JPH09192126A - Image reconstitution processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve operability by providing the processor with a fan beam reconstituting means for reconstituting a fan beam for reconstituting a tomographic plane image and a cone beam reconstituting means for reconstituting a cone beam for reconstituting a tomographic solid image. SOLUTION: An output signal from an X-ray detector is converted to a digital signal and fetched into a reconstitution processing part 12. While the cone beam reconstitution is designated by a reconstitution method designating part 21-1, a projection curve calculation part 21-2 generates a projection curve for which a boxel line is projected on the surface of the detector, a reconstitution processing control part 21 finds inverse projection data corresponding to the projection curve (performs cone beam reconstitution processing), the data is added to an image memory 27 and the images is stored. Besides, when the fan beam reconstitution is designated by the reconstitution method designating part 21-2, the projection curve calculation part 21-2 generates a straight projection line parallel with the detector line passing through the center of the detector line, the inverse projection data corresponding to the straight projection line are found (fan beam reconstitution processing) and added to the image memory 27 and the image is stored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates an object with conical X-rays emitted from an X-ray source, detects X-rays transmitted through the object with an X-ray detector, and detects the X-rays. The present invention relates to an image reconstruction processing device that reconstructs a tomographic image of the object based on detection data obtained from a detector.

[0002]

2. Description of the Related Art Conventional X-ray CT (computed tomography)
As the apparatus, as shown in FIG. 47, one using a fan beam in which the X-ray beam is emitted from the X-ray source 101 in a fan shape (fan shape) is known. Such an X-ray CT apparatus irradiates a subject with an X-ray beam emitted from an X-ray source 101, and uses an X-ray detector 102 in which approximately 1000 channels of X-rays passing through the subject are arranged in a row in a fan shape. X-ray source 101 and X-ray detector 10 are detected and data is collected.
While rotating 2 around the subject, 1 during 1 rotation
Data is collected about 000 times (one data collection is referred to as one view), and an X-ray cross-sectional image of the subject is reconstructed based on the collected data. FOV103
Indicates an effective visual field. The image reconstruction formula when this fan beam is used is calculated by (Equation 1).

[0003]

[Equation 1]

As can be seen from the equation (1), in the reconstruction of the fan beam, it is necessary to multiply the data obtained from the X-ray detector by a weight depending on the position of the pixel to be reconstructed and backproject. Complex processing. That is, as shown in FIG. 48, a plurality of pixels forming an image to be reconstructed with respect to the effective visual field FOV 103 (see FIG.
Inside, black dots), which are densely arranged in a grid, are set,
The data obtained in each channel of the X-ray detector 102 is
Focus (X of X-ray source 101) as weighting for each pixel
Distance F between line beam emission point F) and corresponding pixel (black point)
Back projection is performed by multiplying the inverse of the square of pixel D (X). Note that Fpixel D means Focus-Pixel-Distance. There is also a method of direct back projection, but in this case, polar coordinate conversion is required, and the calculation becomes complicated.

Therefore, an X-ray CT using a fan beam
In the device (single slice CT), two kinds of image reconstruction methods are currently devised. One method is called the Fan-Para conversion method, which is shown in FIG.
As shown in Fig. 9, the projection data obtained from the X-ray detector by the fan beam is rearranged and interpolated to create parallel beam projection data (including conversion). X-ray C using beam
This is a method of backprojection as is done in the T-apparatus. On the other hand, calculation of data conversion and interpolation processing are required, but when backprojecting, different weighting processing for each reconstructed pixel at the time of fan beam is unnecessary, and one data (parallel beam projection data) (A straight line that connects the radiation point when it becomes a parallel beam and the channel of the X-ray detector)
The process is simple because it is sufficient to backproject to all the pixels of.

Another method is a fan beam reconstruction method using a centering axis, the details of which are disclosed in Japanese Patent Laid-Open No. Sho 5
No. 5-99240. As shown in FIG. 50, once the data obtained from the X-ray detector is projected onto a predetermined reference axis (centering axis) 104 parallel to the pixel row (
Backprojection) and then backproject it again for each reconstructed pixel column. In this way, by backprojecting once on the centering axis, different weighting processing for each pixel becomes the same for each pixel column, so high-speed and simple processing becomes possible.

The steps of the fan beam reconstruction method using this centering axis will be described below. 1. The raw data Data-Raw is obtained by multiplying the cos term by various corrections such as X-ray intensity correction of the projection data Data-Proj. The raw data Data-Raw and the reconstruction function are convolved to obtain Data-Conv. 2. Data-Conv is projected by weighting (Equation 2) to a point on a certain reference axis (centering axis, for example, a reference X-axis and Y-axis on which pixels are arranged) to obtain a Data-Center. In this equation (2), FcpD (X) is the distance between the focal point and the centering axis point.

[Equation 2]

The process of 3.2 is repeated to project the fan beam projection data of all the views on the corresponding reference axis. 4. Data of a view projected on the reference axis Data-Cente
Data-Back is obtained by weighting r with the same (Equation 3) weighting for all pixel columns of the image to be reconstructed.
The obtained projection data Data-Back is back projected (added to the address corresponding to the pixel of the image memory). A,
B is shown in FIG.

(Equation 3)

The processing of 5.4 is repeated for all views, and the projection data of all views are backprojected.

Here, with reference to FIG. 50 and transforming (Equation 3),

(Equation 4)

Which is the reconstruction formula of the fan beam,
It agrees with the contents of the integral of (Equation 1).

After projecting on the centering axis once, each pixe
By backprojecting to the l column, the weight (Equation 1) at the time of backprojecting, which was originally different for each pixel, is made equal in each pixel column (Equation 2), and the calculation of the generation of the weight itself is simplified. The number of calculations has been reduced. Although not described in detail here, the complicated correspondence between the detector elements arranged at equal angles on a circular arc and the pixels arranged at equal pitches on a straight line is also simplified. In a conventional X-ray CT apparatus using a fan beam, high-speed image reconstruction processing is realized by either of the two methods described above.

On the other hand, as shown in FIG. 51, a cone beam in which an X-ray beam is radiated from the X-ray source 201 in a cone shape and a fan beam detector row are stacked in N rows in the Z-axis direction. A detector element (M channel ×
An X-ray CT apparatus that captures an X-ray fluoroscopic image using a two-dimensional X-ray detector 202 in which N columns are arranged has been devised. Typical cone beam reconstruction (Feldkamp reconstruction) in an X-ray CT apparatus using such a cone beam is disclosed in the following document.

"Practical cone-beam algorithm" LAFeldkamp, LCDavis, and JWKress J. Opt. Soc. Am. A / Vol.1, No.6, pp.612-619 / June 19
84 This is a mathematically exact reconstruction of the fan beam (2
In-dimensional plane) Reconstruction algorithm [Filtered-Backproje
ction (filtered backprojection method)] in the Z-axis direction is an approximate three-dimensional reconstruction algorithm. This cone-beam reconstruction method is intended for conventional scanning by cone-beam, and consists of the following steps. In this cone beam, voxels as three-dimensional pixels are used as shown in FIG. 52, instead of pixels as two-dimensional pixels.

1. Weighting of projection data The projection data is multiplied by a term dependent on the Z coordinate and a cos term. 2. Convolution operation The convolution operation of the data obtained by the process 1 and the same reconstruction function as that of the fan beam is performed. 3. BackProjection (Backprojection) The data obtained by the process 2 is backprojected onto the path (from the focal point to the channel of the detector) through which the X-ray has passed. That is, the point at which the straight line passing through the voxel backprojected from the focal point intersects the detector plane is calculated, and backprojected data is created by interpolation or the like from the data of the two processes around that point, and it is expressed as FvoxelD (X ) Is weighted by the reciprocal of the square of (2) and backprojected.
This back projection is performed over 360 ° (one rotation).

When expressed by a formula similar to the fan beam reconstruction formula, it becomes as follows. Note that FvoxelD (X) = Focus-Voxel-Di
stance is the focal point-voxel distance.

(Equation 5)

This three-dimensional reconstruction formula (cone beam reconstruction formula) (Equation 4) is very similar to the fan beam reconstruction in formula, but it is explained that the back projection method of Data-Back is greatly different. To do. In the two-dimensional fan beam reconstruction, as shown in FIG. 53, the back projection is performed from the data of the detectors arranged in one dimension for all the pixels in the reconstruction plane, while the cone is used. In the beam (Feldkamp) reconstruction, as shown in FIG. 54, the point where the straight line connecting the focal point and the reconstructed voxel intersects the two-dimensional X-ray detector plane and is involved in the intersection. The data obtained from the detector elements is backprojected to all voxels located on that straight line.

Therefore, in cone beam reconstruction, when reconstructing a surface like fan beam reconstruction, the data of a specific detector row and channel is backprojected only to some voxels of the reconstruction surface. Therefore, since it is necessary to select the data (detector row and detector channel) to be backprojected for each voxel, the three-dimensional structure of the straight line focused on the reconstructed voxel and the X-ray detector surface is selected. The positional relationship becomes important. Moreover, considering a detector row having the same Z coordinate and a straight line focusing on the detector element, a voxel passing through the straight line on a certain plane (reconstructed plane) is detected around the focus. Similar figure of the surface (in the case of cylindrical detector,
The calculation of this positional relationship is very complicated because they are arranged on concentric circles).

Further, in the X-ray CT apparatus, as shown in FIG. 55 (a), a conventional scanning method is defined as a scanning method in which the X-ray tube and the X-ray detector orbit the same circular orbit around the subject. In addition, as shown in FIG. 55 (b), the X-ray tube and the X-ray detector continuously orbit around the subject in a spiral manner, and the bed on which the subject is placed is synchronized with the rotation. There is a continuous rotation method (helical scan method) that is defined as a scanning method that moves along an axis.

In particular, Fe in continuous rotation (helical scan) imaging using a two-dimensional array type X-ray detector
A method of applying the ldkamp reconstruction method to perform the reconstruction by the three-dimensional reconstruction method is disclosed in the following document.

