JP2022148869A - Image positioning device, method and program - Google Patents

Abstract

To accurately position a slice image between three-dimensional images with a relatively small calculation amount in an image positioning device, method and program.SOLUTION: A processor acquires a first three-dimensional image formed of at least one slice image and a second three-dimensional image formed of a plurality of slice images, matches at least one of the gravity center of a subject region in the slice image surface and the inclination of an inertia main axis between one comparison source slide image included in the first three-dimensional image and two or more comparison destination slice images of the plurality of slice images included in the second three-dimensional image, derives an evaluation value expressing the similarity between the comparison source slice image and each of the two or more comparison destination slice images after matching at least one of the gravity center of the subject region and the inertia main shaft, and decides a comparison target slice image corresponding to the comparison source slice image among the comparison destination slice images based on the evaluation value.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to an image alignment device, method and program.

In recent years, advances in medical equipment such as CT (Computed Tomography) devices and MRI (Magnetic Resonance Imaging) devices have enabled image diagnosis using medical images of higher quality and higher resolution. In particular, image diagnosis using three-dimensional images such as CT images and MRI images enables accurate identification of lesion regions, and appropriate treatment is being performed based on the identified results. .

In addition, there are cases in which a plurality of three-dimensional images taken at different times are simultaneously displayed for follow-up observation of the same patient. In such a case, by displaying slice images of corresponding anatomical positions for a plurality of three-dimensional images, comparative interpretation of the plurality of three-dimensional images can be easily performed.

For this reason, various techniques have been proposed for alignment between a plurality of three-dimensional images. For example, in Patent Document 1 and Non-Patent Documents 1 and 2, a joint histogram is derived for a comparison source image and a comparison target image, and an evaluation value called mutual information is calculated from the joint histogram. has been proposed. The mutual information is an evaluation index that becomes high when the density of the corresponding pixel to be compared can be predicted with high probability when the density of the pixel to be compared is determined. Even images between different modalities can be registered.

A method has also been proposed for aligning images by finding the center of gravity and the principal axis of inertia of each image among multiple images of the same site and matching the center of gravity and the principal axis of inertia between the images ( See Patent Document 2).

JP 2011-239812 A JP-A-05-015525

"Alignment by maximization of mutual information", P. Viola & W.M. Wells, Proceedings of IEEE International Conference on Computer Vision, 1995, DOI: 10.1109/ICCV.1995.466930 “Multimodality image registration by maximization of mutual information”, F. Maes et al., IEEE Transactions on Medical Imaging, Volume: 16, Issue: 2, April 1997, P.187-198, DOI: 10.1109/42.563664

However, registration using mutual information requires iterative evaluation of mutual information multiple times until an optimal solution is obtained. For this reason, when aligning slice images at the same anatomical position among three-dimensional images made up of a plurality of slice images, the amount of calculation required to specify images to be compared increases. Therefore, when performing registration using mutual information, it is not suitable to perform real-time calculations during comparative interpretation. Further, the method described in Patent Document 2 only performs processing for matching the center of gravity and the principal axis of inertia between images, so the accuracy of alignment is not so high.

The present disclosure has been made in view of the circumstances described above, and an object of the present disclosure is to enable alignment of slice images between three-dimensional images to be performed with high accuracy with a relatively small amount of calculation.

An image registration apparatus according to the present disclosure comprises at least one processor,
a processor obtains a first three-dimensional image consisting of at least one slice image and a second three-dimensional image consisting of a plurality of slice images;
Between one comparison source slice image included in the first three-dimensional image and each of two or more comparison target slice images among a plurality of slice images included in the second three-dimensional image, slice image in-plane at least one of the center of gravity of the subject area and the inclination of the principal axis of inertia of
deriving an evaluation value representing the degree of similarity between the comparison source slice image and each of the two or more comparison target slice images after matching at least one of the center of gravity and the principal axis of inertia of the subject region;
A comparison target slice image corresponding to the comparison source slice image among the comparison target slice images is determined based on the evaluation value.

Note that in the image alignment device according to the present disclosure, the processor may derive the evaluation value only once between the comparison source slice image and each of the two or more comparison target slice images.

Further, in the image registration device according to the present disclosure, the processor derives at least one of the center of gravity of the object region and the inclination of the principal axis of inertia in the comparison source slice image,
At least one of the center of gravity of the object region and the inclination of the principal axis of inertia in each of the two or more slice images to be compared may be derived.

Further, in the image alignment device according to the present disclosure, the processor regards the densities of the comparison source slice image and the comparison destination slice image as a rigid body having their surface densities, so that the center of gravity and the inertia of the subject region in the comparison source slice image The tilt of the principal axis and the tilt of the center of gravity of the object region and the tilt of the principal axis of inertia in the slice image to be compared may be derived.

Further, in the image registration device according to the present disclosure, the processor binarizes the comparison source slice image and the comparison target slice image into a subject region and a background region,
By regarding the subject area as a rigid body with a constant surface density, the center of gravity and the inclination of the principal axis of inertia of the subject area in the comparison source slice image and the inclination of the center of gravity and the principal axis of inertia of the subject area in the comparison destination slice image are derived. There may be.

Further, in the image registration apparatus according to the present disclosure, the binarization processing may include filtering processing by combining expansion and contraction of the binarized image.

Further, in the image alignment device according to the present disclosure, the evaluation value is the amount of mutual information between the comparison source slice image and each of the two or more comparison target slice images, the sum of the absolute values of the differences, the sum of the squares of the differences, and the normalization It may be any of the cross-correlation coefficients.

Further, in the image registration device according to the present disclosure, the processor determines at least one of the center of gravity of the subject region and the inclination of the principal axis of inertia in both the comparison source slice image and the two or more comparison target slice images as a reference position and axis. At least one of the center of gravity of the subject region and the inclination of the principal axis of inertia may be matched between the comparison source slice image and two or more comparison target slice images.

Further, in the image alignment device according to the present disclosure, the processor may display the comparison source slice image and the comparison target slice image on the display.

Further, in the image registration device according to the present disclosure, the processor includes a comparison source slice image for matching at least one of the center of gravity of the subject region and the inclination of the principal axis of inertia between the comparison source slice image and the comparison target slice image. and the comparison target slice image may be stored.

Further, in the image alignment device according to the present disclosure, when the comparison source slice image is switched, the processor uses the stored alignment amount to perform the switching comparison source slice image and the two or more comparison destination slice images. , at least one of the center of gravity of the subject area and the inclination of the main axis of inertia may be matched.

Further, in the image registration device according to the present disclosure, when the comparison source slice image is switched, the processor determines whether the switched comparison source slice image satisfies a predetermined condition, and the determination is If not, at least one of the center of gravity of the subject region and the tilt of the principal axis of inertia is calculated between the switched comparison source slice image and each of the two or more comparison target slice images using the stored registration amount. match,
If the determination is affirmative, a new alignment amount is derived between the switched comparison source slice image and each of the two or more comparison target slice images, and at least one of the center of gravity of the subject region and the inclination of the principal axis of inertia is calculated. may be matched.

