JP2005021675A - Tomograph apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of a false image of a reconstruction image by realizing strict calibration without depending on the shape of a track and to efficiently obtain a required image by enabling a process for calibration to be performed with little labor. <P>SOLUTION: Projection images of a calibration phantom are picked up and stored (S1). Three-dimensional position information on an X-ray tube and a plane detector is obtained from the projection images and three-dimensional arrangement information on markers inside the calibration phantom (S2). Three-dimensional position information is obtained for all projection images (S3), and stored in a three-dimensional position information storage unit (S4). Projection images of an object under examination are picked up by following the same tracks and the same sequence as when radiographing the calibration phantom (S5). Radiographic data of the projection images is read. A reconstructing calculation is carried out for the object based on the three-dimensional position information on the X-ray tube and the plane detector relative to the calibration phantom, to create tomograms or three-dimensional volume data of a selected site of the object (S6). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is used in the medical field and the industrial field, such as an X-ray fluoroscopic table, a C-arm apparatus, an X-ray CT, and a general imaging apparatus, The surface detection means having a plurality of pixels arranged in an array so as to detect the electromagnetic wave transmitted through the subject is disposed opposite to the irradiation means with the sample interposed therebetween, and the irradiation means and the surface detection means are moved in conjunction with each other. The moving means and the moving means to irradiate an arbitrary subject with electromagnetic waves from different directions to obtain a projected image of the subject, reconstruct the projected image of the subject, The present invention relates to a tomographic apparatus including an image creating means for creating a tomographic image and / or a three-dimensional image.

  In this type of tomography apparatus, it is necessary to perform maintenance and calibration of the apparatus, for example, during imaging of a subject, during periodic inspections, or during maintenance inspections such as occurrence of a failure. Therefore, what is conventionally disclosed in Patent Document 1 is known.

According to this conventional example, the calibration phantom is placed on the top plate on which the subject is placed, the irradiation means and the surface detector are scanned once by the scanning means, and the projection line of the rotating tomographic axis is obtained from the obtained projection image. It is a requirement to prevent the generation of false images in the tomographic image, and the existence of the irradiation means and the surface detector on the exact circular orbit around the determined rotational tomographic axis, and the projection line of the rotational tomographic axis The surface detector is moved and adjusted so that a predetermined pixel column of the surface detector matches the above.
JP-A-2003-61944

  However, in the case of the conventional example, when the orbits of the irradiation means and the surface detector are slightly deviated from the exact circular orbit around the rotational tomographic axis, exact calibration is impossible. Further, in order to obtain the projection line of the rotating tomographic axis, it is necessary to rotate at least 180 ° or more. For example, even when the scanning range is narrow such as 40 °, a wide range of scanning must be performed, and calibration is performed. There was a drawback that it took time.

  Further, finally, the movement of the surface detector must be adjusted, and there is a drawback that a great deal of labor is required to obtain a necessary image.

  The present invention has been made in view of the above points, and performs strict calibration to prevent generation of a false image, and also enables processing for calibration to be performed with less effort. The purpose is to be able to efficiently obtain.

  In order to achieve the above object, the present invention has the following configuration.

  That is, the invention according to claim 1 is configured to irradiate a subject with a penetrating electromagnetic wave, and to dispose the electromagnetic wave transmitted through the subject, disposed opposite the irradiation unit with the subject interposed therebetween. A surface detection unit having a plurality of pixels arranged in an array so as to detect, a moving unit that moves the irradiation unit and the surface detection unit in conjunction with each other, and a different direction with respect to an arbitrary subject by the moving unit An image creation means for obtaining a projection image of the subject by irradiating electromagnetic waves from the image, and reconstructing the projection image of the subject to create a tomographic image or / and a three-dimensional image at an arbitrary position In the tomography apparatus, a calibration phantom in which four or more markers that are not on the same plane are three-dimensionally arranged is arranged as a subject to obtain a projection image, and the projection image of the calibration phantom and the calibration phantom Based on the three-dimensional arrangement information of the marker in the partial structure, three-dimensional position information of the irradiation means and the surface detection means with respect to the calibration phantom is obtained, and based on the three-dimensional position information of the irradiation means and the surface detection means. The image creating means is configured to perform reconstruction calculation processing on the specimen.

  [Operation / Effect] According to the configuration of the tomography apparatus of the invention according to claim 1, the irradiation means and the surface detection means for the calibration phantom based on the three-dimensional arrangement information of the markers in the internal structure of the calibration phantom specified in advance. It is possible to obtain 3D position information and accurately determine from what direction and position it was projected onto the calibration phantom.When the calibration phantom is replaced with another subject, the same conditions are used. By imaging, reconstruction calculation processing can be performed on the subject based on the three-dimensional position information.

  Therefore, since the three-dimensional position information of the irradiation means and the surface detection means for the calibration phantom can be obtained separately in any projection image, scanning is performed on a trajectory other than the irradiation means and the surface detection means or a strict circular orbit. Even in this case, strict calibration is possible. In calibration, it is only necessary to scan the calibration phantom as much as the scanning range for the subject. Compared to the conventional case where the projection line of the rotating tomographic axis is always obtained by performing a wide scanning, Processing can be done with less effort.

  In addition, mechanical adjustment operations such as moving and adjusting the surface detector so that a predetermined pixel column of the surface detector matches the projection line can be made unnecessary, and overall, calibration processing can be performed with less effort. In this way, necessary images can be efficiently obtained.

