JP4823780B2 - Panoramic tomographic image generation apparatus and panoramic tomographic image generation program - Google Patents

Description

  The present invention relates to a panoramic tomographic image generation apparatus and a panoramic tomographic image generation program capable of obtaining a panoramic tomographic image having a thickness in a direction perpendicular to the body axis of a subject using projection data obtained by a two-dimensional detector. About.

  There is an X-ray measuring apparatus in which an X-ray source and a two-dimensional X-ray detector are installed at both ends of a support so as to face each other. As the shape of the column, there are a C shape, a U shape, a U shape, and the like. There are shapes that suspend the column from the ceiling, shapes that support the column from the floor, and shapes that attach the column to another column that stands on the floor. In addition, there is an X-ray measurement device in which an X-ray source and a two-dimensional X-ray detector are installed on a gantry so as to face each other. In these apparatuses, it is possible to perform X-ray measurement by rotating a support column or a gantry while rotating a pair of an X-ray source and a detector around the subject. Alternatively, the X-ray measurement can be performed while fixing the X-ray source and the detector and rotating the subject. There is CT measurement or cone beam CT measurement in which reconstruction calculation processing is performed on a series of measurement data obtained by these rotation measurements to obtain a three-dimensional image.

  A panoramic imaging principle that obtains a panoramic image of a specific tomographic plane by relatively moving an X-ray source and a film at a predetermined ratio is generally known. An X-ray measurement device that can set up an X-ray source and detector on a U-shaped support and rotate around the subject. It has a CT measurement mode and a panorama measurement mode. Japanese Patent Laid-Open No. 10-225455 discloses a technique for obtaining a CT image by performing measurement without moving the rotation center, and obtaining a panoramic image by performing measurement while moving the rotation center along the envelope in the panorama measurement mode. It is described in the publication. Further, Japanese Patent Laid-Open No. 4-145548 discloses a technique for obtaining a panoramic image by performing measurement without moving the rotation center, extracting predetermined data from a series of obtained data, and pasting them together. The photographing principle of this method is the same as the panoramic photographing principle using a film, except that a panoramic image of an arbitrary tomogram can be generated by selecting a data extraction interval and a shift amount after photographing. In addition, in Japanese Patent Laid-Open No. 4-145548, in order to remove the obstacle shadow from the panorama image of the subject, a panorama image of the obstacle shadow is created separately from the panorama image of the subject, and the panorama image of the obstacle shadow is set as the subject position. A method is described in which a blurred image when projected is estimated and the blurred image is subtracted from the panoramic image of the subject. Specifically, the blur image of the spine that overlaps the dental arch image is removed. Japanese Patent Laid-Open No. 4-145549 discloses a technique for obtaining a panoramic image of an inclined tomographic plane by setting several tomographic planes on a subject, obtaining panoramic images of the respective tomographic planes, and combining them. Yes.

Japanese Patent Laid-Open No. 10-225455 Japanese Patent Laid-Open No. 4-144548 Japanese Patent Laid-Open No. 4-145549

  In the apparatus of Japanese Patent Laid-Open No. 10-225455, in order to obtain a panoramic image, the center of the X-ray source and the detector needs to move on a complicated trajectory, and there is a problem that the structure of the apparatus becomes complicated. . As a result, it can be realized with a sitting-type device whose rotation axis is perpendicular to the floor surface, but it is extremely difficult to implement with a supine-type device whose rotation axis is parallel to the floor surface.

  Japanese Patent Application Laid-Open No. 4-145548 specifies that the obstruction shadow is a blurred image, and does not describe the case where the obstruction shadow is a clear image. If this method is applied to a clear obstacle shadow, a clear image is estimated instead of a blurred image when a panoramic image of the obstacle shadow is projected onto the subject position. As a result, it is difficult to obtain an accurate image, and a shift occurs when subtracting from the panoramic image of the subject. On the contrary, image quality deterioration such as enhancement of the edge of the obstacle shadow image occurs. For example, in an apparatus in which the distance between the X-ray source and the subject is about 300 mm and the distance between the subject and the detector is about 300 mm, since the subject is close to the X-ray source, the dentition and the head located in front of the head The enlargement rate differs greatly in the spine located behind. As a result, the vertebral image that becomes an obstacle shadow on the dentition to be observed becomes a blurred image as assumed in this publication. In an apparatus in which the distance between the X-ray source and the subject is about 800 mm and the distance between the subject and the detector is about 400 mm, the magnification of the dentition and the spine is not greatly different because the subject is away from the X-ray source. As a result, both are measured as clear images, and it is difficult to remove the obstacle shadow by the method of this publication.

  Japanese Patent Application Laid-Open No. 4-145549 is a technique for creating a curved tomographic image by partially cutting out and pasting a panoramic image of each cross section. Therefore, when using the obstacle shadow removal method described in Japanese Patent Laid-Open No. 4-145548, a failure shadow image corresponding to each cross section is created, and a blur image of the obstacle shadow when projected onto the subject position is estimated. There is a problem that the processing is complicated and difficult.

