FIELD OF THE INVENTION

The present invention relates to navigation systems and, more particularly, to a system and method to using a probe trace to provide fiducial free tracking on a rigid body.

BACKGROUND

Image-guided surgical placement of dental implants significantly improves accuracy of placement of the dental implants, which improves the accuracy of the dental restoration, leading to better aesthetics and improved patient comfort. Current state-of-the-art image-guided surgical implant systems use stereo cameras to track and locate tracking reference components. One tracking reference component is rigidly attached to the dental drill that will be used to deliver the implant, which allows its position and orientation to be tracked. A second tracking reference component is affixed to the teeth, gums, or bone on the jaw that will receive the implant, allowing the drill's motion to be determined relative to a fixed reference frame on the surgical jaw

In order to be useful for image guidance, the surgical jaw's reference frame must be related back to the computed tomography (CT) volume in which the dental anatomy can be visualized, and in which the desired implant locations are defined by the surgeon. State-of-the-art systems facilitate the determination of this relation by relying upon attaching a fixture to the patient's surgical jaw, teeth, and/or gums prior to obtaining a cone-beam computed tomography (CBCT) volume. The fixture contains fiducials that are in an a prior known arrangement. The fiducials are made of material that can be located in the CBCT volume. The prior system uses the fiducials to determine the location and orientation of the fixture within the pre-operative CBCT scan. During the operation, the same fixture is replaced on the dental anatomy in the same location and the tracking reference components are attached to the fixture during surgery in order to relate pre-operative planning information to the real-time surgical tracking environment.

The conventional method for determining the relation between the real-time surgical tracking environment and the pre-operative CBCT planning environment imposes a number of limitations. Firstly, any discrepancy between where the fixture was during the CBCT scan, and where it is placed when attached during surgery results in inaccuracy of the guidance. Secondly, due to limited space within the oral cavity, the size of the fixture must be relatively small. As such, any inaccuracy grows with distance from the surgical site, this can limit accuracy. Thirdly, the requirement that the fixture be placed prior to CBCT acquisition imposes workflow burden. Surgeons often don't know whether a case is suitable for guidance until after analysis of the CBCT acquisition. The CBCT may be sent in from a referring doctor, which imposes coordination issues, and the doctors must manage an inventory of patient-specific fixtures between CBCT acquisition and time of surgery. The surgical environment also imposes additional placement constraints that may not be apparent at CBCT acquisition time, which may cause usability issues.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art by determining the relationship between the pre-operative CBCT and the real-time surgical environment without the aid of fiducials present in the pre-operative CBCT. This allows a fixture to be placed immediately prior to surgery, without the need for any fixture to be present in the pre-operative CBCT volume. As such, the present invention allows for use of any CBCT image to be used for performing guided surgery.

In a second embodiment of the invention, if a fixture is present in the CBCT scan, the present invention allows for correcting for imprecise placement of the fixture between pre-operative CBCT and a scan taken at the time of surgery-time.

In an embodiment of the invention, a method for referencing a tracking system's coordinate frame to a rigid body's coordinate frame is disclosed. The method involves providing the following (i) a 3D model depicting some of the surfaces of the rigid body, (ii) a probe with an affixed tracking reference component, and (iii) a rigidly affixed tracking reference component on the rigid body. The method tracks locations of the probe as it moves along surfaces of the rigid body, and determines a transform that relates the probe locations to the 3D model of the rigid body.

In one embodiment a method is disclosed for referencing a tracking system's coordinate frame to a rigid body's coordinate frame. The method includes providing (i) a 3D data set depicting some of the surfaces of the rigid body, (ii) a probe with an affixed tracking reference component, (iii) a rigidly affixed tracking reference component on the rigid body, and (iv) an initial transform that approximately relates the probe locations to the 3D data set of the rigid body. The method tracks the locations of the probe as it moves along surfaces of the rigid body and visually depicts the probe location in relation to the 3D dataset. The system then determines a plurality of estimates of the error between a given probe location and a portion of the surfaces in the 3D dataset. Using that data, the system determines a transform that relates the probe locations to the 3D model of the rigid body.

In another embodiment, a method is disclosed for referencing a tracking system's coordinate frame to a rigid body's coordinate frame. the method includes providing a computer display and displaying on the display a 3D data set depicting multiple surfaces of the rigid body, the rigid body including a person's oral cavity and at least some of the surfaces corresponding to the person's teeth or jawbone. The method includes providing a probe with an affixed tracking reference component, the probe having a probe tip, and a rigidly affixed tracking reference component on the rigid body. A signal is received when the probe tip is placed against a surface of the multiple surfaces and an approximate first location of the probe and probe tip is displayed on the 3D data set of the rigid body based on an initial transform. A line is generated on the display that is orthogonal to the first location of the probe tip. A signal is received to move the line relative to the 3D data set to a second location which corresponds to the depicted location in the 3D data set of an image corresponding to the surface of the multiple surfaces. An error value is determined that corresponds to the difference in location of the first and second locations and the error value is stored. A signal is received when the probe tip is placed against second surface of the multiple surfaces. Another line is generated on the display that is orthogonal to the depicted location of the probe tip relative to the second surface. A signal is received to move the line relative to the 3D data set to a second location which corresponds to the depicted location in the 3D data set of an image corresponding to the second surface. An error value is determined that corresponds to the difference in location of the first and second locations of the line with respect to the second surface and the error value is stored. A transform is determined based on the error values that relates the probe locations to the 3D model of the rigid body.

The 3D model in the embodiments disclosed herein can be a surface extracted from a computed tomography image of a patient's anatomy.

In any of the embodiments, the tracking system's coordinate frame may be attached to an electromagnetic field generator and the tracking reference components may be electromagnetic sensor coils.

In any of the embodiments, the tracking system's coordinate frame may be attached to a stereo optical tracking system.

In any of the embodiments, the tracking reference components may include contrast patterns.

In any of the embodiments, the tracking reference components may be arrays of reflective spheres.

In any of the embodiments, the tracking reference components may be arrays of light-emitting devices.

The probe in the embodiments disclosed herein may be an instrument with a spherical tip or a conical point.

The rigid body in the embodiments disclosed herein may be a dental mandible or maxilla of a patient.

In the methods disclosed herein the probe may be traced along and around the patient's teeth or along and around the patients jaw bone.

In the embodiments, the estimate of error is a correspondence between a probe tip location and a plane in the 3D data set.

The foregoing and other features of the invention and advantages of the present invention will become more apparent in light of the following detailed description of the preferred embodiments, as illustrated in the accompanying figures. As will be realized, the invention is capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not as restrictive.

