A processing is executed for identifying an image area which blocks an observation target, and removing the identified area. An image processing apparatus 10 is provided, which allows multiple projection drawings to be generated by projecting a three-dimensional image from any projecting direction and determines a removal target area, out of the designated area in each projection drawing. The image processing apparatus 10 is provided with an input section 40 for allowing a user to roughly specify an image area that blocks the observation target, the image area forming a maximum area, and an area judgment section 32 for identifying a removal target image area, and an image processing section 31 for constructing an image where the removal target image area has been removed.

BACKGROUND

The present invention relates to a technique for detecting a specific image area and performing a removal process.

There is known a technique such as a volume rendering for generating a two-dimensional projection drawing from a three-dimensional image (volume data) which is made up of tomographic images (angio data) of a test object, the tomographic images being obtained by a tomographic apparatus such as an X-ray CT (Computed Tomography) apparatus and an MRI (Magnetic Resonance Imaging) apparatus.

The MIP (Maximum Intensity Projection) method is one of the volume rendering techniques. The MIP method is a method for applying a projection process to the volume data in an optional direction, and displaying on a projection plane, a maximum luminance value in the projection path. With this method, if there exists an area where bones and the like are displayed, which may hamper the observation of blood vessels or the like being a diagnostic object on the projection plane, a user has been allowed to select to a high degree of detail, the area which is desired to be removed. Accordingly, it has been possible to create a display where such area is removed (see, “Oh, I see!! Medical three-dimensional image; Bible of Way of thinking and Processing method”, supervised by Yutaka Imai, p. 141 (2003)(non-patent document 1), for instance).

SUMMARY

However, according to the technique described in non-patent document 1, the user has been required to designate an area on the display screen in detail, i.e., only the area to be removed, in order to execute removing of the area such as bones and the like. Therefore, it has been necessary to perform complicated removal works.

Given the situation above, an object of the present invention is to provide a technique which utilizes that a luminance value is higher in a bone area than in a blood vessel area, thereby estimating the bone area from a roughly designated area, and enables execution of a process for removing a desired area from the display screen, just by a simple removal operation.

In order to solve the problem above, an image processing apparatus according to the present invention provides a technique which identifies a removal target area from an image area.

By way of example, it is directed to an image processing apparatus which projects a three-dimensional image from any projecting direction, and generates multiple projection drawings, the apparatus having an input accepting section for displaying the multiple projection drawings on a display part and accepting an input of a designated area which includes a removal target area as to each of the projection drawings, a luminance value calculation section for specifying a luminance value of the removal target area from the designated area, and an area judgment section for determining as the removal target area, an area where the luminance value belongs to a specific range, out of the image on a virtual ray that projects the designated area, with respect to each of the multiple projection drawings.

As described above, according to the present invention, it is possible to provide a technique that enables a bone area as the removal target to be estimated based on the luminance value of the designated area that the user has designated roughly on the projection drawing, whereby the user is allowed to remove a desired area by a simple removal operation.

DENOTATION OF REFERENCE NUMERALS

10•60: IMAGE PROCESSING APPARATUS,20: STORAGE PART,21: ANGIO DATA STORAGE AREA,22: VOXEL DATA STORAGE AREA,23: PIXEL DATA STORAGE AREA,30•70: CONTROL PART,31•71: IMAGE PROCESSING SECTION,32•72: AREA JUDGMENT SECTION,33: LUMINANCE VALUE RANGE CALCULATION SECTION,73: LUMINANCE THRESHOLD CALCULATION SECTION,40: INPUT PART,50: DISPLAY PART,610: VOLUME DATA,600•620: PROJECTION DRAWING,621: PIXEL,700: DESIGNATED AREA,80: BONE AREA,90: BLOOD VESSEL,800: REMOVAL TARGET AREA

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1is a block diagram showing a functional configuration of the image processing apparatus10relating to the first embodiment according to the present invention.

As illustrated, the image processing apparatus10is provided with a storage part20, a control part30, an input part40, and a display part50.

The storage part20incorporates an angio data storage area21, a voxel data storage area22, and a pixel data storage area23.

The angio data storage area21stores angio data which is a three-dimensional image made up of multiple two-dimensional tomographic images which are obtained by a tomographic apparatus (not illustrated) that takes images of a specific portion respectively at positions each being spaced every predetermined distance.