  The panoramic image obtained by the conventional technique has a thickness in a direction (depth direction) perpendicular to the body axis of the subject. However, since the panoramic tomographic image is an image of one section, it does not have a thickness in the depth direction. Therefore, the panoramic tomographic image is a clear image with a thin cross section, and the position of the case necessary for diagnosis is known and is effective when it is on the cross section. However, the position of the case is rarely known, and in many cases, the position is shifted from the cross section, resulting in a blurred image. In that case, since it is necessary to reacquire data in the prior art, there is a problem that the exposure of the subject increases.

  An object of the present invention is to provide an X-ray measurement apparatus capable of obtaining a panoramic tomographic image having a thickness in a direction perpendicular to the body axis of a subject (depth direction). In particular, data is acquired by a two-dimensional detector, and data used for tomographic processing is used for depth processing, thereby obtaining a panoramic tomographic image having a thickness in the depth direction without causing remeasurement or an increase in subject exposure. Make it possible.

  The above-described object is to provide an X-ray source that irradiates an X-ray to an inspection object, an X-ray detector that is installed facing the X-ray source and detects the X-ray, and the X-ray source and the X-ray detection A rotating means for rotating the container relative to the inspection object, and a plurality of points of interest located on the first orbit of the object in the space set on the inspection object, respectively. Means for calculating one normal, means for calculating a first position of the X-ray source corresponding to the point of interest based on the first normal, one point of interest and a rotation center point of the rotating means A means for calculating a line segment connecting the line segment, a means for identifying an intersection of the second trajectory of the object in the space set on the inspection object and the line segment, and a second of the intersection with respect to the second trajectory. A means for calculating a normal and corresponding to the intersection based on the second normal From means for calculating the second position of the X-ray source, first data detected by the X-ray detector with respect to the first position, and second data detected by the X-ray detector with respect to the second position This is achieved by an X-ray measuring apparatus having means for creating image data for one of the points of interest and creating panoramic image data by combining the image data corresponding to each of the plurality of points of interest.

  That is, the panoramic tomographic image generation apparatus of the present invention includes a subject holding unit, an X-ray source, an X-ray detector provided at a position facing the X-ray source with the subject holding unit interposed therebetween, and an X-ray A drive unit that rotationally drives the source and the X-ray detector around the subject holding unit, a curve representing the shape of the panoramic tomographic image generation region in the subject, the depth thickness of the panoramic tomographic image generation region, and the panoramic tomography The X-ray source and the X-ray source are rotated while the drive unit rotates the X-ray source and the X-ray detector with respect to the subject held in the subject holding unit. A control unit for acquiring a set of two-dimensional pixel data composed of a rotation axis direction based on X-rays detected by an X-ray detector at a rotation position and a direction perpendicular to the rotation axis direction, and a set of the acquired two-dimensional pixel data Storage unit to store and secondary stored in storage unit A processing unit that performs processing for generating a panoramic tomogram from a set of pixel data, and the processing unit is positioned on the normal line of the curve at the point of interest for each of a plurality of points of interest set at predetermined intervals on the curve. Calculated by adding pixel data based on X-rays generated from the X-ray source and detected by the X-ray detector through the point of interest in a predetermined angle range centered on the angular position of the X-ray source The depth direction for each of a plurality of points of interest in the depth direction set at predetermined intervals within the range set as the depth thickness on the line connecting the development center and the point of interest with the tomographic data at the point of interest X-ray detector generated from the X-ray source in a predetermined angle range centered on the angular position of the X-ray source located on a straight line passing through the point of interest and parallel to the normal line and passing through the point of interest in the depth direction X-rays detected in A plurality of tomographic data composed of the tomographic data for each point of interest in the depth direction obtained by adding pixel data based on the pixel data is added to calculate final tomographic data for each point of interest set on the curve The final tomographic data is pasted in the direction along the curve to generate a panoramic tomographic image.

  Further, the panoramic tomographic image generation method according to the present invention stores information based on the curve representing the shape of the panoramic tomographic image generation region in the subject and the depth thickness information of the panoramic tomographic image generation region input from the input device. The rotational axis direction based on the X-rays detected by the X-ray detector at each rotational position of the X-ray source while rotationally driving the X-ray source and the X-ray detector arranged with the subject sandwiched therebetween And a method of generating a panoramic tomographic image by processing a set of two-dimensional pixel data having a direction perpendicular to the rotation axis direction in the processing unit, wherein the processing unit includes a plurality of points of interest on the curve at predetermined intervals. For each point of interest, X-rays generated from the X-ray source in a predetermined angle range centered on the angular position of the X-ray source located on the normal line of the curve at the point of interest are detected through the point of interest. Based on X-rays detected by the instrument The tomographic data at the target point is calculated by adding pixel data, and the depth direction is set at a predetermined interval within the range set as the depth thickness on the line connecting the development center and the point of interest when obtaining the panoramic tomographic image. A plurality of points of interest are set, and for each of the plurality of points of interest in the depth direction, the angular position of an X-ray source located on a straight line passing through the point of interest in the depth direction and parallel to the normal is centered The pixel data based on the X-rays generated from the X-ray source in the predetermined angle range and detected by the X-ray detector through the point of interest in the depth direction is added to calculate tomographic data, and on the curve The tomographic data of the set point of interest and the tomographic data of the plurality of points of interest in the depth direction are added to calculate final tomographic data for each set point of interest set on the curve, and the final tomographic data is converted to the curve. In Cormorant by laminating in the direction to generate a panoramic tomographic image. This method can be executed by a computer program.