An image registration method according to the present disclosure acquires a first three-dimensional image consisting of at least one slice image and a second three-dimensional image consisting of a plurality of slice images;
Between one comparison source slice image included in the first three-dimensional image and each of two or more comparison target slice images among a plurality of slice images included in the second three-dimensional image, slice image in-plane at least one of the center of gravity of the subject area and the inclination of the principal axis of inertia of
Deriving an evaluation value representing the degree of similarity between the comparison source slice image and each of the two or more comparison target slice images after matching at least one of the center of gravity and the principal axis of inertia of the subject region,
A comparison target slice image corresponding to the comparison source slice image among the comparison target slice images is determined based on the evaluation value.

Note that the image registration method according to the present disclosure may be provided as a program for causing a computer to execute the image registration method.

According to the present disclosure, alignment of slice images between three-dimensional images can be accurately performed with a relatively small amount of calculation.

1 is a diagram showing a schematic configuration of a medical information system to which an image alignment device according to a first embodiment of the present disclosure is applied; FIG. 1 is a diagram showing a schematic configuration of an image registration apparatus according to a first embodiment; FIG. 1 is a functional configuration diagram of an image registration apparatus according to a first embodiment; FIG. A diagram for explaining processing for identifying a subject region Diagram showing the concept of the first alignment Diagram for explaining the first alignment Diagram for explaining determination of slice images to be compared A diagram showing a display screen of a CT image Flowchart showing processing performed in the first embodiment Flowchart showing processing performed in the second embodiment Flowchart showing processing performed in the second embodiment Flowchart showing processing performed in the third embodiment Flowchart showing processing performed in the third embodiment

Embodiments of the present disclosure will be described below with reference to the drawings. First, the configuration of a medical information system 1 to which the image registration apparatus according to the first embodiment is applied will be described. FIG. 1 is a diagram showing a schematic configuration of a medical information system 1. As shown in FIG. A medical information system 1 shown in FIG. 1 captures an examination target region of a subject based on an examination order from a doctor of a clinical department using a known ordering system, and produces medical images such as three-dimensional images obtained by the imaging. This is a system for storage, interpretation of medical images by an interpreting doctor and creation of an interpretation report, and viewing of the interpretation report by a doctor of the department that requested the request and detailed observation of the medical image to be interpreted.

As shown in FIG. 1, a medical information system 1 includes a plurality of imaging devices 2, a plurality of image interpretation WSs (WorkStations) 3 which are image interpretation terminals, a medical examination WS 4, an image server 5, an image database (hereinafter referred to as an image DB (DataBase)). ) 6, a report server 7 and a report database (hereinafter referred to as report DB) 8 are connected to each other via a wired or wireless network 10 so as to be communicable with each other. A specific example of the medical information system 1 is PACS (Picture Archiving and Communication Systems).

Each device is a computer in which an application program for functioning as a component of the medical information system 1 is installed. The application program is stored in a storage device of a server computer connected to the network 10 or in a network storage in an externally accessible state, and is downloaded and installed in the computer upon request. Alternatively, it is recorded on recording media such as DVDs (Digital Versatile Discs) and CD-ROMs (Compact Disc Read Only Memory) and distributed, and installed in computers from the recording media.

The imaging device 2 is a device (modality) that generates a medical image representing the diagnostic target region by imaging the diagnostic target region of the subject. Specifically, it is a simple X-ray imaging device, a CT device, an MRI device, a PET (Positron Emission Tomography) device, and the like. In this embodiment, it is assumed that the imaging device 2 acquires a three-dimensional image made up of a plurality of slice images as a medical image. A medical image generated by the imaging device 2 is transmitted to the image server 5 and stored in the image DB 6 .

The interpretation WS3 is a computer used by, for example, a radiology doctor to interpret medical images and create an interpretation report, and includes the image registration apparatus according to the first embodiment. The interpretation WS 3 requests the image server 5 to view medical images, performs various image processing on the medical images received from the image server 5 , displays the medical images, interprets the medical images, creates an interpretation report based on the interpretation results, and requests the report server 7 . A request for registering an interpretation report, a request for browsing, and a display of the interpretation report received from the report server 7 are performed. These processes are performed by the interpretation WS3 executing a software program for each process.

The clinical WS 4 is a computer used by doctors in clinical departments for detailed observation of images, viewing of interpretation reports, and creation of electronic medical charts. Consists of The medical examination WS 4 requests the image server 5 to view images, displays the images received from the image server 5 , requests the report server 7 to view interpretation reports, and displays the interpretation reports received from the report server 7 . These processes are performed by the clinical WS 4 executing a software program for each process.

The image server 5 is a general-purpose computer in which a software program that provides the functions of a database management system (DBMS) is installed. Further, the image server 5 has a storage in which an image DB 6 is configured. The storage may be a hard disk device connected to the image server 5 via a data bus, or a disk device connected to a NAS (Network Attached Storage) connected to the network 10 and a SAN (Storage Area Network). There may be. When the image server 5 receives a registration request for a medical image from the imaging device 2 , the image server 5 prepares the medical image into a database format and registers it in the image DB 6 .

Image data of medical images acquired by the imaging device 2 and additional information are registered in the image DB 6 . The incidental information includes, for example, an image ID (identification) for identifying individual medical images, a patient ID for identifying a subject, an examination ID for identifying an examination, a unique ID assigned to each medical image ( UID (unique identification), examination date when the medical image was generated, examination time, type of imaging device used in the examination to acquire the medical image, patient information such as patient name, age, and gender, examination site (imaging part), imaging information (imaging protocol, imaging sequence, imaging method, imaging conditions, use of contrast agent, etc.), and information such as series number or collection number when multiple medical images are acquired in one examination . Further, in this embodiment, the image DB 6 stores and manages a plurality of medical images for a plurality of patients. The plurality of medical images also includes medical images captured on different dates and times for the same patient, or multiple medical images captured by different imaging devices (that is, modalities) for the same patient. For example, the image DB 6 stores and manages CT images of the same patient taken at different times, and CT and MRI images of the same patient acquired at the same time by a CT apparatus and an MRI apparatus.

When the image server 5 receives a viewing request from the interpretation WS 3 and the medical care WS 4 via the network 10 , the image server 5 searches for medical images registered in the image DB 6 and distributes the retrieved medical images to the requesting interpretation WS 3 and the medical care WS 4 . Send to WS4.

The report server 7 incorporates a software program that provides the functions of a database management system to a general-purpose computer. When the report server 7 receives a registration request for an interpretation report from the interpretation WS 3 , the interpretation report is formatted for a database and registered in the report DB 8 .

An interpretation report created by an interpretation doctor using the interpretation WS3 is registered in the report DB8. The interpretation report may include, for example, a medical image to be interpreted, an image ID for identifying the medical image, an interpreting doctor ID for identifying the interpreting doctor who performed the interpretation, a lesion name, and lesion position information. .

