1. Department of Mathematics, University of Houston, Houston, Texas 77204, USA;
2. Oden Institute of Computational Engineering and Sciences, The University of Texas at Austin, Austin, Texas 78712, USA;,
3. Center for Biomedical Image Computing and Analytics (CBICA); Department of Radiology; and Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA;,