Organic Molecules for Optical Imaging - The Chemistry of Molecular Imaging - page 270

ICG has an absorption peak at around 800 nm, and it is employed as a diagnostic aid for measuring blood volume, cardiac
output, or hepatic function. ICG is also applied in noninvasive photoacoustic angiography of animal brains, whereupon
injecting ICG into the circulation system of a rat, the absorption contrast between the blood vessels and the background tis-
sues will be enhanced significantly. Photoacoustic imaging allows the reconstruction of the vascular distribution in the rat
brain with high spatial resolution and low background as a result of the ability of near-infrared light penetrating deep into
brain tissues through the skin and the skull. However, the resolution was found to deteriorate slowly with increasing imaging
depth [175].

11.9 conclusIon and future perspectIVes

An outline of the development of molecular imaging has been summarised in this chapter, with an array of representative
organic probes. With prominent advantages of luminescent organic materials in aqueous solutions—their ability, availability,
and applicability to be used as imaging agents to provide accurate and detailed diagnostic information, they have been
manipulated to understand the processes involved in certain therapeutic treatments on a molecular level, thus acting as a tool
to evaluate the efficacy of such treatments. More importantly, to modify and complement these luminescent organic mate-
rials, a large variety of tracers or probes can be devised and developed and be equipped themselves with a more precise
vector to bolster their effectiveness when used as imaging agents. Most importantly, foresight tells us that the next break-
through in this aspect, perhaps, lies elsewhere—time-resolved near-infrared imaging agents and the new epoch involving the
coupled benefits of time-resolved microscopy and NIr-emissive materials that will demonstrate a profound capacity to
improve the imaging sensitivity. recently, metal-based organic systems emissive in the NIr region have been being studied
extensively, and a decent profile of their luminescent properties has been established while technicality issues, in particular
instrumentation for NIr emission imaging, has yet to be mature, or even, prove possible.

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