Figure 2.

New approaches for imaging expression of the target protein. (A) Imaging of the expression of carcinoembryonic antigen (CEA) with radiolabeled antibody fragments in mice. Mice were implanted with a CEA-expressing tumor at the left shoulder and CEA-negative tumor at the right shoulder. An [¹²⁴I]-labeled anti-CEA antibody (top row) accumulates in the CEA-positive tumor (solid arrow), but the background and CEA-negative tumor (open arrow) have relatively low levels of CEA expression. The contrast is much higher for sc-Fv-Fc antibody fragments (bottom row) owing to faster blood clearance. Permission obtained from Nature Publishing Group © Wu AM and Senter PD (2005) Nat Biotechnol 23: 1137–1146. (B) Multiplexed optical imaging using quantum dots. Quantum dots of three different colors were subcutaneously injected into the back of a mouse and imaged simultaneously. The right side of the panel shows microscopic images of the injected quantum-dot-encoded microbeads (diameter 0.5 µm). Permission obtained from Nature Publishing Group © Gao X et al. (2004) Nat Biotechnol 22: 969–976. (C) Optical fluorescence tomography of the expression of cathepsin B in a mouse bearing an orthotopic human glioma xenograft in the right hemisphere of the brain (arrow). The top panel shows the reconstructed optical image (cross-section) obtained after injection of an activatable optical probe that is cleaved by cathepsin B. The bottom panel shows an overlay of the optical image and an MRI scan. Permission obtained from Nature Publishing Group © Ntziachristos V et al. (2002) Nat Med 8: 757–760.