1. Institut National de la Recherche Scientifique, Centre Énergie, Matériaux et Télécommunications, Université du Québec, Varennes, Québec J3X 1P7, Canada
2. Department of Physics and CICECO−Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal
3. Molecular Imaging Program at Stanford Department of Radiology Stanford University 1201 Welch Road, Lucas Center (exp.), Stanford, California 94305-5484, United States