The photo-electric current in laser-Doppler flowmetry by Monte Carlo simulations

Abstract

Monte Carlo (MC) simulations significantly contributed to a better understanding of laser-Doppler flowmetry (LDF). Here it is shown that the data obtained from standard MC simulations can be reinterpreted and used to extract more information such as the photo-electric current (i(t)). This is important because i(t) is the starting point for evaluating any existing or new algorithm to be used in LDF instrumentation. This circumvents the tedious procedure of generating a specific model (often approximated if possible at all) each time a different algorithm is considered. By a series of tutorial examples, the influence of various parameters is investigated, e.g. sampling rate, total acquisition time and dc filtering. These cases also demonstrate the fundamental role played by the photons' random phase in the shaping of the LDF signal. In particular, it is demonstrated by MC simulation that when the number of photon-moving red blood cell interactions is too low, then the Siegert relation that exists between the field and photo-electric current autocorrelation functions does not hold. This is an important point because the validity of the Siegert relation is implicitly admitted in the majority of the classical analytical models for the autocorrelation function in LDF (the classical MC approach does not allow one to study this problem). The proposed method and examples could stimulate new ideas and help the scientific community develop, test and validate new approaches in LDF.

A fast time-domain algorithm for the assessment of tissue blood flow in laser-Doppler flowmetry

“…As reported in section 3, the 'noise-like' component of i(t) is an intrinsic property of LDF measurements and requires us to average N avg moments to obtain a reliable result. As already explained elsewhere (Binzoni et al 2009), the presence of this 'noise-like' component is due to the random phase accumulated by the photons before reaching the detector. This is a pure physical phenomenon generated by the interaction between the biological tissue and the photons.…”

“…From each simulation, 100 different i(t) realizations taking into account the possible random phase accumulated by the photons along their travel inside the tissue were obtained (Binzoni et al 2009). Intuitively, the random phase manifests itself as the noise-like appearance of i(t) and explains also why it is experimentally necessary to average many power spectra (obtained from different i(t)) to obtain one noise-free spectrum (in the present case we have the choice to average from 1 up to 100 spectra); the chosen number of averages is denoted by N avg .…”

Monte Carlo Methods to Numerically Simulate Signals Reflecting the Microvascular Perfusion

“…The reason for that was attributed to the physical characteristics of the phantom used (Fredriksson et al, 2006). A recent study (Binzoni et al, 2009) suggested a reinterpretation of the Monte Carlo simulation in order to obtain more information, relevant to LDF measurements. The authors suggested a method for photo-electric current determination in Monte Carlo simulations which will allow that any algorithm used in real LDF instrument could be tested and validated.…”

Laser double Doppler flowmeter

“…The surface of the tissue was then scanned with a laser beam, thus generating an image of the spatial variability of blood perfusion. Another method, using a CMOS matrix, was proposed by Serov et al, with a view to accelerating the imaging procedure [6].…”