficient. The operator selects a smoothing coefficient out of the smoothing coefficients set in advance via the increase instruction region  0704  or the reduction instruction region  0705 . The operator performs an instruction using a finger or the input device such as the mouse or the keyboard included in the operation unit  0004 . Processing performed by the control unit  0003  when a smoothing coefficient is set or changed by the operator is the same as the processing in the example shown in  FIG. 7(   a ). 
         [0099]    Note that, in the example shown in  FIG. 7(   c ), the increase instruction region  0704  and the reduction instruction region  0705  are included in the coefficient display region  0702 . However, the increase instruction region  0704  and the reduction instruction region  0705  do not always need to be included in the coefficient display region  0702 . 
         [0100]    The interface with which the operator sets and changes a smoothing coefficient is not limited to the above. 
         [0101]    The interface for setting and changing a smoothing coefficient may be used as the interface for setting and adjusting a weight coefficient as well. In this case, the interface includes a component configured to receive, from the operator, an instruction concerning which coefficient is changed. According to the instruction, the interface receives the instruction as a change of a coefficient corresponding to the instruction. 
         [0102]    As explained above, according to this embodiment, in the three-dimensional image processing, combined volume data is generated by multiplying tomographic volume data and smoothed volume data, which is obtained by applying the smoothing to the tomographic volume data, with a weight coefficient and adding up the volume data. The rendering processing is applied to the generated combined volume data to generate a three-dimensional image. 
         [0103]    In this embodiment, it is possible to change intensity of smoothing of combined volume data by changing a weight coefficient used during addition. Therefore, the operator can arbitrarily change, by arbitrarily setting a weight coefficient, information concerning unevenness that the operator desires to suppress and fine form information that the operator desires to retain. Since the weight coefficient used during addition can be arbitrarily changed in real time, it is possible to freely adjust smoothing intensity of the combined volume data in real time. Therefore, it is possible to easily obtain a three-dimensional image subjected to desired smoothing and obtain an optimum image according to necessity. 
         [0104]    When a plurality of images after the rendering processing are combined, for example, when an integrated value of opacity is 1, a voxel value before the integrated value is not reflected on an output image. Therefore, even if the voxel value is subjected to weighted addition, the voxel value is not reflected on an image after the addition either. On the other hand, according to this embodiment, intensity of smoothing is adjusted in a state of volume data before rendering. Therefore, it is possible to obtain combined volume data having the adjusted intensity of the smoothing without losing information concerning respective voxels. Since a three-dimensional image is generated from the combined volume data, it is possible to obtain, from acquired all volume data, a three-dimensional image on which more information is reflected. 
         [0105]    Texture data and smooth data to be subjected to weighted addition in order to adjust smoothing intensity are generated from the same tomographic volume data. Therefore, deterioration in image quality due to a temporal and/or spatial change does not occur. 
         [0106]    Further, in the three-dimensional image processing for performing the smoothing, a component added anew is only the weighted addition high in speed and having little load on the device. The rendering processing having a large load on the device is performed only once as in the past. As explained above, a processing amount of the rendering processing is enormous. The rendering processing takes long time and has a large load on the device. Therefore, it is possible to obtain a three-dimensional image having desired image quality at high speed without increasing a load on the device. 
         [0107]    Note that, in this embodiment, the averaging filter is used as the spatial smoothing in the three-dimensional smoothing unit  0201 . However, the spatial smoothing is not limited to this. For example, a low-pass filter, a median filter, or the like may be three-dimensionally used. Expansion processing by dilation may be three-dimensionally performed. 
       Second Embodiment 
       [0108]    Next, a second embodiment to which the present invention is applied is explained. In the first embodiment, the three-dimensional image processing unit  0014  combines, using a predetermined weight coefficient, tomographic volume data itself, which is an output of the three-dimensional coordinate conversion unit  0013 , and volume data obtained by applying the smoothing to the tomographic volume data and generates combined volume data. On the other hand, in this embodiment, a three-dimensional image processing unit adds up, using a predetermined weight coefficient, two volume data respectively obtained by applying different kinds of smoothing to an output of the same three-dimensional coordinate conversion unit and generates combined volume data. 
         [0109]    The ultrasonic diagnostic device  0001  in this embodiment basically has a configuration same as the configuration of the ultrasonic diagnostic device  0001  in the first embodiment. However, since three-dimensional image processing is different as explained above, the ultrasonic diagnostic device  0001  includes a three-dimensional image processing unit  0014   a  instead of the three-dimensional image processing unit  0014  in the first embodiment. In this embodiment, the three-dimensional image processing unit  0014   a  is mainly explained below. 
