Patent ID: 12236531

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, an embodiment of the present disclosure will be described with reference to the drawings.FIG.1is a hardware configuration diagram illustrating an overall diagnosis support system to which a meniscus projection plane setting apparatus according to the embodiment of the present disclosure is applied. As illustrated inFIG.1, in the diagnosis support system, a meniscus projection plane setting apparatus1according to the present embodiment, a three-dimensional imaging apparatus2, and an image storage server3are communicably connected via a network4.

The three-dimensional imaging apparatus2is an apparatus that images a diagnosis-target body part of a test subject thereby generating a three-dimensional image representing the body part. Specifically, the three-dimensional imaging apparatus2is a CT apparatus, an MRI apparatus, a positron emission tomography (PET) apparatus, or the like. A three-dimensional image generated by the three-dimensional imaging apparatus2is transmitted to the image storage server3and is stored therein. Note that in the present embodiment, the diagnosis-target body part of a patient who is a test subject is a knee joint, the three-dimensional imaging apparatus2is an MRI apparatus, and an MM image of the test subject's knee joint is generated by the three-dimensional imaging apparatus2as a three-dimensional image.

The image storage server3is a computer that stores and manages various types of data and includes an external mass storage device and database management software. The image storage server3communicates with the other apparatuses via the network4by wire or wirelessly to transmit and receive image data or the like. Specifically, the image storage server3acquires various types of data including image data of a three-dimensional image or the like generated by the three-dimensional imaging apparatus2via the network and stores the image data in a recording medium such as the external mass storage device to manage the image data. Note that the form of storage of image data and communication between the apparatuses via the network4conform to a protocol such as Digital Imaging and Communication in Medicine (DICOM).

The meniscus projection plane setting apparatus1is a single computer in which a meniscus projection plane setting program according to the present disclosure is installed. The computer may be a workstation or a personal computer that a physician who performs diagnosis directly operates, or may be a server computer connected to the work station or personal computer via the network. The meniscus projection plane setting program is stored in a storage device of the server computer connected to the network or a network storage in an externally accessible state, is downloaded to a computer used by a physician on demand, and is installed. Alternatively, the meniscus projection plane setting program is recorded on a recording medium such as a digital versatile disc (DVD) or a compact disc read only memory (CD-ROM), is distributed, and is installed in a computer from the recording medium.

FIG.2is a diagram illustrating a schematic configuration of the meniscus projection plane setting apparatus according to the embodiment of the present disclosure, implemented by the meniscus projection plane setting program being installed in a computer. As illustrated inFIG.2, the meniscus projection plane setting apparatus1includes a central processing unit (CPU)11, a memory12, a storage13, and a communication interface (I/F)14as a configuration of a standard workstation. In addition, a display6and an input device7such as a mouse or a keyboard is connected to the meniscus projection plane setting apparatus1.

Various types of information are stored in the storage13. The various types of information include a three-dimensional image of a test subject and information necessary for processing, which are acquired from the image storage server3via the network4. Note that this embodiment assumes that a three-dimensional image V0in which a knee joint of a test subject is a diagnosis-target body part is stored in the storage13.

The communication I/F14is a network interface for controlling transmission of various types of information to/from an external apparatus such as the image storage server3via the network4.

In the memory12, the meniscus projection plane setting program read out by the CPU11is temporarily stored. As processing to be executed by the CPU11, the meniscus projection plane setting program prescribes an image acquisition process in which the three-dimensional image V0of the knee joint is acquired; a plane setting process in which a plane that approximates a joint surface of the knee joint is set as a projection plane for generating a projection image, which will be described later, by projecting menisci at the knee joint included in the three-dimensional image; a projection process in which the menisci are projected onto the projection plane and the projection image is generated; a quantification process in which a quantitative value of the menisci is derived on the projection image; and a display control process in which the quantitative value derived by the quantification is displayed on the display6.

By the CPU11executing these processes in accordance with the program, the computer functions as an image acquisition unit21, a plane setting unit22, a projection unit23, a quantification unit24, and a display control unit25.

