Mobile radiography calibration for tomosynthesis using epipolar geometry
A method for geometric calibration of a mobile radiography apparatus, executed at least in part by a computer, acquires a series of tomosynthesis projection images of a patient positioned between an x-ray source of the mobile radiography apparatus and a detector that is positionally uncoupled from the x-ray source. A vector field is generated having a first set of vectors indicative of feature movement between a first acquired projection image and a second acquired projection image. The generated vector field is associated with an epipolar geometry according to an optimization of an energy relationship between an epipolar model and the generated vector field values. The mobile radiography apparatus is calibrated according to the associated model epipolar geometry. At least a portion of the tomosynthesis image is reconstructed and displayed.
1. A method for geometric calibration of a mobile radiography apparatus having an x-ray source, the method executed at least in part by a computer, comprising:
calculating an x-ray source path;
calculating a pitch of the x-ray source path:
acquiring a series of tomosynthesis projection images of a patient positioned between the x-ray source and a detector positionally uncoupled from the x-ray source, the series including a first and second acquired projection image;
generating a vector field having a first set of vectors indicative of feature movement between the first and second acquired projection images;
generating an associated model epipolar geometry by associating the generated vector field with an epipolar geometry according to an optimization of an energy relationship between an epipolar model and the generated vector field;
calibrating the mobile radiography apparatus according to the associated model epipolar geometry;
reconstructing at least a portion of one of the acquired tomosynthesis projection images according to the calibration; and
displaying, on a display, the reconstructed tomosynthesis projection image.
2. The method of claim 1 wherein the optimization of the energy relationship is determined by computing dot product calculations between the first set of vectors and vector data from the model epipolar geometry.
3. The method of claim 1 wherein acquiring the series of tomosynthesis projection images includes translating the x-ray source along the x-ray source path.
4. The method of claim 1 wherein acquiring the series of tomosynthesis projection images includes using an array of x-ray sources.
5. The method of claim 1 further comprising normalizing the first set of vectors to unit vectors.
6. A method for geometric source-detector calibration of a mobile radiography apparatus having an x-ray source, the method executed at least in part by a computer, comprising:
calculating an x-ray source path;
calculating a pitch of the x-ray source path:
acquiring a series of tomosynthesis projection images of a patient using a detector positioned behind the patient relative to the x-ray source, the detector being mechanically uncoupled from the x-ray source, the series including a first and second acquired projection image;
generating a vector field having a first set of unit vectors indicative of an image feature movement between the first and second acquired projection images;
calculating an epipolar geometry for the acquired series of tomosynthesis projection images according to the vector field;
calibrating the x-ray source path to an image plane according to the calculated epipolar geometry;
reconstructing at least a portion of one of the acquired tomosynthesis images according to the calibrated x-ray source path; and
displaying, on a display, the reconstructed tomosynthesis projection image.
7. The method of claim 6 wherein generating the vector field is accomplished using a set of image features.
8. The method of claim 6 wherein calculating an epipolar geometry includes calculating a spatial location of an epipole disposed outside of the image plane.
9. A method for geometric calibration of a mobile radiography apparatus having an x-ray source, the method executed at least in part by a computer, comprising:
calculating an x-ray source path;
calculating a pitch of the x-ray source path:
moving the x-ray source along the x-ray source path to acquire a series of tomosynthesis projection images of a patient on a digital detector positioned behind the patient relative to the x-ray source, the series including a first acquired projection image acquired at a first x-ray source position and a second acquired projection image acquired at a second x-ray source position;
generating a vector field having a first set of vectors indicative of feature movement between the first and second acquired projection images;
calculating a spatial location of an epipole according to the generated vector field;
calculating a source-to-detector distance according to (i) the epipole spatial location, (ii) a difference between the first and second x-ray source positions, and (iii) a relative movement distance of an image feature between at least two acquired projection images;
calibrating the x-ray source path to the detector according to the calculated source-to-detector distance; and
reconstructing at least a portion of one of the acquired tomosynthesis projection images according to the calibrated x-ray source path; and
displaying, on a display, the reconstructed tomosynthesis projection image.
10. The method of claim 9 further comprising calculating a skew between the x-ray source path and the detector.
11. The method of claim 9 wherein calculating the source-to-detector distance comprises using a marker positioned in the x-ray source path.