Information processing device, information processing method, and information processing program

Abstract

This information processing device uses three-dimensional point cloud data, which was obtained by imaging a reference surface that has a section overlapping with a subject and a radiation detector along the radiation direction of radiation radiated from a radiation source, to derive information representing one or more reference surface candidates, determines the appropriateness of the derived reference surface candidate or candidates, and uses the information representing a reference surface candidate which is in accordance with the appropriateness determination results to derive at least one among the distance between the radiation source and the radiation detector, and the angle of incidence of the radiation radiated from the radiation source with respect to the reference surface candidate.

Description

Information processing device, information processing method, and information processing program

[0001] This disclosure relates to an information processing device, an information processing method, and an information processing program.

[0002] Japanese Patent Publication No. 2011-092612 discloses a technique for calculating the distance between a radiation source and a radiation detector based on the distance between markers captured in an image taken by a camera.

[0003] Incidentally, a technique is known in which the distance between a radiation source and a radiation detector is measured using a distance measuring sensor placed near the radiation source. However, with this technique, it can be difficult to accurately derive at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation, for example, when an object is present between the radiation source and the radiation detector.

[0004] This disclosure is made in view of the above circumstances and aims to provide an information processing device, an information processing method, and an information processing program that can accurately derive at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation.

[0005] The first embodiment of the information processing device includes a processor which uses three-dimensional point cloud data obtained by photographing a reference plane having a portion that overlaps with the subject and the radiation detector along the irradiation direction of the radiation emitted from the radiation source to derive information representing one or more candidate reference planes, determines the validity of the derived candidate reference planes, and uses the information representing the candidate reference planes according to the validity determination result to derive at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation emitted from the radiation source with respect to the candidate reference plane.

[0006] In the second embodiment of the information processing apparatus, the processor determines validity based on an index value using far-field data, which is data of points located further away from a candidate reference plane in the three-dimensional point cloud data, with respect to the sensor used to acquire the three-dimensional point cloud data.

[0007] In the third embodiment of the information processing device, the index value is the ratio of the number of far-field data to the number of points in the three-dimensional point cloud data used to derive candidate reference planes, as in the information processing device of the second embodiment.

[0008] In the fourth embodiment of the information processing apparatus, the index value is the number of remote data points, as in the information processing apparatus of the second embodiment.

[0009] In the fifth embodiment of the information processing apparatus, the processor determines validity based on the derived distance, in the information processing apparatus of the first embodiment.

[0010] In the sixth embodiment of the information processing device, the processor determines that the reference surface candidate with the longest derived distance among a plurality of reference surface candidates is valid.

[0011] The seventh embodiment of the information processing apparatus is an information processing apparatus of any one of the first to sixth embodiments, in which the processor repeatedly performs a process to determine validity, changing the candidate reference surface until it is determined that the candidate reference surface is valid.

[0012] In the information processing apparatus of the eighth embodiment, if the number of executions of the validation determination process reaches the upper limit, the processor derives at least one of the distance and the angle of incidence using information representing the candidate of the reference surface with the highest validity among a plurality of candidate reference surfaces for which validity has been determined.

[0013] The information processing apparatus of the ninth embodiment, in the information processing apparatus of the seventh embodiment, does not perform the process of deriving at least one of the distance and the angle of incidence when the number of executions of the process for determining validity reaches the upper limit.

[0014] The tenth embodiment of the information processing apparatus is an information processing apparatus of any one embodiment from the seventh to the ninth embodiment, in which the processor determines the validity of the n (where n is an integer of 2 or more)th candidate reference surface, and determines the object to be determined for validity based on the similarity with the first to n-1 candidate reference surfaces.

[0015] In the eleventh embodiment of the information processing apparatus, in the tenth embodiment of the information processing apparatus, when the processor determines the validity of the nth reference surface candidate, it includes reference surface candidates that it has determined are not similar to the first to n-1 reference surface candidates as the subject of validity determination.

[0016] In the twelfth embodiment of the information processing apparatus, in the tenth or eleventh embodiment, the processor uses the cosine similarity of the normal vectors of the candidate reference planes or the absolute value of the difference of the constant term in the expression representing the candidate reference plane as the similarity.

[0017] The information processing apparatus of the 13th embodiment, in the information processing apparatus of the 10th embodiment or the 11th embodiment, uses the cosine similarity of a four-dimensional vector using the coefficients of an expression representing a candidate reference plane as the similarity.

[0018] The 14th embodiment of the information processing device is an information processing device of any one of the first to 13 embodiments, in which the processor derives the distance by deriving the intersection point of a straight line along the direction of irradiation and a candidate reference plane in three-dimensional space.

[0019] The fifteenth embodiment of the information processing device is an information processing device of any one of the first to fourteenth embodiments, in which the processor derives the angle of incidence using the normal vector of a candidate reference plane and an inverse trigonometric function.

[0020] The sixteenth embodiment of the information processing device is an information processing device according to any one of the first to fifteenth embodiments, in which the processor derives information representing candidate reference planes using a regression algorithm.

[0021] The 17th aspect of the information processing method involves an information processing device equipped with a processor, in which the processor derives information representing one or more candidate reference planes using three-dimensional point cloud data obtained by photographing a reference plane having a portion that overlaps with the subject and the radiation detector along the irradiation direction of the radiation emitted from the radiation source, determines the validity of the derived candidate reference planes, and performs a process to derive at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation emitted from the radiation source with respect to the candidate reference plane, using the information representing the candidate reference plane according to the validity determination result.

[0022] The information processing program of the 18th embodiment causes the processor of an information processing device equipped with a processor to derive information representing one or more candidate reference planes using three-dimensional point cloud data obtained by photographing a reference plane having a portion that overlaps with the subject and the radiation detector along the irradiation direction of the radiation irradiated from the radiation source, determine the validity of the derived candidate reference planes, and derive at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation irradiated from the radiation source with respect to the candidate reference plane using the information representing the candidate reference plane according to the validity determination result.