1. "Three-dimensional helical scan CT using cone beam projection" Hiroyuki Kudo, Tohoku University, Tsuneo Saito Journal of the Institute of Electronics, Information and Communication Engineers DII Vol.J74-D-II, No.8, pp.11
08-1114, August 1991 2. Japanese Patent Application No. 7-169963 “X-ray computed tomography apparatus”. In Japanese Patent Application No. 7-169963, “An X-ray tube that irradiates a subject with cone-beam-shaped X-rays moves two-dimensionally through an X-ray transmitted through the subject while moving in a spiral orbit relative to the subject. X-ray computed tomography to obtain backprojection data that reflects the X-ray absorption rate for each of a plurality of voxels defined in the imaging region by backprojecting the projection data obtained by detection with an array type X-ray detector In the apparatus, the backprojection data of a specific voxel in the region where the cone beam X-ray flux from the k-th rotation X-ray tube and the cone beam X-ray flux from the k + 1-th rotation X-ray tube overlap, By obtaining based on the collected projection data along the X-ray path passing through the specific voxel and the projection data along the X-ray path passing through the specific voxel collected at the (k + 1) th rotation, either one is obtained. Zui quality as compared to conventional determined is described as. "Improved.

[0022]

A tomographic plane image reconstructed by fan-beam reconstruction using fan-beam X-rays and a tomography reconstructed by cone-beam reconstruction using cone-beam X-rays. Each of the three-dimensional images has advantages and disadvantages, and it is necessary to use them properly according to the intended use. For example, the fan-beam reconstruction process can be processed faster than the cone-beam reconstruction process. Depending on the type of diagnosis, a tomographic plane image may be more suitable than a tomographic stereoscopic image.

However, in order to obtain two types of images, a fan-beam image and a cone-beam image, it is currently necessary to provide two fan-beam X-ray CT devices and cone-beam X-ray CT devices. However, there is a problem that the cost is high and the operability is poor. In addition, regarding fan beam images, it may be necessary to display a plurality of fan beam reconstructed images in order to support biopsies such as CT fluoroscopy. Furthermore, in CT fluoroscopy and IVR-CT in biopsy, since the fan-beam reconstructed image is rarely observed later, when switching between fan-beam reconstruction and cone-beam reconstruction, it is necessary to change the data storage method. Must be done at the same time. Therefore, the present invention is used in an apparatus that uses cone-beam-shaped X-rays, can perform both fan-beam reconstruction and cone-beam reconstruction, and can further improve operability. An object is to provide a processing device.

[0024]

The invention corresponding to claim 1 is:
Irradiate the object with X-rays emitted in a conical shape from the X-ray source,
The X-rays transmitted through this object are detected by an X-ray detector,
In an image reconstruction processing device that reconstructs a tomographic image of an object based on the detection data obtained from the X-ray detector, the tomographic image is detected based on the detection of X-rays that have passed through the object by the X-ray detector. Cone beam reconstruction for reconstructing a tomographic stereoscopic image is performed on the basis of fan beam reconstruction means for performing fan beam reconstruction for reconstructing a planar image and detection of X-rays transmitted through an object by the X-ray detection means. And a cone beam reconstruction means. The invention corresponding to claim 2 is:
In the invention corresponding to claim 1, the fan beam reconstructing means bundles the detection data from the X-ray detector in the thickness direction of the tomographic plane image. The invention corresponding to claim 3 is
In the invention corresponding to claim 1, the reconstruction switching means for switching between the fan beam reconstruction means and the cone beam reconstruction means is provided. The invention corresponding to claim 4 is claim 3
In the corresponding invention, the reconstruction switching means switches the reconstruction means according to the slice position. According to a fifth aspect of the present invention, in the third aspect of the invention, there is provided data storage control means for controlling storage or non-save of the detection data or the reconstruction data according to the reconstruction means switched by the reconstruction switching means. It is provided. The invention according to claim 6 is the invention according to claim 3, further comprising display control means for controlling the display in accordance with the reconstruction means switched by the reconstruction switching means.

According to a seventh aspect of the present invention, the X-rays emitted from the X-ray source in a conical shape are radiated to the object in a continuous rotation system, and the X-rays transmitted through the object are detected by an X-ray detector. In an image reconstruction processing device that reconstructs a tomographic image of an object based on the detection data obtained from this X-ray detector, based on the detection of X-rays that have passed through the object by the X-ray detection means, Cone beam reconstruction means for performing cone beam reconstruction for reconstructing a tomographic three-dimensional image is provided, and this cone beam reconstruction means continuously reconstructs a tomographic three-dimensional image with a cone beam. The invention according to claim 8 is the invention according to claim 7, wherein the cone beam reconstruction means is
The difference between the data obtained by one irradiation and the data before one rotation is obtained, and the result obtained by backprojecting this difference is added to the tomographic stereoscopic image obtained by the irradiation before the predetermined time to reconstruct the cone beam. It is something to do. The invention corresponding to claim 9 is:
Irradiate the object with X-rays emitted in a conical shape from the X-ray source,
The X-rays transmitted through this object are detected by an X-ray detector,
In an image reconstruction processing device that reconstructs a tomographic image of an object based on the detection data obtained from the X-ray detector, the tomographic image is detected based on the detection of X-rays that have passed through the object by the X-ray detector. A fan beam reconstruction means for performing fan beam reconstruction for reconstructing a plane image is provided, and this fan beam reconstruction means simultaneously reconstructs a plurality of tomographic plane images by a fan beam.

According to a tenth aspect of the present invention, the object is irradiated with X-rays emitted in a conical shape from the X-ray source in a continuous rotation system,
The X-rays transmitted through this object are detected by an X-ray detector,
In an image reconstruction processing device that reconstructs a tomographic image of an object based on the detection data obtained from the X-ray detector, the tomographic image is detected based on the detection of X-rays that have passed through the object by the X-ray detector. A fan beam reconstruction unit for performing a fan beam reconstruction for reconstructing a surface image is provided, and the fan beam reconstruction unit obtains a difference between the data obtained by one irradiation and the data one rotation before, and the difference is inverted. The fan beam reconstruction is performed by adding the projection result to the tomographic stereoscopic image obtained by the irradiation before the predetermined time.

The invention according to claim 11 is the invention according to claim 10, wherein the fan beam reconstructing means reconstructs the plurality of tomographic plane images at the same time by the fan beam.

According to a twelfth aspect of the invention, in the invention according to the third aspect, when the object is irradiated with X-rays by a continuous rotation method, the fan beam reconstructing means may, if necessary, provide a plurality of slice planes. At the same time for the image, the difference between the data obtained by one irradiation and the data before one rotation is obtained, and the result obtained by back-projecting this difference is added to the tomographic stereoscopic image obtained by the irradiation before the predetermined time to obtain the fan beam. Reconstruction is performed, and the cone-beam reconstruction means obtains a difference between the data obtained by one irradiation and the data obtained before one rotation, and the result obtained by backprojecting the difference is compared with the data before the predetermined time. Cone beam reconstruction is performed by adding to the tomographic stereoscopic image obtained by irradiation.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram of an X-ray CT apparatus according to the first embodiment. FIG.
FIG. 3 is an external view of the gantry of FIG. 1. A gantry (also referred to as a gantry) 1 as a projection data measurement system includes an X-ray source 3 that generates a cone-beam-shaped X-ray flux similar to a cone, and a plurality of X-ray detection elements arranged two-dimensionally 2 And a three-dimensional array type X-ray detector 5. The X-ray source 3 and the X
The line detector 5 is mounted on the rotating ring 2 so as to face the subject placed on the slide top plate of the bed 6 with the subject interposed therebetween. As the X-ray detector 5, a plurality (1000 channels) of detection elements are arranged so that one-dimensional array type detectors for fan beams are arranged in a plurality of rows (10 rows). (See Figure 51)
), The rotary ring 2 is mounted. Here, one detecting element is defined as corresponding to one channel.

The X-rays from the X-ray source 3 are X-ray filters 4
Is exposed to the subject via the. The X-rays that have passed through the subject are detected as electric signals by the X-ray detector 5. The X-ray controller 8 supplies a trigger signal to the high-voltage generator 7. This high voltage generator 7 applies a high voltage to the X-ray source 3 at the timing of receiving the trigger signal. This allows X from the X-ray source 3.
The line is exposed. The gantry bed controller 9 is the gantry 1
The rotation of the rotating ring 2 and the slide of the slide top of the bed 6 are controlled in synchronization with each other. The system controller 10 serving as the control center of the entire system includes a so-called continuous rotation (where the X-ray source 3 moves in a spiral orbit when viewed from the subject).
For example, the X-ray controller 8 and the gantry bed controller 9 are controlled so as to execute a helical scan. Specifically, the rotating ring 2 continuously rotates at a constant angular velocity, the slide table of the bed 6 moves at a constant velocity, and the X
X-rays are continuously or intermittently emitted from the radiation source 3.

The output signal from the X-ray detector 5 is amplified by the data collecting section 11 for each channel and converted into a digital signal. The projection data output from the data collection unit 11 is taken into the reconstruction processing unit 12. The reconstruction processing unit 12 obtains backprojection data reflecting the X-ray absorption rate for each voxel based on the projection data. In a continuous rotation type X-ray CT apparatus using a cone beam, the effective field of view (FOV, imaging area) becomes a cylindrical shape centering on the rotation center axis of continuous rotation, and the reconstruction processing unit 12
Defines a plurality of voxels (three-dimensionally arranged pixels) in this effective visual field (see FIG. 52), and obtains backprojection data of each voxel from the projection data from the X-ray detector 5.
The three-dimensional image data or tomographic image data created based on the back projection data is sent to the display device 14 and visually displayed as a three-dimensional image or tomographic image.

As shown in FIGS. 3 (a) and 3 (b),
The geometry of this X-ray CT system is: detector row number M = 20, height of each row in the Z-axis direction Dseg = 2 mm, X-ray detector thickness M × Dseg = 40 mm, channel number N = 1000, focus- Distance between rotation centers FCD (Focus-center-Distance
) = 600 mm, distance between focus and detector FDD (Focus-Detector-Distan
ce) = 1200 mm, effective visual field diameter FOV (Field of View) = 50
0 mm, and the effective viewing angle (fan angle) θ = 50 °.

FIG. 4 is a block diagram showing a main configuration of the reconstruction processing unit 12. Reference numeral 21 denotes a reconstruction process which constitutes the control unit main body of the reconstruction processing unit 12 for controlling data selection, weighting, centering process, backprojection and other calculations in the convolution process and backprojection process, and the overall three-dimensional reconstruction process. It is a control unit. The convolution operation unit 22 performs a convolution process on the projection data collected by the data collection unit 11, and the convolution data obtained by this convolution process is stored in the first data memory 23.

