Abstract:
A method for applying correction adapted to the shape of a subject to be imaged. The method includes applying edge enhancement is applied to data D(r, v, c) of interest if the difference between the data D(r, v, c) of interest and data D(r, v+1, c) in a view adjacent to the view corresponding to the data D(r, v, c) is large, while smoothing is applied to the data D(r, v, c) of interest when the difference is small.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a data correction method and an X-ray CT (computer tomography) apparatus, and more particularly to a data correction method and an X-ray CT apparatus capable of applying correction adapted to the shape of a subject to be imaged.  
         [0002]     There is known a conventional X-ray CT apparatus for: if data has a larger value than an upper threshold, applying smoothing to the data; if data has a smaller value than a lower threshold, taking the data as is; and if data has a value between the upper and lower thresholds, applying smoothing to the data, the degree of which smoothing is lower than that for the data of a larger value than the upper threshold, and becomes higher in proportion as the data has a larger value (for example, see Patent Document 1).  
         [0003]     [Patent Document 1] Japanese Patent Application Laid Open No. 2000-5159.  
         [0004]     In such a conventional X-ray CT apparatus, the degree of correction processing is changed simply according to the magnitude of data.  
         [0005]     However, assuming that the shape of a subject to be imaged is so complex as to make one of data elements adjacent to each other in the view or channel direction have a larger value and the other have a smaller value, the technique as described above causes the degree of smoothing to be increased for one of the adjacent data elements and decreased for the other, which is unreasonable. That is, the conventional X-ray CT apparatus poses a problem that correction adapted to the shape of the subject to be imaged can sometimes not be applied.  
       SUMMARY OF THE INVENTION  
       [0006]     It is therefore an object of the present invention to provide a data correction method and an X-ray CT apparatus capable of applying correction adapted to the shape of an subject to be imaged.  
         [0007]     As used herein, the term “relative rotation”and the like include all of the following: for a subject to be imaged placed in between an X-ray tube and a detector, rotating at least one of the X-ray tube and detector around the subject to be imaged without rotating the subject to be imaged; rotating the subject to be imaged around its axis without rotating the X-ray tube and detector; and rotating the subject to be imaged around its axis and counter-rotating at least one of the X-ray tube and detector around the subject to be imaged.  
         [0008]     Moreover, collection of data is done by one of techniques including an axial scan in which the X-ray tube and detector are not moved rectilinearly relative to the subject to be imaged and a helical scan in which they are rectilinearly moved relative to the subject to be imaged.  
         [0009]     In its first aspect, the present invention provides a data correction method characterized in comprising: for a set of data collected while relatively rotating at least one of an X-ray tube and a detector around a subject to be imaged, differentiating the degree or method of correction processing in a view direction according to the magnitude of variation of the data in the view direction.  
         [0010]     According to the data correction method of the first aspect, the degree or method of correction processing in the view direction is differentiated between a case in which the shape of the subject to be imaged is so complex in the view direction as to make one of data elements adjacent to each other in the view direction have a larger value and the other have a smaller value, and a case in which the shape of the subject to be imaged is simple in the view direction to make data elements adjacent to each other in the view direction have values of the same magnitude. That is, correction adapted to the shape of the subject to be imaged can be achieved.  
         [0011]     In its second aspect, the present invention provides a data correction method characterized in comprising: for a set of data collected while relatively rotating at least one of an X-ray tube and a detector around a subject to be imaged, differentiating the degree or method of correction processing in a channel direction according to the magnitude of variation of the data in the channel direction.  
         [0012]     According to the data correction method of the second aspect, the degree or method of correction processing in the channel direction is differentiated between a case in which the shape of the subject to be imaged is so complex in the channel direction as to make one of data elements adjacent to each other in the channel direction have a larger value and the other have a smaller value, and a case in which the shape of the subject to be imaged is simple in the channel direction to make data elements adjacent to each other in the channel direction have values of the same magnitude. That is, correction adapted to the shape of the subject to be imaged can be achieved.  
         [0013]     In its third aspect, the present invention provides a data correction method characterized in comprising: for a set of data collected while relatively rotating at least one of an X-ray tube and a multi-row detector around a subject to be imaged, differentiating the degree or method of correction processing in a detector row direction according to the magnitude of variation of the data in the detector row direction.  
         [0014]     According to the data correction method of the third aspect, the degree or method of correction processing in the detector row direction is differentiated between a case in which the shape of the subject to be imaged is so complex in the detector row direction as to make one of data elements adjacent to each other in the detector row direction have a larger value and the other have a smaller value, and a case in which the shape of the subject to be imaged is simple in the detector row direction to make data elements adjacent to each other in the detector row direction have values of the same magnitude. That is, correction adapted to the shape of the subject to be imaged can be achieved.  
         [0015]     In its fourth aspect, the present invention provides a data correction method characterized in comprising: for a set of data collected while relatively rotating at least one of an X-ray tube and a detector around a subject to be imaged, applying correction processing in a view direction in a range in which variation of the data in the view direction is larger, and applying no correction processing in the view direction in a range in which said variation of the data is smaller.  
