Abstract:
An X-ray imaging apparatus includes an X-ray irradiating unit configured to irradiate an X-ray to an object, an X-ray detecting unit configured to detect the irradiated X-ray, an image creating unit configured to create X-ray image data based on data detected by the X-ray detecting unit, a moving mechanism configured to move the X-ray detecting unit to the object, a capacitance sensing unit, including an electrode which is positioned so as to cover at least part of a detection plane of the X-ray detecting unit, configured to obtain a capacitance value of the X-ray detecting unit by the electrode and a distance measurement unit configured to measure a distance between the object and the X-ray detecting unit based on the capacitance value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-349433 filed on Oct. 8, 2003, the entire contents of which are incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates generally to an X-ray imaging apparatus and a method for moving X-ray detector. 
   BACKGROUND 
   Generally, an angio X-ray imaging apparatus includes an X-ray generating part, an X-ray detecting part, a supporting part which supports the X-ray generating part and the X-ray detecting part, a bed and a processor, for example. The supporting part is a C-arm or an Ω-arm, for example, and the supporting part moves such that images of a patient are obtained from several angles or positions. 
   As a detector of the detecting part, an X-ray film or an I.I. (Image Intensifier) is used, for example. In an imaging of the I.I., an X-ray tube of the X-ray generating part irradiates an X-ray to the patient, and the I.I. transfers the X-ray penetrated through the patient into an optical image. The optical image is changed to electric signals by an X-ray TV camera. The electric signals are converted by A/D converter and are displayed on a monitor as an X-ray image. In an imaging of the film, it is impossible to display the X-ray image in real time, however in the imaging of the I.I., a real time imaging can be performed. In addition, digital signals are obtained, several image processes can be performed. Recently, in stead of the I.I., a X-ray flat panel detector (referred to as a flat panel detector below) which has detection elements arranged in two dimension is developed. 
   It is required that an imaging part including the X-ray generating part and the X-ray detecting part speedily moves in a wide range in order to move the C-arm according to a flow of a contrast agent in a blood vessel. 
   In this case, in order to obtain clear image data, it is required to arrange the flat panel detector in a predetermined position close to a surface of a body of the patient surface, and when the flat panel detector contacts the body of the patient, a movement of the X-ray detecting part stops by using a contact type sensor as one method. 
   However, in this method, it is difficult to stop the X-ray detecting part quickly, and the patient may be contacted-to the X-ray detecting part. 
   Therefore, non-contact type capacitance sensor is used, recently. 
   In this method, the capacitance sensor is attached around the flat panel detector of the X-ray detecting part. Using information of the capacitance which changes according to a position of the patient, a distance of the patient&#39;s body surface and the flat panel detector is measured. Based on information of the measured distance, speed of the movement of the X-ray detecting part is slowed down gradually, and the X-ray detecting part stops at a predetermined position near the patient. In this method, it is possible to move the X-ray detecting part at high speed to a position close to the patient&#39;s body surface, and efficiency for diagnosis improves. And it is possible to obtain an image even if the flow of the blood is fast. 
   However, In the method using an above-mentioned capacitance sensor, even if the distance between the flat panel detector and the patient&#39;s body surface is constant, a value of the measured capacitance changes according to a shape, sex, age, degree of obesity, etc. of the patient. For this reason, it is difficult to stop the flat panel detector at a desired position, since the distance between the flat panel detector to be stopped and the patient body surface is different by each patient. 
   Regarding the problem caused by the above-mentioned patient&#39;s shape, first, by presuming the patient&#39;s surface based on change of the value of the capacitance according to the movement of the X-ray detecting part. Thereafter, the value of the capacitance to be measured is corrected based on the presumed patient&#39;s surface. Thereby, X-ray detecting part can be positioned at a desired position. The technique is disclosed in Japanese Patent Publication (Kokai) No. 2001-241910 (pp 4–7 and FIG. 1 to 9). 
   In this method, it is possible to set the X-ray detecting part at a appropriate position automatically by correcting the value of the capacitance measured even if the shape of the patient&#39;s body surface differs. However, since this method is complex, it is difficult to correct the value of the capacitance, constantly. Or, since the capacitance sensor is attached around the X-ray detecting part, an electromagnetic field formed is not be uniformed to the patient&#39;s body surface. When the surface of the patient is an odd-shaped, it is difficult to measure the distance between the patient and the X-ray detecting part correctly. 
