Patent Publication Number: US-2023148976-A1

Title: Direct-conversion x-ray detector, method of detecting x-ray, and x-ray computed-tomography apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-188178, filed on Nov. 18, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a direct-conversion X-ray detector, a method of detecting an X-ray, and an X-ray computed-tomography apparatus. 
     BACKGROUND 
     One problem to be solved by embodiments disclosed in the present specification and the drawings is to reduce deterioration of space resolution in a direction of cone angle of a direct-conversion X-ray detector. Note that problems to be solved by the embodiments disclosed in the present specification and the drawings are not limited to the above problem. Problems corresponding to respective effects obtained by respective components disclosed in the embodiments described later may be regarded as other problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram illustrating one example of a configuration of an X-ray CT apparatus according to a first embodiment; 
         FIG.  2    is a diagram illustrating one example of a configuration of an X-ray detector according to the first embodiment; 
         FIG.  3    is a diagram illustrating one example of a configuration of an X-ray detector according to a comparative example; 
         FIG.  4    is a diagram illustrating one example of a direction of electric field of the X-ray detector according to the first embodiment in detail; 
         FIG.  5    is a flowchart illustrating one example of a flow of detecting an X-ray in the X-ray CT apparatus according to the first embodiment; 
         FIG.  6    is a diagram illustrating one example of a configuration of an X-ray detector according to a second embodiment; 
         FIG.  7    is a diagram illustrating one example of a configuration of an X-ray detector according to a third embodiment; 
         FIG.  8    is a diagram illustrating one example of a configuration of an X-ray detector according to a fourth embodiment; and 
         FIG.  9    is a diagram illustrating another example of a configuration of the X-ray detector according to the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of a direct-conversion X-ray detector, a method of detecting an X-ray, and an X-ray computed-tomography apparatus will be explained in detail, referring to the drawings. 
     First Embodiment 
       FIG.  1    is a diagram illustrating one example of a configuration of an X-ray computed-tomography (CT) apparatus  1  (hereinafter, “X-ray CT apparatus  1 ”) according to a first embodiment. The X-ray CT apparatus  1  may be referred to as radiation diagnostic-imaging apparatus also. 
     As illustrated in  FIG.  1   , the X-ray CT apparatus  1  includes a gantry  10 , a table  30 , a console  40 . 
     In the present embodiment, a rotation axis of a rotation frame  13  in a non-tilted state or a direction of length of a table  33  of the table  30  is defined as Z-axis direction, an axial direction that is orthogonal to the Z-axis direction, and that is horizontal to a floor surface is defined as X-axis direction, and an axial direction that is orthogonal to the Z-axis, and that is perpendicular to the floor surface is defined as Y-axis direction. Although more than one gantry  10  is illustrated in  FIG.  1    for convenience of explanation, only a single unit of the gantry  10  is provided in the actual configuration of the X-ray CT apparatus  1 . 
     The gantry  10  and the table  30  operate based on an operation by a user through the console  40 , or based on an operation by a user through an operating unit arranged in the gantry  10  or the table  30 . The gantry  10 , the table  30 , and the console  40  are connected to one another wiredly or wirelessly so that mutual communication is possible. 
     The gantry  10  is a device including an imaging system that irradiates an X-ray  100  to a subject P, and that collects detection data of the X-ray  100  that has passed through the subject P. More specifically, the gantry  10  includes an X-ray tube  11  (X-ray generating unit), a wedge  16 , a collimator  17 , an X-ray detector  12 , an X-ray high-voltage generator  14 , a data acquisition system (DAS)  18 , the rotation frame  13 , and a controller  15 . 
     The X-ray tube  11  is a vacuum tube that receives application of a high voltage from the X-ray high-voltage generator  14 , and supply of a filament current, and that thereby irradiates thermo electrons from an anode (filament) to a cathode (target), to generate the X-ray  100 . As the thermo electron collides with a target, the X-ray  100  is generated. The X-ray  100  generated at a focal spot in the X-ray tube  11  is shaped into a cone shape, for example, through the collimator  17 , to be irradiated to the subject P. For example, the X-ray tube  11  includes a rotating-cathode X-ray tube that generates an X-ray by irradiating a thermo electron to a rotating cathode. 
     As illustrated in  FIG.  1   , the X-ray  100  irradiated in a cone beam shape is to have a shape spreading in a fan shape in the X-axis direction. Accordingly, an angle indicating the spread in the X-axis direction of the X-ray  100  irradiated in a cone beam shape is referred to as fan angle. Moreover, a depth in the Z-axis direction of the X-ray  100  irradiated in the cone beam shape is referred to as cone angle. Therefore, the X-axis direction is also referred to as fan angle direction, and the Z-axis direction is also referred to as cone angle direction. 
     The X-ray detector  12  detects an X-ray that has been irradiated from the X-ray tube  11  and has passed through the subject P, and outputs an electrical signal corresponding to an amount of the X-ray to the DAS  18 . 
     The X-ray detector  12  has plural rows of detecting devices in which plural detecting devices are aligned in a channel direction along an arc about the focal spot of the X-ray tube  11 . Each of the plural detecting devices detects an incident amount of the X-ray  100 . The X-ray CT apparatus  1  includes various types, such as a rotate/rotate type (third generation CT) in which the X-ray tube  11  and the X-ray detector  12  rotate around the subject P as an integrated unit, and a stationary/rotate type (fourth generation CT) in which many X-ray detecting devices arrayed in a ring shape are fixed, and in which only the X-ray tube  11  rotates around the subject P, and the like, and any type is applicable to the present embodiment. 
     More specifically, the X-ray detector  12  is a direct-conversion X-ray detector that has a semiconductor device converting an incident X-ray into an electric charge. The X-ray detector  12  of the present embodiment includes at least one high voltage electrode, at least one semiconductor device, and plural read electrodes. The semiconductor device is also referred to as X-ray conversion device. 
     Moreover, the X-ray detector  12  includes a potential control device  120  that controls a potential of the high voltage electrode. The potential control device  120  is one example of electric-field forming circuitry in the present embodiment. Details of a configuration of the X-ray detector  12  is described later. 
     Furthermore, the X-ray detector  12  according to the present embodiment may be of energy-integrated collection system, or of photo-counting collection system. 
