Multi-mode tomosynthesis/mammography gain calibration and image correction using gain map information from selected projection angles
A multi-mode tomosynthesis/mammography system and method in which a mammography gain map is used to gain correct mammographic images of a patient's breast but enhanced gain maps for respective projection angled are used to correct tomosynthesis images acquired with the same system.
1. A method of operating an x-ray breast tomosynthesis system comprising:
acquiring a multiplicity of x-ray tomosynthesis projection images of a patient's breast at respective projection angles of an imaging x-ray beam relative to the breast;
computer-processing the multiplicity of x-ray tomosynthesis projection images into a plurality of tomosynthesis slice images of the patient's breast, each tomosynthesis slice image representing a three-dimensional slab of breast tissue extending along a plane that is at respective angle relative to the breast;
generating, by a computer-implemented map generator, correction information that relates differences between image information from measured values and image information from expected values for at least one of the multiplicity of x-ray tomosynthesis projection images and the plurality of tomosynthesis slice images;
said correction information having been derived from multiple x-ray projection images of a phantom taken at respective different angles of an imaging x-ray beam to the phantom where said expected values relate to known information about the phantom;
applying, by a computer process, said correction information to at least one of the multiplicity of x-ray tomosynthesis projection images and the plurality of tomosynthesis slice images to obtain display images of the patient's breast; and
displaying the display images of the patient's breast on a display device.
2. The method of claim 1 , in which said generating comprises measuring x-rays transmitted through a phantom.
3. The method of claim 2 , in which said generating comprises measuring x-rays transmitted through a flat field phantom.
4. The method of claim 1 , in which said generating comprises generating respective correction information for each of a multiplicity of angles of an x-ray beam relative to an imaging position.
5. The method of claim 4 , in which said generating comprises generating initial correction information and deriving therefrom enhanced correction information, and said applying comprises applying the enhanced correction information.
6. The method of claim 5 , in which the initial correction information is derived for a first set of angles of an x-ray beam relative to an imaging position and the enhanced correction information is derived for a second set of angles of an x-ray beam relative to the imaging position, wherein the first and second set of angles are not identical.
7. The method of claim 4 , in which said applying comprises applying, to individual images selected from at least one of the multiplicity of x-ray tomosynthesis projection images and the plurality of tomosynthesis slice images, correction information derived for some but not all of said multiplicity of angles.
8. The method of claim 4 , in which said applying comprises applying the same correction information to each of plural images selected from at least one of the multiplicity of x-ray tomosynthesis projection images and the plurality of tomosynthesis slice images.
9. The method of claim 4 , in which said applying comprises applying, to respective images selected from at least one of the multiplicity of x-ray tomosynthesis projection images and the plurality of tomosynthesis slice images, different values of said correction information.
10. The method of claim 1 , in which said generating comprises retrieving, from one or more tables stored in a computer, data related to said correction information.
11. The method of claim 1 , in which said generating comprises:
obtaining x-ray tomosynthesis projection images of a phantom at each of a multiplicity of projection angles of an x-ray beam relative to the phantom;
obtaining respective initial gain maps for said multiplicity of projection angles relative to the phantom wherein said initial gain maps are related to differences between expected and actual characteristics of pixel values in said x-ray projection images of the phantom;
obtaining respective enhanced gain maps for said multiplicity of projection angles relative to the breast, said enhanced gain maps having been generated by computer-processing parameters derived from said initial gain maps; and
using the enhanced gain maps in said applying of correction information.
12. The method as in claim 11 , in which said enhanced gain map for a given projection angle relative to the breast is derived in a computer-implemented process that comprises using parameters of at least one initial gain map for a projection angle relative to the phantom that is closest in angle value to the given projection angle relative to the breast.
13. The method of claim 1 , in which the generating step comprises accessing a table of correction information for a multiplicity of angles of an x-ray beam relative to a breast platform, and the applying step comprises combining entries in the table to calculate correction information to apply to said multiplicity of x-ray tomosynthesis projection images or plurality of tomosynthesis slice images.
14. The method of claim 13 , in which said table contains correction information organized by angle of an x-ray beam relative to a breast platform and the applying step comprises applying, to a respective x-ray tomosynthesis projection image or tomosynthesis slice image of the breast, correction information interpolated from less than all entries in the table, selected from all entries based on closeness to a respective angle of the imaging beam relative to the breast or the angle of a slice plane.
15. The method of claim 1 , including applying a computer-aided detection process to at least one of the multiplicity of x-ray tomosynthesis projection images, the display images, and the plurality of tomosynthesis slice images.
16. The method of claim 1 , in which said acquiring comprises acquiring the multiplicity of x-ray tomosynthesis projection images of the patient's breast at projection angles in which the patient's breast is generally in an MLO orientation.
