JP6546107B2 - Ultrasonic imaging system - Google Patents

Description

  The present invention relates to an ultrasound imaging apparatus, and more particularly to an apparatus for forming a color three-dimensional ultrasound image based on ultrasound volume data.

  As an ultrasonic image processing apparatus, other than an ultrasonic diagnostic apparatus, an information processing apparatus that processes volume data acquired by the ultrasonic diagnostic apparatus can be mentioned. In the ultrasound image processing apparatus, a three-dimensional ultrasound image (an image representing a target tissue in a three-dimensional manner) is formed by a rendering operation based on ultrasound volume data (hereinafter simply referred to as "volume data"). The volume rendering method is known as the method.

  In the volume rendering method, a plurality of rays (gaze lines) coming out of a viewpoint are set for volume data, and a rendering operation is performed for each ray to obtain a pixel value (luminance). More specifically, the output light quantity calculation (voxel calculation) using opacity (opacity) is repeatedly performed along the depth direction from the start point on the ray, and the output light quantity at the time when the predetermined termination condition is satisfied, that is, calculation The pixel value is determined by the output light quantity at the end point. The predetermined ending condition is a first ending condition whose content is that the opacity cumulative added value has reached 1 or a value close thereto, and that the output light quantity calculation has reached the last sample point on the ray. The second termination condition, etc. are known. The opacity cumulative added value is generally obtained by cumulatively adding the opacity used there for each output light amount calculation. Various formulas are known as output light quantity computing formulas. The plurality of luminances determined for the plurality of rays is conceptualized as a luminance map, which constitutes a three-dimensional ultrasound image.

  As a special volume rendering method different from the general volume rendering method as described above, there is known a volume rendering method which generates a distance map with luminance increase and forms a color three-dimensional image based on them. In this method, in rendering operation in units of rays, in addition to the output light quantity (brightness) at the end point, the depth of the end point etc. is specified as the distance, and thereby a distance consisting of a plurality of distances corresponding to a plurality of rays. A map is generated. For example, by changing the hue according to the distance, it is possible to increase the sense of depth in a color three-dimensional ultrasound image.

  Patent documents 1 and 2 propose coloring according to distance in formation of a three-dimensional ultrasound image. Specifically, in the volume rendering method disclosed in Patent Document 1, an average depth map is generated as a distance map. In the volume rendering method disclosed in Patent Document 2, a distance map indicating the distance from the projection plane is generated as the distance map.

  Patent Document 3 shows a three-dimensional region of interest set for volume data. The region of interest has a rendering start plane (hereinafter referred to as "start plane") as a clipping plane. The starting surface is a deformable surface (in addition, parallel movement in the height direction and tilting movement are also possible). For example, if the starting surface is deformed in accordance with the shape of the gap between the fetus and the placenta, it is possible to render the fetus as a rendering target while excluding the placenta from the imaging target.

Patent No. 5117490 gazette Patent No. 5525930 gazette JP, 2011-83439, A

  When the distance constituting the above distance map is defined as the length of the section from the rendering start point to the rendering end point, the distance depends on the shape of the start surface. When the starting surface is curved, even if the surface shape of the object is flat, the content of the distance map changes depending on the degree of the above-mentioned curvature. Due to this, an unnecessary hue change occurs at the color processing stage. In particular, when the starting surface is deformed in a complicated manner, complex hue changes occur in response to the deformation.

  An object of the present invention is to prevent the influence of the deformation of the rendering start surface from directly affecting the distance map when forming a three-dimensional ultrasound image based on the brightness map and the distance map. Alternatively, an object of the present invention is to improve the quality of a three-dimensional ultrasound image.

  An ultrasonic image processing apparatus according to the present invention comprises: setting means for setting a three-dimensional region of interest defining target data to be rendered for volume data acquired from three-dimensional space in a living body; Means for setting a plurality of rays for each of the plurality of rays, and performing a rendering operation along the rays in units of rays, wherein a plurality of luminance maps corresponding to the plurality of rays and a plurality of rays corresponding to the plurality of rays And image forming means for forming a color three-dimensional image based on the brightness map and the distance map, wherein the setting means includes the three-dimensional region of interest. Setting a reference plane having an intersecting relation to the plurality of rays, separately from the deformable start plane as a clipping plane possessed by Means for calculating the luminance by executing the rendering operation from the start plane in units of rays, and a distance map for calculating the distance from the reference plane to the end point of rendering operations in units of rays. And generating means.

