Three-dimensional optoacoustic imaging as a new noninvasive technique to study long-term biodistribution of optical contrast agents in small animal models.

We used a 3-D optoacoustic (OA) tomography system to create maps of optical absorbance of mice tissues contrasted with gold nanorods (GNRs). Nude mice were scanned before and after injection of GNRs at time periods varying from 1 to 192 h. Synthesized GNRs were purified from hexadecyltrimethylammonium bromide and coated with polyethylene glycol (PEG) to obtain GNR-PEG complexes suitable for in vivo applications. Intravenous administration of purified GNR-PEG complexes resulted in enhanced OA contrast of internal organs and blood vessels compared to the same mouse before injection of the contrast agent. Maximum enhancement of the OA images was observed 24 to 48 h postinjection, followed by a slow clearance trend for the remaining part of the studied period (eight days). We demonstrate that OA imaging with two laser wavelengths can be used for noninvasive, long-term studies of biological distribution of contrast agents.