[0023] According to this disclosure, at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation can be accurately derived.

[0024] This is a front view showing an example of a radiography system. This is a side view showing an example of a radiography system. This is a diagram illustrating the positional relationship between the radiation source and the ToF camera. This is a front view showing an example of a radiography system. This is a block diagram illustrating an example of the console's hardware configuration. This is a block diagram illustrating an example of the console's functional configuration. This is a diagram illustrating the SSD derivation process. This is a diagram illustrating the SSD derivation process. This is a diagram illustrating the reference plane derivation process. This is a diagram illustrating the effect of re-deriving the plane. This is a diagram illustrating the validity determination process. This is a diagram illustrating the incident angle derivation process. This is a diagram illustrating the incident angle derivation process. This is a flowchart illustrating an example of the SID and incident angle derivation process. This is a flowchart illustrating an example of the reference plane derivation process.

[0025] Hereinafter, with reference to the drawings, examples of embodiments for carrying out the technology of this disclosure will be described in detail.

[0026] First, the configuration of the radiography system 1 will be described with reference to Figures 1 and 2. As shown in Figures 1 and 2, the radiography system 1 is a system that takes a radiographic image of a subject H by irradiating the subject H with radiation R such as X-rays, and is operated by a user such as a radiologic technologist. The radiography system 1 includes a radiation source 10, an imaging device 13, a radiation detector 14, a patient table 15, and a console 16. Figure 1 is a front view when looking from the head side to the foot side of the subject H, and Figure 2 is a side view when looking from the right side to the left side of Figure 1. The console 16 is an example of an information processing device relating to the disclosed technology.

[0027] The radiation source 10 includes a radiation tube 11 that emits radiation R and a field limiter (also called a collimator) 12 that limits the irradiation field of radiation R. The radiation tube 11 is provided with, for example, a filament, a target, and a grid electrode. A voltage is applied from a voltage generator between the filament, which is the cathode, and the target, which is the anode. This voltage applied between the filament and the target is called the tube voltage. The filament emits thermionic electrons toward the target in accordance with the applied tube voltage. The target emits radiation R through collisions with thermionic electrons emitted from the filament. The grid electrode is placed between the filament and the target. The grid electrode changes the flow rate of thermionic electrons from the filament toward the target in accordance with the voltage applied from the voltage generator. This flow rate of thermionic electrons from the filament toward the target is called the tube current.

[0028] The irradiation field limiter 12 has an entrance aperture through which radiation R from the radiation tube 11 enters, and an exit aperture through which radiation R exits. Four shielding plates are provided near the exit aperture. The shielding plates are made of a material that shields radiation R, such as lead. The shielding plates are arranged on each side of a rectangle, in other words, in a checkered pattern, forming a rectangular irradiation aperture that allows radiation R to pass through. The irradiation field limiter 12 changes the size of the irradiation aperture by changing the position of each shielding plate, thereby changing the irradiation field of radiation R.

[0029] The imaging device 13 is mounted on the outside of the irradiation field limiter 12. The imaging device 13 includes an optical camera 17 and a ToF (Time of Flight) camera 18 (see Figure 3). The optical camera 17 is a camera capable of capturing R (Red), G (Green), and B (Blue) color images by detecting reflected light from the subject H. The optical camera 17 includes an optical system and an image sensor such as a CCD (Charge Coupled Device) image sensor. The optical camera 17 outputs the image obtained by capturing the subject H (hereinafter referred to as the "optical image") to the console 16. In the example in Figure 1, the imaging device 13 is shown mounted on the outside of the irradiation field limiter 12, but the imaging device 13 may also be mounted on the ceiling or the like. In this case, it is sufficient to be able to obtain the positional relationship between the imaging device 13 and the radiation source 10.

[0030] The ToF camera 18 is a camera capable of capturing a distance image representing the distance between itself and the object being photographed using a ToF sensor. The ToF camera 18 outputs the distance image obtained by photographing the reference plane P to the console 16. Details of the reference plane P will be described later. In this embodiment, the distance in the distance image represents the distance between the focal point of the ToF camera 18 and the object being photographed.

[0031] The radiation detector 14 is portable and acquires a radiation image of the subject H by detecting radiation R that has passed through the subject H. The radiation detector 14 outputs the radiation image of the subject H to the console 16. The radiation detector 14 is used in a position corresponding to the imaging area between the surface of the examination table 15 on which the subject H lies and the subject H. In the example in Figure 1, the examination table 15 is shown as a bed in a hospital room in a supine position, but it may also be in a semi-sitting position, or the examination table 15 may be a supine examination table in an imaging room that houses the radiation detector 14.

[0032] The console 16 has functions for the user to confirm and input radiation irradiation conditions R, and functions for image processing on radiation images obtained by the radiation detector 14. Examples of the console 16 include personal computers or server computers.

[0033] The reference plane P according to this embodiment is a plane serving as a reference when measuring the body thickness of the subject H, and is a plane having a portion overlapping the subject H and the radiation detector 14 along the irradiation direction D of the radiation R irradiated from the radiation source 10. That is, the reference plane P is a plane located on the path along which the radiation R is irradiated. Further, the reference plane P is a plane of the bed 15 with which at least a part of the subject H is in contact, and is a plane parallel to the detection surface of the radiation R of the radiation detector 14. The parallelism here means parallelism within a range including an allowable error. In the example of FIG. 1, the plane of the bed 15 with which the subject H lying on it is in contact is the reference plane P. Note that the reference plane P may be a part of the plane of the bed 15. When the bed 15 is a bed, the reference plane P is the plane of the bed with which the subject H is in contact, and when the bed 15 is a lying position imaging table in which the radiation detector 14 is housed, the reference plane P is the plane of the top plate of the lying position imaging table with which the subject H is in contact. The distance image described above also includes distances to objects other than the reference plane P, such as a pillow, a bed, and the subject H.

