JP5954770B2 - X-ray CT apparatus and control method of X-ray CT apparatus - Google Patents

Description

  Embodiments described herein relate generally to an X-ray CT apparatus and a method for controlling the X-ray CT apparatus.

  An X-ray CT (Computed Tomography) apparatus is an apparatus that scans a subject using X-rays and processes the collected data by a computer, thereby imaging the inside of the subject.

  Specifically, the X-ray CT apparatus irradiates the subject a plurality of times from different directions along a circular orbit centered on the subject. The X-ray CT apparatus collects a plurality of detection data by detecting X-rays transmitted through a subject with an X-ray detector. The collected detection data is A / D converted by the data collection unit and then transmitted to the console device. The console device pre-processes the detection data and creates projection data. Then, the console apparatus performs reconstruction processing based on the projection data, and creates volume data based on tomographic image data or a plurality of tomographic image data. Volume data is a data set representing a three-dimensional distribution of CT values corresponding to a three-dimensional region of a subject.

  The X-ray CT apparatus can perform MPR (Multi Planar Reconstruction) display by rendering the volume data in an arbitrary direction. Hereinafter, a cross-sectional image displayed in MPR by rendering volume data may be referred to as an “MPR image”. The MPR image includes, for example, an axial image showing a cross section orthogonal to the body axis, a sagittal image showing a cross section of the subject along the body axis, and a coronal image showing a cross section of the subject along the body axis. There is. Furthermore, an arbitrary cross-sectional image (oblique image) in the volume data is also included in the MPR image. The plurality of created MPR images can be simultaneously displayed on a display unit or the like.

  In addition, there is an imaging method called CT fluoroscopy (CTF) performed using an X-ray CT apparatus. CT fluoroscopy is an imaging method in which an image relating to a region of interest of a subject is obtained in real time by continuously irradiating the subject with X-rays. In CT fluoroscopy, images are created in real time by reducing the detection data collection rate and reducing the time required for reconstruction processing. CT fluoroscopy is used, for example, for confirming the positional relationship between the tip of a puncture needle and a part from which a specimen is collected during a biopsy, or for confirming the position of a tube when performing a drainage method. The drainage method is a method of draining body fluid accumulated in a body cavity with a tube or the like.

  On the other hand, as one of scanning methods using an X-ray CT apparatus, there is a method of performing X-ray exposure only in a predetermined section of a circular orbit centered on a subject. For example, in a method called half scan, X-ray exposure is performed only in a section of 180 degrees (+ fan angle) corresponding to half of the entire circular orbit. The half scan is effective in reducing the exposure dose as compared with the full scan (method of performing the X-ray exposure in the entire circular orbit (360 degrees)).

  Further, the distance between the position where X-rays are exposed (the position of the X-ray generation source) and the region of interest (for example, a lesion) in the subject is proportional to the image SD (Standard Deviation). It is known. That is, the image based on the detection data detected in a state where the position where the X-ray is exposed and the target site are close to each other is an image with a good image SD (an image with little influence of noise).

JP 2003-290214 A JP 2004-208799 A

  Here, in the case of the half scan, depending on the section in which the X-ray scan is performed, the X-ray scan is performed in a state where the distance between the position where the X-ray is exposed and the target region is long. In this case, the image SD in the image of the attention site is deteriorated. Therefore, since the image is an image that is greatly affected by noise, there is a high possibility that the observation of the attention site will be hindered. In addition, when only an image having a large influence of noise (an image having a bad image SD) can be obtained, there is a high possibility that another X-ray scan is necessary. As a result, the exposure dose is not reduced despite the use of half scan.

  Embodiments have been made to solve the above-described problems, and provide a technique capable of reducing an exposure dose and obtaining an image with a good image SD (an image with less influence of noise). With the goal.

In order to solve the above-described problem, the X-ray CT apparatus according to the first embodiment includes an X-ray generation unit rotatably provided along a circular orbit centered on a subject, and the X-ray generation unit An X-ray CT apparatus that scans the subject by exposing the subject to X-rays to obtain detection data, reconstructs projection data based on the detection data, and A reconstruction processing unit that creates data, a specifying unit that specifies a position of a site of interest in the subject based on the volume data, and a position of the site of interest and any position on the circular orbit The calculation unit for obtaining the position on the circular orbit when the ellipse is the shortest, and the X-ray is exposed to only a part of the circular orbit including the obtained position on the circular orbit. Scan control unit for controlling the X-ray generation unit It has a.
In addition, the second embodiment has an X-ray generator that is rotatably provided along a circular orbit centered on the subject, and the subject is exposed to X-rays from the X-ray generator. An X-ray CT apparatus that scans the subject by X-rays to acquire detection data, reconstructs projection data based on the detection data, and creates volume data; and Based on the volume data, the specifying unit for specifying the position of the region of interest in the subject, and the center of the circular orbit and the point on the circular orbit in one coordinate system including the volume data and the circular orbit An extraction unit for obtaining a shorter section on the circular orbit formed by two intersecting points at which two lines intersecting the circular orbit intersect with the target region, and a section obtained by the extraction unit Some sections on the circular orbit including Having a scan control unit for controlling the X-ray generating unit to the irradiation of X-rays in.

