Abstract
Purpose:
Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) is an imaging technique that allows non-invasive in vivo measurement of fluorescence lifetimes of natural fluorophores in the retina after excitation with picosecond laser pulses. We address to characterize fluorescence lifetimes in four different mouse strains in order to gain basic information about natural fluorophores of their retina.
Methods:
Fluorescence lifetime imaging is performed using a Fluorescence Lifetime Imaging Ophthalmoscope (FLIO) based on a Heidelberg Engineering Spectralis® system. The fluorescence excitation wavelength was 473 nm and decay times were measured in a short and in a long spectral channel (SSC: 498-560 nm and LSC: 560-720 nm resp.) Four different strains of mice were examined: pigmented (C57BL/6), non-pigmented (BALBc) and CX3CR1GFP+ mice, and a mouse model of retinal degeneration (RDS; C3A.Cg-Pde6b + Prph2Rd2/J). Corresponding OCT-images (optical coherence tomography) were acquired.
Results:
Fluorescence lifetime measurement was highly specific and reproducible for each mouse strain with coefficients of variation of 2 to 15% in the short (SSC) and 10 to 25% in the long spectral channel (LSC). CX3CR1GFP+ mice showed the most distinct lifetime values in both spectral channels with the biggest standard deviation. In both spectral channels, mean lifetime (Tm) was the longest in CX3CR1GFP+ mice (SSC: Tm=1925 picoseconds (ps), LSC: Tm = 518 ps). In the short spectral channel, CX3CR1GFP+ mice were followed by pigmented (Tm = 956 ps), RDS (Tm = 883 ps) and non-pigmented mice (Tm = 801 ps). In the long spectral channel, Tm was similar in pigmented (Tm = 290 ps) and RDS-mice (Tm = 288 ps), followed by non-pigmented mice with the shortest Tm (Tm = 241 ps).
Conclusions:
Fluorescence lifetime values differ between the mouse strains with little variance within the groups. GFP marked areas lead to distinct fluorescence lifetimes. These are promising results for further analysis of fluorescence lifetime characteristics in mouse models to identify the contribution of different structural and metabolic states in the murine retina.
Keywords: 551 imaging/image analysis: non-clinical •
688 retina •
552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)