JP4482012B2 - Computed tomography equipment - Google Patents

Description

Detailed Description of the Invention

  The present invention relates to a computer tomography apparatus that captures a tomographic image of a subject, and more particularly to a computer tomography apparatus that can reduce the burden on an operator when planning an examination.

  An example of a computed tomography apparatus is an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT apparatus). This X-ray CT apparatus has been used for medical diagnosis or for various researches for a relatively long time, and has undergone a major change in history.

  In the early days, single-slice X-ray CT apparatuses were used. In the case of this single-slice X-ray CT apparatus, since an image of a slice surface of a subject has been obtained, it is difficult to capture a wide range of images in a short time. ) And there was a strong demand to shoot images over a wide range.

  In order to meet this demand, in recent years, multi-slice X-ray CT apparatuses have been developed and are quite popular. This multi-slice CT apparatus has a structure in which a plurality of detector arrays used in a single-slice X-ray CT apparatus are arranged in a direction orthogonal to the array, and a total of M channel × N segment detection elements are included. A dimension detector is used. The multi-slice X-ray CT apparatus includes an X-ray source that exposes a fan beam X-ray having a width spread in the slice direction, and the above-described two-dimensional detector, and has a conical X-ray beam (effective field of view). By detecting X-rays transmitted through the subject based on the diameter FOV) with a two-dimensional detector, projection data of the multi-slice surface of the subject can be collected at one time, compared to a single-slice X-ray CT apparatus, High-definition and wide-range images can be collected.

  For this reason, at present, the mainstream of X-ray CT apparatuses is shifting to multi-slice X-ray CT apparatuses. Currently, the multi-slice X-ray CT apparatus in use is a 4-slice type, but further multi-rows such as an 8-slice type or a 16-slice type multi-slice X-ray CT apparatus are also desired.

  Further, in recent years, as this multi-slice X-ray CT apparatus, a so-called multi-slice helical X-ray CT apparatus that performs a helical scan method is also known.

  By the way, in the multi-slice X-ray CT apparatus, the cone beam is sliced despite being irradiated with a fan beam X-ray having a spread width in the slice direction (that is, actually a cone-shaped X-ray beam). A fan beam reconstruction method that considers a beam parallel to a direction perpendicular to the direction is performed to reconstruct a desired slice.

  However, when the number of rows has increased, the fan beam reconstruction method cannot be considered to have parallel X-ray paths between rows in a direction perpendicular to the slice direction. If this is regarded as parallel and an image is simply reconstructed as a multi-slice for each column, there are many artifacts and the image is not practically usable. As a reconstruction method for overcoming this problem, a so-called cone beam reconstruction method with few artifacts has been proposed.

  Typically, the cone beam reconstruction method is applied to the number of slice columns that simultaneously acquire data = 8 columns, while the fan beam reconstruction method is applied to the number of slice columns that are simultaneously acquired data = 4 columns. Examples are known.

  Therefore, in order to make full use of the cone beam reconstruction method and the fan beam reconstruction method in one X-ray CT apparatus, if the slice thickness per slice is the same, the number of slice rows is large, that is, imaging. When the slice width (= slice thickness × number of slices) is wide, the cone beam reconstruction method is used for image generation. On the other hand, when the number of slice rows is small, that is, when the imaging slice width is narrow, fan beam reconstruction is used for image generation. That is, the construction method may be used.

  The operation of setting the reconstruction method is performed by an operator in an actual shooting plan, but each reconstruction method has advantages and disadvantages. For example, the cone beam reconstruction method is superior in terms of image quality as described above, but is inferior in scan time compared to the fan beam reconstruction method. For example, in the case of the cone beam reconstruction method, compared with the fan beam reconstruction method, since the image artifacts are small even if the number of rows is increased, the data collection range (imaging slice width) can be set wide, so that the scan time Can be shortened accordingly. However, since the cone beam reconstruction method needs to perform reconstruction in consideration of the cone angle, especially when a large number of images with thick slices are reconstructed at the same time, the reconstruction time is determined by fan beam reconstruction. It will be longer than the construction method.

  For this reason, in order to always set the optimal reconstruction method for each patient, it is necessary to fully understand the characteristics of each reconstruction method. It has become. Even experienced operators have been forced to reduce patient throughput because the setting is very nervous and therefore time consuming.

  Conventionally, various types of shooting planning systems for assisting shooting planning have been known. As described above, an optimum reconstruction method is set from different types of reconstruction methods in consideration of shooting conditions. It was not a thing.

  The present invention has been made in view of the above-described circumstances, and an optimum reconstruction method can always be easily and quickly set by an operator who is not so skilled in a shooting plan, and the shooting plan can be reduced in labor and effort. An object of the present invention is to provide a radiation CT apparatus such as an X-ray CT apparatus that can be efficiently and accurately set up.

In order to achieve the above object, a computer tomography apparatus according to the present invention, according to one aspect thereof, reconstructs projection data obtained by scanning a subject with radiation to obtain a tomographic image of a slice of the subject. In the computed tomography apparatus provided with the reconstruction apparatus for obtaining the information, the designation means for designating information on at least the entire scan region, the reconstruction slice thickness, and the number of slices related to the imaging region of the subject, and designated by the designation means Information on a reconstruction method that can be used for reconstruction of the projection data by the reconstruction device according to information is presented, and the reconstruction method includes a fan beam reconstruction method and a cone beam reconstruction method Reconfiguration method information presenting means configured as described above, and Based on is subjected to a reconstruction process will generate the tomographic image data of the slice, the information reconstruction scheme, characterized in that it comprises the parameters of the respective reconstruction mode available names and respective reconstruction mode It is what.

