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1. CA2861420 - METHOD FOR THREE-DIMENSIONAL LOCALIZATION OF AN OBJECT FROM A TWO-DIMENSIONAL MEDICAL IMAGE

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]
CLAIMS
1. A method for determining a three-dimensional location of an interventional medical device using a two-dimensional x-ray image obtained with an xray imaging system, the steps of the method comprising: a) obtaining x-ray images with the x-ray imaging system; b) producing an initial image by down-sampling one of the obtained x-ray images by a down-sampling factor; c) determining an initial position estimate of the medical device using the
initial image produced in step b); d) updating the initial position estimate by iteratively calculating a shiftinvariant similarity measure between the initial image and a template image, the template image depicting a synthesized x-ray projection of the medical device positioned at the initial position estimate, in which the initial position estimate and template image are updated in successive iterations and the shift-invariant similarity measure is iteratively calculated until the shift-invariant similarity measure exceeds a threshold value; e) refining the updated position estimate by iteratively calculating a shiftvariant similarity measure between the image and a template image, the template image depicting a synthesized x-ray projection of the medical device positioned at the updated position estimate, in which the updated position estimate and template image are updated in successive iterations and the shift-variant similarity measure is iteratively calculated until the shift-variant similarity measure exceeds a threshold value; and determining from the refined position estimate, at least one of the threedimensional location and orientation of the medical device.
2. The method as recited in claim 1 in which the initial position estimate is updated in step d) by adjusting a depth and three orientation position variables, and in which the updated position estimate is updated in step e) by adjusting a depth and three orientation position variables.
3. The method as recited in claim 1 in which the shift-invariant similarity
measure is a normalized cross-correlation, and in which the shift-variant similarity measure is a normalized similarity integral.
4. A method for determining a three-dimensional location of an object using
a two-dimensional image obtained with a medical imaging system, the steps of the method comprising: a) obtaining images with the medical imaging system; b) selecting one of the images obtained in step a); c) producing an initial image by down-sampling the image selected in step )
by a down-sampling factor; d) selecting an initial position estimate of the three-dimensional location of the object; e) calculating an updated position estimate by comparing the initial image with a template image of the object, the template image depicting a synthesized projection image of the object positioned in the medical imaging system at a position estimate that is in a neighborhood about the selected initial position estimate; calculating a refined position estimate by comparing the image selected in step b) with an updated template image, the updated template image depicting a
synthesized projection image of the object positioned in the medical imaging system at the updated position estimate; and h) determining from the refined position estimate calculated in step f), at least one of the three-dimensional location and orientation of the object.
5. The method as recited in claim 4 in which the down-sampling factor is four.
6. The method as recited in claim 4 in which the initial position estimate is selected in step d) by: i) calculating a similarity measure between the initial image and a plurality of stored template images, each stored template image depicting a synthesized projection image of the object positioned in the medical imaging system at a different initial position estimate; ii) identifying a stored template image that produces the largest similarity measure; and ii) selecting the initial position estimate as the different initial position estimate corresponding to the identified stored template image.
7. The method as recited in claim 6 in which the similarity measure calculated in step c)i) is a normalized cross-correlation.
8. The method as recited in claim 4 in which comparing the initial image and the template image in step e) includes calculating a similarity measure therebetween.
9. The method as recited in claim 8 in which the similarity measure is
normalized cross-correlation.
10. The method as recited in claim 9 in which calculating the normalized cross-correlation includes calculating shift values that shift the template image in a plane of the template image using a fast Fourier transform.
11. The method as recited in claim 10 in which calculating the normalized cross-correlation includes calculating a variance of the initial image using sum tables.
12. The method as recited in claim 8 in which step e) is performed iteratively until the similarity measure exceeds a threshold value, in which successive iterations include updating the position estimate and comparing the initial image with a template image depicting a synthesized projection image of the object positioned in the medical imaging system at the updated position estimate.
13. The method as recited in claim 4 in which comparing the image selected in step b) and the template image in step f) includes calculating a similarity measure therebetween.
14. The method as recited in claim 13 in which the similarity measure is a normalized similarity integral.
15. The method as recited in claim 14 in which step f) is performed iteratively until the similarity measure exceeds a threshold value, in which successive iterations include refining the position estimate and comparing the image selected in step b) with a template image depicting a synthesized projection image of the object positioned in the medical imaging system at the refined position estimate.
16. The method as recited in claim 4 in which the medical imaging system is
at least one of an x-ray imaging system and a magnetic resonance imaging system.
17. The method as recited in claim 16 in which the x-ray imaging system is
C-arm x-ray imaging system.
18. The method as recited in claim 4 in which the medical imaging system is
an x-ray imaging system, and the template images are synthesized x-ray projection images.
19. The method as recited in claim 4 in which the object is at least one of an interventional medical device and a marker.
20. The method as recited in claim 19 in which the interventional medical device is at least one of an electrophysiology catheter and an ablation catheter.