JP5607196B2 - X-ray tomography equipment - Google Patents

Description

  The present invention relates to a technique of an X-ray tomographic imaging apparatus that realizes image quality improvement of dual energy imaging in a medical X-ray CT (Computed Tomography) apparatus helical scan.

Even in a conventional X-ray CT apparatus, a part of a subject to be imaged with dual energy is imaged at the same part with a low X-ray tube voltage and a high X-ray tube voltage, and a dual energy tomographic image is obtained by a dual energy image reconstruction method. I was able to.
However, in the conventional conventional scan or cine scan method, there is a time lag in the scan time, so that a position shift occurs due to body movement such as breathing, pulsation, and pulsation of the subject, resulting in a dual energy image. Misalignment artifacts were likely to occur on the top.

In contrast imaging, since it is necessary to keep adding a contrast medium from the start of the first scan to the end of the second scan, the amount of contrast medium injected into the subject is large, and the burden on the subject is large.
Furthermore, recently, an X-ray tomographic imaging apparatus using two X-ray tubes has been proposed in order to increase the scanning speed.
JP 2006-187453 A

The X-ray tomographic imaging apparatus using a plurality of X-ray tubes is intended only to increase the scanning speed, and does not disclose any dual energy imaging in helical scanning.
In addition, when performing dual energy imaging using an X-ray tomography apparatus using a plurality of X-ray tubes, it is possible to simultaneously obtain projection data from the same direction because the X-ray tube is displaced by a predetermined angle. There was a problem that it was not possible.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray tomographic imaging apparatus that realizes image quality improvement of a dual energy tomographic image by helical scanning of an X-ray tomographic imaging apparatus having a plurality of X-ray tubes.

An X-ray tomography apparatus according to a first aspect of the present invention includes a bed on which a subject is placed, and irradiation of the subject while rotating around the subject about the body axis direction of the subject. A first X-ray generator that generates X-rays having a predetermined beam width, and the subject with respect to the subject from an angular direction different from the first X-ray generator while rotating around the subject together with the first X-ray generator. A second X-ray generator for generating X-rays of a predetermined beam width to be irradiated, and the first X-ray generator and the second X-ray generator, which are disposed opposite to the first X-ray generator and the second X-ray generator, respectively. An X-ray detection device that collects X-ray projection data of the subject based on X-rays generated from each of the generation devices, and the first X-ray generation device and the second X-ray generation device with the body axis direction of the subject as an axis Rotating unit for rotating, and the rotating unit An imaging control unit that performs helical scanning by rotating the first X-ray generator and the second X-ray generator and relatively moving the first X-ray generator and the second X-ray generator and the bed. X-ray tomography apparatus having X-ray projection data based on X-rays generated from each of the first X-ray generator and the second X-ray generator, and having the same view angle at the same position in the body axis direction X-ray projection data control means for collecting line projection data is further provided.
The X-ray tomography apparatus according to the first aspect provides a short time difference between X-ray projection data of the same view angle at the same Z-direction coordinate position in the X-ray projection data of the first X-ray tube and the second X-ray tube obtained by helical scanning. Can collect X-ray data. For this reason, since X-ray projection data can be interpolated during image processing such as image reconstruction, image quality improvement processing and the like are facilitated.

In an X-ray tomography apparatus according to a second aspect, the X-ray projection data control means is arranged by disposing the first X-ray generator and the second X-ray generator by a predetermined distance in the body axis direction. Assume that X-ray projection data at the same view angle at the same body axis direction is collected.
In the X-ray tomography apparatus according to the second aspect, each X-ray projection data has the same coordinates by shifting the distance between the first X-ray generator and the second X-ray generator in the body axis direction (Z-axis direction). X-ray projection data having the same view angle at the position can be obtained.

According to a third aspect of the X-ray tomography apparatus, the X-ray projection data control means moves one of the first X-ray generator and the second X-ray generator in the body axis direction at the predetermined distance. A wire tube moving mechanism is provided.
With this configuration, the X-ray tomography apparatus separates the distance between the first X-ray generator and the second X-ray generator to an appropriate distance calculated based on, for example, a predetermined beam width and a predetermined helical pitch. Can do.

According to a fourth aspect of the X-ray tomography apparatus, the X-ray projection data control means is based on X-rays generated from the first X-ray generator and the second X-ray generator arranged at the same position in the body axis direction. At least one of the first tomographic image and the second tomographic image having different positions in the body axis direction and reconstructed using the projection data is X-ray projection data having the same view angle at the same position in the body axis direction. Assume that reprojection processing is performed.
An X-ray tomography apparatus according to a fourth aspect selects an X-ray projection data sequence of an optimal column from X-ray projection data of an X-ray beam having a width in the Z-axis direction, and the same Z coordinate with a small time difference, X-ray projection data having the same view angle can be selected.

According to a fifth aspect of the X-ray tomography apparatus, the X-ray projection data control means is based on X-rays generated from the first X-ray generator and the second X-ray generator arranged at the same position in the body axis direction. At least one of the first tomographic image and the second tomographic image having different positions in the body axis direction and reconstructed using the projection data is X-ray projection data having the same view angle at the same position in the body axis direction. Assume that reprojection processing is performed.
In the X-ray tomography apparatus according to the fifth aspect, X-ray data acquisition is performed at the same time even if the view direction angles collected by the X-ray tube are different, and a tomographic image at the same time in the same z-direction coordinate is reconstructed. Even in this case, the reprojection processing unit performs reprojection processing from the tomographic image, so that X-ray projection data in the same view direction can be obtained at the same z-direction coordinates at the same time.

In the X-ray tomography apparatus according to the sixth aspect, the reprojection process includes a fan beam reprojection process in a beam direction having a fan angle or a parallel beam reprojection process in a parallel beam direction.
Thus, the reprojection process can be performed from at least two types of directions.

In an X-ray tomography apparatus according to a seventh aspect, the first X-ray generator generates X-rays having a first energy spectrum, and the second X-ray generator has a second energy spectrum different from the first energy spectrum. A dual energy image reconstruction unit configured to reconstruct a dual energy image using X-ray projection data generated and based on the X-rays of the first energy spectrum and the X-rays of the second energy spectrum;
In the X-ray tomography apparatus of the seventh aspect, the first and second X-ray generators are controlled so as to output one X-ray tube voltage, so that efficient dual energy imaging that suppresses unnecessary exposure can be performed. It can be carried out.

The imaging control unit of the X-ray tomography apparatus according to the eighth aspect is configured so that the dual energy image image reconstruction unit is based on the X-ray of the first energy spectrum and the X-ray of the second energy spectrum. After performing the weighted subtraction process between the X-ray projection data of the same view angle at the position of, the dual energy image is reconstructed by performing the back projection process.
The X-ray tomography apparatus according to the eighth aspect can obtain a high-quality dual energy image in dual energy imaging.

  According to the X-ray tomography apparatus of the present invention, in the helical scan of the X-ray tomography apparatus, the tomographic image representing the X-ray tube voltage-dependent information in the X-ray absorption coefficient related to the distribution of atoms, so-called dual energy image quality An X-ray tomography apparatus that optimizes the above can be realized.