The voxel data storage area22stores a voxel data table220in units of voxel; the table storing volume data which is made up of the angio data. As shown inFIG. 2, the voxel data table220includes a voxel position storage field22a, a voxel value storage field22b, a removal target area flag storage field22c, an X-Y plane side direction flag storage field22d, a Z-X plane side direction flag storage field22e, and a Y-Z plane side direction flag storage field22f.

The voxel position storage field22astores a voxel coordinate position (X, Y, Z) which is a constitutional element of the volume data. The voxel value storage field22bstores a voxel luminance value (voxel value V) at the voxel position (X, Y, Z) which is identified by the voxel position storage field22a. The removal target area flag storage field22cstores a removal target area flag, which is set when the voxel identified by the voxel position (X, Y, Z) is judged as a bone area.

When the voxel at the voxel position (X, Y, Z) identified by the voxel position storage field22ais judged as a bone area candidate, a direction flag is set in the X-Y plane side direction flag storage field22d, in the Z-X plane side direction flag storage field22e, and in the Y-Z plane side direction flag storage field22f, respectively, in the following cases; the case where the projecting direction of the projection drawing including the designated area which is used as a basis for the judgment, is the X-Y plane side direction, the case where it is the Z-X plane side direction, and the case where it is the Y-Z plane side direction.

It is to be noted here that a pixel is obtained by developing a point into the two-dimensional direction (X, Y), and a voxel is obtained by developing the pixel further into the Z-direction. The voxel is a cube having information items respectively in the X, Y, and Z directions, which constitute the voxel data, and a luminance value (voxel value V) and opacity are assigned to each voxel.

The pixel data storage area23stores a pixel data table230for storing the projection drawing in the units of pixel, the drawing being obtained by projecting the volume data from any projecting direction. As shown inFIG. 3, the pixel data table230includes a projecting direction information storage field23a, a pixel position storage field23b, a pixel value storage field23c, and a designated area flag storage field23d.

The projecting direction information storage field23astores projecting direction information for specifying the projecting direction of the projection drawing. The projecting direction information indicates any direction in which the control part30projects the volume data. For example, the direction may be represented by coordinate axes based on the developing direction of the volume data, such as the direction of the X-Y plane side (front direction), the direction of the Y-Z plane side (lateral direction), and the direction of the Z-X plane side (upper direction), (seeFIG. 5(a) toFIG. 5(c)), or represented by an identifier such as a numerical character.

The pixel position storage field23bstores each of the coordinate positions (X, Y) of the pixels, each being a constitutional element of the projection drawing. Here, the pixels are generated when the volume data is projected in the projecting direction that is stored in the projecting direction information storage field23a.

The pixel value storage field23cstores each luminance value of the pixel (pixel value P) which is identified, by the projecting direction that is stored in the projecting direction information storage field23aand the pixel position (X, Y) which is specified in the pixel position storage field23b.

The designated area flag storage field23dsets a designated area flag, when it is judged that the pixel, which is identified by the projecting direction stored in the projecting direction information storage field23aand the pixel position (X, Y) specified in the pixel position storage field23b, is included in the designated area, having been designated by a user.

The control part30is provided with an image processing section31, an area judgment section32, and a luminance value range calculation section33.

The image processing section31executes a process to generate a projection drawing from the volume data according to the MIP method. In addition, it reconstructs the volume data based on the information stored in the voxel data table220.

The area judgment section32identifies the following areas; a designated area which is designated by the user on the projection drawing, a bone candidate area within the volume data, the area being determined by the pixel value P of the pixel within the designated area, and a removal target area (bone area) in the volume data, the area being determined based on the bone candidate area.

The luminance value range calculation section33generates a histogram indicating a distribution with respect to each segment, as to the pixel value P of the pixel within the designated area, executes a process for specifying a cluster of the bone area, and calculates the luminance value range Cr. Hereinafter, with reference toFIG. 4andFIGS. 5(5(a) to5(d)) process executed by the control part30will be explained specifically.

