Monte Carlo simulations and laser Doppler flow measurements with high penetration depth in biological tissuelike head phantoms

Soelkner, Gerald; Mitic, G.; Lohwasser, Robert

doi:10.1364/ao.36.005647

Cited by 27 publications

(22 citation statements)

References 10 publications

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“…a high degree of multiple Doppler shifts, where the Doppler spectrum only depend on µ s and not the anisotropy. 8,28 Binzoni et al 9 have suggested an alternative approach that takes multiple Doppler shifts into account. Their approach, based on a theoretical framework by Bonner et al, 3 assumes a Gaussian RBC velocity distribution in the tissue and that the RBC phase function is described by the Rayleigh-Gans approximation.…”

Section: Discussionmentioning

confidence: 99%

Toward a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum

Larsson

Strömberg

2006

J. Biomed. Opt.

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Section: Discussionmentioning

confidence: 99%

Toward a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum

Larsson

Strömberg

2006

J. Biomed. Opt.

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“…The photon packet steps were generated by means of the variable step size method (Prahl et al 1989). The model describing the change of the photon packet direction after each collision was represented by the Henyey-Greenstein probability density function (Henyey and Greenstein 1941) independently of the fact that the scatterer was a moving particle or not (Soelkner et al 1997, Kienle 2001. Reflection of the photon packets on the boundaries was treated as an all-or-none problem by using the probability density functions derived from the Snell-Descartes law and Fresnel's formulae.…”

Section: Monte Carlo Methods and Generation Of The Power Spectrummentioning

confidence: 99%

“…The laser-Doppler shift for each individual photon (packet) was computed by means of the method published in Soelkner et al (1997) (see equation (1)). After each scattering event it was decided if the scatterer was a moving particle by sampling a uniform random number ξ ∈ [0, 1] and by defining the probability of having a moving particle P move ∈ [0, 1].…”

Section: Monte Carlo Methods and Generation Of The Power Spectrummentioning

confidence: 99%

“…The model describing the velocity distribution ( V , mm s −1 ) of the moving particles was represented by the probability density function p( V ) (see below). Thus, once V was generated using the law given by p( V ), the laser-Doppler frequency shift ( ν q , Hz) for the qth scattering event with a moving particle was computed as (Soelkner et al 1997) …”

Section: Monte Carlo Methods and Generation Of The Power Spectrummentioning

confidence: 99%

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Full-field laser–Doppler imaging and its physiological significance for tissue blood perfusion

Binzoni¹,

Ville²

2008

Phys. Med. Biol.

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Using Monte Carlo simulations for a semi-infinite medium representing a skeletal muscle tissue, it is demonstrated that the zero-and first-order moments of the power spectrum for a representative pixel of a full-field laserDoppler imager behave differently from classical laser-Doppler flowmetry. In particular, the zero-order moment has a very low sensitivity to tissue blood volume changes, and it becomes completely insensitive if the probability for a photon to interact with a moving red blood cell is above 0.05. It is shown that the loss in sensitivity is due to the strong forward scatter of the propagating photons in biological tissues (i.e., anisotropy factor g = 0.9). The first-order moment is linearly related to the root mean square of the red blood cell velocity (the Brownian component), and there is also a positive relationship with tissue blood volume. The most common physiological interpretation of the first-order moment is as tissue blood volume times expectation of the blood velocity (in probabilistic terms). In this sense, the use of the first-order moment appears to be a reasonable approach for qualitative real-time blood flow monitoring, but it does not allow us to obtain information on blood velocity or volume independently. Finally, it is shown that the spatial and temporal resolution trade-off imposed by the CMOS detectors, used in full-field laser-Doppler hardware, may lead to measurements that vary oppositely with the underlying physiological quantities. Further improvements on detectors' sampling rate will overcome this limitation.

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“…The proposed method implies only a slight modification of the 'classical' MC approach as it exists for direct generation of P i (ω) (see e.g. Soelkner et al (1997)). …”

Section: Introductionmentioning

confidence: 99%

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

2009

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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.

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Monte Carlo simulations and laser Doppler flow measurements with high penetration depth in biological tissuelike head phantoms

Cited by 27 publications

References 10 publications

Toward a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum

Toward a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum

Full-field laser–Doppler imaging and its physiological significance for tissue blood perfusion

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

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