When the report server 7 receives a viewing request for an interpretation report from the interpretation WS 3 and the medical care WS 4 via the network 10, the report server 7 searches for the interpretation report registered in the report DB 8, and sends the retrieved interpretation report to the requested interpretation report. Send to WS3 and medical care WS4.

A network 10 is a wired or wireless local area network that connects various devices in a hospital. Various devices connected to the network 10 are not limited to those in the same facility. It may also be located at geographically remote facilities such as other hospitals and clinics. In this case, the network 10 may have a configuration in which local area networks of respective facilities are connected to each other via the Internet or a dedicated line.

Next, an image registration device according to the first embodiment of the present disclosure will be described. FIG. 2 explains the hardware configuration of the image alignment device according to the first embodiment. As shown in FIG. 2, the image alignment device 20 includes a CPU (Central Processing Unit) 11, a non-volatile storage 13, and a memory 16 as a temporary storage area. The image alignment device 20 also includes a display 14 such as a liquid crystal display, an input device 15 such as a keyboard and a mouse, and a network I/F (InterFace) 17 connected to the network 10 . CPU 11 , storage 13 , display 14 , input device 15 , memory 16 and network I/F 17 are connected to bus 18 . The CPU 11 is an example of a processor in the present disclosure.

The storage 13 is implemented by a HDD (Hard Disk Drive), SSD (Solid State Drive), flash memory, or the like. An image alignment program 12 is stored in the storage 13 as a storage medium. The CPU 11 reads out the image alignment program 12 from the storage 13 , develops it in the memory 16 , and executes the developed image alignment program 12 .

Next, the functional configuration of the image alignment device according to the first embodiment will be described. FIG. 3 is a diagram showing the functional configuration of the image alignment device according to the first embodiment. As shown in FIG. 3, the image registration device 20 includes an image acquisition section 21, a first derivation section 22, a first registration section 23, a second derivation section 24, a second registration section 25, and a display control section 26. . As the CPU 11 executes the image alignment program 12, the CPU 11 controls the image acquisition unit 21, the first derivation unit 22, the first alignment unit 23, the second derivation unit 24, the second alignment unit 25, and the display control. It functions as part 26 .

Here, the image registration apparatus 20 according to the present embodiment performs image registration when performing comparative reading of two three-dimensional images taken at different times for the same patient. In this embodiment, the three-dimensional image is assumed to be a CT image composed of slice images of a plurality of axial sections. Hereinafter, of the two three-dimensional images, the three-dimensional image photographed more recently is referred to as a first three-dimensional image G1, and the three-dimensional image photographed earlier is referred to as a second three-dimensional image G2.

In order to perform comparative interpretation, the display control unit 26 displays the first three-dimensional image G1 and the second three-dimensional image G2 side by side on the display 14 as described later. At this time, a slice image of a desired anatomical position is displayed for the first three-dimensional image G1. The displayed slice image becomes the comparison source slice image. In the present embodiment, two or more of the plurality of slice images included in the second three-dimensional image G2 are compared with the comparison target slice image corresponding in anatomical position to one displayed comparison source slice image. Position alignment between the first three-dimensional image G1 and the second three-dimensional image G2 is performed by determining from the previous slice image. Therefore, the image alignment in this embodiment is a process of matching slice images of corresponding anatomical positions in the first and second three-dimensional images G1 and G2.

The image acquisition unit 21 acquires a first three-dimensional image G1 and a second three-dimensional image G2 for creating an interpretation report from the image server 5 in accordance with an instruction from the input device 15 by an interpretation doctor who is an operator. .

The window level and window width are set so that the first and second three-dimensional images G1 and G2 can be displayed on the display 14 and observed. A window level is a CT value that is the center of a site to be observed among gradations that can be displayed by the display 14 when a three-dimensional image such as a CT image having a wide range of signal values is displayed on the display 14 . The window width is the width between the lower limit value and the upper limit value of the CT value of the site to be observed. In the coordinate system of the first and second three-dimensional images G1 and G2, the z direction is the direction from the feet to the head of the subject, the x direction is the direction toward the left of the subject on the slice plane, and the back of the subject on the slice plane. Let the direction be the y direction.

The first deriving unit 22 derives the center of gravity of the subject region and the inclination of the principal axis of inertia in one comparison source slice image included in the first three-dimensional image G1. Note that the comparison source slice image is one slice image displayed on the display 14 by the display control unit 26 . The first deriving unit 22 also derives the center of gravity of the subject region and the inclination of the principal axis of inertia in two or more comparison target slice images among the plurality of slice images included in the second three-dimensional image G2. Note that the two or more slice images to be compared may be all slice images included in the second three-dimensional image G2, or may be a part of the slice images. Some of the slice images may be slice images thinned out at predetermined intervals among all slice images included in the second three-dimensional image G2. Also, the part of the slice images is a slice image predicted to correspond to the comparison source slice image and one or more slice images adjacent thereto among all the slice images included in the second three-dimensional image G2. There may be.

Derivation of the center of gravity of the object region and the inclination of the principal axis of inertia in the comparison source slice image will be described below. The first derivation unit 22 identifies the subject region in the comparison source slice image when deriving the center of gravity of the subject region and the inclination of the principal axis of inertia in the comparison source slice image. FIG. 4 is a diagram for explaining the process of identifying the subject area. In FIG. 4, the horizontal direction is the x direction, and the vertical direction is the y direction. First, the first derivation unit 22 binarizes the comparison source slice image SL1 into a subject area and a background area. The threshold for the binarization process is set to an appropriate value for separating the subject area and the background area included in the comparison source slice image SL1. In FIG. 4, the background area of the binarized comparison source slice image SL1-1 is shown in white, and the subject area is shown in black.

As shown in FIG. 4, in the comparison source slice image SL1-1 binarized as shown in FIG. 4, there is a small area (hereinafter referred to as a hole) having a value of 0 in the subject area due to the influence of noise or the like. do. In order to include the hole 40 in the subject area, the first derivation unit 22 performs filtering on the binarized comparison source slice image SL1-1 using a combination of expansion and contraction. Filter processing can be, for example, opening processing or closing processing using a morphology filter. As a result, as shown in FIG. 4, a binarized comparison source slice image SL1-2 from which the hole 40 included in the object region is removed is derived. Note that instead of the opening processing or closing processing, filter processing is performed to correct the background region, which is included in the subject region and has an area equal to or less than a predetermined threshold value, to the same color as the subject region using an arbitrary filter. You may do so.

The first derivation unit 22 regards the object region of the binarized and filtered comparison source slice image SL1-2 as a two-dimensional flat plate-like rigid body having a constant surface density, thereby obtaining the comparison source slice The center of gravity of the subject area in image SL1 and the inclination of the principal axis of inertia in the image plane are derived. Specifically, first, the center of gravity (x0, y0) is derived by the following equation (1). In equation (1), ρ(i, j) is the surface density corresponding to the density at the pixel position (i, j) of the binarized comparison source slice image SL1-2.

