Calibration for surgical navigation
Examples of the disclosure include methods and systems for calibrating a C-arm imaging device for surgical navigation. Calibrating the C-arm imaging device may include, for a plurality of positions of the C-arm imaging device, determining the position of the C-arm imaging device, receiving an image of a calibration fixture from the C-arm imaging device, determining the position of the calibration fixture and a tracking array positioned on the C-arm imaging device, determining intrinsic parameters using the image and the position of the calibration fixture, and determining extrinsic parameters using the position of the tracking array relative to a detector of the C-arm imaging device. Calibrating the C-arm imaging device may include modeling parameters for the C-arm imaging device and iteratively tuning the model.
1. A method for calibrating a C-arm imaging device, comprising:
for each of a plurality of positions of the C-arm imaging device:
determining an angulation value and an orbital value of the C-arm imaging device,
preoperatively receiving an image of a calibration fixture from the C-arm imaging device, the imaging having been taken while the C-arm imaging device had the angulation value and the orbital value,
determining the position of the calibration fixture and the position of a tracking array positioned on the C-arm imaging device relative to a detector plane of a detector of the C-arm imaging device using a tracking system,
determining intrinsic parameters using the image of the calibration fixture and the position of the calibration fixture, and
determining extrinsic parameters using the position of the tracking array relative to the detector plane; and
generating a model configured to receive orbital and angulation values for a current pose of the C-arm imaging device as input and configured to provide as output extrinsic and intrinsic parameters of the C-arm imaging device, wherein generating the model includes:
determining initial parameters using the intrinsic parameters, the extrinsic parameters, the angulation value, and the orbital value of the plurality of positions of the C-arm imaging device,
determining intermediate parameters using the intrinsic parameters, the angulation value, and the orbital value of the plurality of positions of the C-arm imaging device, and a fixed set of extrinsic parameters, and
determining final parameters using the initial parameters and the intermediate parameters,
wherein at least two of the images received were taken while the C-arm imaging device is in motion.
2. The method of claim 1 , wherein the intrinsic parameters comprise:
a focal length;
a first offset in a first axis between an emitter of the C-arm imaging device and the detector; and
a second offset in a second axis between the emitter and the detector.
3. The method of claim 1 , wherein the extrinsic parameters comprise:
a first translation in a first axis between the tracking array and the detector plane;
a second translation in a second axis between the tracking array and the detector plane;
a third translation in a third axis between the tracking array and the detector plane;
a first rotational offset in the first axis between the tracking array and the detector plane;
a second rotational offset in the second axis between the tracking array and the detector plane; and
a third rotational offset in the third axis between the tracking array and the detector plane.
4. The method of claim 1 , wherein:
determining the intermediate parameters comprises tuning the initial parameters to form the intermediate parameters.
5. The method of claim 1 , wherein the model is a functional form model; and
wherein generating the model includes performing a functional fit for the intrinsic parameters and the extrinsic parameters.
6. The method of claim 1 , wherein, for each of the plurality of positions of the C-arm imaging device, the image, the position of the calibration fixture, and the position of the tracking array positioned on the C-arm imaging device relative to the detector plane are time synchronized.
7. The method of claim 1 , further comprising using the model for at least three months without updating the model.
8. The method of claim 7 , further comprising:
updating the model, wherein the updating includes:
for two new positions of the C-arm imaging device:
determining the angulation value and the orbital value of the C-arm imaging device,
receiving a new image of the calibration fixture from the C-arm imaging device,
determining the position of the calibration fixture and the position of the tracking array positioned on the C-arm imaging device relative to the detector plane using the tracking system,
determining new intrinsic parameters using the new image of the calibration fixture and the position of the calibration fixture, and
determining new extrinsic parameters using the position of the tracking array relative to the detector plane; and
updating the model based on the new intrinsic parameters, the new extrinsic parameters, the angulation value, and the orbital value for the two new positions of the C-arm imaging device.
9. A system for calibrating a C-arm imaging device, comprising:
a calibration fixture configured to be imaged by the C-arm imaging device;
a tracking array configured to be positioned on the C-arm imaging device;
a tracking device configured to track the calibration fixture and the tracking array; and
a C-arm calibration device comprising one or more processors and a memory, wherein the memory comprises instructions that, when executed by the one or more processors, causes the one or more processors to:
for each of a plurality of positions of the C-arm imaging device:
determine an angulation value and an orbital value of the C-arm imaging device,
preoperatively receive an image of the calibration fixture from the C-arm imaging device,
determine the position of the calibration fixture and the position of the tracking array positioned on the C-arm imaging device relative to a detector plane of a detector of the C-arm imaging device using the tracking device,
determine intrinsic parameters using the image of the calibration fixture and the position of the calibration fixture,
determine extrinsic parameters using the position of the tracking array relative to the detector plane;
generate a model using the intrinsic parameters, the extrinsic parameters, the angulation value, and the orbital value of the plurality of positions of the C-arm imaging device, and
update the model after no less than three months.
10. The system of claim 9 , wherein the memory further comprises instructions that, when executed by the one or more processors, causes the one or more processors to perform an iterative functional form calibration to refine the model.
11. The system of claim 10 , wherein to perform the iterative functional form calibration to refine the model comprises to:
fix a set of extrinsic parameters;
determine intermediate parameters using the intrinsic parameters, the angulation value, and the orbital value of the plurality of positions of the C-arm imaging device and the fixed set of extrinsic parameters; and
determine final parameters of the C-arm imaging device using the parameters and the intermediate parameters.
12. The system of claim 9 , wherein the model is configured to receive orbital and angulation values for a current pose of the C-arm imaging device as input and configured to provide as output extrinsic and intrinsic parameters of the C-arm imaging device.
13. The system of claim 9 , where generating the model includes to perform a functional fit for the intrinsic parameters and the extrinsic parameters.
14. The system of claim 9 , wherein the intrinsic parameters comprise:
a focal length;
a first offset in first axis between an emitter of the C-arm imaging device and the detector; and
a second offset in a second axis between the emitter and the detector.
15. The system of claim 9 , wherein the extrinsic parameters comprise:
a first translation in a first axis between the tracking array and the detector plane;
a second translation in a second axis between the tracking array and the detector plane;
a third translation in a third axis between the tracking array and the detector plane;
a first rotational offset in the first axis between the tracking array and the detector plane;
a second rotational offset in the second axis between the tracking array and the detector plane; and
a third rotational offset in the third axis between the tracking array and the detector plane.
16. The system of claim 9 , where to update the model comprises to:
for two new positions of the C-arm imaging device:
determine the angulation value and the orbital value of the C-arm imaging device,
cause the C-arm imaging device to capture a new image of the calibration fixture,
determine the position of the calibration fixture and the position of the tracking array positioned on the C-arm imaging device relative to the detector plane,
determine new intrinsic parameters using the new image of the calibration fixture and the position of the calibration fixture, and
determine new extrinsic parameters using the position of the tracking array relative to the detector plane; and
update the model based on the new intrinsic parameters, the new extrinsic parameters, the angulation value, and the orbital value for the two new positions of the C-arm imaging device.
17. The system of claim 9 , further comprising a display device configured to display images, wherein the memory further comprises instructions that, when executed by the one or more processors, causes the one or more processors to:
render a surgical instrument in a location in a medical image; and
cause the display device to display the medical image including the rendered surgical instrument.
18. The system of claim 9 , wherein to generate the model is performed offline.