With the advancement in modern genomic and proteomic technologies in the past decade, knowledge of the molecular and cellular mechanisms of cancer initiation and progression is expanding at an unprecedented rate. A prudent approach for clinicians and scientists would be to extract salient information and apply it to address significant challenges in the current practices of cancer management. An important issue is how best to query the molecular and physiological information relevant to cancer in patients. Molecular imaging is a particular useful technology in the pursuit of this quest, as it allows the visualization of critical molecular signaling pathways in action in living subjects, in a noninvasive and longitudinal manner. Metastasis, manifested often in the late stages of cancer (although most work today supports metastasis as an earlier event than previously recognized), is the main cause of mortality in patients with solid tumors. To be able to prevent or control metastasis is considered one of most significant challenges in clinical oncology.

Whole-body in vivo molecular imaging is ideally suited to assess the very complex process of metastasis, in which the location(s) and magnitude of disseminated lesions are changing in time. For cancer metastasis, the common imaging modalities employed for repetitive, noninvasive imaging include positron emission tomography (PET), computed tomography (CT), single photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), and optical imaging by bioluminescence (e.g., firefly luciferase [FL or Luc]) or fluorescence (e.g., green fluorescent protein [GFP]).