   Further, in this method, it is also difficult to correct the value of the capacitance caused by error factors other than the patient&#39;s shape, the X-ray detecting part does not stop at a desired position. 
   SUMMARY 
   One object of the present invention is to ameliorate at least one problem described above. 
   According to one aspect of the present invention, there is provided an X-ray imaging apparatus includes an X-ray irradiating unit configured to irradiate an X-ray to an object, an X-ray detecting unit configured to detect the irradiated X-ray, an image creating unit configured to create X-ray image data based on data detected by the X-ray detecting unit, a moving mechanism configured to move the X-ray detecting unit to the object, a capacitance sensing unit, including an electrode which is positioned so as to cover at least part of a detection plane of the X-ray detecting unit, configured to obtain a capacitance value of the X-ray detecting unit by the electrode and a distance measurement unit configured to measure a distance between the object and the X-ray detecting unit based on the capacitance value. 
   According to another aspect of the present invention, there is provided an X-ray imaging apparatus includes an X-ray irradiating unit configured to irradiate an X-ray to an object, an X-ray detecting unit configured to detect the irradiated X-ray, an image creating unit configured to create X-ray image data based on data detected by the X-ray detecting unit, a moving mechanism configured to move the X-ray detecting unit to the object, a capacitance sensing unit configured to obtain a capacitance value of the X-ray detecting unit by the electrode, an environment sensing unit configured to obtain environment information around the object, a capacitance correction unit configured to correct the capacitance value based on the environment information and a distance measurement unit configured to measure a distance between the object and the X-ray detecting unit based on the corrected capacitance value. 
   According to another aspect of the present invention, there is provided an X-ray imaging apparatus includes an X-ray irradiating unit configured to irradiate an X-ray to an object, an X-ray detecting unit configured to detect the irradiated X-ray, an image creating unit configured to create X-ray image data based on data detected by the X-ray detecting unit, a moving mechanism configured to move the X-ray detecting unit to the object, a capacitance sensing unit configured to obtain a capacitance value of the X-ray detecting unit by the electrode, an input device configured to input information of the object, a capacitance correction unit configured to correct the capacitance value based on the object information and a distance measurement unit configured to measure a distance between the object and the X-ray detecting unit based on the corrected capacitance value. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the detailed description when considered in connection with the accompanying drawings. In the drawings: 
       FIG. 1  is block diagram of an X-ray imaging apparatus according to an embodiment; 
       FIG. 2  is a block diagram of a flat panel detector according to the embodiment; 
       FIGS. 3  is an illustration for explaining movement direction of the flat panel detector according to the embodiment; 
       FIG. 4  is a block diagram of a sensor and a distance detection part; and 
       FIGS. 5A and 5B  are graphs for explaining a measurement method of a value of capacitance according to the embodiment; 
       FIG. 6  is a flow chart for explaining an operation of position setting of the flat panel detector according to the embodiment; 
       FIGS. 7A and 7B  are a cross sectional view and a perspective view of a capacitance sensor according to the embodiment; and 
       FIG. 8A through 8C  are a cross sectional view, a perspective view and a top view of the capacitance sensor. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Hereafter, with reference to drawings, an embodiment is explained below. 
   In this embodiment, a capacitance sensor is a sheet shaped, and the capacitance sensor covers an X-ray detection plane of the flat panel detector. 
   Furthermore, in this embodiment, when the distance between the X-ray detection plane and the patient&#39;s body surface is presumed, a predetermined correction value corresponding to the patient&#39;s shape, age, sex and degree of obesity is applied to the value of the capacitance which is previously measured, and the presumption of the distance is performed based on the corrected value of the capacitance. 
   An X-ray imaging apparatus is explained, referring to  FIG. 1  through  FIG. 5 .  FIG. 1  shows a block diagram of the X-ray imaging apparatus. 