The image acquisition unit21acquires the three-dimensional image V0of the knee joint of the test subject from the image storage server3. Note that, in a case where the three-dimensional image V0is already stored in the storage13, the image acquisition unit21may acquire the three-dimensional image V0from the storage13.FIG.3is a diagram illustrating the three-dimensional image V0of the knee joint. As illustrated inFIG.3, the three-dimensional image V0includes a femur30and a tibia31. Note that a patella is omitted fromFIG.3for description. There are a cartilage32in a portion of the femur30facing the tibia31and a cartilage33in a portion of the tibia31facing the femur30. In addition, there are menisci34between the cartilage32and the cartilage33. In the present embodiment, the three-dimensional image V0is an MRI image, and the range of signal values (voxel values) in the three-dimensional image V0differs in each of a bone region, a cartilage region, a meniscus region, and other muscle, fat, etc. regions. The image acquisition unit21extracts a bone region and a meniscus region from the three-dimensional image V0through a threshold process on the signal values. Specifically, a region of a range corresponding to a signal value of a bone is extracted as the bone region from the three-dimensional image V0. In addition, a region of a range corresponding to a signal value of a meniscus is extracted as the meniscus region from the three-dimensional image V0. Note that the image acquisition unit21may also extract a cartilage region from the three-dimensional image V0. In this case, the image acquisition unit21extracts a region of a range corresponding to a signal value of a cartilage as the cartilage region from the three-dimensional image V0. The bone region includes the femur30and the tibia31, the cartilage region includes the cartilages32and33, and the meniscus region includes the menisci34.

The image acquisition unit21extracts the bone region, the cartilage region, and the meniscus region from the three-dimensional image V0in the present embodiment, but the present disclosure is not limited to this. A means that extracts the bone region, the cartilage region, and the meniscus region from the three-dimensional image V0may be additionally provided. Note that in the present embodiment, the cartilage33of the tibia31is extracted as the cartilage region. In addition, extraction of the bone region, the cartilage region, and the meniscus region from the three-dimensional image V0is not limited to the threshold process. For example, a determiner that has been subjected to machine learning by deep learning or the like so as to extract the bone region, the cartilage region, and the meniscus region from the three-dimensional image V0may be used.

On the other hand, when the three-dimensional imaging apparatus2acquires the three-dimensional image V0, the knee joint is imaged in a state where the knee is stretched or slightly bended (10 to 20 degrees). In the three-dimensional image V0, as illustrated inFIG.3, the direction in which the femur30and the tibia31extend from top to bottom is set as z direction, the direction from back to front when viewing the knee joint from the front is set as y direction, and the direction from left to right when viewing the knee joint from the front is set as x direction.

The plane setting unit22sets a plane that approximates a joint surface of the knee joint as a projection plane for generating a projection image, which will be described later, by projecting the three-dimensional image V0, more specifically, menisci at the knee joint included in the three-dimensional image V0. Now, a process performed by the plane setting unit22will be described. First, the plane setting unit22sets a minimal three-dimensional region surrounding the tibia31included in the three-dimensional image V0.FIG.4is a diagram illustrating the three-dimensional region. As illustrated inFIG.4, the plane setting unit22sets a minimal three-dimensional region40surrounding the tibia31. Note that directions of the sides of the three-dimensional region40are made to match the x direction, the y direction, and the z direction of the three-dimensional image V0.

Subsequently, the plane setting unit22extracts, as a joint surface region, a region excluding a region between condyles from a top surface40A of the three-dimensional region40.FIG.5is a diagram for describing extraction of joint surface regions. As illustrated inFIG.5, the plane setting unit22sets, as a region42between condyles, a region having a width that corresponds to a predetermined ratio to the length of a side41on the basis of the middle point of the side41extending in the x direction of the top surface40A. Note that the predetermined ratio may be 15 to 25%, preferably 20%, but the present disclosure is not limited to this. Then, the plane setting unit22sets, as joint surface regions43and44, two regions that are on the left and right of the region42between condyles on the top surface40A. Note that the joint surface region43corresponds to a region on the medial condyle side in the joint of the tibia31and the joint surface region44corresponds to a region on the lateral condyle side in the joint of the tibia31.