1 is a block diagram of an X-ray CT apparatus according to a first embodiment. It is a figure which supplements description of the specific | specification part which concerns on 1st Embodiment, a calculation part, and a scan control part. It is a figure which supplements description of the specific | specification part which concerns on 1st Embodiment, a calculation part, and a scan control part. It is a figure which supplements description of the specific | specification part which concerns on 1st Embodiment, a calculation part, and a scan control part. It is a figure which supplements description of the specific | specification part which concerns on 1st Embodiment, a calculation part, and a scan control part. It is a flowchart which shows the outline | summary of operation | movement of the X-ray CT apparatus which concerns on 1st Embodiment. It is a block diagram of the X-ray CT apparatus which concerns on 2nd Embodiment. It is a figure which supplements description of the specific part which concerns on 2nd Embodiment, a coordinate transformation part, an extraction part, and a scanning control part. It is a figure which supplements description of the specific part which concerns on 2nd Embodiment, a coordinate transformation part, an extraction part, and a scanning control part. It is a figure which supplements description of the specific part which concerns on 2nd Embodiment, a coordinate transformation part, an extraction part, and a scanning control part. It is a figure which supplements description of the specific part which concerns on 2nd Embodiment, a coordinate transformation part, an extraction part, and a scanning control part. It is a flowchart which shows the outline | summary of operation | movement of the X-ray CT apparatus which concerns on 2nd Embodiment.

(First embodiment)
The configuration of the X-ray CT apparatus 1 according to the first embodiment will be described with reference to FIGS. 1 to 3. Since “image” and “image data” have a one-to-one correspondence, in the present embodiment, they may be regarded as the same. In the present embodiment, the “X-ray dose” and the “(X-ray) exposure dose” may be regarded as the same.

<Device configuration>
As shown in FIG. 1, the X-ray CT apparatus 1 includes a gantry device 10, a bed device 30, and a console device 40.

[Mounting device]
The gantry device 10 is an apparatus that irradiates the subject E with X-rays and collects detection data of the X-rays transmitted through the subject E. The gantry device 10 includes an X-ray generator 11, an X-ray detector 12, a rotating body 13, a high voltage generator 14, a gantry driver 15, an X-ray diaphragm 16, a diaphragm driver 17, And a data collection unit 18.

  The X-ray generator 11 includes an X-ray tube that generates X-rays (for example, a vacuum tube that generates a cone-shaped or pyramid-shaped X-ray beam, not shown). The X-ray generator 11 exposes the generated X-rays to the subject E.

  The X-ray detection unit 12 includes a plurality of X-ray detection elements (not shown). The X-ray detection unit 12 detects X-rays that have passed through the subject E. Specifically, the X-ray detection unit 12 detects X-ray intensity distribution data (hereinafter sometimes referred to as “detection data”) indicating the intensity distribution of X-rays transmitted through the subject E with an X-ray detection element. The detection data is output as a current signal. As the X-ray detection unit 12, for example, a two-dimensional X-ray detector (plane detector) in which a plurality of detection elements are arranged in two directions (slice direction and channel direction) orthogonal to each other is used. The plurality of X-ray detection elements are provided, for example, in 320 rows along the slice direction. By using a multi-row X-ray detector in this way, it is possible to image a three-dimensional imaging region having a width in the slice direction by one rotation scan (volume scan). The slice direction corresponds to the body axis direction of the subject E, and the channel direction corresponds to the rotation direction of the X-ray generation unit 11.

  The rotating body 13 is a member that supports the X-ray generation unit 11 and the X-ray detection unit 12 so as to face each other with the subject E interposed therebetween. The rotating body 13 has an opening 13a penetrating in the slice direction. In the gantry device 10, the rotating body 13 is arranged so as to rotate in a circular orbit around the subject E. That is, the X-ray generation unit 11 and the X-ray detection unit 12 are provided so as to be rotatable along a circular orbit centered on the subject E.

  The high voltage generator 14 applies a high voltage to the X-ray generator 11 (hereinafter, “voltage” means the voltage between the anode and the cathode in the X-ray tube). The X-ray generator 11 generates X-rays based on the high voltage. The high voltage generator 14 can change the value of the applied high voltage based on the control of the scan controller 44 (described later). Along with the change of the applied high voltage, the X-ray dose (X-ray exposure amount) that the X-ray generation unit 11 exposes to the subject E is also changed.

  The gantry driving unit 15 drives the rotating body 13 to rotate. The X-ray diaphragm section 16 has a slit (opening) having a predetermined width, and by changing the width of the slit, the fan angle (expansion angle in the channel direction) of X-rays exposed from the X-ray generation section 11 and X Adjust the cone angle of the line (the spread angle in the slice direction). The diaphragm drive unit 17 drives the X-ray diaphragm unit 16 so that the X-rays generated by the X-ray generation unit 11 have a predetermined shape.

  A data collection unit 18 (DAS: Data Acquisition System) collects detection data from the X-ray detection unit 12 (each X-ray detection element). The data collection unit 18 converts the collected detection data (current signal) into a voltage signal, periodically integrates and amplifies the voltage signal, and converts the voltage signal into a digital signal. Then, the data collecting unit 18 transmits the detection data converted into the digital signal to the console device 40. In addition, when performing CT fluoroscopy, the data collection part 18 shortens the collection rate of detection data.