  According to a second aspect of the present invention, in the tomography apparatus according to the first aspect, a calibration marker phantom is held on a support member made of a low X-ray absorber and a spherical marker made of a high X-ray absorber. Let me configure.

  [Operation and Effect] According to the configuration of the tomographic apparatus of the invention according to claim 2, X-rays are absorbed for a spherical marker that is an even projection image from any position, and the support material for the marker Makes it difficult to absorb X-rays.

  Therefore, the difference in shading in the obtained projection image becomes clear, the marker can be grasped clearly, three-dimensional position information can be obtained accurately, and a high-quality image can be obtained.

  According to a third aspect of the present invention, in the tomography apparatus according to the first or second aspect, the calibration phantom includes at least four or more markers that are not on the same plane, including a marker serving as a reference for coordinates. Consist of what you have.

  [Operation / Effect] According to the configuration of the tomography apparatus of the invention according to claim 3, when imaging by the precession trajectory, the markers can be prevented from overlapping each other, the positions of the markers can be easily detected, and the tertiary The original position information can be obtained accurately, and a high-quality image can be obtained upon imaging by the precession trajectory.

  According to a fourth aspect of the present invention, in the tomography apparatus according to the first or second aspect, the calibration phantom includes at least three sets of two markers that are point-symmetric with respect to a coordinate reference position. There are the above and all markers are not on the same plane.

  [Operation / Effect] According to the configuration of the tomography apparatus of the invention according to claim 4, when imaging is performed by a circular or circular orbit, the markers can be prevented from overlapping each other, and the position of the marker can be easily detected. In addition, three-dimensional position information can be accurately obtained, and a high-quality image can be obtained in imaging using a circular or circular orbit.

  As described above, according to the tomographic apparatus of the invention of claim 1, the tertiary of the irradiation means and the surface detection means for the calibration phantom based on the three-dimensional arrangement information of the markers in the internal structure of the calibration phantom specified in advance. The original position information can be obtained to accurately determine from what direction and position the calibration phantom has been projected. When the calibration phantom is replaced with another subject, imaging is performed under the same conditions. This makes it possible to perform reconstruction calculation processing on the subject based on the three-dimensional position information, so that even when the irradiation means and the surface detection means scan on a trajectory other than a strict circular trajectory, strict calibration is performed. Is possible. In calibration, it is only necessary to scan the calibration phantom as much as the scanning range for the subject. Compared to the conventional case where the projection line of the rotating tomographic axis is always obtained by performing a wide range of scanning, the processing for calibration is performed. It can be done with less effort.

  In addition, mechanical adjustment operations such as moving and adjusting the surface detector so that a predetermined pixel column of the surface detector matches the projection line can be made unnecessary, and overall, calibration processing can be performed with less effort. In this way, necessary images can be efficiently obtained.

  Next, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram showing an embodiment of a tomography apparatus according to the present invention. As an irradiating means for irradiating a subject with X-rays in a divergent shape across a top plate 1 on which the subject is placed. An X-ray tube 2 and a flat detector 3 serving as a surface detecting means having a plurality of pixels arranged in an array so as to detect X-rays transmitted through the subject are held by a C-shaped arm 4 and are imaged. Is configured.

  The C-shaped arm 4 is provided in a driving unit 6 as a moving means so as to be rotatable around a horizontal axis that faces the longitudinal direction of the top plate 1 and a horizontal axis that is orthogonal to the horizontal axis. A mechanical control device 7 is connected to the unit 6 (imaging unit 5), and is configured to be able to rotate on a precession trajectory, a circular trajectory, or an arc trajectory according to an imaging target. Further, the drive unit 6 can move the X-ray tube 2 and the flat detector 3 integrally by moving the C-shaped arm 4.

  An X-ray control device 8 is connected to the imaging unit 5 to control X-ray irradiation by the X-ray tube 2.

  In addition, an image creating unit 9 that creates a tomographic image or / and a three-dimensional image at an arbitrary position is connected to the imaging unit 5, and an image display device 10 is connected to the image creating unit 9. The image display device 10 corresponds to the image display means in this invention.

  The image creating means 9 includes a data collection device 11, a captured image storage unit 12, a three-dimensional position information detection unit 13, a three-dimensional position information storage unit 14, a reconstruction calculation unit 15, and a tomogram / three-dimensional volume data storage unit 16. Is provided.

  The data collection device 11 collects data of a calibration phantom [calibration phantom FS for precession trajectory or calibration phantom FA for arc trajectory (circular trajectory) described later] obtained by the flat detector 3 and projection image of the subject. It has become.

  The photographic image storage unit 12 stores the photographic data of the calibration phantom and the projection image of the subject collected by the data collection device 11.

  The three-dimensional position information detection unit 13 obtains two-dimensional position information of a calibration phantom marker (to be described later) based on the projection image data of the calibration phantom stored in the captured image storage unit 12, and the internal structure of the calibration phantom. The three-dimensional position information of the X-ray tube 2 and the flat detector 3 with respect to the calibration phantom is obtained on the basis of the three-dimensional arrangement information of the markers in FIG.

  The three-dimensional position information storage unit 14 stores the three-dimensional position information of the X-ray tube 2 and the flat detector 3 with respect to the calibration phantom obtained by the three-dimensional position information detection unit 13.

  In the reconstruction calculation unit 15, the imaging data of the projection image of the subject that is captured after the calibration phantom is captured and stored in the captured image storage unit 12 is read, and the X for the calibration phantom stored in the three-dimensional position information storage unit 14 is read out. Based on the three-dimensional position information of the tube 2 and the flat detector 3, reconstruction calculation processing is performed on the subject, and a tomographic image or three-dimensional volume data at an arbitrary position of the subject is created.

