X-ray imaging apparatus and device position detection method using x-ray image

Abstract

To provide a technique capable of monitoring the three-dimensional position of a device with high accuracy by reducing the influence of aperiodic motion generated during interventional imaging.SOLUTION: In order to monitor a device position in interventional imaging, a combination of X-ray images in which an influence of body motion is minimized is obtained from a plurality of X-ray images acquired at different imaging positions, and the device position is calculated. At this time, the motion of the feature point extracted from the plurality of X-ray images is analyzed, the motion of the body motion generated during imaging is classified, and the combination of the X-ray images used for the calculation of the device position is selected according to the classification result to calculate the device position.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an X-ray imaging device, and more particularly to a technique for grasping the three-dimensional position of a treatment device inserted inside an examination target in an interventional procedure in which an image of the treatment target area is captured and the treatment is performed while checking the acquired image when performing a treatment such as surgery. [Background technology]

[0002] X-ray imaging devices can grasp the characteristic structure of a subject in real time, and are widely used as an imaging method during procedures such as surgery (interventional imaging method). When imaging during a procedure, it is extremely important to understand the position of the device relative to the subject. With X-ray imaging devices, the position within the projection plane can be determined in real time from the device projected on the X-ray image, but it is difficult to grasp the position and structure in the projection direction.

[0003] Cone beam CT, which acquires 3D images by rotating the X-ray source and detector around the subject, can determine the 3D position of the device from the 3D images. However, cone beam CT has the problem that it takes longer to acquire one image than X-ray imaging equipment, and the accuracy of the device's position decreases if the subject moves during rotation.

[0004] In response to this, a technology has been proposed that uses an X-ray imaging device in which the X-ray source and X-ray detector are oscillatably supported, and uses X-ray images acquired from different perspectives to calculate the depth of a device from the positional relationship of the device in these X-ray images (Patent Document 1), and a technology to calculate the three-dimensional position (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5587861 [Patent Document 2] Japanese Patent Publication No. 2022-91427 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] When calculating the target position of a device or the like using multiple images using the methods described in the prior art, the imaging times of the multiple images differ, and therefore, if the subject moves between the acquisition of the multiple X-ray images, the accuracy of the position calculation deteriorates. In the technology described in Patent Document 2, in order to reduce the influence of body movement, a parameter that serves as an index of the degree of influence of body movement among multiple image combinations is calculated, and the 3D position is calculated using a combination that minimizes the influence of body movement, thereby preventing deterioration in accuracy. With this technology, for periodic movements such as respiratory movement, a combination of images with approximately the same time phase of body movement can be used, allowing for highly accurate calculation of the 3D position.

[0007] However, apart from periodic movements such as respiratory movements, unexpected movements such as physiological reflexes of the subject (hereinafter referred to as non-periodic movements) may occur. If such non-periodic movements occur during imaging, particularly while monitoring the device position, it may be difficult to maintain the accuracy of position calculation even with the technology described in Patent Document 2.

[0008] The present invention aims to provide a technology that can reduce the effects of non-periodic motion that occurs during imaging and monitor the three-dimensional position of a device with high accuracy, thereby providing an X-ray imaging device that can accurately indicate the device position while performing continuous imaging. [Means for solving the problem]

[0009] In order to monitor the device position during interventional imaging, the present invention calculates the device position by determining a combination of X-ray images from multiple X-ray images acquired at different imaging positions that minimizes the influence of body movement. In this process, the movement of feature points extracted from the multiple X-ray images is analyzed, body movement that occurred during imaging is classified, and the combination of X-ray images to be used for calculating the device position is selected according to the classification result, and the device position is calculated.

[0010] That is, the X-ray imaging device of the present invention includes an X-ray source that irradiates X-rays and an X-ray detector disposed opposite the X-ray source across an object of inspection, an imaging unit that generates an X-ray image of the object of inspection from X-rays that have passed through the object of inspection and are detected by the X-ray detector, and a processor (arithmetic unit) that analyzes multiple X-ray images taken at different X-ray irradiation angles relative to the object of inspection and calculates the three-dimensional position of a device inserted into the object of inspection. The processor (arithmetic unit) classifies the movement of the object of inspection from the multiple X-ray images taken at different imaging positions, selects a combination of two or more X-ray images with different irradiation angles from the multiple X-ray images according to the classified type of body movement, and calculates the three-dimensional position of the device using the selected combination.

[0011] Furthermore, the device position detection method using X-ray images of the present invention is a method for detecting the three-dimensional position of a device shown in a plurality of X-ray images taken at different X-ray irradiation angles, and includes the steps of extracting feature points from each of the plurality of X-ray images and calculating a movement vector of the feature points between the images, classifying the movement of the imaged subject that occurred while the plurality of X-ray images were being taken based on the movement vector, and selecting, based on the classified movement, a group of images from the plurality of X-ray images that were taken when no non-periodic movement was occurring, and calculating the three-dimensional position of the device using the selected group of images.