1 is a block diagram showing an X-ray CT apparatus 100 having a plurality of X-ray tubes according to an embodiment of the present invention. (A) is a figure which shows how to obtain | require the tomogram of the X-ray tube voltage dependence information by the X-ray absorption coefficient in projection data space. (B) is a figure which shows the classification | category of each substance by a dual energy ratio. (A) is a figure which shows the 3rd generation system of two X-ray tubes. (B) is a figure which shows the locus | trajectory on the expanded view of the X-ray tube which shifted | deviated 90 degree | times. (C)-(e) is a figure which shows the state which two X-ray tubes left | separated 180 degree | times. (F) is a diagram showing two X-ray tubes and one multi-row X-ray detector. (A) It is a figure which shows the 3rd generation system of three X-ray tubes. (B) It is a figure which shows the 3rd generation system of three X-ray tubes using a plane detector. (A) is a figure which shows the positional relationship of the X-ray detector fan of each channel by the 4th generation system by two X-ray tubes. (B) is a figure which shows the positional relationship of the X-ray detector fan of each channel by the 4th generation system by three X-ray tubes. (A) is a figure which shows the position in yz plane of the two X-ray tubes which shifted | deviated to the Z-axis direction in the time t1, t2. (B) is a figure which shows the position in xy plane of the two X-ray tubes which shifted | deviated to the Z-axis direction in the time t1, t2. (Figure explanation P0038) It is a flowchart which shows the process which aligns the Z-axis direction of an X-ray tube, and performs the helical scan of dual energy imaging | photography. (A) is a figure which shows the position in yz plane in the two X-ray tubes in the Z-axis direction in time t1, t2. (B) is a figure which shows the position in xy plane in the two X-ray tubes in the Z-axis direction in time t1, t2. It is a flowchart which shows the process which performs the helical scan of dual energy imaging | photography when the position of a X-ray tube corresponds to a Z-axis direction. It is a figure which shows the position in yz plane of the X-ray beam restrict | squeezed by the collimator of the two X-ray tubes in the Z-axis direction in time t1, t2. (A) is a figure which shows the locus | trajectory on the expanded view of the X-ray tube which shifted | deviated 90 degree | times, and the locus | trajectory of the reprojected X-ray projection data. (B) is a figure which shows the process which changes the view direction of X-ray projection data by performing a reprojection process. It is a flowchart of the dual energy imaging | photography which performed the reprojection process of one tomogram, and match | combined with the view direction of the X-ray projection data of the other X-ray acquisition system XS. It is a figure which shows a fan beam reprojection process. It is a flowchart of a fan beam reprojection process of a certain Z-axis direction range [zs, ze]. It is a flowchart which shows the tomogram image reconstruction method by the parallel beam reprojection of dual energy imaging | photography. It is a figure which shows a parallel beam reprojection process. It is a figure which shows the parallel beam reprojection process example 1 of (theta) direction. It is a figure which shows the parallel beam reprojection process example 2 of (theta) direction. 6 is a flowchart of raster scanning in the θ direction.

<Overall configuration of X-ray CT apparatus>
FIG. 1 is a block diagram showing the configuration of an X-ray CT apparatus 100 according to an embodiment of the present invention. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry 20.

  The operation console 1 includes an input device 2 such as a keyboard or a mouse that receives input from the operator, a central processing unit 3 that executes preprocessing, image reconstruction processing, postprocessing, and the like, and X-ray detection collected by the scanning gantry 20 And a data collection buffer 5 for collecting the vessel data. Further, the operation console 1 includes a monitor 6 that displays a tomographic image reconstructed from projection data obtained by preprocessing X-ray detector data, a program, X-ray detector data, projection data, and X-ray tomography. And a storage device 7 for storing an image. The photographing condition is input from the input device 2 and stored in the storage device 7. The imaging table 10 includes a cradle 12 on which the subject HB is placed and taken in and out of the opening of the scanning gantry 20. The cradle 12 is moved up and down and moved linearly by a motor built in the imaging table 10.

  The scanning gantry 20 includes an X-ray tube 21, an X-ray controller 22, a collimator 23, a beam forming X-ray filter 28, a multi-row X-ray detector 24, and a data acquisition device (DAS: Data Acquisition System) 25. It has. In the present embodiment, the X-ray tube 21 and the multi-row X-ray detector 24 are provided at another position 90 degrees different from each other. The X-ray control unit 22 controls the tube voltage and current of the two X-ray tubes 21. The gantry rotating unit 15 holds the X-ray tube 21 and the multi-row X-ray detector 24 and is rotatable through a bearing. Since there is another set of the X-ray tube 21 and the multi-row X-ray detector 24, another set of the gantry rotating unit 15 may be prepared.

  Further, the scanning gantry 20 communicates with the X-ray control unit 22, the rotation control unit 26 that controls the gantry rotation unit 15 rotating around the body axis of the subject HB, and the rotation control unit 26 and the cradle 12. And a gantry control unit 29 for transmitting and receiving signals. The data acquisition device 25 converts the analog signal from the multi-row X-ray detector 24 into a digital signal. The beam forming X-ray filter 28 has the thinnest filter thickness in the X-ray direction toward the center of rotation, which is the imaging center, and the filter thickness increases toward the periphery so that X-rays can be absorbed more. X-ray filter. The scanning gantry 20 according to the first embodiment described later includes an X-ray tube driving mechanism 32 that moves one X-ray tube 21 in the Z-axis direction.

The central processing unit 3 includes a preprocessing unit 33, an image reconstruction unit 34, a dual energy image reconstruction unit 35, and an imaging control unit 37. The imaging control unit 37 has a reprojection processing unit 38.
The pre-processing unit 33 corrects non-uniform sensitivity between channels for the raw data collected by the data collection device 25, and causes an extreme decrease in signal intensity or signal due to an X-ray strong absorber, mainly a metal part. Pre-processing such as X-ray dose correction for correcting omission is executed. Also, beam hardening processing is performed.

The image reconstruction unit 34 receives the projection data preprocessed by the preprocessing unit 33 and reconstructs an image based on the projection data. The projection data is subjected to a fast Fourier transform (FFT) for transforming it into the frequency domain, and a reconstruction function Kernel (j) is superimposed on the projection data to perform an inverse Fourier transform. Then, the image reconstruction unit 34 performs a three-dimensional backprojection process on the projection data obtained by superimposing the reconstruction function Kernel (j), and obtains a tomographic image for each body axis direction (Z-axis direction) of the subject HB. (Xy plane) is obtained. The image reconstruction unit 34 stores this tomographic image in the storage device 7.
The dual energy image reconstruction unit 35 generates a two-dimensional distribution tomogram of X-ray tube voltage-dependent information related to the distribution of atoms, so-called dual energy, from projection data of a low X-ray energy spectrum and projection data of a high X-ray energy spectrum. Reconstruct a tomographic image.