  In the above configuration, the start plane functions as a clipping plane that separates the imaging object from the others, which is a deformable plane. Preferably, the starting surface is a surface that is tiltable and can move back and forth relative to the viewpoint. According to the invention, in addition to such a starting surface, a special or reference surface is established which is the basis for the distance calculation. Desirably, the reference surface is a plane having an orthogonal relationship to the plurality of rays, but it may be slightly tiltable. It is desirable that the reference plane be set closer to the viewpoint than the three-dimensional region of interest. The fact that the reference surface serves as a reference for distance calculation prevents the influence of deformation of the starting surface and the like from directly affecting each distance. Therefore, it is possible to prevent unnecessary hue change on a color three-dimensional image and to improve its quality.

  The three-dimensional region of interest described above is set automatically or manually so as to include an imaging target (for example, a fetus) and exclude a non-imaging target tissue (for example, a placenta). At that time, as described above, deformation or the like of the starting surface which is a clipping surface is performed. The start plane defines a rendering start point in each ray, and specifically, a plurality of rendering start points corresponding to a plurality of rays are set on the start plane. The luminance constituting the luminance map is generally defined as the output light quantity at the time when the rendering end condition is satisfied, that is, the output light quantity at the rendering end point. In the process of repeatedly executing the output light quantity calculation (voxel calculation) along the ray according to the volume rendering method, the opacity is cumulatively added, and if the accumulated sum reaches a predetermined value of 1 or before, the rendering ends And the next output light quantity calculation is not performed. That is, the rendering operation for the ray is completed at that time, and the luminance is defined. At the same time, the distance from the start point (rendering start point) to the rendering end point is calculated. For example, if the opacity and other parameters are set such that the rendering operation is completed exclusively on the fetal surface or in the surface, the distance map will represent the fetal shape. If a color operation is performed according to such a distance map, the three-dimensional form of the fetus is represented by the hue change in addition to the luminance change on the three-dimensional image. In such a case, according to the above configuration, the contents of the distance map can be refined, so that the color representation of the three-dimensional image is also refined. Various formulas are known as formulas for volume rendering.

  The reference plane may be defined as the initial shape of the clip plane (the starting plane before deformation) of the three-dimensional region of interest. In addition to the case where the starting surface is a concave surface bulging toward the object, the starting surface may be a convex surface bulging toward the viewpoint. The reference plane may be always set on the viewpoint side of the start plane. In the case where the rendering end point is on the viewpoint side of the reference plane, the distance may be exceptionally forced to be zero to prevent the distance from becoming an abnormal value (minus value). That is, desirably, the distance map generation unit sets the distance to zero when the rendering operation end point is closer to the viewpoint than the reference plane.

  Preferably, the distance map generation unit calculates a first distance from the start surface to the rendering operation end point in the ray unit, and a second distance from the reference surface to the start surface in the ray unit. And means for calculating the distance by adding the first distance and the second distance in units of rays. The above configuration can easily calculate the distance by utilizing the existing configuration rather than directly calculating the distance from the reference surface to the rendering end point. The echo value at each operation point (sample point) on a ray is usually determined by interpolation from a plurality of echo values around that point.

  Desirably, the image forming means comprises: a first conversion table for determining a first color value based at least on luminance; a second conversion table for determining a second color value based on at least luminance; Means for weighting and combining the first color value determined by the first conversion table and the second color value determined by the second conversion table according to the distance; A plurality of subsequent color values constitute the color three-dimensional image. It is desirable to configure the weighting and combining conditions to be freely variable by the user. Preferably, smoothing means is provided for smoothing the distance map prior to formation of the color three-dimensional image. In the distance map there is a tendency to lack smoothness, especially at the edges, which results in unwanted changes in hue. According to the above configuration, it is possible to prevent or reduce the occurrence of such an unnatural change in hue due to the smoothing of the distance map.

  According to the present invention, when forming a three-dimensional ultrasound image based on the brightness map and the distance map, it is possible to make the distance map not directly affected by the deformation of the rendering start surface. Alternatively, according to the present invention, the image quality of a three-dimensional ultrasound image can be improved.

