Free isocentric 3d imaging and a novel approach for wobble trajectories using a modified standard c-arm

In this article the authors describes the modifications of an standard c-arm for free isocentric 3D imaging. To provide an isocentric movement of the x-ray source and the x-ray detector the passive mechanism of a standard c-arm was equipped with additional motors and encoders. A robot control system moves the imaging system on an isocentric path around the patient. The acquired x-ray images are then processed with a reconstruction algorithm using the algebraic reconstruction technique. For speed issues the reconstruction algorithm is implemented on a modern PC- graphics board. To overcome the known artifacts produced by the c-arm´s limited rotation of 135deg, the use of a novel wobble trajectory is proposed for theses systems. The presented robotic approach for the motion of the c-arm´s mechanism allows it to expand the isocentric movement to the surface of a sphere. With the new wobble trajectory the reconstruction artifacts can be significantly reduced.