         [0016]     According to the data correction method of the fourth aspect, correction processing is applied in a case in which the shape of the subject to be imaged is so complex in the view direction as to make one of data elements adjacent to each other in the view direction have a larger value and the other have a smaller value, and no correction processing is applied in a case in which the shape of the subject to be imaged is simple in the view direction to make data elements adjacent to each other in the view direction have values of the same magnitude. That is, correction adapted to the shape of the subject to be imaged can be selectively achieved.  
         [0017]     In its fifth aspect, the present invention provides a data correction method characterized in comprising: for a set of data collected while relatively rotating at least one of an X-ray tube and a detector around a subject to be imaged, applying correction processing in a channel direction in a range in which variation of the data in the channel direction is larger, and applying no correction processing in the channel direction in a range in which said variation of the data is smaller.  
         [0018]     According to the data correction method of the fifth aspect, correction processing is applied in a case in which the shape of the subject to be imaged is so complex in the channel direction as to make one of data elements adjacent to each other in the channel direction have a larger value and the other have a smaller value, and no correction processing is applied in a case in which the shape of the subject to be imaged is simple in the channel direction to make data elements adjacent to each other in the channel direction have values of the same magnitude. That is, correction adapted to the shape of the subject to be imaged can be selectively achieved.  
         [0019]     In its sixth aspect, the present invention provides a data correction method characterized in comprising: for a set of data collected while relatively rotating at least one of an X-ray tube and a multi-row detector around a subject to be imaged, applying correction processing in a detector row direction in a range in which variation of the data in the detector row direction is larger, and applying no correction processing in the detector row direction in a range in which said variation of the data is smaller.  
         [0020]     According to the data correction method of the sixth aspect, correction processing is applied in a case in which the shape of the subject to be imaged is so complex in the detector row direction as to make one of data elements adjacent to each other in the detector row direction have a larger value and the other have a smaller value, and no correction processing is applied in a case in which the shape of the subject to be imaged is simple in the detector row direction to make data elements adjacent to each other in the detector row direction have values of the same magnitude. That is, correction adapted to the shape of the subject to be imaged can be selectively achieved.  
         [0021]     In its seventh aspect, the present invention provides the data correction method having the aforementioned configuration, characterized in comprising: increasing the degree of said correction processing in proportion as said variation of the data is larger.  
         [0022]     According to the data correction method of the seventh aspect, the degree of correction processing is increased for a more complex shape of the subject to be imaged. That is, correction at a degree adapted to the shape of the subject to be imaged can be achieved.  
         [0023]     In its eighth aspect, the present invention provides the data correction method having the aforementioned configuration, characterized in that: said correction processing is edge enhancement.  
         [0024]     According to the data correction method of the eighth aspect, spatial resolution is improved through edge enhancement for a complex shape of the subject to be imaged. On the other hand, no edge enhancement or a lower degree of edge enhancement is applied to prevent exaggeration of noise for a simple shape of the subject to be imaged.  
         [0025]     In its ninth aspect, the present invention provides a data correction method characterized in comprising: for a set of data collected while relatively rotating at least one of an X-ray tube and a detector around a subject to be imaged, applying correction processing in a view direction in a range in which variation of the data in the view direction is smaller, and applying no correction processing in the view direction in a range in which said variation of the data is larger.  
         [0026]     According to the data correction method of the ninth aspect, correction processing is applied in a case in which the shape of the subject to be imaged is simple in the view direction to make data elements adjacent to each other in the view direction have values of the same magnitude, and no correction processing is applied in a case in which the shape of the subject to be imaged is so complex in the view direction as to make one of data elements adjacent to each other in the view direction have a larger value and the other have a smaller value. That is, correction adapted to the shape of the subject to be imaged can be selectively achieved.  
         [0027]     In its tenth aspect, the present invention provides a data correction method characterized in comprising: for a set of data collected while relatively rotating at least one of an X-ray tube and a detector around a subject to be imaged, applying correction processing in a channel direction in a range in which variation of the data in the channel direction is smaller, and applying no correction processing in the channel direction in a range in which said variation of the data is larger.  
         [0028]     According to the data correction method of the tenth aspect, correction processing is applied in a case in which the shape of the subject to be imaged is simple in the channel direction to make data elements adjacent to each other in the channel direction have values of the same magnitude, and no correction processing is applied in a case in which the shape of the subject to be imaged is so complex in the channel direction as to make one of data elements adjacent to each other in the channel direction have a larger value and the other have a smaller value. That is, correction adapted to the shape of the subject to be imaged can be selectively achieved.  
         [0029]     In its eleventh aspect, the present invention provides a data correction method characterized in comprising: for a set of data collected while relatively rotating at least one of an X-ray tube and a multi-row detector around a subject to be imaged, applying correction processing in a detector row direction in a range in which variation of the data in the detector row direction is smaller, and applying no correction processing in the detector row direction in a range in which said variation of the data is larger.  
         [0030]     According to the data correction method of the eleventh aspect, correction processing is applied in a case in which the shape of the subject to be imaged is simple in the detector row direction to make data elements adjacent to each other in the detector row direction have values of the same magnitude, and no correction processing is applied in a case in which the shape of the subject to be imaged is so complex in the detector row direction as to make one of data elements adjacent to each other in the detector row direction have a larger value and the other have a smaller value. That is, correction adapted to the shape of the subject to be imaged can be selectively achieved.  
