X-ray computed tomography apparatus

Abstract

An X-ray computed tomography apparatus includes an X-ray tube, a high voltage generator which generates a high voltage to be applied to the X-ray tube, an X-ray detector having a plurality of X-ray detection element lines, a scanogram generating unit which generates a scanogram on the basis of an output from the X-ray detector, a reconstructing unit which reconstructs an image on the basis of an output from the X-ray detector, a tube current determining unit which determines a tube current value on the basis of the pixel values of a plurality of pixels included in a two-dimensional partial region of the scanogram, and a control unit which controls the high voltage generator on the basis of the determined tube current value.

What is claimed is:  
     
         1 . An X-ray computed tomography apparatus comprising: 
 an X-ray tube configured to generate X-rays with which an object to be examined is irradiated;    a high voltage generator configured to generate a high voltage to be applied to said X-ray tube;    an X-ray detector configured to have a plurality of X-ray detection element lines for detecting X-rays transmitted through the object;    a scanogram generating unit configured to generate a scanogram on the basis of an output from said X-ray detector;    a reconstructing unit configured to reconstruct an image on the basis of the output from said X-ray detector;    a tube current determining unit configured to determine a tube current value for said X-ray tube on the basis of pixel values of a plurality of pixels included in a two-dimensional partial region of the scanogram; and    a control unit configured to control said high voltage generator on the basis of the determined tube current value.    
     
     
         2 . An apparatus according to  claim 1 , wherein the two-dimensional partial region has a size corresponding to the number of detection element lines corresponding to an aperture width of a collimator in a slice direction, which is placed between said X-ray tube and the object, and the number of channels constituting each of the detection element lines.  
     
     
         3 . An apparatus according to  claim 1 , wherein said tube current determining unit determines a tube current value for said X-ray tube on the basis of an average of pixel values of a plurality of pixels included in the two-dimensional partial region.  
     
     
         4 . An apparatus according to  claim 3 , further comprising a storing unit which stores a table in which the tube current value is associated with the average.  
     
     
         5 . An apparatus according to  claim 1 , wherein said tube current determining unit determines a tube current value for said X-ray tube on the basis of a maximum or minimum value of pixel values of a plurality of pixels included in the two-dimensional partial region.  
     
     
         6 . An apparatus according to  claim 1 , wherein said tube current determining unit determines a plurality of tube current values at a plurality of discrete positions, and said control unit dynamically changes a tube current of said X-ray tube on the basis of the determined plurality of tube current values upon movement of the object.  
     
     
         7 . An apparatus according to  claim 6 , wherein said tube current determining unit interpolates a tube current value corresponding to an intermediate position of the plurality of discrete positions from the determined tube current value.  
     
     
         8 . An apparatus according to  claim 1 , wherein said reconstructing unit reconstructs the image on the basis of outputs from at least two X-ray detection element lines selected from said plurality of X-ray detection element lines in accordance with a user instruction.  
     
     
         9 . An apparatus according to  claim 8 , wherein the two-dimensional partial region has a size corresponding to the number of channels constituting each of said X-ray detection element lines and the number of selected X-ray detection element lines.  
     
     
         10 . An apparatus according to  claim 1 , further comprising a display unit which displays the a size of scanogram together with a frame representing the two-dimensional partial region.  
     
     
         11 . An apparatus according to  claim 10 , further comprising an input device which is used to arbitrarily change a size of the frame.  
     
     
         12 . An apparatus according to  claim 10 , further comprising an input device which is used to arbitrarily change a shape of the frame.  
     
     
         13 . An X-ray computed tomography apparatus comprising: 
 an X-ray tube configured to generate X-rays with which an object to be examined is irradiated;    a high voltage generator configured to generate a high voltage to be applied to said X-ray tube;    an X-ray detector configured to have a plurality of X-ray detection element lines for detecting X-rays transmitted through the object;    a reconstructing unit configured to reconstruct an image on the basis of outputs from at least two X-ray detection element lines selected in accordance with a slice thickness and the number of slices indicated by a user instruction;    a tube current determining unit configured to determine a tube current value for said X-ray tube on the basis of an output distribution, X-ray transmission factor distribution, or X-ray attenuation factor distribution of said X-ray detector which corresponds to a range corresponding to the slice thickness and the number of slices; and    a control unit configured to control said high voltage generator on the basis of the determined tube current value.    
     