   The X-ray imaging apparatus  100  shown in  FIG. 1  includes an X-ray generating part  1  which irradiates an X-ray to a patient  150 , a high voltage generating part  4  which generates a high voltage supplied to the X-ray generating part  1 , an X-ray detecting part  2  which detects the X-ray passed through the patient  150 , a C-arm  5  which supports the X-ray generating part  1  and the X-ray detecting part  2 , and a mechanical control part  3  which controls rotation of the C-arm  5  and movement of a bed plate  17  which the patient  150  is put on. 
   Moreover, the X-ray imaging apparatus  100  includes an image process memory part  7  which stores X-ray image data and performs several image processes to the X-ray image data, a display part  8  which displays the X-ray image data stored in the image process memory part  7 , an operation part  9  by which an operator inputs patient information and several instructions or sets an imaging condition, a distance detection part  6  which detects the distance between the patient  150  and the X-ray generating part  1 , and a system controller  10  which controls each part. 
   The X-ray generating part  1  includes an X-ray tube  15  irradiated to the patient  150 , and an X-ray limiting device  16  which forms a cone-shaped X-ray from the X-ray generated by the X-ray tube  15 . The X-ray tube  15  is a vacuum tube which generates the X-ray. The X-ray is generated when an electron emitted from a filament is accelerated and collision between the accelerated electron and a tungsten anode occurs. The X-ray limiting device  16  is positioned between the X-ray tube  15  and the patient  150 , and limits the X-ray irradiated from the X-ray tube  15  to a size of a predetermined field of view. 
   The X-ray detecting part  2  includes a flat panel detector  21  where the X-ray passed through the patient  150  is transferred to an electric charge and the electric charge is accumulated, a gate driver  22  which reads out the accumulated electric charge as an X-ray signal, a projection data creating part  13  which creates X-ray projection data based on the electric charge, and a sensor part  26  which measures the distance between the patient  150  and the X-ray detecting part  2 . As the flat panel detector  21 , a direct conversion type X-ray detector which directly converts the X-ray into the electric charge, or an indirect conversion type X-ray detector which converts the X-ray into the optical signal and then converts the optical signal into the electric charge, may be applied. In this embodiment, the direct conversion type X-ray detector is explained, however the indirect conversion type X-ray detector may be used. 
   As shown in  FIG. 2 , the flat panel detector  21  includes a plurality of detection elements  51  which are arranged in two dimensions in a segment direction and a line direction. Each detection element  51  includes a photoelectric film  52  which generates the electric charge according to the incident X-ray, a charge accumulating capacitor  53  which accumulates the electric charge generated in the photoelectric film  52 , and a TFT (Thin Film Transistor)  54  which reads out the accumulated electric charge by a predetermined period. To simplify an explanation, it is explained that the flat panel detector includes 2×2 detection elements in the segment direction (up and down direction in  FIG. 2 ) and the line direction (right and left direction in  FIG. 2 ). 
   First terminals of photoelectric films  52 - 11 ,  52 - 12 ,  52 - 21  and  52 - 22  in  FIG. 2  are connected to first terminals of the capacitors  53 - 11 ,  53 - 12 ,  53 - 21  and  53 - 22 . Connection points between the first terminals of the photoelectric films and the first terminals of the capacitors are connected to source terminals of the TFT  54 - 11 ,  54 - 12 ,  54 - 21  and  54 - 22 . Second terminals of the photoelectric films  52 - 11 ,  52 - 12 ,  52 - 21  and  52 - 22  are connected to a bias power supply. Second terminals of the capacitors  53 - 11 ,  53 - 12 ,  53 - 21  and  53 - 22  are grounded. Gate terminals of the TFT  54 - 11  TFT  54 - 21  arranged in the line direction are commonly connected to an output terminal  22 - 1  of the gate driver  22 , and gate terminals of the TFT  54 - 12  TFT  54 - 22  are commonly connected to an output terminal  22 - 2  of the gate driver  22 . 
   Moreover, drain terminals of the TFT  54 - 11  and  54 - 12  arranged in the segment direction are commonly connected to a signal output line  59 - 1 , and drain terminals of the TFT  54 - 21  and  54 - 22  are commonly connected to a signal output line  59 - 2 . The signal output lines  59 - 1  and  59 - 2  are connected to the projection data creating part  13 . 
   In order to read the signal electric charge which is generated in the photoelectric film  52  of the detection element  51  by X-ray irradiation and which is accumulated in the capacitor  53 , the gate driver  22  supplies a driving pulse to the gate terminal of the TFT  54 . 
