Defining the Zone of Acute Peripheral Nerve Injury Using Fluorescence Lifetime Imaging in a Crush Injury Sheep Model.

Purpose: Current technologies to define the zone of acute peripheral nerve injury intraoperatively are limited by surgical experience, time, cumbersome electrodiagnostic equipment, and interpreter reliability. In this pilot study, we evaluated a real-time, label-free optical technique for intraoperative nerve injury imaging. We hypothesize that fluorescence lifetime imaging (FLIm) will detect a difference between the time-resolved fluorescence signatures for acute crush injuries versus uninjured segments of peripheral nerves in sheep.

Methods: Label-free FLIm uses ultraviolet laser pulses to excite endogenous tissue fluorophores and detect their fluorescent decay over time, generating real-time tissue-specific signatures. A crush injury was produced in eight peripheral nerves of two sheep. A hand-held FLIm instrument captured the time-resolved fluorescence signatures of injured and uninjured nerve segments across three spectral emission channels (390/40 nm, 470/28 nm, and 540/50 nm). The average FLIm parameters (ie, lifetime and intensity ratios) for injured and uninjured nerve segments were compared. We used linear discriminant analysis to differentiate between crushed and uninjured nerve segments.

Results: A total of 23,692 point measurements were collected from eight crushed peripheral nerves of two sheep. Histology confirmed the zone of injury. Average lifetime at 470 nm and 540 nm were significantly different between crushed and uninjured sheep nerve segments. The linear discriminant analysis differentiated between crushed and uninjured areas of eight nerve segments with 92% sensitivity, 85% specificity, and 88% accuracy.

Conclusions: In this pilot study, FLIm detected differing average lifetime values for crushed versus uninjured sheep peripheral nerves with high sensitivity, specificity, and accuracy.

Clinical relevance: With further investigation, FLIm may guide the peripheral nerve surgeon to the precise zone of injury for reconstruction.