Method and apparatus for detecting prospective abnormal patterns

• US 6,272,233 B1
• Filed: 08/26/1998
• Issued: 08/07/2001
• Est. Priority Date: 08/27/1997
• Status: Expired due to Fees

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Takeo, Hideya
• Primary Examiner(s): Mancusco, Joseph
• Assistant Examiner(s): Tabatabai, Abolfazl
• Application Number:
  US09/140,774
• Time in Patent Office: 1,077 Days
• Field of Search: 382/128, 382/132, 382/129, 382/257, 382/130, 382/131, 250/587, 378/37
• US Class Current: 382/128
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 2207/30068 Mammography; Breast
• CPC Class Codes: G06T 2207/30096 Tumor; Lesion
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 7/0012 Biomedical image inspection
• CPC Class Codes: G06T 7/11 Region-based segmentation
• CPC Class Codes: G06T 7/66 of image moments or centre of gravity
• CPC Class Codes: Y10S 128/922 including image analysis

Abstract

A prospective abnormal pattern is detected in accordance with one of image signals representing radiation images of the right and left mammae of an object. A region of the detected prospective abnormal pattern in one radiation image, which is represented by the one image signal, and a region in the other mamma radiation image, which region corresponds to the position of the region of the detected prospective abnormal pattern in the one radiation image, are set. Iris filter processing is carried out on image signal components, which represent picture elements located in the region of the detected prospective abnormal pattern in the one radiation image, and on image signal components, which represent picture elements located in the region in the other mamma radiation image. Iris filter output signals are thereby obtained. A calculation is made to find a difference value between the iris filter output signals, which have been obtained with respect to corresponding picture elements in the regions. A definite prospective abnormal pattern is detected in accordance with the difference value.

Claims

1. A method of detecting a definite prospective abnormal pattern, in which an image signal representing a radiation image of a right mamma of an object and an image signal representing a radiation image of a left mamma of the object are obtained, each of the image signals being made up of a series of image signal components representing picture elements in the radiation image, and wherein a prospective abnormal pattern is detected from one of the radiation images of either one of the right and left mammae in accordance with the image signals, the method comprising the steps of:

(a) detecting the prospective abnormal pattern in one of the image signals representing the radiation images of the right and left mammae,

(b) setting a region of the detected prospective abnormal pattern in one radiation image, which is represented by the one image signal, and setting a region in the radiation image of the opposite mamma, which region corresponds to the position of said region of the detected prospective abnormal pattern in the one radiation image,

(c) carrying out iris filter processing on image signal components, which represent picture elements located in both regions set in step (b), respective iris filter output signals being thereby obtained,

(d) calculating a difference value between said respective iris filter output signals, which have been obtained with respect to corresponding picture elements in said both regions, and

(e) determining the definite prospective abnormal pattern from said difference value calculated in step (d).

2. A method as defined in claim 1 wherein the detection of the prospective abnormal pattern is carried out with a process comprising the steps of:

(1) for each picture element among all of the picture elements in the one radiation image of the mamma, which is represented by the one image signal, calculating a gradient vector of the image signal,

(2) setting an arbitrary picture element, which is among all of the picture elements in the radiation image, as a picture element of interest,

(3) setting a plurality of radial direction lines on the radiation image, said radial direction lines extending radially from said picture element of interest and being adjacent to one another at predetermined angle intervals,

(4) calculating an index value cos θ

il for each picture element among the picture elements, which are located along each of said radial direction lines and fall within the range from said picture element of interest to a picture element that is located at a length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, said index value cos θ

il being calculated from an angle θ

il that is made between said gradient vector, which has been calculated for said each picture element, and the direction along which said each radial direction line extends,

(5) calculating a mean value of the index values cos θ

il having been calculated for the picture elements, which are located along each of said radial direction lines and fall within the range from a starting point to an end point, said starting point being set at said picture element of interest, said end point being set at one of the picture elements that are located between a position at a length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected and the position at the length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, a plurality of the mean values being obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(6) calculating the maximum value of said mean values of said index values cos θ

il, which mean values have been obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(7) calculating a total sum of the maximum values, which have been obtained for all of the plurality of said radial direction lines, a value of the degree of centralization of the gradient vector group with respect to said picture element of interest being thereby calculated,

