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Matthias Klemm, Dietrich Schweitzer; An adaptive binning approach in auto-fluorescence lifetime ophthalmology (FLIO) applied to healthy volunteers and patients with diabetes mellitus without diabetic retinopathy. Invest. Ophthalmol. Vis. Sci. 2014;55(13):209.
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© ARVO (1962-2015); The Authors (2016-present)
To improve detection of metabolic changes using FLIO before morphologic alterations are visible. A 3-exponential approximation is optimal for FLIO but requires 10000s of photons / pixel, which can’t be measured due to light exposure and time constraints. Thus, neighboring pixels are binned (static binning, SB) to increase photons / pixel. E.g. eyelashes or cataract cause inhomogeneous auto-fluorescence (AF) intensity. SB may not collect enough photons and cause wrong fluorescence lifetimes. Adaptive binning (AB) ensures required number of photons / pixel at highest possible spatial resolution. SB smoothes all image parts with same strength. AB smoothes dark parts stronger and bright parts less, preserving more detail.
In 37 healthy volunteers (62.6±11.9 years) and 34 diabetes patients without diabetic retinopathy (64.0±9.1 years) time-resolved retina AF was measured (scanning laser ophthalmoscope: 30° of fundus, 40µm resolution; excitation: diode laser with pico-second pulses, 446nm, 80MHz repetition rate; detection: spectral channels 490-560nm (ch1) and 560-700nm (ch2), time-correlated single photon counting method). All subjects had a crystalline lens. SB (factor 1) combines fluorescence in 3x3 surrounding pixels for each pixel. AB combines surrounding pixels with identical distances. Distance increases per iteration until a threshold (50k, 100k, 150k, 200k photons / pixel) is reached. A modified 3-exponential approach was applied to determine the fluorescence lifetimes. Regions of 100x70 pixels at similar locations in the macula were selected in each subject.
Results are mean ± std. For healthy volunteers SB resulted in: τ1: 73±10ps, τ2: 355±62ps, τ3: 2580±297ps. AB (100k photons) resulted in: τ1: 69±6ps, τ2: 349±20ps, τ3: 2577±156ps. For diabetes patients SB resulted in: τ1: 79±12ps, τ2: 375±83ps, τ3: 3018±256ps. AB (100k photons) resulted in: τ1: 75±8ps, τ2: 353±28ps, τ3: 2796±163ps. The average goodness of fit value (χ2) of 1.3 is identical for volunteers and patients for both binning approaches. Results of ch2 are similar to ch1.
Determination of fluorescence lifetimes is improved. AB reduces std by nearly 50% in comparison to SB for volunteers and patients. Fluorescence lifetimes τ2 and τ3 are slightly reduced in patients by AB. AB is valuable to improve the FLIO method.
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