The imaging control unit 37 relatively moves the first X-ray generator and the second X-ray generator and the bed while rotating the first X-ray generator and the second X-ray generator by the rotating unit. The scanning gantry 20, the imaging table, and the like are controlled so as to perform helical scanning.
The X-ray CT apparatus 100 includes X-ray projection data control means (not shown). The X-ray projection data control means can acquire X-ray projection data in the same view direction with respect to the shift angle in the view direction of the plurality of X-ray tubes 21 at the same body axis direction (Z-axis direction) position. Take control. Specifically, this will be described in detail using Examples 1 to 3 described later.

  An example of performing helical scan dual energy imaging using a plurality of X-ray tubes in the X-ray CT apparatus 100 as described above will be described below.

<Dual energy imaging using multiple X-ray tubes>
First, the dual energy imaging method required in each embodiment will be described.
<Dual energy tomographic image reconstruction method>
A method for creating a contrast agent equivalent image and a calcium equivalent image of a dual energy tomographic image or a scout image to be reconstructed is as follows.

FIG. 2A shows an outline of an image reconstruction method for dual energy imaging in the projection data space.
The image reconstruction unit 34 multiplies the X-ray projection data D-Low of X-rays irradiated using a low X-ray tube voltage by a weighted addition coefficient w1, and similarly X-rays irradiated using a high X-ray tube voltage. The X-ray projection data D-High is multiplied by the weighted addition coefficient w2, and weighted addition processing is performed together with the constant C1, thereby creating a dual energy tomographic image G-CSI. The image reconstruction unit 34 can obtain a dual energy tomographic image G-CSI by performing weighted addition processing in the image space and tomographic image space in the same manner as in the projection data space. These weighted addition coefficients w1 and w2 and the constant C1 are determined by the atom to be extracted, the atom to be emphasized, the atom or part to be deleted on the display.

For example, the weighted addition processing unit erases the calcium component on the display in order to separate a bone component having a close CT value, a calcium component (Ca component) constituting calcification, and a contrast agent (Iodine component) containing iodine as a main component. That is, when the pixel value is set to 0, the contrast agent component is extracted and can be displayed with emphasis.
On the other hand, when the contrast agent component is erased on the display, that is, when the pixel value is set to 0, the calcium component is extracted and the bone and calcified portions can be emphasized and displayed.
As X-ray projection data used at this time, X-ray projection data subjected to preprocessing and beam hardening correction is used. In particular, in beam hardening correction, the X-ray tube voltage dependence of substances other than water can be more correctly evaluated by setting the water-equivalent X-ray transmission path length for the non-water-equivalent material at each X-ray tube voltage. Can do.

  Dual energy imaging is possible not only in the projection data space but also in the tomographic image space. By performing such processing, the image reconstruction unit 34 can create a contrast agent equivalent image and a calcium equivalent image.

<Dual energy ratio image reconstruction>
As another method for reconstructing another contrast agent equivalent image and calcium equivalent image, there is a method of using pixel values in X-ray tomographic images irradiated using respective X-ray tube voltages.
For example, in the graph of FIG. 2B, the vertical axis represents each pixel value in a tomographic image with an X-ray tube voltage of 80 kV, and the horizontal axis represents each pixel value in a tomographic image with an X-ray tube voltage of 140 kV. Thereby, the pixel value of calcium having an X-ray tube voltage of 80 kV and an X-ray tube voltage of 140 kV, or the pixel value of iodine as the main component of the contrast agent, the calcium straight line in the figure and the distribution range in the vicinity thereof, the iodine straight line And the distribution range in the vicinity thereof.
In the graph of the dual energy ratio, each inclination in the xy plane represents an effective mass number, so that component analysis and composition analysis of a substance can be performed by classifying each pixel within the inclination range.
Such a dual energy ratio image is subjected to image reconstruction and image display.

Next, an example of the type of the X-ray CT apparatus 100 using a plurality of X-ray tubes will be shown.
<Scanning gantry with multiple X-ray tubes>

<Two-tube, two-detector type: 3rd generation method>
The X-ray CT apparatus 100 according to the present embodiment includes two first X-ray tubes 21-1 and 21-2, as shown in FIG. And a second multi-row X-ray detector 24-2. The first X-ray tube 21-1 and the second X-ray tube 21-2 are arranged so as to be shifted from each other by 90 degrees.
Since the two first X-ray tubes 21-1 and 21-2 rotate together on one rotating unit 15 of the scanning gantry 20, X-ray data collection in the same view direction is performed at the same time. I can't. In this case, the locus of the developed view of the X-ray tube 21 in which the helical scan is performed is that the first X-ray tube 21-1 is always 90 ° clockwise from the second X-ray tube 21-2 as shown in FIG. 3A (b). Move ahead and collect X-ray data. For this reason, as will be described later, if the first X-ray tube 21-1 is displaced in the Z-axis direction, X-ray data collection in the same view direction can be performed at the same time.

  At this time, the deviation angle between the first X-ray tube 21-1 and the second X-ray tube 21-2 is 90 degrees, but may be 120 degrees or 180 degrees. When the angle is shifted by 180 degrees, the facing X-ray tube 21 and multi-row X-ray detector 24 overlap in the Z-axis direction as shown in FIG. 3B (c). When the X-ray tube 21 and the multi-row X-ray detector 24 are viewed from the X-axis direction, the result is as shown in FIG. 3B (d) or (e).

<1 detector type with 2 tubes: 3rd generation method>
In FIG. 3B (f), the scanning gantry 20 includes a first X-ray tube 21-1, a second X-ray tube 21-2, and one third-generation multi-row X-ray detector 24. In FIG. 3B (f), the first X-ray fan beam by the first X-ray tube 21-1 and the second X-ray fan beam by the second X-ray tube 21-2 are arranged at intervals of 90 degrees, but may be 120 degrees. Absent. This is the same as the case where two X-ray tubes 21 and two multi-row X ship detectors 24 are arranged.

<3-tube type with 3 detectors: 3rd generation method>
FIG. 4A shows three first X-ray tubes 21-1, a second X-ray tube 21-2, a third X-ray tube 21-3, three first multi-row X-ray detectors 24-1, and a second. The case where the multi-row X-ray detector 24-2 and the third multi-row X-ray detector 24-3 are displaced by 120 degrees each is shown. That is, three X-ray tubes 21 are arranged every 120 degrees. The multi-row X-ray detector 24 is a third generation system. All of these three X-ray tubes 21 are arranged on the rotating portion 15 of the scanning gantry 20 at intervals of 120 degrees and are rotated simultaneously.

  Similarly, in FIG. 4B, the three X-ray tubes 21 are similarly shifted by 120 degrees, but the multi-row X-ray detector 24 has a matrix structure typified by a flat panel X-ray detector. A first two-dimensional X-ray area detector 24-1, a second two-dimensional X-ray area detector 24-2, and a third two-dimensional X-ray area detector 24-3 are used.

