“…In molecular imaging, biological processes in living systems can be observed, analyzed, and measured at the molecular by imaging modalities such as ultrasound, magnetic resonance imaging (MRI), positron emission tomography (PET), and single photon emission computed tomography (SPECT) [ 53 , 54 , 55 , 56 , 57 ]. PET and SPECT are sophisticated imaging modalities utilized to visualize biological processes at the molecular level [ 58 , 59 , 60 , 61 ]. PET is more sensitive while SPECT is more widely available, less expensive, and has better imaging properties than PET [ 62 ].…”