A Method for Extracting 3D Information of Cylinder in C-arm Image

Aiming at the failure of the distal locking in the computer assisted distal locking of intramedullary nails because of the intersection angle between the nail hole axis and the projection axis of the C-arm, a method of three-dimensional information estimation of the nail hole from two-dimensional X-ray image coordinates was proposed, basing on the perspective projection mode of the C-arm and the reduction of the nail hole to a cylinder. Due to the characteristics of the cylinder, we proposed a sampling points coordinates´ modification method basing on the different coordinates compensation to distinguish the projection ellipse´s parameters estimation of the top and bottom caps of the cylinder. The simulation results showed that the ellipse s parameters estimation had less effect on the 3-D information estimation of the cylinder, while the C-arm´s stability significantly affects the calculation precision of the Z-axis of the cylinder position. After the sample points´ coordinates´ compensation for the ellipse detection, the estimation precision of the cylinder´s location is improved.