  The tomogram / three-dimensional volume data storage unit 16 stores and saves a tomogram or three-dimensional volume data at an arbitrary position of the subject created by the reconstruction calculation process in the reconstruction calculation unit 15, and according to a request. As appropriate, it can be output to the image display device 10.

  As shown in the explanatory diagram of the three-dimensional position information in FIG. 2, the above-described three-dimensional position information has 3 degrees of freedom (position) that can be regarded as one point of the X-ray tube 2 and 6 degrees of freedom of the flat detector 3 ( There are nine types (position and tilt direction), which are as follows. In addition, the dashed-dotted line which attached | subjected the code | symbol G is a projection line on the XY plane of the axis | shaft which connects the X-ray tube 2 and the origin SP.

SOD: origin (calibration phantom origin, the same applies hereinafter) distance from SP to X-ray tube 2 BP angle: azimuth angle of X-ray tube 2 LM angle: elevation angle of X-ray tube 2 OID: along X-ray passing through origin SP Further, the distance CENTER from the origin SP to the flat detector 3: the u-coordinate MIDDLE of the point H where the X-ray tube 2 passing through the origin SP intersects the flat detector 3: the X-ray tube 2 passing through the origin SP and the flat detector 3 V-coordinate σ angle of intersecting point H: angle between the v-axis direction of the flat detector 3 and the Z-axis projection image of the calibration phantom
(Σ angle = θσ)
u Tilt: Tilt angle about X-ray passing through origin SP and u axis of flat detector 3
(U inclination = θu−90 °)
v Tilt: Tilt angle about the X-ray passing through the origin SP and the v-axis of the flat detector 3
(V slope = θv−90 °)
Next, the processing operation by the image creating means 9 will be described with reference to the flowchart of FIG.

  First, while the C-shaped arm 4 is rotated by the mechanical control device 7, the X-ray control device 8 controls the X-ray tube 2 to irradiate X-rays, and the projection image of the calibration phantom is taken (S1). The projection image is collected in the data collection device 11 by the plane detector 3 and stored in the photographed image storage unit 12, and the X-ray tube 2 and the plane detector are obtained from the projection image and the three-dimensional arrangement information of each marker inside the calibration phantom. The three-dimensional position information 3 is obtained by the three-dimensional position information detection unit 13 (S2).

  After obtaining the three-dimensional position information for all the projected images (S3), the three-dimensional position information is stored and saved in the three-dimensional position information storage unit 14 (S4).

  Here, a certain relationship is established among the positions of the X-ray tube 2, the flat detector 3, the marker, and the projected image of the marker. The positions here are all positions with respect to the calibration phantom, and specifically are coordinate information of the XYZ coordinates of the origin SP shown in FIG. The X-ray tube 2, the marker, and the projected image of the marker are all point positions, and the position of the flat detector 3 is a plane position. The marker is inside the calibration phantom, and the coordinates of the marker are known in advance.

  The above-described fixed relationship can be expressed by a relational expression relating to the relationship between the positions of the marker, the projected image of the marker, the X-ray tube 2, and the flat detector 3. Then, by substituting each piece of information obtained for the marker into this relational expression, an equation is derived. By decomposing this equation for each component of the XYZ coordinates, three equations per one marker are derived. Since the three-dimensional position information of the X-ray tube 2 and the flat detector 3 to be obtained is the nine unknown information listed, the three-dimensional position information can be obtained by solving twelve simultaneous equations derived from the four markers. Can be requested.

Hereinafter, an example thereof will be described with reference to FIG. Consider a case where four markers m1, m2, m3, and m4 are three-dimensionally arranged as shown in FIG. In the XYZ coordinates where the origin is SP, the coordinates which are the three-dimensional arrangement information of each marker m1, m2, m3, m4 are point M ₁ , point M ₂ , point M ₃ , and point M ₄ . The points M ₁ to M ₄ are known. Further, the XYZ coordinates of the X-ray tube 2 are set as a point F. Point F is unknown. When the X-ray tube 2 irradiates X-rays, the XYZ coordinates of the images of the markers m1, m2, m3 and m4 projected on the flat detector 3 are points Q ₁ , Q ₂ , Q ₃ and Q ₄ . . The XYZ coordinates of the point Q ₁ to Q _4, positional information of the flat detector 3 itself points Q ₁ ~ point Q ₄ also becomes unknown because it is unknown. However, the coordinates (uv coordinates) on the flat detector 3 which are the two-dimensional position information of the projection images of the markers m1 to m4 are obtained from the detected projection images and become known.

Here, the vector SPQ ₁ from the origin SP to the point Q ₁ to the point Q ₄ (Hereinafter, when distinguishing the vector, it is referred to as “vector...” And the vector symbol is omitted for convenience) For the vector SPQ ₄ , the formula group shown in Formula 1 is established.

一方、点Ｆと原点ＳＰとを結ぶ直線が平面検出器３と交わる点を点Ｈとすると、原点ＳＰから点Ｑ₁〜点Ｑ₄へのベクトルＳＰＱ₁〜ベクトルＳＰＱ₄については、数式２に示す式群のように表現することもできる。

On the other hand, the point at which a straight line connecting the point F and the origin SP intersects the flat detector 3 when the point H, for the vector SPQ ₁ ~ vector SPQ ₄ from the origin SP to point Q ₁ ~ point Q _4, in Equation 2 It can also be expressed like the formula group shown.

