Targeted in vivo imaging of angiogenesis: present status and perspectives

Angiogenesis, the process whereby new capillaries are formed by outgrowth from existing microvessels, is required for tumor growth and metastasis, and is also necessary for natural healing after ischemic injury. Because angiogenesis, excessive or deficient, underlies many pathological situations, there is a need for the development of noninvasive imaging to allow monitoring of angiogenesis related molecular events. Furthermore, specific imaging of angiogenesis would help define the pathophysiology of angiogenesis in living subjects, identify those patients likely to respond to anti-angiogenic or angiogenic therapies, and enable the efficacies of these molecular therapies to be assessed. Herein, we review the targeted imaging of angiogenesis using nuclear medicine modalities (positron emission tomography; PET and single photon emission computed tomography; SPECT) and suitable radiotracers based on potential targets including integrin, extracellular matrix, VEGF and its receptors, activated endothelial cells, and matrix metalloproteinases.