Computer assisted targeting device for use in orthopaedic surgery

A method for accurately superimposing a representation of a surgical tool over images of a body part, comprising the steps of:

• providing an imaging device with an imaging model with imaging model parameters that are dependent on an orientation of the imaging device;
• positioning the imaging device in a plurality of orientations and measuring said orientations;
• providing a calibration grid having markers disposed in fixed and known locations, visible in x-ray images;
• using the imaging device to take an x-ray image of the calibration grid at each orientation of the imaging device, said x-ray image of the calibration grid having shadows corresponding to the markers on the calibration grid;
• calculating first imaging model parameters corresponding to each orientation of the imaging device by locating the shadows of the markers on the calibration grid in the x-ray image of the calibration grid;
• storing the first imaging model parameters with the corresponding measured orientation of the imaging device for the plurality of orientations of the imaging device;
• positioning the imaging device relative to the body part and measuring the orientation of the imaging device;
• using the imaging device to take an x-ray image of the body part;
• calculating second imaging model parameters through interpolation of the stored first imaging model parameters based on the measured orientation of the imaging device;
• determining a pose of the surgical tool relative to the imaging device;
• mathematically projecting the representation of the surgical tool through an imaging model using the second imaging model parameters;
• and
• superimposing the projected representation of the surgical tool on a display of the x-ray image of the body part.

An image guided surgery system to enable a surgeon to move one or more surgical tools into a desired pose relative to a body part, comprising:

• an imaging device for generating a plurality of images of the body part, the imaging device outfitted with localizing emitters wherein the imaging device has an imaging source and an imaging receiver;
• one or more surgical tools outfitted with localizing emitters;
• a localizing device comprising two or more sensor units, each with a coordinate frame and comprising a plurality of sensor elements, including a first sensor unit able to view and calculate the pose of the imaging device and a second sensor unit able to view and calculate the pose of the one or more surgical tools;
• means for displaying representations of the one or more surgical tools relative to images of the body part;
• means for determining a relationship among the coordinate frames of the two or more sensor units;
• and an imaging model with imaging model parameters for modeling the projection and mapping of points between the imaging source and the imaging receiver of the imaging device to the plurality of images wherein the imaging model parameters are dependent on the orientation of the imaging device.

A computer assisted surgery system to enable a surgeon to move one or more tracked objects into a desired pose relative to a body part, comprising:

• at least two tracked objects, wherein one of the tracked objects is an imaging device having an imaging source and an imaging receiver for generating a plurality of images of the body part;
• a localizing device for measuring the poses of the tracked objects, said localizing device comprising two or more sensor units, each with an associated coordinate frame and comprising a plurality of individual sensor elements, each sensor unit being capable of providing sufficient data to permit the calculation of the poses of the tracked objects;
• means for determining the poses of the tracked objects based on the data from one or more sensor units;
• means for determining the relationship among the coordinate frames of the sensor units
• and an imaging model with imaging model parameters for modeling the projection and mapping of points between the imaging source and the imaging receiver of the imaging device to the plurality of images wherein the imaging model parameters are dependent on the orientation of the imaging device.

A method for determining the pose of a surgical tool relative to an imaging device wherein the surgical tool is located on a first side of a surgical drape and the imaging device is located on a second side of the surgical drape, comprising the steps of:

• providing a localizing device with two or more sensor units, each sensor unit having a coordinate frame wherein the two or more sensor units comprise at least a first sensor unit and a second sensor unit;
• positioning a registration object such that its pose may be measured by at least the first sensor unit and the second sensor unit;
• using at least the first sensor unit to measure the pose of the registration object relative to the coordinate frame of said first sensor unit;
• using at least the second sensor unit to measure the pose of the registration object relative to the coordinate frame of said second sensor unit;
• calculating the relationships among the coordinate frames of at least the first and second sensor units;
• placing the surgical drape between the imaging device and the surgical tool such that the first sensor unit is able to measure the pose of the imaging device on the first side of the surgical drape, and the second sensor unit is able to measure the pose of the surgical tool on the second side of the surgical drape and wherein the surgical drape covers the imaging device;
• and using the previously calculated relationships among the coordinate frames of at least the first and second sensor units to calculate the pose of the surgical tool relative to the imaging device.

A method for measuring the pose of a tracked object located on either side of an obstructing object, comprising the steps of:

• providing a localizing device with two or more sensor units, each sensor unit having its own coordinate frame;
• selecting the coordinate frame of one of the two or more sensor units as a reference coordinate frame;
• placing a registration object in view of all of the two or more sensor units;
• using each of the sensor units to measure the pose of the registration object relative to that sensor unit's coordinate frame;
• calculating the relationships among the coordinate frames of all sensor units;
• placing the obstructing object such that the first sensor unit is able to measure the pose of a first tracked object on a first side of the obstructing object, wherein the first tracked object is an imaging device and wherein the obstructing object is a surgical drape and the second sensor unit is able to measure the pose of a second tracked object on a second side of the obstructing object, wherein the second tracked object is a surgical tool and wherein the surgical drape covers the imaging device;
• placing the first and second tracked objects in the view of at least one sensor unit and measuring its pose with said sensor unit;
• and using the previously calculated relationships among the coordinate frames of the two or more sensor units to calculate the pose of the first and second tracked objects relative to the reference coordinate frame.

An image guided surgery system to enable a surgeon to move a surgical tool into a desired pose relative to an object, comprising:

• an imaging device for generating a plurality of two-dimensional images of the object,
• a localizing device for determining the pose of the surgical tool and the pose of the imaging device;
• a stored computer model of the object said computer model having imaging model parameters for modeling the projection and mapping of the object wherein the imaging model parameters are dependent on the orientation of the imaging device;
• means for determining the pose of the object;
• means for displaying a representation of the surgical tool relative to the plurality of two-dimensional images of the object;
• and means for displaying the representation of the surgical tool relative to the computer model of the object;
• wherein the computer model of the object is projected onto a picture plane that is oriented so as to provide a view of the object distinct from the views represented by the plurality of two-dimensional images.

A method for verifying the accuracy with which an image guided surgery system displays a representation of a surgical tool relative to image data comprising the steps of:

• providing a localizing device;
• positioning a surgical tool such that an imaging device may acquire an image of the surgical tool;
• acquiring the image of the surgical tool with the imaging device and using the localizing device to read the pose of the surgical tool relative to the imaging device;
• recording said pose of the surgical tool relative to the imaging device;
• displaying the image of the surgical tool;
• calculating the position of a representation of the surgical tool relative to the image of the surgical tool based on the recorded pose of the surgical tool relative to the imaging device;
• generating the representation of the surgical tool having imaging model parameters for modeling the projection and mapping of the surgical tool wherein the imaging model parameters are dependent on the orientation of the imaging device;
• and
• retaining the surgical tool representation overlaid on the image of the surgical tool for a period of time sufficient for the surgeon to determine the accuracy of the positioning of the representation of the surgical tool relative to the image of the surgical tool.

An image guided surgery system for positioning a surgical tool relative to a body part comprising:

• an optical localizer;
• a C-arm fluoroscope with an attached flat panel that contains localizing emitters;
• one or more surgical tools;
• a display means for displaying a representation of the surgical tool relative to images of the body part;
• and
• a sterile light transparent surgical drape, a section of the drape having an inelastic pouch which is similar in dimension to the flat panel being adapted to cover said flat panel containing the localizing light emitters, wherein the drape fits flush and flat against the localizing light emitters.