“…Unlike multi-isotope SPECT, where energy discrimination can be used to identify photons from each tracer, all PET tracers give rise to indistinguishable 511 keV photon pairs. It has been previously shown that, when using dynamic scanning with staggered injections, the imaging signals from 2â3 PET tracers can be reliably recovered through application of appropriate kinetic constraints for each tracer (Koeppe et al 1998, Koeppe et al 2001, Converse et al 2004, Koeppe et al 2004, Kadrmas and Rust 2005, Kudomi et al 2005, Rust and Kadrmas 2006, Black et al 2008, 2009, Gao et al 2009, Joshi et al 2009, Kadrmas et al 2010, 2013, Kadrmas and Hoffman 2013). Perhaps the most robust multi-tracer PET signal-separation algorithms rely upon parallel compartment modeling of all tracers present in order to apply the kinetic constraints and recover imaging estimates from each individual tracer.…”