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

Abstract

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.

Fig. 1

Schematic of the OA mouse imaging system: (a) side view and (b) top-down view, where items labeled 2 are the light sources and 1 is the arc probe.

Fig. 2

Absorption spectra of GNR before (GNR-CTAB) and after PEGylation, sedimentation, and filtration (GNR-PEG), with maximum plasmon resonance around 760 nm.

Fig. 3

Three-dimensional OA volumes reconstructed from a mouse before and after intravenous injection of an OA contrast agent based on the GNR-PEG solution. (a) Dorsoventral, (b) left medio-lateral, and (c) right medio-lateral views. 765 nm laser illumination. The locations of the image areas used for analysis of organ-specific changes on each view are outlined: 1—left kidney, 2—right kidney, 3—spleen, 4—spine, 5—whole body. Starting from pre-injection (Video 1) to post-injection after a day (Video 3), there is a visible increase in contrast. (Video 1, QuickTime, 1.75 MB) [URL: http://dx.doi.org/10.1117/1.JBO.17.10.101506.1]; (Video 3, QuickTime, 1.71 MB). [URL: http://dx.doi.org/10.1117/1.JBO.17.10.101506.3].

Fig. 4

Three-dimensional OA volumes reconstructed from a mouse before and after intravenous injection of OA contrast agent based on the GNR-PEG solution. (a) Dorsoventral, (b) left medio-lateral, and (c) right medio-lateral views. 1064 nm laser illumination. The locations of the image areas used for analysis of organ-specific changes on each view are outlined: 1—left kidney, 2—right kidney, 3—spleen, 4—spine, 5—whole body. Starting from pre-injection (Video 2) to post-injection after two days (Video 4), there is a visible increase in contrast. (Video 2, QuickTime, 1.68 MB) [URL: http://dx.doi.org/10.1117/1.JBO.17.10.101506.2]; (Video 4, QuickTime, 1.71 MB). [URL: http://dx.doi.org/10.1117/1.JBO.17.10.101506.4].

Fig. 5

Average brightness of the segmented parts on the OA images prior to the injection of GNRs.

Fig. 6

Change of the average brightness inside the segmented parts on the OA images after the injection of GNRs. Images acquired using (a) 765 nm and (b) 1064 nm laser illumination.

Fig. 7

Normalized absorption spectra of GNR-PEG incubated in heparinized blood.