         [0110]      FIG. 8  is a functional block diagram of the three-dimensional image processing unit  0014   a  in this embodiment. As shown in the figure, the three-dimensional image processing unit  0014   a  in this embodiment includes two three-dimensional smoothing units (filter processing units)  0201  ( 0201   a  and  0201   b ), the weighted addition unit  0202 , the gradient calculating unit  0203 , and the rendering unit  0204 . 
         [0111]    Each of functions of the two three-dimensional smoothing units  0201  is basically the same as the function of the three-dimensional smoothing unit (the filter processing unit)  0201  in the first embodiment. That is, the three-dimensional smoothing units  0201  apply spatial smoothing to tomographic volume data using a set smoothing coefficient. However, smoothing coefficients used in the two three-dimensional smoothing units (the filter processing units)  0201   a  and  0201   b  are different from each other. The three-dimensional smoothing units (the filter processing units)  0201  apply each of a plurality of kinds of three-dimensional filter processing to the tomographic volume data and respectively generate processed volume data. 
         [0112]    Hereinafter, for explanation, a side where a smoothing coefficient with a weak smoothing effect (a first smoothing coefficient) is used is referred to as first three-dimensional smoothing unit  0201   a  and a side where a smoothing coefficient with a smoothing effect stronger than the smoothing effect of the first smoothing coefficient is used is referred to as second three-dimensional smoothing unit  0201   b . Hereinafter, in this embodiment, volume data generated by the first three-dimensional smoothing unit  0201   a  is referred to as texture volume data (weakly smoothed volume data) and volume data generated by the second three-dimensional smoothing unit  0201   b  is referred to as smoothed volume data (intensely smoothed volume data). 
         [0113]    Like the smoothing coefficient in the first embodiment, the first smoothing coefficient and the second smoothing coefficient are designated by an operator via the operation unit  0004  out of smoothing coefficients set in advance. The first three-dimensional smoothing unit  0201   a  and the second three-dimensional smoothing unit  0201   b  respectively receive the designated first smoothing coefficient and the designated second smoothing coefficient via the control unit  0003  and set the first smoothing coefficient and the second smoothing coefficient. As in the first embodiment, the number of averaged voxels in a smoothing filter is set in the first smoothing coefficient and the second smoothing coefficient. 
         [0114]    A function of the weighted addition unit  0202  is basically the same as the function in the first embodiment. However, in this embodiment, a plurality of pieces of volume data generated from the same tomographic volume data to be subjected to weighted addition are two volume data, i.e. texture volume data subjected to weak smoothing and smoothed volume data subjected to intense smoothing. 
         [0115]    Functions of the other components (the gradient calculating unit  0203  and the rendering unit  0204 ) are basically the same as the functions in the first embodiment. As in the first embodiment, a configuration not including the gradient calculating unit  0203  is also possible. 
         [0116]    Next, a procedure of image processing by the three-dimensional image processing unit  0014   a  in this embodiment is explained using  FIG. 9 .  FIG. 9  is a processing flow of image processing by the three-dimensional image processing unit  0014   a  in this embodiment. 
         [0117]    Volume data to be generated is explained using  FIG. 4 .  FIG. 4  is used for the explanation of the three-dimensional image processing unit  0014  in the first embodiment. However,  FIG. 4  is a figure for explaining an overview of an effect and does not indicate that the three-dimensional image processing unit  0014  in the first embodiment and the three-dimensional image processing unit  0014   a  in the second embodiment produce the same result. 
         [0118]    The three-dimensional smoothing unit  0201   a  sets a first smoothing coefficient (step S 1201 ), applies smoothing to tomographic volume data, which is output data of the three-dimensional coordinate conversion unit  0013 , and generates the texture volume data  0401  shown in  FIG. 4(   a ) (step S 1202 ). 
         [0119]    Next, the three-dimensional smoothing unit  0201   b  sets a second smoothing coefficient (step S 1203 ), applies smoothing to tomographic volume data which is output data of the three-dimensional coordinate conversion unit  0013 , and generates the smoothed volume data  0402  shown in  FIG. 4(   b ) (step S 1204 ). 
         [0120]    Note that processing order of the first three-dimensional smoothing unit  0201   a  and the second three-dimensional smoothing unit  0201   b  may be any order. The first three-dimensional smoothing unit  0201   a  and the second three-dimensional smoothing unit  0201   b  may be configured to set the first smoothing coefficient and the second smoothing coefficient first and thereafter perform the smoothing respectively. 