数式１と数式２より、マーカ、マーカの投影像、Ｘ線管２、及び平面検出器３の各位置の関係に関する関係式は、数式３に示す式群のようになる。

From Equations 1 and 2, the relational expression regarding the relationship between the marker, the projected image of the marker, the X-ray tube 2, and the flat detector 3 is expressed by the following equation group.

数式３に示す各式は、ＸＹＺ座標のＸ成分、Ｙ成分、Ｚ成分の３個の成分があり、成分ごとに３個の関係式に分解できる。このような数式３に示す式群の各式について、既知の点Ｍ₁〜Ｍ₄のＸＹＺ座標と、既知の投影像のｕｖ座標を代入して、方程式を得る。そして、各方程式についてＸＹＺ座標の成分ごとに３個の方程式に分解すると、計１２個の連立方程式となる。この１２個の連立方程式を解くことで、Ｘ線管２と平面検出器３の三次元位置情報を求めることができる。

Each equation shown in Equation 3 has three components of the X, Y, and Z components of the XYZ coordinates, and can be decomposed into three relational expressions for each component. For each of the equations in the equation group shown in Equation 3, an equation is obtained by substituting the XYZ coordinates of the known points M _{1 to} M ₄ and the uv coordinates of the known projection image. When each equation is decomposed into three equations for each XYZ coordinate component, a total of 12 simultaneous equations are obtained. By solving these twelve simultaneous equations, the three-dimensional position information of the X-ray tube 2 and the flat detector 3 can be obtained.

Further, the relational expression shown in Equation 3 will be described in detail. First, since the origin SP and the points M ₁ to M ₄ are known in advance, the vectors SPM ₁ to SPM ₄ are known. Since the vector M ₁ Q ₁ to the vector M ₄ Q ₄ are located on a straight line connecting the point F and the point M ₁ to the point M ₄ with the points Q ₁ to Q ₄ , Can be stood.

ここで、係数ｒ₁〜係数ｒ₄は、数式５に示す式群を満足する、未知の実数である。

Here, the coefficient r ₁ to the coefficient r ₄ are unknown real numbers that satisfy the expression group shown in Expression 5.

さらに、ベクトルＳＰＦは、原点ＳＰから点Ｆへ向かう単位ベクトルＵ_SPFに、原点ＳＰから点Ｆまでの距離ＳＯＤを乗じたものに等しい。また、数式３に示す式群の右辺に含まれるベクトルＳＰＨも、同様に、原点ＳＰから点Ｈへ向かう単位ベクトルＵ_SPHに、原点ＳＰから点Ｈまでの距離ＯＩＤを乗じたものに等しく、また、（単位ベクトルＵ_SPH）＝−（単位ベクトルＵ_SPF）の関係が成り立つ。よって、ベクトルＳＰＦ、ベクトルＳＰＨは、数式６に示す式群のように表すことができる。

Further, the vector SPF is equal to the unit vector U _SPF from the origin SP to the point F multiplied by the distance SOD from the origin SP to the point F. Similarly, the vector SPH included in the right side of the formula group shown in Formula 3 is also equal to the unit vector U _SPH from the origin SP to the point H multiplied by the distance OID from the origin SP to the point H. , (Unit vector U _SPH ) = − (unit vector U _SPF ). Therefore, the vector SPF and the vector SPH can be expressed as an equation group shown in Equation 6.

ただし、Ｒ_BP、Ｒ_LMは、それぞれ数式７、数式８に示される回転行列である。

However, R _BP and R _LM are rotation matrices shown in Equations 7 and 8, respectively.

上記各式からわかるように、回転行列Ｒ_BPは、直線ＦＨのＺ軸周りのＢＰ角（θ_BP）分の回転であり、回転行列Ｒ_LMは、直線ＦＨの（−Ｙ）軸周りのＬＭ角（θ_LM）分の回転である。なお、ＳＯＤ、ＯＩＤ、θ_BP、θ_LMは、すべて未知である。

As can be seen from the above equations, the rotation matrix R _BP is the rotation of the straight line FH by the BP angle (θ _BP ) around the Z axis, and the rotation matrix R _LM is the LM around the (−Y) axis of the straight line FH. The rotation is an angle (θ _LM ). Note that SOD, OID, θ _BP , and θ _LM are all unknown.

Finally, the vectors HQ ₁ to HQ ₄ will be described. The coordinates (uv coordinates) of the projected image of each marker on the plane detector 3 are respectively (s ₁ , t ₁ ), (s ₂ , t ₂ ), (s ₃ , t ₃ ), (s ₄ , t _4). ). Further, the coordinates (uv coordinates) of the point H on the flat detector 3 are (CENTER, MIDDLE). Further, if the unit vectors in the u-axis and v-axis directions of the flat detector 3 are a unit vector U _u and a unit vector U _v , the vectors HQ ₁ to HQ ₄ can be expressed as a group of equations of Equation 9. it can.

なお、数式９に示す式群においてｓ₁〜ｓ₄、ｔ₁〜ｔ₄は既知であり、ＣＥＮＴＥＲ、ＭＩＤＤＬＥ、単位ベクトルＵ_u、単位ベクトルＵ_vは、未知である。

In the formula group shown in Formula 9, s _{1 to} s ₄ and t _{1 to} t ₄ are known, and CENTER, MIDDLE, unit vector U _u , and unit vector U _v are unknown.

Here, the uv plane can be considered as a rotational movement of a plane parallel to the YZ plane. Therefore, the unit vector U _u and the unit vector U _v are given by rotating the unit vectors in the Y-axis and −Z-axis directions, respectively. Specifically, the equation group shown in Equation 10 is obtained.