  JP-A-10-225455, JP-A-4-144548, and JP-A-4-145549 describe means for obtaining a panoramic tomographic image having a thickness in a direction perpendicular to the body axis of the subject. It has not been. Further, the present invention differs from Japanese Patent Laid-Open No. 10-225455 in the algorithm for creating a panoramic image, different from Japanese Patent Laid-Open No. 4-144548 in the algorithm for removing the shadow image, and is different from Japanese Patent Laid-Open No. 4-145549. The panoramic image creation algorithm is different.

  According to the present invention, a panoramic tomographic image having an arbitrary thickness in the depth direction of a subject can be obtained in a system in which an X-ray source and a detector move in an arbitrary trajectory. Thereby, it is possible to obtain a panoramic image having a thickness according to the application, such as a very thin and high-resolution image, an image having a thickness of a tooth or a jaw bone, and a thick image including a wide range of information.

Examples of the present invention will be described below.
FIG. 2 shows a side view of the X-ray measuring apparatus according to the present invention. The X-ray measurement apparatus includes an X-ray source 201, a detector 202, a support 203, a rotation device 204, a subject holding device 205, and a control processing device 206 in an X-ray tube 200. The X-ray source 201 and the detector 202 are installed on the column 203. As the support 203, a C-shaped arm, a U-shaped arm, a U-shaped arm, a gantry, or the like is used. There are a form in which the support 203 is suspended from the ceiling and a form in which the support 203 is supported from the floor. The support 203 is rotated by a rotating device 204. As a result, the X-ray source 201 and the detector 202 installed on the column 203 rotate around the subject 208 on the subject holding device 205 around the rotation axis 207. As the subject holding device 205, a chair or a bed is used. In FIG. 2, an example in which a U-shaped arm is hung from another support supported on the floor, and the X-ray source 201 and the detector 202 are rotated around a subject 208 sitting on a chair in a plane parallel to the floor surface. Show. There is also a form in which a U-shaped arm is supported on the floor and the periphery of the subject 208 sitting on a chair is rotated in a plane parallel to the floor surface. As shown in FIG. 3, the subject holding device is a bed 301, the rotating shaft 207 is parallel to the floor, and the X-ray source 201 and the detector 202 installed on the column 203 are lying on the bed. There is also a form that rotates around 208. The column 203 is a C-shaped arm in FIG. 3, but there is also a form in which it is a gantry. In these forms, it is possible to set the rotation axis 207 obliquely with respect to the axis of the subject 208 by moving both or one of the support and the subject holding device.

  X-rays generated from the X-ray source 201 are transmitted through the subject 208, converted into an electrical signal corresponding to the X-ray intensity by the detector 202, and input as measurement data to the control processor 206. The control processing device 206 controls the X-ray generation in the X-ray source 201, the acquisition of data in the detector 202, and the rotation of the column 203 in the rotating device 204. As a result, the X-ray measurement apparatus can perform rotation measurement for generating X-rays and acquiring measurement data while rotating the support column 203. The control processing device 206 performs preprocessing on the measurement data to obtain a projection image, executes panorama image creation processing to acquire a panoramic image, and executes reconstruction calculation processing to perform three-dimensional processing. A reconstructed image can be acquired. The control processing device 206 has storage means inside, and stores presence / absence of panorama processing, functions, parameters, conditions, etc. necessary for processing. As input means, key input from a keyboard, reading from a file, and replacement of a storage chip can be considered.

  As the detector 202, a two-dimensional detector is used. Examples of the two-dimensional detector include a planar X-ray detector, a combination of an X-ray image intensifier and a CCD camera, an imaging plate, a CCD detector, and a solid state detector. As a flat type X-ray detector, there is a combination of an amorphous silicon photodiode and a TFT, which are arranged on a square matrix and directly combined with a fluorescent plate. By using the two-dimensional detector, it is possible to acquire a panoramic image from data measured in a state where the relative position of the detector with respect to the X-ray source is fixed. In addition, since the detector is a two-dimensional detector that is perpendicular to the body axis and has a width in the direction perpendicular to the depth of the subject, the X-ray source and the detector can be moved at a constant speed on a simple concentric orbit. It is possible to acquire a panoramic tomographic image having a depth from the acquired data.

As the detector 202, a one-dimensional detector extending in a direction parallel to the rotation shaft 207 can be used. In this case, by adding a detector moving mechanism to the measuring device, it is possible to obtain a panoramic image from the data measured while placing the detector at a position u _i obtained according to the procedure of FIG.

  An X-ray filter 210 can be installed between the X-ray source 201 and the detector 202. Thereby, the irradiation range of X-rays can be limited and the exposure dose can be reduced. The filter 210 is made of a metal such as aluminum, copper or brass, ceramic, resin or the like.