For this reason, the operator designates information on at least the entire scan area, the reconstruction slice thickness, and the number of slices, so that multiple types of reconstruction methods including a fan beam reconstruction method and a cone beam reconstruction method can be performed by the operator. Presented to. Thus, the assistance from the apparatus side can be obtained, so that the operator can shorten the time required for determining the reconstruction method, and can easily and reliably perform the shooting plan. In addition, it is not necessary to have a skill level as high as that in the past to create a shooting plan. Furthermore, the reconstruction method most suitable for the designated content is automatically determined only by the operator specifying at least information on the entire scan area, the reconstruction slice thickness, and the number of slices. As a result, the time required for the shooting plan is reduced, and the skill level of the shooting plan required by the operator is reduced accordingly.

  According to the present invention, even an operator who is not so skilled in a shooting plan can always easily and quickly set an optimal reconstruction method, and can set up a shooting plan with little effort and with high efficiency. A radiation CT apparatus such as a line CT apparatus can be provided.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows a configuration of an X-ray CT apparatus as a radiation X-ray CT apparatus according to an embodiment of the present invention.

  The X-ray CT apparatus 100 includes a bed (not shown) on which a subject (for example, a patient) P is placed and a diagnostic opening OP for performing diagnosis by inserting the subject P. Projection data of the subject P And a data processing unit U that controls the operation of the entire platform G, collects projection data, and performs image reconstruction processing, image display, and the like based on the projection data.

  The bed has a top plate that is slidable in the longitudinal direction by driving a bed driving unit (not shown). Usually, the subject P is placed so that the body axis direction coincides with the longitudinal direction.

  The gantry G includes an X-ray tube 101 as an X-ray source and an X-ray detector 103 as a radiation detector, which are arranged to face each other with a subject P inserted into the diagnostic opening OP, and a switch group. 103a (see FIG. 3), a data collection circuit (DAS) 104, a non-contact data transmission device 105, a gantry driving unit 107, and a slip ring 108.

  The X-ray tube 101, the X-ray detector 103, and the data collection device 104 are provided in a rotating ring 102 that can rotate within the gantry G, and the rotating ring 102 rotates by drive control from the gantry driving unit 107. Thus, both can rotate integrally around the rotation center axis parallel to the body axis direction of the subject P inserted in the diagnostic opening OP of the gantry 3. The rotating ring 102 is driven to rotate at a high speed of 1 second or less per rotation.

  The X-ray tube 101 generates X-rays having a cone beam (quadrangular pyramid) shape or a fan beam shape with respect to the subject P placed in the effective visual field region FOV. The X-ray tube 101 is supplied with electric power (tube voltage and tube current) necessary for X-ray exposure from the high voltage generator 109 via the slip ring 108. As a result, the X-ray tube 101 generates so-called cone beam X-rays or fan beam X-rays that spread in two directions: a slice direction parallel to the rotation center axis and a channel direction orthogonal to the slice direction. In normal diagnosis, the subject P is placed on the top plate along the longitudinal direction of the bed, so that the slice direction coincides with the body axis direction of the subject P.

  A cone-shaped or fan-shaped X-ray beam exposed from the X-ray focal point of the X-ray tube 101 is shaped between the X-ray tube 101 in the gantry G and the subject P to have a required size. A slit (not shown) for forming the X-ray beam is provided.

  The X-ray detector 103 is a device that detects X-rays that have passed through the subject P, and a plurality of X-ray detection elements are arranged in an array in two orthogonal directions (slice direction and channel direction). Thus, a two-dimensional X-ray detector is formed. In the present embodiment, the X-ray detector 103 is composed of a plurality (for example, 38) of detector modules, and the plurality of detection modules are arranged in the channel direction.

  FIG. 2 shows a development view of one of the detector modules 1030. The detector module 1030 includes a scintillator and a photodiode chip having a plurality of detection elements 1031 and 1032 made of photodiodes. The plurality of detection elements 1031 and 1032 are arranged in a matrix in two directions of the channel direction and the slice direction. In the X-ray CT apparatus according to the present embodiment, each of the plurality of detector modules 1030 is not planar but is arranged along one arc centered on the focal point of the X-ray tube 101.

  As described above, the detector module 1030 has a switching chip (forming the switching group 103a) and a DAS chip (forming the DAS 104) together with the photodiode chip having the plurality of detecting elements 1031 and 1032. These photodiode chip, switching chip, and DAS chip are mounted on a single rigid printed wiring board.

  One detection element 1031 has a sensitive area with a width of 1.0 mm in the slice direction and a width of 0.5 mm in the channel direction. The other detection element 1032 has a sensitive area with a width of 0.5 mm in the slice direction and a width of 0.5 mm in the channel direction.

  The width of the sensitive area of the photodiode is defined as a converted value on the rotation center axis of the X-ray tube. In other words, “a photodiode having a sensitive area width of 1 mm” means “a photodiode having a sensitive area width corresponding to 1 mm on the rotation center axis of the X-ray tube”. For this reason, considering that X-rays diffuse radially, the actual sensitive area width of the photodiode is the distance between the X-ray focal point and the photosensitive area of the photodiode with respect to the distance between the X-ray focal point and the rotation center axis. It is slightly wider than 1 mm according to the actual distance ratio.

  For example, 16 detection elements 1032 having a width of 0.5 mm are arranged in the slice direction. The 16 detection elements 1032 arranged in the slice direction are referred to as a first detection element array group. In addition, a plurality of, for example, twelve detection elements 1031 each having a width of 1 mm are arranged on both sides of the first detection element array group in the slice direction, the number being smaller than the number of detection elements 1032 arranged. The twelve detection elements 1031 arranged in the slice direction C are each referred to as a second detection element array group.