(8) comparing the value of said degree of centralization of the gradient vector group, which value has been calculated by the operation of step (7) defined above, and a predetermined threshold value with each other,

(9) judging that said picture element of interest is located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is not smaller than the predetermined threshold value, and judging that said picture element of interest is not located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is less than the predetermined threshold value,

(10) successively setting the picture element of interest at all of the picture elements in the radiation image, repeating the operations of steps (3) to (9) defined above, and making judgments as to whether the respective picture elements are or are not located within the region of the prospective abnormal pattern,

(11) calculating the center of gravity on a region constituted of the picture elements, which have been judged as being located within the region of the prospective abnormal pattern,

(12) taking a picture element corresponding to the position, at which the center of gravity is located, as the picture element of interest, and thereby specifying a picture element corresponding to the end point that is associated with the mean value of the index values cos θ

il having been calculated for each of said radial direction lines, which mean value takes the maximum value in the operation of step (6) defined above,

(13) setting said specified picture element, which corresponds to said end point on each of said radial direction lines, as a marginal point of the region of the prospective abnormal pattern in the direction along which said each radial direction line extends, a plurality of the marginal points being thereby set on the plurality of said radial direction lines, and

(14) connecting the adjacent marginal points, which have been set on the plurality of said radial direction lines, by predetermined lines, the region surrounded by the connecting lines being extracted as the prospective abnormal pattern.

3. A method as defined in claim 1 wherein the detection of the prospective abnormal pattern is carried out with a process comprising the steps of:

(1) for each picture element among all of the picture elements in the one radiation image of the mamma, which is represented by the one image signal, calculating a gradient vector of the image signal,

(2) setting an arbitrary picture element, which is among all of the picture elements in the radiation image, as a picture element of interest,

(3) setting a plurality of radial direction lines on the radiation image, said radial direction lines extending radially from said picture element of interest and being adjacent to one another at predetermined angle intervals,

(4) calculating an index value cos θ

il for each picture element among the picture elements, which are located along each of said radial direction lines and fall within the range from a picture element that is located at a length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected, the length of distance being taken from said picture element of interest, to a picture element that is located at a length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, the length of distance being taken from said picture element of interest, said index value cos θ

il being calculated from an angle θ

il that is made between said gradient vector, which has been calculated for said each picture element, and the direction along which said each radial direction line extends,

(5) calculating a mean value of the index values cos θ

il having been calculated for the picture elements, which are located along each of said radial direction lines and fall within the range from a starting point to an end point, said starting point being set at the picture element that is located at the length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected, said end point being set at one of the picture elements that are located between the position at the length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected and the position at the length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, a plurality of the mean values being obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(6) calculating the maximum value of said mean values of said index values cos θ

il, which mean values have been obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(7) calculating a total sum of the maximum values, which have been obtained for all of the plurality of said radial direction lines, a value of the degree of centralization of the gradient vector group with respect to said picture element of interest being thereby calculated,

(8) comparing the value of said degree of centralization of the gradient vector group, which value has been calculated by the operation of step (7) defined above, and a predetermined threshold value with each other,

(9) judging that said picture element of interest is located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is not smaller than the predetermined threshold value, and judging that said picture element of interest is not located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is less than the predetermined threshold value,

(10) successively setting the picture element of interest at all of the picture elements in the radiation image, repeating the operations of steps (3) to (9) defined above, and making judgments as to whether the respective picture elements are or are not located within the region of the prospective abnormal pattern,

(11) calculating the center of gravity on a region constituted of the picture elements, which have been judged as being located within the region of the prospective abnormal pattern,

(12) taking a picture element corresponding to the position, at which the center of gravity is located, as the picture element of interest, and thereby specifying a picture element corresponding to the end point that is associated with the mean value of the index values cos θ

il having been calculated for each of said radial direction lines, which mean value takes the maximum value in the operation of step (6) defined above,

(13) setting said specified picture element, which corresponds to said end point on each of said radial direction lines, as a marginal point of the region of the prospective abnormal pattern in the direction along which said each radial direction line extends, a plurality of the marginal points being thereby set on the plurality of said radial direction lines, and

(14) connecting the adjacent marginal points, which have been set on the plurality of said radial direction lines, by predetermined lines, the region surrounded by the connecting lines being extracted as the prospective abnormal pattern.

