This Medical Image Computing and Computer Assisted Intervention (MICCAI) 2003 paper by Lefohn et al. describes a brain tumor segmentation study performed with a new GPU-based level-set solver. This paper demonstrates that the ability to interact with a level-set computation in real time enables users to quickly produce segmentations from MRI data that qualitatively and quantitatively compare favorably with expert hand-segmentations. (Interactive, GPU-Based Level Sets for 3D Brain Tumor Segmentation. Aaron E. Lefohn, Joshua E. Cates and Ross T. Whitaker. To appear at “Medical Image Computing and Computer Assisted Intervention,” (MICCAI) 2003.)