1. Advanced Technology Institute, Department of Electrical and Electronic Engineering, University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom
2. Siemens Healthineers, Technology Center, Guenther-Scharowsky-Strasse 1, 91058 Erlangen, Germany
3. Department of Physics and Astronomy, University of Sheffield, Hicks Building, Sheffield, S3 7RH, United Kingdom