[0034] In FIG. 1, the case where the subject H is in a lying position is illustrated, but the subject H may be in a standing position. In this case, a standing position imaging table is used instead of the bed 15. The reference plane P in this case is the plane of the standing position imaging table in which the radiation detector 14 provided in the imaging room is housed and with which the subject H is in contact. Further, the radiation detector 14 in this case does not have to be a portable type.

[0035] In Figure 1, arrow Y1 represents the distance between the focal point of the ToF camera 18 and the surface of the bed 15. Arrow Y2 represents the distance between the radiation source 10 and the surface of the bed 15. Hereafter, the distance between the radiation source 10 and the surface of the bed 15 will also be referred to as "SID (Source to Image receptor Distance)". In this embodiment, since the height difference between the surface of the bed 15 and the detection surface of the radiation detector 14 is relatively small, the distance between the radiation source 10 and the surface of the bed 15 will be treated as the distance between the radiation source 10 and the radiation detector 14. In this embodiment, the case where the distance between the focal point of the radiation source 10 and a preset position such as the center of the detection surface of the radiation detector 14 is applied as the SID will be explained as an example. In Figure 1, arrow Y3 represents the distance between the radiation source 10 and the body surface of the subject H. Hereafter, the distance between the radiation source 10 and the body surface of the subject H will also be referred to as "SSD (Source to Surface Distance)".

[0036] Next, with reference to Figure 3, the positional relationship between the focal point of the radiation source 10 and the focal point of the ToF camera 18 will be explained. In this embodiment, a three-dimensional Cartesian coordinate system using the X, Y, and Z axes is used. Below, the direction of the first side of the field of view of the ToF camera 18 (the direction of the long side in this embodiment) will be described as the X-axis direction. The direction of the second side that intersects (orthogonal in this embodiment) the first side of the field of view of the ToF camera 18 (the direction of the short side in this embodiment) will be described as the Y-axis direction. The irradiation direction D of the radiation R will be described as the Z-axis direction. The irradiation direction D of the radiation R means the axis direction of the radiation R that is irradiated in a cone-beam shape. The axis of the radiation R means the axis connecting the focal point of the radiation source 10 and a predetermined position such as the center of the radiation detector 14. The X-axis direction and the Y-axis direction correspond to the width direction and body axis direction of the subject H when the ToF camera 18 and the subject H are facing each other.

[0037] As shown in FIG. 3, the distance between the focal point of the radiation source 10 along the X-axis direction and the focal point of the ToF camera 18 is represented as Δx. Also, the distance between the focal point of the radiation source 10 along the Y-axis direction and the focal point of the ToF camera 18 is represented as Δy. Further, the distance between the focal point of the radiation source 10 along the Z-axis direction and the focal point of the ToF camera 18 is represented as Δz. In the present embodiment, the focal point of the ToF camera 18 is set as the origin in the three-dimensional orthogonal coordinate system. That is, in the example of FIG. 3, the coordinates of the focal point of the radiation source 10 are represented as (−Δx, Δy, −Δz).

[0038] In such a three-dimensional space, the reference plane P can be represented by the equation (1) which is the equation of a plane. In FIG. 1, an example where the irradiation direction D of the radiation R is orthogonal to the reference plane P is shown. However, as shown in FIG. 4, even when the radiation R is incident obliquely to the reference plane P, the reference plane P can be represented by the equation (1). ax + by + cz + d = 0 ··· (1)

[0039] Referring to FIG. 5, the hardware configuration of the console 16 according to the present embodiment will be described. As shown in FIG. 5, the console 16 includes a CPU (Central Processing Unit) 31, a memory 32 as a temporary storage area, and a non-volatile storage unit 33. Further, the console 16 includes a display 34 such as a liquid crystal display, an input device 35 such as a keyboard and a mouse, and a network I / F (InterFace) 36. The CPU 31, the memory 32, the storage unit 33, the display 34, the input device 35, and the network I / F 36 are connected to a bus 37. The CPU 31 is an example of a processor. The console 16 performs data transmission and reception with each of the radiation source 10, the radiation detector 14, the optical camera 17, and the ToF camera 18 via the network I / F 36.

[0040] The storage unit 33 is realized by an HDD (Hard Disk Drive), an SSD (Solid State Drive), a flash memory, or the like. An information processing program 40 is stored in the storage unit 33 as a storage medium. The CPU 31 reads the information processing program 40 from the storage unit 33 and then expands it in the memory 32, and executes the expanded information processing program 40.

[0041] Next, referring to FIG. 6, the functional configuration of the console 16 will be described. As shown in FIG. 6, the console 16 includes an acquisition unit 50, a conversion unit 52, a first derivation unit 54, a second derivation unit 56, a third derivation unit 58, and a display control unit 60. When the CPU 31 executes the information processing program 40, it functions as the acquisition unit 50, the conversion unit 52, the first derivation unit 54, the second derivation unit 56, the third derivation unit 58, and the display control unit 60.

[0042] The acquisition unit 50 acquires the distance image obtained by photographing the reference plane P by the ToF camera 18 via the network I / F 36. The conversion unit 52 converts the distance image acquired by the acquisition unit 50 into three-dimensional point cloud data by a known conversion algorithm. At this time, the conversion unit 52 sets the focal point of the ToF camera 18 at the origin and sets the irradiation direction D of the radiation R in the Z-axis direction. The three-dimensional point cloud data obtained by the conversion unit 52 is an example of the three-dimensional point cloud data obtained by photographing the reference plane according to the disclosed technology.