[0012] In this specification, "different imaging positions" includes or is synonymous with different irradiation angles of X-rays irradiated from the X-ray source to the subject, and "irradiation angles" may be used when describing "imaging positions" or vice versa. [Effects of the Invention]

[0013] According to the present invention, the type of body movement that occurred during the acquisition of multiple X-ray images with different irradiation angles obtained for device position detection is determined based on the movement trajectory of a predetermined shape (feature point) displayed on the X-ray image, and the combination of X-ray images used for device position detection is adjusted depending on whether the body movement is periodic or non-periodic.This makes it possible to eliminate the influence of body movement even when non-periodic body movement occurs, and to calculate the three-dimensional position of the device with high accuracy. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an overall outline of an X-ray imaging device to which the present invention is applied; [Figure 2] FIG. 1 is a diagram showing an example of an X-ray imaging device to which the present invention is applied. [Figure 3] FIG. 1 is a diagram showing another example of an X-ray imaging device to which the present invention is applied. [Figure 4] Functional block diagram of a processor according to the first embodiment [Figure 5] FIG. 1 is a diagram showing a processing flow by a processor according to the first embodiment. [Figure 6] Illustrates images taken at different illumination angles [Figure 7] An example of feature points extracted from an X-ray image [Figure 8] FIG. 10 is a diagram for explaining the determination of the type of body movement by the body movement classification unit. [Figure 9] Diagram showing types of body movements [Figure 10] Figure showing a group of images acquired for one type of body movement (Case 1) [Figure 11] Figure showing a group of images acquired with a different type of body movement (Case 2) [Figure 12] FIG. 10 shows an example of image combination for parameter calculation. [Figure 13] Diagram explaining the parameter calculation method [Figure 14] Functional block diagram of the calculation unit of the second embodiment [Figure 15] FIG. 10 is a diagram showing a processing flow by a processor according to a second embodiment. [Figure 16] FIG. 10 is a diagram illustrating position correction according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the X-ray imaging apparatus of the present invention will be described.

[0016] 1, the X-ray imaging device 1 of this embodiment includes an imaging unit 10 having an X-ray source 11 and an X-ray detector 12, a controller 21 that controls the entire device including the imaging unit 10, and a processor 20 that functions as an arithmetic unit 22 that processes image data generated using X-rays detected by the X-ray detector 12, and a display device 30 that displays X-ray images, etc. Although not shown, the device may further include an input device that allows a user to input necessary commands and data to the controller 21 and the arithmetic unit 22, and a storage device that stores data necessary for processing and previously acquired 3D images of a subject 50.

[0017] An X-ray tube is usually used as the X-ray source 11, and the X-ray tube is connected to a high voltage generator (not shown). Furthermore, the X-ray detector 12 is not limited to, but may be, for example, an FPD (flat panel detector).

[0018] The imaging unit 10 further includes a drive unit 13 that drives the X-ray source 11, and a data collection unit 14 that inputs an electrical signal corresponding to the transmitted X-rays output from the X-ray detector 12 and collects the signal as two-dimensional image data for each imaging time. The drive unit 13 includes a drive source such as a motor that drives a mechanism (e.g., the support mechanism 15 in FIG. 2) that supports the X-ray source 11 and the X-ray detector 12, and a power supply unit for driving the X-ray source 11. The image data collected by the data collection unit 14 is displayed on the display device 30 as an X-ray image, and is used for processing such as position detection in the calculation unit 22 as needed.

[0019] There are different types of X-ray imaging devices 1 depending on the support structure of the X-ray source 11 and the X-ray detector 12, the position of the X-ray source 11, etc. However, this embodiment can be applied to any type as long as it has a structure suitable for interventional procedures and is capable of changing the position of the X-ray source 11 (X-ray irradiation angle) relative to the subject. For example, this embodiment can be applied to an X-ray imaging device 10A called an over-tube type fluoroscopy device as shown in Fig. 2 or a C-arm type X-ray imaging device 10B as shown in Fig. 3.

[0020] 2, an X-ray imaging device 1A has an X-ray source 11 set above a bed 16 on which a subject lies, and a detector panel constituting an X-ray detector 12 is installed inside the bed 16. In this X-ray imaging device 1A, the X-ray source 11 is fixed to a support base 17 via a support mechanism 15, and the support mechanism 15 has a support column 151 that supports the X-ray source 11 and a support arm 152 that supports the support column 151 rotatably with respect to the support base 17. The bed 16 that houses the X-ray detector 12 is supported by the support arm 152 so as to be movable horizontally and vertically.