On the other hand, when deriving the inclination of the principal axis of inertia, the first derivation unit 22 first derives the inertia tensor I by the following equation (2).

The inclination of the principal axis of inertia in the image plane corresponds to coordinate transformation such that the off-diagonal component (product of inertia) of the inertia tensor I becomes zero. Therefore, based on the condition that the off-diagonal component is 0, the inclination θ of the principal axis of inertia can be obtained by the following equation (3) using the formula for solving the quadratic equation.

Here, in the subject area included in the slice image of the axial section of the three-dimensional image, generally the head is vertically elongated and the body is horizontally elongated. Therefore, the principal axis of inertia becomes vertical and horizontal. In the present embodiment, the first derivation unit 22 obtains the inclination θ of the principal axis of inertia in order to obtain the difference in relative inclination between the comparison source slice image SL1 and the comparison target slice image SL2. Therefore, the first derivation unit 22 selects the solution with the smaller absolute value of the two solutions calculated by Equation (3) (the one that is not close to ±90 degrees when the angle formed with the x-axis is assumed to be 0 degrees). solution) is interpreted as the tilt of the subject, and derived as the tilt θ of the principal axis of inertia.

The first derivation unit 22 also derives the center of gravity of the object region and the inclination of the main axis of inertia of the two or more slice images SL2 to be compared included in the second three-dimensional image G2 in the same manner as described above.

The first alignment unit 23 performs a first alignment in which at least one of the center of gravity of the subject region and the inclination of the principal axis of inertia is matched between the comparison source slice image SL1 and two or more comparison target slice images SL2. FIG. 5 is a diagram showing the concept of the first alignment. In this embodiment, as shown in FIG. 5, first alignment is performed between one comparison source slice image SL1 and two or more comparison target slice images SL2.

In the present embodiment, both the center of gravity of the subject region and the inclination of the principal axis of inertia are made to match between the comparison source slice image SL1 and two or more comparison target slice images SL2, but the present invention is limited to this. not a thing Only one of the center of gravity of the subject region and the inclination of the principal axis of inertia may be matched between the comparison source slice image SL1 and two or more comparison target slice images SL2.

FIG. 6 is a diagram for explaining the first alignment. As shown in FIG. 6, the center of gravity g1 and the center of gravity g2 of the comparison source slice image SL1 and the comparison destination slice image SL2 are at different positions. In addition, the inclination θ1 of the main inertia axis 41 and the inclination θ2 of the main inertia axis 42 are different. The difference in the positions of the centers of gravity g1 and g2 and the difference in the inclinations .theta.1 and .theta.2 of the principal axes of inertia 41 and 42 shown in FIG. be.

The first alignment unit 23 derives a relative translation amount between the comparison source slice image SL1 and the comparison target slice image SL2 for matching the center of gravity g1 and the center of gravity g2. Then, the comparison source slice image SL1 and the comparison destination slice image SL2 are translated relative to each other based on the derived translation amount, thereby matching the center of gravity g1 and the center of gravity g2. Further, the first alignment unit 23 sets the post-matching centers of gravity g1 and g2 to match the inclination θ1 of the principal axis of inertia 41 of the slice image SL1 to be compared with the inclination θ2 of the principal axis of inertia 42 of the slice image SL2 to be compared. Derive the amount of relative rotation around the center. Then, the first alignment unit 23 relatively rotates the comparison source slice image SL1 and the comparison destination slice image SL2 around the matched centers of gravity g1 and g2 based on the derived rotation amount, thereby inertially The inclinations of the main shafts 41 and 42 are matched. The derived translation amount and rotation amount are an example of the alignment amount.

At this time, the first alignment may be performed so as to match the comparison source slice image SL1 with the comparison destination slice image SL2, and the first position alignment may be performed so as to match the comparison destination slice image SL2 with the comparison source slice image SL1. Alignment may be performed. Furthermore, both the comparison source slice image SL1 and the comparison destination slice image SL2 are moved and rotated so that the center of gravity g1 and the center of gravity g2 match the reference position, and the inclination θ1 of the principal axis of inertia and the inclination θ2 of the principal axis of inertia coincide with the reference angle. The first alignment may be performed by allowing the As the reference position, the center positions of the images of the comparison source slice image SL1 and the comparison destination slice image SL2 can be used. 0 degrees can be used as the reference angle. 0 degree is the angle at which the principal axis of inertia coincides with the x-axis in the comparison source slice image SL1 and the comparison destination slice image SL2.

The second derivation unit 24 derives an evaluation value representing the degree of similarity between the comparison source slice image SL1 after the first alignment and each of the two or more comparison target slice images SL2. Mutual information, for example, can be used as the evaluation value representing the degree of similarity. When deriving the mutual information, the second derivation unit 24 derives combined histograms of the comparison source slice image SL1 after the first alignment and each of the two or more comparison target slice images SL2.

The joint histogram represents a two-dimensional frequency distribution of the pixel values of the comparison source slice image SL1 and the pixel values of one comparison target slice image SL2. In the present embodiment, if the slice image SL1 to be compared and the slice image SL2 to be compared have 256 levels of gradation, the joint histogram has a size of 256 pixels×256 pixels, and the pixel value of each pixel is a frequency of 256 pixels. It can be represented by a dimensional image.

The second derivation unit 24 derives mutual information using the joint histogram. Any method such as the method described in Patent Document 1 and Non-Patent Documents 1 and 2 can be used for mutual information. Here, mutual information is a scale that quantifies the amount of information about event B that event A has for two events A and B. FIG. The mutual information used in image registration is called normalized mutual information. The normalized mutual information NMI(A, B) is obtained from the two-dimensional joint histogram Hist(a, b) of event A and event B by the following formula (4).

In equation (4), H(A) is the entropy of event A, H(B) is the entropy of event B, and H(A,B) is the joint entropy of events A and B. p(a) is the probability density distribution of a, p(b) is the probability density distribution of b, and p(a, b) is the joint probability distribution of a and b. a, b). That is, the joint probability distribution p(a,b) is the joint histogram H(a,b) divided by the total frequency of the joint histogram H(a,b). The probability distribution p(a) is obtained by adding the joint probability distribution p(a, b) in the b direction. The probability distribution p(b) is obtained by adding the joint probability distribution p(a, b) in the a direction.

The second derivation unit 24 applies the comparison source slice image SL1 to the events A and a, and the comparison target slice image SL2 to the events B and b in the equation (4), so that the comparison source slice image SL1 and two or more comparison targets A mutual information amount NMIj (j is a number indicating the order of the slice images SL2 to be compared) with each of the slice images SL2 is derived. The second deriving unit 24 derives the mutual information amount between the comparison source slice image SL1 and each of the two or more comparison target slice images SL2 only once.