     The rotation frame  13  supports the X-ray tube  11  and the X-ray detector  12  rotatably about a rotation axis. Specifically, the rotation frame  13  is a ring-shaped frame that supports the X-ray tube  11  and the X-ray detector  12  in an opposing manner, and that rotates the X-ray tube  11  and the X-ray detector  12  by the controller  15  described later. The rotation frame  13  is rotatably supported by a fixing frame that is made from metal, such as aluminum. The rotation frame  13  rotates about the rotation axis at a uniform angular speed, receiving a power from a driving mechanism of the controller  15 . 
     The rotation frame  13  further supports the X-ray high-voltage generator  14  and the DAS  18  in addition to the X-ray tube  11  and the X-ray detector  12 . The rotation frame  13  as described is housed in casing in a substantially cylindrical shape in which an opening (bore) to form imaging space is formed. A center axis of the opening coincides with the rotation axis of the rotation frame  13 . 
     The X-ray high-voltage generator  14  includes an electric circuitry such as a transformer and a rectifier, and includes a high-voltage generating device having a function of generating a high voltage to be applied to the X-ray tube  11  and a filament current to be supplied to the X-ray tube  11 , and an X-ray control device that controls an output voltage according to an X-ray to be irradiated by the X-ray tube  11 . The high-voltage generating device may be of transformer type, or may be of inverter type. The X-ray high-voltage generator  14  may be arranged in the rotation frame  13 , or may be arranged on the fixing frame (not illustrated) side of the gantry  10 . The fixing frame is a frame rotatably supporting the rotation frame  13 . 
     The controller  15  includes a processing circuitry having a central processing unit (CPU) and the like, and a driving mechanism, such as a motor and an actuator. The processing circuitry includes, as hardware resources, a processor, such as a CPU and a microprocessor unit (MPU), and a memory, such as a read-only memory (ROM) and a random access memory (RAM). Moreover, the controller  15  may be implemented by a processor, such as a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a programmable logic device (for example, simple programmable logic device (SPLD), complex programmable logic device (CPLD)), and a field programmable gate array (FPGA). For example, when the processor is CPU, the processor implements a function by reading and executing a program stored in a memory. On the other hand, when the processor is ASIC, instead of storing a program in a memory, the function is directly installed in a circuit of the processor as a logic circuit. Respective processors of the present embodiment are not limited to be configured as a single circuit per processor, but plural independent circuits may be combined as one processor, to implement the function. Furthermore, plural components may be integrated into a single processor, to implement the function. 
     Furthermore, the controller  15  has a function of controlling operation of the gantry  10  and the table  30  by receiving an input signal from an input interface  43  that is attached to the console  40  or the gantry  10 . For example, receiving the input signal, the controller  15  performs control of rotating the rotation frame  13 , a control of tilting the gantry  10 , a control of operating the table  30  and the table  33 . The control of tilting the gantry  10  may be implemented by rotating the rotation frame  13  about an axis parallel to the X-axis direction by the controller  15  based on inclination angle (tilt angle) information input by the input interface  43  attached to the gantry  10 . Moreover, the controller  15  may be arranged in the gantry  10 , or may be arranged in the console  40 . 
     The wedge  16  is a filter to adjust an X-ray dosage of the X-ray  100  irradiated by the X-ray tube  11 . Specifically, the wedge  16  is a filter that attenuates the X-ray  100  irradiated by the X-ray tube  11  as it passes therethrough so that the X-ray  100  to be irradiated to the subject P from the X-ray tube  11  has a predetermined distribution. The wedge  16  is, for example, wedge filter or bow-tie filter, and is a filter formed by processing aluminum to obtain a predetermined target angle or a predetermined thickness. 
     The collimator  17  is a lead plate or the like to narrow the X-ray  100  that has passed through the wedge  16  into an X-ray irradiation range, and forms a slit by combination of plural lead plates or the like. 
     The DAS  18  includes an amplifier that performs amplification processing with respect to an electrical signal output from the respective X-ray detecting devices of the X-ray detector  12 , and an A/D converter that converts an electrical signal into a digital signal, and generates detection data. The detection data generated by the DAS  18  is transferred to the console  40 . Moreover, the DAS  18  is one example of a data collecting unit. 
     In the present embodiment, when simply referring to “detection data”, it signifies both pure raw data that is data detected by the X-ray detector  12  before subjected to the preprocessing, and raw data that is obtained by subjecting the pure raw data to the preprocessing. Note that data before preprocessing (detection data) and data after preprocessing can be denoted as projection data collectively. 
     The table  30  is a device on which the subject P to be scanned is placed and that moves the subject P, and includes a base  31 , a table driving device  32 , the table  33 , and a table supporting frame  34 . The base  31  is a casing that supports the table supporting frame  34  movably in a vertical direction. The table driving device  32  is a motor or an actuator that moves the table  33  on which the subject P is placed in a direction of longitudinal axis of the table  33 . The table driving device  32  moves the table  33  according to a control by the console  40  or the controller  15 . The table  33  arranged on an upper surface of the table supporting frame  34  is a plate on which the subject P is placed. The table driving device  32  may move the table supporting frame  34  in a direction of the longitudinal axis of the table  33 , in addition to the table  33 . 
     The console  40  is a device that performs a control of the gantry  10 , generation of CT image data based on a scan result by the gantry  10 , and the like. The console  40  includes a memory  41  (storage unit), a display  42  (display unit), an input interface  43  (input unit), and processing circuitry  44  (processing unit). Data communication among the memory  41 , the display  42 , the input interface  43 , and the processing circuitry  44  is performed through a bus. 
     The memory  41  is implemented, for example, by a semiconductor memory device, such as a RAM and a flash memory, a hard disk drive (HDD), a solid state drive (SSD), an optical disk, or the like. Moreover, the memory  41  may also be a driving device that reads and writes various kinds of information between a portable storage medium, such as a compact disc (CD), a digital versatile disc (DVD), and a flash memory, and a semiconductor memory, such as a RAM, or the like. The memory  41  stores, for example, projection data and reconstructed image data. Furthermore, a storage area of the memory  41  may be in the X-ray CT apparatus  1 , or may be in an external storage device connected through a network. Moreover, the memory  41  stores a control program according to the present embodiment. Furthermore, the memory  41  is one example of a storage unit. 