   In  FIG. 1 , the projection data creating part  13  includes an electric charge/voltage converter  23  which converts the electric charge read from the flat panel detector  21  into voltage, an A/D converter  24  which changes the output of the electric charge/voltage converter  23  into a digital signal, and a parallel serial converter  25  which changes the X-ray projection data which is read in parallel by each line into a time series signal. The sensor part  26  of the X-ray detecting part  2  is explained in a description about the distance detection part  6  below. 
   The mechanical control part  3  includes a bed plate moving mechanism  32  which moves the bed plate  17  where the patient  150  is placed on in a body axis direction (direction perpendicular to  FIG. 1 ) and in the right and left directions an imaging part moving mechanism  31  which rotates the C arm  5  having the X-ray generating part  1  and the X-ray detecting part  2  around the patient  150  and which moves the X-ray detecting part  2  to the patient  150 , and a mechanism controller  33  which controls the rotation and the movement. 
   According to a control signal supplied from the systems controller  10 , the mechanism controller  33  controls the imaging part moving mechanism  31  to set up a direction, amount and speed of the rotation of the C arm  5 , or a direction, amount and speed of the rotation/movement of the X-ray detecting part  2 . In  FIG. 3 , the X-ray detecting part  2  and the X-ray generating part  1  which are set up to the patient  150  are shown. The mechanism controller  33  drives the imaging part moving mechanism  31  to move the X-ray detecting part  2 , and a desired distance LD between the flat panel detector  21  which is attached in front of the X-ray detecting part  2  and the body surface of the patient  150  is set. 
   The high-voltage generating part  4  includes a high-voltage generator  42  which generates the high voltage between the filament and the anode to accelerate the electron generated in the filament of the X-ray tube  15 , and a high-voltage controller  41  which sets up an X-ray irradiation condition, such as tube current, a tube voltage and an irradiation time, according to an instruction signal from the systems controller  10 . 
   The sensor part  26  of the X-ray detecting part  2  and the distance detection part  6  is explained with reference to  FIG. 4 . 
   The sensor part  26  is positioned near the flat panel detector  21  in the X-ray detecting part  2  of  FIG. 1 . The sensor part  26  includes a capacitance sensor  261  which detects the capacitance in front of the flat panel detector  21 , a contact sensor  262  which is positioned on a surface of the capacitance sensor  261 , and detects the existence of contact for the front of the flat panel detector  21 , and a temperature and humidity sensor  263  which measures temperature and humidity near the flat panel detector  21 . The capacitance sensor  261  includes a sheet type electrode, such as a carbon sheet, which scarcely prevent the X-ray from passing through. The front of the flat panel detector  21  is covered with the capacitance sensor  261 . The contact sensor  262  includes pressure-resistance converting device, for example. The capacitance sensor  261  includes a capacitance sensing element  271  and a basic capacitance element  272  shown in  FIG. 7A . The basic capacitance element  272  is grounded. As shown in  FIG. 7B , the capacitance sensing element  271  includes a capacitance sensing body  274 , the carbon sheet  273  and a capacitance detection circuit  278 . The carbon sheet  273  is the substantial same size as the X-ray detection plane. The capacitance sensing body  274  is coated with the carbon sheet. By detecting a capacitance between the carbon sheet  273  and the basic capacitance element  272 , the distance to the patient is measured. The carbon sheet may not be the same size as the X-ray detection plane, and may be positioned on a part of the X-ray detection plane. 
   The distance detection part  6  includes a waveform detection part  60  which supplies a rectangular pulse to the capacitance sensor  261  and measures distortion (delay) of the waveform. The distortion is caused according to the capacitance of the flat panel detector  21 . The distance detection part  6  further includes a contact detection circuit  66  which detects whether the flat panel detector  21  contacts the body surface of the patient  150 , based on an output signal of the contact sensor  262 . The distance detection part  6  further includes a CPU  67  and a memory circuit  68 . 
