Functional guidance of nerve graft surgery using dual-modal photoacoustic and fluorescence imaging of voltage-sensitive dye: ex vivo proof-of-concept study

Nerve graft repair surgery has been accepted for treating peripheral nerve injuries in which the transected nerve ends are incapable of primary end-to-end tensionless neurorrhaphy. In this paper, we present ex vivo proof-of-concept of a functional intra-operative guidance using voltage-sensitive dye (VSD) imaging. In particular, we here evaluate the efficacy of photoacoustic (PA) and fluorescence (FL) imaging modalities, in each of which near-infrared VSD contrast can be obtained by transmembrane VSD redistribution mechanism upon neuronal depolarization events. Realistic nerve graft surgery was mimicked by ex vivo sciatic nerve freshly excised from an anesthetized pig model. The dual-modal PA/FL imaging system was configured to monitor ex vivo sample chamber with wide field-of-view covering a significant portion of the nerve sample. The ex vivo sample chamber was equipped with an arbitrary electrical stimulation and recording system to trigger and monitor the neuronal electrophysiology, respectively. The proof-of-concept study suggested the high VSD signal sensitivity in functional PA VSD imaging with its unique depth profiling capability over the thick nerve tissue (<2-mm diameter). Otherwise, FL imaging indicated unspecific signal trends that might suffer from depth-unspecific imaging mode, which makes it challenging to extract nerve-related signals from background VSD signal clutter unbound to nerve tissue.