ABSTRACT Spinal cord diseases and disorders such as spinal cord injury (SCI) and amyotrophic lateral sclerosis (ALS) are debilitating, often resulting in loss of mobility and decreased quality of life for those affected. One promising treatment involves the transplantation of neural progenitor cells (NPC) into the spinal cord, which has been shown to have neuroprotective properties. However, most NPC-based therapies fail after reaching clinical trials, and without a method to monitor the injected cells and viability, locating injected NPCs is limited to postmortem histology. The ability to track and assess the viability of transplanted cells could be crucial in understanding whether the failure is technical or biological in nature, such as whether the injected cells were delivered to and remain at the correct location or survived transplantation. We propose the development of multi-modal contrast agents and a clinical ultrasound and photoacoustic (US/PA) imaging system for image guided delivery of trans- planted cells and longitudinal monitoring. Together with clinical magnetic resonance imaging (MRI), the use of US/PA imaging can allow for pre-, intra- and post-operative visualization of the cells. The MRI and US imaging modalities are well established in the clinic, and PA can be easily integrated with existing clinical US imaging systems. We hypothesize that visualizing the location and viability of injected neural progenitor cells obtained through the labeling of NPCs with contrast agents will allow for better understanding of transplanted cell behavior and improved translation of cell based therapies. Two contrast agents will be developed: photo-magnetic nano- particles, which will allow for photoacoustic and MRI tracking, and a dye-based apoptosis reporter, which will provide photoacoustic contrast upon apoptotic activity. These will be delivered to the cytosol of the neural pro- genitor cells and assessed for labeling efficiency and toxicity. Once optimized, labeled NPCs in different ratios of live to dead will be injected into the spinal cords of rats to assess the feasibility of distinguishing live and dead cells in vivo. After injection, the NPCs will be monitored longitudinally using trimodal US/PA/MR imaging. After validating the performance of the contrast agents in vivo, a clinical US/PA imaging system will be developed to demonstrate real-time image guided-delivery, US/PA/MRI longitudinal tracking, and PA viability assessment of the labeled cells. The ability to monitor the transplanted cells at every point during and after the procedure will allow for more accurate delivery of the cells and could elucidate common issues and behaviors of injected NPCs that could lead to therapeutic improvements. Furthermore, if successful, it will validate both the contrast agents and US/PA as a valuable tool for tracking and monitoring cell-based therapies to improve clinical translation.

PROJECT NARRATIVE We propose the development of an imaging method to track and assess the viability of transplanted neural progenitor cells in the spinal cord by labeling them with two contrast agent: one that can be imaged through photoacoustic imaging and MRI and another that can signal viability through photoacoustic signal. This work will allow for a better understanding of neural progenitor cell behavior after implantation that can improve future stem cell based therapies, while establishing an imaging technique capable of monitoring implanted cells.