[Bed equipment]
The couch device 30 is a device for placing and moving the subject E to be imaged. The couch device 30 includes a couch 31 and a couch driving unit 32. The couch 31 includes a couch top 33 for placing the subject E and a base 34 that supports the couch top 33. The couch top 33 can be moved by the couch driving unit 32 in the body axis direction of the subject E and in the direction perpendicular to the body axis direction. That is, the bed driving unit 32 can insert and remove the bed top plate 33 on which the subject E is placed with respect to the opening 13 a of the rotating body 13. The base 34 can move the bed top 33 in the vertical direction (a direction perpendicular to the body axis direction of the subject E) by the bed driving unit 32.

[Console device]
The console device 40 is used for operation input to the X-ray CT apparatus 1. The console device 40 has a function of reconstructing CT image data (tomographic image data and volume data) representing the internal form of the subject E from the detection data collected by the gantry device 10. The console device 40 includes a processing unit 41, a specifying unit 42, a calculating unit 43, a scan control unit 44, a display control unit 45, a storage unit 46, a display unit 47, an input unit 48, and a control unit 49. It is comprised including.

  The processing unit 41 executes various processes on the detection data transmitted from the gantry device 10 (data collection unit 18). The processing unit 41 includes a preprocessing unit 41a, a reconstruction processing unit 41b, and a rendering processing unit 41c.

  The pre-processing unit 41a performs pre-processing such as logarithmic conversion processing, offset correction, sensitivity correction, and beam hardening correction on detection data detected by the gantry device 10 (X-ray detection unit 12) to create projection data. To do.

  The reconstruction processing unit 41b creates CT image data (tomographic image data and volume data) based on the projection data created by the preprocessing unit 41a. For reconstruction of tomographic image data, any method such as a two-dimensional Fourier transform method, a convolution / back projection method, or the like can be employed. Volume data is created by interpolating a plurality of reconstructed tomographic image data. For the reconstruction of volume data, for example, an arbitrary method such as a cone beam reconstruction method, a multi-slice reconstruction method, an enlargement reconstruction method, or the like can be adopted. As described above, a wide range of volume data can be reconstructed by volume scanning using a multi-row X-ray detector. Further, when performing CT fluoroscopy, since the collection rate of the detection data is shortened, the reconstruction time by the reconstruction processing unit 41b is shortened. Therefore, real-time CT image data corresponding to scanning can be created.

  The rendering processor 41c performs a rendering process on the volume data created by the reconstruction processor 41b. For example, the rendering processing unit 41c performs MPR display by rendering the volume data created by the reconstruction processing unit 41b in an arbitrary direction (that is, the rendering processing unit 41c creates an MPR image).

  The specifying unit 42 specifies the position of the site of interest in the subject E based on the volume data created by the reconstruction processing unit 41b. The “target region” is a specific region (including the narrowest form of the region) in the subject E such as a lesioned part or the tip of a puncture needle inserted into the subject E. As a specific example, a case where the position of a lesioned part S (target region) is specified from volume data will be described. The specifying unit 42 compares the CT value of each voxel constituting the volume data with a preset threshold value. The threshold value is a value determined corresponding to the lesioned part S (for example, the CT value of the lesioned part), and is a value for determining whether or not the target site is included in the voxel. Then, the specifying unit 42 specifies the coordinate value of the voxel larger (or smaller) than the threshold as the position of the lesioned part S.

  Note that the site of interest need not be identified directly from the volume data. For example, the specifying unit 42 can also specify the coordinate value of the lesioned part S by the region growing method or the like in the MPR image data created based on the volume data.

  Alternatively, it is possible to specify the position of the site of interest based on the tomographic image data constituting the volume data. For example, the specifying unit 42 takes the difference between the tomographic image data and specifies tomographic image data having a large difference. The specifying unit 42 can also perform image processing such as edge detection on the specified tomographic image data to specify the coordinate value of the lesioned part S in the tomographic image data.

  In the calculation unit 43, the X-ray generation unit 11 is most suitable for the position (coordinate value) of the site of interest (lesion site S or the like) on the image data (CT image data, MPR image data, etc.) specified by the specification unit 42. The close proximity position is calculated. When the site of interest has a two-dimensional or three-dimensional range, the “position of the site of interest” may be one point on the outer periphery of the site of interest or the center of gravity of the site of interest . The “proximity position” is a position (coordinate value) on the circular orbit where the X-ray generation unit 11 is closest to the target region.

  The calculation unit 43 in the present embodiment includes a coordinate conversion unit 43a and a distance calculation unit 43b.

  The coordinate conversion unit 43a converts the position (coordinate value) of the site of interest (lesioned portion S or the like) specified by the specifying unit 42 into a coordinate system of a circular orbit. The “circular orbit coordinate system” is a trajectory drawn by the X-ray generator 11 that is rotated by the rotating body 13. That is, the coordinate system of the circular orbit means a coordinate system of the rotating body 13 (the gantry device 10). The distance calculation unit 43b calculates the distance to the circular orbit from the position of the target region subjected to coordinate conversion. The calculation unit 43 calculates the position of the circular orbit at the shortest distance among the distances calculated by the distance calculation unit 43b as the proximity position.

