title: Preface.
authors.affiliation: Associate Professor or Radiology, University of Pennsylvania School of Medicine Chief of Division of Nuclear Medicine, Department of Radiology The Childrens Hospital of Philadelphia, Philadelphia, PA, USA. Electronic address: zhuang@email.chop.edu.
authors.forename: Hongming
authors.initials: H
authors.lastname: Zhuang
authors.affiliation: Professor of Radiology, Director of Research Education, Department of Radiology Hospital of the University of Pennsylvania, Philadelphia, PA, USA. Electronic address: abass.alavi@uphs.upenn.edu.
authors.forename: Abass
authors.initials: A
authors.lastname: Alavi