     
         14 . An X-ray computed tomography apparatus comprising: 
 an X-ray tube which generates X-rays with which an object to be examined is irradiated;    a high voltage generator configured to generate a high voltage to be applied to said X-ray tube;    an X-ray detector configured to have a plurality of X-ray detection element lines for detecting X-rays transmitted through the object;    a reconstructing unit configured to reconstruct an image on the basis of the output from said X-ray detector; and    a control unit configured to dynamically control said high voltage generator on the basis of a profile of the object in a slice direction which is associated with an X-ray transmission factor or a similar index.    
     
     
         15 . An apparatus according to  claim 14 , wherein said control unit dynamically controls said high voltage generator on the basis of an average in a predetermined interval of the profile.  
     
     
         16 . An apparatus according to  claim 14 , wherein the predetermined interval has a size corresponding to the number of detection element lines corresponding to an aperture width of a collimator in a slice direction which is placed between said X-ray tube and the object.  
     
     
         17 . An apparatus according to  claim 15 , further comprising an input device which is used to input a length of the interval.  
     
     
         18 . An apparatus according to  claim 15 , wherein the length of the interval is determined on the basis of the number of X-ray detection lines, which is not less than two, selected from the plurality of X-ray detection element lines to reconstruct the image in accordance with a user instruction.  
     
     
         19 . An X-ray computed tomography apparatus comprising: 
 an X-ray tube configured to generate X-rays with which an object to be examined is irradiated;    a high voltage generator configured to generate a high voltage to be applied to said X-ray tube;    an X-ray detector configured to have a plurality of X-ray detection element lines for detecting X-rays transmitted through the object;    a moving mechanism configured to move the object relative to said X-ray tube and said X-ray detector;    a reconstructing unit configured to reconstruct an image on the basis of outputs from at least two detection element lines selected from said plurality of X-ray detection element lines in accordance with a user instruction; and    a control unit configured to dynamically control a tube current value for said X-ray tube along with relative movement of the object on the basis of outputs from some or all of said at least two selected detection element lines.    
     
     
         20 . An apparatus according to  claim 19 , wherein said control unit controls a tube current value for said X-ray tube on the basis of an output from at least one start line of said at least two selected detection element lines.  
     
     
         21 . An apparatus according to  claim 19 , wherein said control unit determines a tube current value for said X-ray tube on the basis of an average of outputs from at least some of said at least two selected detection element lines.  
     
     
         22 . An apparatus according to  claim 19 , wherein control unit determines a tube current value for said X-ray tube on the basis of a maximum or minimum value of outputs from at least some of said at least two selected detection element lines.  
     
     
         23 . An X-ray computed tomography apparatus comprising: 
 an X-ray source configured to generate X-rays with which an object to be examined is irradiated;    an X-ray detector configured to have a plurality of X-ray detection element lines for detecting X-rays transmitted through the object in a body axis direction of the object;    a scanographic control unit configured to cause scanography of the object to be done by using said X-ray source and said X-ray detector;    a scanogram generating unit configured to generate a scanogram on the basis of X-ray data obtained by the scanography;    a display unit configured to display the scanogram;    a setting unit configured to set a slice thickness and the number of slices by using said display unit;    a tube current determining unit configured to determine a tube current value in a scan on the basis of X-ray data obtained by scanography corresponding to a scan range which is simultaneously scanned with the slice thickness and the number of slices or of an index obtained from the X-ray data; and    a scan control unit configured to cause a scan to be done in the scan range with the tube current value determined by said tube current value determining unit.    
     
     
         24 . An X-ray computed tomography apparatus comprising: 
 an X-ray source configured to generate X-rays with which an object to be examined is irradiated;    a collimator configured to is placed between said X-ray source and the object to collimate the X-rays in a body axis direction of the object;    an X-ray detector configured to have a plurality of X-ray detection element lines for detecting X-rays transmitted through the object in a body axis direction of the object;    a scanographic control unit configured to cause scanography of the object to be done by using said X-ray source and said X-ray detector;    a scanogram generating unit configured to generate a scanogram on the basis of X-ray data obtained by the scanography;    a display unit configured to display the scanogram;    a setting unit configured to set a scan condition through said display unit;    an aperture width determining unit configured to determine an aperture width of said collimator in a scan in accordance with the scan condition; and    a tube current value determining unit configured to determine a tube current value in the scan on the basis of the X-ray data in a range scanned with the aperture width.    
     
     
         25 . An X-ray computed tomography method comprising: 
 performing scanography of an object to be examined;    generating a scanogram on the basis of X-ray data obtained by the scanography;    displaying the generated scanogram;    setting the number of slices and a slice thickness by using the scanogram;    determining a tube current value in a scan on the basis of the X-ray data corresponding to a scan range almost simultaneously scanned with the number of slices and the slice thickness; and    scanning the scan range with the determined tube current value.