FIG. 1 is a block diagram showing an embodiment of an ultrasound image processing apparatus according to the present invention. It is a figure which shows a brightness | luminance map and a distance map. It is a figure which shows a comparative example. It is a figure which shows the 1st example of a reference plane. It is a figure which shows the 2nd example of a reference plane. It is a figure which shows the 3rd example of a reference plane. It is a flowchart which shows the operation example of the apparatus shown in FIG. It is a figure for demonstrating the modification about the operation example shown in FIG. It is a figure for demonstrating the smoothing with respect to a distance map. It is a figure which shows the 1st structural example of a color processing part. It is a figure which shows the 2nd structural example of a color processing part. It is a figure which shows the 3rd structural example of a color processing part. It is a figure for demonstrating weighting composition processing.

  Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

  FIG. 1 shows a preferred embodiment of an ultrasonic image processing apparatus according to the present invention. The ultrasonic image processing apparatus is an ultrasonic diagnostic apparatus in the present embodiment. The ultrasound image processing apparatus may be configured by an information processing apparatus that executes image processing. In that case, the volume data acquired by the ultrasound diagnostic apparatus is passed to the information processing apparatus.

  The ultrasonic diagnostic apparatus shown in FIG. 1 is an apparatus installed in a medical institution to form an ultrasonic image by transmitting and receiving ultrasonic waves to a living body. In the present embodiment, a color three-dimensional image is generated as an ultrasonic image, as described in detail below. For example, it is an image in which the three-dimensional form of the fetus in the uterus is three-dimensionally represented by changes in luminance and hue.

  In FIG. 1, a 3D probe 10 is a transducer for acquiring volume data by transmitting and receiving ultrasonic waves to and from a three-dimensional space in a living body. The 3D probe 10 has, for example, a 2D array transducer, which comprises a plurality of transducer elements arranged in a two-dimensional manner. According to the 2D array transducer, it is possible to electronically scan an ultrasonic beam two-dimensionally. As an electronic scanning method, an electronic sector scanning method or the like is known. Volume data can also be acquired by mechanically scanning the 1D array transducer. In general, volume data is composed of a plurality of scan plane data, and each scan plane data is composed of a plurality of beam data. Each beam data is composed of a plurality of echo data arranged in the depth direction.

  The transceiver unit 12 is an electronic circuit, which functions as a transmit beamformer and a receive beamformer. That is, at the time of transmission, a plurality of transmission signals are supplied from the transmission / reception unit 12 to the 3D probe 10, whereby a transmission beam is formed. At the time of reception, when the reflected wave from inside the living body is received by the 3D probe 10, a plurality of received signals are output from the 3D probe 10 to the transmitting / receiving unit 12. The transmission / reception unit 12 performs phase adjustment addition processing on a plurality of reception signals, and thereby outputs beam data corresponding to reception beams.

  A plurality of beam data are sequentially output from the transmission / reception unit 12 to the beam data processing unit 14. The beam data processing unit 14 is an electronic circuit provided with a detector, a logarithmic converter, and the like. Each beam data processed there is sent to the coordinate conversion unit 16.

  The coordinate conversion unit 16 is an electronic circuit having a coordinate conversion function, an interpolation function, and the like. The coordinate conversion unit 16 executes a process of mapping individual echo data constituting each beam data into a three-dimensional storage space. In practice, mapping of interpolation data is performed. Coordinate conversion may be performed in units of frame data corresponding to the scan plane. Volume data may be generated by repeating this. In that case, a two-dimensional scan converter is used. In any case, in the present embodiment, volume data is stored in the memory 18 of the coordinate conversion unit 16. A two-dimensional tomographic image (B-mode image) is formed based on surface data cut out from such volume data.

  The volume rendering unit 20 functions as a three-dimensional region of interest setting unit, a rendering unit, and the like. It is implemented as an electronic circuit or software function. The three-dimensional region of interest is a region for cutting out a portion to be imaged in the volume data, and conversely, it is a region excluding a portion not to be imaged, and the form and position of the region are automatically Or determined by user input. For example, when it is desired to form a three-dimensional image of the fetus in the uterus, a three-dimensional region of interest is set such that the start plane as the clipping plane is set in the gap between the fetus and the placenta (amniotic fluid). In that case, if the volume data is rotated relative to the viewpoint, the volume data rotates relative to the three-dimensional region of interest accordingly. The clipping or starting plane is a plane in the default state, but it is a plane that can be deformed into a convex or concave surface, as described in US Pat. Furthermore, it is also possible to change its height and inclination.