4. A method of detecting a definite prospective abnormal pattern, in which an image signal representing a radiation image of a right mamma of an object and an image signal representing a radiation image of a left mamma of the object are obtained, each of the image signals being made up of a series of image signal components representing picture elements in the radiation image, and wherein a prospective abnormal pattern is detected from one of the radiation images of either one of the right and left mammae by utilizing the respective image signals, the method comprising the steps of:

(a) detecting the prospective abnormal pattern of one of the image signals representing the radiation images of the right and left mammae,

(b) setting a region of the detected prospective abnormal pattern in one radiation image, which is represented by the one image signal, and setting a region in the radiation image of the opposite mamma, which region corresponds to the position of said region of the detected prospective abnormal pattern in the one radiation image,

(c) carrying out iris filter processing on image signal components, which represent picture elements located in both regions set in step (b), respective iris filter output signals being thereby obtained,

(d) calculating a difference value between said respective iris filter output signals, which have been obtained with respect to corresponding picture elements in said both regions,

(e) calculating a rating function value, which represents a degree of malignancy of the detected prospective abnormal pattern, in accordance with the image signal components, which represent the picture elements located in said region of the detected prospective abnormal pattern in the one radiation image, and

(f) determining the definite prospective abnormal pattern in accordance with said rating function value and said difference value.

5. A method as defined in claim 4 wherein the detection of the prospective abnormal pattern is carried out with a process comprising the steps of:

(1) for each picture element among all of the picture elements in the one radiation image of the mamma, which is represented by the one image signal, calculating a gradient vector of the image signal,

(2) setting an arbitrary picture element, which is among all of the picture elements in the radiation image, as a picture element of interest,

(3) setting a plurality of radial direction lines on the radiation image, said radial direction lines extending radially from said picture element of interest and being adjacent to one another at predetermined angle intervals,

(4) calculating an index value cos θ

il for each picture element among the picture elements, which are located along each of said radial direction lines and fall within the range from said picture element of interest to a picture element that is located at a length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, said index value cos θ

il being calculated from an angle θ

il that is made between said gradient vector, which has been calculated for said each picture element, and the direction along which said each radial direction line extends,

(5) calculating a mean value of the index values cos θ

il having been calculated for the picture elements, which are located along each of said radial direction lines and fall within the range from a starting point to an end point, said starting point being set at said picture element of interest, said end point being set at one of the picture elements that are located between a position at a length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected and the position at the length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, a plurality of the mean values being obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(6) calculating the maximum value of said mean values of said index values cos θ

il, which mean values have been obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(7) calculating a total sum of the maximum values, which have been obtained for all of the plurality of said radial direction lines, a value of the degree of centralization of the gradient vector group with respect to said picture element of interest being thereby calculated,

(8) comparing the value of said degree of centralization of the gradient vector group, which value has been calculated by the operation of step (7) defined above, and a predetermined threshold value with each other,

(9) judging that said picture element of interest is located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is not smaller than the predetermined threshold value, and judging that said picture element of interest is not located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is less than the predetermined threshold value,

(10) successively setting the picture element of interest at all of the picture elements in the radiation image, repeating the operations of steps (3) to (9) defined above, and making judgments as to whether the respective picture elements are or are not located within the region of the prospective abnormal pattern,

(11) calculating the center of gravity on a region constituted of the picture elements, which have been judged as being located within the region of the prospective abnormal pattern,

(12) taking a picture element corresponding to the position, at which the center of gravity is located, as the picture element of interest, and thereby specifying a picture element corresponding to the end point that is associated with the mean value of the index values cos θ

il having been calculated for each of said radial direction lines, which mean value takes the maximum value in the operation of step (6) defined above,

(13) setting said specified picture element, which corresponds to said end point on each of said radial direction lines, as a marginal point of the region of the prospective abnormal pattern in the direction along which said each radial direction line extends, a plurality of the marginal points being thereby set on the plurality of said radial direction lines, and

(14) connecting the adjacent marginal points, which have been set on the plurality of said radial direction lines, by predetermined lines, the region surrounded by the connecting lines being extracted as the prospective abnormal pattern.