The first backprojection unit 24 backprojects (projects) the convolution data stored in the first data memory 23 onto a preset centering plane,
The backprojected centering data is stored in the second data memory 25.

The second backprojection unit 26 performs backprojection (three-dimensional backprojection) on the voxels of the centering data stored in the second data memory 23-2, and the backprojected reconstructed data (image). ) Is stored in the image memory 27.

Reconstruction Here, some points will be considered regarding the three-dimensional reconstruction by the cone beam.
Reconstructed voxel row (straight line), centering plane (planar),
The relationship involving coordinate conversion such as the detector array (arc), the detector surface (cylindrical, but a plane when considered as expanded on the data memory) will be described. First, consider the reconstructed voxel sequence, detector plane, and centering plane. As shown in FIG. 5, it will be explained that the projection of one voxel row (straight line) on the detector surface becomes a curve as shown in FIG.

A view of the reconstructed voxel row, the detector plane, and the centering plane observed from the Z-axis direction (upper) is shown in FIG.
Shown in The channels of the X-ray detector 5 (rows of detectors) are arranged on an arc of equal angle from the focus F in the Z-axis direction, and the rotation angle by the focus rotation (view) is φ, as shown in the figure.
The angle in the channel direction is indicated by θ. Further, at this focus position, the centering surface is on the X axis (included in the X axis Z axis plane), and the X axis coincides with the Xcp axis which is the X axis of the centering surface. Let the coordinates of the reconstructed voxel sequence be (Xv,
Yv) ... (Xv changes with voxels, but Yv is constant). As shown in FIG. 7B, when the length of the line segment FC (focus-rotation center distance) is FCD, the length of the line segment FV0 (focus-voxel distance) is FCD ', and a certain voxel V is considered. Let FCD ″ be the length (in the dotted line in the figure) when the line segment FV is projected onto the XY plane, and FDD is the focal point-detector distance. Also, draw a straight line that passes through the focal point and the voxels, and then on the XY plane. Let Z0 be the Z coordinate and Zv of the voxel V be Zv when the distance from the focal point of FCD is FCD.
Further, the developed coordinates on the detector surface are set to the horizontal axis (Xdet = θ · FDD) and the vertical axis (Zdet) as shown in FIG. 7C.

First, consider projecting the reconstructed voxel sequence on the detector plane. Xcp represents the X coordinate of the line segment FV on the centering plane, and is calculated by the following (Equation 5).

(Equation 6)

Therefore, since ΔFCXcp and ΔFVo Xv are similar, using the following relational expression (Equation 6),

(Equation 7)

## EQU4 ## This (Equation 7) is an equation in the channel direction in the Xv → θ conversion and the projection of the reconstructed voxel column on the detector plane.

Now, since the relationship between the line segment FXcp and the line segment FCD is (Equation 8) shown below, (Equation 9) is obtained.

(Equation 8)

Therefore, the equation in the column direction in the projection of the reconstructed voxel column on the detector plane is as shown in the following (Equation 10).

[Equation 9]

From (Equation 7), it can be seen that when the reconstructed voxel rows arranged at equal pitch are projected onto the detector plane, a non-linear array is formed. Therefore, to the left in the figure, for example, the first voxel and the second voxel
Unlike the interval when the voxels are projected onto the detector surface (for example, 2.4 channels) and the interval between the 511th voxel and the 512th voxel (for example, 3.5 channels) on the right side of the figure, the angle θ is different. It becomes a non-linear array depending on. Further, from (Equation 10), it can be seen that when a linear reconstructed voxel array in which the Z coordinate is fixed at Zv is projected on the detector surface, it becomes a non-linear curve as shown in FIG. 6 depending on the angle θ. However, the Z coordinates Zv and Zdet of the reconstructed voxel column are in a proportional relationship.

This is shown in FIG. 8 and FIG.
Shows the voxel row V, the centering plane C, the detector plane D and their respective variables, and the definitions of the end points and the center points. Note that FIG. 10 shows the voxel row V and the centering surface C. The centering surface C is arranged parallel to the voxel row V. The projection of the voxel row, which is the straight line shown in FIG. 9B, on the centering plane also becomes a straight line as shown in FIG. 9C. The voxel pitch and the pitch of the points on the centering surface have a constant ratio, and no distortion occurs. That is, if the data to be back-projected is linear and equi-pitch on the centering plane, the back-projection on the voxel is also linear and equi-pitch. That is, the relationship between the voxel and the centering surface is a simple scaling relationship.

However, when the voxel array is projected on the detector surface, nonlinear distortion occurs in both the channel direction and the column direction as shown in FIG. 9 (a). However, as shown by the projection of two voxel rows with different Z coordinates Zv, the above-mentioned scaling proportional relationship is established between the projected images of the two voxel rows on the detector surface. ing.

Based on the above consideration, the simplest cone beam reconstruction method is the steps described below. 1. The projection data from the X-ray detector is subjected to Feldkamp weighting processing after correction processing such as X-ray intensity correction, and stored in a data memory. 2. The corrected projection data stored in the data memory is convolved with the reconstruction function and stored in the data memory. 3. According to (Equation 7) and (Equation 10), a projection curve in which the voxel string to be backprojected is projected on the detector surface is calculated, and the data to be backprojected is selected to generate its address. 4. The corresponding data is read out, subjected to predetermined weighting processing, and then added to the position of the corresponding voxel in the image memory.

This is called "direct back projection method". In the process of 3, the projection curve may be calculated in advance and stored as a table in the data memory or the like. This is called the "table method". In either method, the projection curve may be an approximate curve.

Contrary to the consideration in FIG. 9, the case where the pitch and the straight line on the detector plane (or the data memory) are projected on the centering plane will be examined. The ((
(Equation 5) and (Modification of Equation 10) are solved by (Equation 8) (
Equation 11) is shown below.

(Equation 10)

When a straight line on the centering plane is projected on the detector plane, the following (formula 7) and (formula 1)
It is a modification of 1.

[Equation 11]

Therefore, instead of the nonlinear distortion according to (Equation 7) and (Equation 10), the nonlinear distortion according to (Equation 5) and (Equation 11) occurs.

FIG. 11 shows this. 11 (b
), The data of all the channels of the detector array are projected on the centering plane, and as shown in FIG. 11C, Xcp and Zcp are calculated by the above-mentioned nonlinear equations (Equation 4 and Equation 8).
Distorted in both directions. The distortion in the Z direction and the distortion in the array with an equal pitch in the X direction are both opposite to those in the case of FIG. As described above, there is no distortion between the centering surface and the reconstructed voxel row, but as shown in FIG. 11A, when the data of all channels of the detector row is projected on the voxel, the same distortion occurs. That is, the distortion in the Z direction of the projection on the centering plane shown in FIG. 11C and the distortion of the array with an equal pitch in the X direction, and the distortion in the Z direction and the X in the projection on the voxel shown in FIG. 11A. Distortion of an array of equal pitches in the same direction has the same expansion / contraction relationship.

Therefore, the data is resampled on the centering surface by interpolation or the like so that the data are arranged on a straight line at equal pitches. The result is shown in Figure 12.
(a). The relationship between the coordinate systems Xcp and Zcp on the centering plane and the coordinate systems Xv and Zv of the reconstructed voxels is given by (Equation 5
), (Equation 6), (Equation 9), (Equation 10)
(Equation 12) and (Equation 13) are obtained.

(Equation 12)

Therefore, when reconstructing the axial cross section at the slice position Z = Zcp in the reconstructed voxel, considering that axial cross section as a circular FOV inscribed in a square as shown in FIG. 12 (b), (Equation 12) , (Equation 13)
Therefore, Zv is always a constant in the cross section, Yv is a constant in the voxel row, and Xv is changed in voxel units. Therefore, the square (indicated by the broken line) and the circular FOV that inscribes it
The projection of is a trapezoid (indicated by the dashed line) and a deformation of the circle inscribed in it (not shown). Further, the straight line obtained by projecting the voxel row on the centering plane moves up and down in parallel in the centering plane corresponding to the position of the voxel row. Therefore, the Z coordinate Zcp corresponding to the voxel sequence to be backprojected is obtained by (Equation 13), and the X coordinate Xcp corresponding to the voxel to be backprojected is given by (Equation 1).
2) Obtain and back-project the corresponding data to the target voxel. This is repeated for all voxels for all views, and backprojection is performed.

The expression is as follows. Note that F
dpD is the distance between the focus and the detector element, and FcpD (X, Z
) Is the distance between the focal point and the centering point.

(Equation 13)

Here, (Equation 14) is an equation showing the convolution processed data, (Equation 15) is an equation showing the centering processed data, and (Equation 16)
Is an equation showing the data back-projected to the voxels.

This (Equation 16) is

[Equation 14]

[Equation 17] is the three-dimensional reconstruction equation
It matches (Equation 3).

That is, the steps of the three-dimensional reconstruction method (cone beam reconstruction method) using the centering surface of the present invention will be described below. 1. The reconstruction processing control unit 21 performs a correction process such as X-ray intensity correction on the projection data Data-Proj from the data collection unit 11 to obtain raw data Data-Raw and stores it in the first data memory 23. 2. The reconstruction processing control unit 21 causes the convolution operation unit 22 to read the data in the first data memory 23, and after the Feldkamp weighting (the first term of (Equation 14)) processing,
Convolution with the reconstruction function Conv-Function (((
The second term of equation 14)) is stored in the first data memory 23.

3. Based on the convolution data stored in the first data memory 23, the reconstruction processing control unit 21 causes the first backprojection unit 24 to execute the following (i) or
The centering processing of (Equation 15) is performed by either one of (ii). (i) According to (Equation 5) and (Equation 11), calculate the projection curve by projecting the data of the detector surface onto the centering surface, weight the convolution data, and then project onto the centering surface to calculate the centering data. Then, the centering data on the centering surface is shown in Fig. 12 (a).
Then, the data is resampled in a grid pattern and stored in the second data memory 25. (ii) According to (formula 7 modification) and (formula 11 modification), the position of the projection point obtained by projecting the position of the grid-like data resampled in (i) on the centering plane onto the detector surface is calculated, After weighting and adding the convolution data of four (2 columns × 2 CH) detector elements around the projection point (Equation 15
) Is weighted in the three-dimensional back projection and projected onto the centering plane to calculate the centering data Data-Center, which is stored in the second data memory 25.