  In the present embodiment, the volume rendering unit 20 also functions as a setting unit of a reference surface to be described later. The reference plane is usually a plane provided on the viewpoint side of the start plane, and is a plane orthogonal to ray groups described later.

  The volume rendering unit 20 sets rays for the three-dimensional region of interest, that is, target data, based on the volume rendering method, and then performs rendering operations for each ray. The plurality of rays are parallel to one another in the present embodiment, and they extend in the depth direction from the viewpoint (or the plane corresponding thereto). The plurality of rays correspond to the plurality of pixels constituting the three-dimensional image. The volume rendering unit 20 repeatedly executes output light quantity calculation (voxel calculation) at a constant pitch from the start point (rendering start point) to the end point (rendering end point) in ray units. More precisely, the output light quantity calculation using the opacity (opacity) is repeatedly executed while sequentially shifting the calculation points until a predetermined end condition is satisfied. The predetermined termination conditions include a first termination condition and a second termination condition. When the cumulative addition value of the opacity used in the output light amount calculation exceeds 1 or a predetermined value (for example, 0.98), it is determined that the first end condition is satisfied. On the other hand, when the output light amount calculation reaches the end surface, it is determined that the second end condition is satisfied. If the opacity function is set appropriately, for example, the first termination condition is satisfied at or near the surface of the fetus. As a result, it is possible to form a three-dimensional image in which the fetal surface is represented. The output light quantity at the time when the predetermined end condition is satisfied, that is, the output light quantity at the end point is taken as the luminance corresponding to that ray. The luminance is mapped on the memory 22. A luminance map is constructed on the memory 22 as a mapping result of a plurality of luminances corresponding to a plurality of rays.

  On the other hand, when computing the output light quantity, cumulative addition of opacity is executed, and when the above-mentioned predetermined ending condition is satisfied, a "distance" representing the depth of the ending point is specified. In this embodiment, the length from the reference plane to the end point is calculated as the distance. Specifically, the first distance from the start plane to the end point is determined by multiplying the number of output light quantity operations until the end condition is satisfied by the sample point pitch on the ray. On the other hand, the length from the reference surface to the start surface is determined as a second distance on the ray or on the extension thereof. By adding the first distance and the second distance, a distance (a normalized distance with reference to the reference surface) can be obtained. The distance is mapped on the memory 24. A distance map is configured on the memory 24 by a plurality of distances corresponding to a plurality of rays. Like the luminance map, it has the same arrangement as the pixel arrangement that constitutes the three-dimensional image.

  Although the generation of the intensity map and the distance map is known per se, in the present embodiment, the individual distances constituting the distance map are the distances from the reference plane, ie the normalized distances. This will be described in more detail later.

  The circuit 26 is provided as needed. It is, for example, an image filter, for example an edge enhancement filter. The smoothing filter 28 functions as a smoothing means, which is constituted by electronic circuits or software. In the distance map, unnatural steps or the like are likely to occur in the contour of the tissue, which is a factor that degrades the image quality of the final three-dimensional image. Therefore, in the present embodiment, the smoothing filter 28 executes smoothing processing of the distance map, and the distance map that has undergone such processing is sent to the color processing unit 32 in the display processing unit 30.

  The display processing unit 30 includes various display processing functions such as a coloring function and an image combining function. Among them, a portion that generates a color three-dimensional image is shown as a color processing unit 32. The color processing unit 32 determines a pixel value (color value) from the luminance and the distance for each pixel. For example, for the three-dimensional black and white image as a luminance map, It is colored according to it. In the present embodiment, the color processing unit 32 has two conversion tables (conversion functions) in order to be able to change the color expression according to the diagnostic purpose and the user's request, and the two colors specified by them The values are weighted and combined according to the distance. The weighting composition condition can be arbitrarily changed by the user. The generated color three-dimensional image is displayed on the display 34. It is a still image or a moving image.

  The control unit 36 is constituted by a CPU and an operation program, and the control unit 36 controls the operation of each configuration shown in FIG. 1. The operation panel 38 constitutes an input device, which can be used to manually set a three-dimensional region of interest or change a weighting composition condition. In particular, when the start plane as the clipping plane is set manually, the operation panel is used. In the present embodiment, the reference plane is automatically set on the viewpoint side of the three-dimensional region of interest, but the reference plane may be set manually. In addition to the color three-dimensional image, an arbitrary cross-sectional image or a so-called triplane image is displayed on the display 34 as needed. Three-dimensional regions of interest are set with reference to those images.