[0021] In the X-ray imaging device 1A configured as described above, by rotating the support column 151 relative to the support base 14, the position of the X-ray source 11 can be changed from a vertical position as shown in FIG. 2(A) to a position as shown in FIG. 2(B), thereby changing the X-ray irradiation angle with respect to the subject lying on the bed 16. Although not shown, a mechanism for moving the support column 151 in a direction perpendicular to the plane of FIG. 2 or for rotating the X-ray source 11 (X-ray tube) fixed to the support column 151 may be provided. In this case, the X-ray irradiation angle can be changed not only two-dimensionally but also three-dimensionally. In this specification, the expression "different irradiation angles" means irradiation angles that are different two-dimensionally and three-dimensionally.

[0022] Although FIG. 2 shows an over-tube type fluoroscopy device that irradiates the subject with X-rays from above, it can also be applied to an under-tube type fluoroscopy device in which the X-ray source is located under the bed.

[0023] 3 shows an X-ray imaging device 1B having a structure in which an X-ray source 11 and an X-ray detector 12 are supported by a C-arm 18, and a bed 16 on which a subject lies is placed in the space between the X-ray source 11 and the X-ray detector 12. The C-arm 18 is fixed to a support table 17 via a support arm 19, and the position of the C-arm 18 supported by the support arm 19 can be changed, thereby changing the position of the X-ray source 11 from directly above the bed 16 as shown in FIG. 3(A) to an inclined position as shown in FIG. 3(B), thereby changing the X-ray irradiation angle. The support arm 19 can also be rotated around an axis P relative to the support table 17, thereby rotating the X-ray source 11 and the X-ray detector 12 in a plane perpendicular to the plane of the drawing, thereby changing the X-ray irradiation angle.

[0024] 4, the processor 20 includes a control unit 21 and a calculation unit 22. The control unit 21 includes an imaging control unit 211 that controls the operation of the imaging unit 10, and controls the movement of the X-ray source 11 by the drive unit 13 and the X-ray irradiation from the X-ray source 11, and a display control unit 213 that controls the display on the display device 30. For example, the imaging control unit 211 controls the imaging unit 10 to collect multiple X-ray images with different imaging times and imaging positions in order to detect the position of a device inserted into the subject during X-ray imaging.

[0025] The calculation unit 22 includes a body motion classifier 221 that analyzes image data collected by the data collection unit 14 for a certain period of time, i.e., multiple X-ray images, and classifies the type of body motion of the subject, and a device position calculator 225 that calculates the device position according to the body motion classification by the body motion classifier 221. In the embodiment shown in FIG. 4, the body motion classifier 221 extracts feature points included in the X-ray images (feature extractor 222) to detect body motion from the X-ray images, and classifies the body motion based on the movement of the feature points in the multiple X-ray images captured at different positions. The device position calculator 225, for example, selects multiple combinations from the multiple X-ray images, calculates a parameter that serves as an index of the influence of body motion for each combination (parameter calculator 226), determines a combination for calculating the device position based on the calculated parameter, and calculates the three-dimensional position of the device using the determined combination (three-dimensional position calculator 227).

[0026] 1 shows the processor 20 as a single block, but in this specification, the processor includes various computers equipped with, for example, a CPU or GPU and memory, and realizing functions by software, as well as hardware such as an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), and a programmable IC, and the functions of each unit included in the above-mentioned processor can be realized by one or more processors. For example, the control unit 21 and the calculation unit 22 can realize some or all of the functions of the subunits included therein by the above-mentioned software or hardware, alone or in combination.

[0027] The X-ray imaging device of this embodiment is characterized by the processing of processor 20, which uses the X-ray imaging device as an interventional imaging tool to detect the position of a device inserted into an object of examination. The detection of the device position is based on a technology for detecting the 3D position of the device using multiple X-ray images acquired by imaging unit 10 at different imaging positions. Then, the body movement of the subject that occurred while acquiring the multiple X-ray images is analyzed and classified. Depending on the type of body movement, a combination of images from the multiple X-ray images to be used for calculating the 3D position is determined. The combination with the least influence of the body movement is selected from the multiple image combinations to calculate the 3D position. Specific methods for classifying body movement and calculating the 3D position are described in detail in the following embodiments.

[0028] According to the X-ray imaging device of this embodiment, prior to calculating the device position, body movement is classified, and the range of images to be used for calculating the device position is specified, particularly depending on whether the body movement is periodic or non-periodic. This prevents a decrease in the accuracy of three-dimensional position calculation when body movement, particularly non-periodic movement, is present, and enables highly accurate position detection.

[0029] <Embodiment 1> In this embodiment, the three-dimensional position of the device is detected using a plurality of X-ray images acquired by the imaging unit 10 at a plurality of irradiation angles within a predetermined angle range.