         [0031]     In its twelfth aspect, the present invention provides the data correction method having the aforementioned configuration, characterized in comprising: increasing the degree of said correction processing in proportion as said variation of the data is smaller.  
         [0032]     According to the data correction method of the twelfth aspect, the degree of correction processing is increased for a simpler shape of the subject to be imaged. That is, correction at a degree adapted to the shape of the subject to be imaged can be achieved.  
         [0033]     In its thirteenth aspect, the present invention provides the data correction method having the aforementioned configuration, characterized in that: said correction processing is smoothing.  
         [0034]     According to the data correction method of the thirteenth aspect, noise can be suppressed through smoothing for a simple shape of the subject to be imaged. On the other hand, no smoothing or a lower degree of smoothing is applied to prevent degradation of spatial resolution for a complex shape of the subject to be imaged.  
         [0035]     In its fourteenth aspect, the present invention provides the data correction method having the aforementioned configuration, characterized in comprising: applying first correction processing in the view direction in a range in which said variation of the data is larger, and second correction processing in the view direction in a range in which said variation of the data is smaller.  
         [0036]     According to the data correction method of the fourteenth aspect, first correction processing in the view direction is applied in a case in which the shape of the subject to be imaged is so complex in the view direction as to make one of data elements adjacent to each other in the view direction have a larger value and the other have a smaller value, and second correction processing in the view direction is applied in a case in which the shape of the subject to be imaged is simple in the view direction to make data elements adjacent to each other in the view direction have values of the same magnitude. That is, correction adapted to the shape of the subject to be imaged can be achieved.  
         [0037]     In its fifteenth aspect, the present invention provides the data correction method having the aforementioned configuration, characterized in comprising: applying first correction processing in the channel direction in a range in which said variation of the data is larger, and second correction processing in the channel direction in a range in which said variation of the data is smaller.  
         [0038]     According to the data correction method of the fifteenth aspect, first correction processing in the channel direction is applied in a case in which the shape of the subject to be imaged is so complex in the channel direction as to make one of data elements adjacent to each other in the channel direction have a larger value and the other have a smaller value, and second correction processing in the channel direction is applied in a case in which the shape of the subject to be imaged is simple in the channel direction to make data elements adjacent to each other in the channel direction have values of the same magnitude. That is, correction adapted to the shape of the subject to be imaged can be achieved.  
         [0039]     In its sixteenth aspect, the present invention provides the data correction method having the aforementioned configuration, characterized in comprising: applying first correction processing in the detector row direction in a range in which said variation of the data is larger, and second correction processing in the detector row direction in a range in which said variation of the data is smaller.  
         [0040]     According to the data correction method of the sixteenth aspect, first correction processing in the detector row direction is applied in a case in which the shape of the subject to be imaged is so complex in the detector row direction as to make one of data elements adjacent to each other in the detector row direction have a larger value and the other have a smaller value, and second correction processing in the detector row direction is applied in a case in which the shape of the subject to be imaged is simple in the detector row direction to make data elements adjacent to each other in the detector row direction have values of the same magnitude. That is, correction adapted to the shape of the subject to be imaged can be achieved.  
         [0041]     In its seventeenth aspect, the present invention provides the data correction method having the aforementioned configuration, characterized in comprising: increasing the degree of the first correction processing in proportion as said variation of the data is larger, and increasing the degree of the second correction processing in proportion as said variation of the data is smaller.  
         [0042]     According to the data correction method of the seventeenth aspect, the degree of the first correction processing is increased for a more complex shape of the subject to be imaged, and the degree of the second correction processing is increased for a simpler shape of the subject to be imaged. That is, correction by a method and at a degree adapted to the shape of the subject to be imaged can be achieved.  
         [0043]     In its eighteenth aspect, the present invention provides the data correction method having the aforementioned configuration, characterized in that: said first correction processing is edge enhancement, and said second correction processing is smoothing.  
         [0044]     According to the data correction method of the eighteenth aspect, edge enhancement is applied when the shape of the subject to be imaged is so complex as to make one of data elements adjacent to each other have a larger value and the other have a smaller value, thereby improving spatial resolution. On the other hand, smoothing is applied when the shape of the subject to be imaged is simple to make data elements adjacent to each other have values of the same magnitude, thereby suppressing noise.  
         [0045]     In its nineteenth aspect, the present invention provides an X-ray CT apparatus characterized in comprising: an X-ray tube; a detector; scanning means for collecting a set of data while relatively rotating at least one of said X-ray tube and said detector around a subject to be imaged; and data correction processing means for correcting said data with the degree or method of correction processing in a view direction differentiated according to the magnitude of variation of the data in the view direction.  
         [0046]     According to the X-ray CT apparatus of the nineteenth aspect, the data correction method of the first aspect is suitably implemented.  