   The waveform detection part  60  includes a rectangle wave generator  61  which generates the rectangular pulse by a predetermined period, and a driving circuit  62  which amplifies and supplies the rectangular pulse to the capacitance sensor  261 . The waveform detection part  60  further includes a preamplifier  63  which amplifies and reform the rectangular pulse where the waveform distortion occurs according to the capacitance of the capacitance sensor  261 , and a phase discriminator  64  which detects a direct-current component by performing a phase detection between an output of the rectangle wave generator  61  and an output of the preamplifier  63 . 
   An operation of method for measuring the capacitance in the waveform detection part  60  is explained with reference to  FIGS. 5A and 5B . A waveform a- 1  in  FIG. 5A  is a rectangular waveform which is outputted from the rectangle wave generator  61  of the waveform detection part  60 , and a waveform a- 2  is a rectangular waveform which is an input to the preamplifier  63  and which is affected by the waveform distortion. A waveform a- 3  is an output of the preamplifier  63 , the output of which is reformed using a threshold γ to the waveform a- 2 . In this case, when the waveform a- 1  is impressed to the capacitance sensor  261  via the driving circuit  62 , the waveform distortion occurs in the waveform a- 1 , namely the waveform a- 2 , according to the capacitance. A waveform a- 3  is a reformed pulse of the waveform a- 2  and is delayed by a phase difference δt from the waveform a- 1  according to the capacitance. 
   DC output of the phase discriminator  64  which the waveform a- 1  and a- 3  are inputted shows a low value when the distortion is large or the capacitance is large. Therefore, as shown in  FIG. 5B , the capacitance of the flat panel detector  21  is presumed by measuring a size of the output signal of the phase discriminator  64 , and also it is possible to presume the distance (referred to as imaging distance below) between the flat panel detector  21  and the body surface of the patient by obtaining the value of the capacitance while the X-ray detecting part  2  moves. 
   However, patient characteristics, such as a patient&#39;s shape, age, sex and degree of obesity, affect the capacitance, and an error caused by a change of the capacitance can occur to the imaging distance to be presumed. Similarly the capacitance changes according to environment around the X-ray detecting part  2  and the patient  150 . Especially an error resulting from humidity can be important. 
   The patient characteristics and the environment, such as the humidity or temperature, may be corrected. 
   The memory circuit  68  in the distance detection part  6  in  FIG. 4  has a capacitance-imaging distance memory area where a relationship between an imaging distance which is set to a general patient and the capacitance which is presumed based on the output signal from the waveform detection part  60  is stored. The memory circuit  68  further has a patient information memory area where the patient information, such as a diagnosis part, age, sex and degree of obesity of the patient  150  is stored, and an environment information memory area where the environment information, such as the humidity or the temperature, around the flat panel detector  21  is stored. The memory circuit  68  further includes a correction coefficient memory area where a correction coefficient of the capacitance to the patient information or the environment information. 
   Furthermore, the memory circuit  68  includes a detection output-capacitance data memory area where a relationship between the detection output from the waveform detection part  60  shown in  FIG. 4  and the capacitance of the capacitance sensor  261  is stored in advance. 
   The general data of the above mentioned relationship between the imaging distance and the capacitance and the correction coefficient of the capacitance to the patient information and the environment information can be obtained based on a plurality of sets of data which are accumulated in past X-ray imaging, or a phantom can be used instead. Data of the relationship between the output of the phase discriminator  64  and the capacitance can be obtained by performing a basic experimentation in advance. 
   The CPU  67  receives the output of the contact detection circuit  66  and the measured temperature value and the humidity value from the temperature and humidity sensor  263  in addition to the output signal from the phase discriminator  64  in the waveform detection part  60 . When the output signal of the phase discriminator  64  is received, the capacitance is calculated based on this output signal and the relationship data between the detection output and the capacitance stored in the detection output-capacitance data memory area. Furthermore, the capacitance is corrected to obtain corrected capacitance (referred to as corrected capacitance) is calculated by the correction coefficient selected from a plurality of correction coefficients stored in correction coefficient memory area based on the patient information data and the environment information stored in the patient information memory area and the environment information memory area. 
   The CPU  67  calculates the imaging distance based on the relationship data stored in the capacitance-imaging distance memory area. When the calculated imaging distance is a first value α or a second value β, the CPU  67  supplies an approach signal to the system controller  10 . 