<1 detector type with 2 tubes: 4th generation method>
5A shows two rotating first X-ray tubes 21-1 and second X-ray tubes 21-2, and a fixed multi-row X-ray detector 24 arranged in a 360-degree circumferential shape. It is the figure which showed the 4th generation system comprised by.
The first X-ray tube 21-1 and the second X-ray tube 21-2 are arranged on one rotating unit 15 of the scanning gantry 20 at intervals of 90 degrees, 120 degrees, or 180 degrees, and rotate while maintaining the interval. The part 15 rotates. At this time, the image processing unit determines that one channel of the multi-row X-ray detector 24 is regarded as a key of a virtual fan (fan) before or during image reconstruction. It is regarded as line projection data, converted into a so-called detector fan (Detector Fan), and three-dimensional image reconstruction and three-dimensional backprojection are performed.

<One detector type with 3 tubes: 4th generation method>
In FIG. 5B, the scanning gantry 20 arranges three X-ray tubes, the first X-ray tube 21-1, the second X-ray tube 21-2, and the third X-ray tube 21-3, every 90 degrees. ing. The scanning gantry 20 includes a fourth generation multi-row X-ray detector 24. The three X-ray tubes may be arranged not only at 90 degrees but also at every 120 degrees.
Next, a method for collecting X-ray projection data in the same view direction at the same body axis direction position when there are a plurality of X-ray tubes will be described with reference to an embodiment.

<Multiple X-ray tube imaging method: X-ray tube Z-axis direction shift>
In the first embodiment, when the scanning gantry 20 having a plurality of X-ray tubes 21 as described above performs a helical scan, at least one X-ray tube 21 is obtained in the Z-axis direction (body axis) obtained by setting imaging conditions. X-ray projection data in the same view direction at the same Z-axis coordinate is collected. When the X-ray beam width in the Z-axis direction including the rotation center of the X-ray tube 21 is D, and the helical pitch is p, the relative distance between the scanning gantry 20 and the cradle 12 on which the subject is placed at one rotation is D · p.

  For example, FIGS. 6A and 6B are diagrams showing the positional relationship between the time t1 when the helical pitch is 1 and the time t2 after ¼ rotation in the yz plane and the xy plane. In the following description, the scanning gantry 20 will be described with a configuration having two tubes and two detectors.

The scanning gantry 20 includes a first X-ray acquisition system XS1 including a first X-ray tube 21-1 and a first multi-row X-ray detector 24-1, a second X-ray tube 21-2, and a second multi-row X-ray detector. And a second X-ray acquisition system XS2 including 24-2. The positions where the angle θ formed by the first X-ray acquisition system XS1 and the second X-ray acquisition system XS2 is 90 degrees are separated by a distance L shown in the following (Equation 1). Thus, by separating the center position in the Z-axis direction by the distance L in the Z-axis direction, the start view angle of the X-ray projection data acquisition matches between the first X-ray acquisition system XS1 and the second X-ray acquisition system XS2.
. . . (Formula 1)
This distance L can be obtained in the same manner in all the types described above when the angle θ formed by the X-ray tube 21 is 90 degrees in the two-tube system.

When the angle θ between the X-ray tube 21 and the X-ray tube 21 is 120 degrees in the two-tube method, the first X-ray acquisition system XS1 and the second X-ray are separated by separating them in the Z-axis direction by a distance L of the following (Equation 2). The starting view angle with the acquisition system XS2 can be matched.
. . . (Formula 2)
Further, since the angle formed by the three-tube type X-ray tube 21 is θ = 120 degrees, the center positions of the three X-ray tubes 21 in the Z-axis direction are separated in the Z-axis direction by a distance L of (Equation 2). Thus, the view angles of the respective X-ray projection data can be matched.

  In this way, by shifting the plurality of X-ray acquisition systems in the Z-axis direction, the plurality of X-ray acquisition systems can acquire X-ray projection data in the same view direction at the same Z-axis coordinate. In addition, according to the distance L, it is preferable to make it the structure which can move an X-ray acquisition system to a Z-axis direction except for one X-ray acquisition system among several X-ray acquisition systems.

FIG. 7 shows a flowchart for acquiring projection data of the same view in the X-ray CT apparatus 100 having the first X-ray acquisition system XS1 and the second X-ray acquisition system XS2.
In step D1, a scout image is taken. When performing scout imaging, in the case of the X-ray CT apparatus 100 having a plurality of X-ray tubes, scout images in a plurality of directions are collected at once by simply moving the cradle 12 on which the subject is placed in the Z-axis direction. be able to.
In particular, as shown in FIGS. 3A (a) and 3B (f), when the shift angle in the view direction between the first X-ray tube 21-1 and the second X-ray tube 21-2 is 90 degrees, 0 degrees and 90 degrees. Alternatively, two scout images of 90 degrees and 180 degrees can be photographed only by moving once in the Z-axis direction. For this reason, the X-ray CT apparatus 100 can increase the efficiency of scout image capturing.

In step D2, the imaging condition setting of the dual energy imaging helical scan is performed.
Based on the scout image acquired in step D1, the operator sets the helical scan range, the helical pitch, and the rotational speed of the scanning gantry 20 for performing the dual energy imaging. Further, the operator sets the imaging conditions for the main scan such as the width in the Z-axis direction used by the multi-row X-ray detector 24, the width and number of rows of the multi-row X-ray detector 24, and the width in the X-axis direction of the Z-axis. Set. If the X-ray beam width D and the helical pitch p are determined at the time of setting the imaging conditions, the imaging control unit 37 expresses (Equation 1) and (Equation 2) from the deviation angle θ of each X-ray tube 21 in the view direction. Thus, the distance L shifted in the Z-axis direction can be obtained.

  In step D3, Z-axis direction alignment control of the first X-ray tube 21-1 and the second X-ray tube 21-2 is performed. Before the X-ray data acquisition of the main scan, the first X-ray acquisition system XS1 is shifted by the distance L in the Z-axis direction. The movement of the first X-ray acquisition system XS1 controls the X-ray tube moving mechanism 32 from the central processing unit 3 via the gantry control unit 29.

  In step D4, the scanning gantry 20 collects X-ray data. In this case, the first X-ray tube 21-1 emits X-rays with an X-ray tube voltage of 80 kV, and the second X-ray tube 21-2 emits X-rays with an X-ray tube voltage of 140 kV.

In step D5, the image reconstruction unit 34 reconstructs a tomographic image having an X-ray tube voltage of 80 kV.
In step D6, the image reconstruction unit 34 reconstructs a tomographic image having an X-ray tube voltage of 140 kV.
In step D7, the dual energy image reconstruction unit 35 reconstructs a calcium enhanced image and a contrast agent enhanced image as a tomographic image of dual energy imaging.
In step D8, a calcium-enhanced image and a contrast-agent-enhanced image are displayed on the monitor 6 as tomographic images for dual energy imaging.
In step D9, the dual energy image reconstruction unit 35 reconstructs a dual energy ratio image as a tomographic image of dual energy imaging.
In step D10, a dual energy ratio image is displayed on the monitor 6 as a tomographic image for dual energy imaging.

  In this embodiment, the dual energy imaging method can be performed with a short imaging time interval. For example, when the deviation angle θ between the first X-ray tube 21-1 and the second X-ray tube 21-2 is 90 degrees and the rotation speed of the gantry rotating unit 15 is 0.35 seconds / rotation, the imaging time difference ΔT is 0. .09 seconds. As described above, since the dual energy imaging method using the first X-ray tube 21-1 and the second X-ray tube 21-2 can collect X-ray data at an imaging interval shorter than the above-described imaging method, the body motion of the subject can be further increased. Can be suppressed.

