JP2018011860A - X-ray CT apparatus and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus capable of preventing image deterioration of a dual energy image. An X-ray CT apparatus has an X-ray tube that irradiates a subject with first X-rays and second X-rays while rotating around the body axis of the subject, and the first X-rays and the above. A focus that controls a switching control unit that switches between the second X-ray, the position of the first X-ray focus F1 that is irradiated with the first X-ray, and the position of the second X-ray focus F2 that is irradiated with the second X-ray. In the control unit, the position of the first X-ray focus F1 in the view direction when the first X-ray is irradiated and the position of the second X-ray focus F2 in the view direction when the second X-ray is irradiated are A focus control unit is provided which arranges the first X-ray focus F1 and the second X-ray focus F2 at different positions in the X-ray tube in the view direction so as to have an overlapping range. [Selection diagram] FIG. 6

Description

  The present invention relates to an X-ray CT apparatus, and more particularly to a technique for realizing dual-energy imaging.

  As an imaging method using an X-ray computed tomography system (X-ray CT), an imaging method called a dual energy imaging method in which data is collected by switching an X-ray tube voltage in a view direction is known (for example, Patent Documents). 1 and 2 etc.).

  This imaging method is an imaging method that obtains an image in which a specific substance in a subject is emphasized or suppressed (removed) by utilizing the fact that the absorption spectrum (spectrum) of X-ray energy differs depending on the substance. Specifically, for example, a first X-ray projection corresponding to a plurality of views by irradiating a subject including a first substance and a second substance with first X-rays and second X-rays having different energy spectra. Data and second X-ray projection data are collected. Then, the first density image is reconstructed based on the first X-ray projection data, and the second density image is reconstructed based on the second X-ray projection data, and the first density image and the second density image are reconstructed. Based on the density image, a density distribution image indicating a density distribution of a certain substance or a dual energy image which is a monochrome image which is an image of a certain energy spectrum is obtained.

  As a method of collecting the first X-ray projection data and the second X-ray projection data as described above, for example, every X view, that is, every time the gantry of the X-ray CT apparatus rotates by one view, A conceivable method is to collect projection data while alternately switching the tube voltage between the first tube voltage and the second tube voltage.

JP 2004-65975 A JP 2009-1553829 A

  As described above, when the projection data is collected while the X-ray tube voltage is alternately switched between the first tube voltage and the second tube voltage, the position in the view direction of the X-ray focal point when the first X-ray projection data is collected. And the position in the view direction of the X-ray focal point when the second X-ray projection data is collected. Accordingly, there is no second X-ray projection data in the view where the first X-ray projection data exists, while there is no first X-ray projection data in the view where the second X-ray projection data exists. For this reason, since the dual energy image is obtained after performing the interpolation processing in each view, there is a concern that the obtained image may be deteriorated.

  One aspect of the invention made in order to solve the above-mentioned problem is that a first X-ray having a first energy spectrum and a second X-ray having a second energy spectrum different from the first energy spectrum are An X-ray tube that irradiates the subject while rotating around a body axis; a switching control unit that switches the first X-ray and the second X-ray for each view; and the first X-ray tube in the first X-ray tube. A focus control unit that controls a position of a first X-ray focal point irradiated with a second X-ray and a position of a second X-ray focal point irradiated with the second X-ray in the X-ray tube; So that the position of the first X-ray focal point in the view direction when the line is irradiated and the position of the second X-ray focal point in the view direction when the second X-ray is irradiated overlap. The first X-ray focus Said first 2X-ray focal point, an X-ray CT apparatus characterized by comprising: a focus control unit be placed in different positions in the view direction on the target electrode of the X-ray tube.

  In another aspect of the invention, a first X-ray having a first energy spectrum and a second X-ray having a second energy spectrum different from the first energy spectrum are rotated around the body axis of the subject. An X-ray tube that irradiates the subject; a switching control unit that switches between the first X-ray and the second X-ray for each view; and a first X-ray that is irradiated with the first X-ray in the X-ray tube. A focus control unit that controls a position of a 1 X-ray focal point and a position of a second X-ray focal point at which the second X-ray is irradiated in the X-ray tube, the beam direction of the first X-ray and the second X-ray A focus control unit that arranges the first X-ray focal point and the second X-ray focal point on the target electrode of the X-ray tube at different positions in the view direction so that the beam direction of the line is the same direction. X characterized by A CT apparatus.