[0030] In this embodiment, to classify the subject's movement while acquiring the X-ray images, the calculation unit 22 extracts feature points of the device or subject from each of the multiple X-ray images taken at different irradiation angles, and determines whether the subject's movement, including that near the device, is periodic or non-periodic based on the change in the feature point position. Based on this determination result, the multiple X-ray images (image group) to be used for calculating the 3D position are determined. As shown in FIG. 4, the body movement classification unit 221 may include an image selection unit 223 as a functional unit for selecting an image group. When the multiple images are classified into one or more image groups based on the type of body movement, the image selection unit 223 uses the image data for the subsequent device position calculation process, i.e., for calculating parameters for calculating the 3D position, based on a predetermined criterion.

[0031] The operation of the X-ray imaging apparatus of this embodiment, mainly the operation of the processor, will be described below with reference to the flow shown in FIG.

[0032] <Imaging step: S11> The imaging unit 10 starts imaging, and acquires X-ray images at multiple irradiation angles while rotating the X-ray source 11 and the X-ray detector 12 within a preset angle range. The predetermined angle is not particularly limited as long as it is within the movable range of the X-ray imaging device. For example, it may be ±10 degrees (angle range of 20 degrees) when the initial positions of the X-ray source 11 and the X-ray detector 12 are set to zero degrees. FIG. 6 shows an example of acquiring X-ray images within an angular range of 20 degrees. Note that imaging may be performed only once at each of multiple irradiation angles within the set angle range, or imaging may be repeated multiple times at a predetermined irradiation angle to acquire multiple X-ray images for each irradiation angle. When acquiring multiple X-ray images for each irradiation angle, imaging within the predetermined angle range may be repeated multiple times, or imaging may be performed multiple times for each irradiation angle. Furthermore, imaging may be performed step-by-step, or in the case of a C-arm X-ray imaging device, imaging may be performed continuously while continuously rotating the X-ray source 11 or the X-ray detector 12. In the latter case, imaging within a predetermined angle range is repeated to obtain a plurality of X-ray images at the same irradiation angle.

[0033] The imaging target is an area that includes the examination site of the subject, and in this embodiment, the imaging is intended for when a device such as a catheter equipped with a guide wire is inserted toward the examination site and an interventional procedure is performed, and the X-ray image shows the examination site and part of the device moving forward.

[0034] <Body movement classification step: S12> The calculation unit 20 uses the multiple X-ray images obtained by the above imaging to determine whether or not the subject is moving and classify the type of movement. To this end, the feature extraction unit 222 first extracts feature points of the device or a predetermined part of the subject from each X-ray image. The feature points are not particularly limited as long as they are feature points of the shape of tissue or an object that can be detected in an X-ray image and show significant changes in brightness on the X-ray image. Either feature points of the subject's tissue or feature points of the device may be used, but it is preferable to track feature points of the device in order to determine body movement related to the device.

[0035] FIG. 7 shows examples of feature points when the device is an endoscope 40 equipped with a guidewire 41. As shown in FIG. 7, detectable feature points include an end 45a of the guidewire 41 on the endoscope 40 side, an end 45b in the direction of travel, a boundary 45c between the transparent and opaque portions of the guidewire 41, and a marker 45d (a marker made of an X-ray opaque material) attached to the catheter. The feature extraction unit 222 extracts such points with characteristic brightness changes using a general image processing technique and identifies the position coordinates of the feature points in the image. The feature points are used for analyzing body movement and calculating the three-dimensional position of the device, as described below. While one or more feature points may be extracted, using the positions of multiple feature points to calculate the three-dimensional position of a device provides information that can determine the position of a device with length and size.

[0036] The body motion classification unit 221 calculates changes in the positions of feature points based on the coordinates of the feature points in each X-ray image and classifies the body motion of the subject. Specifically, the change in the position of the feature point is calculated by calculating the movement distance or vector of the feature point between adjacent images, the trajectory of the movement of the feature point from the first acquired image to the last acquired image (movement vector), the average of the movement vectors, the sum of the movement vectors, etc. Based on the calculated change in the position of the feature point, the body motion is classified, for example, into periodic and non-periodic motion. The classification criteria may be a combination of the movement vector, the average of the movement vectors, and the sum of the movement vectors, or any one of them alone. In either case, a predetermined threshold is set, and the movement is determined and classified as periodic or non-periodic based on whether the displacement of the feature point over time is within or exceeds the threshold.

[0037] In addition to the two types of classification, periodic and non-periodic movement, it is also possible to further classify into no body movement, periodic movement (movement within a specified range), non-periodic movement 1 (movement in which the position changes significantly and exceeds a specified range but returns to the original position), and non-periodic movement 2 (movement in which the position changes significantly and does not return to the original position).