FIG. 4is a schematic diagram showing a process for generating the projection drawing620by using the volume data610.FIG. 5(a) is a schematic diagram showing a projection drawing620aviewed from the direction of the X-Y plane (front) side of the volume data610,FIG. 5(b) is a schematic diagram showing a projection drawing620bviewed from the direction of the Y-Z plane (lateral) side of the volume data610,FIG. 5(c) is a schematic diagram showing a projection drawing620cviewed from the direction of the Z-X plane (top) side of the volume data610; andFIG. 5(d) is a schematic diagram showing a projection drawing600viewed from the direction of the X-Y plane (front) side of the volume data610where the removal target area has been removed.

The image processing apparatus10relating to the present embodiment stores two-dimensional tomographic images (angio data) taken by a tomographic apparatus (not illustrated) or the like, in the angio data storage area21in the storage part20. Then, the image processing section31reconstructs the angio data at multiple positions associated with the same phase and generates the volume data610which is a three-dimensional image.

As shown inFIG. 4, however, in the volume data610, in addition to the blood vessel90as an observation target, an image such as the bone area80is taken, which blocks the observation of the blood vessel90. Therefore, the control part30firstly executes a process using the MIP method so as to remove the bone area80assuming that this area is the removal target area800and display the overview image of the blood vessel90. The MIP method is a method for converting the volume data610into a two-dimensional image.

The image processing section31irradiates the volume data610with a virtual ray R, as to each voxel which is a constitutional unit of the volume data, from an optional direction (in the present embodiment, it is one of three directions; the direction of the X-Y plane (front) side, the direction of the Y-Z plane (lateral) side, and the direction of the Z-X plane (top) side). Then, a maximum voxel value Vmax is detected from a group of N voxels615, which exist on the virtual ray R. In addition, the image processing section31defines the detected value as a pixel value P of a pixel621on the projection drawing620, the pixel621existing on the virtual ray R. Then, the projection drawing620is generated (reference symbol620aindicates the projection drawing in the direction of the X-Y plane side,620bindicates the projection drawing in the Y-Z plane side, and620cindicates the projection drawing in the direction of the Z-X plane side).

The area judgment section32displays each of the projection drawings (e.g.,FIG. 5(a) toFIG. 5(c)) on a display unit5which is provided in the display part50. Then, via the input part40, the area judgment section accepts from the user an operation for selecting a roughly designated area in such a manner that the bone area80forms a maximum area within the designated area on the projection drawings620ato620c. It is to be noted that the designated area may contain the pixels representing the blood vessel and the like. The area being designated is determined as the designated area700in the unit of pixels, and the area judgment section32specifies the pixel positions of the pixels included in the designated area700.

The area judgment section32detects a voxel having the voxel value V falling into the luminance value range Cr, which will be described below, as to the voxels existing on the virtual ray R that projects the pixel within the designated area700, and identifies the detected voxel as the bone candidate area. In addition, the voxels judged as corresponding to the bone candidate area as to all the projecting directions, are determined as the removal target area800which is targeted for removal.

The luminance value range calculation section33executes a clustering process as described below, as to the pixels within the designated area700, and calculates the luminance value range Cr, so as to specify the luminance value of the pixel and the voxel which are determined as the bone area candidate.

It is to be noted that the angio data stored in the angio data storage area21may be acquired through any kind of method. For example, an interface part directly connected to the tomographic apparatus is provided to directly acquire the angio data from the tomographic apparatus. Alternatively, a communication part is provided, and the angio data may be acquired from a network such as the Internet.

The input part40is a user interface for accepting an input from an operator, and includes a pointing device or the like for manipulating graphics which indicate an intended operation on a GUI. The pointing device may be a mouse, or a touch panel for a direct touch on the screen, for instance.

The display part50is provided with a display unit for displaying at least each of the images being generated, and a CRT (Cathode Ray Tube), an LCD (Liquid Crystal Display) or the like may be selected as the display unit.

Here, a hardware configuration of the image processing apparatus10will be explained.FIG. 13is a block diagram indicating an electrical configuration of the image processing apparatus10.

As shown inFIG. 13, the image processing apparatus10is a general computer on which programs are operated, and it may be a personal computer or a work station, for instance.