   In  FIG. 1 , the image process memory part  7  has a function to generate the X-ray image data to be displayed in the display part  8 . The image process memory part  7  includes an image-processing circuit  71  for performing image processing to the X-ray projection data outputted from the projection data creating part  13 . The image process memory part  7  further includes an image data memory circuit  72  for memorizing the above-mentioned X-ray projection data and the X-ray image data after image processing. The image-processing circuit  71  performs an image processing for generating DSA image data based on subtraction between contrast image data and mask image data which are obtained before and after contrast agent is injected, long image data and 3D image data, for example. 
   The operation part  9  is an input device, such as a keyboard, a trackball, a joystick, a mouse, or a display panel or an interactive interface having various switches, etc, for example. The operation part  9  is used for inputting the patient information, for setting the first value α indicating a deceleration point of the moving speed of the X-ray detecting part  2  and the second value β indicating a stop point of the X-ray detecting part  2 , for inputting a start instruction of the imaging, and for setting an appropriate X-ray imaging condition for the diagnosis part. The imaging condition includes a tube voltage, a tube current impressed to the X-ray tube  15 , and a irradiation time of the X-ray, etc. The patient information includes age, sex, height, weight, degree of obesity, inspection part, past diagnostic history, etc. 
   When a Patient ID is inputted from the operation part  9 , the patient information or the various imaging condition based on the patient information are automatically read from HIS (hospital information system) which is connected through the network, and an operator adjusts the information and the imaging condition, if necessary. 
   The display part  8  is used for displaying the image data stored in the image data memory circuit  72  of the image process memory part  7 . The display part  8  includes a data generation circuit  81  which creates the image data to be displayed, combining the image data and attached information, such as number or a letter. The display part  8  further includes a conversion circuit  82  which creates a display signal, performing D/A conversion and TV format conversion to the image data or the attached information, and a monitor  83 , such as a liquid crystal monitor or CRT monitor, which displays the display signal. 
   A position setting procedure of the imaging part in the X-ray imaging apparatus  100  is explained with reference to  FIG. 1 through 6 .  FIG. 6  is a flow chart which shows the setting procedure of the imaging part. 
   When a power of X-ray imaging apparatus  100  is switched to ON, the X-ray imaging apparatus  100  starts to be connected to a server or HIS which is located in the same medical facilities through the network. Subsequently, when the operator inputs the patient ID of the patient  150  with the operation part  9 , a CPU in the system controller  10  reads out the patient information and the imaging condition which correspond to the patient ID from the server or the HIS. The patient information and the imaging condition are memorized in a memory circuit in the system controller  10  and are displayed in a display panel of the operation part  9 . 
   The operator checks the above-mentioned information displayed on the display panel of the operation part  9  and adjusts them if needed. The operator selects the patient&#39;s  150  diagnosis part, age, sex, degree of obesity, etc. using an input device from the patient information. The selected information is stored in the patient information memory area in the memory circuit  68  of the distance detection part  6 . 
   The operator sets up a moving condition of the imaging part among the various imaging conditions displayed on the display panel of the operation part  9 . For example, the deceleration point value α and the stop point value β (β&gt;α) of the imaging part are set and stored in the memory circuit  68  via the CPU  67  of the distance detection part  6  (Step S 1  of  FIG. 6 ). 
   Subsequently, the CPU  67  of the distance detection part  6  receives the temperature value and humidity value which are obtained from the temperature and humidity sensor  263  positioned inside of the X-ray detecting part  2 , and these values are saved in the environment information memory area of the memory circuit  68  (Step S 2  of  FIG. 6 ). 
   After the patient information and the environment information are stored, the systems controller  10  supplies a command signal for rotating/moving the imaging part to the mechanism controller  33 . The mechanism controller  33  which received the command signal supplies a control signal to the imaging part moving mechanism  31  to rotate the C-arm to a desired angle in a desired direction at a desired speed. Similarly, when an imaging direction is set, the mechanism controller  33  supplies a control signal to the imaging part moving mechanism  31 , and the X-ray detecting part  2  moves close to or far from the patient  150  at a desired speed (Step S 3  of  FIG. 6 ). 