         [0047]     In its twentieth aspect, the present invention provides an X-ray CT apparatus characterized in comprising: an X-ray tube; a detector; scanning means for collecting a set of data while relatively rotating at least one of said X-ray tube and said detector around a subject to be imaged; and data correction processing means for correcting said data with the degree or method of correction processing in a channel direction differentiated according to the magnitude of variation of the data in the channel direction.  
         [0048]     According to the X-ray CT apparatus of the twentieth aspect, the data correction method of the second aspect is suitably implemented.  
         [0049]     In its twenty-first aspect, the present invention provides an X-ray CT apparatus characterized in comprising: an X-ray tube; a multi-row detector; scanning means for collecting a set of data while relatively rotating at least one of said X-ray tube and said multi-row detector around a subject to be imaged; and data correction processing means for correcting said data with the degree or method of correction processing in a detector row direction differentiated according to the magnitude of variation of the data in the detector row direction.  
         [0050]     According to the X-ray CT apparatus of the twenty-first aspect, the data correction method of the third aspect is suitably implemented.  
         [0051]     In its twenty-second aspect, the present invention provides an X-ray CT apparatus characterized in comprising: an X-ray tube; a detector; scanning means for collecting a set of data while relatively rotating at least one of said X-ray tube and said detector around a subject to be imaged; and data correction processing means for applying correction processing in a view direction in a range in which variation of the data in the view direction is larger, and applying no correction processing in the view direction in a range in which said variation of the data is smaller.  
         [0052]     According to the X-ray CT apparatus of the twenty-second aspect, the data correction method of the fourth aspect is suitably implemented.  
         [0053]     In its twenty-third aspect, the present invention provides an X-ray CT apparatus characterized in comprising: an X-ray tube; a detector; scanning means for collecting a set of data while relatively rotating at least one of said X-ray tube and said detector around a subject to be imaged; and data correction processing means for applying correction processing in a channel direction in a range in which variation of the data in the channel direction is larger, and applying no correction processing in the channel direction in a range in which said variation of the data is smaller.  
         [0054]     According to the X-ray CT apparatus of the twenty-third aspect, the data correction method of the fifth aspect is suitably implemented.  
         [0055]     In its twenty-fourth aspect, the present invention provides an X-ray CT apparatus characterized in comprising: an X-ray tube; a multi-row detector; scanning means for collecting a set of data while relatively rotating at least one of said X-ray tube and said multi-row detector around a subject to be imaged; and data correction processing means for applying correction processing in a detector row direction in a range in which variation of the data in the detector row direction is larger, and applying no correction processing in the detector row direction in a range in which said variation of the data is smaller.  
         [0056]     According to the X-ray CT apparatus of the twenty-fourth aspect, the data correction method of the sixth aspect is suitably implemented.  
         [0057]     In its twenty-fifth aspect, the present invention provides the X-ray CT apparatus having the aforementioned configuration, characterized in that: said data correction processing means increases the degree of said correction processing in proportion as said variation of the data is larger.  
         [0058]     According to the X-ray CT apparatus of the twenty-fifth aspect, the data correction method of the seventh aspect is suitably implemented.  
         [0059]     In its twenty-sixth aspect, the present invention provides the X-ray CT apparatus having the aforementioned configuration, characterized in that: said correction processing is edge enhancement.  
         [0060]     According to the X-ray CT apparatus of the twenty-sixth aspect, the data correction method of the eighth aspect is suitably implemented.  
         [0061]     In its twenty-seventh aspect, the present invention provides an X-ray CT apparatus characterized in comprising: an X-ray tube; a detector; scanning means for collecting a set of data while relatively rotating at least one of said X-ray tube and said detector around a subject to be imaged; and data correction processing means for applying correction processing in a view direction in a range in which variation of the data in the view direction is smaller, and applying no correction processing in the view direction in a range in which said variation of the data is larger.  
         [0062]     According to the X-ray CT apparatus of the twenty-seventh aspect, the data correction method of the ninth aspect is suitably implemented.  
         [0063]     In its twenty-eighth aspect, the present invention provides an X-ray CT apparatus characterized in comprising: an X-ray tube; a detector; scanning means for collecting a set of data while relatively rotating at least one of said X-ray tube and said detector around a subject to be imaged; and data correction processing means for applying correction processing in a channel direction in a range in which variation of the data in the channel direction is smaller, and applying no correction processing in the channel direction in a range in which said variation of the data is larger.  
         [0064]     According to the X-ray CT apparatus of the twenty-eighth aspect, the data correction method of the tenth aspect is suitably implemented.  
         [0065]     In its twenty-ninth aspect, the present invention provides an X-ray CT apparatus characterized in comprising: an X-ray tube; a detector; scanning means for collecting a set of data while relatively rotating at least one of said X-ray tube and said detector around a subject to be imaged; and data correction processing means for applying correction processing in a detector row direction in a range in which variation of the data in the detector row direction is smaller, and applying no correction processing in the detector row direction in a range in which said variation of the data is larger.  
         [0066]     According to the X-ray CT apparatus of the twenty-ninth aspect, the data correction method of the eleventh aspect is suitably implemented.  
         [0067]     In its thirtieth aspect, the present invention provides the X-ray CT apparatus having the aforementioned configuration, characterized in that: said data correction processing means decreases the degree of said correction processing in proportion as said variation of the data is larger.  