ただし、Ｒ_uは、平面検出器３のｕ傾き（θ_u−９０°）に相当する回転行列（θ_BP＝０、θ_LM＝０の時、Ｙ軸に平行な軸周り）であり、数式１１の通りである。Ｒ_vは、平面検出器３のｖ傾き（θ_v−９０°）に相当する回転行列（θ_BP＝０、θ_LM＝０の時、Ｚ軸に平行な軸周り）であり、数式１２の通りである。さらに、Ｒσは、平面検出器３のσ角（θσ）に相当する回転行列（θ_BP＝０、θ_LM＝０の時、Ｘ軸に平行な軸周り）であり、数式１３の通りである。なお、θ_u、θ_v、θσは、ともに未知である。

However, R _u is a rotation matrix (around the axis parallel to the Y axis when θ _BP = 0 and θ _LM = 0) corresponding to the u inclination (θ _u −90 °) of the flat detector 3, 11 streets. R _v is a rotation matrix (around the axis parallel to the Z axis when θ _BP = 0 and θ _LM = 0) corresponding to the v slope (θ _v −90 °) of the flat detector 3, Street. Furthermore, Rσ is a rotation matrix corresponding to the σ angle (θσ) of the flat detector 3 (when θ _BP = 0 and θ _LM = 0, around the axis parallel to the X axis). . Note that θ _u , θ _v , and θσ are all unknown.

数式３に示す式群に４個のマーカについて得られる情報を代入し整理すると、１２個の具体的な方程式が導かれる。すなわち、数式３の４個の関係式に数式４、数式６、数式９、数式１０を代入して、数式１４、数式１５、数式１６、数式１７に示す4個の方程式が導かれる。

Substituting information obtained from the four markers into the formula group shown in Formula 3 and rearranging them leads to 12 specific equations. That is, by substituting Equation 4, Equation 6, Equation 9, and Equation 10 into the four relational expressions in Equation 3, four equations shown in Equation 14, Equation 15, Equation 16, and Equation 17 are derived.

なお、数式１４、数式１５、数式１６、数式１７に示す各式は、それぞれＸＹＺ座標の各成分ごとに３個の方程式に分解できるので、数式１４〜数式１７から合計１２個の方程式が得られる。

In addition, since each formula shown in Formula 14, Formula 15, Formula 16, and Formula 17 can be decomposed | disassembled into three equations for every component of an XYZ coordinate, respectively, a total of 12 equations are obtained from Formula 14-Formula 17. .

Here, as pointed out in the series of explanations, the unknowns are nine pieces (SOD, OID, CENTER, MIDDLE, θ _BP , θ _LM , three-dimensional position information of the X-ray tube 2 and the flat detector 3. θ _u , θ _v , θσ) and _four coefficients r ₁ to r ₄ , which is 13 in total.

Therefore, the number of simultaneous equations is one less than the number of unknowns.
In this case, for example, 13 unknowns can be estimated by iterative calculation using the least squares. The procedure will be specifically described below.

(Procedure 1)
First, assuming that the tomography apparatus is not bent or strained at all, theoretical values for the 13 unknowns are obtained from the dimensions of the material of the apparatus, the rotation angle instructed by the mechanical control device 7 to the drive unit 6 and the like. Ask. The theoretical values of the 13 unknowns are called “initial values”.

(Procedure 2)
The coordinates of point M ₁ , point M ₂ , point M ₃ , and point M ₄ , which are the three-dimensional arrangement information of the markers m 1, m 2, m 3, and m ₄ , are substituted into Expressions 14 to 17. Incidentally, was observed by the plane detector 3, the values of _{s 1 ~s 4, t 1 ~t} 4 is the coordinate (uv coordinate) of the projected image of each marker m1 to m4 (hereinafter, respectively "measurement" Do not assign).

(Procedure 3)
In Expressions 14 to 17 in which the three-dimensional arrangement information of each marker is assigned, “initial values” are assigned to 13 unknowns. Then, eight s _{1 to} s ₄ and t _{1 to} t ₄ are solved. At this time, since there are eight values to be obtained for the twelve simultaneous equations, they can be obtained analytically. Thus, the obtained values of s ₁ to s ₄ and t _{1 to} t ₄ are respectively referred to as “back calculation values”.

Then, the _{s 1 ~s 4, t 1 ~t} 4, obtains a difference each as "measured value" and the "back calculated value". _{Here, s 1, s 2, s} 3, s 4 and "measurement value" a difference value between "back calculated value" respectively Δ1, Δ2, Δ3, and _{Δ4, t 1, t 2,} t 3, t 4 The difference values between “measured value” and “back-calculated value” are Δ5, Δ6, Δ7, and Δ8, respectively.

  Further, the sum of the squares of the difference values is obtained according to Equation 18. Hereinafter, this value is referred to as “error sum of squares a”.

（手順４）
次に、（手順３）で示した計算を、１３個の未知数のそれぞれについて、一つずつ、少しだけ値を変えた場合について繰り返し行い、「誤差二乗和ａ」を求めていく。そして、「誤差二乗和ａ」が最小となる場合を見つける。ここで、変化させる値のステップ量は、経験的に得られた効果的な値である。

(Procedure 4)
Next, the calculation shown in (Procedure 3) is repeated for each of the 13 unknowns, one by one, with the value slightly changed, and the “sum of squared errors a” is obtained. Then, a case where the “error sum of squares a” is minimum is found. Here, the step amount of the value to be changed is an effective value obtained empirically.