   Next, the rectangle-wave generator  61  of the waveform detection part  60  supplies the rectangular pulse to the capacitance sensor  261  in a predetermined cycle through the driving circuit  62  while the X-ray detecting part  2  moves. At this time, the waveform distortion occurs to the rectangular pulse supplied to the capacitance sensor  261  having a capacitance. The rectangular pulse with the waveform distortion is amplified and reformed in the preamplifier  64  of the waveform detection part  60 , and is inputted into the first input terminal of the phase discriminator  63 . The rectangular pulse outputted from the rectangle wave generator  61  is inputted into the second input terminal of the phase discriminator  64 . In the phase discriminator  64 , the rectangular pulse outputted from the rectangle wave generator  61  and the output of the preamplifier  63  are discriminated by phase, and are inputted into the CPU  67  (Step S 4  of  FIG. 6 ). 
   The CPU  67  calculates the capacitance corresponding to the size of the output (direct-current component) of the phase discriminator  64  based on the relationship data of the detection output and the capacitance stored in the detection output-capacitance data memory area of the memory circuit  68  (Step S 5  of  FIG. 6 ). 
   The CPU  67  reads out the temperature information and humidity information stored in the environment information memory area of the memory circuit  68 , and the patient information, such as diagnosis part, body information (height, weight degree of obesity), age and sex stored in the patient information memory area of the memory circuit  68 . The correction coefficient is selected from the correction coefficient information memory area based on the patient information and the environment information. The capacitance obtained in Step S 5  is corrected using the correction coefficient to obtain the corrected capacitance (Step S 6  of  FIG. 6 ). 
   The CPU  67  calculates the imaging distance Lx according to the corrected capacitance in Step S 6  using the relationship information of the capacitance and the imaging distance stored in the capacitance-imaging distance memory area of the memory circuit  68  (Step S 7  in  FIG. 6 ). 
   When the obtained imaging distance Lx is bigger than the imaging distance of the first value α (Step S 8  in  FIG. 6 ), the X-ray detecting part  2  moves at a constant speed to the patient  150 , and Step S 3  through S 7  are repeated. When the imaging distance Lx is not more than the deceleration imaging distance of the first value α, the imaging distance Lx is compared with the stop imaging distance of the second value β (Step S 9  in  FIG. 6 ) 
   When the imaging distance Lx is bigger than the stop imaging distance of the second value β, the CPU  67  supplies a first approach signal to the systems controller  10 , and the mechanism controller  33  which received a command signal from the systems controller  10  based on the first approach signal controls the imaging part moving mechanism  31  and decelerates the speed of the X-ray detecting part  2  (Step S 10  of  FIG. 6 ). Step S 4  and S 10  are repeated. 
   When the imaging distance Lx is not more than the stop imaging distance of the second value β, the CPU  67  supplies the second approach signal to the systems controller  10 , and the mechanism controller  33  which received a command signal from the systems controller  10  based on the second approach signal supplies a stop signal to the imaging part moving mechanism  31 , and the movement of the X-ray detecting part  2  stops (Step S 11  of  FIG. 6 ). 
   As stated above, when the X-ray detecting part  2  which moves at the constant speed towards a the patient  150  reaches the deceleration imaging distance, it starts to decelerate, and when the imaging distance reaches to the stop imaging distance, the X-ray detecting part  2  stops. 
   When the X-ray detecting part  2  is set as the desired imaging distance of the second value β, the operator inputs the start command of the X-ray imaging with the operation part  9 . The X-ray imaging starts by supplying the start command to the systems controller  10  (Step S 12  of  FIG. 6 ). 
   The high voltage controller  41  of the high voltage generating part  4  receives the start command from the systems controller  10 , controls the high voltage generator  42  based on the already set-up X-ray irradiation condition, impresses the high voltage to the X-ray tube  15  of the X-ray generating part  1 , and irradiates the X-ray to the patient  150  through the X-ray limiting device  16 . The X-ray which passes through the patient  150  is detected by the flat panel detector  21  of the X-ray detecting part  2  positioned behind the patient  150 . 
   The flat panel detector  21  including the X-ray detection elements  51  which are arranged in the line direction and the segment direction as shown in  FIG. 2 . The X-ray detection elements  51  receives the X-ray which passes the patient  150 , and the signal electric charge corresponding to intensity of the X-ray irradiation is accumulated in the charge accumulating capacitor  53  of the X-ray detection element  51 . After the X-ray irradiation is completed, the gate driver  22  to which a clock pulse is supplied from the systems controller  10  reads the signal electric charge accumulated in the charge accumulating capacitor  53  of the X-ray detection element  51  by supplying the driving pulse to the flat panel detector  21 . 