Subsequently, the plane setting unit22sets, as the projection plane, a plane that approximates a joint surface included in the joint surface regions43and44. Specifically, the plane setting unit22derives, as the projection plane, a plane on which distances from voxels constituting the joint surface included in the joint surface regions43and44are minimal by the least squares method.FIG.6is a diagram for describing deriving of the projection plane. Note that a cross section perpendicular to the y axis of the tibia31is illustrated inFIG.6for easy description. In addition, only some of the voxels in the joint surface regions43and44are represented by the black circles, while the distances from the voxels to the plane, that is, a projection plane45, are represented by the arrows. As illustrated inFIG.6, the plane setting unit22derives, as the projection plane45, a plane on which the sum total of the distances from the voxels in the joint surface regions43and44is minimal.

Subsequently, the plane setting unit22sets a new projection plane by excluding a voxel whose distance corresponds to a predetermined ratio from the maximum among the distances from the voxels in the joint surface regions43and44to the projection plane45.FIG.7is a diagram for describing exclusion of the voxel. Note thatFIG.7illustrates a cross section of the tibia31in the zy plane. In the present embodiment, the plane setting unit22derives the projection plane45on which the distances from the voxels constituting the joint surface included in the joint surface regions43and44are minimal. However, on the joint surface, there is a voxel whose distance from the projection plane45is larger than the other voxels, as in a voxel P1illustrated inFIG.7. If the projection plane is set by using such a voxel, it is not possible to derive the plane that approximates a joint surface accurately.

Accordingly, the plane setting unit22excludes the voxel whose distance corresponds to the predetermined ratio from the maximum among the distances from the voxels in the joint surface regions43and44to the projection plane45. Then, by using voxels other than the excluded voxel, the plane setting unit22derives, as a new projection plane45A, a plane for which the sum total of the distances from the voxels in the joint surface regions43and44is minimal. Here, the predetermined ratio may be 5 to 20%, preferably 10%, but the present disclosure is not limited to this.

In the present embodiment, the plane setting unit22repeatedly performs the above process such that a voxel whose distance corresponds to the predetermined ratio from the maximum among the distances from the voxels in the joint surface regions43and44to the new projection plane45A is further excluded and a new projection plane45B is set, to derive a final projection plane46. For example, when the process of setting a new projection plane is repeated twice, in a case where the above predetermined ratio is 10%, the ratio of voxels that contribute to the setting of the projection plane46is 81% of all the voxels in the joint surface regions43and44. Note that the present embodiment assumes that the above predetermined ratio is 10% and that the process of setting a new projection plane is repeated twice.

The projection unit23generates a projection image by projecting the menisci at the joint in the three-dimensional image V0in the direction orthogonal to the projection plane46. That is, as illustrated inFIG.8, the projection unit23generates a projection image by projecting the menisci34in a direction47orthogonal to the projection plane46. Although the tibia31is also projected when the projection image is generated in the present embodiment, only the menisci34may be projected to generate the projection image. Note that “orthogonal” includes, not only a case of being completely orthogonal, but also a case of being orthogonal with an error of a certain degree, such as about 1 to 2 degrees.

At this time, the projection unit23generates the projection image such that a line connecting the center of gravity of a joint surface of the medial condyle of the tibia31and the center of gravity of a joint surface of the lateral condyle of the tibia31is oriented in a predetermined direction.FIG.9is a diagram for describing deriving of the centers of gravity. The voxels to be used when deriving the projection plane46is reduced to 81% of all the voxels in the joint surface regions43and44by repeating the above-described process of setting a new projection plane. In each of the joint surface regions43and44, using only the voxels used for the process of setting the projection plane46, the projection unit23derives the center of gravity of the joint surface of the medial condyle of the tibia31and the center of gravity of the joint surface of the lateral condyle of the tibia31. At this time, a center of gravity G1of the joint surface of the medial condyle is derived by using the voxels in the joint surface region43, while a center of gravity G2of the joint surface of the lateral condyle is derived by using the voxels in the joint surface region44. Note thatFIG.9illustrates regions where the voxels used for deriving the center of gravity G1and the center of gravity G2are present by surrounding the regions by broken lines.

The projection unit23generates the projection image by projecting the tibia31and the menisci34in the direction orthogonal to the projection plane46such that the line connecting the center of gravity G1and the center of gravity G2is horizontal in the projection image.FIG.10is a diagram illustrating the projection image of the tibia31and the menisci34. In a projection image50illustrated inFIG.10, a line48connecting center of gravity G1and the center of gravity G2is horizontal. Note that meniscus regions54A and54B are hatched inFIG.10. The meniscus region54A corresponds to the medial meniscus, whereas the meniscus region54B corresponds to the lateral meniscus.