  The control processing device 206 includes, for example, means shown in FIG. 12 in order to execute panorama processing shown in FIG. Each means includes target trajectory / depth thickness setting means 1201 for setting the target trajectory and depth thickness, target trajectory focus point setting means 1202 for setting a focus point on the target trajectory, development center position and focus Development center for finding a straight line connecting points—a point-of-interest setting unit 1203, Development center—a center of interest for setting a point of interest on a target trajectory on the target trajectory on the target point line—a point-of-interest setting unit 1204 on the target point line Normal line setting means 1205 for obtaining a normal line at each point of interest, an X-ray source on a straight line passing through the point of interest and a position on the detector in a predetermined angle range centered on the X-ray source position on each normal line X-ray source / detector position setting means 1206, tomographic data calculation means 1207 for obtaining tomographic data by weighted addition of projection data at positions on each detector, panoramic data for creating a panoramic image by combining the tomographic data Calculation means 1208 and data storage unit 1209.

FIG. 9 shows the entire procedure from measurement to obtaining a panoramic image. First, measurement data is obtained by rotational measurement (S901) (S902). Now, as shown in FIG. 13, it is assumed that a two-dimensional detector 202 is used in which X-ray detection elements for m pixels in the rotation direction, n pixels in the rotation axis direction, and a total of m × n pixels are arranged. In addition, the origin is set at the lower left corner of the two-dimensional detector, the pixel number in the rotation direction is expressed as _nx , the pixel number in the rotation axis direction is expressed as _ny, and the column supporting the X-ray source and the two-dimensional detector is rotated. angle is denoted pixel positions on the two-dimensional detector (n _x, n _y) of the output signal from the detector elements of _{Sig (θ, n x, n} y) and the time of theta, the rotation angle theta _1, theta _2, ..., if incorporating detection signal of each pixel of the two-dimensional detector when theta _n, measurement data obtained by the rotation measurement is a set of _{Sig (θ, n x, n} y). _{However, θ = θ 1, θ 2} , ..., θmax; n x = 1,2, ..., m; n y = 1,2, ..., a n.

When the sensitivity of the detector and the thickness of the X-ray filter differ depending on the position, the measurement data has an intensity distribution. In that case, the X-ray is irradiated and measured without setting the subject to obtain the intensity distribution data, the measurement is performed without irradiating the X-ray to obtain the offset data, and the measurement data and the intensity distribution data are respectively used. After subtracting the offset data, the intensity correction processing is performed by dividing the measurement data by the intensity distribution data (S903). Further, a logarithmic conversion process of logarithmically converting the intensity correction data and multiplying by -1 is performed (S904) to obtain projection data (S905). Projection data, measured data _{Sig (θ, n x, n} y) corresponds _{to, D (θ, n x,} n y) is obtained as a. _{However, θ = θ 1, θ 2} , ..., θmax; n x = 1,2, ..., m; n y = 1,2, ..., a n.

  The measurement data and projection data are temporarily stored in the data storage unit 1209, and the process of creating a panoramic tomographic image of the present invention is executed on the projection data stored in the data storage unit 1209. The intensity correction process and the logarithmic conversion process may be executed by an arithmetic unit mounted inside the detector. Using the projection data, panorama processing described later is performed (S906), and a panoramic image is obtained (S907). The panoramic image is smoothed (S908) to obtain a smoothed image (S909). After the smoothed image is multiplied by a coefficient, a weighted difference process is performed to make a difference from the panoramic image (S910), and a differential panoramic image is obtained (S911). By the smoothing process and the difference process, it is possible to remove unevenness in intensity in the panoramic image, and an image quality with high contrast and clear edges can be obtained. Particularly, when a panoramic image includes an obstacle shadow such as a spine, the obstacle shadow appears as a blurred image by the tomographic processing, so that the effect of improving the image quality by removing the intensity unevenness is great. If there is no unevenness in intensity in the panoramic image, smoothing and difference processing are unnecessary, and the processing can be speeded up.

  FIG. 1 shows a panorama processing procedure according to the present embodiment. Here, the object is assumed to be a dentition as an example, and will be described with reference to FIGS. 4, 5 and 6 show the same plane. A plane perpendicular to the rotation axis is shown, and the intersection with the rotation axis is set at the center of the XY axis. In the following, processing of measurement data obtained from a detection element array of a two-dimensional X-ray detector that intersects the plane of FIG. 4, for example, one detection element indicated by an arrow in FIG. 13 will be described. The measurement data obtained from the detection element arrays are similarly processed, and the final panorama image is calculated by connecting the panorama images corresponding to the detection element arrays.

  First, on the plane shown in FIG. 4, a development center position 400 that is the center of development when a panoramic image is obtained is set. The development center position can be arbitrarily set, but the processing can be simplified by making it coincide with the rotation axis. In FIG. 4, the development center position is set to the rotation axis, that is, the origin of the XY axis. The development center position may be set as a rotation axis by default in the apparatus without being set every time, and may be changed only when necessary.

  Next, the target trajectory and depth thickness L are set on the plane shown in FIG. This process is performed by the target trajectory / depth thickness setting means 1201. The target trajectory is a dentition shape in the present embodiment, but a standard shape may be obtained from a known simulated subject or clinical data and applied. Alternatively, the shape may be designated by designating several points or drawing a line on FIG. Alternatively, a CT image of the same subject may be pasted on the surface of FIG. 4 and the shape may be designated on FIG. Alternatively, the shape may be automatically set by attaching a CT image of the same subject on the surface of FIG. 4, identifying the target on FIG. 4, and extracting the center line. A numerical value may be input for the depth thickness. For example, in the case of a dentition, it is about 10 mm. The thickness may be changed on the trajectory of the object. For example, the thickness may be 3 mm in the front tooth region and 15 mm in the back tooth region. Alternatively, when drawing the trajectory of the object on FIG. 4, the thickness may be specified by drawing the front and the back. The depth thickness can be specified by a width centered on the target trajectory, and can also be specified by a distance from the front or rear trajectory.