  According to the first aspect of the invention, the position of the X-ray focal point in the view direction when the first X-ray is irradiated by moving the X-ray focal point in the X-ray tube in the view direction; Since there is a range where the position of the X-ray focal point in the view direction when the second X-ray is irradiated, the data obtained by irradiating the first X-ray and the second X-ray without performing an interpolation process It is possible to create an image based on the data obtained by irradiation. Therefore, image deterioration of the obtained image can be prevented.

  According to another aspect of the invention, when the X-ray focal point in the X-ray tube moves in the view direction, the beam direction of the first X-ray and the beam direction of the second X-ray become the same direction. Therefore, the data consistency in the view direction is improved between the data obtained by irradiating the first X-ray and the data obtained by irradiating the second X-ray. Therefore, an image created based on the data obtained by irradiating the first X-ray and the data obtained by irradiating the second X-ray without performing the interpolation process can prevent image deterioration.

1 is a diagram schematically showing a configuration of an X-ray CT system according to an embodiment. It is a figure which shows the structure of the principal part of an X-ray tube and an X-ray detection part. It is a functional block diagram which shows the function of a scan control part. It is a figure which shows the graph of the time change of a tube voltage, and the graph of the time change of a tube current. It is a figure which shows the 1st X-ray focus and 2nd X-ray focus in an X-ray tube. It is a figure explaining having a range with which the position of the 1st X-ray focus in a view direction and the position of the 2nd X-ray focus in a view direction overlap. It is a figure explaining the position of the 1st X-ray focus in a view direction, and a 2nd X-ray focus. It is a figure which shows the 1st X-ray focus and 2nd X-ray focus in a modification. It is a figure explaining the beam direction of the 1st X-ray, and the beam direction of the 2nd X-ray. It is a figure explaining the position of the 1st X-ray focus and the 2nd X-ray focus in a view direction in a modification.

  Embodiments of the invention will be described below. The invention is not limited thereby.

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

  The operation console 1 has a configuration as a computer. Specifically, the operation console 1 includes an input device 2 such as a keyboard or a mouse that receives an input from the operator, and a center that executes a scan control process, a preprocess, an image generation process, and the like. A processing device 3 and a data collection buffer (buffer) 5 for collecting X-ray detector data collected by the scanning gantry 20 are provided. Further, the operation console 1 includes a monitor 6 for displaying a dual energy image generated by the image generation processing, a program, X-ray detector data, X-ray projection data (projection data), dual energy. And a storage device 7 for storing images and the like. The shooting conditions are input from the input device 2 and stored in the storage device 7.

  The imaging table 10 includes a cradle 12 on which a subject 71 is placed and taken in and out of an opening 20a described later of the scanning gantry 20. The cradle 12 is moved up and down and horizontally moved by a motor built in the imaging table 10.

  The scanning gantry 20 has an opening 20a through which a subject 71 to be imaged is conveyed. The scanning gantry 20 includes an X-ray tube 21, an X-ray control unit 22 that controls the X-ray tube voltage and X-ray irradiation timing (timing) in the X-ray tube 21, and the X-ray irradiated from the X-ray tube 21. And a collimator 23 having an opening for shaping the line into a fan-shaped X-ray beam 81. Further, the scanning gantry 20 includes a collimator control unit 27 that controls the opening of the collimator 23, an X-ray detector 24 that detects X-rays emitted from the X-ray tube 21, and an X-ray from the output of the X-ray detector 24. And a data acquisition device (DAS: Data Acquisition System) 25 that collects detector data (also referred to as raw data).

  The scanning gantry 20 holds an X-ray tube 21, a collimator 23, and an X-ray detector 24, and rotates to control the gantry rotating unit 15 and a gantry rotating unit 15 that rotates around the body axis of the subject 71. And a control unit 26. Further, the scanning gantry 20 includes a gantry control unit 29 that exchanges control signals between the operation console 1, the X-ray control unit 22, the rotation control unit 26, the imaging table 10, and the like. In the implementation, the scanning gantry 20 includes a beam forming X-ray filter that spatially controls the dose of the X-ray beam 81 and an X-ray filter that controls the quality of the X-ray beam 81. The gantry rotating unit 15 is configured to hold these filters between the collimator 23 and the opening 20a, but illustration and detailed description thereof are omitted here.

  FIG. 2 is a diagram showing the configuration of the main parts of the X-ray tube 21 and the X-ray detection unit 24. Here, the vertical direction is the y-axis direction, and the conveyance direction of the imaging table 10 (usually coincides with the thickness direction of the X-ray beam 81 or the body axis direction of the subject 71) is the z-axis direction, y-axis direction, and z. A direction (channel direction) perpendicular to the axial direction is defined as the x-axis direction.