The image processing apparatus10incorporates a CPU (Central Processing Unit)1which is a major portion of the computer for collectively controlling each unit, and a memory2for storing various data in a rewritable manner. The image processing apparatus10is further provided with an external storage unit3for storing various programs, data generated by the programs, and the like, an input unit4such as a keyboard and a mouse for giving various operational instructions, and a display unit5for displaying image data and the like. Each of these units is connected to the CPU1via a signal line6such as a bus. It is a matter of course that the image processing apparatus is additionally provided with a communication unit for establishing communication with an external unit.

The CPU1loads on the memory2, the programs stored in the external storage unit3, and executes the programs, thereby implementing various processes. As a manner of course, the programs may also be downloaded on the external storage unit3from the network via the communication unit, and then they are loaded on the memory2to be executed by the CPU1.

The external storage unit3is provided with an HDD (Hard Disk Drive) but it is not limited to the HDD, and it may be further provided with a drive of a CD-ROM, DVD-ROM or the like, as a mechanism for reading computer software being a distributed program and data.

With reference to the flowchart as shown inFIG. 7, an explanation will be made as to the process performed in the image processing apparatus10according to the present embodiment configured as described above.

Firstly, the image processing section31of the image processing apparatus10reads any angio data stored in the angio data storage area21, and accumulates and reconstructs multiple images associated with the same phase on the axis, thereby generating the volume data (S11).

In addition, the image processing section31stores information as to each voxel being the constitutional element of the volume data, in the voxel data table220which is stored in the voxel data storage area22. In other words, the image processing section stores the coordinate position (X, Y, Z) of each voxel in the voxel position storage field22a, and stores a voxel value V specified by the voxel position storage field22ain the voxel value storage field22b.

Next, the image processing section31projects the volume data being generated, from any projecting direction according to the aforementioned MIP method, and generates multiple projection drawings (S12). In the present embodiment, it is assumed that three projection drawings are generated, which are projected from three directions, the X-Y plane side, the Y-Z plane side, and the Z-X plane side.

In addition, the image processing section31stores information as to each pixel being a constitutional element of these projection drawings, in the pixel data table230which is stored in the pixel data storage area23. In other words, the image processing section stores the projecting direction information specifying the projecting direction of each projection drawing made up of the pixels, in the projecting direction information storage field23a, the coordinate position (X, Y) of each pixel of the projection drawing, which is projected from the projecting direction stored in the projecting direction information storage field23a, in the projecting direction information storage field23b, and a pixel value P of the pixel specified by the projecting direction information storage field23aand the pixel position storage field23b, in the pixel value storage field23c.

Next, the area judgment section32displays each of the projection drawings on the display unit5provided in the display part50, and accepts as a designated area, a rough designation of bone area in which the bone area forms a maximum area (S13). By way of example, when a user specifies the designated area, the area judgment section32detects a projecting direction of the projection drawing as to which the designated area is specified on the display unit5, and specifies a record which stores the projecting direction that agrees with the detected projecting direction, in the projecting direction information storage field23aof the pixel data table230. Then, the area judgment section further extracts a record which is stored in the pixel position storage field23bof the record being specified, the pixel position that agrees with the coordinate position of the pixel within the designated area. Subsequently, the area judgment section32sets a designated area flag in the designated area flag storage field23dof the record being extracted, and specifies the pixel corresponding to the designated area.

Any method may be employed for specifying the designated area. By way of example, it is possible to configure such that the user uses a mouse or the like to draw a free closed curve, so as to decide the designated area. In such a case, a GUI may be utilized; in the GUI, a left-click on the mouse may allow a decision of the area having a specified size, and a right-click on the mouse may allow a release of designation of the area. Alternatively, the area may be specified by changing the size or the position of a preset circle or the like.

Next, the luminance value range calculation section33calculates a luminance value range (S14). With reference to the flowchart as shown inFIG. 8, an explanation will be made regarding a process for calculating the luminance value range.

The luminance value range calculation section33firstly executes a clustering process as to the range of the pixel value (S141).

FIG. 6is a histogram showing a distribution of the pixels as to all the pixels included in each designated area, with the vertical axis representing a frequency (number of times), and the horizontal axis representing segments of the pixel value P.

By way of example, the luminance value range calculation section33divides the segments of the pixel value P into clusters. In the histogram shown inFIG. 6, the range of the pixel value P is divided into three clusters C1, C2, and C3.