  In FIG. 10, as an input screen for the target trajectory and depth thickness, a CT image of the same subject is pasted on the surface of FIG. 4, the shape is designated on FIG. An example of setting By displaying the CT image superimposed on the input screen, the relationship between the actual dentition and the position and size of the input dentition is clarified, and consistency can be ensured. On the CT image 1001, the field of view 1002 is circular. For example, it is assumed that teeth 1004 are arranged in the head 1003 and the target object is a dentition. The target trajectory is set by setting a plurality of points 1005 indicated by black circles on the CT image. Next, an approximate function 1006 passing through these points is calculated by taking the X axis in the horizontal direction and the Y axis in the vertical direction on the image and using, for example, the least square method. As an approximate function, all functions such as a polynomial, an ellipse, a hyperbola, and a combination of a plurality of functions are conceivable. By using the approximate function, even if the target object has a very complicated shape, a normal line can be uniquely obtained as a mathematical expression, and a panoramic image can be created. For example, the depth thickness can be set by designating a line segment as indicated by an arrow 1007 on the CT image 1001.

Here, a case will be described in which the trajectory in front of the target is set in FIG. 4 and the depth is set by the distance from the trajectory in front. A function f (401) approximating the target trajectory is set on the plane shown in FIG. 4 (S101). A first point of interest P ₁ (402) is set on the approximate function f (S102), and a normal h ₁ (403) of the approximate function f at the _first point of interest P ₁ is obtained (S103). The point of interest on the approximate function f is set by the point-of-interest setting unit 1202 on the target trajectory. The target point setting unit 1202 on the target trajectory sets, for example, a target point on the target trajectory for each distance d along the trajectory. The normal h ₁ of the approximate function f at the _first point of interest P ₁ is obtained by the normal setting means 1205. Next, determine the position u ₁ of on the detector 405 which faces the X-ray source position S ₁ normals h ₁ passes (404) through which the normal line h ₁ (406). The position u ₁ on the detector is obtained by the X-ray source / detector position setting means 1206. X-ray source / detector position setting means 1206 is the distance from the rotation center to the X-ray source, the distance from the rotation center to the detector, the relative positional relationship between the X-ray source, the rotation center, and the detector. Using the known information unique to the apparatus such as the arrangement of the detection elements, the dimensions of the individual detection elements, and the position information and normal information of the point of interest, the rotational angle position of the X-ray source and the detector 405 The position u ₁ (406) of is calculated. If the rotational angle position θ of the X-ray source and the position u ₁ on the detector are specified, necessary data can be extracted from the above-mentioned projection data set D (θ, _nx , _ny ).

Next, the X-ray source position S ₁ is swung back and forth, and projection data at a position 409 where a straight line connecting the X-ray source and the first point of interest P ₁ passes on the detector 408 facing each X-ray source position 407. D is extracted (S104 to S107). This process is also performed by the position setting means 1206 on the X-ray source / detector, and a plurality of sets of the rotational angle position θ of the X-ray source and the position u ₁ on the detector are obtained, and a plurality of sets corresponding to each set are obtained. Projection data D (θ, _nx , _ny ) is extracted. In the figure, M indicates the number of forward and backward data centered on the X-ray source position S ₁ among the plurality of projection data. That is, the number of projection data is M at the front and rear, and the total of the projection data is (2M + 1).

Tomographic data calculating means 1207 obtains the tomographic data Q ₁ in the first focus point P ₁ the projection data obtained by adding weighted (S108). By performing tomographic processing that adds weighted projection data when the X-ray source position S ₁ is swung back and forth, the image on the point of interest at the focal position remains clear and the image other than on the point of interest is blurred. be able to. As a result, the obstacle shadow can be blurred and removed. For example, in order to erase the spine that is an obstruction shadow, when the distance between the X-ray source and the subject is about 800 mm and the distance between the subject and the detector is about 400 mm, the X-ray source position is about ± 10 °. Projection data in the angular range is required for tomographic processing.

Next, as shown in FIG. 5, on the straight line 502 connecting the development center position 400 and the first point of interest P ₁ (402), the second point of interest P at an arbitrary distance from the first point of interest P _{1. 2} Set (503) (S109). In this process, a straight line connecting the development center position and the point of interest is obtained by the development center-point-of-interest line setting means 1203, and then, from the point of interest on the target trajectory on the straight line by the point-of-interest setting means 1204 on the development center-point of interest line. This is done by setting a point of interest at an arbitrary distance d ′.