  A specific example of processing of the specifying unit 42 and the calculation unit 43 (the coordinate conversion unit 43a and the distance calculation unit 43b) will be described with reference to FIGS. 2A to 2C. 2A to 2C are cross-sectional views of the subject E and the rotating body 13 (X-ray generation unit 11). Here, it is assumed that the rotating body 13 (the gantry device 10) and the subject E have different coordinate systems (the coordinate system of the rotating body 13: XYZ, the coordinate system of the subject E: xyz). The X direction indicates the lateral direction of the rotating body 13. The Y direction indicates the vertical direction of the rotating body 13. The x direction indicates the lateral direction (coronal direction) of the subject E. The y direction indicates the vertical direction (sagittal direction) of the subject E. In the following description, the position in the Z (z) direction (the body axis direction of the subject E) is not considered, but the region of interest including the position in the Z (z) direction is specified, coordinate conversion, etc. It is also possible to do this.

First, the specifying unit 42 specifies the coordinate values (x ₀ , y ₀ ) of the lesioned part S (see FIG. 2A). Here, it is assumed that the position of the center of gravity of the lesioned part S is specified as a coordinate value.

The coordinate conversion unit 43a converts the coordinate value (x ₀ , y ₀ ) in the coordinate system of the rotating body 13 to obtain the coordinate value (X ₀ , Y ₀ ) (see FIG. 2B). A known method can be used for coordinate conversion (movement, rotation, etc.).

The distance calculation unit 43b calculates a distance r _k (k = 1 to n) between the coordinate value (X ₀ , Y ₀ ) and the circular orbit C along which the X-ray generation unit 11 moves. Specifically, the distance calculation unit 43b connects a plurality of points P _k (k = 1 to n) assumed on the circular orbit C and coordinate values (X ₀ , Y ₀ ), and a plurality of distances r. _k is calculated (see FIG. 2B). In Figure 2B, it indicates the distance between the X-ray generation unit 11 and the lesion S at a point P _n in r _n.

Calculating section 43, among the calculated distance _{r k,} the shortest position of the distance _{r S (1 ≦ s ≦ n} ) X -ray generator 11 in the (point _{P s} on the circular orbit C), X-ray generation unit 11 is calculated as the proximity position N closest to the lesioned part S (see FIG. 2C).

  The scan control unit 44 controls various operations related to the X-ray scan. For example, the scan control unit 44 controls the high voltage generation unit 14 to apply a high voltage to the X-ray generation unit 11. The scan control unit 44 controls the gantry driving unit 15 so as to rotationally drive the rotating body 13. The scan control unit 44 controls the aperture driving unit 17 to operate the X-ray aperture unit 16. The scan control unit 44 controls the bed driving unit 32 to move the bed 31.

  In addition, the scan control unit 44 in the present embodiment exposes the X-ray generation unit 11 via the high voltage generation unit 14 so that only a part of the circular orbit C including the proximity position N is exposed to X-rays. To control. That is, the “X-ray generator” is a concept including the high voltage generator 14.

  Furthermore, the scan control unit 44 in the present embodiment is configured to include a setting unit 44a. The setting unit 44a sets a partial section c of the circular orbit C so that the proximity position N becomes the intermediate position H.

  As a specific example, the setting unit 44a sets the intermediate position H as the proximity position N based on a preset half-scan range (180 degrees + fan angle; hereinafter, the fan angle will be omitted). . FIG. 2D is a cross-sectional view of the subject E and the rotating body 13 (X-ray generation unit 11). When the half scan is performed in a range of 180 degrees, as shown in FIG. 2D, a range of ± 90 degrees from the proximity position N is set as a partial section c. The scan control unit 44 controls the X-ray generation unit 11 (high voltage generation unit 14) so as to emit X-rays only in a set partial section c.

  The display control unit 45 performs various controls related to image display. For example, control is performed to display the MPR image (axial image, sagittal image, coronal image, oblique image) or the like created by the rendering processing unit 41c on the display unit 47. When the display control unit 45 displays a plurality of MPR images, for example, it becomes easier to grasp the puncture state (angle, directionality) of the puncture needle and the positional relationship between the puncture needle and the target of interest.

  The storage unit 46 is configured by a semiconductor storage device such as a RAM or a ROM. The storage unit 46 stores detection data, projection data, or CT image data after reconstruction processing.

  The display unit 47 includes an arbitrary display device such as an LCD (Liquid Crystal Display) or a CRT (Cathode Ray Tube) display. For example, the display unit 47 displays an MPR image obtained by rendering volume data.

  The input unit 48 is used as an input device that performs various operations on the console device 40. The input unit 48 is composed of, for example, a keyboard, a mouse, a trackball, a joystick and the like. As the input unit 48, a GUI (Graphical User Interface) displayed on the display unit 47 can be used.

  The control unit 49 performs overall control of the X-ray CT apparatus 1 by controlling operations of the gantry device 10, the couch device 30, and the console device 40. For example, the control unit 49 controls the scan control unit 44 to cause the gantry device 10 to perform a preliminary scan and a main scan and collect detection data. In addition, the control unit 49 controls the processing unit 41 to perform various processing (preprocessing, reconstruction processing, MPR processing, etc.) on the detected data. Alternatively, the control unit 49 controls the display control unit 45 to display the CT image on the display unit 47 based on the image data stored in the storage unit 46.

<Operation>
Next, the operation of the X-ray CT apparatus 1 according to the present embodiment will be described with reference to FIG. Here, a case will be described in which half scanning (180 degrees + fan angle) is performed after the proximity position N is obtained by performing X-ray scanning.

  First, the X-ray CT apparatus 1 performs an X-ray scan on the subject E to create volume data.

