Optical fluorescence imaging is increasingly being used to obtain images of biological functions of specific targets and in small animals (1, 2). Near-infrared (NIR) fluorescence (700–900 nm) detection avoids the background fluorescence interference of natural biomolecules, providing a high contrast between target and background tissues. NIR fluorescence imaging is becoming a non-invasive alternative to radionuclide imaging and in small animals. Magnetic resonance imaging (MRI) maps information about tissues spatially and functionally. Protons (hydrogen nuclei) are widely used to create images because of their abundance in water molecules, which comprise >80% of most soft tissues. The contrast of proton MRI images depends mainly on the nuclear density (proton spins), the relaxation times of the nuclear magnetization (T1, longitudinal; T2, transverse), the magnetic environment of the tissues, and the blood flow to the tissues. However, insufficient contrast between normal and diseased tissues requires the use of contrast agents. Most contrast agents affect the T1 and T2 relaxation times of the surrounding nuclei, mainly the protons of water. T2* is the spin–spin relaxation time composed of variations from molecular interactions and intrinsic magnetic heterogeneities of tissues in the magnetic field (3). Cross-linked iron oxide (CLIO) nanoparticles and other iron oxide formulations affect T2 primarily and lead to a decreased signal. A multimodal nanoparticle probe that consists of a contrast agent and a NIR fluorochrome may provide consistent information. CLIO nanoparticles can be internalized by cells of the reticuloendothelial system and have long circulating times within an animal body. The blood half-life of CLIO is about 10 h in mice (4). The accumulation of nanoparticles in cells causes a reduction in signal intensity with T2-weighted (T2*W) spin-echo pulse sequences. NIR fluorochromes (e.g., Cy5.5) provide an improved optical (NIR) signal from tissue. CLIO-Cy5.5 has been developed as a probe for multimodality imaging (5). Endothelial cells are important in inflammatory responses (6, 7). Bacterial lipopolysaccharide (LPS), virus, inflammation, and tissue injury increase tumor necrosis factor α (TNFα), interleukin-1 (IL-1), and other cytokine and chemokine secretion. Emigration of leukocytes from blood is dependent on their ability to roll along endothelial cell surfaces and subsequently adhere to endothelial cell surfaces. Inflammatory mediators and cytokines induce chemokine secretion from endothelial cells and other vascular cells and increase their expression of cell-surface adhesion molecules, such as intracellular adhesion molecule-1, vascular cell adhesion molecule-1 (VCAM-1), integrins, and selectins. Chemokines are chemotactic toward leukocytes and toward sites of inflammation and tissue injury. The movement of leukocytes through endothelial junctions into the extravascular space are highly orchestrated through various interactions with different adhesion molecules on endothelial cells (8). VCAM-1 is found in very low levels on the cell surface of resting endothelial cells and other vascular cells, such as smooth muscle cells and fibroblasts (9-13). VCAM-1 binds to its counterligand, very late antigen-4 (VLA-4) integrin, on the cell surface of leukocytes. IL-1 and TNFα increase expression of VCAM-1 and other cell adhesion molecules on the vascular endothelial cells, which leads to leukocyte adhesion to the activated endothelium. Furthermore, VCAM-1 expression was also induced by oxidized low-density lipoproteins under atherogenic conditions (14). Overexpression of VCAM-1 by atherosclerotic lesions plays an important role in their progression toward vulnerable plaques, which may erode and rupture. CLIO nanoparticles targeted with anti-VCAM-1 antibody are being developed as a non-invasive agent for VCAM-1 expression in vascular endothelial cells during different stages of inflammation in atherosclerosis (15). Anti-VCAM-1 M/K-2.7 monoclonal antibody (mAb) conjugated cross-linked iron oxide-Cy5.5 nanoparticles (VCAM-CLIO-Cy5.5 or VCAM-NP) is a multimodal agent that consists of CLIO nanoparticles with attachment of M/K-2.7 mAb and Cy5.5.