Next, the position S ₂ (505) of the X-ray source passing through the second focus point P ₂ and passing through the second normal h ₂ (504) whose inclination is equal to the normal h ₁ (403) is obtained and opposed. A second position u ₂ (507) through which the second normal h ₂ passes on the detector 506 is obtained. Further, as shown in FIG. 6, the X-ray source position S ₂ is swung back and forth, and the X-ray source 601 and the second point of interest P ₂ (503) on the detector 602 facing each X-ray source position 601. Projection data D at the second position 603 through which the straight line connecting the two passes is extracted (S110 to S114). These processes are performed by the position setting means 1206 on the X-ray source / detector, and a plurality of projection data D corresponding to the determined set of the rotational angle position θ of the X-ray source and the position u ₁ on the detector. (θ, _nx , _ny ) is extracted.

Then, as in the case of tomographic data Q _1, tomographic data calculation means 1207 obtains the tomographic data Q ₂ in the projection data obtained by adding the weighted second focus point P ₂ (S115). Tomographic data calculating means 1207 obtains the tomographic data W ₁ obtained by adding weighted tomographic data Q ₂ in the tomographic data Q ₁ and the second focus point P ₂ in the further first focus point P ₁ (S116). Thereby, tomographic data having a thickness in the depth direction can be obtained. In the figure, L indicates the depth thickness. That is, the number of tomographic data Q added to obtain the tomographic data W is L / d ′.

A first focus point P ₁ is moved on the approximation function by a predetermined distance d, similarly, obtains tomographic data Q ₂ in the tomographic data Q ₁ and the second focus point P ₂ in the first focus points P ₁ The weighted tomographic data W ₂ is obtained. This is repeated until the end of the target trajectory, and the panorama data calculation means 1208 creates a panoramic image by pasting the tomographic data W _i (i = 1 to N) (S117). In the figure, N indicates the number of data points in the horizontal direction in the panoramic image. Thereby, a panoramic image having a thickness in the depth direction can be obtained.

  A trajectory 508 along which the second point of interest moves is similar to the approximate function 401, which is a trajectory along which the first point of interest moves, centered on the development center position. As a result, when adding in the depth direction, data can be added without causing a positional shift in the developing direction as viewed from the developing center, so that a highly accurate panoramic image can be obtained. Moreover, by adding data in the depth direction, noise can be reduced and a panoramic image with a high S / N can be obtained.

  As with the second point of interest, the third, fourth,..., Jth point of interest can be set in the depth direction by setting the third, fourth,. A panoramic image with a thickness of can be obtained. At this time, the depth d ′ for moving each point of interest on the straight line 502 is set at an interval equivalent to the distance d for moving the first point of interest on the approximate function f (x) (401). A panoramic image having a resolution equivalent to that in the horizontal direction can be obtained.

Another embodiment is shown. FIG. 7 shows the procedure. As shown in FIG. 8, in the case of the target trajectory for the shape of the dentition, that is, in this embodiment, the shape of the dentition is set on the input screen (S701), and the function f (x) ( 401) sets the _first point of interest P ₁ (402) on (S702). A normal h ₁ (403) of the approximate function f at the _first point of interest P ₁ is calculated (S703), and a first X-ray source position S ₁ (404) through which the normal passes is obtained (S704). At the first point of interest P ₁ (402), the first X-ray source position S ₁ (404) and the first point of interest on the detector 405 facing the first X-ray source position S ₁ (404). A first position u ₁ (406) through which a straight line 403 connecting the points P ₁ (402) passes is obtained (S705). Each X-ray source position is obtained by shaking the X-ray source back and forth (S706).

Next, on the straight line 502 connecting the development center position 400 and the first focus point P ₁ (402), the second focus point P ₂ (503) at an arbitrary distance from the first focus point P ₁ (402). Is set (S707). In the second focused point P ₂ (503), on the detector 405 opposite the first X-ray source position S ₁ (404), the first X-ray source position S ₁ and (404) second focus of A second position u ₂ (802) through which a straight line 801 connecting the points P ₂ (503) passes is obtained. Similarly, at the third, fourth,... Points of interest, on the first detector 405 facing the first X-ray source position, the first X-ray source and the third, fourth,. The position through which the straight line connecting the points of interest passes is obtained (S708). Data D at each position is extracted (S709), and data R subjected to weighted addition processing is obtained (S710). This makes it possible to continuously extract the first, second,... Data from the same image data, thereby reducing the number of times image data is read and speeding up the processing.

The X-ray source positions each X-ray source position obtained by shaking back and forth, the same processing and weighted addition processing data R obtained by performing obtaining tomographic data Q ₁ in (S711). The first point of interest P ₁ is moved by a predetermined distance d on the approximate function f, and the tomographic data Q ₂ is similarly obtained. This is repeated to the end of the target trajectory, and the tomographic data Q _i (i = 1 to N) is pasted to create a panoramic image (S712). Thereby, a panoramic image having a thickness in the depth direction can be obtained.

  FIGS. 1 and 7 show an example in which when the X-ray source is moved back and forth, the number of data before and after is made equal, and the same number of data is taken at all X-ray positions. Thereby, processing can be simplified and speeded up. It is also possible to vary the number of data depending on the X-ray source position. For example, the number of data is increased when the obstacle shadow exists, and the number of data is decreased when it does not exist. As a result, it is possible to reduce the number of data used in the processing and speed up the processing while maintaining the effect of removing the obstacle shadow. It is also possible to vary the number of data before and after. For example, when the same number of data does not exist at the end of the target trajectory, the existing data is used for processing. Thereby, a wide range of panoramic data can be obtained.