  In the present embodiment, the number (for example, 16) of the detection elements 1032 arranged in the slice direction is larger than the number (for example, 12) of the detection elements 1031 arranged on both sides thereof, and the total number (for example, 24). Designed to be less than

  That is, in the present embodiment, the X-ray detector 103 is configured by arranging 912 detection elements in the channel direction (row direction) and 40 detection elements in the slice direction (column direction). In the X-ray detector 103 of the present embodiment, a two-dimensional detector having a non-uniform pitch is formed by a detection element having a width of 0.5 mm and a detection element having a width of 1.0 mm. Two-dimensional detectors arranged in the row and column directions may be used, and the detection element size is not limited to 0.5 mm or 1.0 mm, but is not limited to this example such as a detection element having a width of 1.25 mm.

  M × N detected by such an X-ray detector 103 (in the above example, M = 24 rows × 38 pieces = 912 and N = 40 (= 16 columns + 2 × 12 columns)). ) Enormous amount of data (that is, data of M × N channels per view (two-dimensional projection data)) is once collected in the DAS 104 formed as a chip through the switch group 103a.

  Specifically, the X-ray projection data detected by each detection element of the X-ray detector 103 is, for example, detected for each channel detection element array (40 detection elements 1031 and 1032) via the switch group 103a. , The DAS 104 having data collecting elements of 8 columns (912 rows × 8 columns) or 4 columns (912 rows × 4 columns) less than 40 columns.

  In order to transfer the X-ray projection data to the DAS 104, the switch group 103a receives a control signal from the host controller and adds the X-ray projection data for each column in the slice direction (that is, the data for each column). (Bundled) to generate two-dimensional equivalent data of the required number of columns.

  The two-dimensional projection data output from the DAS 104 is transmitted to a data processing unit U (to be described later) via a non-contact data transmission device 105 that applies optical communication all at once. Here, the non-contact data transmission device 105 applying optical communication is described as an example of the data transmission device, but a contact data transmission device such as a slip ring may be used.

  The detection operation by the X-ray detector 103 is repeated, for example, about 1000 times during one rotation (about 1 second), so that an enormous amount of 2D projection data for M × N channels per second (1 rotation). The DAS 104 and the non-contact data transmission device 105 are designed to perform ultra-high-speed processing in order to transmit such enormous and high-speed generated two-dimensional projection data 1000 times without delay.

  FIG. 3 is a perspective view schematically showing the structure of the two-dimensional X-ray detector 103, the switch group 103a, and the DAS 104 in the present embodiment. As shown in the figure, the X-ray detector 103 has detection elements arranged in an array, and the switch group 103a is configured by mounting a switching element such as an FET on a switch substrate, for example. Further, the data collection elements of the DAS 104 are arranged in an array like the respective detection elements of the X-ray detector 103.

  Each data collection element of the DAS 104 collects projection data for eight slices or four slices of the subject P by performing amplification processing, A / D conversion processing, or the like on the transmitted X-ray projection data. ing.

  As will be described later, in this embodiment, which of the data collection elements for 8 columns or 4 columns is adopted in this DAS 104 is a reconstruction determined when an imaging plan (also called an inspection plan) is made. The method is determined by whether the fan beam reconstruction method or the cone beam reconstruction method. In this embodiment, when performing fan beam reconstruction (for example, 2 mm × 4 slices), four columns of data collection elements (for example, 912 rows × 4 columns) are used, and cone beam reconstruction is performed ( For example, 0.5 mm × 8 slices) uses 8 columns of data collection elements (eg, 912 rows × 8 columns).

  The data processing unit U is centered on the host controller 110, and includes a preprocessing device 106 that performs preprocessing such as data correction, a storage device 111, an auxiliary storage device 112, a data processing device 113, a reconstruction device 114, an input device 115, and Display devices 116 are connected to each other via a data / control bus 116. Further, the bus 116 is connected to an external image processing apparatus 200. The image processing apparatus 200 includes an auxiliary storage device 201, a data processing device 202, a reconstruction device 203, an input device 204, and a display device 205.

  The pre-processing device 106 performs sensitivity correction, X-ray intensity correction, and the like on the projection data transmitted from the non-contact data transmission device 105. The 360-degree, that is, 1000 sets of two-dimensional projection data subjected to sensitivity correction, X-ray intensity correction, and the like in the preprocessing device 106 are temporarily stored in the storage device 111.

  The reconstruction device 114 performs reconstruction processing of the fan beam reconstruction method or the cone beam reconstruction method on the projection data stored in the storage device 111 to generate slice tomographic image data.

  In the reconstruction process using the cone beam reconstruction method, an image reconstruction of projection data is performed mainly using a reconstruction algorithm called the Feldkamp method.

  The Feldkamp reconstruction method treats a wide target area in the slice direction as an aggregate of a plurality of voxels, and uses three-dimensional distribution data (hereinafter referred to as “volume data (a plurality of voxel data is three-dimensional (three-dimensional) Is an approximate reconstruction method improved on the basis of the fan beam convolution back projection method. That is, in the Feldkamp reconstruction method, data is considered as fan projection data and convolved, and then back projection is performed along an oblique ray corresponding to the actual cone angle with respect to the rotation center axis.

  As reconstruction processing of the cone beam reconstruction method, the Feldkamp reconstruction method is performed, and if any of the following correction processing is performed, the error of the reconstruction processing can be reduced.

  The first correction process is a correction process in which the length of the X-ray beam passing through the subject is increased due to the X-ray beam being cured and entering the reconstruction plane (slice plane). Is to be applied. That is, different beam path lengths are corrected according to the position of the cone beam X-ray in the body axis direction with respect to projection data (which may or may not be subjected to preprocessing or the like) obtained by the data acquisition device.