         [0068]     According to the X-ray CT apparatus of the thirtieth aspect, the data correction method of the twelfth aspect is suitably implemented.  
         [0069]     In its thirty-first aspect, the present invention provides the X-ray CT apparatus having the aforementioned configuration, characterized in that: said correction processing is smoothing.  
         [0070]     According to the X-ray CT apparatus of the thirty-first aspect, the data correction method of the thirteenth aspect is suitably implemented.  
         [0071]     In its thirty-second aspect, the present invention provides the X-ray CT apparatus having the aforementioned configuration, characterized in that: said data correction processing means applies first correction processing in the view direction in a range in which said variation of the data is larger, and second correction processing in the view direction in a range in which said variation of the data is smaller.  
         [0072]     According to the X-ray CT apparatus of the thirty-second aspect, the data correction method of the fourteenth aspect is suitably implemented.  
         [0073]     In its thirty-third aspect, the present invention provides the X-ray CT apparatus having the aforementioned configuration, characterized in that: said data correction processing means applies first correction processing in the channel direction in a range in which said variation of the data is larger, and second correction processing in the channel direction in a range in which said variation of the data is smaller.  
         [0074]     According to the X-ray CT apparatus of the thirty-third aspect, the data correction method of the fifteenth aspect is suitably implemented.  
         [0075]     In its thirty-fourth aspect, the present invention provides the X-ray CT apparatus having the aforementioned configuration, characterized in that: said data correction processing means applies first correction processing in the detector row direction in a range in which said variation of the data is larger, and second correction processing in the detector row direction in a range in which said variation of the data is smaller.  
         [0076]     According to the X-ray CT apparatus of the thirty-fourth aspect, the data correction method of the sixteenth aspect is suitably implemented.  
         [0077]     In its thirty-fifth aspect, the present invention provides the X-ray CT apparatus having the aforementioned configuration, characterized in that: said data correction processing means increases the degree of the first correction processing in proportion as said variation of the data is larger, and increases the degree of the second correction processing in proportion as said variation of the data is smaller.  
         [0078]     According to the X-ray CT apparatus of the thirty-fifth aspect, the data correction method of the seventeenth aspect is suitably implemented.  
         [0079]     In its thirty-sixth aspect, the present invention provides the X-ray CT apparatus having the aforementioned configuration, characterized in that: said first correction processing is edge enhancement, and said second correction processing is smoothing.  
         [0080]     According to the X-ray CT apparatus of the thirty-sixth aspect, the data correction method of the eighteenth aspect is suitably implemented.  
         [0081]     It should be noted that in the present invention, two or more of the following may be simultaneously applied: correction processing in the view direction, channel direction and detector row direction.  
         [0082]     Moreover, correction other than that in accordance with the present invention may be employed in combination. For example, correction on the magnitude of data may be employed in combination.  
         [0083]     According to the data correction method and X-ray CT apparatus of the present invention, correction adapted to the shape of the subject to be imaged can be achieved.  
         [0084]     The data correction method and X-ray CT apparatus of the present invention may be applied for improving image quality of a CT image.  
         [0085]     Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0086]      FIG. 1  is a configuration diagram showing an X-ray CT apparatus in accordance with Example 1.  
         [0087]      FIG. 2  is a flow chart showing the general operation of the X-ray CT apparatus in accordance with Example 1.  
         [0088]      FIG. 3  is a conceptual diagram of collected data set.  
         [0089]      FIG. 4  is a flow chart showing data correction processing in the detector row direction in accordance with Example 1.  
         [0090]      FIG. 5  is an explanatory diagram showing a case in which the shape of the subject to be imaged is complex in the detector row direction.  
         [0091]      FIG. 6  is an explanatory diagram showing a case in which the shape of the subject to be imaged is simple in the detector row direction.  
         [0092]      FIG. 7  is a flow chart showing data correction processing in the channel direction in accordance with Example 1.  
         [0093]      FIG. 8  is an explanatory diagram showing a case in which the shape of the subject to be imaged is simple in the channel direction.  
         [0094]      FIG. 9  is an explanatory diagram showing a case in which the shape of the subject to be imaged is complex in the channel direction.  
         [0095]      FIG. 10  is a conceptual diagram of a data set after fan-parallel conversion.  
         [0096]      FIG. 11  is a flow chart showing data correction processing in the view direction in accordance with Example 2.  
         [0097]      FIG. 12  is an explanatory diagram showing a case in which the shape of the subject to be imaged is complex in the rotation direction.  
         [0098]      FIG. 13  is an explanatory diagram showing a case in which the shape of the subject to be imaged is simple in the rotation direction.  
         [0099]      FIG. 14  is a flow chart showing data correction processing in the channel direction in accordance with Example 2.  
         [0100]      FIG. 15  is an explanatory diagram showing a case in which the shape of the subject to be imaged is complex in the channel direction.  
         [0101]      FIG. 16  is an explanatory diagram showing a case in which the shape of the subject to be imaged is simple in the channel direction. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0102]     The present invention will now be described in more detail with reference to embodiments shown in the accompanying drawings. It should be noted that the present invention is not limited to the embodiments.  