         [0121]    As in the first embodiment, the weighted addition unit  0202  receives and sets a weight coefficient (step S 1205 ). The weighted addition unit  0202  weights and adds up, for each voxel, the texture volume data and the smoothed volume data according to Equation (1) and obtains the combined volume data  0403  shown in  FIG. 4(   c ) (step S 1206 ). 
         [0122]    For example, even if the texture volume data  0401  shown in  FIG. 4(   a ) is insufficiently subjected to the smoothing and the smoothed volume data  0402  shown in  FIG. 4(   b ) is excessively subjected to the smoothing, by adding up both the volume data using the weighted addition unit  0202 , it is possible to obtain the combined volume data  0403  subjected to smoothing intermediate between the texture volume data  0401  and the smoothed volume data  0402 . By changing the weight coefficient, it is possible to obtain combined volume data having desired smoothing intensity intermediate between the smoothed volume data  0402  and the texture volume data  0401 . 
         [0123]    Thereafter, as in the first embodiment, the gradient calculating unit  0203  performs a gradient calculation for the combined volume data  0403  (step S 1207 ). That is, the gradient calculating unit  0203  calculates, every time processed volume data is generated, luminance gradients of a respective generated plurality of pieces of the processed volume data. The rendering unit  0204  applies rendering processing to the combined volume data  0403  and generates a three-dimensional image (step S 1208 ). That is, the rendering unit  0204  generates, every time an input of a weight coefficient is received via an interface, a three-dimensional image from the plurality of pieces of processed volume data. The generated three-dimensional image is changed to display data by the display data generating unit  0016  and displayed on the display device  0009 . 
         [0124]    Note that, in this embodiment, an effect of a weight coefficient set by the operator is basically the same as the effect in the first embodiment. In the texture volume data  0401  with low smoothing intensity, information such as wrinkles of fingers and a face of a fetus is retained but, on the other hand, unevenness remains on a boundary line of an image. In the smoothed volume data  0402  with high smoothing intensity, the boundary line of the image is smooth without unevenness but, on the other hand, information such as the wrinkles of the fingers and the face of the fetus is lost. 
         [0125]    In this embodiment, as in the first embodiment, the ultrasonic diagnostic device includes an interface for adjusting a weight coefficient. The operator adjusts the weight coefficient and adjusts smoothing intensity of combined volume data by changing the weight coefficient in real time while looking at an image displayed on the display device  0009 . 
         [0126]    In this embodiment, as in the first embodiment, the ultrasonic diagnostic device may include an interface for changing a first smoothing coefficient and a second smoothing coefficient in real time. In this embodiment, the ultrasonic diagnostic device may include, for each coefficient, an interface same as the interface in the first embodiment or may be configured to receive a change of both the coefficients in one interface according to an instruction from the operator. Further, as in the first embodiment, the interface may be used as an interface for adjustment of a weight coefficient as well. 
         [0127]    As explained above, according to this embodiment, in the three-dimensional image processing, combined volume data is generated by multiplying texture volume data and smoothed volume data, which are obtained by applying the smoothing to one tomographic volume data at smoothing intensities different from each other, with a weight coefficient set in advance and adding up the volume data. Then, the rendering processing is applied to the generated combined volume data to generate a three-dimensional image. 
         [0128]    Therefore, as in the first embodiment, it is possible to easily obtain a three-dimensional image subjected to desired smoothing and obtain an optimum image according to necessity. Since it is possible to obtain an image having smoothing intensity intermediate between images smoothed at two different smoothing intensities, it is possible to set a smoothing level at a higher degree of freedom compared with the first embodiment. That is, the operator can have a wide span of adjustable range of smoothing for a three-dimensional image. 
         [0129]    Otherwise, the second embodiment has a configuration same as the configuration of the first embodiment. Therefore, various effects same as the effects of the first embodiment are obtained. It is possible to obtain a three-dimensional image having a desired image quality at high speed without increasing a load on the device. 
         [0130]    Note that, in the embodiment, the configuration including the two three-dimensional smoothing units  0201  is explained as an example. However, the configuration of the ultrasonic diagnostic device is not limited to this configuration. The ultrasonic diagnostic device may be configured to sequentially apply, with one three-dimensional smoothing unit  0201 , smoothing to the same tomographic volume data using different smoothing coefficients and subject outputs of the smoothing to weighted addition. 