A publicly known method, the Fuzzy C-Means (FCM) or the like which employs a membership function, may be used as the clustering process. The FCM is a method obtained by expanding the K-Means by adding an idea of belonging degree.

The K-Means is a clustering method used in the case where the number of clusters (K) is determined in advance, and the present embodiment requires at least three clusters; the background area, the blood vessel area, and the bone area.

Firstly, an appropriate center value is given as a representative point of the cluster, and each element is made to belong to the cluster having the closest center value, and a membership value of each pixel relative to the center value (belonging degrees to all the clusters) is obtained. The pixel may belong to multiple clusters simultaneously. Subsequently, a new cluster center value is calculated based on the membership value for each of the clusters, and a new cluster is obtained. This operation is repeated until each center value stops changing, and clustering is completed at the stage reaching a designated parameter (convergence condition) or less.

The parameters (the number of clusters, the membership function, parameters (convergence condition), and the like) which are necessary for the clustering may be certain values determined in advance, or they may be values which a user is allowed to input optionally.

The luminance value range calculation section33further identifies a cluster representing the pixels that correspond to the bone area, out of the clusters (S142).

Here, in the present embodiment, in the designated area that the user roughly specifies by hand in such a manner that the bone area forms the maximum area, it is considered that the pixels representing the bone area form the largest range. It is further possible to assume that there mainly exist pixels representing blood vessels having a pixel value P smaller than the bone area, and a background area having a pixel value P which is much smaller than the pixels representing the blood vessels.

In the histogram shown inFIG. 6, the cluster C1, for instance, has a minimum pixel value P, and the range of the pixel value P is also small. Therefore, it is assumed that the cluster C1is a group of pixels representing the background area. The cluster C2has the pixel value P and the frequency, both smaller than the cluster C3, and therefore, it is assumed as a group of pixels representing the blood vessels. The cluster C3has the pixel value P and the frequency, both being large, and it is assumed as a group of pixels representing the bone area forming a large area within the designated area.

Therefore, in the present embodiment, the luminance value range calculation section33identifies the cluster C3as the bone area pixels. A method for identifying the bone area and the clustering process are not limited to those described above, and any method may be applicable.

Subsequently, the luminance value range calculation section33calculates the luminance value ranges Cr1, Cr2, and Cr3respectively for the designated areas of the projection drawings (Cr1: luminance value range of the designated area in the projection drawing in the X-Y plane side direction, Cr2: luminance value range of the designated area in the projection drawing in the Z-X plane side direction, and Cr3: luminance value range of the designated area in the projection drawing in the Y-Z plane side direction. If it is not necessary to make a distinction among those three value ranges, it is denoted as the luminance value range Cr) (S143).

For example, the luminance value range calculation section33detects from the pixel group of the cluster C3, which is assumed as the bone area, a minimum pixel value Pmin and a maximum pixel value Pmax, and obtains the range from Pmin to Pmax as the luminance value range Cr of the cluster C3.

Referring toFIG. 7again, the area judgment section32scans the voxels on the virtual ray R in the projecting direction, with respect to each pixel within the designated area, and identifies the voxels having the voxel value V included in the luminance value range Cr, as the bone candidate area (S15).

Firstly, an explanation will made as to the case where the area judgment section32detects the bone candidate area based on the luminance value range Cr1in the designated area of the projection drawing in the X-Y plane side direction. For example, the area judgment section32extracts a record in which a designated area flag is set in the designated area flag storage field23dof the pixel data table230, and the projecting direction information storage field23astores information that specifies the projecting direction as the X-Y plane side direction. Then, the area judgment section32acquires the pixel position from the pixel position storage field23bof the record being extracted.

Then, the area judgment section32detects coordinate positions of all the voxels located on the virtual ray R, based on the pixel position and the projecting direction information (here, the X-Y plane side direction). By way of example, if the pixels position is (A, B), the voxels whose coordinate positions are (A, B, (1 to Zn)) are targeted for the scanning (“Zn” indicates the number of voxels in the Z direction).

Subsequently, the area judgment section32extracts a record whose voxel position agrees with any of the coordinate positions (A, B, (1 to Zn)) of the voxels located on the virtual ray R, in the voxel position storage field22aof the voxel data table220. The area judgment section32further extracts a record, whose voxel value V stored in the voxel value storage field22bof the record being extracted falls into the luminance value range Cr1.