       EXAMPLE 1  
       [0103]      FIG. 1  is a configuration diagram showing an X-ray CT apparatus  100  in accordance with Example 1.  
         [0104]     The X-ray CT apparatus  100  comprises an operation console  1 , a table apparatus  10 , and a scan gantry  20 .  
         [0105]     The operation console  1  comprises an input device  2  for accepting inputs by a human operator, a central processing apparatus  3  for executing data collection processing, data correction processing, image reconstruction processing, and the like, a data collection buffer  5  for collecting data acquired at the scan gantry  20 , a CRT  6  for displaying a CT image reconstructed from the data, and a storage device  7  for storing programs, data, and X-ray CT images.  
         [0106]     The table apparatus  10  comprises a table  12  for laying thereon a subject to be imaged and transporting the subject into/out of a bore (cavity portion) of the scan gantry  20 . The table  12  is vertically and horizontally/rectilinearly moved by a motor incorporated in the table apparatus  10 .  
         [0107]     The scan gantry  20  comprises an X-ray tube  21 , an X-ray controller  22 , a collimator  23 , a detector  24 , a DAS (data acquisition system)  25 , a rotator-side controller  26  for controlling the X-ray controller  22 , collimator  23  and DAS  25 , an overall controller  29  for communicating control signals etc. with the operation console  1  and imaging table  10 , and a slip ring  30 .  
         [0108]     While a multi-row detector is assumed as the detector  24  here, the detector  24  may be a single-row detector.  
         [0109]      FIG. 2  is a flow chart showing the general operation of the X-ray CT apparatus  100 .  
         [0110]     At Step S 1 , data D(z, r, θ, c) represented by a rectilinear motion position z, a detector row index r, a fan angle θ, and a channel index c are collected while rotating the X-ray tube  21  and detector  24  around the subject to be imaged.  
         [0111]      FIG. 3  shows the collected data D(z, r, θ, c).  
         [0112]     The rectilinear motion position z is detected by an encoder in the table apparatus  10 , and it is constant in an axial scan while it varies in a helical scan. An axial scan is assumed here.  
         [0113]     The detector row index r(=1, 2, . . . , R) is a sequential number given to the detector rows, and R≧2 for a multi-row detector, and R=1 for a single-row detector.  
         [0114]     The fan angle θ(=0, δ, . . . , Θ) is an angle formed by the centerline of a fan beam with respect to a vertical axis, i.e., y-axis, and θ=0 when the centerline of a fan beam is parallel to the vertical axis i.e., y-axis, and the X-ray tube  21  lies on the upper side.  
         [0115]     The channel index c(=1, 2, . . . , C) is a sequential number given to the channels in each detector row.  
         [0116]     Referring again to  FIG. 2 , at Step S 2 , the collected data set is subjected to data correction processing in the detector row direction ( FIG. 4 ) and data correction processing in the channel direction ( FIG. 7 ), which will be described in detail later, and then to fan-parallel conversion.  
         [0117]     At Step S 3 , the data set is subjected to pre-processing (offset correction, log correction, X-ray dose correction, sensitivity correction, etc.).  
         [0118]     At Step S 4 , the data set is subjected to image reconstruction to produce a CT image.  
         [0119]     At Step S 5 , the produced CT image is subjected to post-processing for display.  
         [0120]      FIG. 4  is a flow chart showing details of data correction processing in the detector row direction.  
         [0121]     At Step Q 1 , the fan angle θ is initialized as θ=0.  
         [0122]     At Step Q 2 , the channel index c is initialized as c=1.  
         [0123]     At Step Q 3 , the detector row index r is initialized as r=1.  
         [0124]     At Step Q 4 , if the difference between data D(r, θ, c) of interest and data D(r+1, θ, c) at a detector row adjacent to the detector row corresponding to the data D(r, θ, c) is greater than a threshold Kr (empirically determined), the process goes to Step Q 5 ; otherwise to Step Q 7 .  
         [0125]     For example, if bones B extend in the channel direction and intercept an X-ray beam  21  a that otherwise impinges upon detector rows separated by one detector row as shown in  FIG. 5 , the difference between the data D(r, θ, c) of interest and the data D(r+1, θ, c) at a detector row adjacent to the detector row corresponding to the data D(r, θ, c) is greater than the threshold Kr, and accordingly the process goes to Step Q 5 . On the other hand, if bones B extend in the detector row direction and cause no difference in the X-ray beam  21   a  that impinges upon adjacent detector rows as shown in  FIG. 6 , the difference between the data D(r, θ, c) of interest and the data D(r+1, θ, c) at a detector row adjacent to the detector row corresponding to the data D(r, θ, c) is not greater than the threshold Kr, and accordingly the process goes to Step Q 7 .  
         [0126]     At Step Q 5 , edge enhancement is applied to the data D(r, θ, c) of interest in the detector row direction so that the degree of enhancement is increased for a larger difference between the data D(r, θ, c) of interest and the data D(r+1, θ, c) at a detector row adjacent to the detector row corresponding to the data D(r, θ, c). The process then goes to Step Q 7 .  
