Time will tell in fluorescence guided surgery

Fluorescence is now well-established as a powerful surgical tool in both manual and robotic procedures [1]. However, there is an urgent need to improve intraoperative precision down to +/- 1 mm in order to minimise damage to healthy tissue and reduce the need for repeat surgery.
Intraoperative use of fluorescence in surgery was first demonstrated using fluorescein in the late 1940s [2], but fluorescence guided robotic surgery in use today would have been thought to be fantasy when fluorescence started to emerge as a major molecular research technique in the 1960s and 1970s. Back then the measurement of fluorescence quantum yield and lifetime were on a par as researchers sought to combine them to determine fluorescence rate parameters [3]. However, the difficulties associated with quantum yield requiring intensity measurement, as compared to the higher precision, independence of dye concentration and ease of measuring lifetimes, soon led to the latter becoming the most popular method of measuring changes in fluorescence associated with changes in fluorophore environment; a property that is critical to fluorescence guided surgery.
Current fluorescence surgical procedures are based solely on fluorescence intensity whether they be manual or robotic. We have developed single photon timing systems using simple liquid light guide macroscopic coupling and multiplexed microscopic array detection [4]. In this talk we will demonstrate their potential in obtaining the +/- 1 mm surgical precision desired, which, when fully implemented, will bring to bear their intrinsic advantages in terms of minimising the effect of variations in local dye concentration, excitation and emission non-uniformity, background fluorescence and scattering.
All the indications are that the advantages of fluorescence lifetime measurements are poised to translate to the benefit of robotic surgical procedures in the not-too-distant future.

1. Fluorescence guided surgery, H L Stewart and D J S Birch, Methods Appl. Fluoresc. 9 042002, 2021.
2. Moore, G.E. et. al. The clinical use of fluorescein in neurosurgery. J Neurosurgery,5(4), 392-8, 1948.
3. Photophysics of Aromatic Molecules, J.B. Birks, Wiley-Interscience, London, 1970.
4. Characterization of single channel liquid light guide coupling and SPAD array imaging for tumour margin estimation using fluorescence lifetime. H L Stewart, G Hungerford and D J S Birch. Meas. Sci. Technol. 31, 125701, 2020.