Note that an Akagi line may be derived on a joint surface of the tibia31, and the projection image may be generated by projecting the tibia31and the menisci34in the direction orthogonal to the projection plane46such that the Akagi line is oriented in the perpendicular direction of the projection image. The Akagi line is a line connecting a posterior cruciate ligament attachment and the medial border of a patellar tendon attachment.FIG.11is a diagram illustrating the projection image generated such that the Akagi line is oriented in the perpendicular direction of the projection image. Note that as illustrated inFIG.11, in the projection image50, an Akagi line49is perpendicular.

Furthermore, the projection unit23sets a region of interest in the projection image50. In the present embodiment, the projection unit23sets, as regions of interest, regions corresponding to subchondral bone regions at the joint.FIG.12is a diagram for describing setting of the regions of interest. In the projection image50illustrated inFIG.12, for describing setting of the subchondral bone regions, the meniscus regions are omitted, and cartilage regions51A and51B are illustrated. In addition, inFIG.12, each of the cartilage region51A on the joint surface of the medial condyle and the cartilage region51B on the joint surface of the lateral condyle are hatched.

Here, the subchondral bone regions are regions where the joint of the tibia31and the joint of the femur30wear each other. The peripheries of the cartilage regions51A and51B in the projection image50and the joint of the femur30do not wear each other. Thus, the projection unit23extracts, as the subchondral bone regions, regions excluding regions in predetermined ranges from the edges of the cartilage regions51A and51B in the projection image50, and sets the extracted subchondral bone regions as a region of interest52A and a region of interest52B. On the other hand, in the tibia31, an outline that defines a region in which a cartilage is supposed to be present in the joint is included in the joint surface as a protruding portion. Thus, the projection unit23may set the region of interest52A and the region of interest52B by regarding, as the cartilage regions51A and51B, the regions surrounded by the protruding portions on the joint surface. In addition, the projection unit23may include a determiner that has been subjected to machine learning by deep learning or the like so as to extract the subchondral bone regions from the projection image50, and the subchondral bone regions may be extracted by using the determiner.

The quantification unit24derives quantitative values of the meniscus regions54A and54B in the projection image50. A quantitative value is derived for each of the medial meniscus and the lateral meniscus in the present embodiment, but the present disclosure is not limited to this. The quantitative value may be derived by combining the medial meniscus and the lateral meniscus together.

FIG.13is a diagram for describing deriving of the quantitative values. First, the quantification unit24derives the areas of the region of interest52A and the region of interest52B and the areas of the meniscus regions54A and54B. The quantification unit24further derives the areas of meniscus regions54A and54B within the region of interest52A and the region of interest52B. The areas of meniscus regions54A and54B within the region of interest52A and the region of interest52B are the areas of in-region-of-interest meniscus regions55A and55B hatched inFIG.13. Here, the area of each pixel is known in the projection image50. Thus, the quantification unit24counts the number of pixels in the region of interest52A and the region of interest52B and the meniscus regions54A and54B, and multiplies the counted number of pixels by the area per pixel, thereby deriving areas S1A and S1B of the region of interest52A and the region of interest52B and areas S2A and S2B of the meniscus regions54A and54B. The quantification unit24further derives areas S3A and S3B of the meniscus regions54A and54B within the region of interest52A and the region of interest52B, that is, the in-region-of-interest meniscus regions55A and55B. Note that each of the areas S3A and S3B of the in-region-of-interest meniscus regions55A and55B is one of the quantitative values. Also, each of the areas S2A and S2B of the meniscus regions54A and54B is one of the quantitative values.

In the present embodiment, the quantification unit24derives, as one of the quantitative values, each of coverages of the meniscus regions54A and54B in the region of interest52A and the region of interest52B. The coverage of the meniscus region54A in the medial region of interest52A is derived as S3A/S1A, which is the area S3A of the in-region-of-interest meniscus region55A to the area S1A of the region of interest52A. The coverage of the meniscus region54B in the lateral region of interest52B is derived as S3B/S1B, which is the area S3B of the in-region-of-interest meniscus region55B to the area S1B of the region of interest52B.