[0038] An example of classifying body movements into periodic and non-periodic movements is shown in Figure 8. This example shows the tip 45b of guidewire 41 being tracked as a feature point, with the feature point moving from the circled numbers 1 to 4. Periodic and non-periodic movements are classified based on the movement vector of the feature point or its average. When classifying based on the movement vector, for example, if the average of the movement vector falls within the range of periodic movements (predetermined threshold range) 800 indicated by the dotted line, it is determined to be periodic, and if it exceeds the range 800, it is determined to be non-periodic.

[0039] The period for calculating vectors (the period for calculating vectors at four points in Figure 8) is, for example, the shortest possible interval between projection images, and the period for determining body movement based on this depends on the type of body movement; for example, it can be 1 second per cycle when targeting body movement with a short period such as pulsation, and 3 to 5 seconds per cycle when targeting respiratory movement.

[0040] In addition, for the range 800 of periodic motion, if it is respiratory motion or pulsation, the range (displacement amount) of the movement of the surrounding tissues associated with these is known. For example, in the case of pulsation, it is about 10 mm, and in the case of respiratory motion, it is about 20 mm, so it can be set based on that displacement amount. The average of the movement vectors of the feature points converges to almost zero over time in the case of periodic motion, but does not converge to zero and becomes a large value in the case of aperiodic motion. Therefore, when the average or sum of the movement vectors approaches zero, it is determined as periodic motion, and when it exceeds the threshold value (TH), it is determined as aperiodic motion.

[0041] <Determination of X-ray image group: S13> The body motion classification unit 221 (image selection unit 223) specifies an image group to be used for three-dimensional position detection based on the classification result (type of body motion) of the body motion that occurred during a plurality of images acquired within a predetermined angle range. The types of body motion that can occur while acquiring a plurality of images are various. For example, as shown in FIG. 9, when all X-ray images are acquired in a state where the body motion is classified as no body motion or periodic motion (Case 1), immediately after the start of imaging, it is in a state where the body motion is classified as no body motion or periodic motion, but at a certain point, aperiodic motion occurs, and then returns to periodic motion at the displaced position (Case 2), or after periodic motion, aperiodic motion continues for a certain period of time (Case 3), etc. are possible. Note that the vertical axis in FIG. 9 shows the magnitude of the average or sum of the movement vectors, but it may also show the displacement amount of the body motion. "TH" is the threshold value.

[0042] The image selection unit 223 specifies an image group to be used for three-dimensional position calculation based on the classification of the body motion, the classification of the X-ray images based on this, and the type according to the occurrence of the body motion. As criteria for specifying the image group, the number of images belonging to the image group, the priority of the image group, etc. can be used. When there are a plurality of criteria, the priority for applying the criteria may be set in advance.

[0043] FIGS. 10 and 11 show examples of images obtained with different types of body motion. FIG. 10 is an example of Case 1 described above, where there is no body motion within the predetermined angle range, or the displacement range of the device is periodic motion with limited displacement. In this case, all X-ray images obtained within the predetermined angle range are used for calculating the device position.

[0044] Figure 11 shows an example of Case 2 described above. Within the irradiation angle range (Θmin to Θmax), body motion was periodic up to the X-ray irradiation angle Θk. However, body motion classified as non-periodic occurred between irradiation angles Θk and Θk+1 or within a predetermined range between them. The device position then shifted from its initial position and returned to periodic motion. In this example, based on the classification of body motion, multiple images are divided into an image group for irradiation angles (Θmin to Θk-1), an image group for irradiation angles (Θk to Θk+1) acquired during non-periodic motion, and subsequent image groups (Θk+2 to Θmax). In this case, for example, in Case 2 described above, if the multiple acquired X-ray images include a first image group and a second image group, the image group with the largest number of images is selected as the image group used for 3D position calculation. Alternatively, if the number of images belonging to the first image group is equal to or greater than a predetermined number, the first image group is identified; if the number is less than the predetermined number, the second image group is identified. Alternatively, a group of images with a large angular range between Θmin and Θk-1 and between Θk+2 and Θmax may be used to calculate the three-dimensional position.

[0045] Although not shown, in the case of Case 3 shown in Fig. 9, the image group acquired during periodic motion is selected. Also, if the number of images included in the image group acquired during periodic motion is small, or if sufficient images cannot be obtained to ensure the accuracy of 3D position detection, the acquired image data may be discarded and imaging within the specified angle range may be performed again. That is, the body motion classifier 221 passes the classification result to the control unit 21, and the imaging control unit 211 controls the imaging unit 10 to perform reimaging.

[0046] <<Device location detection>> <Parameter calculation: S14> The parameter calculation unit 226 uses the multiple X-ray images belonging to the identified image group to calculate a parameter that serves as an index of the influence of body movement in multiple combinations of X-ray images with different imaging positions. The combinations of X-ray images are not limited, but for example, as shown in Fig. 12, when multiple (N) X-ray images are obtained at multiple (M) imaging positions (angle range (Θj1 to ΘjM)), X-ray images 1 to N at each irradiation angle are combined with X-ray images with different irradiation angles in a round-robin manner to obtain M x N combinations.