FIG. 11 shows an example of weights in the addition process. In the addition process, the added data is divided by the sum of the weights and normalized. In FIG. 11, for example, it is assumed that the weight for the reference data is 1.0. The reference data is, for example, projection data at the X-ray source position S ₁ in a tomographic process in which projection data when the X-ray source position S ₁ is shaken back and forth is added with weight. Alternatively, the tomographic data Q ₁ to definitive first target point, and fault data Q ₂ in the second point of interest, the tomographic data Q ₃ in the third focus point, the tomographic data W ₁ a ... plus weighted Is obtained, the tomographic data Q1 at the _first point of interest is used as reference data.

  In the example of FIG. 11 (a), all the weights are 1.0. This is a general addition average, the setting of the weight is simple, the calculation is simple, and the speed can be increased. FIG. 11B shows an example in which the weight for the reference data is 1.0, and the weight decreases at a certain rate as the distance from the reference data increases. FIG. 11 (c) shows an example in which the weight for the reference data is 1.0, and the weight decreases smoothly as the distance from the reference data increases. For example, a sin function or a hyperbola can be considered. 11 (b) and 11 (c) are weights emphasizing the reference data, and a natural image can be obtained as compared with FIG. 11 (a). In FIG. 11 (c), the change in weight is smoother than that in FIG. 11 (b), so that a more natural image can be obtained. In FIG. 11, it is assumed that the number of data before and after the reference data is the same, and the weights are symmetrical. When the number of data before and after is different, the change rate of the weight may be different before and after the reference data so that the weight is 0 in the first and last data. Even if the number of data before and after is the same, the rate of change in weight may be different before and after the reference data. By changing the rate of change, it becomes possible to emphasize or weaken the data to be added, and the effect of tomographic processing can be enhanced.

  As described above, the projection data used when obtaining the tomographic data of the second, third, and fourth points of interest can be shared with the projection data used when obtaining the tomographic data of the first point of interest. That is, projection data necessary for depth processing can be shared with projection data used for tomographic processing necessary for obtaining a basic panoramic image. Accordingly, it is possible to obtain a panoramic tomographic image having a thickness in the depth direction without causing remeasurement or an increase in exposure of the subject due to the depth processing.

  If the obtained panoramic image is blurred, it is possible to obtain a high-accuracy panoramic image by resetting the approximation function f and recreating the panoramic image. In this case, since reprocessing can be performed using already measured data, it is possible to obtain a high-accuracy panoramic image without causing remeasurement or an increase in subject exposure.

  In the apparatus of FIGS. 2 and 3, the X-ray source 201 and the detector 202 are fixed so as to oppose each other by a support column 203, and are moved concentrically by a rotating device 204. However, if the projection data D exists at the position u on the detector shown in FIGS. 1 and 7, the X-ray source and the detector do not need to face each other, and one is arranged at a position shifted from the front of the other. Alternatively, the X-ray source and the detector may be tilted, and neither of them needs to move on a concentric circle. That is, no matter how the X-ray source 201 and the detector 202 move during measurement, a panoramic tomographic image having a thickness can be acquired using this method.

  Furthermore, if the projection data D exists at the position u shown in FIGS. 1 and 7, the detector need not be two-dimensional. That is, by moving the X-ray source 201 and the detector 202 to positions where necessary projection data is measured at the time of measurement, a panoramic tomographic image having a thickness can be acquired using this method.

The figure which shows an example of the panorama processing procedure which concerns on this invention. Schematic which shows an example of an X-ray measuring device. Schematic which shows the other example of an X-ray measuring device. Explanatory drawing of the panorama process which concerns on this invention. Explanatory drawing of the panorama process which concerns on this invention. Explanatory drawing of the panorama process which concerns on this invention. The figure which shows the example of another panorama processing procedure which concerns on this invention. Explanatory drawing of the panorama process which concerns on this invention. The figure which shows the whole procedure from a measurement to obtaining a panoramic image. The figure which shows the example which sets the trajectory and depth thickness of the target object using CT image. The figure which shows the example of the weight in an addition process. The figure which shows the structural example of a control processing apparatus. Explanatory drawing of a two-dimensional detector.

Explanation of symbols

201: X-ray source, 202: detector, 203: support, 204: rotating device, 205: subject holding device, 206: control processing device, 207: rotating shaft, 208: subject, 210: filter

Claims (11)