  These components are supported by a predetermined base portion of the gantry rotating portion 15 and maintain the positional relationship as shown in the figure. That is, the X-ray tube 21 and the X-ray detector 24 are arranged to face each other with the opening 20a interposed therebetween. Then, the X-rays radiated from the X-ray tube 21 pass through a slit formed by a collimator 23 (not shown in FIG. 2), whereby a fan-shaped X having a predetermined thickness (cone angle) and spread (fan angle). A line beam 81 is formed.

  The X-ray tube 21 has a structure in which a cathode sleeve 21 s containing a focusing electrode and a cathode filament and a rotating target electrode 21 t are accommodated in a housing 21 h, and generates X-rays that diverge from the X-ray focal point F.

  The X-ray detection unit 24 includes, in the z-axis direction (X-ray beam This is a so-called multi-row X-ray detector in which a plurality, for example, 64 are arranged in the thickness direction of 81. Here, numbers 1, 2, 3,..., 64 are assigned to the respective detection element arrays from the end. Thereby, a so-called 64-column multi-slice X-ray CT is realized. However, the 64 detection element rows are merely examples here, and the present invention is not limited to this. The X-ray detector 24 forms an X-ray detection surface 24s for detecting the X-ray beam 81 transmitted through the subject 71 by the plurality of X-ray detection elements 24a. The X-ray detection element 24a is configured as a so-called solid state detector, for example, by a combination of a scintillator and a photodiode.

  The central processing unit 3 includes a scan control unit 32, a preprocessing unit 34, and an image generation unit 35. The central processing unit 3 is a processor (Processor) such as a CPU (Central Processing Unit), for example. The central processing unit 3 executes the functions of the scan control unit 32, the preprocessing unit 34, and the image generation unit 35 by reading and executing the program stored in the storage device 7. The program is an example of a control program according to the present invention.

  The scan control unit 32 controls the X-ray control unit 22, the rotation control unit 26, the collimator control unit 27, and the imaging table 10 via the gantry control unit 29 so as to perform dual energy imaging of the subject 71. Specifically, the scan control unit 32 collects X-ray projection data by controlling the above-described units to rotate the X-ray tube 21 and the X-ray detector 24 around the subject 71. Further, the scan control unit 32 executes the functions of the switching control unit 321 and the focus control unit 322 shown in FIG. However, only some functions of the scan control unit 32 are illustrated in FIG. 3, and other functions are not illustrated.

  The switching control unit 321 controls the X-ray control unit 22 via the gantry control unit 29 so as to sequentially switch the X-ray tube voltage V among a plurality of target tube voltages for each view. In the present embodiment, the target tube voltages are the first tube voltage V1 and the second tube voltage V2. For example, the first tube voltage V1 is 80 kV and the second tube voltage V2 is 140 kV. The switching control unit 321 is an example of an embodiment of the switching control unit in the present invention. The function of the switching control unit 321 is an example of the embodiment of the switching control function in the present invention.

  The X-ray irradiated when the tube voltage of the X-ray tube 21 is the first tube voltage V1 is a first X-ray, and the X-ray irradiated when the tube voltage is the second tube voltage V2 is a second X-ray. Since the first X-ray and the second X-ray have different tube voltages, the first energy spectrum of the first X-ray and the second energy spectrum of the second X-ray are different from each other.

  While the X-ray tube voltage V is switched for each view by the switching control unit 321, X-ray projection data (180 ° + fan angle α or 360 ° corresponding to 360 °) corresponding to the number of views necessary for image reconstruction. X-ray projection data) is collected. Thereby, the first X-ray projection data p1 corresponding to the first tube voltage V1 and the second X-ray projection data p2 corresponding to the second tube voltage V2 are collected.

  The focus control unit 322 controls the position of the X-ray focus in the X-ray tube 21. Details will be described later. The focus control unit 322 is an example of an embodiment of the focus control unit in the present invention. The function of the focus control unit 322 is an example of the embodiment of the focus control function in the present invention.