         [0131]    As in the first embodiment, it is possible to three-dimensionally use an averaging filter, a low-pass filter, or a median filter as spatial smoothing in the three-dimensional smoothing units  0201   a  and  0201   b . Expansion processing by dilation may be three-dimensionally performed. 
       Third Embodiment 
       [0132]    Next, a third embodiment to which the present invention is applied is explained. In the second embodiment, the three-dimensional image processing unit  0014   a  subjects two kinds of volume data, which are obtained by applying the smoothing to an output of the three-dimensional coordinate conversion unit  0013  at different smoothing intensities, to the weighted addition and generates combined volume data. On the other hand, in this embodiment, a three-dimensional image processing unit adds up volume data after a plurality of kinds of filter processing, which are obtained by applying different kinds of filter processing to an output of the same three-dimensional coordinate conversion unit, using a predetermined weight coefficient and generates combined volume data. 
         [0133]    The ultrasonic diagnostic device  0001  in this embodiment basically has a configuration same as the configuration of the ultrasonic diagnostic device  0001  in the first embodiment. However, since the three-dimensional image processing is different as explained above, the ultrasonic diagnostic device  0001  includes a three-dimensional image processing unit  0014   b  instead of the three-dimensional image processing unit  0014  in the first embodiment. In this embodiment, the three-dimensional image processing unit  0014   b  is mainly explained below. Note that, here, as an example, two kinds of processing, i.e., three-dimensional sharpening and three-dimensional smoothing are performed as different kinds of filter processing. 
         [0134]      FIG. 10  is a functional block diagram of the three-dimensional image processing unit  0014   b  in this embodiment. As shown in the figure, the three-dimensional image processing unit  2014  in this embodiment includes the three-dimensional smoothing unit  0201 , a three-dimensional sharpening unit  0206 , the weighted addition unit  0202 , the gradient calculating unit  0203 , and the rendering unit  0204 . 
         [0135]    The three-dimensional sharpening unit  0206  applies sharpening to tomographic volume data, which is output data of the three-dimensional coordinate conversion unit  0013 . In this embodiment, volume data after the sharpening is referred to as texture volume data (sharpened volume data). As the sharpening performed here, there are sharpening in which a high-pass filter is three-dimensionally used, retraction processing by three-dimensional erosion processing, and the like. Spatially-sharpened volume data is generated by using the three-dimensional high-pass filter. Volume data with enhanced structure is generated by the retraction processing by the three-dimensional erosion processing. 
         [0136]    The sharpening is performed using a sharpening coefficient for determining intensity of sharpening. Like the smoothing coefficient in the first embodiment, the sharpening coefficient is designated by an operator via the operation unit  0004  out of sharpening coefficients set in advance. The three-dimensional sharpening unit  0206  receives the designated sharpening coefficient via the control unit  0003  and sets the sharpening coefficient. 
         [0137]    The three-dimensional smoothing unit  0201  is basically the same as the three-dimensional smoothing unit  0201  in the first embodiment. In this embodiment, volume data generated by applying the smoothing to tomographic volume data is referred to as smoothed volume data (smooth volume data). In this embodiment, as spatial smoothing, a low-pass filter, a median filter, or the like may be three-dimensionally used. Expansion processing by dilation may be three-dimensionally performed. In this way, in this embodiment, it is possible to give an arbitrary smoothing effect to a three-dimensional ultrasonic image. 
         [0138]    A function of the weighted addition unit  0202  is basically the same as the function in the first embodiment. However, a plurality of pieces of volume data generated from the same tomographic volume data to be subjected to weighted addition are two volume data, i.e., the texture volume data subjected to the sharpening and the smoothed volume data subjected to the smoothing. 
         [0139]    Functions of the other components (the gradient calculating unit  0203  and the rendering unit  0204 ) are basically the same as the functions in the first embodiment. As in the first and second embodiments, a configuration not including the gradient calculating unit  0203  is also possible. 
         [0140]    Next, a procedure of image processing by the three-dimensional image processing unit  0014   b  in this embodiment is explained using  FIG. 11 .  FIG. 11  is a processing flow of the image processing by the three-dimensional image processing unit  0014   b  in this embodiment. As in the second embodiment, in order to explain an overview of an effect, volume data to be generated is explained using  FIG. 4 . 
