Photoacoustic Imaging of Labeled Cells in Vivo

All animal studies were performed in accordance with the Institutional Animal Care and Use Committee (IACUC) at the University of California, San Diego (UCSD). Male nude mice (20 g) (n = 3) were anesthetized with 1–2% isoflurane and positioned underneath the transducer with coupling media. Then, 0.4 million of unlabeled or labeled hMSCs in 50% matrigel/PBS (60 µL) were injected subcutaneously with a 28.5 gauge catheter and imaged using the same Visualsonics LAZR photoacoustic scanner. Different numbers of labeled hMSCs (100 × 10³, 50 × 10³, 25 × 10³, and 12.5 × 10³) suspended in 50% matrigel/ PBS (60 µL) were injected subcutaneously and imaged. For brain intraparenchymal injections, 50 × 10³ of unlabeled or labeled cells were suspended in 20 µL of PBS and then injected. Images were obtained via 3-D mode with a 30 MHz transducer and pulsed laser excitation at 730 nm.