Specifically, assuming that the initial value of CENTER, which is one of the unknowns, is “C ₀ ” and the amount of step to be changed is “ΔC”, “CENTER” is set to “initial value” in Expressions 14 to 17. Substituting a value (C ₀ + ΔC) obtained by adding the quantity, each of the other 12 unknowns is set to “
Substitute “Initial Value”. Then, the “error sum of squares a” in that case is obtained. Next, from Formula 14 to Formula 17, a value (C ₀ −ΔC) obtained by subtracting the step amount from “Initial value” is substituted for CENTER, and each “Initial value” is substituted for the other 12 unknowns. Then, “the sum of squared errors a” is obtained. This calculation is sequentially performed for each of the remaining twelve unknowns such as MIDDLE when the step amount is increased or decreased. As a result, according to (Procedure 4), there are 26 ways (when adding the step amount to any one of the 13 unknown initial values), 13 ways to add the step amount, and any one of the 13 unknowns to the initial value. When the step amount is reduced, there are 13 ways, and a total of 26 ways) is obtained.

  The above-described method of changing the “initial value” is shown as a specific example, and is appropriately selected and changed. In addition, although 26 types of “error sum of squares a” are obtained, of course, this number is not particularly limited.

(Procedure 5)
A case where the value of “error square sum a” is the smallest among all “error square sum a” obtained from procedure 3 and procedure 4 is specified. Then, the values assigned to the 13 unknowns at this time are replaced with “initial values” of 13 unknowns.

If the above-described “initial value” is changed in (Procedure 4), a total of 27 “sum of squared errors a” are obtained from Procedure 3 and Procedure 4. Further, when CENTER is a value (C ₀ + ΔC) obtained by adding the step amount to the “initial value” and the other 12 unknowns are “initial values”, the minimum “sum of squared errors a” is obtained. When this happens, only the “initial value” of CENTER is replaced with (C ₀ + ΔC).
Next, the specified minimum “error square sum a” is compared with a predetermined value of “error square sum a” (hereinafter simply referred to as “specified value”), and the minimum “ It is determined whether or not the value of the error sum of squares a is less than a specified value.

  When it is determined that the value of the minimum “sum of squared errors a” is equal to or larger than the specified value, the “initial value” of the 13 unknowns that have been replaced is used again to (Procedure 3). Returning, the same calculation is repeated, and the minimum “sum of squares of error a” is obtained again, and “initial values” of 13 unknowns are replaced. By repeatedly performing the calculation in this way, the value of the “error sum of squares a” gradually decreases.

  On the other hand, when it is determined that the value of the minimum “sum of squared errors a” is less than the specified value, the “initial value” of the 13 unknowns replaced is estimated as the value of 13 unknowns. And a series of calculation is complete | finished.

  Here, what kind of prescribed value is used, in other words, how far the value of “error sum of squares a” converges is determined by the resolution of the flat detector 3.

For example, when the pixel of the flat panel detector 3 is square, s ₁ ~s _4, the difference value of t ₁ ~t ₄ is on average, the distance D _D between pixels corresponding to one side of the square 1 / If it is less than 2, it is considered that there is no problem as a tomography apparatus. Therefore, in this case, if the prescribed value is 2D _D ² and it is determined that Expression 19 is satisfied, the series of calculations may be terminated.

ここで、ａ_minは、（手順５）で特定される最小の「誤差二乗和ａ」である。

Here, a _min is the minimum “sum of squared errors a” specified in (procedure 5).

  The above-described method for determining the specified value is also an example, and is appropriately selected and changed.

  The above is the procedure for estimating 13 unknowns by iterative calculation using the least squares.

  In addition, when the number of markers is increased, it can be obtained analytically without performing iterative calculation using the least squares. In this case, it can be obtained more accurately at high speed.

  Even in the case of the precession trajectory calibration phantom FS and the arc trajectory calibration phantom FA, which will be described later, the technique for obtaining the three-dimensional position information of the X-ray tube and the flat detector is the same.

  With reference to FIG. 3 again, the processing operation by the image creating means 9 will be described. Thereafter, the projection image of the subject to be reconstructed is imaged at the same trajectory and timing as when the calibration phantom was imaged, and the projection image is stored in the imaging image storage unit 12, or the imaging image storage unit The photographing data of the projection image of the subject stored in the memory 12 is read (S5).

  Based on the imaging data of the projection image of the subject and the three-dimensional position information of the X-ray tube 2 and the flat detector 3 with respect to the calibration phantom stored in the three-dimensional position information storage unit 14, reconstruction calculation processing for the subject To create a tomographic image or three-dimensional volume data at an arbitrary position of the subject (S6).

  A series of procedures for creating the three-dimensional volume data will be outlined with reference to FIG. First, a simple back projection (simple back projection: simple BP) is performed on the group of photographing data to generate a simple BP intermediate image. Next, this simple BP intermediate image is subjected to three-dimensional Fourier transform, and converted from real space data to Fourier space data, a three-dimensional Fourier distribution image (corresponding to the one displayed in three-dimensional Fourier space coordinates in FIG. 5). Generate). Next, filtering processing is performed on the three-dimensional Fourier distribution image (| ω | filtering (absolute value omega filtering) or low-pass filtering). Next, the filtered three-dimensional Fourier distribution image is subjected to three-dimensional inverse Fourier transform to return from the Fourier space data to the real space data. The three-dimensional volume data (displayed on the right end side in FIG. (Corresponding to a cylindrical shape in which several broken lines are shown). In this way, image reconstruction for generating the three-dimensional volume data of the region of interest is performed. By selecting an image of an arbitrary tomographic plane from the three-dimensional volume data, the selected tomographic image can be seen (FIG. 5 shows a thin cylindrical shape displayed at the rightmost end. Corresponding to things). As described above, a method of once generating a simple BP intermediate image and subjecting the simple BP intermediate image to a predetermined filtering process in Fourier space is called an F (Fourier) spatial filter method.