4. The reconstruction processing control unit 21 uses the equation (12)
And, according to (Equation 13), calculate the projection point (straight line) obtained by projecting the voxel (column) to be reconstructed on the centering plane, and select the data to be backprojected, for example, 4 (2 columns x 2 CH) and set its address. generate. 5. The reconstruction processing control unit 21 reads the corresponding centering data Data-Center from the second data memory 25 by the second backprojection unit 26, weights and adds it when the number of data is plural, and reconstructs the two-dimensional fan beam. As in the case of backprojection of the centering data in the configuration, after the weighting process of the square of A / B (this validity is proved by (Expression 17)), it is added to the position of the corresponding voxel of the image memory 27. . With the above, three-dimensional reconstruction is possible. The flow of this three-dimensional reconstruction processing is shown in FIG.

In the calculation of back projection (projection) data from a point on the detector surface or a point on the centering surface to a point or voxel on the centering surface in the processing of 3 and 5 described above, 4 points Bi -Linear interpolation such as Linear interpolation and Spli
Resampling may be performed using non-linear interpolation such as ne interpolation or other interpolation. Further, the back projection data may be calculated by selecting the point closest to the corresponding projection point as, for example, Nearest Neighbor without performing the interpolation. In the four-point Bi-Linear interpolation, four points Data (j, n) and Data (j, n +) of, for example, the j-th column and the j + 1-th column, the n-channel and the n + 1-channel are set for one projection point.
1), Data (j + 1, n), and Data (j + 1, n + 1) are the objects to be calculated as the interpolated data. At this time, the following calculation is performed in the 4-point Bi-Linear interpolation. Data (j, n) × wch + Data (j, n + 1) × (1-wch) ... CH (j) Data (j + 1, n) × wch + Data (j + 1, n + 1) × (1-wch ) ... CH (j + 1) CH (j) × wro + CH (j + 1) × (1-wro) ... SEG (j, j + 1) The above processing is sequentially repeated for a plurality of projection points. become. That is, CH (j) is calculated, and then C
H (j + 1) is calculated, and SEG (j, j
Calculate +1). Then, for the next projection point, CH (j)
Is calculated, then CH (j + 1) is calculated, and SEG (j, j + 1) is calculated from the calculated results. In the same manner, interpolation processing is repeatedly performed for each projection point. This iterative interpolation process takes time. Therefore, CH (j) and C
H (j + 1) is processed in parallel and SEG (j, j + 1) is pipelined so as to connect the parallel processings, thereby shortening the processing time and almost the same as the two-point interpolation. Interpolation processing can be performed in processing time.

When the number of centering columns is greater than or equal to the number of voxel columns, the closest point to the corresponding projection point is selected as Nearest Neighbor and the backprojection data is calculated. Compared to the Bi-Linear interpolation, the processing time is reduced to about 1/3, and the processing time is shortened.

Although omitted here, the single slice C
As with T (fan beam CT), for the purpose of only nonlinearity in the channel direction and simplification of weight generation during backprojection, 3
It is also possible to omit the resampling process on the centering plane in the process No. 4 and generate a projection curve corresponding to the centering data corresponding to the voxels to be backprojected in the process No. 4. The cost of omitting the resampling process is that the projection curve at the time of backprojection becomes complicated, but it has the advantage of reducing the total number of interpolations.

In this embodiment and the following embodiments, the cone beam X having the cylindrical X-ray detector is used.
Although a line CT apparatus has been described, the present invention is not limited to this. For example, a cone beam X-ray CT apparatus having a planar X-ray detector as shown in FIG. 14 can also obtain the same effect. Is. That is, as shown in FIG. 15, with respect to the voxel row indicated by the straight line arrow and the broken line arrow in the effective field of view FOV, in the projection onto the plane type X-ray detector surface, as shown in FIG. And the broken line arrow does not generate distortion (including nonlinear distortion) in the channel direction (horizontal direction). In addition, the column direction (
No distortion is generated in the vertical direction as well, but since the projection line is an inclined straight line, this is less than in the case of a cylindrical X-ray detector, but the weight generation during data selection and back projection is complicated. is there.

Therefore, by performing the centering processing of backprojecting (projecting) onto the centering surface by intermediary,
As shown in FIG. 17, when the voxel row indicated by the straight line arrow and the broken line arrow in the effective field of view FOV is projected onto the plane type X-ray detector surface, the centering row used for backprojection data calculation in voxel row units is obtained. Since it can be fixed, both data selection and weight generation can be simplified. Note that the weight at the time of back projection can be reduced from the calculation in voxel unit to the calculation in voxel column unit, as in the case of the cylindrical X-ray detector. Further, if the number of centering rows is increased, the effect of improving the interpolation accuracy is the same as that of the cylindrical X-ray detector.

By the way, when the interpolation is repeated, the blur generated in the image is amplified. However, in order to simplify the projection curve and the weight, when backprojecting once to the centering plane and then backprojecting to a voxel, two interpolations are inevitable. That is, as shown in FIG. 18, in the case of the one-time interpolation, the voxel data DB is D
When the position between 1 and D2 is divided into 8: 1, DB = (1/9) × D1 + (8/9) × D2, which is determined by the data positions D1 and D2, and the other of D3, etc. Data interference is completely eliminated. On the other hand, as shown in FIG. 19, in the case of double interpolation in which back projection is performed once on the centering surface, first, the centering points Dc1 and Dc2 are
Backprojects (projects) the detector array onto the centering plane (
When the original () data position (D1, D2, D3) is at a position that divides D1 and D2 into 5: 4 and a position that divides D2 and D3 into 2: 1, Dc1 = ( 4/9) × D1 + (5/9) × D2 Dc2 = (1/3) × D2 + (2/3) × D3, and the voxel data (point) DB is 3 between Dc1 and Dc2: When the position is divided into 5, DB = (5/8) × Dc1 + (3/8) × Dc2 = (5/18) × D1 + (17/36) × D2 + (1/4) × D3. That is, the voxel data DB is actually D
Despite being between 1 and D2, the interference term of D3 is added by two times of interpolation, and the terms of D1 and D2 also include an error by that amount, which causes blurring to be amplified in the actual image. Become. However, it is necessary to reduce the blur generated in the image by improving the accuracy of interpolation.

There are the following two examples of methods for improving the interpolation accuracy. FIG. 20 shows a first example of highly accurate double interpolation. Backprojection of the detector array onto the centering plane (projection).
(Original) data position (D1, D2, D3)
The centering point on the centering surface so that
(Dc1, Dc4, Dc6) are set, and interpolation points (Dc2, Dc3, D) are equally spaced between the centering points.
c5) has been set. This makes it possible to reduce the blurring of the two-time interpolation. For example, voxel data D
When B is in a position that divides Dc3 and Dc4 into 2: 1, DB = (1/3) × Dc3 + (2/3) × Dc4 = (1/9) × D1 + (8/9) × It becomes D2, and the interference term of D3 is completely eliminated at the original data position. However, the projection curve of the detector array on the centering plane has a non-linear distortion, and the original detector data exists between adjacent channels, that is, at the adjacent centering points in the Xcp direction.
Since the coordinates are slightly different, the interpolation point (centering point
) Is difficult to set.

FIG. 21 shows a second example of highly accurate double interpolation. The number of equal-pitch interpolation points (centering points) is set as large as possible in consideration of the balance with the calculation time.
Interpolation points do not necessarily have to exist at the original data positions. However, since the number of centering rows is greater than the number of detector rows, the interpolation accuracy is high at most positions, and blurring due to interpolation occurs because the second interpolation position (voxel) is the original data position. It is only when it is between two interpolation points of the first time (for example, between Dc9 and Dc10).

For example, if the voxel data DB is Dc8 and Dc
When there is a 1: 1 division between c9 and DB, DB = (1/2) x Dc8 + (1/2) x Dc9 = (1/10) x D1 + (9/10) x D2, which is the original The interference term of D3 is completely eliminated at the data position. Also, the voxel data DB is
When it is in a position where the distance between Dc9 and Dc10 is divided into 1: 1 (just the position corresponding to D2), DB = (1/2) × Dc9 + (1/2) × Dc10 = (1/40) × D1 + ( 14/15) × D2 + (1/24) × D3, and the interference term of D3 (in this case, D1 also applies) is not excluded, but the weights (coefficients) of D1 and D3 are D
Since it is smaller than 2, the blur is reduced as compared with the conventional blur, and the range in which this blur occurs is limited to the distance between Dc9 and Dc10 as described above.

An example in which this is applied to the centering surface is shown in FIG.
It is shown in FIG. FIG. 22 (a) is a projection curve on the centering plane of the five detector rows and shows the original data position. As described in the step of the three-dimensional reconstruction method (cone beam reconstruction method) using the centering surface described in the first embodiment, the original data are arranged in a grid pattern on the centering surface. Create centering data. FIG. 22B shows a case in which the number of rows (centering rows) of the grating is the same as the number of detector rows, that is, five rows. A straight line S indicates a data position to be backprojected on a certain voxel column. The second centering row C2 is used for interpolation with a light weight, and the third centering row C3 is used for interpolation with a heavy weight. It can be seen that the width of the data used for this interpolation widens in the Zcp direction and blurring occurs. This corresponds to the example of the double interpolation in FIG.

FIG. 22C shows an example (10 rows) in which the number of centering rows is larger than the number of detector rows. The data position to be backprojected onto a certain voxel column is shown by the straight line S as in the above. The fourth centering column C4 is used for interpolation with a light weight, and the fifth centering column C5 is used for interpolation with a heavy weight. The width of the data used for this interpolation is Z
It can be seen that it becomes narrower in the cp direction and blurring can be suppressed. This corresponds to the second example of highly accurate double interpolation in FIG.
Note that, in FIG. 21, the interpolation method is also linear linear interpolation based on the inverse ratio of the distance. However, the arrow point ((
Interpolation accuracy when DB is located between Dc8 and Dc9 is very high. In addition, the number of centering columns is significantly increased with respect to the number of detector columns (for example, 50 or 500 centering columns with respect to 5 detector columns), and the second interpolation is performed by zero-order interpolation, that is, the closest centering. Select columns
It is also good to use Nearest Neighbor.

Here, three examples will be described with respect to the configuration capable of switching between cone beam reconstruction and fan beam reconstruction, which is the gist of the present invention. The first example is a method of switching the projection curve to be generated. As shown in FIG. 23, the reconstruction processing control unit 21 is provided with a reconstruction method designating unit 21-1 and a projection curve calculation unit 21-2, and the reconstruction method designating unit 21
The projection curve calculation unit 21-2 generates a projection curve or a projection line according to the reconstruction method designated (set or determined) by -1.