6. A method as defined in claim 4 wherein the detection of the prospective abnormal pattern is carried out with a process comprising the steps of:

(1) for each picture element among all of the picture elements in the one radiation image of the mamma, which is represented by the one image signal, calculating a gradient vector of the image signal,

(2) setting an arbitrary picture element, which is among all of the picture elements in the radiation image, as a picture element of interest,

(3) setting a plurality of radial direction lines on the radiation image, said radial direction lines extending radially from said picture element of interest and being adjacent to one another at predetermined angle intervals,

(4) calculating an index value cos θ

il for each picture element among the picture elements, which are located along each of said radial direction lines and fall within the range from a picture element that is located at a length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected, the length of distance being taken from said picture element of interest, to a picture element that is located at a length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, the length of distance being taken from said picture element of interest, said index value cos θ

il being calculated from an angle θ

il that is made between said gradient vector, which has been calculated for said each picture element, and the direction along which said each radial direction line extends,

(5) calculating a mean value of the index values cos θ

il having been calculated for the picture elements, which are located along each of said radial direction lines and fall within the range from a starting point to an end point, said starting point being set at the picture element that is located at the length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected, said end point being set at one of the picture elements that are located between the position at the length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected and the position at the length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, a plurality of the mean values being obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(6) calculating the maximum value of said mean values of said index values cos θ

il, which mean values have been obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(7) calculating a total sum of the maximum values, which have been obtained for all of the plurality of said radial direction lines, a value of the degree of centralization of the gradient vector group with respect to said picture element of interest being thereby calculated,

(8) comparing the value of said degree of centralization of the gradient vector group, which value has been calculated by the operation of step (7) defined above, and a predetermined threshold value with each other,

(9) judging that said picture element of interest is located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is not smaller than the predetermined threshold value, and judging that said picture element of interest is not located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is less than the predetermined threshold value,

(10) successively setting the picture element of interest at all of the picture elements in the radiation image, repeating the operations of steps (3) to (9) defined above, and making judgments as to whether the respective picture elements are or are not located within the region of the prospective abnormal pattern,

(11) calculating the center of gravity on a region constituted of the picture elements, which have been judged as being located within the region of the prospective abnormal pattern,

(12) taking a picture element corresponding to the position, at which the center of gravity is located, as the picture element of interest, and thereby specifying a picture element corresponding to the end point that is associated with the mean value of the index values cos θ

il having been calculated for each of said radial direction lines, which mean value takes the maximum value in the operation of step (6) defined above,

(13) setting said specified picture element, which corresponds to said end point on each of said radial direction lines, as a marginal point of the region of the prospective abnormal pattern in the direction along which said each radial direction line extends, a plurality of the marginal points being thereby set on the plurality of said radial direction lines, and

(14) connecting the adjacent marginal points, which have been set on the plurality of said radial direction lines, by predetermined lines, the region surrounded by the connecting lines being extracted as the prospective abnormal pattern.

7. An apparatus for detecting a definite prospective abnormal pattern, in which an image signal representing a radiation image of a right mamma of an object and an image signal representing a radiation image of a left mamma of the object are obtained, each of the image signals being made up of a series of image signal components representing picture elements in the radiation image, and wherein a prospective abnormal pattern is detected from one of the radiation images of either one of the right and left mammae using the respective image signals, the apparatus comprising:

(a) detection means for detecting the prospective abnormal pattern of one of the image signals representing the radiation images of the right and left mammae,

(b) region setting means for setting a region of the detected prospective abnormal pattern in one radiation image, which is represented by the one image signal, and for setting a region in the radiation image of the opposite mamma, which region corresponds to the position of said region of the detected prospective abnormal pattern in the one radiation image,

(c) iris filter processing means for carrying out iris filter processing on image signal components, which represent picture elements located in both regions set by said region setting means, respective iris filter output signals being thereby obtained,

(d) difference value calculating means for calculating a difference value between said respective iris filter output signals, which have been obtained with respect to corresponding picture elements in said both regions, and

(e) definite prospective abnormal pattern detecting means for detecting the definite prospective abnormal pattern using said difference value calculated by said difference value calculating means.