  FIG. 2 schematically shows how to generate the luminance map and the distance map. However, FIG. 2 shows a general production method, in which no reference plane is shown.

  A plurality of rays 42 are set parallel to each other with respect to the three-dimensional region of interest 40. X-Y-Z represents an orthogonal coordinate system. The Z direction is the depth direction. An arrow 41 indicates a projection direction coming out of the viewpoint. A plurality of rays 42 are set in parallel to the direction. Note that it is possible to set a viewpoint at an arbitrary position for volume data.

  In the illustrated example, reference numeral 40A indicates a start plane as a clipping plane. It is drawn as a plane. In practice, it is possible to freely change the shape of the starting surface and the like. In each ray, the output light amount calculation is repeatedly executed in the depth direction (the Z direction in the illustrated example) from the start point on the start surface 40A. Opacity is cumulatively added each time the operation is performed. When the above-mentioned end condition is satisfied, the output light amount calculation is stopped, that is, the rendering operation is ended. Thus, the end point 44 is identified for each ray 42. The output light quantity at the end of the rendering operation is mapped on the memory as luminance. A luminance map 46 is configured as the mapping result of the plurality of luminances corresponding to the plurality of rays 42. It corresponds to a black and white volume rendering image. On the other hand, the depth of the end point 44 in units of rays is mapped on the memory as a distance. A distance map 48 is configured as a mapping result of a plurality of distances corresponding to a plurality of rays 42. As shown in the gray scale 50, in the illustrated example, the distance from the minimum distance to the maximum distance is expressed as a brightness change. However, the distance may be expressed as another numerical value.

  The luminance map 46 and the distance map 48 have the same two-dimensional pixel array as the two-dimensional pixel array constituting the three-dimensional image. Based on the intensity map 46 and the distance map 48, a color three-dimensional image is formed. For example, as described above, a luminance map corresponding to a black and white three-dimensional image is colored in accordance with the distance corresponding to each pixel.

  A comparative example is shown in FIG. Reference numeral 54 denotes a fetus, and reference numeral 56 denotes a placenta. Reference numeral 57 indicates amniotic fluid. Reference numeral 52 denotes volume data, and reference numeral 58 denotes a three-dimensional region of interest (a cross section of the three-dimensional region of interest appears in FIG. 3). The three-dimensional region of interest 58 is a box having a start surface 60 that functions as a clipping surface, an end surface 65 as a bottom (bottom) surface, and four side surfaces (two side surfaces 62 and 64 appear in FIG. 3) It has the form of a letter. The concave deformation of the initiation surface 60 inserts the initiation surface 60 into the gap between the fetus 54 and the placenta 56. Thus, once the three-dimensional region of interest 58 has been defined, rendering operations are performed for each individual ray set against it. In FIG. 3, each downward arrow 62 indicates a rendering operation path, and the tip of the arrow 62 indicates the end point. In addition, although the thing which has not reached to the fetal surface layer is contained in FIG. 3 among the some down arrow 62, it is based on the convenience on drawing. In the comparative example shown in FIG. 3, the reference surface is not employed. That is, in each ray, the length from the start plane to the end point is calculated as the distance, and the distance is referred to as it is in the coloring process. Therefore, the curvature of the starting surface 60 causes a distance gradient in the distance map that is not related to the fetal surface morphology. It causes unnecessary hue change.

  An embodiment is shown in FIG. The same components as those shown in FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted. The same applies to FIGS. 5 and 6 described later.

  In FIG. 4, the reference surface 66 is set on the side closer to the viewpoint than the start surface 60. The reference plane 66 is a plane having a relationship orthogonal to the plurality of rays. The start surface 60 in the default state may be defined as the reference surface. The reference plane 66 covers the entire three-dimensional region of interest 58. Specifically, the reference plane is defined as a plane connected to the upper sides of the four side surfaces of the three-dimensional region of interest 58. However, the reference plane may be set at a position closer to the viewpoint. It is desirable to position the reference surface 66 so that the reference surface 66 does not cross the tissue to be observed.