The reconstruction process performed with such a configuration is as follows. When the cone-beam reconstruction is designated by the reconstruction method designating unit 21-1, the projection curve computing unit 21-2 projects the voxel string onto the detector plane as shown in FIG. A curve is generated, and then the reconstruction processing control unit 21 obtains backprojection data corresponding to the projection curve (cone beam reconstruction processing (three-dimensional reconstruction processing)) and adds it to the image memory 27 to generate an image. Remember. 2. When the fan beam reconstruction is designated by the reconstruction method designating unit 21-1, the projection curve computing unit 21-2 passes the center of a certain detector row as shown in FIG. 24 (a) (or As shown in FIG. 24 (b), a projection straight line parallel to the detector row (slice plane) is generated between a plurality of detector rows, and then the reconstruction processing control unit 21 causes the inverse projection line corresponding to the projection straight line. The projection data is obtained (fan beam reconstruction processing) and added to the image memory 27 to store the image.

In this fan beam reconstruction, the reconstruction processing control unit 21 can take either one of (1) and (2) described below in the data selection processing and the interpolation weight generation processing. it can.

(1) As shown in FIG. 25 (a), select the data of one detector row closest to the generated straight line,
Weight 0%. (2) As shown in Fig. 25 (b), select the data of multiple detector rows that are close to the generated straight line and perform weighted interpolation (addition).
I do. By performing 100% weighting on the data of one detector row selected by the former, it is possible to simultaneously reconstruct images of a plurality of slices for each detector row. In addition, by performing the weighted interpolation of the selected detector rows in the latter case, the data of the detector rows can be bundled and reconstructed as a fan beam. A flowchart of this reconstruction processing is shown in FIG.

The second example is a method of switching the control of writing the convolution data to the first data memory 23. As shown in FIG. 27, the reconstruction processing control unit 21 is provided with a reconstruction method designating unit 21-1 and a data control unit 21-3, and the reconstruction method designated by the reconstruction method designating unit 21-1. Accordingly, the data control unit 21-3 controls the storage of the convoluted data in the first data memory 23. The reconfiguration process performed with such a configuration is as follows. When cone beam reconstruction is designated by the reconstruction method designating unit 21-1, the data control unit 21-3
As shown in FIG. 28, the convolution data of each detector array is stored in the corresponding area of the first data memory 23, and then the reconstruction processing control unit 21 calculates the projection curve and outputs the data for backprojecting. The image is obtained and added to the image memory 27 to store the image. 2. When the fan beam reconstruction is designated by the reconstruction method designating unit 21-1, the data control unit 21-3
As shown in FIG. 29 (a) or FIG. 29 (b), the same convolution data of one column is stored in the first data memory 23.
Multiple storage in the area of. After that, the reconstruction processing control unit 2
1 calculates a projection curve, obtains data for backprojection, adds it to the image memory 27, and stores the image.

As described above, it is possible to switch to fan beam reconstruction by making the data of all or a certain range of detector rows the same in the row direction. In addition, 2. Therefore, the convolution data of one column stored in the regions of all columns of the first data memory 23 is a certain detector one column (third column in the figure) as shown in FIG. 29 (a). Alternatively, for example, as shown in FIG. 29 (b), data of a plurality of detector rows (for example, convolution data of the second and third rows) is created by weighted interpolation (addition). Data (= 0.4 x 2nd row + 0.6 x 3rd row)
May be If the latter weighted interpolation of a plurality of detector rows is performed, the data of a plurality of detector rows can be bundled and regarded as a fan beam for reconstruction. A flowchart of this reconstruction processing is shown in FIG.

In the third example, as shown in FIG. 31, the reconstruction processing unit 12 performs a three-dimensional reconstruction processing (using a gate array or the like) using the centering plane or a reconstruction processing using the direct back projection method ( You may use the table method)
The cone beam reconstruction unit 12-1 (by a general-purpose computer or the like) and the fan beam reconstruction process such as the fan-para conversion reconstruction process or the reconstruction process using the centering axis as described in the prior art is performed ( It is composed of a fan beam reconstruction unit 12-2 (by a well-known gate array), and these reconstruction units are switched and used. Although the third example may be implemented by hardware as described above, when the reconstruction processing unit 12 is composed of a general-purpose computer, the cone beam reconstruction processing program and the fan beam reconstruction processing are performed. It may be realized as software by having two types of programs of configuration processing and selecting and starting both of them.

When performing fan beam reconstruction (when switching to the fan beam reconstruction unit 12-2), in the reconstruction process using the centering axis, as shown in FIG. 32 (see FIG. 12), 1 In order to form two images (tomographic planes), one column (centering axis) S on the centering plane is used for each voxel column (substantially a pixel column) of the image. Backprojection to the same). At this time, there is a scaling relationship between the length of the focus-reconstructed voxel sequence and the length of the focus-centering sequence S, and the backprojected data of the centering sequence is the range (positions at both ends
) Is different.

In the following, when the data of a plurality of detector rows in the above-described first to third examples are bundled and regarded as a fan beam for reconstruction, the timing of bundling the data, the method of selecting the data to be bundled, and the bundling The number of sheets will be described.
Also in the third example, since the X-ray detector is a two-dimensional array type composed of a plurality of detector rows, the fan beam reconstruction is performed in order to effectively use the obtained data of each row. In, the process of bundling data in the column direction is performed.

First, the timing for bundling data is the first
In the case of the above example, it is immediately before back projection after the calculation of the projection line.
When calculating the data for backprojection from the projection line, for example, data for four detector rows close to the projection line is calculated by, for example, (0.
1, 0.33, 0.33, 0.24), the data for four columns will be bundled. The reconstruction processing control unit 21 determines the number of data and weighting, and the weighting may be linear or non-linear.

In the cases of the second and third examples, there are the following two types of timing for bundling the data, and either of them may be used. 1. After performing the convolution processing, the convolution data is weighted and added and bundled. 2. At the stage of raw data, weighted addition is performed and bundled and regarded as one column of data, weighting of cos (cosine function) and convolution operation with the function are performed, and the created data is stored in the first data memory 23. And reconfigure. However, in the second example, it is necessary to previously input the information (detector array) of the position to be reconfigured into the data control section 21-3 and the corresponding control section in the third example.

Next, there are the following six methods for selecting the data to be bundled and the number of data to be bundled. 1. Use all columns of data and bundle into multiple data. Create multiple data by using the data from all detector rows once. For example, as shown in FIG. 33 (a), a total of 2
The data of the detectors in 0 columns are weighted and added every 5 columns to create 4 data.

2. Only the data of the detector array located in the central part is used and bundled into multiple data. Since the detector rows located at both ends have a large cone angle, the accuracy of data decreases. Therefore, the data of the detector rows located at both ends are not used, but only the data of the detector rows located in the center are used to create a plurality of data. For example,
As shown in Figure 33 (b), of the 20 detector rows in total, 4 detector rows at each end (8 rows in total) are not used, but the detector row in the center is not used. The data of (total of 12 columns from the 5th column to the 16th column) are weighted and added every 4 columns to create 3 data.

3. One data is created only by the data of the detector row in the central part. The data of the detector rows located at both ends are not used, but one data is created using only the data of the detector rows located at the center. For example, as shown in FIG. 33 (c), of the 20 detector rows in total, 4 detector rows at each end (8 rows in total) are not used, but the detector row at the center is not used. The data of (total of 12 columns from the 5th column to the 16th column) are weighted and added to create one data.

[0086] 4. Extract and bundle data at regular intervals. Data is deliberately extracted at regular intervals, and the data in the detector array between them is bundled to create multiple data. For example, FIG.
As shown in 3 (d), the data in 20 columns is replaced by every 7 columns.
The columns are left blank, and 6 columns are weighted and added to create three data.

5. Overlap and bundle. The data of some detector rows is used multiple times to create multiple data. For example, as shown in FIG. 33 (e),
8 detector rows at both ends of 20 detector rows ×
2 (1st to 8th columns, 13th to 20th columns) of data and 8 detector rows located in the center (7th to 7th columns)
The data in the 14th column) is weighted and added to create three data. There is an overlapping part (7th and 8th columns and 13th and 14th columns).

6. Change the number of data to be bundled. The number of detector rows used depends on the data to be created. For example, as shown in FIG. 33 (f), the detector rows among the 20 detector rows are weighted and added by 6, 8 and 6 rows to create three data.

Data may be created by combining the above 1, 2, 4, 5, and 6. For example, by combining 2, 5 and 6, as shown in FIG. 33 (g), the data of 4 detector rows at each end (8 rows in total) is not used, but the data is placed at the center. Of the four detector rows, four detector rows (fifth to eighth rows), eight detector rows (seventh to fourteenth rows), four detector rows (13th to 16th columns
The data in the (column) is weighted and added to create three data. There is an overlapping part (7th and 8th columns and 13th and 14th columns).

In addition to the bundling method described above, the bundling method may be changed depending on the conditions of the X-ray detector and the subject (object). Also, simple average addition or the like may be used instead of weighted addition.

In the first embodiment having such a configuration, for example, X-ray photography is performed as described below. 1. The operator switches the scan mode in order to perform biopsy under low dose fluoroscopy. 2. The system control unit 10 instructs the reconstruction processing unit 12 to switch the reconstruction method from "cone beam reconstruction" to "fan beam reconstruction", and switches to the fan beam reconstruction method. 3. The system control unit 10 notifies the operator that the data processing method is switched to "no data storage" and the display method is switched to "real time image display". 4. The operator confirms and starts scanning. 5. The system control unit instructs the X-ray controller 8 to irradiate X-rays, the data collection unit 11 collects data, performs processing such as data bundling, and the reconstruction processing unit 12 reconstructs the fan beam. 6. Images reconstructed one after another by the reconstruction processing unit 12 are updated and displayed on the monitor of the display device 14. 7. Data that is no longer used for reconstruction is not stored in the data storage device (hard disk or memory), and the data is overwritten.