8. An apparatus as defined in claim 7 wherein said detection means comprises:

(i) a gradient vector calculating means for calculating a gradient vector of the image signal, the calculation being made for each picture element among all of the picture elements in the one radiation image of the mamma, which is represented by the one image signal,

(ii) a picture-element-of-interest setting means for setting an arbitrary picture element, which is among all of the picture elements in the radiation image, as a picture element of interest, the picture elements being successively set as said picture element of interest,

(iii) a detection size setting means for setting the minimum size and the maximum size of the prospective abnormal pattern to be detected,

(iv) a direction line setting means for setting a plurality of radial direction lines on the radiation image, said radial direction lines extending radially from said picture element of interest and being adjacent to one another at predetermined angle intervals,

(v) an index value calculating means for calculating an index value cos θ

il for each picture element among the picture elements, which are located along each of said radial direction lines and fall within the range from said picture element of interest to a picture element that is located at a length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, said index value cos θ

il being calculated from an angle θ

il that is made between said gradient vector, which has been calculated for said each picture element, and the direction along which said each radial direction line extends,

(vi) a maximum value calculating means for calculating a mean value of the index values cos θ

il having been calculated for the picture elements, which are located along each of said radial direction lines and fall within the range from a starting point to an end point, said starting point being set at said picture element of interest, said end point being set at one of the picture elements that are located between a position at a length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected and the position at the length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, a plurality of the mean values being obtained for each of said radial direction lines by successively setting said end point at the picture elements,

said maximum value calculating means extracting the maximum value of said mean values of said index values cos θ

il, which mean values have been obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(vii) a centralization degree calculating means for calculating a total sum of the maximum values, which have been obtained for all of the plurality of said radial direction lines, and thereby calculating a value of the degree of centralization of the gradient vector group with respect to said picture element of interest,

(viii) a comparison and judgment means for comparing the value of said degree of centralization of the gradient vector group, which value has been calculated by said centralization degree calculating means, and a predetermined threshold value with each other,

said comparison and judgment means judging that said picture element of interest is located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is not smaller than the predetermined threshold value, and judging that said picture element of interest is not located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is less than the predetermined threshold value,

(ix) a center-of-gravity calculating means for calculating the center of gravity on a region constituted of the picture elements, which have been judged as being located within the region of the prospective abnormal pattern,

(x) a marginal point setting means for taking a picture element corresponding to the position, at which the center of gravity is located, as the picture element of interest, and thereby specifying a picture element corresponding to the end point that is associated with the maximum value having been extracted by said maximum value calculating means, said picture element corresponding to the end point being specified with respect to each of said radial direction lines,

said marginal point setting means setting said specified picture element, which corresponds to said end point on each of said radial direction lines, as a marginal point of the region of the prospective abnormal pattern in the direction along which said each radial direction line extends, a plurality of the marginal points being thereby set on the plurality of said radial direction lines, and

(xi) a contour extracting means for connecting the adjacent marginal points, which have been set on the plurality of said radial direction lines, by predetermined lines, and extracting the region, which is surrounded by the connecting lines, as the prospective abnormal pattern.