Subsequently, the area judgment section32sets a direction flag in the X-Y plane side direction flag storage field22dof the record being extracted. The processing above is executed as to all the pixels within the designated area. Furthermore, the area judgment section32executes the similar processing by using the luminance value range Cr2for the pixels within the designated area of the projection drawing in the Z-X plane side direction, and by using the luminance value range Cr3for the pixels within the designated area of the projection drawing in the Y-Z plane side direction.

Next, the area judgment section32specifies as a removal target area, the voxels identified as the bone candidate area in all the projecting directions (S16). Hereinafter, with reference to the flowchart as shown inFIG. 9, a process for specifying the removal target area will be explained.

The image processing section31specifies a record from the voxel data table220, except the record in which the direction flag is set in all the following fields; the X-Y plane side direction flag storage field22d, the Z-X plane side direction flag storage field22e, and the Y-Z plane side direction flag storage field22f. Then, the image processing section31projects the volume data made up of only the voxel data stored in this specified record from any projecting direction, generates a projection drawing, and then displays the projection drawing on the display unit5(see S151andFIG. 5(d)).

Next, the area judgment section32accepts a permit to finalize the removal target area, via the input part40from the user (S152).

If the bone area is removed and a desired result is obtained in the projection drawing displayed on the display unit5, for instance, the user is allowed to execute an instructing operation to permit finalization of the removal target area via the input part40. On the other hand, if a desired result is not obtained, such as the bone area has not been removed sufficiently, the user is allowed to input an instructing operation for re-editing via the input part40(S154).

In the step152, upon accepting the permit to finalize the removal target area (YES), the area judgment section32extracts a record from the voxel data table220, the record in which the direction flag is set in all the following fields; the X-Y plane side direction flag storage field22d, the Z-X plane side direction flag storage field22e, and the Y-Z plane side direction flag storage field22f. Then, the area judgment section sets a removal target area flag in the removal target area flag storage field22cof the record being extracted, specifies the voxels corresponding to the removal target area, and terminates the process (S153).

In the step154, upon accepting the instructing operation of re-editing (YES), the area judgment section32jumps to the step of the point for re-editing. There are provided multiple points for the re-editing point, such as the point of specifying the designated area (S13) and the point of identifying the cluster of the bone area (S142), and the user is allowed to select any of the defined re-editing points.

The image processing section31removes the voxels identified as the removal target area, as to the volume data on which the removal target area is specified according to the procedure as described above, and reconstructs the volume data.

It is to be noted that the processing for removing the removal target area can be implemented according to the following procedure, for instance; a mean value of the pixel values of the cluster is calculated, the cluster being assumed as the background area in the clustering process (seeFIG. 6, C1), and the voxel value V of the voxels on which the removal target area flag is set is overwritten by the mean value. As a matter of course, the procedure is not limited to the method as described above, and it is alternatively possible to execute a process such as subtracting the voxel value V of the voxels on which the removal target area flag is set, and thereafter the voxels are combined.

In the process for creating the histogram, the pixel segment serving as the unit of the frequency distribution may be a predefined value, or it may be configured as settable by the user.

Furthermore, when the projection drawing from which the bone area is removed is displayed (seeFIG. 5(d)), the image processing section31is able to use a predetermined value as the voxel value V of the voxels in the removal target area. In the configuration as described above, according to the change of the color or the like of the removal target area, the user is allowed to confirm intuitively whether or not the removal process has been executed.

It is to be noted that the removal target area is not limited to the bone area. It is further possible to configure such that voxels provided with a large luminance value such as a noise can be determined as a removal target.

With the configuration as described above, the image processing apparatus10relating to the present embodiment is able to identify the bone area as the removal target according to the clustering process, out of multiple designated areas having been roughly specified in such a manner that the bone area forms a maximum area, and the user is allowed to remove a desired area spatially according to a simple operation.

Next, an image processing apparatus60relating to a second embodiment of the present invention will be explained. As shown inFIG. 10, the image processing apparatus60incorporates the storage part20, a control part70, the input part40, and the display part50.

In the image processing apparatus60according to the second embodiment, the process executed by the control part70is different from the image processing apparatus10according to the first embodiment. Therefore, hereinafter, an explanation will be made regarding such differences.

