Tracking method and apparatus

A method of determining a path of a tubular structure comprises: obtaining volumetric medical imaging data that represents anatomy of a subject including the tubular structure; performing a position-determining procedure that comprises: obtaining an initial position of a current point on said path of the tubular structure; selecting a sub-region based on said initial position; obtaining values of at least one parameter representative of the tubular structure; inputting to a trained model both data from said selected sub-region and said parameter values, the trained model having been trained to determine paths of tubular structures; outputting by the trained model a position for a next point on said path of the tubular structure; and updating said initial position to said next point; and repeating the position-determining procedure for updating the initial position thereby to obtain the path of the tubular structure.