  The preprocessing unit 34 performs preprocessing on the X-ray projection data obtained by the dual energy imaging. Specifically, with respect to the first X-ray projection data p1 and the second X-ray projection data p2, a channel for the raw data collected by the offset (off-set) correction, logarithmic conversion, and the data collection device 25 is used. Sensitivity correction to correct sensitivity non-uniformity between X-rays, X-ray dose correction to correct signal drop or signal drop due to strong X-ray absorbers such as metal parts, X-ray beam hardening correction, etc. Pre-processing is performed. Further, as pre-processing, fan-para conversion that converts fan beam X-rays into parallel beam X-rays is performed on the first X-ray projection data p1 and the second X-ray projection data p2. As the fan-para conversion, image degradation can be prevented by using, for example, a method disclosed in Japanese Patent Laid-Open No. 62-49831.

  The image generation unit 35 generates a dual energy image DE in which a specific substance is emphasized or suppressed based on the first X-ray projection data p1 and the second X-ray projection data p2 preprocessed by the preprocessing unit 34.

  As a method of generating the dual energy image DE, a method of performing weighted subtraction processing in the image data space and a method of performing weighted subtraction processing in the projection data space can be considered, but either method may be adopted.

  In the method of generating the dual energy image DE by performing the weighted subtraction process in the image data space, the first image P1 is reconstructed based on the first X-ray projection data p1, and the second image X2 is based on the second X-ray projection data p2. Two images P2 are reconstructed, and a weighted subtraction process is performed between the first image P1 and the second image P2 to generate a dual energy image DE. On the other hand, in the method of generating the dual energy image DE by performing weighted subtraction processing in the projection data space, weighted subtraction processing is performed in view units between the first X-ray projection data p1 and the second X-ray projection data p2, and the result A dual energy image DE is reconstructed based on the obtained processed X-ray projection data.

  Image reconstruction can be performed using, for example, a conventionally known Feldkamp method, a three-dimensional image reconstruction method, another three-dimensional image reconstruction method, or a two-dimensional image reconstruction method. The procedure is as follows. First, these X-ray projection data are subjected to a fast Fourier transform (FFT) for transforming into the frequency domain, and multiplied by a reconstruction function Kernel (j) to perform an inverse Fourier transform. Then, back projection processing is performed on the X-ray projection data multiplied by the reconstruction function Kernel (j), and it corresponds to the same slice when the subject 71 is sliced in the body axis direction (z-axis direction). Tomographic image (xy plane) to be obtained.

  The operation of the X-ray CT apparatus 100 according to the present embodiment will be described. The X-ray tube 21 and the X-ray detector 24 rotate around the body axis of the subject to collect projection data. At this time, the switching control unit 321 switches the X-ray tube voltage of the X-ray tube 21 between the first tube voltage V1 and the second tube voltage V2 as shown in the graph G1 of FIG. In the graph G1, the horizontal axis represents time, and the vertical axis represents tube voltage. Accordingly, the X-ray tube 21 alternately irradiates the first X-ray and the second X-ray while rotating around the body axis of the subject.

  The switching control unit 321 switches the X-ray tube current A of the X-ray tube 21 between the first tube current A1 and the second tube current, as shown by a graph G2 in FIG. The first tube current A1 is a tube current when the X-ray tube 21 is at the first tube voltage V1, and the second tube current A2 is a tube current when the X-ray tube 21 is at the second tube voltage V2. is there. For example, the first tube current A1 is 300 mA, and the second tube current A2 is 100 mA.

  In the state where the X-ray tube 21 is at the first tube voltage V1, the switching control unit 321 reduces the X-ray tube current A from the first tube current A1, and then changes the first tube voltage V1 to the second tube voltage. Switch to V2. Then, the switching control unit 321 switches the tube current A to the second tube current A2 after switching to the second tube voltage. In addition, the switching control unit 321 reduces the X-ray tube current A from the first tube voltage V1 to the second value after reducing the X-ray tube current A from the second tube current A1 in a state where the X-ray tube 21 is at the second tube voltage V2. Switch to tube voltage V2. Then, the switching control unit 321 switches the tube current A to the first tube current A1 after switching to the first tube voltage. In FIG. 4, the timing at which the first tube voltage V1 is switched to the second tube voltage V2 and the timing at which the second tube voltage V2 is switched to the first tube voltage V1 (switching timing) are indicated by a symbol Ts.

  In this example, the tube current A is zero at the switching timing Ts. However, the tube current A at the switching timing Ts may not be zero. For example, the tube current A at the switching timing Ts may be a tube current that is about 1/100 of the first tube current A1 and the second tube current A2.