  In this embodiment, since the X-ray tube voltages applied by the first X-ray tube 21-1 and the second X-ray tube 21-2 are respectively assigned to 80 kV and 140 kV, there is no need to switch the X-ray tube voltage. For this reason, it is not necessary to switch the aforementioned X-ray tube voltage for each view, and there is no need to worry about aliasing artifacts due to insufficient views.

  In the present embodiment, in the X-ray CT apparatus 100 having two or three X-ray tubes 21, each X-ray acquisition system is shifted to an appropriate position in the Z-axis direction when performing a dual energy imaging helical scan. Thus, X-ray projection data in the same view direction can be collected at the same Z-axis coordinate.

  When the helical pitch is varied as in the helical shuttle scan and the variable pitch helical scan, the imaging control unit 37 sets the X-ray tube movable mechanism 32 so as to change the distance L of each X-ray tube 21 each time. Let me control. However, when the acceleration / deceleration range is not so wide in the Z-axis direction, the imaging control unit 37 has a small influence even if the helical pitch p and the distance L between the X-ray tubes 21 are not optimal. There is no need to change it.

<Multiple X-ray tube imaging methods: data extraction>
In Example 2, as shown in FIG. 8A or 8B, the Z-axis coordinates of the center lines of the first X-ray tube 21-1 and the second X-ray tube 21-2 match. An example of extracting X-ray projection data in the same view direction with the same Z-axis coordinate is shown below.

FIG. 9 shows a flowchart of X-ray projection data in the same view direction with the same Z-axis coordinate.
In step D41, a scout image is taken.
In step D42, the operator sets imaging conditions for helical scanning for dual energy imaging.
In step D43, X-ray data is collected by helical scanning. If necessary, the X-ray collimator 23 controls the collimator width in the Z-axis direction to reduce unnecessary exposure.
In step D44, the preprocessing unit 33 preprocesses the X-ray projection data of the X-rays irradiated using the X-ray tube voltage of 80 kV.
In step D45, the preprocessing unit 33 preprocesses the X-ray projection data of the X-rays irradiated using the X-ray tube voltage 140 kV. In step D44 and step D45, processing up to pre-processing of image reconstruction processing, up to beam hardening correction, or up to z-filter convolution processing is performed.
In step D46, the dual energy image reconstruction unit 35 weights the X-ray projection data of the X-rays irradiated using the X-ray tube voltage 80 kV and the X-ray projection data of the X-rays irradiated using the X-ray tube voltage 140 kV. Addition processing is performed to obtain X-ray projection data of the calcium enhanced image and X-ray projection data of the contrast agent emphasized image which are dual energy tomographic images.
In Step D47, the dual energy image reconstruction unit 35 performs image reconstruction of a contrast-emphasized image that performs image reconstruction of a calcium-weighted image.
In step D48, a calcium-enhanced image and a contrast-agent-enhanced image are displayed on the monitor 6 as tomographic images for dual energy imaging.

<Detailed description of steps>
In Step D41 to Step D42, the same processing as Step D1 to Step D2 in FIG. 7 can be performed. Therefore, in step D41, two scout images can be taken at a time, and in step D42, the shift amount L of each X-ray tube 21 can be set based on the imaging conditions.

  In step D43, for example, X-ray projection data collection of the X-rays irradiated using the X-ray tube voltage 80 kV is performed in the first X-ray acquisition system XS1, and the X-ray tube voltage 140 kV is used in the second X-ray acquisition system XS2. X-ray projection data collection of irradiated X-rays is performed. Control of waste exposure by the collimator 23 will be described in the detailed description of step D46.

  In step D46, the dual energy image reconstruction unit 35 calculates the X-ray X-ray projection data irradiated using the X-ray tube voltage 80 kV and the X-ray X-ray projection data irradiated using the X-ray tube voltage 140 kV. When performing a weighted addition process, it is necessary to perform a weighted addition process on X-ray projection data of the same Z-axis coordinate in the same view direction. For this reason, the image reconstruction unit 34 converts the X-ray projection data of a certain column of the second multi-row X-ray detector 24-2 that is shifted by a distance L from the certain row of the first multi-row X-ray detector 24-1. It is necessary to extract and perform weighted addition processing. Further, when the position shifted by the distance L is between a certain column of the second multi-row X-ray detector 24-2 and a certain column, the certain column and the certain column are subjected to interpolation processing or weighted addition processing. Thus, X-ray projection data shifted by the distance L can be obtained. By using the three-dimensional image reconstruction process, it is possible to suitably perform image reconstruction of a tomographic image at a position shifted from the center position.

In addition, each X-ray tube 21 may have the X-ray beam position shifted in advance.
For example, as shown in FIG. 10, when the first X-ray acquisition system XS1 and the second X-ray acquisition system XS2 are shifted by 90 degrees, L = D / 4 when the helical pitch p = 1. In this case, the collimator control unit shifts the X-ray beam of the first X-ray acquisition system XS1 by D / 4 in the positive direction of the Z-axis direction by the first collimator 23-1, and the X-ray beam of the second X-ray acquisition system XS2 Is shifted by D / 4 in the positive direction of the Z-axis direction by the second collimator 23-2. At this time, the X-ray beam has a column of the second X-ray acquisition system XS2 shifted by D / 4 in the X-ray beam. In addition, shifting the X-ray beam with the collimator 23 in this way reduces the amount of X-ray beam that is wasted and increases X-ray utilization efficiency.

  The image reconstruction unit 34 performs beam hardening on the X-ray projection data of the contrast-enhanced image as the calcium equivalent image and the X-ray projection data of the calcium-enhanced image as the contrast agent equivalent image thus obtained. Correction can also be performed.

  In step D47, the dual energy image reconstruction unit 35 may perform image reconstruction as a tomographic image of dual energy imaging based on the calcium-enhanced image X-ray projection data and the contrast agent-enhanced image X-ray projection data. it can.

  In this way, the X-ray CT apparatus of the second embodiment has the same Z-axis coordinates from among the X-ray beams when the Z-axis coordinates of the center lines of the plurality of X-ray tubes 21 match. X-ray projection data at the view angle can be extracted to reconstruct a dual energy tomographic image. In addition, the collimator control unit controls the X-ray collimator 23-1 and the X-ray collimator 23-2 to shift the position of the X-ray beam of the X-ray tube 21 in the Z-axis direction, thereby reducing unnecessary exposure. Can do.

<Multiple X-ray tube imaging method: Reprojection method>
The third embodiment will explain a case where the first X-ray acquisition system XS1 and the second X-ray acquisition system XS2 acquire X-ray projection data whose positions in the view direction do not match. The X-ray CT apparatus according to the third embodiment reconstructs X-ray projection data with the view direction shifted in this way, and then re-projects it to convert it into X-ray projection data with the same view direction.
In the present embodiment, the present invention can be applied to any of the above-described two-tube and three-tube X-ray tubes 21.