[0043] The first derivation unit 54 derives the SSD by searching the three-dimensional point cloud data obtained by the conversion unit 52 along the irradiation direction D. Specifically, as shown in FIG. 7, the coordinates (X ｘｒａｙ 、Y ｘｒａｙ 、Z ｘｒａｙ ) of the focal point of the radiation source 10 are searched for the presence or absence of points included in the three-dimensional point cloud data along the Z-axis direction, and the coordinates (X ｘｒａｙ 、Y ｘｒａｙ 、Z Ｓｕｒｆａｃｅ ) of the point closest to the focal point of the radiation source 10 among the detected points are derived. Point B1 in FIG. 7 represents the focal point of the radiation source 10, and point B2 represents the point closest to the focal point of the radiation source 10 among the points detected by the first derivation unit 54. Then, the first derivation unit 54 derives the SSD by subtracting Z Ｓｕｒｆａｃｅ from Z ｘｒａｙ according to the following formula (2). SSD = Z Ｓｕｒｆａｃｅ - Z ｘｒａｙ ... (2)

[0044] For example, as shown in Figure 8, the first derivation unit 54 detects point B2 by searching within a set range of the X-Y plane along the irradiation direction D from point B1, which is the focal point of the radiation source 10. In Figure 8, the set range of the X-Y plane is defined as having a side length in the X-axis direction of X. ｒａｎｇｅ And the length of the side in the Y-axis direction is Y ｒａｎｇｅ This shows an example of a rectangular area. In this case, the set area may also be a circular area. Furthermore, the first derivation unit 54 sequentially searches for multiple points, such as the second and third closest points, not just the point closest to the focal point of the radiation source 10, and calculates the average of the Z coordinates of the multiple points that were searched. Ｓｕｒｆａｃｅ This is also acceptable. This helps to suppress variations in search results due to noise contained in the distance image.

[0045] The second derivation unit 56 uses the three-dimensional point cloud data obtained by the transformation unit 52 to derive information representing one or more candidate reference planes P. In this embodiment, the second derivation unit 56 derives equation (1) above as information representing candidate reference planes P. In addition, in this embodiment, the second derivation unit 56 derives information representing candidate reference planes P by iterative processing using three-dimensional point cloud data and a regression algorithm. A specific example of the derivation process performed by the second derivation unit 56 will be described below.

[0046] The second derivation unit 56 uses RANSAC (RANDOM SAmple Consensus), a robust algorithm, as the regression algorithm. As an example, as shown in Figure 9, the second derivation unit 56 first randomly selects three points from the 3D point cloud data and derives information representing a plane passing through the three selected points. In the example in Figure 9, point C represents the three points. The second derivation unit 56 derives equation (1), which represents the plane passing through the three points, as information representing the plane.

[0047] Next, as shown in Figure 10, the second derivation unit 56 derives the number of points in the 3D point cloud data whose distance from the derived plane is within a threshold δ. For each of several different sets of three points, the second derivation unit 56 derives information representing the plane and the number of points whose distance from that plane is within a threshold δ. Then, the second derivation unit 56 selects the plane with the largest number of derived points.

[0048] Furthermore, the second derivation unit 56 uses points whose distance from the selected plane is within a threshold δ to re-derive the plane according to an optimization algorithm such as the least squares method, and uses the information representing the derived plane as information representing a candidate for the reference plane P. As an example, as shown in Figure 11, by re-deriving the plane, the second derivation unit 56 can select a plane that is closer to the target plane than the plane selected based on the number of points whose distance is within a threshold δ as a candidate for the reference plane P.

[0049] The second derivation unit 56 determines the validity of the derived reference plane P candidate. In this embodiment, the second derivation unit 56 uses the ToF camera 18, which is an example of a sensor used to acquire the 3D point cloud data, as a reference, and determines the validity based on an index value using far-field data, which is data of points located further away than the reference plane P candidate in the 3D point cloud data. The second derivation unit 56 uses the ratio of the number of far-field data to the number of points included in the 3D point cloud data used to derive the reference plane P candidate as the index value. For example, the second derivation unit 56 derives the index value by dividing the number of far-field data by the total number of points included in the 3D point cloud data.

[0050] As an example, as shown in Figure 12, among the candidates for the reference plane P, the fewer the number of distant data points, the more likely it is to be a correct plane as the reference plane P. In the example in Figure 12, the dashed line represents the candidate for the reference plane P. Therefore, the second derivation unit 56 determines that a candidate for the reference plane P is valid if the derived index value is less than or equal to a preset threshold, and that it is invalid if the index value exceeds the threshold.

[0051] The second derivation unit 56 repeatedly performs this validity determination process, changing the candidate reference surface P until it is determined that the candidate reference surface P is valid. In other words, the second derivation unit 56 determines the validity of the derived candidate reference surface P within the iterative process using the regression algorithm described above.

[0052] The second derivation unit 56 may use the number of far-field data points included in the 3D point cloud data as an index value using far-field data.

[0053] The third derivation unit 58 uses information representing candidate reference planes P according to the validity determination result by the second derivation unit 56 to derive the SID and the incident angle of the radiation R irradiated from the radiation source 10 with respect to the candidate reference plane P. In this embodiment, the case in which the third derivation unit 58 derives both the SID and the incident angle is described as an example, but the third derivation unit 58 may derive only one of the SID or the incident angle.

[0054] Specifically, the third derivation unit 58 derives the SID and incidence angle using information representing candidate reference planes P determined to be valid by the second derivation unit 56. Furthermore, if the number of executions of the validity determination process by the second derivation unit 56 reaches the upper limit, the third derivation unit 58 derives the SID and incidence angle using information representing the candidate reference plane P with the highest validity among the multiple candidate reference planes P whose validity has been determined by the second derivation unit 56. The candidate reference plane P with the highest validity is, for example, the candidate reference plane P with the smallest index value.