     The display  42  displays various kinds of information. For example, the display  42  outputs a medical image (CT image) generated by the processing circuitry  44 , a graphical user interface (GUI) to accept various kinds of operations from an operator, and the like. For example, as the display  42 , a liquid crystal display (LCD), an organic electroluminescence display (OELD), a plasma display, or other arbitrary displays can be used appropriately. Moreover, the display  42  may be arranged in the gantry  10 . The display  42  may be of desktop type, or may be configured with a tablet terminal that can communicate with the console  40  wirelessly, or the like. 
     The input interface  43  accepts various kinds of input operations from an operator, and converts the accepted input operation into an electrical signal, to output to the processing circuitry  44 . For example, the input interface  43  accepts a collection condition when projection data is collected, a reconstruction condition when a CT image is reconstructed, an image processing condition when a post processing image is generated from a CT image, and the like from an operator. As the input interface  43 , for example, a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touch pad, a touch panel display, and the like can be appropriately used. 
     In the present embodiment, the input interface  43  is not limited to ones having a physical operating part, such as a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touchpad, and a touch panel display. For example, processing circuitry of an electrical signal that receives an electrical signal corresponding to an input operation from an external input device arranged separately from the device, and that outputs this electrical signal to the processing circuitry  44  is also included in examples of the input interface  43 . Furthermore, the input interface  43  is one example of an input unit. The input interface  43  may be arranged in the gantry  10 . Moreover, the input interface  43  may be configured with a tablet terminal that is capable of wireless communication with the console  40 . 
     The processing circuitry  44  controls overall operation of the X-ray CT apparatus  1  according to an electrical signal of an input operation output from the input interface  43 . For example, the processing circuitry  44  includes a system control function  441 , a preprocessing function  442 , a reconstruction processing function  443 , a scan control function  444 , an image processing function  445 , and a display control function  446 . For example, respective processing functions performed by the system control function  441 , the preprocessing function  442 , the reconstruction processing function  443 , the scan control function  444 , the image processing function  445 , and the display control function  446 , which are components of the processing circuitry  44  illustrated in  FIG.  1    are stored in the memory  41  in a form of computer-executable program. The processing circuitry  44  is, for example, a processor, and reads respective programs from the memory  41 , and implements functions corresponding to the read programs by executing the programs. In other words, the processing circuitry  44  that has read the respective programs is to have the respective functions illustrated in the processing circuitry  44  in  FIG.  1   . The system control function  441  is one example of a control unit. The preprocessing function  442  is one example of the preprocessing unit. The reconstruction processing function  443  is one example of a reconstruction processing unit. The scan control function  444  is one example of the scan control unit. The image processing function  445  is one example of the image processing unit. The display control function  446  is one example of a display control unit. Moreover, the processing circuitry  44  may be one example of the control unit. 
     Although a case in which the system control function  441 , the preprocessing function  442 , the reconstruction processing function  443 , the scan control function  444 , and the display control function  446  are implemented by a single unit of the processing circuitry  44  is illustrated in  FIG.  1   , but embodiments are not limited thereto. For example, the processing circuitry  44  may be configured by combining plural independent processors, and may implement the respective processing functions by executing the respective programs by the respective processors. Furthermore, the respective processing functions included in the processing circuitry  44  may be implemented by a single or plural processing circuits in a distributed or integrated manner. 
     The system control function  441  controls the respective functions of the processing circuitry  44  based on an input operation accepted from an operator through the input interface  43 . 
     The preprocessing function  442  generates data obtained by subjecting detection data output from the DAS  18  to preprocessing, such as logarithmic conversion processing, offset correction processing, sensitivity correction processing among channels, and beam hardening correction. 
     The reconstruction processing function  443  generates CT image data by performing reconstruction processing using the filtered back-projection method, the successive approximation construction method, and the like with respect to projection data generated by the preprocessing function  442 . 
     The scan control function  444  acquires two-dimensional positioning image data of the subject P to determine a scan range, an imaging condition, and the like. The positioning image data is also referred to as scanno-image data or scout image data. 
     The image processing function  445  converts the CT image data generated by the reconstruction processing function  443  by a publicly known method into tomography data of an arbitrary section or three-dimensional image data based on an input operation accepted from an operator through the input interface  43 . Generation of three-dimensional image may be performed by the reconstruction processing function  443  directly. 
     The display control function  446  causes the display  42  to display the tomography image and the three-dimensional image processed by the image processing function  445 . Moreover, the display control function  446  causes the display  42  to display various kinds of GUI. 
     Next, details of the X-ray detector  12  will be explained. 
       FIG.  2    is a diagram illustrating one example of a configuration of the X-ray detector  12  according to the first embodiment.  FIG.  2    illustrates a state in which the X-ray detector  12  is viewed from the X-axis direction. 
     The X-ray detector  12  includes plural high voltage electrodes  121   a  to  121   e , one semiconductor device  122 , and plural read electrodes  123   a  to  123   e . The plural high voltage electrodes  121   a  to  121   e , the semiconductor device  122 , and the plural read electrodes  123   a  to  123   e  constitute one detection module  124 . The X-ray detector  12  includes plural detection modules  50  in a fan angle direction. The number of the high voltage electrodes  121   a  to  121   e  and the read electrodes  123   a  to  123   e  included in one detection module  124  is not limited to the example illustrated in  FIG.  2   . 
     Hereinafter, when the respective high voltage electrodes  121   a  to  121   e  are not distinguished from one another, it is denoted simply as high voltage electrode  121 . Moreover, the respective read electrodes  123   a  to  123   e  are not distinguished from one another, it is denoted simply as read electrode  123 . 
     Moreover, in an upper part in  FIG.  2   , a graph showing a distribution of potential of the high voltage electrodes  121   a  to  121   e  of each position in the cone angle direction of an X-ray incident on the X-ray detector  12  is illustrated. Because the high voltage electrodes  121   a  to  121   e  have a negative potential, the unit of the vertical axis of the graph is “−V”. 
     In the present embodiment, in one detection module  124 , the plural read electrodes  123   a  to  123   e  and the plural high voltage electrodes  121   a  to  121   e  are respectively aligned in the cone angle direction of the X-ray  100 . 
     In the X-ray detector  12 , the plural detection modules  124  are aligned in a curved shape in the fan angle direction. Therefore, the shape of the X-ray detector  12  is an arc-shaped plane in the fan angle direction. Moreover, the shape of the X-ray detector  12  is a flat plane in the cone angle direction. Therefore, in the X-ray detector  12 , at a portion having a larger cone angle, an incident angle of the X-ray  100  with respect to the semiconductor device  122  is larger. 