  The focus control unit 322 sets the position of the X-ray focal point F as the first position in the X-ray tube 21 when the X-ray tube voltage V is the first X-ray tube voltage V1. The X-ray focal point F at the first position is defined as a first X-ray focal point F1. Further, when the X-ray tube voltage V is the second X-ray tube voltage V2, the focus control unit 322 sets the position of the X-ray focus F to a second position different from the first position in the X-ray tube 21. The X-ray focal point F at the second position is defined as a second X-ray focal point F2.

  FIG. 5 shows the first X-ray focal point F1 and the second X-ray focal point F2 on the target electrode 21t. The first X-ray focal point F1 is irradiated with the first X-ray, and the second X-ray focal point F2 is irradiated with the second X-ray. The positions of the first X-ray focal point F1 and the second X-ray focal point F2 are different in the x direction. The x direction coincides with the view direction.

  In FIG. 5, symbol B indicates a reference position in the target electrode 21t. The reference position B indicates the position of the X-ray focal point in conventional dual energy imaging. The reference position B is an example of an embodiment of the reference position in the present invention. The first X-ray focal point F1 is a position moved in the positive view direction + Vd with respect to the reference position B, and the second X-ray focal point F2 is opposite to the positive view direction + Vd with respect to the reference position B. This is the position moved in the negative view direction -Vd. However, the reference position B, the position of the first X-ray focal point F1, and the position of the second X-ray focal point F2 in the figure are examples, and are not limited to those illustrated.

  The distance D1 at the target electrode 21t between the reference position B and the first X-ray focal point F1 and the distance D1 at the target electrode 21t between the reference position B and the second X-ray focal point F2 are the length of the circumference around which the X-ray tube 21 rotates. The distance D2 obtained by dividing by the number of times of switching between the first tube voltage V1 and the second tube voltage V2. A distance D3 between the first X-ray focal point F1 and the second X-ray focal point is a distance D2 (D3 = D2 = D1 × 2). Since the reference position B1, the first X-ray focal point F1, and the second X-ray focal point F3 are in the positional relationship as described above, the first X-ray in the view direction when the first X-ray is irradiated as shown in FIG. There is a range in which the position of the focal point F1 and the position of the second X-ray focal point F2 in the view direction when the second X-ray is irradiated overlap.

  Incidentally, since the X-ray tube 21 emits the first X-ray and the second X-ray while drawing the circular orbit C, as shown in FIG. 6, the first X-ray focal point F1 and the second X-ray focal point F2 move in the view direction. In FIG. 6, the trajectory of the first X-ray focal point F1 and the trajectory of the second X-ray focal point F2 are indicated by solid arrows, and the trajectory of the first X-ray focal point F1 and the trajectory of the second X-ray focal point F2 are overlapping. Further, the trajectory of the first X-ray focal point F1 and the trajectory of the second X-ray focal point F2 overlap in the real space. However, although the locus of the first X-ray focal point F1 and the locus of the second X-ray focal point F2 are actually located on the same circular orbit, they are shown shifted in the vertical direction in FIG. 6 for convenience of explanation.

  On the other hand, in FIG. 6, the broken-line arrows indicate X when the X-ray focal point is the reference position B when the X-ray tube voltage V is the first tube voltage V1 and when the X-ray tube voltage V2 is the second tube voltage V2. The locus of the line focus is shown. Symbol BF1 is a first X-ray focal point that irradiates the first X-ray with the first tube voltage V1, and symbol BF2 is a second X-ray focal point that irradiates the second X-ray with the second tube voltage V2. Thus, conventionally, the first X-ray focal point BF1 and the second X-ray focal point BF2 do not overlap in the view direction. The first X-ray focal point F1 in this example is a position moved in the positive view direction with respect to the conventional first X-ray focal point BF1, and the second X-ray focal point F2 in this example is relative to the conventional second X-ray focal point BF2. Thus, the first X-ray focal point F1 and the second X-ray focal point F2 overlap each other in the view direction.

  The positions of the first X-ray focal point F1 and the second X-ray focal point F2 will be described in more detail based on FIG. FIG. 7 shows the position of the X-ray tube 21 in the view direction, the first X-ray focal point F1 and the second X-ray focal point F2 in the X-ray tube 21 (target electrode 21t). Although the position of the X-ray tube 21 is actually located on the same circular orbit, FIG. 7 shows the position shifted in the vertical direction for convenience of explanation. In FIG. 7, the position of the X-ray tube 21-1 at the required time t after the X-ray tube voltage V is switched to the first tube voltage V1 and the X-ray tube voltage V are switched to the second tube voltage V2. The position of the X-ray tube 21-2 at the required time point t after the change is shown. That is, the position of the X-ray tube 21 at the same time after the X-ray tube voltage V is switched is shown. In addition, the position of the X-ray tube 21 for each distance D2 is shown in the view direction. That is, the distance between the adjacent X-ray tubes 21-1 and 21-2 in FIG. 7 is the distance D2.