Here, when the simple BP intermediate image is generated, a three-dimensional lattice group K is virtually set in the region of interest of the imaged subject as shown in FIG. The detection data at the point D _P on a plane detector 3, back projection to the lattice point J of the three-dimensional lattice K in a straight line connecting the X-ray tube 2 and the point D _P.

The three-dimensional lattice group K is virtually located at the same position as the calibration phantom. That is, the XYZ coordinates of the three-dimensional lattice group K are hypothesized so as to coincide with the XYZ coordinates of the calibration phantom photographed with the same trajectory and the same timing. Thus, the coordinates of the grid point J is calculated in step S2, based on the three-dimensional position information of the X-ray tube 2 and the area detector 3 for the calibration phantom, precise from the position of the point D _P obtained in the imaging of the subject Is required. The detection data at the point D _P is the pixel value at point D _P, determining the pixel values for the pixel d1~d4 recent contact for example four points in this respect D _P weighted average of. Then, by obtaining such detection data from various angles and accumulating at the lattice points, back projection can be performed on the lattice points. Then, back projection is performed on the remaining lattice points of the three-dimensional lattice group K in the same manner as described above, and further, similar back projection is performed for each scanning position, thereby generating a simple BP intermediate image. . Note that a blur prevention filter process or the like may be applied to the captured image of the subject in advance.

  Thereafter, the created tomographic image or three-dimensional volume data of an arbitrary position of the subject is stored and stored in the tomographic image / three-dimensional volume data storage unit 16, and is output to the image display device 10 and displayed as required. (S7).

  After the above step S7, further image processing is performed from the tomographic image or the three-dimensional volume data to display and save, or processing such as transfer of data to other devices via a network or media is performed. Also good.

  Next, each of the precession trajectory calibration phantom FS and the arc trajectory (circular trajectory) calibration phantom FA used in the above embodiment will be described.

(1) Precession orbit calibration phantom FS As shown in the schematic configuration diagram of FIG. 7, the support material 21 made of a low X-ray absorber and directed in the three-dimensional direction of XYZ has a high X at a position serving as a reference of the origin. A marker m3 made of a steel ball made of a wire absorber is provided, and markers m1, m2, m4, m5 made of a steel ball in the same manner as the marker m3 at the positive and negative positions in the XYZ three directions around the marker m3. The precession orbit calibration phantom FS is configured by providing m6 and m7. When such a precession trajectory calibration phantom FS is used, the projection images of all the markers m1, m2, m3, m4, m5, m6, and m7 can be photographed so that they do not overlap. , M4, m5, m6, and m7 can be easily detected.

  Here, the precession trajectory refers to a line segment L passing through an arbitrary point on the line segment L connecting any one point of the X-ray tube 2 and the flat detector 3 as shown in the schematic configuration diagram of FIG. It refers to a trajectory in which the X-ray tube 2 and the flat detector 3 rotate around a different straight line (for example, an angle formed by the line segment L is 15 °) P.

  In the present invention, not only the precession trajectory as described above, but, for example, an elliptical trajectory or a more complicated trajectory, or any one point of the rotation axis P, the X-ray tube 2 and the flat detector 3 in the course of the trajectory. A trajectory in which the angle formed by the connecting line segment L changes, a trajectory in which the distance from the rotation axis P to the X-ray tube 2 or the flat detector 3 changes, or a rattling of the mechanism for each projection, etc. For this reason, the X-ray tube 2 and the flat detector 3 may be displaced in a discontinuous orbit.

(2) Calibration Phantom FA for Arc Trajectory (Circular Trajectory) As shown in FIGS. 9A, 9B, and 9C, an arc trajectory serving as a reference for coordinates is provided on a cylindrical support material 31 made of a low X-ray absorber. 4 sets of 8 markers m1, m2, m3, m4, m5, m6, m7, m8 made of steel balls made of high X-ray absorber are provided at positions that are point symmetric with respect to the center of the calibration phantom FA Thus, a calibration phantom FA for an arc orbit (circular orbit) is configured.

  With this configuration, as shown in the schematic configuration diagram of FIG. 10, a straight line passing through an arbitrary point on a line segment L connecting the X-ray tube 2 and an arbitrary point on the flat detector 3 is rotated as a rotation axis. 9A, the intersection of the line segment L1 connecting the markers m2 and m7 and the line segment L2 connecting the markers m3 and m6 is obtained as shown in FIG. 9A, or the marker as shown in FIG. 9B. The intersection of the line segment L3 connecting m1 and m8 and the line segment L4 connecting the markers m4 and m5 is obtained, and the X-ray passing through the center C of the calibration phantom FA for circular arc trajectory (circular trajectory) is detected by the flat detector 3. The coordinates incident on are calculated. For this reason, it is not necessary to provide a marker at the center C of the arc phantom (circular orbit) calibration phantom FA, the structure of the arc phantom (circular orbit) calibration phantom FA can be simplified and inexpensive, and a decrease in accuracy can be avoided. ing.