  As shown in FIG. 11A, when a helical scan is performed with the first X-ray tube 21-1 and the second X-ray tube 21-2 shifted by 90 degrees in the view direction, the X-ray projection of the first X-ray acquisition system XS1 The data can be collected by 90 degrees earlier than the X-ray projection data of the second X-ray acquisition system XS2. Therefore, the image reconstruction unit 34 performs image reconstruction processing once using the X-ray projection data of the second X-ray acquisition system XS2 as a tomographic image. Next, the reprojection processing unit 38 reprojects the X-ray projection data of the second X-ray acquisition system XS2 in the direction of the fan beam in the direction indicated by the arrow ARR in FIG. 11B, so that the first X-ray acquisition system XS1. The X-ray projection data of the X-ray projection data of the second X-ray acquisition system XS2 can be matched with the view direction.

When this process is shown in the development view of FIG. 11A, the reprojection processing unit 38 reconstructs the X-ray projection data of the second X-ray acquisition system XS2 and then reconstructs the first X-ray acquisition at the same Z-axis coordinate. Fan beam reprojection processing or parallel beam reprojection processing is performed in the same view direction as in the system XS1, and X-ray projection data REX having the same Z-axis coordinate and the same view direction angle is obtained.
Further, the dual energy image reconstruction unit 35 performs nonlinear correction such as beam hardening correction of an X-ray absorption region of a contrast agent or bone in image reconstruction processing of an X-ray dual energy image in the projection data space of the X-ray projection data. To obtain an X-ray dual energy tomographic image with few beam hardening artifacts.

FIG. 12 is a flowchart of dual energy imaging in which reprojection processing of one tomographic image is performed and the view direction of the X-ray projection data of the other X-ray acquisition system XS is matched.
In step D61, a scout image is taken. As with step D1 in FIG. 7, two scout images can be taken at a time.

  In step D62, the operator sets imaging conditions for helical scanning for dual energy imaging. In the third embodiment, as in the first and second embodiments, the imaging control unit 37 determines the X-ray projection data of the first X-ray acquisition system XS1 and the second X-ray acquisition system XS2 based on the helical scan setting conditions and the like. It is not necessary to obtain the deviation amount L. What is used in the present embodiment is a view direction deviation angle θ between the first X-ray acquisition system XS1 and the second X-ray acquisition system XS2. The image reconstruction unit 34 performs reprojection processing in the direction of the deviation angle θ.

  In step D63, the first X-ray acquisition system XS1 collects X-ray data of the X-rays irradiated using the X-ray tube voltage 140 kV, and the second X-ray acquisition system XS2 applies the X-rays irradiated using the X-ray tube voltage 80 kV. X-ray data collection.

In Step D64, the image reconstruction unit 34 performs image reconstruction of a tomographic image of X-rays irradiated using the X-ray tube voltage 80 kV of the second X-ray acquisition system XS2 including the second X-ray tube 21-2.
In step D65, the reprojection processing unit 38 reprojects the X-ray tomographic image irradiated using the X-ray tube voltage 80 kV of the second X-ray acquisition system XS2 in the same direction as the view direction of the first X-ray acquisition system XS1. To obtain preprocessed X-ray projection data of X-rays irradiated using an X-ray tube voltage of 80 kV. In other words, a 360-degree full-scan X image having the same view angle as the X-ray projection data of the X-rays irradiated with the 80 kV tomogram of the second X-ray acquisition system XS2 using the X-ray tube voltage 140 kV of the first X-ray acquisition system XS1. Fan beam reprojection processing is performed as line projection data or X-ray projection data of 180 ° + fan angle half scan.

In Step D66, the preprocessing unit 33 preprocesses the X-ray projection data of the X-rays irradiated using the X-ray tube voltage 140 kV.
In step D67, the dual energy image reconstruction unit 35 uses the same X-ray projection data for X-rays irradiated using an X-ray tube voltage of 80 kV and X-ray projection data for X-rays irradiated using an X-ray tube voltage of 140 kV. The weight addition processing is performed between the views, and the X-ray projection data of the calcium-weighted image and the X-ray projection data of the contrast agent-weighted image are obtained as a tomographic image of dual energy imaging. The weighted addition process can be a primary or secondary higher-order weighted addition process.

In step D68, the dual energy image reconstruction unit 35 performs image reconstruction of a contrast-emphasized image that performs image reconstruction of a calcium-weighted image.
In step D69, a calcium-enhanced image and a contrast agent-enhanced image are displayed on the monitor 6 as tomographic images for dual energy imaging.

<Fan beam reprojection processing>
FIG. 13 is a diagram showing an outline of the fan beam reprojection process, and FIG. 14 is a flowchart of the fan beam reprojection process. However, a reprojection profile is obtained by a reprojection process of a tomographic image in the range [zs, ze], where P is the reconstruction area, zs is the start point in the Z-axis direction, and ze is the end point in the Z-axis direction.

In step T1, θ = 0 and z1 = zs.
In step T2, the reprojection processing unit 38 reads a tomographic image g (x, y) having a certain Z-axis coordinate zn.
In step T3, the reprojection processing unit 38 performs fan beam reprojection processing assuming that the X-ray focal point is in the θ direction, and obtains θ direction profile data Pθ (β).
In step T4, the reprojection processing unit 38 determines whether θ ≧ 360 degrees in the case of full scan or θ ≧ 180 degrees in the case of half scan. If YES, the process goes to step T5, and if NO. Go to step T6.
In step T5, the reprojection processing unit 38 determines whether zn ≧ ze. If YES, the reprojection processing unit 38 ends. If NO, the process proceeds to step T7.
In step T6, θ = θ + Δθ. Thereafter, the process returns to step T2.
In step T7, n = n + 1. Thereafter, the process returns to step T2.

  In this way, X-ray projection data of X-rays irradiated using the X-ray tube voltage 140 kV of the first X-ray acquisition system XS1 in the same view direction with the same Z-axis coordinate and the X-ray tube voltage of the second X-ray acquisition system XS2 X-ray projection data of X-rays irradiated using 80 kV can be obtained.

  FIG. 13A shows how the fan beam reprojection process is performed from the X-ray focal point in the θ direction in step T3. The reprojection processing unit 38 is along a straight line shifted by an angle β formed by a straight line connecting the X-ray focal point and each pixel g (x1, y1) and an X-ray focal point having an angle θ and a straight line passing through the rotation center O. Perform reprojection processing. That is, the reprojection processing unit 38 adds pixels on a straight line that is shifted by an angle β with respect to the center direction of the X-ray tube 21, and sets a channel at a point on the circular arc that is the position of the multi-row X-ray detector 24. The direction profile Pθ (β) is taken.

The reprojection processing unit 38 re-converts the pixels in the tomographic image and the X-ray focal point in the fan direction (fan direction) within the range of the channel direction angle [−γ, γ]. Projection processing, that is, addition processing is performed.
In this way, the reprojection processing unit 38 uses the obtained channel direction profile Pθ obtained by the fan beam reprojection processing as X-ray projection data.