  Specifically, the X-ray generation unit 11 emits X-rays to the subject E. The X-ray detection unit 12 detects X-rays that have passed through the subject E (S10). Detection data based on the X-rays detected by the X-ray detection unit 12 is collected by the data collection unit 18 and sent to the processing unit 41 (pre-processing unit 41a).

  The preprocessing unit 41a performs preprocessing such as logarithmic conversion processing on the detection data acquired in S10, and creates projection data (S11). The created projection data is sent to the reconstruction processing unit 41b based on the control of the control unit 49.

  The reconstruction processing unit 41b creates a plurality of tomographic image data based on the projection data created in S11. The reconstruction processing unit 41b creates volume data by performing interpolation processing on a plurality of tomographic image data (S12).

  The specifying unit 42 specifies the position of the lesioned part S in the subject E based on the volume data created in S12 (S13).

  The coordinate conversion unit 43a converts the position (coordinate value) of the lesioned part S specified in S13 into the coordinate system of the circular orbit C (S14).

  The distance calculation unit 43b calculates the distance to the circular orbit C from the position of the lesioned part S coordinate-converted in S14 (S15).

  The calculating unit 43 calculates the position of the circular orbit C at the shortest distance among the distances calculated in S15 as the proximity position N (S16).

  Through the processing from S10 to S16, the position (proximity position N) where the image SD of the CT image obtained by the X-ray scan is the best can be obtained. The processing from S10 to S16 is an example of the “first mode” in the present embodiment.

  Next, the setting unit 44a sets a part of the section c so that the proximity position N calculated in S16 becomes the intermediate position H (S17). Specifically, the setting unit 44a sets a range of ± 90 degrees from the proximity position N as a partial section c.

  The scan control unit 44 controls the X-ray generation unit 11 (high voltage generation unit 14) to emit X-rays only in a set partial section c (S18). That is, the scan control unit 44 starts the operation of S18 (S17) after the first mode is completed.

  With the processing of S17 and S18, half scanning can be performed around the position where the image SD is the best (proximity position N). The processing of S17 and S18 is an example of the “second mode” in the present embodiment.

  As described above, the X-ray scan in the first mode can be said to be a scan for determining the range in which the second mode is performed (X-ray scan range in which a good image of the image SD can be obtained). On the other hand, the X-ray scan in the second mode can be said to be a scan for obtaining a CT image (an image having a good image SD) by reducing the exposure dose. That is, the first mode and the second mode can obtain an image with a good image SD while reducing the exposure dose.

  The processing unit 41, the specifying unit 42, the calculating unit 43, the scan control unit 44, the display control unit 45, and the control unit 49 are, for example, a CPU (Central Processing Unit), a GPU (Graphic Processing Unit), or an ASIC (Application Specific). A processing device (not shown) such as an integrated circuit (ROM) and a storage device (not shown) such as a ROM (Read Only Memory), a RAM (Random Access Memory), or an HDD (Hard Disc Drive) may be used. The storage device stores a processing program for executing the function of the processing unit 41. The storage device stores a specific unit processing program for executing the function of the specific unit 42. The storage device stores a calculation unit processing program for executing the function of the calculation unit 43. Further, the storage device stores a scan control program for executing the function of the scan control unit 44. The storage device stores a display control program for executing the function of the display control unit 45. The storage device stores a control program for executing the function of the control unit 49. A processing device such as a CPU executes the functions of each unit by executing each program stored in the storage device.

<Action and effect>
The operation and effect of this embodiment will be described.

  The X-ray CT apparatus 1 according to the present embodiment includes an X-ray generation unit 11 that is rotatably provided along a circular orbit C centered on the subject E, and the X-ray generation unit 11 applies to the subject E. Then, X-ray scanning is performed on the subject E by exposing X-rays, and detection data is acquired. The X-ray CT apparatus 1 includes a reconstruction processing unit 41b, a specifying unit 42, and a scan control unit 44. The reconstruction processing unit 41b reconstructs projection data based on the detection data and creates volume data. The specifying unit 42 specifies the position of the site of interest in the subject E (lesioned part S) based on the volume data. The scan control unit 44 emits X-rays only in a partial section c including the proximity position N where the X-ray generation unit 11 is closest to the identified region of interest (lesioned portion S) in the circular orbit C. The X-ray generator 11 is controlled to do so.

  In addition, the X-ray CT apparatus 1 of the present embodiment has a calculation unit 43. The calculation unit 43 calculates the proximity position N at which the X-ray generation unit 11 is closest to the identified site of interest (lesion site S).

  As described above, the calculation unit 43 calculates the proximity position N at which the X-ray generation unit 11 is closest to the target site based on the position of the target site specified by the specifying unit 42. The scan control unit 44 controls the X-ray generation unit 11 so that only a part of the circular orbit C including the proximity position N is exposed to X-rays. The position to which the X-ray is exposed (the position of the X-ray generation unit 11) and the distance to the site of interest in the subject E are proportional to the image SD. Therefore, the image based on the detection data detected at the proximity position N is the image with the best image SD (the image with the least influence of noise). Further, in the circular orbit C, the X-ray is exposed only in a part of the section c including the proximity position N, so that the X-ray is exposed over the entire circumference of the circular orbit C. The exposure amount of the specimen E can be reduced. That is, according to the X-ray CT apparatus 1 of the present embodiment, it is possible to reduce the exposure dose and obtain an image with a good image SD (an image with a small influence of noise). For example, in biopsy using CT fluoroscopy, since the same part of the subject E is repeatedly exposed to X-rays, there is a problem that the exposure dose as a whole increases. In such a case, the X-ray CT apparatus 1 in this embodiment is effective.