  In the second correction process, the actually measured X-ray path is deviated from the calculated X-ray path connecting the X-ray focal point and the center of the voxel defined in the reconstruction process. This error is corrected. Is. That is, a predetermined calculation process is performed on the projection data actually measured along a plurality of actual (for example, four) X-ray paths existing around the calculated X-ray path. Back projection data is taken along a straight line shown in the calculated X-ray path, and this is back projected with a predetermined weight. In particular, in the case of helical scanning, the positional relationship in the slice direction between the desired reconstruction plane and the X-ray focal point changes, so that the detection element array (used for the calculation process) for each X-ray focal point position (or for each view) It is desirable to change the contribution of the data) or the detection element array. If a reconstruction process using such a cone beam reconstruction method is performed, a detector wide in the slice direction can be used effectively.

  As an algorithm of this cone beam reconstruction method, for example, as known in Japanese Patent Laid-Open No. 8-187240, the ASSR method “virtual plane determined from two-dimensional projection data (with respect to the central axis of the helical scan) An algorithm that extracts approximate projection data of an X-ray path that approximates the position of an inclined oblique section is more effective), and reconstructs an image using the approximate projection data. Other algorithms may be adopted as long as the image is reconstructed using information.

  On the other hand, the reconstruction by the fan beam reconstruction method uses the fan beam convolution back projection method as known in, for example, Japanese Patent Application Laid-Open Nos. 10-248837 and 10-21372. In projection, it is assumed that the X-ray ray is orthogonal to the rotation center axis (assuming that the projection data is obtained by X-rays perpendicular to the body axis direction), and an image is reconstructed based on the projection data.

  In the fan beam reconstruction method, the image reconstruction is performed on the assumption that the projection data is an X-ray beam in a direction orthogonal to the rotation center axis by the reconstruction device 114. Therefore, the data processing device 113 is obtained as described above. Helical interpolation is performed using the projection data.

  In this helical interpolation, projection data (360 degrees or 180 degrees + fan angle projection data) necessary for reconstruction of a desired slice is linearly interpolated with projection data of the same phase obtained in the vicinity of the slice plane. Say to get. In the present embodiment, this helical interpolation is improved, and in the fan beam reconstruction mode, the data acquisition device 113 virtually sets a predetermined number of resampling points in a certain range near the desired slice plane, Resampled data at the resampling point is obtained by linear interpolation using the same phase data sandwiching each resampling point, and weighted addition by a predetermined filter is applied to this resampled data, so that the projection data of the desired slice Is generated. The reconstruction device 114 generates an image by fan beam reconstruction processing based on the generated projection data.

  In the cone beam reconstruction method, the data processor 113 does not perform helical interpolation as in the fan beam reconstruction method, but the first or second correction processing described above is appropriately executed.

  The reconstructed volume data is directly or once stored in the storage device 111, and then sent to the data processing device 113. Based on the instructions of the operator, the tomographic image of an arbitrary cross section that has already been widely used, It is converted into so-called pseudo three-dimensional image data such as a projected image from an arbitrary direction or a three-dimensional surface image of a specific organ by rendering processing, and is displayed on the display device 116.

  The operator can select and set an arbitrary display form from the tomographic image of the arbitrary cross section, the projected image from the arbitrary direction, the three-dimensional surface image, and the like according to the purpose of the inspection / diagnosis. . In this case, images in different forms are generated from one volume data and displayed. In addition, when displaying, not only one type of image but also a mode in which a plurality of types of images are displayed at the same time can be switched to a mode in which one image is displayed according to the purpose. Yes.

  The host controller 110 is equipped with a computer circuit having a CPU, and is connected to the high voltage generator 109 and is connected to a bed driving unit (not shown), the platform driving unit 107, and the radiation detector 103 in the frame via a bus. Each is connected. In addition, the host controller 110, the data processing device 113, the storage device 111, the reconstruction device 114, the display device 116, and the input device 115 are interconnected via a bus, and image data and control data are mutually connected at high speed via the bus. Etc. can be delivered.

  The host controller 110 executes control as described below, for example, to collect X-ray transmission data (projection data). That is, the host controller 110 stores a scan condition such as a slice thickness input from the operator via the input device 115 in the internal memory, and the stored scan condition (or is directly set by the operator in the manual mode). Of the high voltage generator 109, the bed driving unit, the bed driving unit 107, and the amount of feeding of the bed in the body axis direction, the feeding speed, the table (X-ray tube 2014 and the radiation detector 103). The high voltage generator 109, the bed driving unit, and the gantry driving unit 107 are driven while controlling the rotation speed, the rotation pitch, the X-ray exposure timing, and the like. Accordingly, a cone-shaped X-ray beam is irradiated from a plurality of directions to a desired imaging region of the subject, and transmitted X-rays transmitted through the imaging region of the subject are transmitted through each detection element of the radiation detector 103. It can be detected as X-ray transmission data.

  At the same time, the host controller 110 turns on / off the switching elements of the switch group 103a as necessary based on the scanning conditions set by the input device 115 (particularly, the imaging slice width (slice thickness × slice number)). Control. As a result, the connection state between the detection element (photodiode) column of the X-ray detector 103 and the DAS element column of the DAS 104 is changed according to the slice thickness, so-called signal bundling before DAS (signals between columns). Addition) is performed.

  Depending on the commanded slice thickness, the collected data of the DAS 104 can also be added between the columns by calculation, and so-called bundling after DAS is performed. This bundling process after DAS can be executed by, for example, the pre-processing device 106.

  In addition to controlling the connection state of the switch group 103a described above, the host controller 110 also determines the number of DAS columns in the slice direction used for data collection in the DAS 104 (for example, four columns for fan beam reconstruction and one for cone beam reconstruction). 8 columns). As a result, multiple slices of X-ray projection data corresponding to the scan conditions and reconstruction conditions are output from the DAS 104.

  Although not shown, the input device 115 is an interactive interface including a CPU for arithmetic processing, a keyboard, various switches, a mouse, and the like, and is used when an operator makes a shooting plan before an actual scan. It also functions as a planning system. The imaging plan creation function of this imaging plan creation system includes the examination target part, the flow from scanning to image recording, scanning conditions for data collection, reconstruction conditions for image reconstruction, and reconstructed images. Input and setting such as image display / recording conditions for display and recording are included.