[0055] The third derivation unit 58 derives the SID by deriving the intersection point A (see Figure 1) of a straight line along the irradiation direction D in three-dimensional space and a candidate reference plane P. As mentioned above, the coordinates of the focal point of the radiation source 10 are known coordinates (-Δx, Δy, -Δz), and equation (1) is derived by the second derivation unit 56 as information representing a candidate reference plane P. Therefore, the third derivation unit 58 can derive the SID from the three-dimensional positional relationship between the focal point of the radiation source 10 and the intersection point A.

[0056] Furthermore, the third derivation unit 58 derives the incident angle using the normal vector of the candidate reference plane P and inverse trigonometric functions. Referring to Figures 13 and 14, a specific example of the incident angle derivation process performed by the third derivation unit 58 will be explained. As shown in Figures 13 and 14, the normal vector n, which is the unit normal vector of the candidate reference plane P represented by equation (1), is (a, b, c), and the unit vector x of the radiation irradiation direction D is (0, 0, 1). The relationship between the normal vector n and the unit vector x, and the angle θ between the normal vector n and the unit vector x, is expressed by the following equation (3). θ corresponds to the incident angle in three-dimensional space. x・n=c=cosθ・・・(3)

[0057] As shown in Figure 14, if ψ is the angle between the vector obtained by projecting the normal vector n onto the Y-Z plane and the direction of illumination D, then tanψ is expressed by equation (4) below. Therefore, ψ is expressed by equation (5) below. ψ corresponds to the angle of incidence in the Y-Z plane. tanψ = b / c ... (4) ψ = atan(b / c) ... (5)

[0058] Similarly, if φ is the angle between the vector obtained by projecting the normal vector n onto the Z-X plane and the direction of illumination D, then tanφ is expressed by equation (6) below. Therefore, φ is expressed by equation (7) below. φ corresponds to the angle of incidence in the Z-X plane. tanφ = a / c ... (6) φ = atan(a / c) ... (7)

[0059] The third derivation unit 58 in this embodiment derives ψ and φ as the angle of incidence of the radiation R with respect to a candidate reference plane P, using the normal vector n(a, b, c) and atan as an example of an inverse trigonometric function, according to equations (5) and (7).

[0060] Furthermore, the third derivation unit 58 may derive θ as the angle of incidence of the radiation R with respect to a candidate reference plane P, using the normal vector n(a, b, c) and acos as an example of an inverse trigonometric function, according to equation (8) below: θ = acos(c) ... (8)

[0061] The display control unit 60 controls the display of the SID and incident angle derived by the third derivation unit 58. For example, the display control unit 60 controls the display of the SID and incident angle derived by the third derivation unit 58 on a display provided on the outer surface of the irradiation field limiter 12. As a result, the user can grasp the SID and incident angle, thereby supporting the positioning work of the radiation source 10 and subject H performed by the user. The display control unit 60 may also control the display of the SID and incident angle on the display 34, on a display installed on a display cart with casters, or on multiple displays.

[0062] Next, the operation of the console 16 will be explained with reference to Figure 15. The CPU 31 executes the information processing program 40, which performs the SID and incidence angle derivation process shown in Figure 15. The SID and incidence angle derivation process is performed, for example, when the user inputs an instruction to start execution, or when the position of the radiation source 10 is changed.

[0063] In step S10 of Figure 15, the acquisition unit 50 acquires a distance image obtained by photographing the reference plane P with the ToF camera 18 via the network I / F 36. In step S12, the conversion unit 52 converts the distance image acquired in step S10 into 3D point cloud data. In step S14, the first derivation unit 54 derives the SSD by searching the 3D point cloud data obtained by the processing in step S12 along the irradiation direction D.

[0064] In step S16, the second derivation unit 56 uses the three-dimensional point cloud data obtained in step S12 to perform the reference plane derivation process shown in Figure 16.

[0065] In step S30 of Figure 16, the second derivation unit 56 initializes the variable N by assigning 0 to the variable N used to count the number of times the validity determination process is executed. In step S32, as described above, the second derivation unit 56 derives information representing the candidate reference surface P using RANSAC. In step S34, the second derivation unit 56 derives the index value described above for the candidate reference surface P derived in step S32. In step S36, the second derivation unit 56 determines whether the candidate reference surface P is valid by determining whether the index value derived in step S34 is below a threshold. If this determination is negative, the process proceeds to step S38.

[0066] In step S38, the second derivation unit 56 adds 1 to the variable N. In step S40, the second derivation unit 56 determines whether the number of executions of the validity determination process has reached the upper limit by determining whether the variable N is equal to the upper limit number of times. If this determination is negative, the process returns to step S32, where information representing a candidate reference plane P is derived based on three new points. If the determination in step S40 is positive, the process proceeds to step S42. In step S42, the second derivation unit 56 selects the candidate reference plane P with the highest validity from among the multiple candidate reference plane P whose validity has been determined during the repeated processing from steps S32 to S40. When the processing in step S42 is completed, the reference plane derivation process is completed.

[0067] If the determination in step S36 is positive, the process proceeds to step S44. In step S44, the second derivation unit 56 selects the candidate reference surface P that was determined to be valid in step S36 as the candidate reference surface P to be used in subsequent processes. When the process in step S42 is completed, the reference surface derivation process is completed.

[0068] The above reference plane derivation process derives information representing either a candidate reference plane P that has been determined to be valid, or the candidate reference plane P that has the highest validity among those that have been determined to be invalid. Once the reference plane derivation process is completed, the process moves to step S18 in Figure 15.

[0069] In step S18, the third derivation unit 58 uses the information representing the candidate reference plane P derived in step S16 to derive the SID and the incident angle of the radiation R irradiated from the radiation source 10 with respect to the candidate reference plane P. In step S20, the display control unit 60 performs control to display the SID and incident angle derived in step S18. When the processing in step S20 is completed, the derivation process of the SID and incident angle is completed.