17. The method of claim 1 , in which said acquiring comprises acquiring the multiplicity of x-ray tomosynthesis projection images of the patient's breast from imaging position of a source of the imaging x-ray beam that are all to one side of the head of a sitting or upright patient.
18. The method of claim 1 , in which said acquiring comprises immobilizing the patient's breast between a breast platform and a compression paddle that are angled relative to a horizontal plane.
19. The method of claim 18 , in which the breast platform and the compression paddle are angled to place the breast in an MLO orientation.
20. The method of claim 1 , in which said acquiring comprises stopping a source of the imaging x-ray beam to take one of said multiplicity of x-ray tomosynthesis projection images of the breast and then moving the source to another position to take another one of said multiplicity of x-ray tomosynthesis projection images of the breast.
21. The method of claim 1 , in which said acquiring comprises continuously moving a source of the imaging x-ray beam while taking said multiplicity of x-ray tomosynthesis projection images of the breast.
22. A method of imaging a patient's breast with x-rays comprising:
acquiring a multiplicity of x-ray tomosynthesis projection images of the patient's breast at respective projection angles of an imaging x-ray beam relative to the breast;
wherein the acquiring step comprises acquiring said multiplicity of x-ray tomosynthesis projection images while the patient's breast is immobilized between surfaces that are angled to a long axis of the patient;
computer-processing the multiplicity of x-ray tomosynthesis projection images into a plurality of tomosynthesis slice images of the patient's breast, each slice image representing a three-dimensional slab of breast tissue extending along a plane that is at respective angle relative to the breast;
generating, by a computer-implemented map generator, correction information that relates differences between image information from measured values and image information from expected values for at least one of the multiplicity of x-ray tomosynthesis projection images and the plurality of tomosynthesis slice images;
said correction information having been derived from multiple x-ray projection images of a phantom taken at respective different angles of an imaging x-ray beam to the phantom where said expected values relate to known information about the phantom;
applying, by a computer process, said correction information to at least one of the multiplicity of x-ray tomosynthesis projection images and the plurality of tomosynthesis slice images to obtain display images of the patient's breast; and
displaying the display images of the patient's breast on a display device.
23. The method of claim 22 , in which said surfaces between which the breast is immobilized position the breast in an MLO orientation.
24. The method of claim 22 , in which said multiplicity of x-ray tomosynthesis projection images of the breast are acquired using an imaging x-ray beam originating from imaging positions that are all to one side of a long axis of the patient.
25. The method of claim 22 , in which said generating comprises retrieving data related to said correction information from one or more tables stored in computer memory.
26. An x-ray breast tomosynthesis system comprising:
an acquisition unit configured to acquire a multiplicity of x-ray tomosynthesis projection images of a patient's breast at respective angles of an imaging x-ray beam relative, to the breast;
a processing unit configured to computer-process the multiplicity of x-ray tomosynthesis projection images into a plurality of tomosynthesis slice images of the patient's breast, each tomosynthesis slice image representing a three-dimensional slab of breast tissue extending along a plane that is at respective angle relative to the breast;
a correction information generator configured to generate correction information that relates differences between image information from measured values and image information from expected values for at least one of the multiplicity of x-ray tomosynthesis projection images and the plurality of tomosynthesis slice images;
said correction information having been derived from multiple x-ray projection images of a phantom taken at respective different angles of an imaging x-ray beam to the phantom where said expected values relate to known information about the phantom;
said processing unit being further configured to apply the correction information to at least one of the multiplicity of x-ray tomosynthesis projection images and the plurality of tomosynthesis slice images to thereby obtain display images of the patient's breast; and
a display facility displaying the display images of the patient's breast.
27. The x-ray breast tomosynthesis system of claim 26 , including a breast platform and a compression paddle extending along planes angled to place the patient's breast in an MLO orientation for acquiring said multiplicity of x-ray tomosynthesis projection images with the acquisition unit.
28. The x-ray breast tomosynthesis system of claim 26 , including a source of said imaging x-ray beam and a support thereof moving the source along a path such that said multiplicity of x-ray tomosynthesis projection images of the breast are acquired from imaging positions of the source that are all to one side of a long axis of the patient.
29. The x-ray breast tomosynthesis system of claim 26 , in which said acquisition unit positions the patient's breast in an MLO orientation for acquiring said multiplicity of x-ray tomosynthesis projection images of the breast.
30. The x-ray breast tomosynthesis system of claim 26 , in which said correction information generator is configured to measure x-ray transmission through a phantom at plural angles of an imaging x-ray beam to the phantom and relate the measured transmission values to expected values of transmission through a phantom.