Specifically, the calculation unit 43 includes a coordinate conversion unit 43a and a distance calculation unit 43b. The coordinate conversion unit 43a converts the position of the identified attention site (lesion portion S) into the coordinate system of the circular orbit C. Distance calculating unit 43b from the position of the coordinate transformed attention site (lesion S), and calculates the distance r _k to the circular orbit C. Calculating section 43, among the calculated distance r _k, it calculates the position of the circular orbit C in the shortest distance r _S as a proximity position N. The scan control unit 44 includes a setting unit 44a. The setting unit 44a sets a part of the section c so that the intermediate position H of the part of the section c becomes the proximity position N. The scan control unit 44 controls the X-ray generation unit 11 so as to emit X-rays only in a set partial section.

Thus, the calculation unit 43, of the distance r _k to the circular orbit C from the position of the target sites are coordinate transformation, to calculate the position of the circular orbit C in the shortest distance r _S as a proximity position N. The setting unit 44a sets a part of the section c so that the intermediate position H of the part of the section c becomes the proximity position N. Then, the scan control unit 44 controls the X-ray generation unit 11 so as to emit X-rays only in a set partial section. By setting the X-ray scan range (partial section c) with the proximity position N as the center, the X-ray is mainly used for the range where the image SD is improved (the range where the target region and the X-ray generation unit 11 are close). Can be exposed. That is, according to the X-ray CT apparatus 1 of the present embodiment, it is possible to reduce the exposure dose and obtain an image with a good image SD (an image with a small influence of noise).

  In addition, the configuration of the present embodiment can be realized as a control method for the X-ray CT apparatus 1. In the control method of the X-ray CT apparatus 1, the scan control unit 44 causes the X-ray CT apparatus 1 having the first mode and the second mode to start the second mode after the first mode is completed. In the first mode, the subject E is exposed to X-rays by exposing the subject E to X-rays from an X-ray generator 11 that is rotatably provided along a circular orbit C centered on the subject E. Scanning and obtaining detection data. The first mode includes a step in which the reconstruction processing unit 41b reconstructs projection data based on detection data and creates volume data. The first mode includes a step in which the specifying unit 42 specifies the position of the site of interest in the subject E based on the volume data. The first mode includes a step in which the calculation unit 43 calculates the proximity position N at which the X-ray generation unit 11 is closest to the identified site of interest. In the second mode, the scan control unit 44 controls the X-ray generation unit 11 so that only a part of the circular orbit C including the proximity position N calculated in the first mode is exposed to X-rays. .

  As described above, the scan control unit 44 starts the second mode after the first mode in which the proximity position N is calculated. Therefore, X-rays can be exposed only in a partial section c including the proximity position N where the image SD is the best. That is, even with the control method of the X-ray CT apparatus 1 of the present embodiment, it is possible to reduce the exposure dose and obtain an image with a good image SD (an image with little influence of noise).

(Modification of the first embodiment)
In the first embodiment, the example in which the coordinate conversion unit 43a converts the position of the target region into the coordinate system of the circular orbit C in the proximity position calculation process has been described. On the other hand, the method for calculating the proximity position is not limited to this.

In general, the rotation center position of the rotator 13 and the position (point P _k ) in the circular orbit C of the X-ray generation unit 11 with respect to the rotation center position are predetermined for each gantry device 10. Therefore, the reconstruction processing unit 41b can set a coordinate system in advance based on the information about the rotation center position and the position of the X-ray generation unit 11 in the circular orbit C, and can also create volume data using the coordinate system. As described above, the reconstruction processing unit 41b creates volume data based on the coordinate system of the rotating body 13, thereby eliminating the need to convert the circular orbit C into the coordinate system. That is, a configuration without the coordinate conversion unit 43a is also possible.

(Second Embodiment)
The configuration of the X-ray CT apparatus 1 according to the second embodiment will be described with reference to FIGS. In the present embodiment, a configuration in which a part of the section c is determined without directly calculating the proximity position N will be described. Detailed description of the same configuration as that of the first embodiment will be omitted.

[Console device]
FIG. 4 is a block diagram showing a configuration of the console device 40 in the present embodiment. The console device 40 includes a processing unit 41, a specifying unit 42, a scan control unit 44, a display control unit 45, a storage unit 46, a display unit 47, an input unit 48, a control unit 49, and an extraction unit 50. It is comprised including.

  The extraction unit 50 extracts a section including the proximity position N in which the X-ray generation unit 11 is closest to the position of the site of interest (lesioned portion S or the like) specified by the specifying unit 42 from the circular orbit C. The extraction unit 50 includes a coordinate conversion unit 50a. Since the function of the coordinate conversion unit 50a is the same as that of the coordinate conversion unit 43a in the first embodiment, detailed description thereof is omitted.

  A specific example of the processing of the specifying unit 42 and the extracting unit 50 will be described with reference to FIGS. 5A to 5D. 5A to 5D are cross-sectional views of the subject E and the rotating body 13 (X-ray generation unit 11), similarly to FIGS. 2A to 2D. Similarly to the first embodiment, the Z (z) direction is not considered in the following description.

