Influence of tissue phantom optical properties and emitting - receiving fiber distance on Laser Doppler flowmetry

• The influence of emitting - receiving fiber distance on the perfusion signal in laser Doppler flowmetry (LDF) for a range of optical properties has been studied. A custom made LDF probe with eight 230 μm fibers arranged in a row was used. Measurements were made on a tissue phantom with three different sets of optical properties (P={μs; μa} [mm-1]; P1={14.7; 0.212}, P2={44.9; 0.226} and P3=(45.6; 0.0532}). A single moving disc simulated flow at four different depths. The noise-corrected perfusion for a given set of optical properties (P), fiber distance (l) and disc depth (d) is defined as Perf(ν,P,d,l)=k(P,d,l) v, where v is the speed of the rotating disc. The relative difference between two slopes, Δk(Pa,Pb,l,d), indicates how sensitive the LDF readings are to changes in optical properties (Pb → Pa) for given disc depth and fiber distance. Evaluation of Δk(P1,P2,d,l) (reflects changes in scattering coefficient, μs) and Δk(P3,P2,d,l) (reflects changes in absorption coefficient, μa) indicated that LDF perfusion was more sensitive to the changes in μs than in μa. The sensitivity also increased with increasing disc depth. A fiber distance of 920 [μm] was found to minimize these effects. E.g. the sensitivity due to the variations in μs, for fiber distance l1=920, l2=230 [μm] and for all disc depths, was Δk(P1,P2,l1)=[0.76, 1.06, 1.58, 2.40] and Δk(P1,P2,l2)=[1.61, 2.98, 5.04, 7.67].

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