     The high voltage electrodes  121   a  to  121   e  are positioned on an incidence side of the X-ray  100  relative to the read electrodes  123   a  to  123   e , and oppose to the read electrodes  123   a  to  123   e . The high voltage electrodes  121   a  to  121   e  are one example of a cathode electrode in the present embodiment. The high voltage electrodes  121   a  to  121   e  are aligned along the cone angle direction of the incident X-ray  100 . 
     The semiconductor device  122  is positioned between the high voltage electrodes  121   a  to  121   e  and the read electrodes  123   a  to  123   e , and converts the X-ray  100  incident from the high voltage electrodes  121   a  to  121   e  side into an electric charge. 
     The read electrodes  123   a  to  123   e  read the electric charge converted from the X-ray  100  by the semiconductor device  122  as an electrical signal. The electrical signal read by the read electrodes  123   a  to  123   e  is amplified by the DAS  18 , to be converted into a digital signal, and is transferred to the console  40  as detection data. The read electrodes  123   a  to  123   e  are one example of an anode electrode in the present embodiment. Reading of an electric charge by the read electrodes  123   a  to  123   e  is also expressed as collection of an electric charge. 
     The high voltage electrodes  121   a  to  121   e  have a negative potential, and the read electrodes  123   a  to  123   e  have a positive potential. By a potential difference between the high voltage electrodes  121   a  to  121   e  and the read electrodes  123   a  to  123   e , the electric charge converted from the X-ray by the semiconductor device  122  moves to the read electrodes  123   a  to  123   e . Between the high voltage electrodes  121   a  to  121   e  and the read electrodes  123   a  to  123   e , an electric field is formed. 
     More specifically, the electric field between the high voltage electrodes  121   a  to  121   e  and the read electrodes  123   a  to  123   e  is formed by a set of electric fields formed by a great number of point charges. A distribution of size and density of the respective point charges determines a direction of the electric field as a whole. 
     Moreover, in the present embodiment, the potential control device  120  controls each of the high voltage electrodes  121   a  to  121   e  such that the high voltage electrode  121  positioned farther from the center (midplane) in the cone angle direction has a higher potential out of the high voltage electrodes  121   a  to  121   e  aligned in the cone angle direction of the incident X-ray  100 . For example, the potential control device  120  applies different voltages to the plural high voltage electrodes  121   a  to  121   e  depending on a position along the cone angle direction, to thereby generate an electric field in a direction based on a cone angle. The potential control device  120  receives a supply of power from a power source device not illustrated. 
     As illustrated in  FIG.  2   , a potential of the high voltage electrode  121   c  positioned at a center of the cone angle direction is the lowest, and a potential of the high voltage electrode  121   a  and the high voltage electrode  121   e  positioned at end portions in the cone angle direction are the highest. 
     Specific values of potential of the plural high voltage electrodes  121   a  to  121   e  are not particularly limited, but are determined according to a length of the Z-axis direction of the X-ray detector  12 , the size of the cone angle of the X-ray  100 , and the like. The polarity of the high voltage electrodes  121   a  to  121   e , the number of the high voltage electrodes  121   a  to  121   e , and the like may be changed according to characteristics of the X-ray detector  12 . 
     Note that even the potential of the high voltage electrodes  121   a  and  121   e  that are the highest among the plural high voltage electrodes  121   a  to  121   e  is lower than a potential of the read electrodes  123   a  to  123   e . Moreover, the potentials of the plural high voltage electrodes  121   a  to  121   e  are uniform. 
     Specifically, the direction of the electric field between the high voltage electrodes  121   a  to  121   e  and the read electrodes  123   a  to  123   e  is a direction straight ahead from the high voltage electrode  121   c  toward the read electrode  123   c  in a center area in the cone angle direction of the X-ray detector  12 . Moreover, the direction of the electric field is directed more toward the opposite side to the center of the cone angle direction of the X-ray detector  12  at a position farther away from the center of the cone angle direction of the X-ray detector  12 . Therefore, the direction of the electric field between the high voltage electrodes  121   a  to  121   e  and the read electrodes  123   a  to  123   e  is to be a direction based on the cone angle of the X-ray  100 . Because an electric charge moves along a direction of an electric field, the electric charge converted from the X-ray  100  by the semiconductor device  122  moves toward the read electrodes  123   a  to  123   e  along a direction based on the cone angle of the X-ray  100 . 
     The direction of the electric field between the high voltage electrodes  121   a  to  121   e  and the read electrodes  123   a  to  123   e  is inclined so as to spread symmetrically toward the both end portions with respect to a center in the cone angle direction straight from the X-ray tube  11 . The direction of the electric field may be not completely equal to the cone angle of the X-ray  100 , as long as at least the direction of inclination is the same. 
     For example, an electric charge converted from the X-ray  100  from the X-ray tube  11  traveling straight and incident on the high voltage electrode  121   c  of the X-ray detector  12  continues to travel straight along the direction of the electric field, and moves to the read electrode  123   c . In this case, the electric charge converted from the X-ray  100  incident on the high voltage electrode  121   c  is read as an electrical signal from the read electrode  123   c . Moreover, an electric charge converted from the X-ray  100  incident on the high voltage electrode  121   e  moves diagonally along the direction of the electric field, and moves to the read electrode  123   e . Therefore, the electric charge converted from the X-ray  100  incident on the same high voltage electrode  121  is read by the same read electrode  123 . 
     A relationship between a direction of an electric field and reading of an electric charge will be explained in detail by using  FIG.  3    and  FIG.  4   . 
     First, a configuration of a general X-ray detector will be explained as a comparative example. 
       FIG.  3    is a diagram illustrating an example of a configuration of an X-ray detector  5  according to a comparative example.  FIG.  3    illustrates a state in which a part of the X-ray detector  5  according to the comparative example is viewed from the X-axis direction. A right side in  FIG.  3    is a center side in a cone angle direction in the X-ray detector  5 , and a left side in  FIG.  3    is an end portion side. 
