Incorporation of a radiofrequency coil extending over a length of the instrument body can be used in visualising long, flexible instruments such as catheters and guidewires in magnetic resonance. Acquiring images with this RF coil results in a profile of the coil. In this work, the algorithm for an automatic identification of the coil profile centerline is presented. The algorithm consists of image segmentation and consequent instrument profile approximation with Bspline curves. The performance of the algorithm was evaluated with two profiling coil designs.