The control part70incorporates an image processing section71, an area judgment section72, and a luminance threshold calculation section73. With reference toFIG. 4andFIG. 5, processing of these elements will be specifically explained.

The image processing section71executes a processing for generating a projection drawing from the volume data according to the MIP method. In addition, the image processing section reconstructs the volume data from the information stored in the voxel data table220.

The area judgment section72accepts from a user via the input part40, an operation for specifying a rough bone area80in such a manner that the bone area forms a maximum area in the projection drawing620, detects a designated area700as to each projection drawing, and identifies a pixel position included in the designated area700. Furthermore, the area judgment section72determines as the bone candidate area, the voxel having the voxel value V, which is equal to or higher than the after-mentioned luminance threshold ThP and also equal to or higher than ThV, on the virtual ray R which projects each of the pixel within the designated area. In addition, the area judgment section identifies the voxel determined as corresponding to the bone candidate area, with regard to all the projecting directions, as the removal target area800which is a target for removal.

The luminance threshold calculation section73detects a maximum pixel value Pmax, out of the pixel values P of the pixels included in each designated area700. Subsequently, the luminance threshold calculation section73scans the voxels on the virtual ray R projecting the pixels included in the designated area700, and detects the maximum voxel value Vmax. The luminance threshold calculation section73multiplies the pixel value Pmax by a parameter A, and multiples the voxel value Vmax by a parameter B, thereby calculating the luminance thresholds ThP and ThV.

The luminance thresholds ThP and ThV are values which are provided for specifying the range of the voxel value V assumed as the bone area. In the present embodiment, the voxel having the voxel value V satisfying the conditions; ThP≦V and ThV≦V, is determined as the bone candidate area.

Here, for the Pmax and Vmax, if any pixel representing a blood vessel is included in the designated area, the pixel value of the pixel representing the blood vessel may be assumed as the maximum value. The parameter A and the parameter B are provided in order to avoid that the voxel having the luminance value representing the blood vessel is recognized as the bone area. Therefore, the parameter A and the parameter B are values less than one, and in the present embodiment, it is preferable that the value is around 0.8, for instance. It is to be noted that the parameter A and the parameter B may be freely configured by the user, considering the luminance value and the like of the angio data.

With reference to the flowcharts as shown inFIG. 11andFIG. 12, an explanation will be made as to the processing of the image processing apparatus60according to the present embodiment configured as described above.

Since the processes from the step21to step23as shown inFIG. 11are the same as those from the step11to step13which are executed in the image processing apparatus10relating to the first embodiment, detailed explanation will not be tediously made.

Hereinafter, with reference toFIG. 12, a detailed explanation will be made as to the processing in the step24.FIG. 12is a flowchart showing the luminance threshold calculation process that is executed by the image processing apparatus60relating to the second embodiment.

The luminance threshold calculation section73detects maximum pixel values Pmax1, Pmax2, and Pmax3out of the pixel values P of the pixels, respectively included in the designated areas of the projection drawings (here, Pmax1: the maximum pixel value of the designated area in the projection drawing in the X-Y plane side direction, Pmax2: the maximum pixel value of the designated area in the projection drawing in the Z-X plane side direction, and Pmax3: the maximum pixel value of the designated area in the projection drawing in the Y-Z plane side direction. If it is not necessary to make a distinction among these three values, the maximum pixel value is denoted as Pmax. (S241). Hereinafter, an explanation will be made as to the case where the luminance threshold calculation section73calculates the luminance threshold value from the designated area of the projection drawing in the X-Y plane side direction.

The luminance threshold calculation section73extracts a record in which a designated area flag is set in the designated area flag storage field23dof the pixel data table230, and stores information specifying the X-Y plane side direction in the projecting direction information storage field23a. Next, a maximum pixel value Pmax1is detected from the pixel value storage field23cof the record being extracted.

The luminance threshold calculation section73further scans the voxels on the virtual ray R in the projecting direction as to all the pixels included in the designated area in each projection drawing, and detects a maximum voxel value (X, Y, Z) (S242). By way of example, the luminance threshold calculation section73extracts a record in which a designated area flag is set in the designated area flag storage field23dof the pixel data table230, and stores information specifying the X-Y plane side direction in the projecting direction information storage field23a. Then, the luminance threshold calculation section acquires a pixel position from the pixel position storage field23bof the record being extracted.