  First, the specifying unit 42 specifies the position of the lesioned part S (see FIG. 5A). Here, it is assumed that the lesioned part S has an area in a certain range. The coordinate conversion unit 50a converts the region of the lesioned part S in the coordinate system of the rotator 13 and obtains the position of the lesioned part S (hereinafter referred to as “S ′”) in the coordinate system of the rotator 13 (see FIG. 5B). ).

The extraction unit 50 draws _two tangents T ₁ and T ₂ from the center M of the circular orbit C to the position S ′, and points t ₁ and t _{2 at} which the tangents T ₁ and T ₂ and the circular orbit C intersect. A section c ′ is extracted (see FIG. 5C). Here, the proximity position N is a position on the circular orbit C where the X-ray generation unit 11 is closest to the lesioned part S. Accordingly, any position in the section c ′ becomes the proximity position N. That is, the section c ′ includes the proximity position N.

  The scan control unit 44 in the present embodiment controls the X-ray generation unit 11 so that only a part of the circular orbit C including the extracted section c ′ is exposed to X-rays (see FIG. 5D). .

<Operation>
Next, the operation of the X-ray CT apparatus 1 according to the present embodiment will be described with reference to FIG. Here, a case will be described in which half scanning (180 degrees + fan angle) is performed after the proximity position N is obtained by performing X-ray scanning.

  First, the X-ray CT apparatus 1 performs an X-ray scan on the subject E to create volume data.

  Specifically, the X-ray generation unit 11 emits X-rays to the subject E. The X-ray detection unit 12 detects X-rays transmitted through the subject E (S20). The preprocessing unit 41a performs preprocessing such as logarithmic conversion processing on the detection data acquired in S20, and creates projection data (S21). The reconstruction processing unit 41b creates a plurality of tomographic image data based on the projection data created in S21. Further, the reconstruction processing unit 41b creates volume data by performing interpolation processing on a plurality of tomographic image data (S22). The specifying unit 42 specifies the position of the lesioned part S in the subject E based on the volume data created in S22 (S23). The coordinate conversion unit 50a converts the position of the lesioned part S specified in S23 into the coordinate system of the circular orbit C (S24). As a result, the position (S ′) of the lesioned part S in the coordinate system of the circular orbit C can be obtained.

The extraction unit 50 draws _two tangents T ₁ and T ₂ from the center M of the circular orbit C to the position S ′ coordinate-transformed in S24, and the tangents T ₁ and T ₂ intersect with the circular orbit C. extracting the section c'between t ₁ and _{t 2} (S25).

  By the processing from S20 to S25, the section c ′ including the position (proximity position N) where the image SD of the CT image obtained by the X-ray scan is best can be obtained. The processing from S20 to S25 is an example of the “first mode” in the present embodiment.

  The scan control unit 44 includes the X-ray generation unit 11 (high voltage generation unit) so as to emit X-rays only in a part of the circular orbit C including the extracted section c ′ (180 degrees + fan angle). 14) is controlled (S26). That is, the scan control unit 44 starts the operation of S26 after the first mode is completed.

  By the process of S26, half scan can be performed in the section c including the position where the image SD is the best (proximity position N). The process of S26 is an example of the “second mode” in the present embodiment.

  The extraction unit 50 may be configured by a processing device (not shown) such as a CPU, GPU, or ASIC, and a storage device (not shown) such as a ROM, RAM, or HDD, for example. The storage device stores an extraction processing program for executing the function of the extraction unit 50. A processing device such as a CPU executes the functions of each unit by executing each program stored in the storage device.

<Action and effect>
The operation and effect of this embodiment will be described.

  The X-ray CT apparatus 1 according to the present embodiment includes an extraction unit 50. The extraction unit 50 extracts a section c ′ including the proximity position N closest to the X-ray generation unit 11 with respect to the position of the identified site of interest in the circular orbit C. The scan control unit 44 controls the X-ray generation unit 11 so that only a part of the circular orbit C including the extracted section c ′ is exposed to X-rays.

  Specifically, the extraction unit 50 includes a coordinate conversion unit 50a. The coordinate conversion unit 50a converts the position of the identified part of interest into the coordinate system of the circular orbit C. The extraction unit 50 extracts a section c ′ including the proximity position N that is closest to the X-ray generation unit 11 with respect to the position of the target region that has undergone coordinate conversion.

  The section c ′ extracted by the extraction unit 50 includes the proximity position N. The scan control unit 44 controls the X-ray generation unit 11 to emit X-rays only in a part of the section c including the extracted section c ′. As described above, the image based on the detection data detected at the proximity position N is the image with the best image SD (the image with the least influence of noise). Therefore, by performing an X-ray scan in a section including the proximity position N, an image with a good image SD can be obtained. Further, in the circular orbit C, the X-ray is exposed only in a part of the section c including the section c ′, so that the X-ray is exposed over the entire circumference of the circular orbit C. The exposure amount of the specimen E can be reduced. That is, according to the X-ray CT apparatus 1 of the present embodiment, it is possible to reduce the exposure dose and obtain an image with a good image SD (an image with a small influence of noise).

