Clinical assessment of the endothelium and vasculature by magnetic resonance imaging (MRI) has conventionally focused on assessment of lumen integrity using contrast and noncontrast angiographic techniques and assessment of macroscopic alterations in vessel wall structure (1–5). Phase contrast MRI may be employed to measure intravascular flow velocity, and cine MRI may be used to assess vascular distensibility (6). These techniques can be applied to detect endothelial dysfunction as measured by flow-mediated dilation (as has been studied more extensively using ultrasound techniques) (7). Thus, MRI offers a range of applications for the assessment of the macroscopic structure and function of the vascular system. In addition, MRI may be used to assess microvascular characteristics and effects, including microvascular density and vascular permeability (8,9), regional tissue perfusion (10), and microvascular obstruction (11). Building on these MRI capabilities, the development of molecular MRI targeted to detect alterations in the endothelial cell (EC) and its environment may allow integration of novel information about the state of the endothelium into conventional MRI vascular assessment. The endothelium is a particularly appealing site for targeting by molecular probes because of its functional importance and because it is bathed by the bloodstream into which such probes are conventionally administered.

The imaging of molecular targets is a developing method for improving the characterization and detection of normal and disease states. MRI can provide high spatial resolution and structural definition, which is useful for imaging processes at the molecular and cellular level (12). Furthermore, the availability of a wide range of MR scanners, ranging from small bore animal scanners to whole-body clinical systems, provides a means to bridge the gap between experimental models and clinical application.