FIG.14is a diagram illustrating a display screen of the quantitative values of the menisci. As illustrated inFIG.14, on a display screen60of the quantitative values of the menisci, the projection image50, a coverage61of the medial meniscus, and a coverage62of the lateral meniscus are displayed. The display screen60enables an operator to understand, in addition to the state of the menisci34, that the coverage61of the medial meniscus is 0.548 and the coverage62of the lateral meniscus is 0.479.

Note that over-time observation may be performed for the same test subject by comparing a plurality of three-dimensional images whose imaging timings are different. In such a case, in a case where a projection image is generated from a first three-dimensional image V1whose imaging timing is in the past, a projection image is preferably generated from a second three-dimensional image V2whose imaging timing is new for over-time observation. Note that the first three-dimensional image V1corresponds to another three-dimensional image according to the present disclosure. In this case, although the menisci34may wear or become deformed over time, the shape of the joint does not become deformed. Thus, upon generating the projection image from the first three-dimensional image V1, information representing the projection plane46is preferably stored in the image storage server3, and the projection image from the second three-dimensional image V2is preferably generated by acquiring the information of the projection plane stored for the same test subject and using the acquired information of the projection plane.

This can reduce the calculation amount when the projection image from the second three-dimensional image V2is generated. In addition, in this case, in a case where the region of interest52A and the region of interest52B are set in the projection image from the first three-dimensional image V1, the same regions of interest as those in the projection image from the first three-dimensional image V1are preferably set in the projection image from the second three-dimensional image V2. Thus, the quantitative values of the menisci34in the first three-dimensional image V1and the quantitative values of the menisci34in the second three-dimensional image V2can be temporally compared with each other with ease.

FIG.15is a diagram illustrating a display screen for temporal comparison of the quantitative values of the menisci. As illustrated inFIG.15, on a display screen65for temporal comparison, a previous projection image66acquired during a previous examination and a current projection image67acquired during a current examination are displayed. Below the previous projection image66, an imaging date of the three-dimensional image and coverages (a coverage of the medial meniscus and a coverage of the lateral meniscus)68of the meniscus regions in the regions of interest acquired from the previous projection image66are displayed. Below the current projection image67, an imaging date of the three-dimensional image and coverages (a coverage of the medial meniscus and a coverage of the lateral meniscus)69of the meniscus regions in the regions of interest acquired from the current projection image67are displayed. The display screen65enables an operator to understand over-time changes in the menisci34. InFIG.15, the imaging date is displayed, however, an imaging time may also be displayed in addition to the imaging date.

Note that the region of interest52A and the region of interest52B are not limited to the subchondral bone regions. As illustrated inFIG.16, the cartilage regions may also be set as a region of interest56A and a region of interest56B. In this case, the projection image50including the meniscus region too is as illustrated inFIG.17. Note that part of the cartilage is lost on the region of interest56A side. In a case where coverages of the meniscus regions in the regions of interest are to be derived as the quantitative values in this case, it is assumed that the area of the region of interest56A is S4A, the area of the region of interest56B is S4B, the areas of the meniscus regions54A and54B within the region of interest56A and the region of interest56B are S5A and SSB. Thus, the coverage of the meniscus region54A in the medial region of interest56A is derived as S5A/S4A. The coverage of the meniscus region54B in the lateral region of interest56B is derived as S5B/S4B.

In addition, although the projection plane is set on the basis of the tibia31, the projection plane may alternatively be set on the basis of the femur30. In this case, for example, the projection plane may be set such that the direction in which the central axis of the femur extends is the projection direction.

The quantification unit24may also derive the volumes of the menisci34as the quantitative values. In this case, the quantification unit24may derive the volumes of the menisci34by counting the number of pixels of the meniscus regions54A and54B in the three-dimensional image and multiplying the number of pixels by the volume per pixel.

