Gallium-68 Based Positron Emission Tomography (PET) Probes for Myocardial Perfusion Imaging

Myocardial perfusion imaging (MPI) is routinely used for clinical evaluation and therapeutic guidance of myocardial ischemia (MI). So far, technetium-99m (99mTc) labeled Single Photon Emission Tomography (SPECT) imaging agents have been the mainstay of MPI, primarily due to the in-house availability of 99mTc radioisotope via generators and the ease of radiolabelling. Over the last decade, Positron Emission Tomography (PET) has emerged as a superior imaging technique with improved imaging quality and image quantification. To utilize the key features of PET in the diagnosis of MI, various Gallium-68 (68Ga) based PET imaging agents were designed and evaluated. Gallium-68 is a generatorbased positron-emitting nuclide and, like 99mTc, can be obtained on an as-needed basis from an in-house 68Ge/68Ga generator system. The ease of radiolabeling and optimal physical half-life of 68Ga (68 min) position it as an ideal PET isotope for MPI. The design of 68Ga-based MPI agents discussed in this review closely followed the physicochemical requirements established for clinically used 99mTc-based MPI agents. We compare and contrast various 68Ga-based complexes used in MPI animal studies and can conclude that select compounds meet the standards set by 99mTc-based MPI agents based on their physicochemical and in vivo properties.