Molecular Imaging and Stroke

Abstract

Molecular imaging (MI) is a rapidly developing field that encompasses many new (and old) imaging modalities that seeks to present patient-specific and disease-specific molecular and genetic information in conventional 2-dimensional and 3-dimensional anatomic imaging readouts. The foundations of MI are based on the fusion of a “promoter” agent that will be altered in a particular environment or disease state with an observable “reporter” agent that would register any change in the signal or contrast from the promoter. Much of MI is being done in experimental models of cancer, but only some of the developments can be scaled up to a clinical reality for eventual diagnostic and prognostic usefulness in stroke. The most commonly used modalities in MI research have been optical-based near-infrared or visible light sensors, bioluminescence,1,2 cameras sensitive to the firefly luciferase–luciferin generation of green light, nuclear medicine (NM)-based single-photon and positron tomography, and now, most recently, magnetic resonance (MR). Optical imaging techniques developed early for molecular and cellular biology using a wide variety of wavelengths. The noninvasive imaging in vivo with light photons has largely come from the advances in targeted bioluminescence probes, near-infrared fluorochromes, activated near-infrared fluorescence agents, and primarily from light emitted from the luciferase entity (reporter) in the presence of a substrate (luciferin).1,2 Optical techniques using multiple wavelength probes such as quantum dots holds the potential for multichannel imaging. However, most fundamental to the widespread use of in vivo optical imaging of stroke or ischemia in living subjects is the difficulty of detecting light from the brain, primarily because of the presence of the skull. Because of this, MI using optical techniques has been largely limited to nonneuro studies of cancer in rodent models. Nonetheless, optical imaging has a bright future in neuroimaging research. Advances in the use of near-infrared for diagnostic,3–5 …