         [0141]    The three-dimensional sharpening unit  0206  sets a sharpening coefficient (step S 1301 ), applies the sharpening to tomographic volume data, which is output data of the three-dimensional coordinate conversion unit  0013 , and generates the texture volume data  0401  shown in  FIG. 4(   a ) (step S 1302 ). 
         [0142]    Next, the three-dimensional smoothing unit  0201  sets a second smoothing coefficient (step S 1303 ), applies the smoothing to the tomographic volume data, which is the output data of the three-dimensional coordinate conversion unit  0013 , and generates the smoothed volume data  0402  shown in  FIG. 4(   b ) (step S 1304 ). 
         [0143]    Note that processing order of the three-dimensional sharpening unit  0206  and the three-dimensional smoothing unit  0201  may be any order. The three-dimensional sharpening unit  0206  and the three-dimensional smoothing unit  0201  may be configured to set both the coefficients first and thereafter perform both the kinds of processing. 
         [0144]    As in the first embodiment, the weighted addition unit  0202  receives and sets a weight coefficient (step S 1305 ). Then, the weighted addition unit  0202  weights and adds up, for each voxel, the texture volume data and the smoothed volume data according to Equation (1) and obtains the combined volume data  0403  shown in  FIG. 4(   c ) (step S 1306 ). 
         [0145]    Thereafter, as in the first embodiment, the gradient calculating unit  0203  performs a gradient calculation for the combined volume data  0403  (step S 1307 ). The rendering unit  0204  applies the rendering processing to the combined volume data  0403  and generates a three-dimensional image (step S 1308 ). Note that the generated three-dimensional image is changed to display data by the display data generating unit  0016  and displayed on the display device  0009 . 
         [0146]    Note that, in this embodiment, the influence of a weight coefficient set by the operator is basically the same as the influence in the first embodiment. In this embodiment, as in the first embodiment, the ultrasonic diagnostic device includes an interface for adjusting a weight coefficient. The operator changes the weight coefficient in real time and adjusts the weight coefficient while looking at an image displayed on the display device  0009 . 
         [0147]    In this embodiment, as in the first embodiment, the ultrasonic diagnostic device may include an interface for changing, in real time, a smoothing coefficient used for the smoothing and a sharpening coefficient used for the sharpening. 
         [0148]    In this embodiment, the ultrasonic diagnostic device may include an interface with which the operator selects a processing method used for sharpening and a processing method used for smoothing. The interface with which the operator selects these processing methods is explained using  FIG. 12 . 
         [0149]      FIG. 12(   a ) is an example in which the interface for selecting processing methods is configured by a changing dial  0801  included in the operation unit  0004 , a processing method display region  0802 , and the three-dimensional image display region  0600 . The operation unit  0004  includes the changing dial  0801 . The operator selects desired processing methods out of sharpening methods, smoothing methods, and the like prepared in advance by operating the changing dial  0801 . 
         [0150]    The display device  0009  includes the processing method display region  0802  and the three-dimensional image display region  0600 . Note that the three-dimensional image display region  0600  is a region in which a three-dimensional image generated by the three-dimensional image processing unit  0014   b  is displayed. 
         [0151]    The control unit  0003  displays, every time the operator sets or changes three-dimensional filter processing methods via the changing dial  0801 , each of the selected processing methods in the processing method display region  0802 . The control unit  0003  notifies, every time the operator selects or changes processing methods via the changing dial  0801 , the three-dimensional image processing unit  0014   b  of the processing methods. The three-dimensional image processing unit  0014   b  receives the notification and executes the changed processing and the weighted addition processing and the subsequent processing. The generated three-dimensional image is displayed in the three-dimensional image display region  0600 . The operator sets optimum processing methods while checking the three-dimensional image displayed in the three-dimensional image display region  0600 . 
         [0152]      FIG. 12(   b ) is an example in which the interface for selecting processing methods is configured by the touch panel on the display device  0009 , the processing method display region  0802 , and the three-dimensional image display region  0600 . The display device  0009  includes a slide bar  0803  for receiving selection of processing methods. The operator selects desired processing methods out of the sharpening methods, the smoothing methods, and the like prepared in advance by operating the slide bar  0803  using a finger or the input device such as the mouse, the trackball, or the keyboard included in the operation unit  0004 . Processing performed by the control unit  0003  when the processing methods are selected by the operator is the same as the example shown in  FIG. 12(   a ). 