The second alignment unit 25 determines a comparison target slice image SLT2 corresponding to the comparison source slice image SL1 among the two or more comparison target slice images SL2 based on the evaluation value. Specifically, the comparison target slice image having the maximum mutual information amount is determined as the comparison target slice image SLT2. FIG. 7 is a diagram for explaining how slice images to be compared are determined. In addition, in FIG. 7, for the sake of explanation, it is assumed that there are five slice images to be compared. As shown in FIG. 7, the mutual information with the comparison source slice image SL1 for each of the five comparison target slice images SL2-1 to SL2-5 is 1.1, 1.2, 1.9, 1.0. 5 and 1.4. In this case, the second alignment unit 25 selects the comparison target slice image SL2-3 having the maximum mutual information amount of 1.9 among the five comparison target slice images SL2-1 to SL2-5. Decide on SLT2.

The display control unit 26 displays the first and second three-dimensional images G1 and G2 on the display 14. FIG. FIG. 8 is a diagram showing a display screen of a three-dimensional image. As shown in FIG. 8, a three-dimensional image display screen 50 includes an image display area 51 and a text display area 52 . The image display area 51 displays slice images included in the first three-dimensional image G1 and the second three-dimensional image G2. The slice images to be displayed can be displayed by selecting the first three-dimensional image G1 as a comparison source using the input device 15 and using a scroll wheel or the like provided on the mouse of the input device 15 to switch and display. Note that when the second three-dimensional image G2 is selected and switched and displayed, the second three-dimensional image G2 becomes the comparison source. Alignment in the xy direction between the first three-dimensional image G1 and the second three-dimensional image G2 displayed in the image display area 51 is performed using the center of gravity of the comparison source slice image SL1 derived by the first derivation unit 22. and the center of gravity of the slice image SL2 to be compared with the center of the display area of each image, and further to match the inclination of the principal axis of inertia of the comparison source slice image SL1 with the inclination of the principal axis of inertia of the comparison destination slice image SL2. It can be done by

In the text display area 52 , a finding text representing the result of interpretation of the first three-dimensional image G<b>1 and the second three-dimensional image G<b>2 by the radiologist is input using the input device 15 .

It should be noted that depending on how to interpret radiograms, the anatomical positions of the slice images displayed in the first three-dimensional image G1 and the second three-dimensional image G2 may or may not be desired to match. be. Therefore, in the present embodiment, the synchronization button 56 displayed below the image display area 51 can be used to switch between synchronization and asynchronization of the positions of the displayed slice images. The interpreting doctor selects the synchronization button 56 to switch between synchronization and asynchronization of the displayed slice planes of the first three-dimensional image G1 and the second three-dimensional image G2.

The matching of the slice planes, that is, the anatomical positions, is performed by the first derivation unit 22, the first registration unit 23, the second This is performed by the lead-out section 24 and the second alignment section 25 . In this case, the slice image displayed in the image display area 51 for the first three-dimensional image G1 is the comparison source slice image. In the present embodiment, each time the displayed comparison source slice image is switched, the slice image is calculated by the first derivation unit 22, the first alignment unit 23, the second derivation unit 24, and the second alignment unit 25 as described above. is performed, and the display control unit 26 displays the comparison target slice image SLT2 determined by the second alignment unit 25 in the image display area 52 .

As a result, slice images of the same anatomical position are displayed in the image display area 51 for each of the first three-dimensional image G1 and the second three-dimensional image G2. Therefore, by switching the displayed slice image of the first three-dimensional image G1, the slice image of the second three-dimensional image G2 also represents the same anatomical position as the first three-dimensional image G1. can be switched synchronously. It should be noted that synchronization is canceled when the synchronization button 56 is selected again. This makes it possible to display slice images of separate slice planes for the first three-dimensional image G1 and the second three-dimensional image G2.

A confirmation button 57 is displayed below the text display area 52 . After inputting the observation text, the radiologist can confirm the input contents of the observation text by selecting the confirm button 57 using the input device 15 .

Next, processing performed in the first embodiment will be described. FIG. 9 is a flow chart showing processing performed in the first embodiment. It is assumed that the first and second three-dimensional images G1 and G2 to be aligned are acquired from the image server 5 and stored in the storage 13. FIG. It is also assumed that the synchronization button 56 has been selected to synchronize the slice images. Processing is started when an instruction to display the first and second three-dimensional images G1 and G2 is given, and the display control unit 26 displays the first and second three-dimensional images G1 and G2 on the display screen 50. It is displayed in the area 51 (step ST1). Note that the first slice image to be displayed may be the slice image with the top slice number, for example, for both the first and second three-dimensional images G1 and G2.

Next, it is determined whether or not an instruction to switch the slice images to be displayed has been given (step ST2). A comparison source slice image SL1 is specified (step ST3). If step ST2 is negative, the process proceeds to step ST10, which will be described later.

Next, the first derivation unit 22 derives the center of gravity of the subject region and the inclination of the principal axis of inertia in the comparison source slice image SL1 (step ST4). In addition, the first derivation unit 22 derives the center of gravity of the subject region and the inclination of the principal axis of inertia in each of two or more comparison destination slice images SL2 among the plurality of slice images included in the second three-dimensional image G2 ( step ST5).

Then, the first alignment unit 23 performs a first alignment in which at least one of the center of gravity of the subject region and the inclination of the principal axis of inertia is matched between the comparison source slice image SL1 and the two or more comparison target slice images SL2. (step ST6).

Subsequently, the second derivation unit 24 derives an evaluation value representing the degree of similarity between the comparison source slice image SL1 after the first alignment and each of the two or more comparison target slice images SL2 (step ST7). Further, the second alignment unit 25 determines a comparison target slice image SLT2 corresponding to the comparison source slice image SL1 among the two or more comparison target slice images SL2 based on the evaluation value (step ST8). The display control unit 26 displays the determined comparison target slice image SLT2 in the image display area 51 (step ST9).

Subsequently, it is determined whether or not the confirm button 57 has been selected (step ST10), and if step ST10 is negative, the process returns to step ST2, and the processes after step ST2 are repeated. While the processing after step ST2 is repeated, the slice images other than the comparison source slice image SL1 displayed in the first three-dimensional image G1 are processed in parallel with the processing after step ST2. It is preferable to perform calculations necessary for deriving the inclination of the principal axis of inertia and deriving the evaluation value representing the degree of similarity.

The interpreting doctor thus performs comparative interpretation of the first and second three-dimensional images G1 and G2 and inputs an interpretation report into the character display area 52 . If step ST10 is affirmative, the process is terminated. The created interpretation report is transmitted to and stored in the interpretation report server 6 .

As described above, in the present embodiment, at least one of the center of gravity of the subject region and the inclination of the principal axis of inertia of the comparison source slice image SL1 and each of the two or more comparison destination slice images SL2 is set to the first position. After matching, an evaluation value representing the degree of similarity between the comparison source slice image SL1 and each of the two or more comparison target slice images SL2 is derived, and based on the evaluation value, one of the two or more comparison target slice images SL2 is determined. A comparison target slice image SLT2 corresponding to the comparison source slice image SL1 is determined.

