1. Institute of Computational Mathematics and Mathematical Geophysics , 630090 Novosibirsk , Russia
2. Department of Radiology , University of Pennsylvania , Philadelphia , PA 19104 , USA
3. Department of Physics , Technical University of Denmark , Fysikvej 307, 2800 Kgs. Lyngby , Denmark
4. Institute of Applied Mathematics , 7 Radio street, 690041 Vladivostok , Russia