The quantification unit24may also derive the thicknesses of the menisci34as the quantitative values.FIG.18is a diagram for describing deriving of the thickness of a meniscus. As illustrated inFIG.18, the quantification unit24sets each of reference points O1and O2in the projection image50. The reference point O1is a point at which the average distance therefrom to the nearest edge of the meniscus region54A is minimal, but the present disclosure is not limited to this. The reference point O2is a point at which the average distance therefrom to the nearest edge of the meniscus region54B is minimal, but the present disclosure is not limited to this. Then, from the reference point O1as the center, the quantification unit24sets a plurality of reference lines L1-1, L1-2. . . L1-nradially at equiangular intervals as for the medial meniscus region54A. Then, by using the three-dimensional image V0, the quantification unit24derives the average thickness of a meniscus34on each reference line. Note that the plurality of reference lines may be set at, for example, 10-degree intervals, but the present disclosure is not limited to this.

FIG.19is a cross sectional view of the meniscus for describing deriving of the average thickness of the meniscus. Note thatFIG.19illustrates a cross section of the meniscus34on a certain reference line. As illustrated inFIG.19, the meniscus34has a wedge shape in cross section. Thus, as illustrated by the arrows inFIG.19, the quantification unit24derives the thicknesses of the meniscus34at a plurality of positions on the reference line, and derives the average of the plurality of thicknesses as the thickness of the meniscus34on the reference line. Furthermore, the quantification unit24derives the average of the thicknesses of the meniscus34on the plurality of reference lines as the thickness of the meniscus34. Note that only the thickness of the meniscus34in the medial meniscus region54A is derived inFIG.18andFIG.19, but the meniscus34in the lateral meniscus region54B may be derived in the same manner as that for the meniscus34in the medial meniscus region54A.

Note that the thickness of the meniscus34on each reference line is one of the quantitative values. Each of the plurality of thicknesses of the meniscus34derived on each reference line is also one of the quantitative values. A representative value such as the average, median, minimum, or maximum of the thicknesses of the meniscus34related to all the reference lines is also one of the quantitative values.

The quantification unit24may also divide the meniscus regions54A and54B into a plurality of regions and may derive a quantitative value in each of the divided regions.FIG.20is a diagram for describing dividing of the meniscus regions. As illustrated inFIG.20, the quantification unit24sets the reference points O1and O2, which are substantially the same as those inFIG.18, in the projection image50. Then, the quantification unit24sets a reference line L31extending in the X direction with the reference point O1as the origin, and further sets, with the reference point O1as the origin, reference lines L32and L33at which the angles with the reference line L31are 120 degrees and 240 degrees, respectively, counterclockwise. In addition, the quantification unit24sets a reference line L41extending in the X direction with the reference point O2as the origin, and further sets, with the reference point O2as the origin, reference lines L42and L43at which the angles with the reference line L41are 120 degrees and 240 degrees, respectively, clockwise. Then, the quantification unit24divides the meniscus region54A into a front section54A-F defined by the reference lines L31and L32, a middle section54A-M defined by the reference lines L32and L33, and a back section54A-B defined by the reference lines L33and L31. In addition, the quantification unit24divides the meniscus region54B into a front section54B-F defined by the reference lines L41and L42, a middle section54B-M defined by the reference lines L42and L43, and a back section54B-B defined by the reference lines L43and L41.

Then, as for the meniscus region54A, the quantification unit24derives the quantitative value for each of the front section54A-F, the middle section54A-M, and the back section54A-B. In addition, as for the meniscus region54B, the quantification unit24derives the quantitative value for each of the front section54B-F, the middle section54B-M, and the back section54B-B. Note that the area, volume, and thickness in the meniscus regions54A and54B can be used as the quantitative value of each divided region. In addition, the coverage in the meniscus regions54A and54B within the regions of interest may also be derived as the quantitative value of each divided region.