Therefore, compared to the case of deriving the evaluation value representing the degree of similarity without performing the first alignment, it is possible to reduce the amount of calculation for determining the slice image SLT2 to be compared. Processing can be performed at high speed. Thereby, even if the slice image is switched in the first three-dimensional image G1, the slice image SLT2 to be compared can be displayed in the second three-dimensional image G2 without delay in feeling. In addition, compared to the case where only the process of matching at least one of the center of gravity of the object region and the inclination of the principal axis of inertia is performed, the slice image SLT2 to be compared can be determined with higher accuracy. Therefore, according to the present embodiment, the slice image SLT2 to be compared can be determined quickly and accurately.

Further, in the above-described embodiment, the mutual information amount for each comparison target slice image SL2 is derived only once. Therefore, the calculation time can be significantly reduced as compared with the case of repeating derivation of the mutual information until the mutual information converges.

Here, an implementation example by the inventor of the present application will be described. The inventor of the present application used an Intel Xeon E-2124G 3.40 GHz as a CPU, and performed alignment between the first and second three-dimensional images having a size of 512×512 pixels with 256 gradations. The calculation time of the mutual information for one comparison target slice image was about 2 ms when only the translation of the center of gravity position was performed without considering the rotation of the principal axis of inertia, and about 3 ms when the rotation was also considered. Note that the calculation time is the calculation time for deriving the center of gravity and the tilt of the main axis of inertia, the first alignment, and the mutual information amount for each of the slice image SL2 to be compared with respect to the slice image SL1 to be compared.

Therefore, according to the present embodiment, even if the slice image of the first three-dimensional image G1 is switched, the slice image of the second three-dimensional image G2 can be changed from the slice image of the first three-dimensional image G1 to the slice image of the first three-dimensional image G1 without delay. I have found that it can be synchronized with

In the first embodiment, each time the displayed comparison source slice image SL1 is switched, the gravity center and the inclination of the principal axis of inertia are derived for each of the two or more comparison target slice images SL2. is not limited to For example, after determining the slice image SLT2 to be compared, using the amount of parallel movement of the center of gravity and the amount of rotation of the principal axis of inertia when performing the first alignment with respect to the slice image SLT2 to be compared, another comparison source slice image A first alignment may be performed between SL1 and two or more slice images SL2 to be compared. As a result, the computation time can be further reduced and the processing can be performed at a higher speed. This process will be described below as a second embodiment.

10 and 11 are flow charts showing the processing performed in the image registration apparatus according to the second embodiment. Note that the processing of steps ST11 to ST16 in FIG. 10 is the same as the processing of steps ST1 to ST6 shown in FIG. 9, so detailed description thereof will be omitted here. In the second embodiment, when the first alignment is performed, the first alignment unit 23 calculates the amount of translation of the center-of-gravity position and the amount of rotation of the principal axis of inertia derived at the time of the first alignment, It is stored as an alignment amount (step ST17).

Subsequently, the second derivation unit 24 derives an evaluation value representing the degree of similarity between the comparison source slice image SL1 after the first alignment and each of the two or more comparison target slice images SL2 (step ST18). Further, the second alignment unit 25 determines the comparison target slice image SLT2 based on the evaluation value (step ST19). The display control unit 26 displays the determined comparison target slice image SLT2 in the image display area 51 (step ST20).

Subsequently, it is determined whether or not the enter button 57 has been selected (step ST21). If step ST21 is negative, it is determined whether or not an instruction to switch the displayed slice image has been issued (step ST22). . If step ST22 is negative, the process returns to step ST21. If step ST22 is affirmative, the first derivation unit 22 identifies the comparison source slice image SL1 switched in the first three-dimensional image G1 (step ST23). Further, the first alignment unit 23 reads the stored alignment amount (step ST24), and performs the first alignment using the read alignment amount (step ST25).

Subsequently, the second derivation unit 24 derives an evaluation value representing the degree of similarity between the comparison source slice image SL1 after the first alignment and each of the two or more comparison target slice images SL2 (step ST26). After the process of step ST26, the process returns to step ST19, and the second alignment unit 25 determines the comparison target slice image SL2 with the maximum evaluation value as the comparison target slice image SLT2.

Thus, in the second embodiment, the alignment amount is derived only once. As a result, the amount of calculation can be further reduced, so that the slice image SLT2 to be compared can be determined more quickly.

On the other hand, instead of deriving the alignment amount only once as in the second embodiment, when the switched comparison source slice images satisfy a predetermined condition, the comparison source slice images SL1 and SL2 The center of gravity of the comparison target slice image SL2 and the inclination of the principal axis of inertia may be derived, and the amount of parallel movement of the position of the center of gravity and the amount of rotation of the principal axis of inertia may be derived to derive the alignment amount. Hereinafter, this will be described as a third embodiment. Note that the predetermined condition is that a predetermined number of comparison source slice images have been switched since the previous registration amount was saved (for example, 10 slice images), or a predetermined distance in the axial direction. It may be that the minute-slice image has been switched (for example, 5 mm when the slice interval is 0.5 mm).

12 and 13 are flow charts showing the processing performed in the image registration apparatus according to the third embodiment. Note that the processing of steps ST31 to ST41 shown in FIG. 12 is the same as the processing of steps ST11 to ST21 in the second embodiment shown in FIG. 11, so detailed description thereof will be omitted here.

In the third embodiment, if step ST41 is negative, it is determined whether or not an instruction to switch slice images to be displayed has been given (step ST42). If step ST42 is negative, the process returns to step ST41. When step ST42 is affirmative, the first derivation unit 22 identifies the comparison source slice image SL1 switched in the first three-dimensional image G1 (step ST43). Subsequently, the first derivation unit 22 determines whether or not the specified comparison source slice image SL1 satisfies a predetermined condition (step ST44).

If step ST44 is affirmative, the process returns to step ST34. As a result, the center of gravity and the inclination of the main axis of inertia of the switched comparison source slice image SL1 and the inclination of the center of gravity and the main axis of inertia of each of the two or more comparison target slice images SL2 are derived, and the first alignment and the second alignment are derived. are aligned. Also, the derived new alignment amount is saved.

If step ST44 is negative, the first alignment unit 23 reads the stored alignment amount (step ST45), and performs the first alignment using the read alignment amount (step ST46).

Subsequently, the second derivation unit 24 derives an evaluation value representing the degree of similarity between the comparison source slice image SL1 after the first alignment and each of the two or more comparison target slice images SL2 (step ST47). After the process of step ST47, the process returns to step ST39, and the second alignment unit 25 determines the comparison target slice image SL2 with the maximum evaluation value as the comparison target slice image SLT2.

In the third embodiment, between the slice image SL2 and the comparison source slice image SL1, for which the amount of parallel movement of the center of gravity and the amount of rotation of the principal axis of inertia are not derived, the derived amount of parallel movement and The amount of parallel movement of the center of gravity and the amount of rotation of the principal axis of inertia may be derived by interpolation using the amount of rotation.

