US 2015/0085072 A1 · AMBIGUITY-FREE OPTICAL TRACKING SYSTEM

Abstract

An ambiguity-free optical tracking system (100) includes a position sensor unit (104), a control box (106), a computer (110) and software. The position sensor unit includes two cameras (121 and 122) that track a plurality of individual infra-red reflecting markers (160) affixed on a patient's skin. Coordinates of the cameras in a coordinate system of the cameras are determined as part of a system calibration process by intentionally creating ambiguous markers with two true markers. Using this information, an ambiguity elimination algorithm automatically identifies and eliminates ambiguous markers. A recursive backtracking algorithm builds a one-to-one correspondence between reference markers and markers optically observed during treatment. By utilizing a concept of null markers, the backtracking algorithm deals with missing, misplaced and occluded markers.

Claims10

Dependent claims

A method of optically determining location and orientation of an object, comprising:

providing a position sensor, including two cameras and an illuminator for emitting infrared light;
determining coordinators of each of the two cameras;
placing a plurality of retro-reflective markers on an object;
creating a set of optical markers, and assigning coordinators to each optical marker, based on infrared light reflected by the retro-reflective markers and received by the position sensor;
forming every combination of three optical markers from the set of optical markers;
for each combination, determining if all three optical markers are in a same plane as the two cameras;
for each optical marker in each same-plane combination, determining whether an optical marker is in the vicinity of the other two optical markers, and, if so, determining whether such optical marker is one of:
closer to the two cameras than both of the other optical markers, and
farther from the two cameras than both of the other optical markers, and, if so,
identifying such optical marker as an ambiguous marker, and removing the ambiguous marker from the set of optical markers whereby the remaining optical markers form a set of true optical markers;
and
determining position and orientation of the object from the set of true optical markers.

9 more elements

A method of corresponding a set of reference markers [Ai] from a CT scan to a set of optical markers [Bj] detected by cameras in a radiation treatment room, comprising:

placing retro-reflective markers on a patient;
performing a CT scan of the patient and the retro-reflective markers;
assigning x, y, z coordinates to each reference marker of a set of reference markers that appears in the CT scan;
determining a distance between each reference markers and each of the other reference markers;
viewing the patient and the retro-reflective markers, with cameras in a radiation treatment room;
assigning x, y, z coordinates to each optical marker of a set of optical markers created as a result of the viewing;
determining a distance between each optical marker and each of the other optical markers;
calculating an error function E=Σi=1N-1Σj=2N∥dA(i, j)−dB(C(i), C(j)∥2 in an iterative fashion, where dA(i, j) denotes distance between two reference markers of the set of reference markers [Ai], dB(i, j) denotes distance between two optical markers of the set of optical markers [Bj], C is a mapping function that defines an index of an optical marker that corresponds to a reference marker, and N is a number of markers that are mapped;
and
determining a maximum N that minimizes E, subject to:
E≦δ, and
∥dA(i,j)−dB(C(i),C(j)∥≦ε,∀i,jεA,
where δ and ε depend on one or more of:
CT spatial resolution, CT noise, camera noise, magnitude of motion of the patient near the markers, number of markers, and reproducibility of placement of the markers on the patient.

11 more elements

A computer program product for corresponding a set of reference markers [Ai] that appears in a CT scan performed on a patient on which were located retro-reflective markers to a set of optical markers [Bj] that were created as a result of the retro-reflective markers being detected by cameras viewing the patient when the CT scan was performed, comprising:

a non-transitory computer readable medium;
and
computer program instructions for:
assigning x, y, z coordinates to each reference marker of the set of reference markers,
determining a distance between each reference markers and each of the other reference markers,
assigning x, y, z coordinates to each optical marker of a set of optical markers,
determining a distance between each optical marker and each of the other optical markers,
calculating an error function E=Σi=1N-1Σj=2N∥dA(i, j)−dB(C(i), C(j)∥2 in an iterative fashion, where dA(i, j) denotes distance between two reference markers of the set of reference markers [Ai], dB(i, j) denotes distance between two optical markers of the set of optical markers [Bj], C is a mapping function that defines an index of an optical marker that corresponds to a reference marker, and N is a number of markers that are mapped, and
determining a maximum N that minimizes E, subject to:
E≦δ, and
∥dA(i,j)−dB(C(i),C(j)∥≦ε,∀i,jεA,
where δ and ε depend on one or more of:
CT spatial resolution, CT noise, camera noise, magnitude of motion of the patient near the markers, number of markers, and reproducibility of placement of the markers on the patient.

10 more elements

Dependencies are inferred from the claim text.

Ambiguity-free optical tracking system

Life of this patent

Ambiguity-free optical tracking system

Life of this patent

Abstract

Claims10