         [0153]      FIG. 12(   c ) is an example in which the interface for selecting processing methods is configured by the touch panel on the display device  0009 , the processing method display region  0802 , and the three-dimensional image display region  0600 . The display device  0009  includes instruction regions  0804  and  0805  for receiving instructions for changing processing methods. The operator instructs a change of a processing method via the instruction region  0804  or  0805 . The operator performs the instruction using a finger or the input device such as the mouse or the keyboard included in the operation unit  0004 . Processing performed by the control unit  0003  when processing methods are selected or changed by the operator is the same as the example shown in  FIG. 12(   a ). 
         [0154]    As explained above, according to this embodiment, in the three-dimensional image processing, combined volume data is generated by multiplying processed volume data, which are obtained by applying kinds of filter processing different from each other to one tomographic volume data, with a weight coefficient set in advance and adding up the volume data. Then, the rendering processing is applied to the generated combined volume data to generate a three-dimensional image. 
         [0155]    Therefore, as in the first embodiment, the operator can arbitrarily change, by arbitrarily setting a weight coefficient, information concerning unevenness that the operator desires to suppress and fine form information that the operator desires to retain. The weight coefficient used during addition can be arbitrarily changed in real time. Therefore, it is possible to easily give a desired filter effect. Consequently, it is possible to easily obtain a three-dimensional image subjected to desired filter processing and obtain an optimum image according to necessity. 
         [0156]    Otherwise, the third embodiment has a configuration same as the configuration of the first embodiment. Therefore, various effects same as the effects of the first embodiment are obtained. It is possible to obtain a three-dimensional image having a desired image quality at high speed without increasing a load on the device. 
         [0157]    Note that, in the example explained in the embodiment, the sharpening and the smoothing are performed as the three-dimensional filter processing. However, the three-dimensional filter processing is not limited to this. Kinds of three-dimensional filter processing to be combined are not limited to two. The combination only has to be a combination of kinds of three-dimensional filter processing having different effects. Filter processing may be any kind and the number of kinds of filter processing may be any number. 
         [0158]    When there are three or more kinds of three-dimensional filter processing to be executed, the weighted addition unit performs addition processing such that a total of weight coefficients respectively given to the kinds of three-dimensional filter processing is 1. 
       Fourth Embodiment 
       [0159]    Next, a fourth embodiment to which the present invention is applied is explained. In the respective embodiments explained above, a plurality of pieces of volume data generated by applying the kinds of filter processing having different effects to the same tomographic volume data are subjected to the weighted addition using one weight coefficient to generate combined volume data. On the other hand, in this embodiment, a weight coefficient is changed according to positions of respective voxels to perform the weighted addition. 
         [0160]    The ultrasonic diagnostic device  0001  in this embodiment basically has a configuration same as the configuration of the ultrasonic diagnostic device  0001  in the first embodiment. However, since three-dimensional image processing is different as explained above, the ultrasonic diagnostic device  0001  includes a three-dimensional image processing unit  0014   c  instead of the three-dimensional image processing unit  0014  in the first embodiment. In this embodiment, the three-dimensional image processing unit  0014   c  is mainly explained below. Note that filter processing having different effects may be any kinds. However, here, as an example, as in the second embodiment, the ultrasonic diagnostic device  0001  includes two three-dimensional smoothing units  0201 . The three-dimensional smoothing units  0201  respectively perform smoothing at different smoothing intensities. 
         [0161]      FIG. 13  is a functional block diagram of the three-dimensional image processing unit  0014   c  in this embodiment. As shown in the figure, the three-dimensional image processing unit  0014   c  in this embodiment includes two three-dimensional smoothing units  0201  ( 0201   a  and  0201   b ), two gradient calculating units  0203  ( 0203   a  and  0203   b ), and a distance-weighted rendering unit (a rendering unit)  0207 . 
         [0162]    Each of functions of the two three-dimensional smoothing units  0201  ( 0201   a  and  0201   b ) is basically the same as the function in the second embodiment. As in the second embodiment, as respective smoothing coefficients used for smoothing, smoothing coefficients input by an operator via the operation unit  0004  are set by the control unit  0003 . 
         [0163]    Each of functions of the two gradient calculating units  0203  ( 0203   a  and  0203   b ) is basically the same as the function of the gradient calculating unit  0203  in the first embodiment. However, in this embodiment, the two gradient calculating units  0203  respectively generate gradient information of texture volume data, which is an output of the first three-dimensional smoothing unit  0201   a , and smoothed volume data, which is an output of the second three-dimensional smoothing unit  0201   b , rather than combined volume data. Here, for explanation, a side where the texture volume data is processed is referred to as first gradient calculating unit  0203   a  and a side where the smoothed volume data is processed is referred to as second gradient calculating unit  0203   b.    