The reprojection processing unit 38 repeats this process in the Z-axis direction range [zs, ze] to obtain X-ray projection data in the Z-axis direction range of [zs, ze]. FIG. 13B shows the result of performing the reprojection process.
Note that the X-ray projection data obtained by the reprojection process in step D65 in FIG. 12 does not vary in sensitivity, offset, etc. for each channel of the multi-row X-ray detector 24. There is no need to perform beam hardening correction and Z filter superimposition processing as necessary.

<Parallel beam reprojection processing>
FIG. 15 shows a flowchart of the processing method of the dual energy imaging method by parallel beam reprojection processing.
In step D81, a scout image is taken.
In step D82, the operator sets imaging conditions for helical scanning for dual energy imaging. Similar to step D62 in FIG. 12, it is not necessary to obtain the shift amount L of the X-ray projection data. In this embodiment, it is only necessary to know only the angle θ of the view direction used in the parallel beam reprojection processing.

In step D83, X-ray data collection is performed.
In step D84, the first X-ray acquisition system XS1 collects X-ray data of X-rays irradiated using an X-ray tube voltage of 140 kV, and the image reconstruction unit 34 applies X-rays irradiated using an X-ray tube voltage of 80 kV. The tomogram of the image is reconstructed.
In Step D85, the second X-ray acquisition system XS2 delayed in the 90-degree view direction performs X-ray data acquisition of X-rays irradiated using an X-ray tube voltage of 80 kV. The image reconstruction unit 34 reconstructs an X-ray tomographic image irradiated with an X-ray tube voltage of 140 kV.

In step D86, the X-ray tomographic image irradiated using the X-ray tube voltage 80 kV of the second X-ray acquisition system XS2 is fan-extracted from a certain view direction by 360 degrees full scan or 180 degrees + fan angle half scan. Beam reprojection processing or parallel beam reprojection processing is performed.
In step D87, the X-ray tomographic image irradiated using the X-ray tube voltage 140 kV of the first X-ray acquisition system XS1 is fan-extracted by 360 ° full scan from a certain view direction or 180 ° + fan angle half scan. Beam reprojection processing or parallel beam reprojection processing is performed.
In Step D86 and Step D87, the reprojection processing unit 38 performs a fan beam reprojection process from a tomographic image of each X-ray projection data collection system in the case of 360 degree full scan and 180 degree + fan angle half scan. The start view direction of the X-ray projection data is aligned with the X-ray tube voltage of 80 kV and the X-ray tube voltage of 140 kV. Further, the reprojection processing unit 38 can similarly align the start view direction of the X-ray projection data in the parallel beam reprojection processing.

In step D88, the preprocessing unit 33 preprocesses the X-ray projection data of the X-rays irradiated using the X-ray tube voltage of 80 kV.
In step D89, the preprocessing unit 33 preprocesses the X-ray projection data of the X-rays irradiated using the X-ray tube voltage of 140 kV.
Steps D88 and D89 are basically unnecessary because they are X-ray projection data obtained by reprojecting a tomographic image, and there are no variations in sensitivity, offset, and the like for each channel of the multi-row X-ray detector 24. , Beam hardening correction and z filter superimposition processing are performed as necessary.

  In step D90, the dual energy image reconstruction unit 35 weights the X-ray projection data of the X-rays irradiated using the X-ray tube voltage of 80 kV and the X-ray projection data of the X-rays irradiated using the X-ray tube voltage of 140 kV. Addition processing is performed to obtain X-ray projection data of the calcium-enhanced image and X-ray projection data of the contrast agent-enhanced image as a tomographic image of dual energy imaging.

In step D91, the dual energy image reconstruction unit 35 performs beam hardening correction of the X-ray projection data of the calcium enhanced image and the X-ray projection data of the contrast agent enhanced image.
In step D92, the dual energy image reconstruction unit 35 performs image reconstruction of a contrast-emphasized image that performs image reconstruction of a calcium-weighted image.
In step D93, a calcium-enhanced image and a contrast agent-enhanced image are displayed on the monitor 6 as tomographic images for dual energy imaging.

FIG. 16 shows an outline of the parallel beam reprojection process. In the parallel beam reprojection process, when the X-ray focal point 21 is in the θ direction with respect to the Y axis, the reprojection processing unit 38 reads the tomographic image included in the reconstruction area P in the direction parallel to the θ direction. Each pixel g (x1, y1) is added to perform parallel beam reprojection processing in the θ direction. That is, the reprojection processing unit 38 adds all the pixels on the straight line that are shifted from the center direction of the X-ray tube by the distance r1.
The reprojection processing unit 38 obtains a profile Pθ (r) in a range of [−ra, ra] from the center direction of the X-ray tube 21 and uses the profile Pθ obtained by the parallel beam reprojection processing as X-ray projection data.

FIG. 17 or FIG. 18 shows an outline of the parallel beam reprojection process in step D88 at this time. The flowchart of the process is shown in FIGS. 19 (a) and 19 (b).
In FIG. 17, the parallel beam reprojection processing for the tomographic image in the θ direction can be simplified, and the processing can be performed by raster scanning in the X-axis direction on the tomographic image, which is speeded up as a so-called Stanford algorithm. it can. In other words, in this process, the tomographic image is rotated by the θ direction and the addition is performed in the Y axis direction, so that the reprojection process in the θ direction becomes the addition process in the Y axis direction, and the speed of the raster scan process in the X axis direction is increased. it can.

FIG. 19A shows a flowchart of the raster scan.
In step T11, θ = 0 and z1 = zs.
In step T12, the reprojection processing unit 38 reads a tomographic image g (x, y) having a certain Z-axis coordinate zn.
In step T13, the reprojection processing unit 38 rotates the tomographic image g (x, y) in the θ direction and obtains the rotated tomographic image g (X, Y).
In step T14, the reprojection processing unit 38 reprojects the tomographic image g (X, Y) in the Y direction to obtain θ direction profile data Pθ (x).
In step T15, the reprojection processing unit 38 determines whether θ ≧ 360 degrees in the case of full scan or θ ≧ 180 degrees in the case of half scan. If YES, the process goes to step T16. Go to T17.
In step T16, it is determined whether zn ≧ ze. If YES, the process ends. If NO, the process goes to step T18.
In step T17, θ = θ + Δθ is set. Thereafter, the process returns to step T12.
In step T18, n = n + 1. Thereafter, the process returns to step T12.

In FIG. 18, as in FIG. 17, parallel beam reprojection processing in the θ direction performed on the tomographic image can be simplified and performed by raster scanning in the X axis direction to increase the speed.
In this process, the tomographic image is shifted in the X-axis direction and the addition process is performed in the Y-axis direction, so that the reprojection process in the θ direction becomes the addition process in the Y-axis direction, and the X-axis direction raster scan on the tomographic image The processing can be speeded up.

FIG. 19B shows a flowchart of the processing.
This process can be performed in substantially the same manner as the flowchart of the process of FIG.
The only change is that step T13 in FIG. 19A is replaced with step T23 in FIG. 19B.
In step T23, in the tomographic image g (x, y), when y = y1, the deviation amount in the X-axis direction is set to −y1 · tan θ. In addition, this shift amount shifts the one-dimensional tomographic image data in the X-axis direction by the shift amount even at each Y coordinate.