Further, in each of the above-described embodiments, the mutual information amount between the comparison source slice image SL1 and each of the two or more comparison target slice images SL2 is derived only once, but it is not limited to this. Derivation of mutual information and registration may be repeated until the derived mutual information converges. In this embodiment, the comparison source slice image SL1 and each of the two or more comparison target slice images SL2 are first aligned. Therefore, even if the calculation for deriving the mutual information is performed until the mutual information converges, the calculation amount can be reduced compared to the case where the first alignment is not performed. Synchronization between the three-dimensional image G1 and the second three-dimensional image can be performed at high speed.

In each of the above-described embodiments, the second derivation unit 24 derives the mutual information between the comparison source slice image SL1 and each of the two or more comparison target slice images SL2 as an evaluation value representing the degree of similarity. , but not limited to. In place of the mutual information, the sum of the absolute values of the differences in pixel values at corresponding pixel positions of the comparison source slice image SL1 and two or more comparison target slice images SL2, the sum of the squares of the differences, or the normalized cross-correlation A relational coefficient may be derived as an evaluation value representing the degree of similarity. In this case, the comparison destination slice image with the maximum or minimum evaluation value may be determined as the comparison target slice image SLT2 according to the type of evaluation value. Even when these are used as the evaluation values representing the degree of similarity, the evaluation values may be derived only once, or may be derived until the evaluation values converge.

Also, in the above embodiment, the first three-dimensional image G1 includes a plurality of slice images, but the present invention is not limited to this. The first three-dimensional image G1 may contain only one slice image.

In each of the above-described embodiments, CT images are used for both the first and second three-dimensional images G1 and G2, but the present invention is not limited to this. A CT image may be used as the first three-dimensional image G1, and an MRI image or a PET image may be used as the second three-dimensional image G2. In this case, since the slice plane of the CT image and the slice plane of the PET image can be aligned so as to be in the same anatomical position, it is possible to easily derive a fusion image of the CT image and the PET image. . Further, when aligning slice images between three-dimensional images composed of ultrasound images, or between a three-dimensional image composed of ultrasound images and a three-dimensional image acquired by another modality, each of the above-described implementations can be performed. Alignment can be done as well as morphology. Note that the comparison source slice image and the comparison target slice image may have different pixel intervals (pixel pitches). In this case, one or both of the slice images may be enlarged or reduced in advance to match the pixel intervals, and then the processing of each of the above embodiments may be performed.

In each of the above-described embodiments, slice images are aligned for comparative reading of the first and second three-dimensional images G1 and G2, but the present invention is not limited to this. The technique of the present embodiment can also be applied to the case of deriving a difference image using the first three-dimensional image G1 and the second three-dimensional image G2 of the same subject captured at different times. That is, by deriving the difference image between the comparison source slice image SL1 and the comparison target slice image SLT2 determined by the processing of the present embodiment, it is possible to easily confirm the change over time of the disease on the same slice plane. .

In addition, in each of the above-described embodiments, alignment of slice images is performed using the first three-dimensional image G1 and the second three-dimensional image G2 of the same subject, but the present invention is not limited to this. do not have. The technology of the present embodiment is also applied when aligning the slice image of the first three-dimensional image G1 and the slice image of the second three-dimensional image G2 obtained by photographing the same part of different subjects. It is possible to In this case, it is possible to align the slice images in the same manner as described above regardless of whether the 3D images of different subjects are of the same modality or the 3D images of different subjects are of different modalities. Even in this case, when the pixel intervals are different between the comparison source slice image and the comparison destination slice image, one or both of the slice images are enlarged or reduced in advance to match the pixel intervals, and then the processing of each of the above embodiments is performed. Do it.

In each of the above-described embodiments, image alignment is performed for slice images of axial cross sections in which slice planes are aligned in the axial direction, but the present invention is not limited to this. Alignment of slice images of a coronal section, a sagittal section, or a section in any other direction may be performed. Further, image alignment may be performed for slice images of MPR (Multi Planar Reconstruction, arbitrary cross-sectional reconstruction) in the same manner as in the above embodiments. As a result, slice images of desired slice planes can be aligned with respect to the first and second three-dimensional images G1 and G2.

In each of the above-described embodiments, the first derivation unit 22 derives the center of gravity and the inclination of the principal axis of inertia after filtering the comparison source slice image SL1 and the comparison destination slice image SL2 in the binarization process. However, it is not limited to this. The center of gravity and the tilt of the principal axis of inertia may be derived without filtering. Alternatively, the densities of the comparison source slice image and the comparison target slice image may be regarded as rigid bodies having surface densities without performing the binarization process, thereby deriving the center of gravity and the inclination of the principal axis of inertia.

In each of the above-described embodiments, when the first and second three-dimensional images G1 and G2 are displayed, the first slice image displayed is the slice image with the top slice number. not something. For the slice image displayed first, the slice image SLT2 to be compared is specified by aligning the comparison source slice image SL1 and each of the two or more comparison target slice images SL2 in the same manner as in each of the above-described embodiments. The comparison target slice image SLT2 thus obtained may be displayed.

Further, in each of the above-described embodiments, the comparison source slice image and the comparison target slice image that are displayed when comparative interpretation is performed are aligned, but the present invention is not limited to this. For example, even if a slice image to be compared is specified before performing comparative interpretation and alignment with a slice image to be compared is performed in advance, alignment can be performed by the image alignment apparatus according to the present embodiment. .

Further, in each of the above-described embodiments, the amount of alignment between the slice image to be compared and the slice image to be compared may be stored in the storage 13, the image server 5, or the like in association with the slice image. The alignment amount is not limited to the relative translation amount between the comparison source slice image SL1 and the comparison destination slice image SL2 and the relative rotation amount for matching the inclination of the principal axis of inertia. In the first and second three-dimensional images G1 and G2, the center of gravity and the inclination of the principal axis of inertia derived for each slice image may be stored as alignment amounts in association with each slice image. In this case, the amount of translation and the amount of rotation of each of the slice image SL1 to be compared and the slice image SL2 to be compared may be derived using the saved center of gravity and inclination of the principal axis of inertia.

By storing the center of gravity and the tilt of the principal axis of inertia derived for each slice image in this way, the amount of data to be stored can be reduced compared to the case of deriving the amount of translation and the amount of rotation for all combinations of slice images. can be reduced. Also, when the two three-dimensional images to be compared are different, it is possible to align the slice images using the saved center of gravity and inclination of the principal axis of inertia.

Further, in each of the above embodiments, for example, various processes such as the image acquisition unit 21, the first derivation unit 22, the first alignment unit 23, the second derivation unit 24, the second alignment unit 25, and the display control unit 26 are performed. As the hardware structure of the processing unit (Processing Unit) to be executed, various processors shown below can be used. As described above, the various processors include, in addition to the CPU, which is a general-purpose processor that executes software (programs) and functions as various processing units, GPU (Graphics Processing Unit), FPGA (Field Programmable Gate Array), etc. Programmable Logic Device (PLD), which is a processor whose circuit configuration can be changed after manufacturing, circuit configuration specially designed to execute specific processing such as ASIC (Application Specific Integrated Circuit) and a dedicated electrical circuit, which is a processor having a

One processing unit may be configured with one of these various processors, or a combination of two or more processors of the same or different type (for example, a combination of multiple FPGAs or a combination of a CPU and an FPGA). ). Also, a plurality of processing units may be configured by one processor.