   The read out signal electric charge is converted into the voltage signal in the electric charge/voltage converter  23  in the projection data creating part  13  shown in  FIG. 1 . The voltage signal is changed into a digital signal in the A/D converter  24 , and is temporally memorized as projection data in a memory circuit of the parallel serial converter  25 . The systems controller  10  reads the projection data in order serially per line, and stores the projection data as 2-dimensional projection data in the projection data memory are of the image data memory circuit  72  of the image process memory part  7 . 
   The image-processing circuit  71  of the image process memory part  7  reads the 2-dimensional projection data stored in the image data memory circuit  72 , creates the image data by performing image processing, such as outline emphasis and gradation change, if needed, and stores the created image data in the image data memory are of the image data memory circuit  72 . 
   The systems controller  10  reads the image data stored in the image data memory circuit  72 , and displays the image data on the monitor  83  of the display part  8 . In detail, the systems controller  10  reads the image data stored in the image data memory circuit  72 , and in the data generation circuit  81  for a display of the display part  8 , the attached information, such as number or a letter, is combined to the image data, and the combined data is supplied to a conversion circuit  82 . In the conversion circuit  82 , the D/A conversion and the TV format conversion are performed on the combined data, and the converted data is displayed on the monitor  83 . 
   According to the above embodiment, since the front of the flat panel detector  21  is covered with the capacitance sensor, the imaging distance to the closest part of the patient can be set according to the shape of the patient surface. 
   Moreover, when the capacitance is corrected according to not only the shape of the patient&#39;s diagnosis part but also the patient information, the patient&#39;s shape, age, sex, degree of obesity, etc, the imaging distance can be appropriately set. Furthermore, when the correction of the capacitance is performed based on a database created in advance, the capacitance can be corrected stably and simply. 
   Therefore, the X-ray detecting part can be moved to a desired position to the patient without contact, and it is possible to obtain clear image data efficiently. 
   A modification of the capacitance sensor is explained with reference to  FIG. 8A through 8C . In the modification, as shown in  FIG. 8B , a capacitance sensing element  275  is divided into four elements. As well as the capacitance sensing element  275 , a carbon sheet  276  is also divided into four sheets. The capacitance between each carbon sheet  276  and the basic capacitance element  272  is obtained by each capacitance detection circuit  277 , and the imaging distance is measured. Two lines of the division of the capacitance sensing elements are positioned along the arrangement of the X-ray detection elements in the line direction and the segment direction. The carbon sheet may be positioned such that at least part of the carbon sheet overlaps the X-ray detection plane (indicated as a broken line) of the flat panel detector. In the modification, since a plurality of the capacitance sensing elements are adapted, it is possible to measure the imaging distance appropriately. 
   The embodiment and the modification are mentioned above, however the embodiment and the modification may be modified For instance, in the embodiment, the case where the X-ray detecting part moves to the patient is explained, the embodiment ant the modification may be applied to a case where the X-ray generating part may be move to the patient. As another example, when a plurality of the capacitance sensing elements are used, the line of the division may not be positioned along the arrangement of the X-ray detection elements. As another example, the basic capacitance element may be adjusted instead of grounded. 
   Moreover, although the case where the value of the capacitance is obtained using the sheet type electrode of the capacitance sensor and the capacitance is corrected according to the patient information is explained, at least one of technique of the sheet type electrode of the capacitance sensor and technique of the correction according to the patient information may be used. Moreover, the patient information may not be limited to the patient&#39;s shape, age, sex and degree of obesity. 
   Although the flat panel detector is explained for detecting the X-ray, an I.I and an X-ray TV may be used instead. Although the phase discriminating method for measuring the influence of the capacitance is explained, other method may be used. Although the angio X-ray imaging apparatus including the C-arm is mainly explained, other X-ray imaging apparatus, such as RF X-ray imaging apparatus, may be used. 
   Although two type of the imaging distances of the deceleration point α and the stop point β are explained, only stop point β may be used.