         [0127]     At Step Q 7 , if the detector row index r is not r≧R−1, the process goes to Step Q 8 ; otherwise, goes to Step Q 9 .  
         [0128]     At Step Q 8 , the detector row index r is incremented by one, and the process goes back to Step Q 4 .  
         [0129]     At Step Q 9 , if the channel index c is not c≧C, the process goes to Step Q 10 ; otherwise, goes to Step Q 11 .  
         [0130]     At Step Q 10 , the channel index c is incremented by one, and the process goes back to Step Q 3 .  
         [0131]     At Step Q 11 , if the fan angle θ is not θ≧Θ, the process goes to Step Q 12 ; otherwise, the process is terminated.  
         [0132]     At Step Q 12 , the fan angle θ is incremented by δ, and the process goes back to Step Q 2 .  
         [0133]      FIG. 7  is a flow chart showing details of data correction processing in the channel direction.  
         [0134]     At Step H 1 , the fan angle θ is initialized as θ=0.  
         [0135]     At Step H 2 , the detector row index r is initialized as r=1.  
         [0136]     At Step H 3 , the channel index c is initialized as c=1.  
         [0137]     At Step H 4 , if the difference between data D(r, θ, c) of interest and data D(r, θ, c+1) at a channel adjacent to the channel corresponding to the data D(r, θ, c) is smaller than a threshold Kc (empirically determined), the process goes to Step H 6 ; otherwise to Step H 7 .  
         [0138]     For example, if bones B extend in the channel direction and cause no difference in an X-ray beam  21   a  that impinges upon adjacent channels as shown in  FIG. 8 , the difference between the data D(r, θ, c) of interest and the data D(r, θ, c+1) at a channel adjacent to the channel corresponding to the data D(r, θ, c) is smaller than the threshold Kc, and accordingly the process goes to Step H 6 . On the other hand, if bones B extend in the detector row direction and intercept the X-ray beam  21  a that otherwise impinges upon channels separated by one channel as shown in  FIG. 9 , the difference between the data D(r, θ, c) of interest and the data D(r, θ, c+1) at a channel adjacent to the channel corresponding to the data D(r, θ, c) is not smaller than the threshold Kc, and accordingly the process goes to Step H 7 .  
         [0139]     At Step H 6 , smoothing is applied to the data D(r, θ, c) of interest in the channel direction so that the degree of smoothing is increased for a smaller difference between the data D(r, θ, c) of interest and the data D(r, θ, c+1) at a channel adjacent to the channel corresponding to the data D(r, θ, c). The process then goes to Step H 7 .  
         [0140]     At Step H 7 , if the channel index c is not c≧C−1, the process goes to Step H 8 ; otherwise, goes to Step H 9 .  
         [0141]     At Step H 8 , the channel index c is incremented by one, and the process goes back to Step H 4 .  
         [0142]     At Step H 9 , if the detector row index r is not r≧R, the process goes to Step H 10 ; otherwise, to Step H 11 .  
         [0143]     At Step H 10 , the detector row index r is incremented by one, and the process goes back to Step H 3 .  
         [0144]     At Step H 11 , if the fan angle θ is not θ≧Θ, the process goes to Step H 12 ; otherwise, the process is terminated.  
         [0145]     At Step H 12 , the fan angle θ is incremented by δ, and the process goes back to Step H 2 .  
         [0146]     According to the X-ray CT apparatus  100  of Example 1, edge enhancement is applied when the shape of the subject to be imaged is complex in the detector row direction, thereby improving spatial resolution. On the other hand, no edge enhancement is applied when the shape of the subject to be imaged is simple in the detector row direction, thus preventing exaggeration of noise. Moreover, since smoothing is applied when the shape of the subject to be imaged is simple in the channel direction, noise can be suppressed. On the other hand, no smoothing is applied when the shape of the subject to be imaged is complex in the channel direction, preventing degeneration of spatial resolution.  
       EXAMPLE 2  
       [0147]     In Example 2, the data set collected at Step S 1  in  FIG. 2  is subjected to fan-parallel conversion at Step S 2 , and then to data correction processing in the view direction ( FIG. 11 ) and data correction processing in the channel direction ( FIG. 14 ).  
         [0148]      FIG. 10  shows a data set after fan-parallel conversion.  
         [0149]     The view index v (=1, 2, . . . , V) is a sequential number given to the angle formed by an X-ray beam with respect to a vertical axis, i.e., y-axis.  
         [0150]      FIG. 11  is a flow chart showing details of data correction processing in the detector row direction.  
         [0151]     At Step P 1 , the detector row angle r is initialized as r=1.  
         [0152]     At Step P 2 , the channel index c is initialized as c=1.  
         [0153]     At Step P 3 , the view index v is initialized as v=1.  
         [0154]     At Step P 4 , if the difference between data D(r, v, c) of interest and data D(r, v+1, c) at a view adjacent to the view corresponding to the data D(r, v, c) is greater than a threshold Kv (empirically determined), the process goes to Step P 5 ; otherwise to Step P 6 .  