[0047] The parameter can be the distance between two straight lines (the distance between two straight lines) determined by the position of the X-ray source 11 when each X-ray image was acquired and the position of the feature point on the image. If there is no body movement and the feature point position remains unchanged in the two X-ray images being compared, these two straight lines will intersect and the feature point will be found as a single coordinate. However, if there is a positional shift of the feature point due to body movement, the two straight lines will not intersect and the distance between them will change depending on the magnitude of the positional shift. In other words, the magnitude of the effect of body movement is reflected in the distance between the two straight lines.

[0048] In addition to the distance between two straight lines, parameters can also be the perimeter or area of ​​a polygon generated by connecting the midpoints of line segments expressed as the distance between two straight lines using three or more X-ray images as disclosed in Patent Document 2. For simplicity of explanation, the following describes the case where the distance between two straight lines is calculated.

[0049] The parameter calculation unit 226 calculates the distance between the two lines as follows. As shown in Fig. 13, the position of the X-ray source 11 at the first imaging position is S1, the position at the second imaging position is S2, and the positions of the device on the X-ray detector 12 at the first imaging position and the second imaging position are P1 and P2, respectively. The positions P1 and P2 of the device on the X-ray detector 12 can be calculated from the geometrical arrangement of the X-ray source 11 and the X-ray detector 12 and the positions of the device in the X-ray images I1 and I2 acquired at the respective positions. Here, if the line connecting S1 and P1 is represented by vector v1 and the line connecting S2 and P2 is represented by vector v2, the line segment Q1-Q2 (vector u) located at the shortest distance between these two lines can be obtained by the following equation.

[0050] [Number 1] Q1=P1+(D1-D2*Dv) / (1-Dv*Dv)*v1 Q2=P2+(D2-D1*Dv) / (Dv*Dv-1)*v2 However, D1=(P2-P1)·v1 D2=(P2-P1)·v2 Dv=v1·v2 ("*" is a vector dot product, and "·" is a scalar product or a product of a scalar and a vector.)

[0051] The parameter calculation unit 226 calculates the length D of this line segment (the distance between Q1 and Q2), that is, the distance between the two straight lines, for all combinations of X-ray images belonging to the image group selected by the image selection unit 223.

[0052] <Optimal combination selection and 3D position calculation: S15> After the parameter calculation unit 226 calculates the parameters for all combinations, the three-dimensional position calculation unit 227 calculates the three-dimensional positions of the device's feature points using the combination with the smallest parameter among all combinations. As described above, the combination with the smallest parameter (here, the distance between two lines) is the combination of X-ray images with the least influence of body movement and the smallest displacement difference. Therefore, by using such a combination, the device position can be calculated with high accuracy. When the parameter is the distance between two lines, the three-dimensional position of the device can be calculated as the midpoint of the line segment that specifies it. That is, the three-dimensional position calculation unit 227 calculates the device position (coordinates of the feature points) using the specified parameter values ​​Q1 and Q2 (see FIG. 13 and Equation 1) according to the following equation:

[0053] [Number 2] Q=(Q1+Q2) / 2

[0054] In the case of parameters calculated based on a figure calculated using three or more X-ray images, the center of gravity or center of the figure can be calculated as the feature point position (device position). Note that if multiple feature points are extracted, the position is calculated for each feature point.

[0055] The device position calculated by the three-dimensional position calculation unit 227 is passed to, for example, the display control unit 213, and is displayed on the display device 30 after being mapped onto a three-dimensional image of the subject that has been acquired in advance.

[0056] The above-mentioned steps (S11 to S15) from imaging within a specified angle range to calculating the device position are repeated every time the device position changes or at a specified interval while the interventional procedure is being performed, and each time the mapping results are updated and displayed on the display device 30.

[0057] According to this embodiment, body motion is classified based on the trajectory of the device (feature point) on the X-ray image, and the X-ray image to be used for the subsequent 3D position detection process, including parameter calculation and device position calculation, is selected based on the type of body motion. This enables highly accurate 3D position detection and improves the effectiveness of the X-ray imaging device as an interventional imaging tool. In particular, it is possible to avoid the influence of non-periodic body motion that occurs when acquiring multiple X-ray images at different imaging positions, i.e., at different times, for position detection, thereby improving the accuracy of position detection.

[0058] Furthermore, according to this embodiment, when three-dimensional position is determined by calculating parameters from a combination of multiple X-ray images, image data when non-periodic body movement occurs can be excluded from the calculation, thereby reducing the load on the calculation unit due to parameter calculation.