[0070] As described above, according to this embodiment, the SID and the incident angle of radiation are derived using information representing candidate reference surfaces that have been determined to be valid. Furthermore, if there are no candidate reference surfaces that have been determined to be valid, the SID and the incident angle of radiation are derived using information representing the most valid reference surface among those that have been determined to be invalid. Therefore, the SID and the incident angle of radiation can be derived with high accuracy.

[0071] In the above embodiment, the case in which a distance image is captured by a ToF camera 18 has been described, but the disclosed technology is not limited to this embodiment. For example, the distance image may be captured by a stereo camera.

[0072] Furthermore, in the above embodiment, when the second derivation unit 56 determines the validity of the derived reference surface P candidates, it may derive an SID using information representing the reference surface P candidates by processing in the same manner as the third derivation unit 58. In this case, the second derivation unit 56 may determine the validity based on the derived SID. For example, the second derivation unit 56 may determine that the reference surface P candidate with the longest derived SID among the multiple reference surface P candidates is valid, and determine that the other reference surface P candidates are not valid.

[0073] Furthermore, in the above embodiment, if the number of times the validation process performed by the second derivation unit 56 is executed reaches the upper limit, the third derivation unit 58 does not need to perform the process of deriving at least one of the SID and the incident angle. In this embodiment, if step S40 in Figure 16 is determined to be positive, the SID and incident angle derivation process is terminated without executing steps S42, S18 and S20 in Figure 15. In this case, the display control unit 60 may also perform control to display a message on the display indicating that no candidate reference plane P that is valid was detected.

[0074] Furthermore, in the above embodiment, when the second derivation unit 56 determines the validity of the nth (where n is an integer of 2 or more) candidate reference surface P, it may determine the target of the validity determination based on the similarity with the first to n-1 candidate reference surface P. In this case, when the second derivation unit 56 determines the validity of the nth candidate reference surface P, it may determine that the candidate reference surface P that it has determined is not similar to the first to n-1 candidate reference surface P is the target of the validity determination. In this case, the second derivation unit 56 may determine that the candidate reference surface P whose similarity is below a threshold is not similar to the first to n-1 candidate reference surface P.

[0075] For example, if the second derivation unit 56 selects three points using RANSAC and determines that the plane passing through these three points is similar to the first to (n-1) candidate reference planes P, it may exclude that plane from further RANSAC processing. In this case, the second derivation unit 56 selects three new points. This allows the second derivation unit 56 to select a plane that is not similar to the candidate reference planes P that were determined to be invalid in the previous processing as a new candidate reference plane P.

[0076] The second derivation unit 56 may use the cosine similarity of the normal vectors of the candidate reference plane P as the similarity in this embodiment. In this case, the second derivation unit 56 uses the cosine similarity CosSim as the threshold CosSim, as shown in equation (9) below. ｔｈｒｅｓｈ Similarity can also be determined by determining whether or not the above is true. (9) vec ｋThis represents the normal vector of each candidate reference plane P from the 1st to the (n-1)th, and vec ｃｕｒｒｅｎｔ This represents the normal vector of the nth candidate reference plane P.

[0077]

[0078] Furthermore, the second derivation unit 56 may use the absolute value of the difference of the constant term d in the equation representing the candidate reference surface P as the similarity in this embodiment. In this case, the second derivation unit 56 uses the absolute value of the difference d as shown in equation (10) below. ｄｉｆｆ is the threshold d ｔｈｒｅｓｈ Similarity can also be determined by determining whether the following is true: d in equation (10) ｋ This represents the constant term d for each piece of information representing the first to n-1 candidate reference planes P, and d ｃｕｒｒｅｎｔ This represents the constant term d of the information representing the nth reference plane P candidate. The second derivation unit 56 may also determine that they are similar if both the conditions of equation (9) and equation (10) are satisfied.

[0079]

[0080] The second derivation unit 56 may use the cosine similarity of a four-dimensional vector vec = (a, b, c, d) using the coefficients of the equation representing the candidate reference plane P as the similarity in this embodiment.

[0081] Furthermore, in the above embodiment, the second derivation unit 56 may derive a plane passing through the three selected points as a candidate reference plane P, and if the angle of incidence of radiation R with respect to the candidate reference plane P exceeds a threshold, the candidate reference plane P may be excluded from processing. Specifically, in this case, the second derivation unit 56 may omit the process of deriving the number of points whose distance is within the threshold δ for the candidate reference plane P. This reduces the computation cost. The second derivation unit 56 can derive the angle of incidence in this case in the same way as the third derivation unit 58.

[0082] Furthermore, in the above embodiment, the second derivation unit 56 may derive information representing candidate reference planes P after excluding data within a range set from the SSD derived by the first derivation unit 54 in the irradiation direction D from the 3D point cloud data. For example, the second derivation unit 56 may exclude data within a set range from the 3D point cloud data, or it may exclude data outside a set range from the 3D point cloud data. As a result, the second derivation unit 56 can derive information representing candidate reference planes P after removing data near the body surface of the subject H that is presumed not to be in contact with the surface of the bed 15 from the 3D point cloud data. This can reduce computation costs. Note that the second derivation unit 56 may set a range that is not excluded from the 3D point cloud data.

[0083] Furthermore, in the above embodiment, the second derivation unit 56 may derive information representing candidate reference planes P after excluding data outside a preset range of the X-Y plane from the three-dimensional point cloud data. In this case, for example, by setting the set range to the range of the bed 15, the second derivation unit 56 can derive information representing candidate reference planes P after excluding point cloud data corresponding to objects outside the bed 15, i.e., point cloud data that is not considered to correspond to reference plane P, from the three-dimensional point cloud data. As a result, computation costs can be reduced. The second derivation unit 56 may also exclude the excluded point cloud data in these cases when determining validity.

[0084] Furthermore, in the above embodiment, if the reference plane P and the detection surface of the radiation detector 14 are separated along the Z-axis direction and their positional relationship is known, the third derivation unit 58 may derive the SID by adding the distance between a candidate reference plane P and the detection surface of the radiation detector 14 along the Z-axis direction to the distance between the focal point of the radiation source 10 and the intersection point A.