     The X-ray detector  5  according to the comparative example includes a high voltage electrode  51 , a semiconductor device  52 , and plural read electrodes  53   a  to  53   g . A set of the high voltage electrode  51 , the semiconductor device  52 , and the plural read electrodes  53   a  to  53   g  is referred to as one detection module  50 . The X-ray detector  5  includes plural units of the detection modules  50 . When the respective read electrodes  53   a  to  53   g  are not particularly distinguished from one another, it is denoted simply as read electrode  53 . 
     In the present comparative example, in one detection module  50 , a single unit of high voltage electrode  51  is included. In the high voltage electrode  51  in the present comparative example, there is no potential difference in the cone angle direction, and it is constant. Therefore, the direction of the electric field between the high voltage electrode  51  and the plural read electrodes  53   a  to  53   g  is straight from the high voltage electrode  51  toward the read electrodes  53   a  to  53   g.    
     X-rays  100   a  to  100   c  incident on the high voltage electrode  51  are converted into an electric charge by the semiconductor device  52 , but because a position in the Y-axis direction of the semiconductor device  52  at which the X-ray  100   a  to  100   c  are absorbed is statistically random, the control is difficult. 
     For example, in the example illustrated in  FIG.  3   , the X-ray  100   b  incident on the high voltage electrode  51  is absorbed in a first area  521  or a second area  522  of the semiconductor device  52 . Out of the X-ray  100   b , an electric charge converted from a portion absorbed in the first area  521  of the semiconductor device  52  moves to the read electrode  53   d  along a direction of the electric field, and is read from the read electrode  53   d . Moreover, out of the X-ray  100   b , an electric charge converted from a portion absorbed in the second area  522  of the semiconductor device  52  moves to the read electrode  53   c  along the direction of the electric field, and is read from the read electrode  53   c . That is, in the comparative example, a part of the electric charges converted from the X-ray  100   b  incident on the same position in the high voltage electrode  51  is read from the read electrode  53   d , and another part thereof is read by the read electrode  53   c  adjacent to the read electrode  53   d . Similarly, electric charges converted from the X-rays  100   a ,  100   c  incident on another position of the high voltage electrode  51  are read separately by the plural adjacent read electrodes  53 . 
     Generally, as the reconstruction theory of the detected X-ray  100 , it is regarded that the X-ray  100  has entered at a position on a surface of the semiconductor device  52  where the X-ray  100  has entered. However, in the case of oblique incidence of the X-ray  100 , the X-ray  100  can be absorbed, not limited to the semiconductor device  52  where the X-ray  100  has entered, but also by another semiconductor device adjacent thereto. This can cause deterioration of space resolution in the cone angle direction of the X-ray detector  5 , and it can be factor in degradation of image quality of X-ray image data. Particularly, because the X-ray conversion device that is used in the direct-conversion X-ray detector that directly converts the X-ray  100  into an electric charge is generally thicker than the X-ray conversion device that is used in the indirect conversion X-ray detector, it is more likely to be affected by oblique incidence of an X-ray. 
     On the other hand, in the X-ray detector  12  of the present embodiment, the direction of the electric field between the high voltage electrode  121  and the read electrode  123  is inclined along the cone angle of the X-ray  100 , unlike the X-ray detector  5  of the comparative example. Accordingly, when the X-ray  100  enters the X-ray detector  12  obliquely, an electric charge converted from the X-ray  100  obliquely incident moves in the same direction as the X-ray  100  obliquely incident. 
       FIG.  4    is a diagram illustrating one example of a direction of the electric field of the X-ray detector  12  according to the first embodiment in detail. A right side in  FIG.  4    is a center side in the cone angle direction in the X-ray detector  12 , and a left side in  FIG.  4    is an end portion side. 
     The number of the high voltage electrode  121  and the read electrode  123  included in the detection module  124  of the X-ray detector  12  illustrated in  FIG.  4    differ from those in the example illustrated in  FIG.  2   , but the detection modules  124  illustrated in  FIG.  2    and  FIG.  4    are both one example, and the number of the high voltage electrode  121  and the read electrode  123  is not limited thereto. 
     As illustrated in  FIG.  4   , in the X-ray detector  12  according to the first embodiment, an electric charge moves obliquely in the same direction as the cone angle of the X-ray  100  by the inclination of the direction of the electric field between the high voltage electrodes  121   a  to  121   g  and the read electrodes  123   a  to  123   g.    
     For example, the X-ray  100   b  incident on the high voltage electrode  121   d  is absorbed in an area  1221  of the semiconductor device  122 . The X-ray  100   b  absorbed in the area  1221  of the semiconductor device  122  is converted in to an electric charge by the semiconductor device  122 . The electric charge converted from the X-ray  100   b  moves in a direction apart from the center along the direction of the electric field, and is read by the read electrode  123   c . In the X-ray detector  12  of the present embodiment, an electric charge based on the X-ray  100   b  incident on the high voltage electrode  121   d  is all read by the read electrode  123   c  regardless of a position in a depth direction of the semiconductor device  122  at which it is absorbed. 
     Furthermore, an electric charge based on the X-ray  100   a  incident on the high voltage electrode  121   c  is all read by the read electrode  123   b . An electric charge based on the X-ray  100   c  incident on the high voltage electrode  121   e  is all read by the read electrode  123   d . That is, in the X-ray detector  12  of the present embodiment, out of the high voltage electrodes  121   a  to  121   g  included in the detection module  124 , an electric charge based on the X-ray  100  incident on the same high voltage electrode  121  is read by the same read electrode  123 . Moreover, as illustrated in  FIG.  4   , the X-ray  100  incident on the high voltage electrode  121  is read by the read electrode  123  that is present at a position shifted toward a direction apart from the center position of the X-ray detector  12  along the cone angle direction (Z-axis direction) from the incident position on the high voltage electrode  121 . The gap between the incident position and the read electrode  123  changes according to a size of the cone angle and the incident position. The read electrode  123  is arranged at a position, considering the position gap. In  FIG.  4   , the read electrodes  123   b  to  123   d  are arranged in one to one correspondence respectively with the high voltage electrodes  121   c  to  121   e , but this configuration is one example, and the relationship between the read electrodes  123   b  to  123   d  and the high voltage electrodes  121   c  to  121   e  is not necessarily required to be in one to one correspondence. 
     In other words, projection data based on an electric charge read by the read electrode  123   c  is based on the X-ray  100   b  incident on the X-ray detector  12  from the position of the high voltage electrode  121   d . As for projection data based on an electric charge read by the other read electrode  123  also, it is possible to uniquely identify which one of the X-ray  100  that has entered from which position of which one of the high voltage electrodes  121  in the X-ray detector  12  it is based on. 
