Rotational encoding of C-arm fluoroscope with tilt sensing accelerometer.

PURPOSE: Accurate, practical, and affordable joint encoding on legacy C-arm fluoroscopes is a major technical challenge. Conventional pose tracking methods, like optical cameras and radiographic fiducials, are hampered by significant shortcomings. METHODS: We propose to retrofit legacy C-arms with a tilt sensing accelerometer for rotation encoding. Our experimental setup consists of affixing an accelerometer to a full scale C-arm with a webcam as an alternative to X-ray imaging for this feasibility research. Ground-truth C-arm poses were obtained from the webcam that tracked a checkerboard plate. From these we constructed a series of angle and structural correction equations that can properly relate the accelerometer angle readings to C-arm pose during surgery and compensate for systematic structural C-arm deformations, such as sagging and bending. RESULTS: Real-time tracking of the primary and secondary angle rotations of the C-arm showed an accuracy and precision of less than 0.5 degrees in the entire range of interest.