Fiber tracking is one of the clinically most well-established analysis techniques for Diffusion Tensor Imaging data (DTI). It facilitates the reconstruction of anatomically known white matter structures by tracing trajectories on a tensor field obtained from diffusion weighted MR images. A crucial step when using this technique is the placement and shape of regions-of-interest (ROIs) to identify the structures in question. Typically, free-hand contours or simple geometric shapes like rectangles are placed in regions, where a given structure can be identified using the color coded DTI representation. However, such approaches result in a high variability of the resulting tracts and usually require additional filtering and placement of multiple ROIs. Also, the generation of accurate ROIs using a free-hand tool requires a significant amount of interaction time. We present a method which allows for interactive generation of anatomically meaningful ROIs for DTI fiber tracking based on geometric similarities of the underlying tensor field. The method works similar to the magicwand tool known from image editing software tools to create reasonable, fully image based ROIs using a single mouseclick.