  In general, expert knowledge is required to optimize scanning conditions such as tube voltage, tube current, and X-ray exposure time, and to optimize reconstruction conditions such as imaging slice width (slice thickness x number of slices) and matrix size. To do. The above-described shooting plan creation function is a function that has been developed based on this specialized knowledge so that even an inexperienced operator who has little expertise can set equivalent conditions.

  As the flow from scanning to image recording, there is a conventional scanning flow that repeats scanning with the top plate stopped and top plate movement after scanning, and after all the slice positions have been scanned, image reconstruction / There are a scan & scan mode in which display is performed, a scan & view mode in which an operation of performing image reconstruction / display based on data obtained by the scan immediately after scanning at a set slice position in a conventional scan is repeated at all slice positions.

  In addition, the flow of the helical scan in which the top plate moves during the scan follows the helical scan, and performs fan beam reconstruction processing or cone beam reconstruction processing, and filming is performed during scanning under preset window conditions. Auto filming mode in which filming is performed while observing the image on the display screen. When window conditions need to be adjusted during scanning, the window conditions can be changed interactively during filming. Active auto filming mode in which the filming state is in standby state, reconstruction and image display are performed in real time following the helical scan, and fan beam reconstruction or cone beam reconstruction different from real-time reconstruction is performed after the scan is completed. While observing the composed image There is a real-time mode, and the like that Irumingu.

  In the case of a third generation or fourth generation X-ray CT apparatus, the helical scan (also referred to as a spiral scan or a spiral scan) is to move a subject while continuously rotating an X-ray source. In this helical scan, the position of the subject continuously changes according to the rotation angle of the X-ray source during the operation of exposing the X-rays. That is, the position of the scanning plane with respect to the subject changes continuously.

  A plurality of parameters are related to the projection data collection operation (scan operation). Similarly, a plurality of parameters are involved in both an image generation operation for generating a tomographic image from collected signals and an image display operation for displaying a reconstructed tomographic image.

  Scan conditions (signal acquisition parameters) include the body part (whole body, head, chest, lung field, lower limb, etc.), scan type (conventional scan (multi-slice scan, single slice scan) / helical scan), slice thickness, slice Interval, volume size, gantry tilt angle, tube voltage, tube current, imaging area size, scan speed (rotation speed of X-ray tube and detector), amount of movement of the bed that moves while the X-ray tube makes one rotation, bed There is a movement amount.

  As reconstruction conditions (reconstruction parameters), there are a reconstruction method (fan beam reconstruction method / cone beam reconstruction method), a reconstruction area size, a reconstruction matrix size, a threshold value for extracting a region of interest, and the like. is there.

  Further, image display / recording conditions (image display / recording parameters) include window level, window width, display magnification, and multiplanar (sagittal / coronal / oblique).

  In this embodiment, the operator obtains reference information for setting the reconstruction method (fan beam reconstruction method / cone beam reconstruction method) interactively with the input device 115 (imaging plan creation system). Alternatively, it is possible to automatically set the reconstruction method simply by inputting necessary information. In order to realize this, first to third creation modes are prepared as shown in FIGS.

  In order to complete a series of inspection sequences from signal collection through image generation to final image display, it is required to set the above-described scan conditions, reconstruction conditions, and image display / recording conditions. The flow from setting of these conditions (parameters), signal acquisition, reconstruction, image display, and image recording is collectively referred to as a plan. Therefore, in consideration of the convenience of the setting work for the operator when making an imaging plan, it is possible to register in advance as a plan including the scanning conditions, the reconstruction conditions, and the image display / recording conditions. By selecting a plan, the entire sequence described above can be easily executed.

  With the support of this imaging plan creation system (input device 115), the operator can acquire an imaging plan (inspection target part, flow from scanning to image recording, scanning conditions, reconstruction conditions, image display / recording conditions). Set the schedule. The host controller 110 controls the gantry and the bed according to the set schedule, and sequentially executes the schedule.

  FIG. 4 shows an example of the shooting schedule setting screen. Here, a screen for setting a scan schedule is shown as the shooting schedule setting screen. The shooting schedule setting screen is displayed on the operation screen of the input device, but may be displayed on the display device 116 for image display.

  In the upper right column of the imaging schedule setting screen, a scanogram created based on data obtained by moving the top board with the X-ray tube and the X-ray detector fixed is displayed. A frame line for setting a scan range is displayed on the scanogram. By enlarging / reducing, moving and rotating the frame line, it is possible to set the entire scan area (the entire range to be scanned).

  In addition, a subject (patient) information column is displayed at the center of the upper column of the imaging schedule setting screen, and a processing setting column after data collection is displayed at the left column.

  Furthermore, various buttons that the operator operates as necessary are displayed below the subject information column and the processing setting column. This button includes buttons B1 to B5 for giving priority commands to exposure dose, scan time, total scan and reconstruction time, image quality, and tube OLP (X-ray tube overload protection), and operation There is a confirmation button C for confirming a person's intention.

  Further, a scan schedule table is displayed in the lower column of the setting screen. In this scan schedule table, a plurality of scheduled scan operations are arranged vertically according to the time-series order. The operator arranges the desired scan operations in the desired order using the new (addition), copy, and erase functions of the scan operations according to the desired schedule.

  The row of each scan operation includes a start time of each scan operation starting from an arbitrary time when the operator presses the trigger button, a pause time between scan operations, a scan range (start / end position) of each scan operation, Scan mode (conventional scan (multi-slice scan, single slice scan) / helical scan), number of scan operations, tube voltage supplied from the high voltage generator to the X-ray tube 101, tube current, scan speed (scan total time) , Items such as FOV size, slice width (slice thickness × slice number), scan range, amount of movement of the top plate between scan operations, and the like are arranged. As the value of each item, an initial recommended value is inserted by the photographing plan creation system 11, and the operator can change the value as necessary.