[0085] Furthermore, at least one of the functional units of the console 16 in the above embodiment may be provided by other devices such as the control unit of the radiation source 10, the control unit of the imaging device 13, and the control unit of the radiation detector 14.

[0086] Furthermore, in the above embodiments, each process is executed on any computer. The computer may execute these processes using a processor as hardware, a program as software, or a combination thereof. In this case, the processor is configured to work in cooperation with the program to execute the various processes in the above embodiments, and can function as a unit or means in the above embodiments. The execution order of the processes by the processor is not limited to the order described and may be changed as appropriate. The computer may be a general-purpose computer, a computer designed for a specific purpose, a workstation, or any other system capable of executing each process.

[0087] A processor may consist of one or more hardware components, and the type of hardware is not limited. For example, a processor may consist of programmable logic devices such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), FPGA (Field Programmable Gate Array), dedicated circuits for performing specific processing such as an ASIC (Application Specific Integrated Circuit), a GPU (Graphic Processing Unit), or an NPU (Neural Processing Unit). Furthermore, the type of hardware may be a combination of different types of hardware. When multiple hardware components are configured to execute one or more processes of a processor, these components may reside in physically separate devices or in the same device. Furthermore, in any embodiment, the order of the processes performed by the processor is not limited to the order described above and may be changed as appropriate. The hardware components are composed of electrical circuits (circuits) and the like, which are combinations of circuit elements such as semiconductor elements.

[0088] Furthermore, the program may be firmware or software such as microcode. Alternatively, the program may be, for example, a set of program modules, each function of which may be implemented by a processor configured to perform its respective function. The program may be program code or multiple code segments stored on one or more non-temporary computer-readable media (e.g., storage media or other storage). The program may be divided and stored on multiple non-temporary computer-readable media located on physically separate devices. Program code or code segments may represent any combination of procedures, functions, subprograms, routines, subroutines, modules, software packages, classes, or instructions, data structures, or program statements. Program code or code segments may be connected to other code segments or hardware circuits by sending and receiving information, data, arguments, parameters, or memory contents.

[0089] Furthermore, although the above embodiment describes an embodiment in which the information processing program 40 is pre-stored (installed) in the storage unit 33, the invention is not limited to this. The information processing program 40 may be provided in the form of being recorded on a recording medium such as a CD-ROM (Compact Disc Read Only Memory), DVD-ROM (Digital Versatile Disc Read Only Memory), and USB (Universal Serial Bus) memory. The information processing program 40 may also be provided in the form of being downloaded from an external device via a network. The information processing program 40 can also be provided as a program product. A program product includes any form of product for providing a program. For example, a program product includes a program provided via a network such as the Internet, and a non-temporary computer-readable recording medium such as a CD-ROM or DVD on which the program is stored.

[0090] The following further notes are disclosed regarding the above embodiments. (Note 1) An information processing device comprising a processor, the processor derives information representing one or more candidate reference planes using three-dimensional point cloud data obtained by photographing a reference plane having a portion that overlaps with the subject and the radiation detector along the irradiation direction of the radiation irradiated from the radiation source, determines the validity of the derived candidate reference planes, and derives at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation irradiated from the radiation source with respect to the candidate reference planes using the information representing the candidate reference planes according to the result of the validity determination.

[0091] (Note 2) The information processing apparatus according to Note 1, wherein the processor determines the validity based on an index value using far-field data, which is data of points located further away from the candidate reference plane in the three-dimensional point cloud data, with respect to the sensor used to acquire the three-dimensional point cloud data.

[0092] (Note 3) The information processing device according to Note 2, wherein the index value is the ratio of the number of far-field data to the number of points included in the three-dimensional point cloud data used to derive the candidate reference surface.

[0093] (Note 4) The information processing device described in Note 2, wherein the index value is the number of remote data points.

[0094] (Note 5) The processor is an information processing device according to Note 1 that determines the validity based on the derived distance.

[0095] (Note 6) The information processing apparatus according to Note 5, wherein the processor determines that the candidate reference surface with the longest derived distance among a plurality of candidate reference surfaces is valid.

[0096] (Note 7) The information processing apparatus according to any one of Notes 1 to 6, wherein the processor repeatedly performs the process of determining the validity while changing the candidate reference surface until it is determined that the candidate reference surface is valid.

[0097] (Note 8) The information processing apparatus according to Note 7, wherein when the number of executions of the process for determining validity reaches the upper limit, the processor derives at least one of the distance and the angle of incidence using information representing the candidate of the reference surface with the highest validity among the plurality of candidate reference surfaces for which the validity has been determined.

[0098] (Note 9) The information processing apparatus according to Note 7, wherein the processor does not perform the process of deriving at least one of the distance and the angle of incidence when the number of executions of the process for determining validity reaches the upper limit.

[0099] (Note 10) The information processing apparatus according to any one of Notes 7 to 9, wherein when determining the validity of the n (where n is an integer of 2 or more)th candidate reference surface, the processor determines the object to be determined for validity based on the similarity with the first to n-1 candidate reference surfaces.

[0100] (Note 11) The information processing apparatus according to Note 10, wherein when the validity of the nth candidate reference surface is determined, the candidate reference surface that is determined not to be similar to the first to the (n-1)th candidate reference surfaces is the subject of the validity determination.

[0101] (Note 12) The information processing apparatus according to Note 10 or Note 11, wherein the processor uses the cosine similarity of the normal vectors of the candidate reference planes or the absolute value of the difference of the constant term in the expression representing the candidate reference plane as the similarity.

[0102] (Note 13) The information processing apparatus according to Note 10 or Note 11, wherein the processor uses the cosine similarity of a four-dimensional vector using the coefficients of the formula representing the candidate reference surface as the similarity.