On the other hand, the menisci34may move out of the region of interest due to a load or impact. The term “out of the region of interest” means a more medial area for the medial region of interest52A, while the term “out of the region of interest” means a more lateral area for the lateral region of interest52B. Thus, in the present embodiment, the quantification unit24may derive quantitative values of the menisci34that are out of the regions of interest.FIG.21is a diagram for describing deriving of the quantitative values of the menisci34that are out of the regions of interest. As illustrated inFIG.21, the quantification unit24sets the reference points O1and O2, which are substantially the same as those inFIG.18, in the projection image50. Then, as for the medial meniscus region54A, the quantification unit24determines an out-of-region-of-interest meniscus region57A that sticks out to the medial side of the knee from the region of interest52A on the basis of a line59A perpendicular to the reference point O1in the projection image50. In addition, as for the lateral meniscus region54B, the quantification unit24determines an out-of-region-of-interest meniscus region57B that sticks out to the lateral side of the knee from the region of interest52B on the basis of a line59B perpendicular to the reference point O2in the projection image50. The out-of-region-of-interest meniscus regions57A and57B are hatched inFIG.21. Then, the quantification unit24derives the quantitative values of the menisci34in the out-of-region-of-interest meniscus regions57A and57B. As the quantitative values, the areas, the volumes, and the thicknesses of the out-of-region-of-interest meniscus regions57A and57B can be used. The thicknesses may be representative values of the thicknesses of the menisci34in the out-of-region-of-interest meniscus regions57A and57B or may be the thicknesses of the menisci34at pixel positions of the out-of-region-of-interest meniscus regions57A and57B on the projection image50.

If the thicknesses of the menisci34at pixel positions of the projection image50are derived as the quantitative values, the quantification unit24may derive a thickness map of the thicknesses of the menisci34as the quantitative values.FIG.22is a diagram illustrating a thickness map of the menisci. As illustrated inFIG.22, in a thickness map70, a distribution of the thicknesses of the meniscus regions54A and54B in the projection image is illustrated by 6-level colors. In the thickness map70, the darker the color is, the thicker the meniscus regions54A and54B are. Note that the color differences are represented by hatching differences inFIG.22. In addition, the thickness map70includes a reference71indicating a relationship between the color and the thickness. By referring to the reference71, it is possible to visually recognize the distribution of the thicknesses of the meniscus regions54A and54B in the thickness map70with ease.

Note that the derived quantitative values are transmitted to the image storage server3and stored therein in association with the three-dimensional image V0together with information such as the patient's name, an imaging date, the positions of the region of interest52A and the region of interest52B, and the projection image50. In addition to the imaging date, an imaging time may also be stored on the image storage server3.

The display control unit25causes the display6to display the projection image50together with the quantitative values.

Next, a process performed in the present embodiment will be described.FIG.23is a flowchart illustrating the process performed in the present embodiment. First, the image acquisition unit21acquires the three-dimensional image V0(step ST1) and extracts a bone region and a meniscus region from the three-dimensional image V0(step ST2). Note that, as described above, the image acquisition unit21may also extract a cartilage region. Subsequently, the plane setting unit22sets a plane that approximates a joint surface of a joint of the tibia31as the projection plane46for generating a projection image by projecting the three-dimensional image V0(step ST3).

Subsequently, the projection unit23generates the projection image50by projecting a meniscus34at the joint in the three-dimensional image V0in the direction orthogonal to the projection plane46(step ST4). Then, the quantification unit24derives a quantitative value of the meniscus34in the projection image50(step ST5). Furthermore, the display control unit25causes the display6to display the projection image50and the quantitative value (step ST6), and the process ends.

In the above manner, in the present embodiment, the plane that approximates the joint surface of the joint is set as the projection plane46for generating the projection image by projecting the three-dimensional image V0. This can prevent a lost portion of the meniscus from being projected as if the meniscus is present, in particular, as for a joint surface of a comparatively flat joint, such as the tibia31. Thus, according to the present embodiment, the projection plane for generating the projection image50of the meniscus can be set appropriately from the three-dimensional image V0including the joint.

Note that the projection unit23generates the two-dimensional projection image50in the above embodiment, but the projection unit23may generate a three-dimensional projection image.FIG.24is a diagram illustrating a three-dimensional projection image. As illustrated inFIG.24, a projection image80includes, as in the above embodiment, meniscus regions81A and81B of the tibia31and cross-sectional views82A and82B illustrating the thicknesses of the meniscus regions81A and81B. Note that the positions of cross sections in the cross-sectional views82A and82B may be changeable. For example, the positions of cross sections may be changeable radially from the centers that are the reference points O1and O2inFIG.18. Also for the three-dimensional projection image80generated in this manner, the quantitative values can be derived and displayed in the above-described manner.

In addition, in the above embodiment, when generating projection images from three-dimensional images V0of a plurality of different test subjects, the same projection plane may be set. In this case, the projection plane for further generating projection images is preferably the same in the three-dimensional images V0of the plurality of different test subjects. Thus, states of the menisci of the test subjects can be compared with each other with ease.

