Mobile radiography calibration for tomosynthesis using epipolar data consistency
A method for geometric calibration of a radiography apparatus acquires tomosynthesis projection images of patient anatomy from a detector and an x-ray source translated along a scan path. An epipolar geometry is calculated according to the relative position of the detector to the scan path by estimating a direction for epipolar lines that extend along an image plane that includes the detector. A region of interest of the patient anatomy that is a portion of each projection image and is fully included within each projection image in the series is defined. A consistency metric is calculated for estimated epipolar lines extending within the ROI. The method iteratively adjusts the epipolar line estimation until the consistency metric indicates accuracy to within a predetermined threshold. A portion of a tomosynthesis volume is reconstructed and displayed.
1. A method for geometric calibration of a radiography apparatus, the method executed at least in part by a computer, comprising:
acquiring a series of tomosynthesis projection images of patient anatomy from a detector and an x-ray source at different positions along a scan path;
calculating an epipolar geometry according to the relative position of the detector to the scan path by:
(i) estimating a direction for each of a plurality of epipolar lines that extend along an image plane that includes the detector;
(ii) defining a region of interest (ROI) of the patient anatomy, wherein the ROI is a portion of each projection image and is fully included within each projection image in the series;
(iii) using two or more projection images in the series, calculating a consistency metric that is indicative of the accuracy of epipolar line estimation for each of the plurality of estimated epipolar lines extending within the corresponding ROI; and
(iv) iteratively adjusting the epipolar line estimation and repeating step (iii) until the consistency metric indicates accuracy to within a predetermined threshold;
reconstructing at least a portion of a tomosynthesis volume image according to the calculated epipolar geometry; and
displaying, storing, or transmitting the reconstructed portion of the tomosynthesis volume image.
2. The method of claim 1 wherein acquiring the series of tomosynthesis projection images comprises translating the x-ray source along the source path.
3. The method of claim 1 wherein the x-ray source uses an array of x-ray sources.
4. The method of claim 1 wherein iteratively adjusting the epipolar line estimation comprises calculating a cost function.
5. The method of claim 1 wherein defining the region of interest comprises providing one or more radio-opaque markers in the image content.
6. The method of claim 1 wherein defining the region of interest comprises identifying patient anatomy in each projection image in the tomosynthesis series using template-matching.
7. The method of claim 1 wherein calculating the consistency metric comprises comparing the derivatives of the series of calculated line integrals for the two or more projection images.
8. The method of claim 1 wherein the step of acquiring a series of tomosynthesis projection images of patient anatomy includes acquiring a series of tomosynthesis projection images of the patient's chest.
9. The method of claim 1 wherein calculating the consistency metric comprises calculating a weighted line integral for estimated epipolar lines extending within the corresponding ROI.
10. A method for geometric calibration of a radiography apparatus, the method executed at least in part by a computer and comprising:
a) acquiring a series of tomosynthesis projection images of patient anatomy by energizing an x-ray source of the radiography apparatus at a plurality of positions along a scan path and directing x-ray radiation toward a detector that is positionally uncoupled from the x-ray source;
b) calculating an epipolar geometry according to the relative position of the detector to the scan path by:
(i) identifying a direction for each of a plurality of epipolar lines that extend along an image plane that includes the detector;
(ii) defining a region of interest ROI of the patient anatomy that is a partial portion of each projection image in the series, wherein the ROI is fully included within each acquired projection image in the series; and
(iii) using two or more acquired projection images in the series, calculating a weighted line integral for each of the plurality of epipolar lines extending within the corresponding ROI and optimizing the calculated epipolar geometry according to a comparison of the derivatives obtained from the calculated line integrals for the two or more projection images; and
c) reconstructing and displaying at least a portion of a tomosynthesis volume image according to the calculated epipolar geometry.
11. The method of claim 10 wherein the x-ray source uses an array of x-ray sources.
12. The method of claim 10 wherein the radiography apparatus is a mobile radiography apparatus.
13. The method of claim 10 wherein acquiring the series of tomosynthesis projection images comprises translating the x-ray source along the source path.
14. The method of claim 10 wherein the x-ray source uses an array of x-ray sources.
15. A radiography apparatus, comprising:
an x-ray source configured to provide radiation from different positions along a scan path;
a detector configured to acquire a series of tomosynthesis projection images of patient anatomy corresponding to the different positions of the x-ray source along the scan path;
control circuitry programmed to calculate epipolar consistency according to the relative position of the detector to the scan path by:
(i) estimating a direction for each of a plurality of epipolar lines that extend along an image plane that includes the detector;
(ii) defining a region of interest ROI of the patient anatomy, wherein the ROI is a portion of each projection image and is fully included within each projection image in the series;
(iii) using two or more projection images in the series, calculating a consistency metric that is indicative of the accuracy of epipolar line estimation for each of the plurality of estimated epipolar lines extending within the corresponding ROI;
(iv) iteratively adjusting the epipolar line estimation and repeating step (iii) until the consistency metric indicates accuracy to within a predetermined threshold; and
(v) reconstructing a tomosynthesis volume according to the calculated epipolar consistency; and
a display configured to display at least a portion of the reconstructed tomosynthesis volume.
16. The apparatus of claim 15 wherein the radiography apparatus is a mobile radiography apparatus.
17. The apparatus of claim 15 wherein the x-ray source is an array of x-ray sources.