  It should be noted that the frame line indicating the scan range displayed on the scanogram has the size and position linked to the change if the value of any of the start position, end position, scan range, and FOV size is changed. Be changed. Conversely, if the frame line on the scanogram is clicked and moved, items such as a start position and an end position are changed in conjunction with the movement.

  Next, operational effects of the X-ray CT apparatus according to the present embodiment will be described.

  First, the operator inputs predetermined items such as patient information and processing after data collection on the imaging plan creation screen of the display unit of the input device 115 as the imaging plan creation system j shown in FIG.

  Next, the operator performs scanography of the subject (X-rays are generated from the X-ray tube without rotating the X-ray tube and the radiation detector system, and the top plate is inserted into the diagnostic opening of the gantry for imaging. ). Data obtained by scanography is subjected to predetermined processing, and a scanogram is obtained. This scanogram SN is drawn on the photographing plan creation screen as shown in FIG. The screen example shown in FIG. 4 is a case where the operator has selected the auto filming mode described above.

  Next, on the imaging plan creation screen, the operator obtains the assistance of the imaging plan creation system, and from the scan, such as setting the inspection target region, scan conditions, reconstruction conditions, image display / recording conditions (window conditions), etc. Set the flow until image recording.

  In the present embodiment, the first to third creation modes are prepared in the imaging plan creation system (input device 115) so that this series of setting operations is easy for the operator.

(First creation mode)
The first creation mode is shown in FIGS. This first creation mode is intended to present the operator with possible reconstruction scheme candidates. For this reason, the operator finally determines the reconstruction method with his / her own intention with reference to the presented reconstruction method.

  Specifically, the imaging plan creation system reads the entire scan area, the reconstructed slice thickness, and the number of slices on the imaging plan creation screen (step S1). The entire scan area is designated by moving the frame line on the above-described scanner image SN. By this designation, information on the imaging region and its imaging range is read.

  Next, the imaging plan creation system refers to a lookup table stored in advance, and determines a reconstruction method candidate applicable to all the read scan areas, the reconstruction slice thickness, and the number of slices (step S2). ). Thereby, one or a plurality of reconstruction method candidates to be displayed (presented) to the operator are determined. Candidates for these reconstruction schemes include fan beam reconstruction schemes (including bundling before or after DAS) and / or cone beam reconstruction schemes.

  Next, the shooting plan creation system calculates detailed parameters included in each of the determined reconstruction methods (step S3).

  The feasible reconstruction method and the detailed parameters of each method determined in this way are displayed (presented) in the superposition mode on the photographing plan creation screen, for example, as shown in FIG. 6 (step S4). .

  This superimposition screen lists, for example, two types of reconstruction methods that can be executed in accordance with a given total scan area, reconstruction slice thickness, and number of slices. The reconstruction methods displayed in this way are a fan beam reconstruction method (including bundling processing before or after DAS) and a cone beam reconstruction method according to the illustration of FIG. Each reconstruction method is further subdivided according to the type of scan method (multi-slice scan or helical scan) that can be applied. Thus, the parameters of the reconstruction method are displayed for each type determined by the combination of the reconstruction method and the scanning method.

  This parameter includes information indicating whether the Feldkamp reconstruction method and the ASSR reconstruction method are different when the reconstruction method is a cone beam reconstruction method, and a helical interpolation method during helical scanning. Thereby, for example, a series of flows such as “multi-slice helical scan + bundling process (before or after DAS) + helical interpolation + fan beam reconstruction method (number of slices = 4 columns)” is presented. Further, for example, a series of flows such as “conventional multi-slice scan + beam path length correction + cone beam reconstruction method” is also presented.

  Buttons for the operator to select are displayed at the end of each flow on the presentation screen.

  Therefore, the operator who sees the presentation screen for the reconstruction method selects a desired reconstruction method (including the scanning method) by clicking the selection button. For this reason, the photographing plan creation system determines whether or not the selection button has been clicked (step S5). When this determination is NO, that is, when it is determined that the selection button has not been clicked, it is determined based on another operation information whether or not the operator has canceled the setting of the reconstruction method based on the presentation screen. (Step S6). If NO in this determination as well, the operator recognizes that the user is taking into consideration while viewing the presentation screen, and stands by by returning the process to step S5. When the determination in step S6 is YES, the setting of the reconstruction method based on the presentation screen has been canceled, and the process ends.

  On the other hand, when the determination in step S5 described above is YES, since any reconstruction method (including the scanning method) is selected, information on the selected reconstruction method is stored in the storage device 111. It memorize | stores and complete | finishes a process (step S7).

(Second creation mode)
The second creation mode is shown in FIGS.

  In the second creation mode, in addition to the reconstruction method presented in the first creation mode described above, superiority information of each presented reconstruction method is also presented. Note that only superiority or inferiority information of each reconstruction method may be presented alone.

  In order to present the superiority / inferiority information, the imaging plan creation system executes the processing shown in FIG. This process is obtained by adding steps S3A and S4A to the process of FIG. 5 described above. In step S3A, the superiority / inferiority information of the reconstruction method is read from the superiority / inferiority information table stored in advance, corresponding to the one or more reconstruction methods determined in step S2. Then, the read superiority information is displayed in a superposition mode on the photographing plan creation screen as shown in FIG. 8, for example (step S4A).