Furthermore, in the above embodiment, the areas, volumes, thicknesses, and representative values of the thicknesses of the menisci34, the coverages of the in-region-of-interest meniscus regions55A and55B, and the areas, volumes, thicknesses, or the like of the out-of-region-of-interest meniscus regions57A and57B are derived as the quantitative values. However, any one or any combination of these quantitative values may also be derived.

In addition, the projection plane is set by using both the joint surface regions43and44on the joint surface of the medial condyle and the joint surface of the lateral condyle in the above embodiment, but the present disclosure is not limited to this. The projection plane may be set by using only the joint surface region43on the joint surface of the medial condyle. In this case, by using the set projection plane, the projection image of the joint surface region43on the joint surface of the medial condyle may be generated. On the other hand, the projection plane may be set by using only the joint surface region44on the joint surface of the lateral condyle. In this case, by using the set projection plane, the projection image of the joint surface region44on the joint surface of the lateral condyle may be generated.

Furthermore, the process of setting a new projection plane by excluding a voxel is performed repeatedly in the above embodiment, but the present disclosure is not limited to this. On the initially set projection plane45, voxels whose distance corresponds to the predetermined ratio from the maximum among distances from the voxels in the joint surface regions43and44to the projection plane45may be excluded to set a final projection plane. In this case, the predetermined ratio may be the same as, or larger than, that in a case where the process of setting a new projection plane is performed a plurality of times by excluding a voxel. For example, the predetermined ratio may be 20%.

In addition, in the above embodiment, for example, as a hardware configuration of a processing unit that executes various processes, such as the image acquisition unit21, the plane setting unit22, the projection unit23, the quantification unit24, and the display control unit25, various processors below can be used. The various processors include, in addition to a CPU, which is a general-purpose processor that functions as various processing units by executing software (programs) as described above, a programmable logic device (PLD), which is a processor in which the circuit configuration is changeable after manufacture, such as an FPGA (Field Programmable Gate Array), a dedicated electric circuit, which is a processor having a circuit configuration that is specially designed to execute specific processing, such as an ASIC (Application Specific Integrated Circuit), and the like.

One processing unit may be constituted by one of these various processors or may be constituted by two or more processors of the same type or different types in combination (e.g., a combination of a plurality of FPGAs or a combination of a CPU and an FPGA). In addition, a plurality of processing units may be constituted by one processor.

As a first example for constituting a plurality of processing units by one processor, one processor may be constituted by a combination of one or more CPUs and software, and this processor may function as a plurality of processing units, as typified by a computer such as a client or a server. As a second example, a processor may be used that implements the functions of the entire system including a plurality of processing units with one IC (Integrated Circuit) chip, as typified by a system on chip (SoC) or the like. In this manner, various processing units are constituted by one or more of the above various processors in terms of hardware configuration.

More specifically, the hardware configuration of these various processors may be electric circuitry constituted by combining circuit elements such as semiconductor elements.

REFERENCE SIGNS LIST

1meniscus projection plane setting apparatus2three-dimensional imaging apparatus3image storage server4network6display7input device11CPU12memory13storage14communication I/F21image acquisition unit22plane setting unit23projection unit24quantification unit25display control unit30femur31tibia32,33cartilage34meniscus40three-dimensional region40A top surface41side42region between condyles43,44joint surface region45,45A,45B,46projection plane47direction orthogonal to projection plane48line connecting centers of gravity49Akagi line50projection image51A,51B,56A,56B cartilage region52A,52B,56A,56B region of interest54A,54B,81A,81B meniscus region54A-F,54B-F front section54A-M,54B-M middle section54A-B,54B-B back section55A,55B in-region-of-interest meniscus region57A,57B out-of-region-of-interest meniscus region59A,59B line60,65display screen61,62,68,69coverage66previous projection image67current projection image70thickness map71reference80projection image82A,82B cross-sectional view90tibia91A,91B meniscus92lost portion93projection imageC0central axisG1, G2center of gravityL1-1, L1-2L1-n, L31, L32, L33, L41, L42, L43reference lineP1voxelO1, O2reference pointV0, V1, V2three-dimensional image