  In this way, in the present embodiment, in the X-ray CT apparatus 100 having a plurality of X-ray tubes, even if the Z-axis direction center positions coincide and deviate in the view direction, first, at the same time with the same Z-axis coordinates. After the X-ray projection data whose view direction is shifted is reconstructed as a tomographic image, it can be obtained as X-ray projection data in the same view direction by reprojection processing.

Further, the X-ray tube voltage in each embodiment may be set so that the first X-ray acquisition system XS1 and the second X-ray acquisition system XS2 are reversed.
According to the X-ray CT apparatus 100 having the plurality of X-ray tubes 21 described above, there is an effect of improving the image quality of the tomographic image in the dual energy imaging of the helical scan. Note that, in dual energy imaging, image noise tends to be large in a dual energy image. Therefore, in order to minimize the image noise, the image noise of the tomographic image with the low X-ray tube voltage and the image noise of the tomographic image with the high X-ray tube voltage are made substantially equal in consideration of the weighted addition coefficient. It is preferable.

  In the present invention, X-ray projection data composed of a plurality of X-ray tubes 21 and X-ray projection data of a plurality of X-ray tube voltages can be obtained from views in the same direction at the same body axis direction. Then, by performing X-ray projection data space correction processing on X-ray projection data of a plurality of X-ray tube voltages, dual energy imaging with improved image quality can be performed.

Further, in the present invention, when dual energy imaging is performed with helical scanning using a plurality of X-ray tubes, X-ray data collection from the same view direction is 180 degrees + fan angle even in the case of 360 degrees full scanning. Even in the case of half scan, since correction processing in the X-ray projection data space can be performed, it is advantageous in that image quality can be improved. In particular, in dual energy imaging, the subject may move due to body movement, pulsation, pulsation, breathing, etc., and a plurality of X-ray projection data shifts and misregistration (misregistration miss registration) artifacts occur. there's a possibility that. For such a part, 180-degree + fan-angle half-scan imaging for collecting X-ray data in a short time is performed. The imaging conditions can be optimized by taking a 360-degree full scan for imaging a region with low possibility of body movement.
In the present embodiment, the calcium-enhanced image and the contrast-agent-enhanced image are reconstructed in dual energy imaging. Similarly, enhanced images of other substances can be reconstructed. In addition, although the present embodiment describes the case of the helical scan, the same effect can be obtained in the case of the variable pitch helical scan and the helical shuttle scan. The variable pitch helical scan is an imaging method that collects X-ray projection data by changing the speed of the cradle 12 in the same manner as the helical scan. The helical shuttle scan is a scanning method that collects X-ray projection data by accelerating and decelerating the cradle 12 and reciprocating in the positive direction of the Z axis or the negative direction of the Z axis in the same manner as the helical scan.

Furthermore, although the present Example has described about the case where X-ray data acquisition is not synchronized with a biological signal, the same effect can be produced even if it synchronizes with a biological signal, especially a heartbeat signal.
In this embodiment, the helical scan is realized by moving the cradle 12 of the imaging table 10 in the Z-axis direction. However, in the present embodiment, a relatively similar effect can be obtained by moving the scanning gantry 20 or the rotating unit 15 in the scanning gantry 20 with respect to the cradle 12 of the imaging table 10.

  In the present embodiment, the medical X-ray CT apparatus is described based on the original, but also in an industrial X-ray CT apparatus or an X-ray CT-PET apparatus, an X-ray CT-SPECT apparatus combined with other apparatuses, etc. Available.

DESCRIPTION OF SYMBOLS 1 ... Operation console 2 ... Input device 3 ... Central processing unit (33 ... Pre-processing part, 34 ... Image reconstruction part, 35 ... Dual energy image reconstruction part, 37 ... Imaging | photography control part, 38 ... Reprojection process part)
5 ... Data collection buffer 6 ... Monitor 7 ... Storage device 10 ... Imaging table
DESCRIPTION OF SYMBOLS 12 ... Cradle 15 ... Rotating part 20 ... Scanning gantry 21 ... X-ray tube (21-1 ... 1st X-ray tube, 21-2 ... 2nd X-ray tube)
22 ... X-ray controller 23 ... Collimator 24 ... Multi-row X-ray detector (24-1 ... First multi-row X-ray detector, 24-2 ... Second multi-row X-ray detector)
25 ... Data collection device (DAS)
26: Rotating part controller 28 ... Beam forming X-ray filter 29 ... Control controller 30 ... Slip ring 32 ... X-ray tube moving mechanism dP ... X-ray detector plane P ... Image reconstruction area D ... Multiple rows on the rotation center axis X-ray detector width

Claims (4)

A bed on which the subject is placed;
A first X-ray generator for generating a first X-ray having a predetermined beam width for irradiating the subject while rotating around the subject around the body axis direction of the subject;

The same position as the first X-ray generator in the body axis direction and at a different angular position, and while rotating around the subject together with the first X-ray generator, from a different angle direction than the first X-ray generator. A second X-ray generator for generating second X-rays having a predetermined beam width for irradiating the subject;

Wherein the 1X-ray generator and in opposition to each of the first 2X-ray generator is arranged, the subject of the X-ray projection data based on X-rays generated from each of the first 1X-ray generator and the first 2X-ray generator An X-ray detection device for collecting

A rotating unit for rotating the first 1X-ray generator and the first 2X-ray generating apparatus body axis direction of the subject as an axis,
While rotating the first 1X-ray generator and the first 2X-ray generator by the rotation unit performs a helical scan and the bed and the second 1X-ray generator and the first 2X-ray generator are relatively moved An X-ray tomography apparatus having an imaging control unit,

A tomographic image obtained by using the helical scan and using at least one of the first X-ray projection data based on the first X-ray and the second X-ray projection data based on the second X-ray in different view angle ranges obtained by the same rotation. X-ray projection data control means for obtaining first X-ray projection data based on the first X-ray and second X-ray projection data based on the second X-ray in the same view angle range by performing reprojection processing.

X-ray tomography apparatus characterized by the above. The X-ray tomographic imaging apparatus according to claim 1, wherein the reprojection process includes a fan beam reprojection process in a beam direction having a fan angle or a parallel beam reprojection process in a parallel beam direction.
The first X-ray generator generates X-rays of a first energy spectrum, the second X-ray generator generates a second energy spectrum different from the first energy spectrum;

A dual energy image reconstruction unit that reconstructs a dual energy image using X-ray projection data based on the X-rays of the first energy spectrum and the X-rays of the second energy spectrum is provided. The X-ray tomographic imaging apparatus according to Item 1 or Claim 2.
The dual energy image reconstruction unit performs weighted subtraction processing between X-ray projection data of the same view angle at the same position in the body axis direction based on the X-ray of the first energy spectrum and the X-ray of the second energy spectrum The X-ray tomographic imaging apparatus according to claim 3, wherein a dual energy image is reconstructed by performing a back projection process after performing the above.