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 pm fibers arranged in a row was used. Measurements were made on a tissue phantom with three different sets of optical properties (P={mu(s); mu(a)} [mm(-1)]; P-1={14.7; 0.212}. P-2={44.9; 0.226} and P-3={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(v, P, d, l) = k(P,d,l) v, where v is the speed of the rotating disc. The relative difference between two slopes, Delta k(P-a,P-b,ld), indicates how sensitive the LDF readings are to changes in optical properties (P-b --> P-a) for given disc depth and fiber distance. Evaluation of Delta k(P-1,P-2,d,l) (reflects changes in scattering coefficient, mu(s)) and Delta k(P-3,P-2,d,l) (reflects changes in absorption coefficient, mu(a)) indicated that LDF perfusion was more sensitive to the changes in mu(s) than in mu(a). The sensitivity also increased with increasing disc depth. A fiber distance of 920 [mu m] was found to minimize these effects. E.g. the sensitivity due to the variations in mu(s), for fiber distance l(1)=920, l(2)=230 [mu m] and for all disc depths, was Delta k(P-1,P-2,l(1))=[0.76, 1.06, 1.58, 2.40] and Delta k(P-1,P-2,l(2))=[1.61, 2.98, 5.03, 7.67].