The processing of 8.4 to 7 is repeated, and the scan is completed. The monitor continues to display the last reconstructed image. 9. The operator switches to volume photography mode to confirm the side effects of the examination such as pneumothorax. 10. When the reconstruction method is switched from "fan beam reconstruction" to "cone beam reconstruction", the system control unit 10 instructs the reconstruction processing unit 12 to switch the reconstruction method. 11. The system control unit informs the operator that the data processing method is switched to "data storage" display method to "volume image display". 12. The operator confirms and starts scanning. 13. The system control unit instructs the X-ray controller 8 to emit X-rays, the data collection unit 11 collects data, and the reconstruction processing unit 12 reconstructs the cone beam. 14． The volume image reconstructed by the reconstruction processing unit 12 is displayed on the monitor. 15. Data that is no longer used for reconstruction is stored in a data storage device (hard disk or memory). 16. The scan ends. The operator sees the image and finishes the inspection. As described above, the data storage, the type of display image, etc. are switched in association with the reconstruction method. Alternatively, the number of displayed images may be switched to three when the perspective of the fan beam reconstruction is performed and one when the cone beam is reconstructed.

As described above, according to the first embodiment, both the cone beam reconstruction and the fan beam reconstruction can be performed by switching in the X-ray CT apparatus using the cone beam X-rays. , Interlocking with the switching,
You can switch data storage (data storage / non-storage) and display image types.

Particularly, in the fan beam reconstruction, one or a plurality of tomographic plane images having a desired thickness (arbitrary thickness) can be reconstructed at the same time.

The second embodiment of the present invention will be described with reference to FIGS. The second embodiment is basically the same as the system configuration of the above-described first embodiment, and the same members are designated by the same reference numerals and the description thereof will be omitted. In the first embodiment described above, the image reconstruction method may be specified by a technician (doctor) or the like by manual operation, or may be automatically specified by providing some means for automatically determining. Anything is good.

In the second embodiment, first to third methods are shown as specific examples of automatically switching the image reconstruction method.

The first method for automatically switching the reconstruction method is to switch the method for generating the projection curve on the voxel plane of the detector array depending on the slice position.

FIG. 34 shows the X-ray C of the second embodiment.
It is a block diagram which shows the structure which achieves the 1st method of the reconstruction process control part 21 of T apparatus. The slice position determination unit 21-4, which determines the slice position, supplies the slice position information to the reconstruction method designating unit 21-1, and the reconstruction method designating unit 21-1 supplies the supplied slice position information. Specify the reconstruction method based on. The projection curve calculation unit 21-2
Generates a projection curve for cone beam reconstruction or a projection curve for fan beam reconstruction according to the reconstruction method designated by the reconstruction method designating unit 21-1.

In the first method of the second embodiment having such a configuration, image reconstruction is performed based on the reconstruction processing performed by the reconstruction processing control unit 21 shown in FIG. First, as the processing of step 1 (ST1), it is determined whether or not the slice position to be reconstructed is included in the MidPlane region as a tomographic plane formed by the central axis of the cone beam by the rotation of the X-ray source. For example, when the total number of detector rows of the X-ray detector is 20, when the X-ray source and the X-ray detector are directly faced to each other, MidPlane is generally used as the X-ray source (focus point).
) Is the tomographic plane including the center line of the cone beam, and in the case of this 20-row X-ray detector, the 10th detector row
It is sandwiched between (No. 10) and 11th (No. 11), and the MidPlane area is the 10th detector row (No. 10).
And 11th (No. 11). Therefore, MidPlane
Two slices (No. 10 or No. 11) above and below sandwiching
When reconstructing a slice position other than the above (for example, No. 20), it is determined that the slice position is not included in the MidPlane area, and cone beam reconstruction is designated as the processing of step 2 (ST2), and step 3 As the processing of (ST3), a projection curve as shown in FIG. 36 (a) is generated, and as the processing of step 4 (ST4), the data of the detector array corresponding to the generated projection curve is selected and selected. The data is weighted and added, the backprojection data is calculated, and the cone beam reconstruction is performed.

In the process of step 1, No. 10 or No. When reconstructing 11 slice positions, it is determined that the slice positions are included in the MidPlane area,
As the processing of step 5 (ST5), fan beam reconstruction is designated, and as the processing of step 6 (ST6), focus
The projection curve determined by the positional relationship between the (X-ray source) position and the reconstructed voxel is ignored, and a projection straight line as shown in FIG. 36 (b) is generated, and the generated projection is generated as the process of step 7 (ST7). Select the detector row data corresponding to the straight line,
The selected data is weighted and added to calculate backprojection data to perform fan beam reconstruction.

As described in the first embodiment, the cone beam reconstruction processing and the fan beam reconstruction processing can be modified in various ways (including bundling processing). In the second embodiment, The feature is that the optimum reconstruction method is automatically specified when the slice position is determined depending on the slice position to specify the reconstruction switching. Further, in the above-described reconstruction processing, it is possible to simultaneously reconstruct a plurality of slice images by different reconstruction methods by designating a plurality of slice positions.

The second method for automatically switching the reconstruction method is that the control for storing data in the first data memory 23 can be switched depending on the slice position. FIG.
FIG. 6 is a block diagram showing a configuration for achieving a second method of the reconstruction processing control unit 21 of the X-ray CT apparatus. The slice position determining unit 21-4 supplies the slice position information to the reconstruction specifying unit 21-1, and the reconstruction method specifying unit 21-1 determines the reconstruction method based on the supplied slice position information. specify. The data control unit 21-3 controls the storage of the convoluted data in the first data memory 23 according to the reconstruction method designated by Eve 21-1 by the reconstruction method. In the second method of the second embodiment having such a configuration, image reconstruction is performed based on the reconstruction processing performed by the reconstruction processing control unit 21 shown in FIG. First, as a process of step 11 (ST11),
It is determined whether the slice position to be reconstructed is included in the MidPlane region as a tomographic plane formed by the central axis of the cone beam by the rotation of the X-ray source.

Therefore, as described in the first method, the slice positions (for example, No. 20) other than the upper and lower two slices (No. 10 or No. 11) sandwiching the MidPlane.
) Is reconstructed, it is determined that the slice position is not included in the MidPlane area, cone beam reconstruction is designated as the processing of step 12 (ST12), and step 13 (
As the processing of ST13), as shown in FIG. 39 (a),
The convolution data of each detector array is stored in the corresponding area of the first data memory 23. Next, in step 14 (ST14), a projection curve obtained by projecting the voxel string on the detector surface is calculated (generated), and in step 15 (ST15), weighting and addition are performed based on this projection curve. Then, the back projection data is obtained, and the cone beam back projection is performed.

In the process of step 11, No. 10
Or No. In the case of reconstructing the slice position of 11, the slice position is determined to be included in the MidPlane area, fan beam reconstruction is designated as the processing of step 16 (ST16), and the slice position of step 17 (ST17) is specified. As processing, as shown in FIGS. 39 (b) to 39 (d), N
o. 10 or (and) No. Using the convolution data of the 11 detector rows, the first data memory 23
Multiple storage in. At this time, as shown in FIG. 39 (e), it is not necessary to fill the entire area of the first data memory 23 with the convolution data, and only the area related to the projection curve in which the voxel string is projected on the detector surface is involved. , No.
10 or (and) No. If the convolutional data of the detector array of 11 is used for filling, the time for writing the convolutional data can be shortened.

Next, as the processing of step 18 (ST18), a projection curve in which the voxel string is projected on the detector surface is calculated.
(Occurs), and as the processing of step 19 (ST19),
Based on this projection curve, weighting and addition are performed to obtain backprojection data, and fanbeam backprojection is performed.

In the process of step 17, simply N
o. When reconfiguring No. 10, as shown in FIG. The convolution data of 10 are multiplexed and stored in all the areas of the first data memory 23, and simply N
o. When reconfiguring No. 11, as shown in FIG. The eleven convolution data are multiply stored in all areas of the first data memory 23. In addition, as shown in FIG. 39 (d) in combination, the first data memory 2
No. 3 in the upper half. 10 convolution data,
No. in the lower half 11 convolution data are stored in multiplex. In this way, the No. When reconfiguring No. 10 and No. It is not necessary to rewrite data when reconfiguring 11, and the reconfiguration processing time can be shortened.

In the second method as well, similar to the first method, the cone beam reconstruction processing and the fan beam reconstruction processing can be modified in various ways (including bundling processing), and the reconstruction can be switched. When the slice position is determined depending on the slice position, the optimum reconstruction method is automatically specified.

A third method for automatically switching the reconstruction method is
(When using a general-purpose computer), two types of reconstruction programs, cone beam reconstruction and fan beam reconstruction, are stored, and the reconstruction program to be used is switched depending on the slice position. Alternatively, in the case of a combination of a general-purpose computer that performs cone-beam reconstruction and a fan-beam reconstruction unit that uses a gate array or the like, the general-purpose computer and the fan-beam reconstruction unit are switched and operated depending on the slice position.

FIG. 40 shows an example of the structure for achieving the third method. That is, the cone beam reconstruction unit 1
2-1 and a fan beam reconstruction unit 12-2, and further includes a slice position determination unit 21-4 and a reconstruction method designation unit 2
1-1, the slice position determination unit 21-4 supplies the slice position information to the reconstruction specifying unit 21-1, and the reconstruction specifying unit 21-1 uses the supplied slice position information. Specify the reconstruction method based on Then, the cone beam reconstruction unit 1 corresponding to the specified reconstruction method
Either one of 2-1 and fan beam reconstruction unit 12-2 is activated.

In the second embodiment,
We have described an example of performing fan-beam reconstruction when reconstructing the two slices adjacent to the MidPlane, and cone-beam reconstruction at other times, but the point is to switch the reconstruction method depending on the slice position. A reconstruction method may be used, or switching may be performed according to another slice position.

As described above, according to the second embodiment, it is possible to obtain the effect of the first embodiment described above, and further, the fan beam reconstruction is automatically performed depending on the slice position. The method and the cone beam reconstruction method can be switched. Moreover, when the fan beam reconstruction method is selected, a high quality fan beam image (tomographic image)
Can be obtained.

A third embodiment of the present invention will be described with reference to FIGS. 41 and 42. In the third embodiment, in the continuous rotation method, high speed and continuous (real time) cone beam reconstruction is realized. The gantry 1 is performing continuous rotation scanning, for example, one rotation 900 views.

1. When the rotation of the gantry 1 exceeds 360 °,
The cone beam reconstruction is performed by the Feldkamp method using the data for 360 °. Hereafter, reconstructed voxel data Voxel (N,
Suppose that M-1) was reconfigured. 2. The gantry rotates further and scans. The data Raw (N, M) of the Nth rotation M view is collected. 3. Data Raw (N, M) is weighted and subjected to convolution processing, and convolution data Co of N rotation M views
Get nv (N, M). 4.1 Before one rotation, that is, the difference between the convolution data Conv (N-1, M) and Conv (N, M) of the (N-1) th M view is calculated to obtain difference data Sub (N, M).