As an example of configuring a plurality of processing units in one processor, first, as represented by computers such as clients and servers, one processor is configured by combining one or more CPUs and software, There is a form in which this processor functions as a plurality of processing units. Secondly, as typified by System On Chip (SoC), etc., there is a mode of using a processor that realizes the functions of the entire system including multiple processing units with a single IC (Integrated Circuit) chip. be. In this way, the various processing units are configured using one or more of the above various processors as a hardware structure.

Furthermore, more specifically, as the hardware structure of these various processors, an electric circuit (circuitry) in which circuit elements such as semiconductor elements are combined can be used.

1 medical information system 2 imaging device 3 interpretation WS
4 Clinical Department WS
5 image server 6 image DB
7 report server 8 report DB
10 network 11 CPU
12 image alignment program 13 storage 14 display 15 input device 16 memory 17 network I/F
18 bus 20 image alignment device 21 image acquisition unit 22 first derivation unit 23 first alignment unit 24 second derivation unit 25 second alignment unit 26 display control unit 40 hole 41, 42 principal axis of inertia 50 display screen 51 image display Area 52 Text display area 56 Synchronization button 57 Confirm button g1, g2 Center of gravity G1 First three-dimensional image G2 Second three-dimensional image SL1, SL1-1, SL1-2 Comparison source slice image SL2, SL2-1, SL2- 2, SL2-3, SL2-4, SL2-5 Comparison target slice image θ1, θ2 Inclination of principal axis of inertia

Claims (14)

comprising at least one processor;
The processor
obtaining a first three-dimensional image consisting of at least one slice image and a second three-dimensional image consisting of a plurality of slice images;
slice images between one comparison source slice image included in the first three-dimensional image and each of two or more comparison target slice images among a plurality of slice images included in the second three-dimensional image; matching at least one of the center of gravity of the in-plane subject area and the inclination of the principal axis of inertia;
deriving an evaluation value representing the degree of similarity between the comparison source slice image and each of the two or more comparison destination slice images after matching at least one of the center of gravity and the principal axis of inertia of the subject region;
An image alignment device that determines a comparison target slice image corresponding to the comparison source slice image among the comparison target slice images based on the evaluation value. 2. The image registration apparatus according to claim 1, wherein the processor derives the evaluation value only once between the comparison source slice image and each of the two or more comparison target slice images. The processor derives at least one of the center of gravity of the object region and the inclination of the principal axis of inertia in the comparison source slice image,
3. The image registration apparatus according to claim 1, wherein at least one of the center of gravity of the object region and the inclination of the principal axis of inertia in each of the two or more slice images to be compared is derived. The processor regards the densities of the comparison source slice image and the comparison destination slice image as a rigid body having surface densities thereof, thereby determining the center of gravity of the subject region in the comparison source slice image and the inclination of the main axis of inertia of the comparison source slice image, and the comparison 4. The image registration apparatus according to claim 3, wherein the center of gravity of the object region in the previous slice image and the tilt of the principal axis of inertia are derived. The processor binarizes the comparison source slice image and the comparison destination slice image into the subject region and the background region,
By regarding the subject area as a rigid body having a constant surface density, the center of gravity of the subject area in the comparison source slice image and the inclination of the principal axis of inertia of the subject area, and the inclination of the center of gravity and the principal axis of inertia of the subject area in the comparison target slice image 4. The image registration apparatus of claim 3, which derives . 6. The image registration apparatus according to claim 5, wherein said binarization processing includes filtering by a combination of dilation and erosion of said binarized image. The evaluation value is any one of a mutual information amount between the comparison source slice image and each of the two or more comparison target slice images, a sum of absolute values of differences, a sum of squares of differences, and a normalized cross-correlation coefficient. An image registration device according to any one of claims 1 to 6. The processor matches at least one of the center of gravity of the subject region and the inclination of the principal axis of inertia of both the comparison source slice image and the two or more comparison target slice images with at least one of a reference position and axis. 8. The image according to any one of claims 1 to 7, wherein at least one of the center of gravity of the subject region and the tilt of the principal axis of inertia of the subject region is matched between the comparison source slice image and the two or more comparison target slice images. Alignment device. The image registration apparatus according to any one of claims 1 to 8, wherein the processor displays the comparison source slice image and the comparison target slice image on a display. The processor generates the comparison source slice image and the comparison target slice image for matching at least one of the center of gravity of the subject region and the inclination of the principal axis of inertia between the comparison source slice image and the comparison target slice image. 10. The image registration device according to any one of claims 1 to 9, wherein the registration amounts of are stored. When the comparison source slice image is switched, the processor uses the saved alignment amount to perform the above comparison between the switched comparison source slice image and each of the two or more comparison target slice images. 11. The image alignment device according to claim 10, wherein at least one of the center of gravity of the subject area and the tilt of the principal axis of inertia is matched. When the comparison source slice image is switched, the processor determines whether or not the switched comparison source slice image satisfies a predetermined condition. matching at least one of the center of gravity of the subject region and the inclination of the principal axis of inertia between the switched comparison source slice image and each of the two or more comparison target slice images using the alignment amount;
If the determination is affirmative, a new alignment amount is derived between the switched comparison source slice image and each of the two or more comparison target slice images, and the inclination of the center of gravity of the subject region and the principal axis of inertia 11. The image registration apparatus of claim 10, which aligns at least one of the . obtaining a first three-dimensional image consisting of at least one slice image and a second three-dimensional image consisting of a plurality of slice images;
slice images between one comparison source slice image included in the first three-dimensional image and each of two or more comparison target slice images among a plurality of slice images included in the second three-dimensional image; matching at least one of the center of gravity of the in-plane subject area and the inclination of the principal axis of inertia;
deriving an evaluation value representing the degree of similarity between the comparison source slice image and each of the two or more comparison destination slice images after matching at least one of the center of gravity and the principal axis of inertia of the subject region;
An image registration method for determining a comparison target slice image corresponding to the comparison source slice image among the comparison target slice images based on the evaluation value. obtaining a first three-dimensional image consisting of at least one slice image and a second three-dimensional image consisting of a plurality of slice images;
slice images between one comparison source slice image included in the first three-dimensional image and each of two or more comparison target slice images among a plurality of slice images included in the second three-dimensional image; matching at least one of the center of gravity of the in-plane subject area and the tilt of the principal axis of inertia;
a step of deriving an evaluation value representing the degree of similarity between the comparison source slice image and each of the two or more comparison target slice images after matching at least one of the center of gravity and the principal axis of inertia of the subject region;
and determining a slice image to be compared corresponding to the slice image to be compared among the slice images to be compared based on the evaluation value.

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