  In each ray, the rendering operation is performed in the same manner as in the prior art, but the reference surface 66 is used as an operation reference only in the distance operation. That is, in each ray, the normalized length from the reference plane 66 to the end point is calculated as the distance. In practice, a first distance from the start point to the end point on the start surface 60 is calculated, while a second distance from the reference surface 66 to the start surface 60 is calculated. Then, by adding the first distance and the second distance, the distance mapped as the addition result is calculated. However, the distance from the reference plane to the end point may be determined directly. In this embodiment, since the distance is defined separately from the rendering operation range, it is possible to calculate a standardized distance which does not depend on the form of the start surface.

  FIG. 5 shows a second example of the reference surface. In this second example, in consideration of the form of the placenta 56A, the starting surface 60A of the three-dimensional region of interest 58A constitutes a convex surface, whereby the reference surface 70 on the opposite side to the viewpoint when viewed from the starting surface 60A. Is set. However, the reference plane 70 does not cover the fetus 54, and the distances calculated in each ray are all positive (see reference numeral 72). However, in the second example shown in FIG. 5, the reference surface 70 is likely to hit the tissue to be imaged, so that, for example, the reference surface 70 passes the apex of the start surface 60A so that the reference surface 70 is positioned higher. Thus, it is desirable to change the reference surface setting conditions.

  FIG. 6 shows a third example of the reference surface. In this example, the placenta 56B has a rather complex form, and correspondingly, the starting surface 60B of the three-dimensional region of interest 58B also has a complex form. A reference surface 74 is set on the viewpoint side of the start surface 60B. It is flat but inclined to each ray. The inclination angle is small, and the amount of distance change due to the inclination is quite small. Moreover, since it is uniformly inclined, unnatural distance changes and local distance changes do not occur. Thus, in some cases, it is also possible to use an inclined reference surface 74. However, since an apparent distance increase or decrease occurs due to the inclination, it is desirable to adopt a reference plane (the reference plane shown as the first example) orthogonal to each ray.

  FIG. 7 shows an operation example, in particular, an operation related to generation of a luminance map and a distance map. In S10, k indicating a ray number is initialized, and in S12, d indicating a depth is initialized. In S14, an echo value (voxel value) is calculated for a target point at depth d on the k-th ray. For example, the echo value of the point of interest is calculated by three-dimensional linear interpolation operation based on eight echo values present in the vicinity of the point of interest. In S16, an output light quantity calculation (voxel calculation) based on the echo value at the point of interest, the opacity corresponding to it, and the like is performed. As a result, the output light quantity at the point of interest is determined, and the output light quantity is taken as the input light quantity at the next point of interest. At S16, cumulative addition of opacity is also performed.

  In S18, it is determined whether a predetermined termination condition is satisfied. If not satisfied, d is incremented in S28 and then each step from S14 is repeatedly executed. On the other hand, if it is determined in S18 that the termination condition is satisfied, the final output light quantity is mapped on the memory as luminance in S19.

  In S20, the distance Δd from the reference plane to the start plane is calculated. The distance Δd depends on the position and form of the starting surface. In S22, the depth d of the end point and the distance Δd between the reference surface and the start surface are added, and as a result, the distance Z is determined. At S24, Z is mapped on the memory. In S26, it is determined whether or not k has reached the maximum value, and if no, k is incremented in S30, and the steps after S12 are repeatedly executed.

  After this, a color three-dimensional image is formed based on the brightness map and the distance map. However, prior to the three-dimensional image formation, at least the distance map is subjected to smoothing processing in S27.

  A modification is shown in FIG. In this modification, S32 and S34 are provided between S22 and S24 shown in FIG. In S32, it is determined whether or not Z is a negative value. If Z is a negative value, Z is forcibly set to zero in S34. This prevents the distance from being outliers. However, it is not necessary to adopt such a modification if the reference plane is set so as to always be on the viewpoint side of the start plane. If the user can arbitrarily set the position of the reference plane, it is desirable to adopt the modification shown in FIG.

  FIG. 9 shows the operation of the smoothing filter shown in FIG. Reference numeral 78 indicates the distance map before smoothing. Jaggedness occurs at the edge 78A of the tissue contained therein. When the three-dimensional image is formed on the basis of such a distance map, the above-mentioned jaggedness causes an unnatural hue change in the three-dimensional image. On the other hand, reference numeral 80 denotes a distance map after smoothing by the smoothing filter. After smoothing, the above-mentioned jaggedness disappears and it becomes smooth edge 80A. Of course, the effect of smoothing extends beyond the edges. The image quality can be improved by forming a three-dimensional image on the basis of the distance map after the smoothing. That is, it is possible to cause a hue change, ie, a natural hue change, that does not cause the viewer to feel discomfort on the three-dimensional image.