[0059] In the above explanation, we have described a case where the classification of body movements and the selection of image groups based on the type are performed automatically by the calculation unit 22. However, it is also possible to present the progress to the user or to involve the user's judgment or selection, and such modifications are also encompassed by the present invention.

[0060] <Embodiment 2> This embodiment is an embodiment that deals with the fact that the position of an object on an image changes depending on the irradiation angle, and is characterized by having a function for dealing with position changes of feature points in body movement classification.

[0061] In this embodiment, as in embodiment 1, multiple X-ray images are obtained by capturing images within a predetermined irradiation angle range of the X-ray source, body movements that occurred while acquiring these multiple X-ray images are classified, and parameters are calculated using multiple combinations of X-ray images with different irradiation angles from among the multiple X-ray images, and the three-dimensional position of the device is calculated.

[0062] The following description of this embodiment will focus on the differences from embodiment 1. In the following description, the same contents as embodiment 1 will be explained using the drawings used in the description of embodiment 1, and overlapping explanations will be omitted.

[0063] The function of the calculation unit 22 of this embodiment is shown in Fig. 14, and the processing flow of the calculation unit 22 is shown in Fig. 15. As shown in Fig. 14, the body movement classification unit 221 of this embodiment includes a position correction unit 224 in addition to the feature extraction unit 222 and image selection unit 223 of embodiment 1. The position correction unit 224 corrects the coordinates (positions) of feature points extracted from each X-ray image by the feature extraction unit 222, as shown in S11-2 of Fig. 15.

[0064] To explain the function of the position corrector 224, a change in the position of a point of interest (for example, a feature point) on an image due to the irradiation angle will be described with reference to FIG.

[0065] In an X-ray imaging device in which the X-ray detector 12 is fixed to a bed carrying a subject, as shown in Fig. 16, the position of the object (shown as a single point in Fig. 16 as a point of interest) between the X-ray source 11 and the X-ray detector 12 and displayed in the X-ray image differs when the X-ray source 11 is at an irradiation angle ang1 and when the X-ray source 11 is moved by an angle Θ to an irradiation angle ang2, as shown on the left side of the figure. In other words, even if the point of interest does not move, changing the irradiation angle causes the point of interest to move on the image, making it appear to have moved. Note that the irradiation angle of the X-ray source 11 usually changes within a plane intersecting the X-ray detector 12, so the position of the point of interest moves in one direction (vertical direction in Fig. 16) on the X-ray image.

[0066] Here, if the position of the attention point at irradiation angle ang1 is P1 and the position of the attention point at irradiation angle ang2 is P2, the movement amount of the attention point due to this irradiation angle (P2-P1) can be expressed by the following equation.

[0067] [Number 3] P2-P1 = h * L * sinΘ / (L * cosΘ - h)=ΔP(Θ) (3) In the formula, L is the distance from the X-ray source 11 to the X-ray detector 12, and h is the distance from the X-ray detector 12 (for example, the top surface of a flat panel detector) to the point of interest.

[0068] The distance h from the X-ray detector 12 to the point of interest can be calculated using, for example, the distance from the bed surface to the X-ray detector 12, which is known, and the distance from the bed surface to the predetermined organ of the subject into which the device is inserted, which is a known statistical value. This allows the displacement for each irradiation angle, i.e., the displacement correction amount ΔP(Θ), to be calculated from equation (3).

[0069] The position correction unit 224 corrects the coordinates P' of the feature point actually extracted by the feature extraction unit 222 for each irradiation angle by this correction amount ΔP(Θ), and sets the position P of the feature point for each irradiation angle (P=P'+ΔP, or P=P'-ΔP. The sign of ΔP depends on the sign of Θ relative to the reference irradiation angle).

[0070] The subsequent processing is the same as in embodiment 1. The body movement classification unit 221 calculates movement vectors of the feature points within a predetermined angle range using the positions of the feature points corrected by the position correction unit 224, classifies the body movements (S12), and selects multiple X-ray images (image group) to be used for device position calculation based on the classification. The device position calculation unit 225 uses the selected image group to calculate parameters from combinations of various X-ray images, and calculates the three-dimensional position of the device from the image combination that results in parameters with the smallest degree of influence of body movements (S13 to S15).

[0071] In addition to the same effects as those of the first embodiment, this embodiment makes it possible to correct positional changes of feature points in images with different irradiation angles for an X-ray imaging device in which the X-ray irradiation angle to the X-ray detector changes, thereby enabling highly accurate body motion classification. This makes it possible to detect the 3D position of the device while avoiding the effects of not only periodic body motion but also non-periodic body motion.