9. An apparatus as defined in claim 7 wherein said detection means comprises:

(i) a gradient vector calculating means for calculating a gradient vector of the image signal, the calculation being made for each picture element among all of the picture elements in the one radiation image of the mamma, which is represented by the one image signal,

(ii) a picture-element-of-interest setting means for setting an arbitrary picture element, which is among all of the picture elements in the radiation image, as a picture element of interest, the picture elements being successively set as said picture element of interest,

(iii) a detection size setting means for setting the minimum size and the maximum size of the prospective abnormal pattern to be detected,

(iv) a direction line setting means for setting a plurality of radial direction lines on the radiation image, said radial direction lines extending radially from said picture element of interest and being adjacent to one another at predetermined angle intervals,

(v) an index value calculating means for calculating an index value cos θ

il for each picture element among the picture elements, which are located along each of said radial direction lines and fall within the range from a picture element that is located at a length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected, the length of distance being taken from said picture element of interest, to a picture element that is located at a length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, the length of distance being taken from said picture element of interest, said index value cos θ

il being calculated from an angle θ

il that is made between said gradient vector, which has been calculated for said each picture element, and the direction along which said each radial direction line extends,

(vi) a maximum value calculating means for calculating a mean value of the index values cos θ

il having been calculated for the picture elements, which are located along each of said radial direction lines and fall within the range from a starting point to an end point, said starting point being set at the picture element that is located at the length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected, said end point being set at one of the picture elements that are located between the position at the length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected and the position at the length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, a plurality of the mean values being obtained for each of said radial direction lines by successively setting said end point at the picture elements,

said maximum value calculating means extracting the maximum value of said mean values of said index values cos θ

il, which mean values have been obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(vii) a centralization degree calculating means for calculating a total sum of the maximum values, which have been obtained for all of the plurality of said radial direction lines, and thereby calculating a value of the degree of centralization of the gradient vector group with respect to said picture element of interest,

(viii) a comparison and judgment means for comparing the value of said degree of centralization of the gradient vector group, which value has been calculated by said centralization degree calculating means, and a predetermined threshold value with each other,

said comparison and judgment means judging that said picture element of interest is located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is not smaller than the predetermined threshold value, and judging that said picture element of interest is not located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is less than the predetermined threshold value,

(ix) a center-of-gravity calculating means for calculating the center of gravity on a region constituted of the picture elements, which have been judged as being located within the region of the prospective abnormal pattern,

(x) a marginal point setting means for taking a picture element corresponding to the position, at which the center of gravity is located, as the picture element of interest, and thereby specifying a picture element corresponding to the end point that is associated with the maximum value having been extracted by said maximum value calculating means, said picture element corresponding to the end point being specified with respect to each of said radial direction lines,

said marginal point setting means setting said specified picture element, which corresponds to said end point on each of said radial direction lines, as a marginal point of the region of the prospective abnormal pattern in the direction along which said each radial direction line extends, a plurality of the marginal points being thereby set on the plurality of said radial direction lines, and

(xi) a contour extracting means for connecting the adjacent marginal points, which have been set on the plurality of said radial direction lines, by predetermined lines, and extracting the region, which is surrounded by the connecting lines, as the prospective abnormal pattern.

10. An apparatus for detecting a definite prospective abnormal pattern, in which an image signal representing a radiation image of a right mamma of an object and an image signal representing a radiation image of a left mamma of the object are obtained, each of the image signals being made up of a series of image signal components representing picture elements in the radiation image, and wherein a prospective abnormal pattern is detected from one of the radiation images of either one of the right and left mammae using the respective image signals, the apparatus comprising:

(a) detection means for detecting the prospective abnormal pattern of one of the image signals representing the radiation images of the right and left mammae,

(b) region setting means for setting a region of the detected prospective abnormal pattern in one radiation image, which is represented by the one image signal, and for setting a region in the radiation image of the opposite mamma, which region corresponds to the position of said region of the detected prospective abnormal pattern in the one radiation image,

(c) iris filter processing means for carrying out iris filter processing on image signal components, which represent picture elements located in both regions set by said region setting means, respective iris filter output signals being thereby obtained,

(d) difference value calculating means for calculating a difference value between said respective iris filter output signals, which have been obtained with respect to corresponding picture elements in said both regions,

(e) rating function value calculating means for calculating a rating function value, which represents a degree of malignancy of the detected prospective abnormal pattern, in accordance with the image signal components, which represent the picture elements located in said region of the detected prospective abnormal pattern in the one radiation image, and

(f) definite prospective abnormal pattern detecting means for detecting the definite prospective abnormal pattern using said rating function value, which has been calculated by said rating function value calculating means, and said difference value, which has been calculated by said difference value calculating means.