         [0164]    The distance-weighted rendering unit (the rendering unit)  0207  performs volume rendering processing while subjecting the texture volume data and the smoothed volume data after calculation of a luminance gradient to weighted addition for each voxel according to a distance from a projection surface and generates a three-dimensional image. That is, the distance-weighted rendering unit (the rendering unit)  0207  changes a weight coefficient for first processed volume data and second processed volume data according to a distance to a processing target voxel from the projection surface. 
         [0165]    The weight coefficient used here is a distance weight coefficient set according to position information of the processing target voxel. The operator inputs the distance weight coefficient via the operation unit  0004 . The control unit  0003  notifies the distance weight coefficient. 
         [0166]    Note that the rendering processing is performed using above Equation (2) and Equation (3). However, luminance information (a luminance value of an ith voxel present on a line of sight) C i  and gradient information (a gradient value of the ith voxel present on the line of sight) S i  are calculated according to the following Equation (7) and Equation (8): 
         [0000]        C   i   =K 1 i   ·C 1 i   +K 2 i   ·C 2 i   (7)
 
         [0000]        S   i   =K 1 i   ·S 1 i   +K 2 i   ·S 2 i   (8)
 
         [0000]      where,  K 1 i   +K 2 i =1. 
         [0167]    Here, C 1   i  and C 2   i  are respectively a voxel value of the texture volume data and a voxel value of the smoothed volume data. K 1   i  and K 2   i  are distance weight coefficients set according to the distance from the projection surface. 
         [0168]    As in the first, second, and third embodiments, a configuration not including the gradient calculating units  0203  ( 0203   a  and  0203   b ) is also possible. For example, 1.0 is always given as the gradient value S i  in this case. 
         [0169]    Next, a procedure of image processing in the characteristic three-dimensional image processing unit  0014   c  in this embodiment is explained using  FIG. 14 .  FIG. 14  is a processing flow of the image processing of the three-dimensional image processing unit  0014   c  in this embodiment. As in the embodiments explained above, volume data to be generated is explained using  FIG. 4 . 
         [0170]    The first three-dimensional smoothing unit  0201   a  receives and sets a first smoothing coefficient (step S 1401 ). The second three-dimensional smoothing unit  020   b   1  receives and sets a second smoothing coefficient (step S 1402 ). As in the second embodiment, the first smoothing coefficient and the second smoothing coefficient are respectively designated by the operator via the operation unit  0004  out of smoothing coefficients set in advance and are notified by the control unit  0003 . As explained above, as the second smoothing coefficient, a smoothing coefficient larger than the first smoothing coefficient is set. 
         [0171]    Subsequently, the first three-dimensional smoothing unit  0201   a  applies the smoothing to tomographic volume data, which is output data of the three-dimensional coordinate conversion unit  0013 , and generates the volume data (the texture volume data)  0401  subjected to the weak smoothing shown in  FIG. 4(   a ) (step S 1403 ). The first gradient calculating unit  0203   a  calculates a luminance gradient of the texture volume data (step S 1404 ). 
         [0172]    The second three-dimensional smoothing unit  0201   b  applies the smoothing to the tomographic volume data and generates the smoothed volume data  0402  subjected to the intense smoothing shown in  FIG. 4(   b ) (step S 1405 ). The second gradient calculating unit  0203   b  calculates a luminance gradient of the smoothed volume data (step S 1406 ). 
         [0173]    Note that, in the processing flow explained above, processing order of the setting of the respective smoothing coefficient, the respective kinds of smoothing, and the respective gradient calculations may be any order as long as order for setting the smoothing coefficients, performing the smoothing, and performing the gradient calculations is observed. 
         [0174]    The three-dimensional image processing unit  0014  receives and sets a distance weight coefficient (step S 1407 ). The distance-weighted rendering unit  0207  performs volume rendering processing while subjecting the texture volume data and the smoothed volume data to weighted addition for each voxel using the set distance weight coefficient and according to Equations (2), Equation (3), Equation (7), and Equation (8) and generates a three-dimensional image. The generated three-dimensional image is changed to display data by the display data generating unit  0016  and displayed on the display device  0009 . 