     Therefore, when the reconstruction processing function  443  of the processing circuitry  44  reconstructs projection data, the reconstruction processing can be performed according to the actual correspondence between the high voltage electrodes  121   a  to  121   g  and the read electrodes  123   a  to  123   g.    
     Next, a flow of detection of the X-ray  100  in the X-ray CT apparatus  1  of the present embodiment configured as described above will be explained. 
       FIG.  5    is a flowchart illustrating an example of a flow of detection of the X-ray  100  in the X-ray CT apparatus  1  according to the first embodiment. The flow of processing in this flowchart is common between imaging for positioning and real imaging. The processing of this flowchart is performed when an operation of starting imaging is performed through the input interface  43  of the console  40  by a technician or the like, for example, in a state in which the subject P is placed on the table  33 . Moreover, in explanation of  FIG.  5   , the configuration of the X-ray detector  12  explained in  FIG.  2    is explained as an example. 
     First, the potential control device  120  controls the respective high voltage electrodes  121   a  to  121   e  such that a potential is higher in the high voltage electrode  121  farther away from the center in the cone angle direction out of the high voltage electrodes  121   a  to  121   e  included in the respective plural detection modules  124  in the X-ray detector  12 . Furthermore, the potential control device  120  controls potentials of the read electrodes  123   a  to  123   e  included respectively in the plural detection modules  124  in the X-ray detector  12  (S 1 ). 
     By such a potential control, the direction of the electric field between the high voltage electrodes  121   a  to  121   e  and the read electrodes  123   a  to  123   e  is to be a direction spreading toward the both end portions from the center of the X-ray detector  12  similarly to the cone angle of the X-ray  100 . 
     The potentials of the read electrodes  123   a  to  123   e  included respectively in the plural detection modules  124  are all uniform positive potential. Because the potential of the read electrodes  123  is uniform, it may be configured to maintain the same potential all the time without being controlled by the potential control device  120 . 
     The X-ray tube  11  generates the X-ray  100  by receiving application of a high voltage from the X-ray high-voltage generator  14 , and supply of a filament current. The X-ray  100  generated at the focal spot in the X-ray tube  11  is shaped into a cone beam through, for example, the collimator  17 , to irradiated to the subject P. Moreover, the rotation frame  13  rotates around the subject P in a state holding the X-ray tube  11  and the X-ray detector  12  (S 2 ). 
     The X-ray  100  irradiated from the X-ray tube  11  enters the X-ray detector  12 . The semiconductor device  122  of the X-ray detector  12  converts the incident X-ray  100  into an electric charge (S 3 ). 
     The respective read electrode  123   a  to  123   e  corresponding to the high voltage electrodes  121   a  to  121   e  read the electric charge converted from the X-ray  100  as an electrical signal (S 4 ). 
     The DAS  18  amplifies the electrical signal read by the read electrode  123  of the X-ray detector  12 , and then A/D converts it into a digital signal (S 5 ). 
     The DAS  18  transfers the signal converted in to a digital signal to the console  40  as detection data (S 6 ). At this point, the processing of this flowchart ends. In this flowchart, illustration of the preprocessing, the reconstruction processing, and the like of the detection data performed by the console  40  is omitted. 
     As described, the X-ray detector  12  of the present embodiment includes the plural read electrodes  123  that are aligned in the cone angle direction of the incident X-ray  100 , the plural high voltage electrodes  121  that are positioned on the incidence side of the X-ray  100  relative to the plural read electrodes  123 , and that oppose to the read electrodes  123 , and the potential control device  120  that forms an electric field in a direction based on the cone angle between the plural read electrodes  123  and the read electrode  123 . Therefore, according to the X-ray detector  12  of the present embodiment, by reducing phenomenon in which the X-ray  100  incident on the same position are read by the different read electrodes  123 , deterioration of space resolution in the cone angle of the X-ray detector  12  can be reduced. 
     More specifically, according to the X-ray detector  12  of the present embodiment, because the X-ray  100  incident on the same position is read by the same read electrode  123 , it is possible to match the incident position in the reconstruction theory and an actual incident position when projection data based on the detection data read by the read electrode  123  is reconstructed, and deterioration of space resolution in the cone angle of reconstructed CT image data can be reduced. 
     As another method of reducing deterioration of space resolution in the cone angle, there is a comparative example in which the detection module is arranged to be an alignment of smaller modules, and a plane is directed to the X-ray incident direction in a unit of each small module. In this case, each of the small modules can be directed to a direction according to the cone angle direction. However, by adopting this structure, scatter rays originated from the structure of the small modules can occur or the like, to deteriorate the image quality. On the other hand, according to the X-ray detector  12  of the present embodiment, because measures against the oblique incidence of an X-ray is prepared while configuring the X-ray detector  12  on the same plane, deterioration of space resolution caused by scatter rays can be reduced compared to the comparative example. 
     Moreover, the potential control device  120  of the X-ray detector  12  of the present embodiment applies different voltages to the plural high voltage electrodes  121   a  to  121   e  depending on a position along the cone angle direction, and thereby generates an electric field in a direction based on the cone angle. Therefore, according to the X-ray detector  12  of the present embodiment, by adjusting a distribution of potential of the plural high voltage electrodes  121   a  to  121   e , the direction of the electric field between the high voltage electrodes  121   a  to  121   e  and the high voltage electrodes  121   a  to  121   e  can be changed according to the cone angle. 
     Furthermore, the method performed in the X-ray detector  12  of the present embodiment includes a potential control step of controlling respective potentials of the high voltage electrodes  121   a  to  121   e  such that the potential becomes higher as it is farther away from the center of the cone angle among the plural high voltage electrodes  121   a  to  121   e  included in the X-ray detector  12 , and a reading step of reading an electric charge that is converted from the X-ray  100  by the respective plural read electrodes  123   a  to  123   e  corresponding to the plural high voltage electrodes  121   a  to  121   e  aligned in the cone angle direction of the X-ray  100 . Therefore, according to the X-ray detector  12  of the present embodiment, by reading an electric charge converted from the X-ray  100  incident on a position of the corresponding high voltage electrodes  121   a  to  121   e  by the plural read electrodes  123   a  to  123   e , it is possible to easily identify which one of the X-ray  100  that has entered from which position in the cone angle direction the electric charge that has been read by the respective read electrodes  123   a  to  123   e  is based on. 