11. An apparatus as defined in claim 10 wherein said detection means comprises:

(i) a gradient vector calculating means for calculating a gradient vector of the image signal, the calculation being made for each picture element among all of the picture elements in the one radiation image of the mamma, which is represented by the one image signal,

(ii) a picture-element-of-interest setting means for setting an arbitrary picture element, which is among all of the picture elements in the radiation image, as a picture element of interest, the picture elements being successively set as said picture element of interest,

(iii) a detection size setting means for setting the minimum size and the maximum size of the prospective abnormal pattern to be detected,

(iv) a direction line setting means for setting a plurality of radial direction lines on the radiation image, said radial direction lines extending radially from said picture element of interest and being adjacent to one another at predetermined angle intervals,

(v) an index value calculating means for calculating an index value cos θ

il for each picture element among the picture elements, which are located along each of said radial direction lines and fall within the range from said picture element of interest to a picture element that is located at a length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, said index value cos θ

il being calculated from an angle θ

il that is made between said gradient vector, which has been calculated for said each picture element, and the direction along which said each radial direction line extends,

(vi) a maximum value calculating means for calculating a mean value of the index values cos θ

il having been calculated for the picture elements, which are located along each of said radial direction lines and fall within the range from a starting point to an end point, said starting point being set at said picture element of interest, said end point being set at one of the picture elements that are located between a position at a length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected and the position at the length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, a plurality of the mean values being obtained for each of said radial direction lines by successively setting said end point at the picture elements,

said maximum value calculating means extracting the maximum value of said mean values of said index values cos θ

il, which mean values have been obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(vii) a centralization degree calculating means for calculating a total sum of the maximum values, which have been obtained for all of the plurality of said radial direction lines, and thereby calculating a value of the degree of centralization of the gradient vector group with respect to said picture element of interest,

(viii) a comparison and judgment means for comparing the value of said degree of centralization of the gradient vector group, which value has been calculated by said centralization degree calculating means, and a predetermined threshold value with each other,

said comparison and judgment means judging that said picture element of interest is located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is not smaller than the predetermined threshold value, and judging that said picture element of interest is not located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is less than the predetermined threshold value,

(ix) a center-of-gravity calculating means for calculating the center of gravity on a region constituted of the picture elements, which have been judged as being located within the region of the prospective abnormal pattern,

(x) a marginal point setting means for taking a picture element corresponding to the position, at which the center of gravity is located, as the picture element of interest, and thereby specifying a picture element corresponding to the end point that is associated with the maximum value having been extracted by said maximum value calculating means, said picture element corresponding to the end point being specified with respect to each of said radial direction lines,

said marginal point setting means setting said specified picture element, which corresponds to said end point on each of said radial direction lines, as a marginal point of the region of the prospective abnormal pattern in the direction along which said each radial direction line extends, a plurality of the marginal points being thereby set on the plurality of said radial direction lines, and

(xi) a contour extracting means for connecting the adjacent marginal points, which have been set on the plurality of said radial direction lines, by predetermined lines, and extracting the region, which is surrounded by the connecting lines, as the prospective abnormal pattern.

12. An apparatus as defined in claim 10 wherein said detection means comprises:

(i) a gradient vector calculating means for calculating a gradient vector of the image signal, the calculation being made for each picture element among all of the picture elements in the one radiation image of the mamma, which is represented by the one image signal,

(ii) a picture-element-of-interest setting means for setting an arbitrary picture element, which is among all of the picture elements in the radiation image, as a picture element of interest, the picture elements being successively set as said picture element of interest,

(iii) a detection size setting means for setting the minimum size and the maximum size of the prospective abnormal pattern to be detected,

(iv) a direction line setting means for setting a plurality of radial direction lines on the radiation image, said radial direction lines extending radially from said picture element of interest and being adjacent to one another at predetermined angle intervals,

