X-ray examination method and apparatus

1. An X-ray examination method comprising:

setting a tube voltage of an X-ray tube to a tube voltage that makes an X-ray absorptance difference between a first X-ray propagation medium and a second X-ray propagation medium with an X-ray absorbing power different from that of the first X-ray propagation medium in an object become not more than 10%;

applying an X-ray beam from the X-ray tube to the object while a tube voltage of the X-ray tube is set to the tube voltage; and

detecting a transmitted X-ray image including an X-ray refraction image formed in a region along a contour of a boundary surface between the first X-ray propagation medium and the second X-ray propagation medium by refraction of the X-ray beam by the boundary surface in superimposition on an X-ray absorption image reflecting the X-ray absorbing power difference between the first X-ray propagation medium and the second X-ray propagation medium.

2. A method according to claim 1 , further comprising:

image processing of extracting the X-ray refraction image component from the transmitted X-ray image.

3. A method according to claim 2 , wherein the image processing includes frequency enhancement processing of enhancing a high-frequency component of the transmitted X-ray image.

4. A method according to claim 2 , wherein the image processing comprises image sharpening processing.

5. A method according to claim 2 , wherein the image processing includes subtraction processing of at least partially subtracting a background image from which the X-ray refraction image is excluded from the transmitted X-ray image.

6. A method according to claim 5 , wherein a low-frequency component of the transmitted X-ray image is enhanced in at least part of the background image by frequency enhancement processing.

7. A method according to claim 5 , wherein at least part of the background image is obtained by sampling pixels more roughly than for the transmitted X-ray image.

8. A method according to claim 1 , wherein when a tube voltage is set for the X-ray tube, the tube voltage of the X-ray tube is set to 40 to 150 kVp if the object is a breast.

9. A method according to claim 1 , wherein the transmitted X-ray image is obtained by combining a plurality of images sensed a plurality of times while an application range of the X-ray beam is changed.

10. An X-ray examination apparatus comprising:

an X-ray tube which applies an X-ray beam to an object and a controller configured to set a tube voltage to make an X-ray absorptance difference between a first X-ray propagation medium and a second X-ray propagation medium with an X-ray absorbing power different from that of the first X-ray propagation medium in an object become not more than 10%;

a detector which detects a transmitted X-ray image transmitted through the object; and

an arrangement adjusting unit which sets a distance between the X-ray tube and the object and a distance between the object and the detector so as to obtain the transmitted X-ray image including an X-ray refraction image formed in a region along a contour of a boundary surface between the first X-ray propagation medium and the second X-ray propagation medium by refraction of the X-ray beam by the boundary surface in superimposition on an X-ray absorption image reflecting the X-ray absorbing power difference between the first X-ray propagation medium and the second X-ray propagation medium.

11. An apparatus according to claim 10 , further comprising:

an image processing unit which extracts the X-ray refraction image component from the transmitted X-ray image detected by the detector.

12. An apparatus according to claim 10 , wherein a tube voltage of the X-ray tube is set to 40 to 150 kVp if the object is a breast.

13. An apparatus according to claim 10 , wherein the X-ray tube changes an application direction of the X-ray beam to allow the object to be divisionally imaged a plurality of times while an application range of the X-ray beam is changed.

14. An apparatus according to claim 13 , wherein an application direction of the X-ray beam is changed by rotating the X-ray tube about a focal position.

15. An apparatus according to claim 13 , wherein the detector is adapted to move to receive all X-ray beams within an application range of the X-ray beam in conjunction with a change in the application direction of the X-ray beam.

16. An apparatus according to claim 13 , further comprising:

an image combining unit which forms the transmitted X-ray image by combining a plurality of images obtained by imaging the object a plurality of times while changing the application range of the X-ray beam.

17. An apparatus according to claim 10 , wherein letting p(J) be a maximum span dimension of a projection image of an X-ray focal spot which is transmitted through the object in the application direction J, and P is a set of p(J) throughout all application direction of the X-ray transmitted through the object, p(J)<100 μm for all the directions J, and maximum (P)/minimum (P)<2.

18. An apparatus according to claim 10 , wherein

the X-ray tube is adapted to set a tube voltage such that an X-ray absorptance difference between the first X-ray propagation medium and the second X-ray propagation medium becomes larger than 10%, and

the arrangement adjusting unit is adapted to make adjustment to bring the object and the detector into intimate contact with each other.

19. An apparatus according to claim 10 , wherein

the X-ray tube is adapted to set a tube voltage that makes an X-ray absorptance difference between the first X-ray propagation medium and the second X-ray propagation medium become larger than 10%, and

the arrangement adjusting unit is adapted to make adjustment to bring the object and the X-ray tube close to each other.