A subject holding unit;
An X-ray source;
An X-ray detector provided at a position facing the X-ray source across the subject holding unit;
A drive unit that rotationally drives the X-ray source and the X-ray detector around the subject holding unit;
A setting unit for setting a curve representing the shape of the panoramic tomographic image generation region in the subject, a depth thickness of the panoramic tomographic image generation region, and a development center when obtaining the panoramic tomographic image;
While the X-ray source and the X-ray detector are rotationally driven by the driving unit with respect to the subject held by the subject holding unit, the X-ray detector at each rotational position of the X-ray source A control unit that acquires a set of two-dimensional pixel data including a rotation axis direction based on the detected X-ray and a direction perpendicular to the rotation axis direction;
A storage unit for storing a set of the two-dimensional pixel data;
A processing unit that performs a process of generating a panoramic tomogram from a set of two-dimensional pixel data stored in the storage unit,
The processing unit, for each of a plurality of points of interest set at predetermined intervals on the curve, in a predetermined angle range centered on an angular position of the X-ray source located on a normal line of the curve at the point of interest. Tomographic data at the point of interest calculated by adding pixel data based on X-rays generated from the X-ray source and detected by the X-ray detector through the point of interest, the development center, and the point of interest On a straight line passing through the point of interest in the depth direction and parallel to the normal line for each of a plurality of points of interest in the depth direction set at predetermined intervals within the range set as the depth thickness on the line connecting Pixel data based on X-rays generated from the X-ray source and detected by the X-ray detector through a point of interest in the depth direction in a predetermined angle range centered on the angular position of the X-ray source located at Addition processing A plurality of tomographic data composed of the tomographic data for each point of interest in the depth direction obtained through the above process is added to calculate final tomographic data for each point of interest set on the curve, and the final tomographic data is A panoramic tomographic image generation apparatus that performs processing for generating a panoramic tomographic image by pasting in a direction along the curve.   2. The panoramic tomographic image generation device according to claim 1, wherein the processing unit sets a point of interest setting means for setting the point of interest on the curve, and a development center-point of interest line setting for obtaining a straight line connecting the development center and the point of interest. Means for setting the point of interest in the depth direction at a predetermined distance from the point of interest on the curve on the center of development-the point of interest; means for setting the point of interest on the point of interest line, the normal of the curve at each point of interest X-rays for determining positions on the X-ray source and the X-ray detector on a straight line passing through the point of interest in a predetermined angle range centered on the X-ray source position on each normal line Source / detector position setting means, tomographic data calculation means for obtaining the tomographic data by weighted addition of pixel data at positions on the respective detectors, and a panorama image by combining the tomographic data to create the panoramic image Panoramic tomographic image generation apparatus characterized by having a Madeta calculating means.   2. The panoramic tomographic image generation apparatus according to claim 1, wherein the X-ray detector is a two-dimensional detector.   The panoramic tomographic image generation device according to claim 1, wherein the setting of the curve representing the shape of the panoramic tomographic image generation region is performed by calculating an approximate function passing through a plurality of coordinate points input on the input screen. A featured panoramic tomographic image generator.   The panoramic tomographic image generation device according to claim 1, wherein the depth thickness differs according to a position on the curve.   The panoramic tomographic image generation device according to claim 1, wherein the development center is set in advance in the device.   2. The panoramic tomographic image generation device according to claim 1, wherein the addition process for calculating tomographic data of the point of interest and / or the addition process for calculating final tomographic data of the point of interest set on the curve is a weighted addition process. A panoramic tomographic image generating apparatus characterized by the above.   2. The panoramic tomographic image generation device according to claim 1, wherein the processing unit smoothes the generated panoramic tomographic image to generate a smoothed image, and the smoothed image multiplied by a coefficient is generated from the generated panoramic tomographic image. A panoramic tomographic image generation apparatus characterized by performing a weighted difference process for differentiating. Based on the curve representing the shape of the panoramic tomographic image generation region in the subject input from the input device and the depth thickness information of the panoramic tomographic image generation region, the subject is stored in the storage unit. A rotational axis direction based on the X-rays detected by the X-ray detector at each rotational position of the X-ray source and a direction perpendicular to the rotational axis direction while rotationally driving the arranged X-ray source and X-ray detector A program for causing a computer to execute a method of generating a panoramic tomographic image by processing a set of two-dimensional pixel data comprising:
In the computer,
Setting a plurality of points of interest at predetermined intervals on the curve;
For each point of interest,
Generated from the X-ray source in a predetermined angle range centered on the angular position of the X-ray source located on the normal line of the curve at the point of interest, and detected by the X-ray detector through the point of interest. A step of adding pixel data based on X-rays to calculate tomographic data at the point of interest;
A step of setting a plurality of points of interest in the depth direction at predetermined intervals within a range set as the depth thickness on a line connecting the development center when obtaining the panoramic tomographic image and the point of interest;
For each of a plurality of points of interest in the depth direction, the X in a predetermined angle range centered on an angle position of the X-ray source located on a straight line passing through the points of interest in the depth direction and parallel to the normal line A step of calculating tomographic data by adding pixel data based on X-rays generated from a radiation source and detected by the X-ray detector through a point of interest in the depth direction;
Calculating the final tomographic data for each point of interest set on the curve by adding the tomographic data of the point of interest set on the curve and the tomographic data of the plurality of points of interest in the depth direction;
A program for executing a step of generating a panoramic tomographic image by pasting the final tomographic data in a direction along the curve.   10. The program according to claim 9, wherein the addition process in the step of calculating tomographic data at the point of interest and / or the addition process in the step of calculating final tomographic data of the point of interest set on the curve is a weighted addition process. A program characterized by that. The program according to claim 9, further comprising: a step of smoothing the generated panoramic tomographic image to generate a smoothed image, wherein the computer smoothes the smoothed image multiplied by a coefficient from the generated panoramic tomographic image. A program for executing a step of performing weighted difference processing.

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