Alan Perkins PhD, FIPEM, Hon FRCP is professor of medical physics in radiological sciences in the School of Medicine at the University of Nottingham and honorary consultant clinical scientist at Nottingham University Hospitals NHS Trust. He has more than 30 years of experience in medical physics, providing routine clinical service and research in nuclear medicine, radiopharmacology, drug delivery, ultrasound imaging and radiation protection. He is a former president of the British Nuclear Medicine Society, a former vice president of the Institute of Physics and Engineering in Medicine and an editor of the UK journal Nuclear Medicine Communications. John E. Lees, PhD, CPhys, FInstP, is a professor of imaging for life and medical sciences in the Department of Physics and Astronomy at the University of Leicester. He has more than 28 years of experience in radiation detectors and imaging systems. He was the UK detector scientist on the NASA/UK x-ray telescope Chandra, during which he pioneered the calibration of space instrumentation using synchrotron sources. Currently, he leads the BioImaging Unit in the Space Research Centre which encompasses fundamental detector research along with technology transfer from space instrumentation into medical and life sciences.