ABSTRACT
Cancer, the uncontrolled growth and invasion and sometimes metastasis of malignant cells that can affect almost any tissue of the body and people of all ages, is a major public health burden in the world. In the United States, 1 in 4 deaths is caused by cancer (Jemal et al. 2010), which is the leading cause of death among persons younger than 85 years (Jemal et al. 2010). It is a major challenge to diagnose cancer in the early stage for curative treatment. Molecular imaging, which is broadly defi ned as the in vivo visualization, characterization, and measurement of biologic processes at the cellular and molecular level (Weissleder and Mahmood 2001), is emerging as a promising technology to meet this challenge. The molecular imaging aims to probe molecular processes that are the basis of disease rather than to image the end effects of these molecular alterations, which enabled much earlier detection of disease as well as real-time monitoring of therapeutic responses. Central to the molecular imaging in cancer is the development of high specifi c imaging probes for effective detection of cancer markers that are expressed differently in tumor cells or tissues. An ideal imaging probe used for in vivo imaging should generally meet several key criteria: (a) high specifi city and affi nity to the target tissues or cells; (b) in vivo safety; and (c) high target-to-background ratio.