[0072] Furthermore, according to this embodiment, since images in multiple directions with aligned positions can be acquired while continuously changing the angle, it is possible to acquire three-dimensional positions as quickly and accurately as possible while taking into account body movement. That is, when imaging is repeated for each angle to acquire data for a period while fixing the angle, the accuracy of position detection decreases if there is non-periodic body movement during movement between angles. However, according to this embodiment, since images are acquired continuously, it is possible to determine whether there has been non-periodic body movement during that time, improving the time resolution of judgment and position detection and shortening the acquisition time.

[0073] The above describes embodiments of the present invention, but the present invention also includes embodiments in which known configurations or functions are added to the above-described embodiments, and embodiments in which configurations or functions that can be omitted in the present invention are omitted. [Explanation of symbols]

[0074] 1: X-ray imaging device, 10: imaging unit, 20: processor, 21: control unit, 22: calculation unit, 30: display device, 40: endoscope, 41: guide wire (device), 50: subject, 211: imaging control unit, 213: display control unit, 221: body movement classification unit, 222: feature extraction unit, 223: image selection unit, 224: position correction unit, 225: device position calculation unit, 226: parameter calculation unit, 227: 3D position calculation unit

Claims

1. an imaging unit including an X-ray source that irradiates X-rays and an X-ray detector that is disposed opposite the X-ray source across an object to be inspected, and that generates an X-ray image of the object to be inspected from X-rays that have passed through the object to be inspected and are detected by the X-ray detector; a processor that analyzes a plurality of X-ray images taken at different X-ray irradiation angles relative to the object to be inspected and calculates a three-dimensional position of a device inserted or attached to the object to be inspected; The processor classifies the movement of the subject from multiple X-ray images taken at different imaging positions, selects a combination of two or more X-ray images with different irradiation angles from the multiple X-ray images according to the classified type of body movement, and calculates the three-dimensional position of the device using the selected combination.

2. 2. The X-ray imaging device according to claim 1, The processor extracts feature points from at least one of the object to be inspected and the device from the plurality of X-ray images, and classifies body movement based on the trajectory of the positions of the extracted feature points in the plurality of X-ray images.

3. 2. The X-ray imaging device according to claim 1, The processor extracts feature points of at least one of the object to be inspected and the device from the plurality of X-ray images, and classifies body movement based on movement vectors of the feature points in the plurality of images.

4. 2. The X-ray imaging device according to claim 1, The processor determines the movement of the object to be periodic when the movement vector or its average is within a predetermined threshold, and determines the movement of the object to be non-periodic when the movement vector or its average exceeds the predetermined threshold.

5. 5. The X-ray imaging device according to claim 4, An X-ray imaging device characterized in that, if, as a result of classifying the body movement, the plurality of X-ray images includes an X-ray image acquired when the movement of the subject is non-periodic, the processor selects a group of images from the plurality of X-ray images excluding the X-ray images acquired when there is non-periodic movement, and calculates the three-dimensional position of the device using the selected group of images.

6. 5. The X-ray imaging device according to claim 4, An X-ray imaging device characterized in that, if the classification result of the body movement indicates that the plurality of X-ray images includes a plurality of image groups acquired before and after a non-periodic movement when there is no movement or when there is periodic movement, the processor selects the image group containing the largest number of images, and calculates the three-dimensional position of the device using the selected image group.

7. 2. The X-ray imaging device according to claim 1, The processor calculates a parameter that is an index of the influence of body movement for each of a plurality of combinations of two or more X-ray images included in the plurality of X-ray images, selects a combination of X-ray images that is least influenced by body movement based on the parameter, and calculates the three-dimensional position of the device.

8. 2. The X-ray imaging device according to claim 1, the processor calculates a straight line connecting the X-ray source and a feature point in each of the plurality of X-ray images, and calculates a distance between two straight lines from the plurality of straight lines calculated for each of the X-ray images; An X-ray imaging apparatus characterized in that the three-dimensional position of the device is calculated using a combination of X-ray images with different irradiation angles that results in the shortest distance between the two straight lines.

9. 3. The X-ray imaging apparatus according to claim 2, wherein the X-ray irradiation angle is changed by moving the position of the X-ray source relative to the object and the X-ray detector, The processor is provided with a position correction unit that corrects the positions of the feature points in accordance with the irradiation angle of the X-ray source, and classifies body movements based on the trajectories of the feature points after the positions are corrected.

10. A method for detecting a three-dimensional position of a device shown in a plurality of X-ray images taken at different X-ray irradiation angles, comprising: extracting feature points from each of the plurality of X-ray images and calculating movement vectors of the feature points between the images; classifying, based on the motion vectors, motion of the imaging subject occurring during acquisition of the plurality of X-ray images; selecting, from the plurality of X-ray images, a group of images acquired when no non-periodic motion occurs, based on the classified motion; A device position detection method, comprising: calculating a three-dimensional position of the device using a selected group of images.

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