Virtual Fluoroscopy: Multiplanar X-ray Guidance with Minimal Radiation Exposure

Kevin T. Foley, MD
Y. Raja Rampersand, MD (Toronto, Ontario)
David A. Simon, PhD (Broomfield, CO)

Introduction:

The purpose of this study was to investigate a new technology combining image–guided surgery with C–arm fluoroscopy.

Materials and Methods:

A calibration target with affixed light–emitting diodes was attached to an OEC Model 9600 C–arm fluoroscope. The StealthStation image–guided surgery system was used to track the fluoroscope as well as a dynamic reference array and various spine surgery tools. Fluoroscopic images of the lumbar spine of an intact, unembalmed cadaver were obtained, calibrated, and saved to the StealthStation. The trajectory of a "virtual tool" corresponding to the tracked tool was overlaid onto the saved fluoroscopic views in real–time. Sequential insertion of an LED–fitted probe into the cadaver's pedicles from L1 to S1 bilaterally was performed under virtual fluoroscopic guidance. Live fluoroscopic images of the inserted pedicle probe were then obtained; distances between the probe tips and differences between the trajectory angles of the virtual and fluoroscopically–displayed probes were measured. Surgeon radiation exposure was determined using thermolucent dosimeter (ELD) rings.

Results:

All pedicles were safely probed in virtual fashion. Mean probe tip error was 0.97mm +/– 0.40mm. The 99% confidence interval was 2.2mm. Mean trajectory angle difference between the virtual and fluoroscopically–displayed probes was 2.7o +/– 0.6o. The 99% confidence interval was 4.6o. The TLD rings measured no detectable surgeon radiation exposure.

Conclusions:

Virtual fluoroscopy offers several advantages over conventional fluoroscopy while providing acceptable targeting accuracy. It allows for "saved" fluoroscopic images to be used for procedural guidance. These images can be obtained while the surgical team stands sufficiently far away from the x–ray beam source to minimize exposure to ionizing radiation. Repetitive fluoroscopic imaging for tool placement is unnecessary, decreasing patient irradiation. Simultaneous multiplexer guidance is achievable with a single C–arm.