  Here, the arc trajectory (circular orbit) is a rotation axis that is a straight line passing through an arbitrary point on the line segment L connecting the X-ray tube 2 and an arbitrary point on the flat detector 3. This refers to a trajectory that rotates around a rotation axis while any point on the X-ray tube 2 and the flat detector 3 exists in a vertical plane. In FIG. 9A and FIG. 9B, the shaded marker indicates that it is located on the back side.

  In FIG. 10, the rotation angle is shown as several tens of degrees. However, in the present invention, the angle is not limited, and a trajectory such as a so-called CT apparatus that rotates 360 degrees around the circumference may be used. Further, a trajectory in which the distance from the rotation axis to the X-ray tube 2 or the flat detector 3 changes depending on the projection position, a trajectory in which the X-ray tube 2 and the flat detector 3 do not exist in a certain plane, or Alternatively, the X-ray tube 2 and the flat detector 3 may be displaced in a discontinuous orbit due to mechanical backlash or the like for each projection.

  Further, the scanning trajectory of the X-ray tube 2 and the flat detector 3 may be a parallel two straight line or a trajectory in accordance therewith. In short, any trajectory may be used as long as projection images of the subject can be obtained from a plurality of different directions.

  When there is a piece of 3D position information that does not have an error problem even if the accuracy of the mechanism is handled as a specified value, such as the distance from the origin to the X-ray tube 2 or the flat detector 3, a calibration phantom In the calculation of the three-dimensional position information from the projected image, it is preferable to use the prescribed value. This is because the number of variables required for the reconstruction calculation process can be reduced and the processing speed can be increased.

  In the above embodiment, the X-ray tube 2 for irradiating X-rays is used as the irradiating means. However, the present invention includes visible light, X-rays from a plasma X-ray source, gamma rays from a radioisotope, electronic lilac. Those that irradiate various electromagnetic waves, such as those having a configuration for irradiating with X-rays, and synchrotron orbital radiation light sources (SOR) can be used.

  In the above embodiment, the flat detector 3 is used as the surface detecting means. However, as the present invention, an image intensifier, a multi-row detector, or the like may be used.

  Further, in the above embodiment, the imaging unit 5 is configured by mechanically coupling the X-ray tube 2 and the flat detector 3 by being held by the C-shaped arm 4. However, as long as the drive unit 6 can move the X-ray tube 2 and the flat detector 3 in conjunction with each other, the configuration is not limited to the configuration having the C-shaped arm 4. For example, the drive unit 6 interlocks the X-ray tube 2 and the flat detector 3 with each other by, for example, a configuration in which the X-ray tube 2 and the flat detector 3 are individually held and connected to a common rotational drive shaft. May be moved. In addition, the drive unit 6 is configured to rotate and drive the X-ray tube 2 and the flat detector 3 individually and synchronously with each other while holding the X-ray tube 2 and the flat detector 3 separately. As an example, the driving unit 6 may move each of them in conjunction with each other.

1 is an overall configuration diagram showing an embodiment of a tomography apparatus according to the present invention. It is explanatory drawing of three-dimensional position information. It is a flowchart explaining the image creation operation | movement of the tomography apparatus which concerns on this invention. It is explanatory drawing which calculates | requires the three-dimensional position information of a X-ray tube and a plane detector. It is a schematic diagram for demonstrating the procedure which produces three-dimensional volume data. It is a schematic diagram for demonstrating a back projection method. It is a schematic block diagram of the calibration phantom for precession tracks. It is a schematic block diagram used for description of a precession trajectory. 9A is a side view of the calibration phantom for an arc track, FIG. 9B is a side view of the calibration phantom for the arc track rotated by 90 °, and FIG. 9C is a plan view of the calibration phantom for the arc track. It is a schematic block diagram used for description of a circular arc track.

Explanation of symbols

2 X-ray tube (irradiation means)
3 Flat detector (surface detection means)
6 ... Drive unit (moving means)
9 ... Image creation means FS ... Calibration phantom for precession orbit FA ... Calibration phantom for arc orbit (circular orbit)

Claims (4)

  Irradiation means for irradiating the subject with a transparent electromagnetic wave in a divergent shape, and a plurality of pixels arranged in an array so as to detect the electromagnetic wave transmitted through the subject, disposed opposite the irradiation means with the subject interposed therebetween A surface detecting means comprising: a moving means for moving the irradiating means and the surface detecting means in conjunction with each other; In a tomography apparatus having an image creation means for obtaining a projection image and reconstructing the projection image of the subject to create a tomogram or / and a three-dimensional image at an arbitrary position on the same plane A projection image is obtained by arranging as a subject a calibration phantom in which four or more markers that are not present in three dimensions are arranged, and the projection image of the calibration phantom and the tertiary of the marker in the internal structure of the calibration phantom Based on the arrangement information, the three-dimensional position information of the irradiation means and the surface detection means with respect to the calibration phantom is obtained, and the reconstruction calculation process for the subject is performed based on the three-dimensional position information of the irradiation means and the surface detection means. A tomographic apparatus characterized in that the image creating means is configured as described above.   The tomography apparatus according to claim 1, wherein the calibration phantom has a spherical material made of a high X-ray absorbing material held on a support material made of a low X-ray absorbing material.   The tomography apparatus according to claim 1, wherein the calibration phantom includes at least four or more markers that are not on the same plane, including a marker that serves as a reference for coordinates. 3. The tomography apparatus according to claim 1, wherein the calibration phantom has at least three sets of two markers that are point-symmetric with respect to a coordinate reference position, and all the markers are on the same plane. A tomography device that is not above.

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