[0103] (Note 14) The information processing apparatus according to any one of Notes 1 to 13, wherein the processor derives the distance by deriving the intersection point of a straight line along the irradiation direction and a candidate reference plane in three-dimensional space.

[0104] (Note 15) The information processing apparatus according to any one of Notes 1 to 14, wherein the processor derives the incident angle using the normal vector of the candidate reference plane and an inverse trigonometric function.

[0105] (Note 16) The processor is an information processing device according to any one of Notes 1 to 15, which uses a regression algorithm to derive information representing the candidate reference surface.

[0106] (Note 17) An information processing method comprising an information processing device equipped with a processor, wherein the processor derives information representing one or more candidate reference planes using three-dimensional point cloud data obtained by photographing a reference plane having a portion that overlaps with the subject and the radiation detector along the irradiation direction of the radiation irradiated from the radiation source, determines the validity of the derived candidate reference planes, and uses the information representing the candidate reference planes according to the result of the validity determination to derive at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation irradiated from the radiation source with respect to the candidate reference plane.

[0107] (Note 18) An information processing program for causing the processor of an information processing device equipped with a processor to perform the following processes: derive information representing one or more candidate reference planes using three-dimensional point cloud data obtained by photographing a reference plane having a portion that overlaps with the subject and the radiation detector along the irradiation direction of the radiation irradiated from the radiation source; determine the validity of the derived candidate reference planes; and derive at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation irradiated from the radiation source with respect to the candidate reference planes using the information representing the candidate reference planes according to the result of the validity determination.

[0108] The disclosure of Japanese Patent Application No. 2025-017423, filed on 5 February 2025, is incorporated herein by reference in its entirety. Furthermore, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated as being incorporated by reference.

Claims

1. An information processing device comprising a processor, the processor derives information representing one or more candidate reference planes using three-dimensional point cloud data obtained by photographing a reference plane having a portion that overlaps with the subject and the radiation detector along the irradiation direction of the radiation irradiated from the radiation source, determines the validity of the derived candidate reference planes, and derives at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation irradiated from the radiation source with respect to the candidate reference planes using the information representing the candidate reference planes according to the result of the validity determination.

2. The information processing apparatus according to claim 1, wherein the processor determines the validity based on an index value using far-field data, which is data of points located further away from the candidate reference plane among the three-dimensional point cloud data, with reference to the sensor used to acquire the three-dimensional point cloud data.

3. The information processing apparatus according to claim 2, wherein the index value is the ratio of the number of far-field data to the number of points included in the three-dimensional point cloud data used to derive the candidate reference surface.

4. The information processing apparatus according to claim 2, wherein the index value is the number of remote data points.

5. The information processing apparatus according to claim 1, wherein the processor determines the validity based on the derived distance.

6. The information processing apparatus according to claim 5, wherein the processor determines that the candidate reference surface with the longest derived distance among a plurality of candidate reference surfaces is valid.

7. The information processing apparatus according to claim 1, wherein the processor repeatedly performs the process for determining the validity while changing the candidate reference surface until it is determined that the candidate reference surface is valid.

8. The information processing apparatus according to claim 7, wherein when the number of executions of the process for determining validity reaches the upper limit, the processor derives at least one of the distance and the angle of incidence using information representing the candidate of the reference surface with the highest validity among a plurality of candidate reference surfaces for which the validity has been determined.

9. The information processing apparatus according to claim 7, wherein the processor does not perform the process of deriving at least one of the distance and the angle of incidence when the number of executions of the process for determining validity reaches the upper limit.

10. The information processing apparatus according to claim 7, wherein when the processor determines the validity of the n (where n is an integer of 2 or more)th candidate reference surface, it determines the object to be determined for validity based on the similarity with the first to n-1 candidate reference surfaces.

11. The information processing apparatus according to claim 10, wherein when the processor determines the validity of the nth candidate reference surface, the candidate reference surface that is determined not to be similar to the first to the (n-1)th candidate reference surfaces is the subject of the validity determination.

12. The information processing apparatus according to claim 10, wherein the processor uses the cosine similarity of the normal vectors of the candidate reference planes or the absolute value of the difference of the constant term in the expression representing the candidate reference plane as the similarity.

13. The information processing apparatus according to claim 10, wherein the processor uses the cosine similarity of a four-dimensional vector using the coefficients of the formula representing the candidate reference surface as the similarity.

14. The information processing apparatus according to claim 1, wherein the processor derives the distance by deriving the intersection point of a straight line along the irradiation direction and a candidate reference plane in three-dimensional space.

15. The information processing apparatus according to claim 1, wherein the processor derives the incident angle using the normal vector of the candidate reference plane and an inverse trigonometric function.

16. The information processing apparatus according to claim 1, wherein the processor derives information representing the candidate reference surface using a regression algorithm.

17. An information processing method comprising an information processing device equipped with a processor, wherein the processor derives information representing one or more candidate reference planes using three-dimensional point cloud data obtained by photographing a reference plane having a portion that overlaps with the subject and the radiation detector along the irradiation direction of radiation irradiated from a radiation source, determines the validity of the derived candidate reference planes, and uses the information representing the candidate reference planes according to the result of the validity determination to derive at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation irradiated from the radiation source with respect to the candidate reference plane.

18. An information processing program for causing the processor of an information processing device equipped with a processor to perform the following processes: derive information representing one or more candidate reference planes using three-dimensional point cloud data obtained by photographing a reference plane having a portion that overlaps with the subject and the radiation detector along the irradiation direction of radiation irradiated from a radiation source; determine the validity of the derived candidate reference planes; and derive at least one of the distance between the radiation source and the radiation detector and the angle of incidence of the radiation irradiated from the radiation source with respect to the candidate reference planes using the information representing the candidate reference planes according to the result of the validity determination.

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