A single-channel optical tomography system for quantification of PPIX delayed fluorescence imaging for assessment of tissue hypoxia

Fluorescent markers can improve contrast during tissue resection, making surgery more precise and concise, especially for certain disease types. Protoporphyrin IX (PpIX) is a Heme precursor that is primarily produced in the mitochondria and present in all living cells. Its endogenous production is stimulated by administering the precursor molecule 5-aminolevulinic acid. PpIX emits fluorescence at 635 to 720nm wavelengths and can be imaged superficially with blue light excitation at 405nm or more deeply with red 635nm excitation. PpIX delayed fluorescence is enhanced in tissue environments with low oxygen levels. Herein, we demonstrate a signal prototype of a dual-channel fiber optic-based tomography system for imaging PpIX delayed fluorescence in real-time. As a proof-of-principle, this system was validated in vitro in freshly prepared oxygenated and deoxygenated vials, to collect both PpIX prompt fluorescence (PF) and delayed fluorescence (DF) components. The DF temporal data provided insights into tissue hypoxia. Further, these tests demonstrated that the proposed system could track longitudinal changes in PpIX kinetics, which have a slower uptake and clearance than other approved contrasts like ICG. Results were compared to a wide-field imager for PpIX-based hypoxia.