[0114] 5. The reconstruction processing control unit 21 generates a projection curve as shown in FIG. 6 which results in cone beam reconstruction. 6. The reconstruction processing control unit 21 selects and weights the difference data Sub (N, M) corresponding to the generated projection curve to obtain backprojection data Back (N, M). 7. The backprojection data Back (N, M) is added to the reconstructed voxel data Voxel (N, M-1) up to the previous time to obtain the reconstructed voxel data Voxel (N, M) this time. 8. Every time the gantry rotates and new data is obtained, the above 2-7
The reconstructed voxel data is constantly updated by reconstructing continuously by repeating the above process. FIG. 41 shows a flowchart of this reconstruction process.

By the way, when the reconstruction processing unit 12 can switch the reconstruction method according to the slice position in the above-mentioned second embodiment, the processing of the above-mentioned 5 follows the following 5-1.
It may be extended like the processing of. 5-1. The reconstruction processing unit 12 generates a projection curve (projection straight line) corresponding to the reconstruction method corresponding to the reconstruction slice position.

Furthermore, the reconstruction processing unit 12 uses the above-mentioned first
The configuration described in the above embodiment is adopted, and when it is possible to switch the reconstruction method depending on the mode, the above process 5 may be extended to the following process 5-2.

5-2. The reconstruction processing control unit 21 generates a projection curve (projection straight line) corresponding to the reconstruction method designated by the reconstruction designation unit 21-1.

FIG. 42 is a flowchart of this reconstruction process.
Shown in

As described above, according to the third embodiment, the difference data is 0 after the first reconstruction (first rotation).
Since it is not necessary to backproject, the data to be backprojected can be reduced, and the backprojection processing time can be shortened. In the third embodiment, the reconstructed voxel data is updated one view at a time. However, for example, the reconstructed voxel data is updated 10 times per rotation. You may make it process collectively and may update an image after that.

Further, a certain cross section may be cut out from the reconstructed voxel data and displayed, or a shape obtained by processing the voxel data, for example, maximum value projection (MIP
) Images may be displayed.

Further, in the third embodiment, the back-projection is performed by taking the difference of convolution data, but the back-projection may be performed by taking the difference of other data (centering data) such as raw data. is there.

A fourth embodiment of the present invention will be described with reference to FIGS. 43 to 46. The above-described third embodiment is 1
In contrast to the method for continuously reconstructing one tomographic stereoscopic image at high speed, in the fourth embodiment, a plurality of tomographic plane images are simultaneously and continuously reconstructed in the continuous rotation method. It is what constitutes. 1. When the rotation of the gantry 1 exceeds 360 °, three data for 360 ° are used to perform 3 by the fan beam reconstruction method.
Two images are reconstructed. Reconstructed as data up to the Mth view of the Nth rotation, and the three regions of the image memory 27 are respectively reconstructed images A (N, M-) as shown in FIG.
1), B (N, M-1), C (N, M-1) (these are composed of pixel data) are stored, and 3 of the display device 14 are stored.
It is displayed on each of the two monitors. 2. The gantry 1 further rotates and scans. Collect Raw (N, M) data for N rotations M views. 3. Raw (N, M) is weighted and convolved,
Convolution data C corresponding to images A, B, and C
onv-A (N, M), Conv-B (N, M) and Conv-C (N, M) are obtained. 4.1 Difference data between the convolution data of the M view before the first rotation (N-1th rotation) and the convolution data of the current rotation (Nth rotation) M view, that is, Conv-A (N-
The difference data Sub-A (N, M) between 1, M) and Conv-A (N, M) is calculated. Similarly, Sub-B (N, M) and Sub-C (N, M) are also calculated.

5. The fan beam backprojection data Back-A (N, M) is calculated from the difference data Sub-A (N, M). Similarly B
Get ack-B (N, M) and Back-C (N, M). 6. The backprojection data Back-A (N, M) is added to the reconstructed image A (N, M-1) stored in the image memory 12-3A (reconstructed image A (N, M consisting of pixel data)). M) get Similarly, reconstructed images B (N, M) and C (N, M) are also obtained. 7. Every time the gantry rotates and new data is obtained, the processes of 2 to 6 are repeated to continuously reconstruct three images,
Always update the displayed image. FIG. 44 shows a flowchart of this reconstruction process.

By the above-described reconstruction processing, high-speed and continuous fan-beam reconstruction of a plurality of images can be realized.

As shown in the flow chart of FIG. 45, reconstructed image A (N, M), reconstructed image B (N, M), reconstructed image C (N, M) for one acquisition Conv-A (N, M) and difference data Sub-A (N, M)
, Fan-beam back-projection data Back-A (N, M), reconstructed image A (N, M), and so on. After the calculation of is completed, starting from Conv-B (N, M) to the reconstructed image B (N, M), then starting from Conv-C (N, M) to the reconstructed image C It is possible to calculate up to (N, M).

Although the description of the method of creating the Conv-A to Conv-C data is omitted, as described in the first embodiment, the data of one predetermined detector array is used. Based on the data obtained by weighting and adding the data of a plurality of detector rows, or based on the data obtained by a simple bundling process.

Also in the fourth embodiment, as in the third embodiment described above, back projection is performed by taking the difference of convolution data, but other data such as raw data is also used.
It is also possible to take the difference of (centering data) and carry out back projection. In the fourth embodiment, the reconstruction processing unit 12 may have a single backprojection calculation unit 31 as shown in FIG. 46 (a), for example.
Each data memory area 32-- as shown in FIG. 6 (b)
1, 32-2, 32-3 and each image memory area 33-1, 3
A plurality of backprojection calculation units 31-1, 3 corresponding to 3-2, 33-3
It is also possible to provide 1-2 and 31-3 so that the respective backprojection processing lines operate independently. This Fig. 46 (b)
With the configuration shown in (1), it is possible to realize even faster processing. As described above, according to the fourth embodiment, since it is not necessary to backproject the difference data of 0 after the first reconstruction (first rotation), it is possible to reduce the data to be backprojected. Therefore, the back projection processing time can be shortened. In the fourth embodiment,
The reconstructed image data was updated one view at a time, but for example, it is updated 10 times per rotation, and after some rotation of the gantry, a certain number of views are collectively processed, and then the image is updated. You can

In all the above-mentioned embodiments, the system geometry including the number of detector columns N = 20, the weighting method, the number of columns to be bundled, the number of bundled data, and the number of reconstructed sheets = 3 are examples. However, the present invention is not limited to this.

[0129]

As described in detail above, according to the present invention,
It is used in an apparatus that uses cone-beam-shaped X-rays, can perform both fan-beam reconstruction and cone-beam reconstruction, and can provide an image reconstruction processing apparatus that can improve operability. Therefore, by using this image reconstruction processing apparatus, it is possible to realize an X-ray CT apparatus that can switch between fan-beam reconstruction and cone-beam reconstruction by using cone-beam-shaped X-rays.
Further, in the fan beam reconstruction, since the data of a plurality of detector rows are bundled to perform the fan beam reconstruction, a tomographic plane image having a desired thickness can be easily reconstructed. In the cone-beam X-ray, the upper and lower slices adjacent to the MidPlane are close to the fan-beam X-ray, and by switching the reconstruction method depending on the reconstruction position, a high-quality fan-beam reconstructed image can be obtained. Obtainable.

In fan beam reconstruction and cone beam reconstruction, the difference from the data one rotation before is calculated, and back projection is performed with this difference data and added to the image one view before. Since the backprojection processing of the non-existing portion can be omitted, high-speed continuous reconstruction processing can be performed. In particular, in fan beam reconstruction, it is possible to obtain multiple fan beam images (tomographic plane images) of arbitrary thickness by bundling processing from the data from the detector array, and the reconstruction process for that can be performed. It can be performed continuously at high speed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an X-ray CT apparatus according to a first embodiment of the present invention.

FIG. 2 is an external view showing a gantry of the X-ray CT apparatus according to the same embodiment.

FIG. 3 is a view for explaining the geometry of the X-ray CT apparatus according to the same embodiment.

FIG. 4 is a block diagram showing a main configuration of a reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 5 is a diagram showing projection of voxel rows onto a detector plane in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 6 is a diagram showing a projection curve on a detector plane of a voxel column in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 7 is a diagram for explaining a projection curve on a detector plane of a voxel column in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 8 is a diagram showing a voxel array, a centering plane, a detector plane and their respective variables and a centering plane showing definitions of end points and center points in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment;

FIG. 9 is a diagram showing a projection curve of a voxel array on a detector plane, a voxel array, and a projection curve of a voxel array on a centering plane in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment;

FIG. 10 is a diagram showing a voxel row and a centering surface in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 11 is a view showing a projection curve of a detector array on a voxel, a detector array, and a projection curve of a detector array on a centering plane of the detector in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment;

FIG. 12 is a view for explaining resampling of data such as interpolation processing on the centering plane in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 13 is a diagram showing the flow of three-dimensional reconstruction processing performed by the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 14 is an X used in the X-ray CT apparatus according to the embodiment.
The figure which shows the plane type X-ray detector as another example of a line detector.

FIG. 15 is a diagram showing a positional relationship between a voxel array and a planar X-ray detector in an X-ray CT apparatus using the planar X-ray detector according to the same embodiment.

FIG. 16 is a diagram showing a projection curve of a voxel array onto a detector surface of a flat X-ray detector in an X-ray CT apparatus using the flat X-ray detector according to the same embodiment.

FIG. 17 is a diagram showing a projection curve on a centering plane of a voxel row in an X-ray CT apparatus using the flat panel X-ray detector according to the same embodiment.

FIG. 18 is a diagram for explaining an example of one-time interpolation in back projection of a detector array onto voxels.

FIG. 19 is a diagram for explaining an example of double interpolation in back projection of a detector array onto voxels.

FIG. 20 is a diagram for explaining a first example of highly accurate double interpolation in backprojecting a detector array onto a voxel in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment;

FIG. 21 is a diagram for explaining a second example of high-precision double interpolation in backprojecting a detector array onto a voxel in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 22 is a projection curve to the centering plane of the five detector rows in the reconstruction processing unit of the X-ray CT apparatus of the embodiment, to the centering plane of the voxel row when the number of centering rows is five. FIG. 6 is a diagram showing a centering sequence weighted with the projection curve (projection straight line) and a centering sequence weighted with the projection straight line on the centering surface of the voxel column when the number of centering sequences is 10.