  The positions in the view direction of the first X-ray focal point F1 and the second X-ray focal point F2 in the X-ray tubes (target electrodes) 21-1 and 21-2 having the positional relationship of the distance D2 are the same position. Accordingly, there is a first X-ray beam XB1 and a second X-ray beam XB2 that are irradiated to the same position in the view direction. The first X-ray projection data p1 and the second X-ray projection data p2 corresponding to the first X-ray beam XB1 and the second X-ray beam XB2 irradiated at the same position in the view direction constitute projection data of the same view. Therefore, since the first X-ray projection data p1 and the second X-ray projection data p2 exist for each of all the views, the dual energy image DE can be created without performing an interpolation process.

  According to this example described above, the dual energy image DE can be created without performing the interpolation process, so that the image degradation of the dual energy image can be prevented.

  Next, a modification of the above embodiment will be described. In this modification, the focus control unit 322 includes a first X-ray focal point F1 and a second X-ray focal point F2 so that the direction of the first X-ray beam XB1 and the direction of the second X-ray beam XB2 are the same. Are arranged at different positions in the X-ray tube 21 in the view direction.

  The positions of the first X-ray focal point F1 and the second X-ray focal point F2 will be specifically described. As shown in FIG. 8, the distance D1 ′ at the target electrode 21t between the reference position B and the first X-ray focal point F1 and the distance D1 ′ at the target electrode 21t between the reference position B and the second X-ray focal point F2 are the X-ray tube. This is a distance D2 obtained by dividing the length of the circumference around which 21 rotates by the number of times of switching between the first tube voltage V1 and the second tube voltage V2. That is, the distance D1 ′ is twice the distance D1 in the above-described embodiment. The distance D3 between the first X-ray focal point F1 and the second X-ray focal point F2 is twice the distance D2 (D3 = D2 × 2).

  Since the reference position B1, the first X-ray focal point F1, and the second X-ray focal point F3 are in the above-described positional relationship, as shown in FIG. 9, the direction of the first X-ray beam XB1 and the second X-ray beam XB2 The directions are parallel to each other and are in the same direction. FIG. 9 shows a state in which the circular orbit C of the X-ray tube 21 is viewed from the body axis direction.

  The positions of the first X-ray focal point F1 and the second X-ray focal point F2 will be described in more detail based on FIG. FIG. 10 is the same view as FIG. 7 except that the positions of the first X-ray focal point F1 and the second X-ray focal point F2 are the positions in this modification. The position of the first X-ray focal point F1 in the X-ray tube 21-1 is the same position in the view direction as the reference position B in the X-ray tube 21-2. The position of the second X-ray focal point F2 in the X-ray tube 21-2 is the same position as the reference position B in the X-ray tube 21-1 in the view direction.

  Returning to FIG. 9, reference numeral 24-1 indicates an X-ray detector when detecting the first X-ray from the first X-ray focal point F1, and reference numeral 24-2 indicates the second X-ray from the second X-ray focal point F2. The X-ray detection part at the time of detecting is shown. Note that the X-ray detection units 24-1 and 24-2 are simplified and shown as line segments. The first X-ray beam XB1 is incident on the center of the X-ray detector 24-1 in the channel direction (horizontal direction in FIG. 9), and the second X-ray beam XB2 is in the channel direction of the X-ray detector 24-2. Incident in the center of the.

  In FIG. 9, the symbol XBi1 represents the X-ray from the X-ray focal point at the reference position B in the X-ray tube 21 when the X-ray tube voltage V is the first tube voltage V1, that is, the X-ray tube 21-1. The direction of the beam (hereinafter referred to as “virtual first X-ray beam”) is shown. XBi2 is an X-ray beam from the X-ray focal point at the reference position B in the X-ray tube 21 when the X-ray tube voltage V is the second tube voltage V2, that is, the X-ray tube 21-2 (hereinafter referred to as “virtual”. Direction of the second X-ray beam ”. Further, the symbol IS indicates an isocenter. The virtual first X-ray beam XBi1 is an X-ray beam that is irradiated from the reference position B in the X-ray tube 21-1, passes through the isocenter IS, and is incident on the central portion in the channel direction of the X-ray detection unit 24-1. is there. Further, the virtual X-ray beam XBi2 is irradiated from the reference position B in the X-ray tube 21-2, passes through the isocenter IS, and enters the center of the X-ray detector 24-2 in the channel direction. It is a beam.