     In the present embodiment, the potential control device  120  controls respective potentials of the plural high voltage electrodes  121  included in the X-ray detector  12 , but the control is not limited thereto. For example, the X-ray high voltage generator  14 , the controller  15 , or the processing circuitry  44  of the console  40  may control the respective potentials of the plural high voltage electrodes  121 . For example, the system control function  441  of the processing circuitry  44  may have a function of controlling the respective potentials of the high voltage electrodes  121 . 
     The method of adjusting a potential distribution of the high voltage electrodes  121   a  to  121   e  is not limited to the voltage control by the potential control device  120 . For example, a resistor of different value may be provided for each of the high voltage electrodes  121   a  to  121   e . In this case, it is not necessary for the potential control device  120  to perform individual controls for the high voltage electrodes  121   a  to  121   e . For example, the potential control device  120  simply applies a uniform voltage to the high voltage electrodes  121   a  to  121   e . Alternatively, the X-ray detector  12  may be configured without the potential control device  120 , and the power source device may apply a uniform voltage to the high voltage electrodes  121   a  to  121   e . When such a configuration is applied, the potential control device  120  or the power source device, and the resistors arranged in each of the high voltage electrodes  121   a  to  121   e  are one example of the electric-field forming circuitry. 
     Second Embodiment 
     In the first embodiment described above, the X-ray detector  12  is provided with the plural high voltage electrodes  121   a  to  121   e  in each of the detection module  124 . On the other hand, in a second embodiment, by providing a second electrode that is different from a high voltage electrode positioned on a surface of the semiconductor device  122 , the direction of an electric field is adjusted to a direction along a cone angle. 
       FIG.  6    is a diagram illustrating an example of a configuration of an X-ray detector  12  according to the second embodiment. As illustrated in  FIG.  2   , the X-ray detector  12  of the present embodiment includes a single unit of high voltage electrode  1121 , a single unit of semiconductor device  122 , the plural read electrodes  123   a  to  123   e , and a single unit of second electrode  125  in one detection module  124 . The X-ray detector  12  includes the plural detection modules  50  in the fan angle direction. The number of the read electrodes  123   a  to  123   e  and the second electrode  125  included in one detection module  124  is not limited to the example illustrated in  FIG.  6   . When distinguishing from the second electrode  125 , the high voltage electrode  1121  may be referred to as a first electrode. 
     In the present embodiment, a single unit of the high voltage electrode  1121  is included in each of the detection modules  124 . Therefore, the high voltage electrode  1121  has a negative potential uniform in the cone angle direction. In the present embodiment, the potential control device  120  simply applies a predetermined voltage to the high voltage electrode  1121 . Alternatively, the X-ray detector  12  is configured without the potential control device  120 , and the power source device may apply a predetermined voltage to the high voltage electrode  1121 . 
     The second electrode  125  is an electrode having a negative potential, and is arranged at a position overlapping the high voltage electrode  1121  in the incident direction of the X-ray  100  in at least a part of an area in the cone angle direction of the X-ray  100 . A value of potential of the second electrode  125  is not particularly limited, but is lower than the potential of the high voltage electrode  1121 . The high voltage electrode  1121  and the second electrode  125  are one example of the cathode electrode in the present embodiment. 
     Furthermore, in the present embodiment, a partial area in which the high voltage electrode  1121  and the second electrode  125  overlap is an area near the center of the cone angle as illustrated in  FIG.  6   . Therefore, as shown in a graph in  FIG.  6   , the potential of the cathode electrode near the center in the cone angle direction is lower than potentials of both ends in the cone angle direction. 
     Accordingly, in the present embodiment also, because of the potential difference in the cone angle direction, a direction of an electric field between the high voltage electrode  1121  and the plural read electrodes  123   a  to  123   e  is inclined so as to spread toward both end portions, similarly to the cone angle of the X-ray  100 . That is, in the present embodiment also, the X-ray  100  incident on the same position in the high voltage electrode  1121  is read by the same read electrode  123  regardless of a position in a depth direction of the semiconductor device  122  at which it is absorbed. 
     As described, according to the X-ray detector  12  of the present embodiment, by providing plural cathode electrodes in the incident direction of the X-ray  100  in at least a part of the area in the cone angle direction, effects similar to the first embodiment can be obtained. Moreover, in the X-ray detector  12  of the present embodiment, because it is not necessary to provide plural units of high voltage electrodes in each of the detection module  124 , increase in the number of parts can be suppressed. 
     Modification of Second Embodiment 
     Moreover, in the partial area in which the high voltage electrode  1121  and the second electrode  125  overlap may be the both ends portion in the cone angle direction. In this case, the second electrode  125  has, for example, a positive potential. Because the second electrode  125  makes the potential at the both end portions in the cone angle direction relatively high with respective to the center, the direction of the electric field between the high voltage electrode  1121  and the plural read electrodes  123   a  to  123   e  is inclined so as to spread toward the both end portions, similarly to the cone angle of the X-ray  100 . 
     Moreover, the number of the second electrode  125  is not limited to one or two, but it may be three or more. 
     Third Embodiment 
     In the second embodiment described above, the second electrode  125  is arranged overlapping the high voltage electrode  1121 . On the other hand, in a third embodiment, the X-ray detector  12  includes other electrodes at positions not overlapping the high voltage electrode  1121 . 
       FIG.  7    is a diagram illustrating an example of a configuration of the X-ray detector  12  according to the third embodiment. AS illustrated in  FIG.  7   , the X-ray detector  12  of the present embodiment includes a single unit of the high voltage electrode  1121  and a single unit of the semiconductor device  122 , the plural read electrodes  123   a  to  123   e , a single unit of a third electrode  126 , and a single unit of a fourth electrode  127  in one detection module  124 . The x-ray detector  12  includes plural units of the detection modules  50  in the fan angle direction. 
     The number of the read electrodes  123   a  to  123   e  included in one detection module  124  is not limited to the example in  FIG.  6   . Moreover, in  FIG.  2   , the X-ray detector  12  includes two additional electrodes, which are the third electrode  126  and the fourth electrode  127 , the number of additional electrode is not limited to two. For example, the number of the additional electrode is one or more. 