  The superiority / inferiority information exemplified in FIG. 8 will be described. Here, as the superiority / inferiority information items, the fan beam reconstruction method (when slice columns collected simultaneously = 4) and the cone beam reconstruction method (slice sequences collected simultaneously) Exposure dose, scan time, total time from scan to reconstruction, image quality (low contrast / high contrast), and tube OLP (scan waiting time). In the example of FIG. 8, “excellent” is indicated when relatively superior, and “inferior” characters are indicated when relatively inferior. A symbol such as a mark or a cross may be used.

  The exposure dose is an amount related to the size of the area where data is collected by scanning. When the imaging slice width is wide, the cone beam reconstruction method is superior (less) to the fan beam reconstruction method. On the contrary, when the imaging slice width is narrow, the fan beam reconstruction method is superior (less) to the cone beam reconstruction method.

  As for scan time, the cone beam reconstruction method is superior (shorter) to the fan beam reconstruction method because there are many inferior numbers, but the total time from scanning to reconstruction is generally fan beam reconstruction. The method is superior (shorter) than the cone beam reconstruction method (when the imaging slice width is thick).

  As for image quality, the cone beam reconstruction method is superior (good) to the fan beam reconstruction method. For the tube OLP, the cone beam reconstruction method is superior (good) to the fan beam reconstruction method.

  As described above, in the case of the second creation mode, in addition to the presentation of one or a plurality of reconstruction methods, the characteristics of the items representing the representative characteristics of the reconstruction methods are presented.

  In addition, when only the superiority / inferiority information described above is presented, the processing of steps S3 and S4 may be removed in the series of processing of FIG.

  As described above, according to the first and second creation modes, the operator simply designates the entire scan area, the reconstructed slice thickness, and the number of slices on the imaging plan creation screen. Candidates for configuration methods and parameter information thereof and / or superiority / inferiority information of each reconstruction method are automatically presented. In other words, the operator can immediately obtain important information for determining the reconstruction method on the screen immediately before he / she can easily determine which reconstruction method is most suitable. Become. For this reason, as compared with the conventional method, the degree of skill required for the shooting plan is remarkably eased, and the time required for the shooting plan can be greatly reduced, so that the efficiency of the shooting planning work can be significantly improved. At the same time, the operational burden on the operator required for the imaging planning work is reduced, which is effective in improving patient throughput. In addition, mistakes in setting the shooting plan are reliably prevented, and a shooting plan with high accuracy and reliability is performed.

(Third creation mode)
Next, the third creation mode will be described with reference to FIG. In the third creation mode, the scanning plan creation system automatically sets the scan method and the reconstruction method.

  The imaging plan creation system sequentially executes a series of processes shown in FIG. That is, all the scan areas, the reconstruction slice thickness, and the number of slices are read on the imaging plan creation screen (step S11).

  Next, the imaging planning system determines whether to perform “priority processing” or “consideration necessity processing” based on operation information from the operator (step S12). Here, “priority processing” is an item representing typical characteristics of each reconstruction method, such as exposure dose, scan time, total time from scan to reconstruction, image quality (low contrast / high contrast), And a process of prioritizing one or more of the tube OLP (scan waiting time). This ranking is performed in response to a command from the operator. The “requirement necessity process” means, for example, the scanning method and the reconstruction method in consideration of the exposure dose, the scanning time, the total time from the scanning to the reconstruction, the image quality, and the tube OLP. This process is performed in response to a command from the operator as to whether or not to decide.

  Therefore, when receiving an input indicating that “priority processing” is performed from the operator, the imaging plan creation system, through the processing of steps S13 to S16, the first priority item (for example, exposure dose), the second priority. A rank item (for example, scan time), a third priority item (for example, total time from scanning to reconstruction), and a fourth priority (for example, image quality) are selected in response to an input from the operator. In the present example, the remaining item is the tube OLP (fifth priority). Of course, the first to fifth priorities may not be selected, only the first priority may be selected, or only the first to third priorities may be selected.

  When the priority order is determined in this way, the imaging planning system searches a reference table stored in advance based on the priority order information, and determines an optimum scanning method and reconstruction method (step S17).

  On the other hand, when receiving an input indicating that “consideration necessity processing” is to be performed from the operator, the imaging plan creation system proceeds to step S18, and at least one item to be examined (for example, scan time) is input from the operator. Select according to input. Also in this case, the imaging plan system searches a reference table stored in advance based on the necessity information for examination, and determines an optimal scanning method and reconstruction method (step S19).

  In this way, the scanning method and reconstruction method optimal for the entire scan area, the reconstruction slice thickness, and the number of slices determined in step S17 or S19 are displayed on the imaging plan creation screen in, for example, the superposition mode (step S20). ). Information on the scanning method and reconstruction method is also stored in the storage device 111 (step S21).

  As described above, according to the third creation mode, the operator simply designates the entire scan area, the reconstruction slice thickness, and the number of slices on the imaging plan creation screen, and the optimum scan method and reconstruction method can be selected. Since only one type is automatically set, it is possible to save labor for the photographing plan for the operator. In addition, failure of the shooting plan is automatically prevented, and the degree of skill required for the shooting plan is greatly reduced.

  Through the above scanning method and reconstruction method determination process, an imaging plan is established interactively with the operator by the imaging plan creation system. A plurality of parameters relating to signal acquisition, image generation, and image display associated with the selected imaging plan are loaded into the host controller 110. When the operator gives an instruction to start photographing, a signal acquisition operation is performed on the gantry according to the loaded signal processing parameters, an image is reconstructed by the reconstruction device 114 according to the loaded reconstruction parameters, and the loaded image display An image is displayed on the display device 116 according to the parameters. Then, the image is filmed on a filming device (not shown) according to the loaded window condition.

  Further, FIG. 10 shows an example for modifying and implementing the first to third creation modes described above. In the case of the multi-slice X-ray CT apparatus according to the above-described embodiment, the first to third generation modes are configured to be selectively used in accordance with an operator's command in one apparatus. The multi-slice X-ray CT apparatus according to the example is an example in which any one of the first to third generation modes can be used.