(v) an index value calculating means for calculating an index value cos θ

il for each picture element among the picture elements, which are located along each of said radial direction lines and fall within the range from a picture element that is located at a length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected, the length of distance being taken from said picture element of interest, to a picture element that is located at a length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, the length of distance being taken from said picture element of interest, said index value cos θ

il being calculated from an angle θ

il that is made between said gradient vector, which has been calculated for said each picture element, and the direction along which said each radial direction line extends,

(vi) a maximum value calculating means for calculating a mean value of the index values cos θ

il having been calculated for the picture elements, which are located along each of said radial direction lines and fall within the range from a starting point to an end point, said starting point being set at the picture element that is located at the length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected, said end point being set at one of the picture elements that are located between the position at the length of distance corresponding to the minimum size of the prospective abnormal pattern to be detected and the position at the length of distance corresponding to the maximum size of the prospective abnormal pattern to be detected, a plurality of the mean values being obtained for each of said radial direction lines by successively setting said end point at the picture elements,

said maximum value calculating means extracting the maximum value of said mean values of said index values cos θ

il, which mean values have been obtained for each of said radial direction lines by successively setting said end point at the picture elements,

(vii) a centralization degree calculating means for calculating a total sum of the maximum values, which have been obtained for all of the plurality of said radial direction lines, and thereby calculating a value of the degree of centralization of the gradient vector group with respect to said picture element of interest,

(viii) a comparison and judgment means for comparing the value of said degree of centralization of the gradient vector group, which value has been calculated by said centralization degree calculating means, and a predetermined threshold value with each other,

said comparison and judgment means judging that said picture element of interest is located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is not smaller than the predetermined threshold value, and judging that said picture element of interest is not located within the region of the prospective abnormal pattern in cases where the value of said degree of centralization of the gradient vector group is less than the predetermined threshold value,

(ix) a center-of-gravity calculating means for calculating the center of gravity on a region constituted of the picture elements, which have been judged as being located within the region of the prospective abnormal pattern,

(x) a marginal point setting means for taking a picture element corresponding to the position, at which the center of gravity is located, as the picture element of interest, and thereby specifying a picture element corresponding to the end point that is associated with the maximum value having been extracted by said maximum value calculating means, said picture element corresponding to the end point being specified with respect to each of said radial direction lines,

said marginal point setting means setting said specified picture element, which corresponds to said end point on each of said radial direction lines, as a marginal point of the region of the prospective abnormal pattern in the direction along which said each radial direction line extends, a plurality of the marginal points being thereby set on the plurality of said radial direction lines, and

(xi) a contour extracting means for connecting the adjacent marginal points, which have been set on the plurality of said radial direction lines, by predetermined lines, and extracting the region, which is surrounded by the connecting lines, as the prospective abnormal pattern.

13. A method for detecting a definite prospective abnormal pattern in mammae, said method comprising:

(a) obtaining a first radiation image of a first mamma and a second radiation image of a second mamma;

(b) detecting a prospective abnormal pattern in one of the first and second radiation images;

(c) disposing said first and second radiation images to be symmetrical about an axis of symmetry;

(d) carrying out iris filter processing on image signal components of a region at which the prospective abnormal pattern was detected in one of the first and second radiation images at step (b), and on image signal components in a corresponding region opposite said axis of symmetry in the other one of said first and second radiation images, whereby respective iris filter output signals are obtained for each of said regions, and

(e) determining a definite prospective abnormal pattern based upon the respective iris filter output signals.

14. The method of determining a definite prospective abnormal pattern as claimed in claim 13, wherein determining the definite prospective abnormal pattern based on said respective iris filter output signals comprises, calculating a difference value between the respective iris filter output signals, and comparing the difference value to a predetermined value.

15. The method of determining a definite prospective abnormal pattern as claimed in claim 13, wherein determining the definite prospective abnormal pattern further comprises calculating a rating function value, which represents a degree of malignancy of the detected prospective abnormal pattern.

16. The method of determining a definite prospective abnormal pattern according to claim 15, wherein calculating a rating function value comprises determining a Mahalanobis distance of said prospective abnormal pattern and, comparing the Mahalanobis distance to a predetermined nominal value.