     The third electrode  126  and the fourth electrode  127  are arranged at positions not overlapping the high voltage electrode  1121  and the read electrodes  123   a  to  123   e  in the cone angle direction. 
     The third electrode  126  and the fourth electrode  127  have a positive potential. Therefore, as shown in a graph in  FIG.  7   , the potentials in the high voltage electrode  1121  near the center in the cone angle direction, the third electrode  126 , and the fourth electrode  127  are lower than the potential of the both end portion in the cone angle direction. Therefore, the direction of the electric field between the high voltage electrode  1121  and the read electrodes  123   a  to  123   e  tilts as it is pulled toward the both end portions. 
     By such a configuration, in the present embodiment also, by a potential difference in the cone angle direction, the direction of the electric field between the high voltage electrode  1121  and the read electrodes  123   a  to  123   e  has an inclination so as to spread toward the both end portions, similarly to the cone angle of the X-ray  100 . 
     As described, according to the X-ray detector  12  of the present embodiment, by providing the third electrode  126  and the fourth electrode  127  at positions not overlapping the high voltage electrode  1121  and the read electrodes  123   a  to  123   e  in the cone angle direction, effects similar to those of the first embodiment can be obtained. Moreover, in the X-ray detector  12  of the present embodiment also, because it is not necessary to provide plural units of high voltage electrodes in each of the detection modules  124 , increase in the number of parts can be suppressed. 
     Fourth Embodiment 
     In the second and the third embodiments described above, the X-ray detector  12  includes the second electrode  125 , the third electrode  126 , or the fourth electrode  127  different from the high voltage electrode  1121  that is positioned on a surface of the semiconductor device  122 , but in the fourth embodiment, the direction of the electric field is adjusted by proving a dielectric between the high voltage electrode  1121  and the semiconductor device  122 . 
       FIG.  8    is a diagram illustrating an example of a configuration of the X-ray detector  12  according to the fourth embodiment. As illustrated in  FIG.  8   , the X-ray detector  12  of the present embodiment includes a single unit of the high voltage electrode  1121 , a single unit of the semiconductor device  122 , plural units of the read electrodes  123   a  to  123   e , and a single unit of a dielectric  128  in each of the detection module  124 . The X-ray detector  12  includes plural units of the detection modules  50  in the fan angle direction. 
     The dielectric  128  has a shape that becomes thicker as it departs away from the center of the cone angle direction of the X-ray detector  12 . In the example illustrated in  FIG.  8   , the dielectric  128  has a wedge-shaped concave portion that symmetrically becomes thicker toward end portions from a center in the cone angle direction of the X-ray detector  12 . 
     Because the dielectric  128  serves as a resistor of the electric field between the high voltage electrode  1121  and the read electrodes  123   a  to  123   e , the electric field is weakened at a position at which the dielectric  128  is thicker. Therefore, in the center in the cone angle direction of the X-ray detector  12 , an electric charge straight from the high voltage electrode  1121  to the read electrodes  123   c  is to move obliquely in a direction away from the center as it approaches the end portion in the cone angle direction. In other words, the dielectric  128  deforms the electric field to have an orientation based on the cone angle. In the present embodiment, the potential control device  120  simply applies a predetermined voltage to the high voltage electrode  1121 . Alternatively, the X-ray detector  12  may be configured without the potential control device  120 , and the power source device may apply a predetermined voltage to the high voltage electrode  1121 . The potential control device  120  or the power source device, and the dielectric  128  are one example of the electric-field forming circuitry in the present embodiment. Alternatively, formation of an electric field includes deformation of an electric field, and the dielectric  128  alone may be one example of the electric-field forming circuitry in the present embodiment. 
     By such a configuration, in the present embodiment also, the direction of the electric field between the high voltage electrode  1121  and the read electrodes  123   a  to  123   e  is inclined so as to spread toward both end portions, similarly to the cone angle of the X-ray  100 . 
     As described, according to the X-ray detector  12  of the present embodiment, because the dielectric  128  that becomes thicker as it departs away from the center in the cone angle direction is provided between the high voltage electrode  1121  and the semiconductor  122 , effects similar to the first embodiment can be obtained. 
     Moreover, in the X-ray detector  12  of the present embodiment, because it is not necessary to provide the plural high voltage electrodes  121   a  to  121   e , the second electrode  125 , the third electrode  126 , the fourth electrode  127 , or the like, a high voltage supply system can be a single system, and it contributes to reduction in the number of parts and simplification of the control. 
     The shape of the dielectric  128  is not limited to the example illustrated in  FIG.  8   .  FIG.  9    is a diagram illustrating an example of a configuration of the X-ray detector  12  according to the fourth embodiment. As illustrated in  FIG.  9   , a dielectric  1128  may have a shape in which both surfaces are recessed in a hyperbolic form like a concave lens. In this case also, the dielectric  1128  has a shape in which it becomes thicker as it departs away from the center in the cone angle direction. 
     First Modification of First to Fourth Embodiments 
     In the respective embodiments described above, the X-ray detector  12  included in the X-ray CT apparatus  1  is cited as one example of the direct-conversion X-ray detector, but the direct-conversion X-ray detector is not limited thereto. For example, a flat panel detector (FPD) may be one example of the direct-conversion X-ray detector. 
     Second Modification of First to Fourth Embodiments 
     Furthermore, in  FIG.  2   ,  FIG.  6    to  FIG.  9    of the respective embodiments described above, the high voltage electrodes  121   a  to  121   e ,  1121  are illustrated above and the read electrodes  123   a  to  123   e  are illustrated below, but a positional relationship between the high voltage electrodes  121   a  to  121   e ,  1121  and the read electrodes  123   a  to  123   e  is not limited thereto. For example, the read electrode may be positioned above and the high voltage electrode may be positioned below. 
     Various kinds of data handled in the present specification are typically digital data. 
     According to at least one of the embodiments explained above, deterioration of space resolution in a cone angle direction of a direct-conversion X-ray detector can be reduced. 
     Some embodiments have been explained, but these embodiments are presented as an example, and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various kinds of omission, replacement, changes, and combination of the embodiments are possible within a range not departing a gist of the present invention. These embodiments and their modifications are included in the scop and the gist of the invention, and are, similarly, included in the scope of the invention described in claims and their equivalents. 
     Regarding the embodiments above, following notes are disclosed as one aspect of the invention and selective characteristics thereof.