Figure 3. In vivo monitoring of Au NT labeled MSCs using combined ultrasound and photoacoustic (US/PA) imaging.

(A–D) In vivo ultrasound, photoacoustic, US/PA, and US/spectroscopic images of the LGAS in which PEGylated fibrin gel containing Au NT loaded MSCs (1×10⁵ cells/mL) was injected. PEGylated fibrin gel location is outlined with yellow dotted circle. Injection depth was about 5 mm under the skin. (E–H) Control at the region of the LGAS of the other hind limb without any injection. Photoacoustic images were acquired at the wavelength of 760 nm with a fluence of 11 mJ/cm². Spectral (650–920 nm) analysis of photoacoustic signal was able to differentiate skin (shown in yellow), oxygenated (red) and deoxygenated (blue) blood, and Au NT loaded MSCs (green). The images measure 23 mm laterally and 12.5 mm axially.