Adaptive processing bandwidth adjustment for laser Doppler flowmetry

A novel laser Doppler flowmetry scheme is reported that adjusts the processing bandwidth adaptively to optimise the estimation of flow. To obtain an adequate processing bandwidth, the Doppler spectra is first fitted to the Lorentzian function, and the bandwidth at half the maximum of the Lorentzian function is used as an indicator of the major frequency range of the signal. The processing bandwidth is then tuned accordingly, and a frequency-weighted algorithm is applied to compute the fluid velocity. To investigate the influence of the processing bandwidth, an in vitro experiment was performed. In the experiment, the flow rate was controlled at constant velocity in the range from 0 to 18.52 mm s(-1), and the fluid velocity indices were calculated using adaptive and fixed processing bandwidths, respectively. The results showed that the adaptive processing bandwidth adjustment, not only significantly reduced the biological zero (9.6% of the case using 100 kHz bandwidth), but also enhanced the sensitivity of the laser Doppler measurement (over 20%) and linearly responded to a wider velocity range (R2 = 0.979 for velocity from 0 to 18.52 mm s(-1)).