  In the X-ray detector 24-1, the first X-ray beam XB1 from the first X-ray focal point F1 is incident on the channel on which the virtual first X-ray beam XBi1 is incident. In the X-ray detection unit 24-2, the second X-ray beam XB2 from the second X-ray focal point F2 is incident on the channel on which the virtual second X-ray beam XBi2 is incident. In other words, the first X-ray beam XB1 is an X-ray beam irradiated from the first X-ray focal point F1 and incident on the channel where the virtual first X-ray beam XBi1 is incident in the X-ray detector 24-1. The second X-ray beam direction XB2 is an X-ray beam that is irradiated from the second X-ray focal point F2 and is incident on the channel on which the virtual second X-ray beam XBi2 is incident in the X-ray detector 24-2.

  In this modification, the first X-ray projection data and the second X-ray projection data corresponding to the first X-ray beam XB1 and the second X-ray beam XB2 in the same direction constitute projection data of the same view. Therefore, as in the above embodiment, since the first X-ray projection data p1 and the second X-ray projection data p2 exist for each of all views, a dual energy image DE is created without performing interpolation processing. be able to. In addition, according to this modification, the first X-ray beam XB1 and the second X-ray beam XB2 are slightly misaligned in the view direction, but compared with the conventional interpolation process, The degree of deterioration can be suppressed. According to this modification, since the direction of the beam XB1 of the first X-ray and the direction of the beam XB2 of the second X-ray are the same direction, data consistency in the view direction can be improved.

  The invention is not limited to the present embodiment, and various modifications can be made without departing from the spirit of the invention.

  A program for causing a computer to function as each means for performing control and processing in the X-ray CT apparatus is also an example of an embodiment of the invention.

DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 3 Central processing unit 21 X-ray tube 321 Switching control part 322 Focus control part F1 1st X-ray focus F2 2nd X-ray focus

Claims (12)