  In addition, the configuration of the present embodiment can be realized as a control method for the X-ray CT apparatus 1. In the control method of the X-ray CT apparatus 1, the scan control unit 44 causes the X-ray CT apparatus 1 having the first mode and the second mode to start the second mode after the first mode is completed. In the first mode, the subject E is exposed to X-rays by exposing the subject E to X-rays from an X-ray generator 11 that is rotatably provided along a circular orbit C centered on the subject E. Scanning and obtaining detection data. The first mode includes a step in which the reconstruction processing unit 41b reconstructs projection data based on detection data and creates volume data. The first mode includes a step in which the specifying unit 42 specifies the position of the site of interest in the subject E based on the volume data. In the first mode, the extraction unit 50 includes a step of extracting a section c ′ including the proximity position N in which the X-ray generation unit 11 is closest to the position of the identified site of interest in the circular orbit C. In the second mode, the scan control unit 44 controls the X-ray generation unit 11 so that only a part of the section c including the section c ′ extracted in the first mode is exposed.

  As described above, the scan control unit 44 starts the second mode after the first mode in which the proximity position N is calculated. Therefore, X-rays can be exposed only in a partial section c including the proximity position N where the image SD is the best. That is, even with the control method of the X-ray CT apparatus 1 of the present embodiment, it is possible to reduce the exposure dose and obtain an image with a good image SD (an image with little influence of noise).

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 10 Base apparatus 11 X-ray generation part 12 X-ray detection part 13 Rotating body 14 High voltage generation part 15 Base drive part 16 X-ray aperture part 17 Aperture drive part 18 Data collection part 30 Bed apparatus 32 Sleeper drive part 33 bed table 34 base 40 console device 41 processing unit 41a preprocessing unit 41b reconstruction processing unit 41c rendering processing unit 42 specifying unit 43 calculation unit 43a coordinate conversion unit 43b distance calculation unit 44 scan control unit 44a setting unit 45 display control Unit 46 storage unit 47 display unit 48 input unit 49 control unit E subject S lesion part

Claims (7)

An X-ray generation unit rotatably provided along a circular orbit centered on the subject, and exposing the subject to X by irradiating the subject with X-rays from the X-ray generation unit; An X-ray CT apparatus that scans a line and obtains detection data,
Reconstructing projection data based on the detection data and creating volume data;
Based on the volume data, a specifying unit that specifies the position of the site of interest in the subject;
A calculation unit for obtaining a position on the circular orbit when a line connecting the position of the target region and any position on the circular orbit is the shortest;
A scan control unit for controlling the X-ray generation unit to emit X-rays only in a part of the circular orbit including a position on the obtained circular orbit;
An X-ray CT apparatus comprising: The scan control unit
The X-ray CT apparatus according to claim 1, further comprising a setting unit that sets the partial section so that a position on the circular orbit obtained by the calculation unit is an intermediate position . An X-ray generation unit rotatably provided along a circular orbit centered on the subject, and exposing the subject to X by irradiating the subject with X-rays from the X-ray generation unit; An X-ray CT apparatus that scans a line and obtains detection data,
Reconstructing projection data based on the detection data and creating volume data;
Based on the volume data, a specifying unit that specifies the position of the site of interest in the subject;
In one coordinate system including the volume data and the circular orbit, a line connecting the center of the circular orbit and a point on the circular orbit, and the two lines including the region of interest intersect the circular orbit. An extraction unit for obtaining a shorter section on the circular orbit formed by two intersections;
A scan control unit that controls the X-ray generation unit to emit X-rays in a partial section on the circular orbit including the section obtained by the extraction unit;
An X-ray CT apparatus comprising: The extraction unit is a line connecting a center of the circular orbit and a point on the circular orbit in one coordinate system including the volume data and the circular orbit, and the attention site is sandwiched between the attention portions. Find two tangents that touch the region of the part, and find the shorter section on the circular orbit formed by two intersections where the two tangents intersect the circular orbit
The X-ray CT apparatus according to claim 3. The extraction unit includes:
The coordinate conversion unit configured to convert the position of the region of interest specified based on the volume data into the coordinate system of the circular orbit to be the one coordinate system is provided. 4. The X-ray CT apparatus according to 4. An X-ray scan is performed on the subject by exposing the subject to X-rays from an X-ray generation unit that is rotatably provided along a circular orbit centered on the subject, and detection data is acquired. Steps,
A reconstruction processing unit reconstructs projection data based on the detection data, and creates volume data;
A specifying unit specifying a position of a site of interest in the subject based on the volume data;
A step of calculating a position on the circular orbit when a line connecting the position of the site of interest and any position on the circular orbit is the shortest ;
A first mode including:
A second mode in which a scan control unit controls the X-ray generation unit to emit X-rays only in a part of the circular orbit including a position on the circular orbit obtained in the first mode; ,
For an X-ray CT apparatus having
The X-ray CT apparatus control method, wherein the scan control unit starts the second mode after the first mode is completed. An X-ray scan is performed on the subject by exposing the subject to X-rays from an X-ray generation unit that is rotatably provided along a circular orbit centered on the subject, and detection data is acquired. Steps,
A reconstruction processing unit reconstructs projection data based on the detection data, and creates volume data;
A specifying unit specifying a position of a site of interest in the subject based on the volume data;
In one coordinate system including the volume data and the circular orbit, a line connecting the center of the circular orbit and a point on the circular orbit, and the two lines including the region of interest intersect the circular orbit. Obtaining a shorter section on the circular orbit formed by two intersections ;
A first mode including:
A second mode in which the scan control unit controls the X-ray generation unit to emit X-rays only in a part of the section including the section obtained in the first mode;
For an X-ray CT apparatus having
The X-ray CT apparatus control method, wherein the scan control unit starts the second mode after the first mode is completed.

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