MRI of ICAM-1 upregulation after stroke: the importance of choosing the appropriate target-specific particulate contrast agent.

Purpose: Magnetic resonance imaging (MRI) with targeted contrast agents provides a promising means for diagnosis and treatment monitoring after cerebrovascular injury. Our goal was to demonstrate the feasibility of this approach to detect the neuroinflammatory biomarker intercellular adhesion molecule-1 (ICAM-1) after stroke and to establish a most efficient imaging procedure.

Procedures: We compared two types of ICAM-1-functionalized contrast agent: T 1-shortening gadolinium chelate-containing liposomes and T2(*)-shortening micron-sized iron oxide particles (MPIO). Binding efficacy and MRI contrast effects were tested in cell cultures and a mouse stroke model.

Results: Both ICAM-1-targeted agents bound effectively to activated cerebrovascular cells in vitro, generating significant MRI contrast-enhancing effects. Direct in vivo MRI-based detection after stroke was only achieved with ICAM-1-targeted MPIO, although both contrast agents showed similar target-specific vascular accumulation.

Conclusions: Our study demonstrates the potential of in vivo MRI of post-stroke ICAM-1 upregulation and signifies target-specific MPIO as most suitable contrast agent for molecular MRI of cerebrovascular inflammation.