  FIG. 10 shows a first configuration example of the color processing unit shown in FIG. It has a conversion table 82. The conversion table 82 is configured, for example, as a look-up table that determines a color value P as a pixel value from the luminance I and the distance Z. It may be composed of mathematical functions. FIG. 11 shows a second configuration example of the color processing unit. The conversion tables 84 and 86 determine color values from the luminance I, respectively, from which two color values are output. A weighting combiner 88 weight combines the two color values based on the distance Z. FIG. 12 shows a third configuration example of the color processing unit. The two conversion tables 90 and 92 determine color values in accordance with the combination of the luminance I and the distance Z, respectively. The weighting combiner 94 performs weighting combining on the basis of the distance Z based on the two input color values. The first to third configuration examples are merely examples, and other configuration examples may be adopted.

  An example of weighting composition is shown in FIG. The horizontal axis indicates the distance Z. The vertical axis shows color values, in particular the color values determined by the conversion table (F) and the color values determined by the conversion table (B). The weighting function is shown at 104. Three sections 106, 108 and 110 are set in the vertical axis direction. In the section 106, 100% of the color values of the conversion table (F) are adopted. In the section 110, 100% of the color values of the conversion table (B) are adopted. In the section 108 between them, the weight changes from the color value of the conversion table (F) to the color value of the conversion table (B) according to the distance Z. At the center of the section 108, the weight of both color values is 0.5. The position of Depth1 and Depth2 can be arbitrarily set in the vertical axis direction by the user. If both are matched, the use table can be switched at a certain distance. If the surface of the fetus is in the section 108, the sense of depth of the surface can be remarkably expressed as a hue change.

  In that case, in the present embodiment, the distance is calculated regardless of the form of the start plane as the clipping plane, so it is possible to avoid the problem of hue change due to the deformation of the start plane.

20 Volume rendering unit, 22 memory (memory storing luminance map), 24 memory (memory storing distance map), 32 color processing unit.

Claims (7)

Setting means for setting a three-dimensional region of interest defining target data to be rendered for volume data acquired from a three-dimensional space in the living body;
It is a means for setting a plurality of rays for the target data and performing rendering operation along rays in units of rays, and a plurality of luminance maps corresponding to the plurality of rays and the plurality of rays. Rendering means for generating a distance map consisting of a plurality of corresponding distances; and image forming means for forming a color three-dimensional image based on the brightness map and the distance map;
Including
The setting means sets a reference plane having an intersecting relationship with the plurality of rays, separately from the deformable start plane as the clipping plane of the three-dimensional region of interest.
The rendering means is
Luminance map generation means for calculating the luminance by performing the rendering operation from the start plane in units of rays;
Distance map generation means for calculating the distance from the reference plane to the rendering operation end point in units of rays;
An ultrasonic image processing apparatus comprising: In the device according to claim 1,
The reference plane is a plane having an orthogonal relationship with the plurality of rays.
An ultrasonic image processing apparatus characterized in that. In the device according to claim 1,
The reference plane is set closer to the viewpoint than the three-dimensional region of interest
An ultrasonic image processing apparatus characterized in that. In the device according to claim 1,
The distance map generation unit sets the distance to zero when the rendering operation end point is closer to the viewpoint than the reference plane.
An ultrasonic image processing apparatus characterized in that. In the device according to claim 1,
The distance map generation unit
A unit for calculating a first distance from the start surface to the rendering operation end point in units of rays;
Means for calculating a second distance from the reference surface to the start surface in units of rays;
A unit that calculates the distance by adding the first distance and the second distance in units of rays;
An ultrasound imaging apparatus characterized in that. In the device according to claim 1,
The image forming unit is
A first conversion table for determining a first color value based at least on luminance;
A second conversion table for determining a second color value based at least on the luminance;
A means for weighting and combining the first color value determined by the first conversion table and the second color value determined by the second conversion table according to the distance;
Including
The color three-dimensional image is configured by the plurality of color values after the weighting and combining.
An ultrasonic image processing apparatus characterized in that. In the device according to claim 1,
Smoothing means for smoothing the distance map prior to formation of the color three-dimensional image;
An ultrasonic image processing apparatus characterized in that.