FIG. 23 is a block diagram showing a configuration as a first example of a reconstruction processing control unit of the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

24A and 24B are two examples of projection curves (projection straight lines) of voxel rows on the detector plane for fan beam reconstruction in the first example in the reconstruction processing unit of the X-ray CT apparatus of the same embodiment. FIG.

FIG. 25 shows the projection straight line of the voxel array onto the detector surface and the weighting of each detector array for fan beam reconstruction in the first example in the reconstruction processing unit of the X-ray CT apparatus of the same embodiment. The figure which shows two examples.

FIG. 26 is a diagram illustrating a reconstruction performed by switching between the fan-beam reconstruction method and the cone-beam reconstruction method according to the projection curve in the first example performed by the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment. The figure which shows the flow of a structure process.

FIG. 27 is a block diagram showing the configuration of a second example of the reconstruction processing control unit of the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 28 is a diagram showing the contents of a data memory at the time of cone beam reconstruction in the second example in the reconstruction processing unit of the X-ray CT apparatus of the same embodiment.

FIG. 29 is a view showing two examples of contents of the data memory at the time of fan beam reconstruction in the second example in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 30 is a diagram showing a second example of writing control to a data memory performed by a reconstruction processing unit of the X-ray CT apparatus of the embodiment, in which a fan beam reconstruction method and a cone beam reconstruction method are switched to perform reconstruction. The figure which shows the flow of the reconstruction process which performs a structure.

FIG. 31 is a block diagram showing a configuration as a third example of a reconstruction processing control unit of the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 32 is a view for explaining the projection of the centering row onto the voxel row (pixel row) when the centering plane (axis) in the fan beam reconstruction of the reconstruction processing unit of the X-ray CT apparatus of the same embodiment is used. Illustration.

FIG. 33 is a view for explaining a plurality of methods of bundling processing in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 34 is a block diagram showing a configuration as a first method of a reconstruction processing control unit of the reconstruction processing unit of the X-ray CT apparatus according to the second embodiment of the present invention.

FIG. 35 is a diagram illustrating a first method performed by a reconstruction processing unit of the X-ray CT apparatus according to the embodiment, in which a projection curve is switched to switch a fan beam reconstruction and a cone beam reconstruction to perform reconstruction. The figure which shows the flow of the reconstruction process to perform.

FIG. 36 is a projection curve of a voxel column on the detector surface and a slice position in the MidPlane region, which occurs when the slice position in the first method in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment is outside the MidPlane region. The figure which shows the projection curve (projection straight line) to the detector surface of the voxel sequence which occurs at the time of.

FIG. 37 is a block diagram showing a configuration as a second method of the reconstruction processing control unit in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

38 is a diagram illustrating a second method performed by the reconstruction processing unit of the X-ray CT apparatus according to the embodiment, in which data memory control is switched to switch between fan beam reconstruction and cone beam reconstruction. The figure which shows the flow of the reconstruction process which performs a structure.

FIG. 39 is a view showing an example of contents of a data memory for cone beam reconstruction and fan beam reconstruction by the second method in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment;

FIG. 40 is a block diagram showing an example of a configuration as a third method of a reconstruction processing control unit in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 41 is a diagram showing a flow of reconstruction processing for performing cone-beam reconstruction performed by the reconstruction processing unit of the X-ray CT apparatus according to the third embodiment of the present invention.

FIG. 42 is a view showing the flow of a reconstruction process for performing cone beam reconstruction and fan beam reconstruction performed in the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment;

FIG. 43 is a diagram showing three reconstructed images (image A, image B, image C) in the X-ray CT apparatus according to the fourth embodiment of the present invention.

FIG. 44 is a view showing the flow of a reconstruction process for simultaneously reconstructing a plurality of images by fan beam reconstruction performed by the reconstruction processing unit of the X-ray CT apparatus according to the embodiment.

FIG. 45 is a diagram showing another example of the flow of reconstruction processing for simultaneously reconstructing a plurality of images by fan beam reconstruction performed by the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment;

FIG. 46 is a block diagram showing two examples of the configuration of the reconstruction processing unit of the X-ray CT apparatus according to the same embodiment.

FIG. 47 is a diagram showing a fan beam structure and an FOV in a conventional X-ray CT apparatus.

FIG. 48 is a diagram for explaining pixels in the conventional X-ray CT apparatus.

FIG. 49 is a diagram for explaining a fan-para conversion method in the conventional X-ray CT apparatus.

FIG. 50 is a diagram for explaining a fan beam reconstruction method using a centering axis in a conventional X-ray CT apparatus.

FIG. 51 is a diagram showing a cone beam in a conventional X-ray CT apparatus.

FIG. 52 is a diagram for explaining voxels for a cone beam in a conventional X-ray CT apparatus.

FIG. 53 is a diagram for explaining back projection of detector data onto pixels in an X-ray CT apparatus using a fan beam of a conventional example.

FIG. 54 is a diagram for explaining back projection of detector data onto voxels in an X-ray CT apparatus using a cone beam of a conventional example.

FIG. 55 is a diagram showing a scanning method in the X-ray CT apparatus.

[Explanation of symbols]

 3 ... X-ray source, 5 ... X-ray detector, 12 ... Reconstruction processing unit, 21 ... Reconstruction processing control unit, 21-1 ... Reconstruction method designation unit, 21-2 ... Projection curve calculation unit, 21-3 ... data control unit, 21-4 ... slice position determination unit, 22 ... convolution operation unit, 23 ... first data memory, 24 ... first backprojection unit, 25 ... second data memory, 26 ... second 27, image memory.

Claims (12)

[Claims] 1. An X-ray radiated from an X-ray source in a conical shape is applied to an object, and the X-ray transmitted through the object is detected by an X-ray detector, which is obtained from the X-ray detector. In an image reconstruction processing device that reconstructs a tomographic image of the target object based on detection data, a tomographic plane image is reconstructed based on the detection of X-rays transmitted through the target object by the X-ray detector. Fan beam reconstruction means for performing fan beam reconstruction, and cone beam reconstruction for performing cone beam reconstruction for reconstructing a tomographic stereoscopic image based on detection of X-rays transmitted through the object by the X-ray detection means. And an image reconstruction processing device. 2. The image reconstruction processing apparatus according to claim 1, wherein the fan beam reconstruction means bundles the detection data from the X-ray detector in the thickness direction of the tomographic plane image. Image reconstruction processing device. 3. The image reconstruction processing apparatus according to claim 1, further comprising reconstruction switching means for switching between the fan beam reconstruction means and the cone beam reconstruction means. . 4. The image reconstruction processing apparatus according to claim 3, wherein the reconstruction switching unit switches the reconstruction unit according to a slice position. 5. The image reconstruction processing apparatus according to claim 3, wherein data storage control for controlling storage or non-storage of detection data or reconstruction data in accordance with the reconstruction unit switched by the reconstruction switching unit. An image reconstruction processing apparatus comprising means. 6. The image reconstruction processing apparatus according to claim 3, further comprising display control means for controlling display according to the reconstruction means switched by the reconstruction switching means. Configuration processor. 7. An X-ray radiated in a conical shape from an X-ray source is radiated to an object by a continuous rotation method, and the X-ray transmitted through this object is transmitted.
In an image reconstruction processing apparatus for detecting a ray by an X-ray detector and reconstructing a tomographic image of the object based on detection data obtained from the X-ray detector, Cone beam reconstruction means for performing cone beam reconstruction for reconstructing a tomographic stereoscopic image based on the detection of X-rays transmitted through an object is provided, and the cone beam reconstruction means continuously scans the tomographic stereoscopic image with a cone beam. An image reconstruction processing device characterized by reconstruction. 8. The image reconstruction processing apparatus according to claim 7, wherein the cone beam reconstruction means obtains a difference between data obtained by one irradiation and data obtained before one rotation, and back-projects the difference. An image reconstruction processing device, characterized in that the cone beam reconstruction is performed by adding the obtained result to a tomographic stereoscopic image obtained by irradiation before a predetermined time. 9. An X-ray radiated from an X-ray source in a conical shape is applied to an object, and the X-ray transmitted through the object is detected by an X-ray detector, which is obtained from the X-ray detector. In an image reconstruction processing device that reconstructs a tomographic image of the target object based on detection data, a tomographic plane image is reconstructed based on the detection of X-rays transmitted through the target object by the X-ray detector. An image reconstruction processing apparatus comprising: fan beam reconstruction means for performing fan beam reconstruction, wherein the fan beam reconstruction means simultaneously reconstructs a plurality of tomographic plane images with a fan beam. 10. An X-ray radiated from an X-ray source in a conical shape is applied to an object by a continuous rotation method, and the X-ray transmitted through the object is detected by an X-ray detector. An image reconstruction processing apparatus for reconstructing a tomographic image of the target object based on the detection data obtained from the tomographic image based on detection of X-rays transmitted through the target object by the X-ray detector. A fan beam reconstruction means for performing fan beam reconstruction is provided, and the fan beam reconstruction means obtains the difference between the data obtained by one irradiation and the data one rotation before, and back-projects this difference. An image reconstruction processing device, characterized in that the fan beam reconstruction is performed by adding the obtained result to a tomographic stereoscopic image obtained by irradiation before a predetermined time. 11. The image reconstruction processing apparatus according to claim 10, wherein the fan beam reconstruction means simultaneously reconstructs a plurality of tomographic plane images with a fan beam. 12. The image reconstruction processing apparatus according to claim 3, wherein when the object is irradiated with X-rays by a continuous rotation method, the fan beam reconstruction means, if necessary, a plurality of tomographic planes. At the same time for the image, the difference between the data obtained by one irradiation and the data before one rotation is obtained, and the result obtained by back-projecting this difference is added to the tomographic stereoscopic image obtained by the irradiation before the predetermined time, and the fan beam The cone beam reconstruction means obtains a difference between the data obtained by one irradiation and the data obtained before one rotation, and if necessary, the cone beam reconstruction means obtains the result obtained by backprojecting the difference to a predetermined value. An image reconstruction processing device characterized by performing cone beam reconstruction by adding to a three-dimensional tomographic image obtained by the irradiation of.