Next, the luminance threshold calculation section73detects coordinate positions of all the voxels located on the virtual ray R, based on the pixel position and the projecting direction information (in this example here, it is the X-Y plane side direction). By way of example, if the pixel position is (A, B) and the projecting direction information specifies the X-Y plane side direction, the voxels whose coordinate positions are (A, B, (1 to Zn)) are targeted for the scanning (here, “Zn” represents the number of voxels in the Z-direction).

Subsequently, the luminance threshold calculation section73refers to the voxel position storage field22aof the voxel data table220, and extracts a record storing the voxel position that agrees with any of the coordinate positions (A, B, (1to Zn)) of the voxels located on the virtual ray R. The luminance threshold calculation section73detects a maximum voxel value Vmax from the voxel value storage field22bof the record being extracted.

Furthermore, the luminance threshold calculation section73calculates a luminance threshold ThP1based on the pixel value Pmax1, and the luminance threshold ThV based on the voxel value Vmax (S243). By way of example, the luminance threshold calculation section73multiplies the pixel value Pmax1by the parameter A, and multiples by the parameter B, each voxel value Vmax which is detected on the virtual ray R projecting each of the pixels within the designated area, thereby obtaining the luminance threshold ThP1, and ThV for each pixel.

This processing is executed for each of the designated areas, and the luminance thresholds for the Z-X plane side direction and the luminance thresholds for the Y-Z plane side directions are calculated as well.

Referring toFIG. 11again, the area judgment section72scans the voxels on the virtual ray R which projects each of the pixels within the designated area of each projection drawing, and specifies as the bone candidate area, the voxels having the voxel value V equal to or higher than the luminance threshold ThP, and equal to or higher than ThV which is calculated from Vmax detected from the virtual ray R projecting the pixel (S25). Hereinafter, an explanation will be made as to the case where the area judgment section72specifies the bone candidate area from the designated area of the projection drawing in the X-Y plane side direction.

The area judgment section72extracts a record in which a designated area flag is set in the designated area flag storage field23dof the pixel data table230, and which stores information specifying the X-Y plane side direction in the projecting direction information storage field23a. Then, the area judgment section72acquires a pixel position from the pixel position storage field23bof the record being extracted.

Thereafter, the area judgment section72detects the coordinate positions of all the voxels located on the virtual ray R, from the pixel position and the projecting direction information (here, the X-Y plane side direction). Subsequently, the area judgment section72extracts a record whose voxel position corresponds to the voxel coordinate position located on the virtual ray R, from the voxel data table220in the voxel position storage field22a. The area judgment section72extracts a record having the voxel value V equal to or higher than the luminance threshold ThP1, and equal to or higher than ThV calculated from the Vmax that is detected from the virtual ray R projecting the pixel, and sets the direction flag in the X-Y plane side direction flag storage field22dof the record being extracted. Furthermore, the area judgment section72scans voxels having the voxel value V equal to or higher than a luminance threshold ThP2and equal to or higher than ThV detected from the virtual ray R projecting the pixel which is included in the designated area of the projection drawing in the Z-X plane side direction, and sets the direction flag thereof; and scans voxels having the voxel value V equal to or higher than a luminance threshold ThP3and equal to or higher than ThV detected from the virtual ray R projecting the pixel which is included in the pixels within the designated area of the projection drawing in the Y-Z plane side direction, and sets the direction flag thereof.

Since the process in the step26is the same as that of the step16which is executed in the image processing apparatus10relating to the first embodiment, detailed explanation will not be made tediously.

In addition, as to the volume data in which the removal target area has been identified, the image processing section71removes the voxels specified as the removal target area, and reconstructs the volume data.

It is to be noted that at the re-editing point that is used in the process of step26, it is possible to provide a point for specifying the designated area (S23) and a point for changing the parameters A and B used in the step243.

With the configuration above, the image processing apparatus60according to the present embodiment is able to identify the bone area which is spatially targeted for removal, out of the roughly designated areas in multiple projection drawings, by using the luminance value of the bone area and parameters. Therefore, the user is allowed to remove a desired area according to a simple operation.