Optimizing camera calibration targets for 2D to 3D reconstruction
Described herein are calibration jigs and methods used to design and fabricate calibration jigs as well as associated workflows that may be used for determining the calibration parameters used to create a 2D image of a 3D scene, wherein the calibration jig has the shape of an isosceles right semi-triangular prism and is configured to ergonomically fit an anterior-medial tibial position on a patient's leg.
1. A method for capturing an X-ray image of a patient's leg comprising:
attaching a first calibration jig to the patient's leg in an anterior-medial tibial or posterior-lateral tibial position, wherein the first calibration jig has an isosceles right semi-triangular prism shape; and
verifying that the first calibration jig is in the anterior-medial tibial or posterior-lateral tibial position for the capturing of an X-ray image, wherein the verifying includes positioning an isosceles right side of the first calibration jig against a detector of a device used for the capturing of the X-ray image.
2. The method of claim 1 , further comprising capturing an X-ray image in an anterior-posterior (AP) projection and an X-ray image in a lateral projection.
3. The method of claim 1 , wherein a base of the semi-triangular prism is curved to ergonomically fit against the patient's leg.
4. The method of claim 1 , wherein a base of the semi-triangular prism is curved to ergonomically fit an anterior-medial tibial position on the patient's leg.
5. The method of claim 1 , wherein the first calibration jig includes an enclosure and a plurality of components housed inside the enclosure.
6. The method of claim 5 , wherein a positioning of the components within the enclosure is optimized to minimise an error metric selected from the group consisting of a reprojection error, an overlap error, and a 3D Euclidean distance error.
7. The method of claim 5 , wherein the components include spheres having different radii.
8. The method of claim 5 , further comprising:
providing 2D X-ray images of the first calibration jig attached to the patient's leg, wherein the components have known 3D coordinates within the first calibration jig;
determining a projection matrix from a projection of the known 3D coordinates to 2D image coordinates of the components captured in the 2D X-ray images; and
decomposing the projection matrix into intrinsic and extrinsic parameter matrices and using the intrinsic and extrinsic parameter matrices for 3D reconstruction from the 2D X-ray images,
wherein the extrinsic parameters relate to the position and rotation of an X-ray camera that captured the 2D X-ray images in relation to the 3D coordinates, and wherein the intrinsic parameters define internal parameters of the X-ray camera.
9. The method of claim 1 , further comprising positioning a second calibration jig in a femoral position on the patient's leg.
10. A calibration jig, comprising:
an enclosure;
a plurality of components housed inside the enclosure, and
a rigid adjustable attachment bar attached to the calibration jig and to a secondary calibration jig having the same shape as the calibration jig,
wherein the enclosure has an isosceles right semi-triangular prism shape, and
wherein the calibration jig is configured to be imaged by an X-ray imager.
11. The calibration jig of claim 10 , wherein a base of the semi-triangular prism is curved to ergonomically fit against a patient's leg.
12. The calibration jig of claim 10 , wherein a base of the semi-triangular prism is curved to ergonomically fit an anterior-medial tibial position on a patient's leg.
13. The calibration jig of claim 10 , wherein the components are not radio-opaque.
14. The calibration jig of claim 10 , wherein the components are held in fixed positions within the enclosure.