Title
Stereotactic System for Linear-Trajectory Medical Interventions

Abstract
Computer assisted surgery is an emerging field which combines diagnostic imaging with robotics, providing more quantitative information to the surgeon. Consequently it promises to improve the outcome of surgical procedures.


Two fluoroscopic images are displayed on computer monitors and used to perform accurate intra-operative planning. Once the images and the robot are registered, intra-operative planning is performed on the equivalent of a two-view orthographic projection of the vertebra. The intra-operative plan consists of specifying the pedicle's entry point, and sagittal and transverse orientations. Following the surgical plan, a drill guide held by the robot is moved to the desired position and orientation over the pedicle.

Essential to the overall accuracy of the system is the absolute accuracy and linearity of the fluoroscopic images, and the ability to register them to the patient's coordinate system.

However, standard fluoroscopic equipment produces significant geometric distortions in the images, projecting straight lines in an exposed volume into curves on a image. When fluoroscopic images are to be used for computer assisted surgery, compensation for such distortions is necessary. A mapping function that can transform the deformed image to a linearized image is needed. Such a function describes the behavior of the lens and is used to correct images obtained from the imaging device. After image linearization using the mapping function developed herein, it is possible to determine the coordinates of a known artifact to sub-pixel resolution.

Registration requires that the relationship between the coordinate system of the robot, the coordinate system of the C-arm be determined. Registration is implemented by holding the patient in a fixed position relative to the robot and by matching the spatial coordinates of a registration artifact on the robot's end-effector with their projected image coordinates.

This thesis describes the conventional surgical methodology, justifies the need for stereotactic assistance, and discusses the various approaches to system design. In describing my system, I emphasize key issues that arise with regard to image linearity, system registration, human interface, and robot accuracy.

Source: Master's thesis, Mechanical Engineering Department, Northwestern University, November, 1996

Title
A Stereotactic/Robotic System For Pedicle Screw Placement

Abstract
We are developing a robotic system to assist a surgeon in placing spinal pedicle screws. While several groups have undertaken such systems, our approach differs in that it endeavors to remain as close to current clinical technique as possible, yet achieve stereotactic accuracy.

This paper describes the conventional surgical methodology, justifies the need for stereotactic/robotic assistance, and discusses the various approaches to system design. In describing our system design, we emphasize key issues that arise with regard to robot accuracy, image linearity, and system registration.

Source: Proceedings of Medicine Meets Virtual Reality III, January 1995, San Diego Interactive Technology and the New Paradigm for Healthcare, p. 326-333 R. M. Satava et al., eds. Technology and Informatics vol. 18, IOS Press 1995