         [0155]     For example, if bones B lie side by side in the rotation direction and intercept an X-ray beam  21   a  that otherwise impinges upon views separated by one view as shown in  FIG. 12 , the difference between the data D(r, v, c) of interest and the data D(r, v+1, c) at a view adjacent to the view corresponding to the data D(r, v, c) is greater than the threshold Kv, and accordingly the process goes to Step P 5 . On the other hand, if a bone B extends in the rotation direction and causes no difference in the X-ray beam  21   a  that impinges upon adjacent views as shown in  FIG. 13 , the difference between the data D(r, v, c) of interest and the data D(r, v+1, c) at a view adjacent to the view corresponding to the data D(r, v, c) is not greater than the threshold Kv, and accordingly the process goes to Step P 6 .  
         [0156]     At Step P 5 , edge enhancement is applied to the data D(r, v, c) of interest in the view direction. The process then goes to Step P 7 .  
         [0157]     At Step P 6 , smoothing is applied to the data D(r, v, c) of interest in the view direction. The process then goes to Step P 7 .  
         [0158]     At Step P 7 , if the view index v is not v≧V−1, the process goes to Step P 8 ; otherwise, to Step P 9 .  
         [0159]     At Step P 8 , the view index v is incremented by one, and the process goes back to Step P 4 .  
         [0160]     At Step P 9 , if the channel index c is not c≧C, the process goes to Step P 10 ; otherwise, to Step P 11 .  
         [0161]     At Step P 10 , the channel index c is incremented by one, and the process goes back to Step P 3 .  
         [0162]     At Step P 11 , if the detector row index r is not r≧R, the process goes to Step P 12 ; otherwise, the process is terminated.  
         [0163]     At Step P 12 , the detector row index r is incremented by one, and the process goes back to Step P 2 .  
         [0164]      FIG. 14  is a flow chart showing details of data correction processing in the channel direction.  
         [0165]     At Step F 1 , the detector row index r is initialized as r=1.  
         [0166]     At Step F 2 , the view index v is initialized as v=1.  
         [0167]     At Step F 3 , the channel index c is initialized as c=1.  
         [0168]     At Step F 4 , if the difference between data D(r, v, c) of interest and data D(r, v, c+1) of a channel adjacent to the channel corresponding to the data D(r, v, c) is greater than a threshold Kc (empirically determined), the process goes to Step F 5 ; otherwise, to Step F 6 .  
         [0169]     For example, if bones B lie side by side in the detector row direction and intercept an X-ray beam  21   a  that otherwise impinges upon channels separated by one channel as shown in  FIG. 15 , the difference between the data D(r, v, c) of interest and the data D(r, v, c+1) at a channel adjacent to the channel corresponding to the data D(r, v, c) is greater than the threshold Kc, and accordingly the process goes to Step F 5 . On the other hand, if a bone B extends in the channel direction and causes no difference in the X-ray beam  21   a  that impinges upon adjacent channels as shown in  FIG. 16 , the difference between the data D(r, v, c) of interest and the data D(r, v, c+1) at a channel adjacent to the channel corresponding to the data D(r, v, c) is not greater than the threshold Kv, and accordingly the process goes to Step F 6 .  
         [0170]     At Step F 5 , edge enhancement is applied to the data D(r, v, c) of interest in the view direction so that the degree of enhancement is increased for a larger difference between the data D(r, v, c) of interest and the data D(r, v, c+1) at a view adjacent to the view corresponding to the data D(r, v, c). The process then goes to Step F 7 .  
         [0171]     At Step F 6 , smoothing is applied to the data D(r, v, c) of interest in the channel direction so that the degree of smoothing is increased for a smaller difference between the data D(r, v, c) of interest and the data D(r, v, c+1) at a channel adjacent to the channel corresponding to the data D(r, v, c). The process then goes to Step F 7 .  
         [0172]     At Step F 7 , if the channel index c is not c≧C−1, the process goes to Step F 8 ; otherwise, to Step F 9 .  
         [0173]     At Step F 8 , the channel index c is incremented by one, and the process goes back to Step F 4 .  
         [0174]     At Step F 9 , if the view index v is not v≧V, the process goes to Step F  10 ; otherwise, to Step F 11 .  
         [0175]     At Step F 10 , the view index v is incremented by one, and the process goes back to Step F 3 .  
         [0176]     At Step F 11 , if the detector row index r is not r≧R, the process goes to Step F 12 ; otherwise, the process is terminated.  
         [0177]     At Step F 12 , the detector row index r is incremented by one, and the process goes back to Step F 2 .  
         [0178]     According to the X-ray CT apparatus of Example 2, edge enhancement is applied when the shape of the subject to be imaged is complex in the view direction, thereby improving spatial resolution. On the other hand, since smoothing is applied when the shape of the subject to be imaged is simple in the view direction, noise can be suppressed. Moreover, edge enhancement is applied when the shape of the subject to be imaged is complex in the channel direction, thereby improving spatial resolution. On the other hand, since smoothing is applied when the shape of the subject to be imaged is simple in the channel direction, noise can be suppressed.  
         [0179]     Many widely different embodiments of the invention may be configured without departing from the spirit and the scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.