  In order to realize this, for example, when each multi-slice X-ray CT apparatus is installed, one storage mode to be used is determined for each medical facility, and processing for restricting the remaining generation modes is performed by the storage device 111 (first to first storage devices). The manufacturer performs the third creation mode (installed in advance) (FIG. 10, steps S31 and S32).

  As a result, although it is an apparatus with one specification, for example, a hospital in Japan uses the second creation mode as a standard specification, while a hospital in the United States uses the third creation mode as a standard specification. can get.

  Note that the imaging slice width can be basically set in consideration of the limit of the imaging slice width in which the cone angle affects the image quality. Therefore, by appropriately changing this setting, the number of slices (the number of DAS columns) for data collection under the “fan beam reconstruction method” is not limited to four columns, and is not four columns of one column or two columns. The number of columns can also be set. On the other hand, the number of slices (the number of DAS columns) for data collection under the “cone beam reconstruction method” is not limited to eight, but other columns such as 16, 32, 64, etc. It can also be set to a number. For example, if two rows of DASs 104 are used in the fan beam reconstruction method acquisition mode, a mode in which four rows of DASs 104 are used in the “cone beam reconstruction method” acquisition mode may be used.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention when it is practiced.

  For example, in the present embodiment, the number of DAS sequences used in the body axis direction is switched to 8 columns, 4 columns, etc. according to the reconstruction algorithm selected in the imaging plan and the imaging slice width. Regardless of the algorithm and the imaging slice width, the number of DAS sequences used may be limited to a predetermined number (for example, 8 columns) and fixed. In this case, the number of slices such as 4 slices and 8 slices may be selected on the reconstruction parameter sheet in the imaging plan. Thereby, the operator can save the trouble of selecting the number of slices of the scan condition in the imaging plan.

  In the above embodiment, data processing such as reconstruction and cross-sectional conversion and display operations are performed in the X-ray CT apparatus 100 (such a form is common), but in the present invention. Instead, these data processing and the like may be executed in an external image processing apparatus 200 as shown in FIG. When such an external image processing apparatus 200 is used, the data sent from the X-ray CT apparatus 100 to the image processing apparatus 200 may be before reconstruction, after reconstruction, or immediately before display after data processing. In any state, the effect of the above-described embodiment is not disturbed.

  In the above embodiment, as the X-ray CT apparatus, the rotation / rotation (ROTATE) type in which the currently mainstream X-ray tube and the radiation detector integrally rotate around the subject has been described as an example. It may be applied to various types such as a stationary / rotating type in which a large number of detection elements are arrayed and only the X-ray tube rotates around the subject.

  In the above embodiment, it has been described that projection data for about 360 ° around the subject is necessary as an angle range necessary for reconstructing one slice of tomographic image data. It can be applied to any reconstruction method such as half scan using projection data for “+ view angle”.

  Further, in the above-described embodiment, as a mechanism for converting incident X-rays into electric charges, an indirect conversion type in which X-rays are converted into light by a phosphor such as a scintillator and the light is further converted into electric charges by a photoelectric conversion element such as a photodiode. As described above, the direct conversion type using the generation of electron-hole pairs in the semiconductor by X-rays and the movement of the electron-hole pairs to the electrodes, that is, the photoconductive phenomenon, may be adopted.

  In the above embodiment, a single-tube X-ray CT apparatus has been described. However, in a so-called multi-tube X-ray CT apparatus in which a plurality of pairs of an X-ray tube and an X-ray detector are mounted on a rotating ring. It may be applied.

1 is a block diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention. The top view which shows one of the several detector modules which comprise the X-ray detector employ | adopted as the X-ray CT apparatus of embodiment. The perspective view explaining the outline of the arrangement | positioning relationship of an X-ray detector, a switch group, and a data acquisition circuit (DAS). The schematic diagram which shows an example of the imaging plan setting screen displayed with an imaging plan creation system (function). The schematic flowchart explaining the 1st creation mode used in a photography plan creation system (function). The figure which shows an example of the screen of the reconstruction system shown by a 1st creation mode. The schematic flowchart explaining the 2nd creation mode used in a photography plan creation system (function). The figure which shows an example of the screen of the reconstruction method shown by 2nd creation mode. 14 is a schematic flowchart for explaining a third creation mode used in the imaging plan creation system (function). The schematic flowchart explaining the modification for restrict | limiting the 1st-3rd creation mode to one mode.

Explanation of symbols

100 X-ray CT system (radiation CT system)
101 X-ray tube (X-ray source)
103 X-ray detector (radiation detector)
103a Switch group 104b Data collection circuit (DAS)
109 High-voltage generator 110 Host controller 111 Storage device 114 Reconstruction device 115 Input device (forms the main part of the photographing plan creation system)
116 display device

Claims (2)

In a computed tomography apparatus provided with a reconstruction device for reconstructing projection data obtained by scanning a subject with radiation and obtaining a tomographic image of a slice of the subject,
Designating means for designating at least the entire scan area, the reconstruction slice thickness, and the number of slices related to the imaging region of the subject;
Presenting information on a reconstruction method that can be used for reconstruction of the projection data by the reconstruction device in accordance with information designated by the designation means, the reconstruction method comprising a fan beam reconstruction method and A reconstruction method information presentation means configured to include a cone beam reconstruction method,
The reconstruction device is configured to generate tomographic image data of a slice by performing a reconstruction process based on the reconstruction method set by the reconstruction method information presenting unit ,
The information of the reconstruction method includes a name of each usable reconstruction method and a parameter of each reconstruction method . The computed tomography apparatus according to claim 1, further comprising means for designating a reconstruction method given by an operator to the reconstruction device in response to presentation of reconstruction method information by the reconstruction method information presentation unit. .

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