         [0175]    As explained above, in this embodiment, the weight coefficient can be changed according to the distance. For example, for a voxel at a close distance from the projection surface, K 1   i  is set large and weight of the texture volume data having low smoothing intensity is set large. For a voxel at a far distance from the projection surface, K 2   i  is set large and weight of the smoothed volume data having high smoothing intensity is set large. A conceptual diagram of volume data  0900  generated during processing in this case is shown in  FIG. 15 . 
         [0176]    As shown in the figure, a degree of smoothing is moderately suppressed only in a region of interest in a depth direction. Regions other than the region of interest are excessively smoothed. In this way, it is possible to build a three-dimensional image by refining the volume data at the near distance and blurring the volume data at the far distance. 
         [0177]    Note that, here, as an example of the three-dimensional filter processing for the tomographic volume data, the smoothing performed at different smoothing intensities are explained. However, the three-dimensional filter processing is not limited to this smoothing. As in the third embodiment, different kinds of three-dimensional filter processing may be applied. Kinds of three-dimensional filter processing having different effects to be applied are not limited to two kinds. 
         [0178]    As explained above, according to this embodiment, in addition to the effects of the respective embodiments explained above, it is possible to change a degree of smoothing according to the distance. Therefore, by excessively smoothing voxel data in regions other than a region of interest that the operator desires to look at, it is possible to obtain a three-dimensional image in which the region of interest is more easily recognized. That is, it is possible to improve visibility of the region of interest in the depth direction. 
         [0179]    All the kinds of processing in the respective embodiments explained above are not limitedly applied to a tomographic image and can be applied to a three-dimensional blood flow, elasticity information, and luminance information enhanced by an ultrasound contrast agent that can be acquired by the ultrasonic diagnostic device. 
         [0180]    In the respective embodiments explained above, the ultrasonic diagnostic device  0001  does not have to include the functions of the respective units (the tomographic information calculating unit  0011 , the three-dimensional coordinate conversion unit  0013 , the three-dimensional image processing unit  0014 , the arbitrary tomographic image creating unit  0015 , and the display data generating unit  0016 ) for generating tomographic volume data from RF signal frame data and further generating a two-dimensional image and a three-dimensional image. For example, the functions may be built on an information processing device capable of transmitting and receiving data to and from the ultrasonic diagnostic device  0001  and independent from the ultrasonic diagnostic device  0001 . A part of the respective functions may be built on the independent information processing device. 
         [0181]    Further, in the respective embodiments explained above, the ultrasound diagnostic device is explained as an example of a test device to which the present invention is applied. However, the present invention is not limited to the ultrasonic diagnostic device. The present invention can be applied to various test devices that generate a three-dimensional image from tomographic volume data such as an MRI device and an X-ray CT device. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           0001  Ultrasonic diagnostic device 
           0002  Ultrasonic probe 
           0003  Control unit 
           0004  Operation unit 
           0005  Transmitting unit 
           0006  Receiving unit 
           0007  Transmission and reception control unit 
           0008  Phasing addition unit 
           0009  Display device (display unit) 
           0010  Object 
           0011  Tomographic information calculating unit 
           0012  Three-dimensional tomographic data storing unit 
           0013  Three-dimensional coordinate conversion unit 
           0014  Three-dimensional image processing unit 
           0014   a  Three-dimensional image processing unit 
           0014   b  Three-dimensional image processing unit 
           0014   c  Three-dimensional image processing unit 
           0015  Arbitrary tomographic image creating unit 
           0016  Display data generating unit 
           0201  Three-dimensional smoothing unit 
           0201   a  First three-dimensional smoothing unit 
           0201   b  Second three-dimensional smoothing unit 
           0202  Weighted addition unit 
           0203  Gradient calculating unit 
           0203   a  First gradient calculating unit 
           0203   b  Second gradient calculating unit 
           0204  Rendering unit 
           0206  Three-dimensional sharpening unit 
           0207  Distance-weighted rendering unit 
           0401  Texture volume data 
           0402  Smoothed volume data 
           0403  Combined volume data 
           0501  Three-dimensional image 
           0502  Three-dimensional image 
           0503  Three-dimensional image 
           0600  Three-dimensional image display region 
           0601  Changing dial 
           0602  Coefficient display region 
           0603  Slide bar 
           0604  Increase instruction region 
           0605  Reduction instruction region 
           0701  Changing dial 
           0702  Coefficient display region 
           0703  Slide bar 
           0704  Increase instruction region 
           0705  Reduction instruction region 
           0801  Changing dial 
           0802  Processing method display region 
           0803  Slide bar 
           0804  Instruction region 
           0805  Instruction region