X which irradiates the subject with a first X-ray having a first energy spectrum and a second X-ray having a second energy spectrum different from the first energy spectrum while rotating around the body axis of the subject A wire tube,
A switching control unit that switches between the first X-ray and the second X-ray for each view;
Focus control for controlling the position of the first X-ray focal point where the first X-ray is irradiated in the X-ray tube and the position of the second X-ray focal point where the second X-ray is irradiated in the X-ray tube. A position of the first X-ray focal point in the view direction when the first X-ray is irradiated, and a position of the second X-ray focal point in the view direction when the second X-ray is irradiated. A focus control unit that arranges the first X-ray focus and the second X-ray focus at different positions in the view direction on the target electrode of the X-ray tube, so as to have an overlapping range,
An X-ray CT apparatus comprising: X which irradiates the subject with a first X-ray having a first energy spectrum and a second X-ray having a second energy spectrum different from the first energy spectrum while rotating around the body axis of the subject A wire tube,
A switching control unit that switches between the first X-ray and the second X-ray for each view;
Focus control for controlling the position of the first X-ray focal point where the first X-ray is irradiated in the X-ray tube and the position of the second X-ray focal point where the second X-ray is irradiated in the X-ray tube. The first X-ray focal point and the second X-ray focal point are placed on the target electrode of the X-ray tube so that the beam direction of the first X-ray and the beam direction of the second X-ray are the same direction. A focus control unit arranged at different positions in the view direction at
An X-ray CT apparatus comprising: The first X-ray is irradiated when the X-ray tube is at a first tube voltage, and the second X-ray is irradiated when the X-ray tube is at a second tube voltage different from the first tube voltage. And
The X-ray CT apparatus according to claim 1, wherein the switching control unit switches between a first tube voltage and a second tube voltage. The first X-ray focal point is a position moved in a positive view direction with respect to a reference position in the X-ray tube;
The second X-ray focal point is a position moved in a negative view direction that is opposite to the positive view direction with respect to a reference position in the X-ray tube. An X-ray CT apparatus according to claim 1. The first X-ray focal point is a position moved in a positive view direction with respect to a reference position in the X-ray tube;
The second X-ray focal point is a position moved in a negative view direction which is opposite to the positive view direction with respect to a reference position in the X-ray tube;
The distance between the reference position and the first X-ray focal point and the distance between the reference position and the second X-ray focal point are the length of the circumference around which the X-ray tube rotates, and the first X-ray and the second X-ray. The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is a half of a distance obtained by dividing by the number of times of switching. The first X-ray focal point is a position moved in a positive view direction with respect to a reference position in the X-ray tube;
The second X-ray focal point is a position moved in a negative view direction which is opposite to the positive view direction with respect to a reference position in the X-ray tube;
The distance between the reference position and the first X-ray focal point and the distance between the reference position and the second X-ray focal point are the length of the circumference around which the X-ray tube rotates, and the first X-ray and the second X-ray. The X-ray CT apparatus according to claim 2, wherein the distance is obtained by dividing by the number of times of switching.   The switching control unit switches the tube current of the X-ray tube from the first tube current when the first X-ray is irradiated, and then switches from the first X-ray to the second X-ray, and The first X-ray is switched from the second X-ray after being reduced from the second tube current when the second X-ray is irradiated. X-ray CT system.   The first projection data and the second projection data obtained by irradiating the first X-ray focus and the second X-ray focus from each of the first X-ray focus and the second X-ray focus having the overlapping range in the view direction are the same. The X-ray CT apparatus according to claim 1, wherein the projection projection data is configured. X which irradiates the subject with a first X-ray having a first energy spectrum and a second X-ray having a second energy spectrum different from the first energy spectrum while rotating around the body axis of the subject A wire tube,
A processor;
Characterized by comprising,
The processor is
A switching control function for switching the first X-ray and the second X-ray for each view;
Focus control for controlling the position of the first X-ray focal point where the first X-ray is irradiated in the X-ray tube and the position of the second X-ray focal point where the second X-ray is irradiated in the X-ray tube. A position of the first X-ray focal point in the view direction when the first X-ray is irradiated, and a position of the second X-ray focal point in the view direction when the second X-ray is irradiated. A focus control function for arranging the first X-ray focus and the second X-ray focus at different positions in the view direction on the target electrode of the X-ray tube,
Is executed by a program. X which irradiates the subject with a first X-ray having a first energy spectrum and a second X-ray having a second energy spectrum different from the first energy spectrum while rotating around the body axis of the subject A wire tube,
A processor;
Characterized by comprising,
The processor is
A switching control function for switching the first X-ray and the second X-ray for each view;
Focus control for controlling the position of the first X-ray focal point where the first X-ray is irradiated in the X-ray tube and the position of the second X-ray focal point where the second X-ray is irradiated in the X-ray tube. The first X-ray focal point and the second X-ray focal point are placed on the target electrode of the X-ray tube so that the beam direction of the first X-ray and the beam direction of the second X-ray are the same direction. Focus control function to be arranged at different positions in the view direction in
Is executed by a program. X which irradiates the subject with a first X-ray having a first energy spectrum and a second X-ray having a second energy spectrum different from the first energy spectrum while rotating around the body axis of the subject A wire tube,
A processor;
A control program for an X-ray CT apparatus comprising:
In the processor,
A switching control function for switching the first X-ray and the second X-ray for each view;
Focus control for controlling the position of the first X-ray focal point where the first X-ray is irradiated in the X-ray tube and the position of the second X-ray focal point where the second X-ray is irradiated in the X-ray tube. A position of the first X-ray focal point in the view direction when the first X-ray is irradiated, and a position of the second X-ray focal point in the view direction when the second X-ray is irradiated. A focus control function for arranging the first X-ray focus and the second X-ray focus at different positions in the view direction on the target electrode of the X-ray tube,
A control program for an X-ray CT apparatus, characterized in that X which irradiates the subject with a first X-ray having a first energy spectrum and a second X-ray having a second energy spectrum different from the first energy spectrum while rotating around the body axis of the subject A wire tube,
A processor;
A control program for an X-ray CT apparatus comprising:
In the processor,
A switching control function for switching the first X-ray and the second X-ray for each view;
Focus control for controlling the position of the first X-ray focal point where the first X-ray is irradiated in the X-ray tube and the position of the second X-ray focal point where the second X-ray is irradiated in the X-ray tube. The first X-ray focal point and the second X-ray focal point are placed on the target electrode of the X-ray tube so that the beam direction of the first X-ray and the beam direction of the second X-ray are the same direction. Focus control function to be arranged at different positions in the view direction in
A control program for an X-ray CT apparatus, characterized in that