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Tissue characterization with ballistic photons: counting scattering and/or absorption centres

Corral F., Strojnik M., Paez G.

Opto-Electronics Review

2015

Vol. 23, No. 1

44-52

We describe a new method to separate ballistic from the scattered photons for optical tissue characterization. It is based on the hypothesis that the scattered photons acquire a phase delay. The photons passing through the sample without scattering or absorption preserve their coherence so they may participate in interference. We implement a Mach-Zehnder experimental setup where the ballistic photons pass through the sample with the delay caused uniquely by the sample indices of refraction. We incorporate a movable mirror on the piezoelectric actuator in the sample arm to detect the amplitude of the modulation term. We present the theory that predicts the path-integrated (or total) concentration of the scattering and absorption centres. The proposed technique may characterize samples with transmission attenuation of ballistic photons by a factor of 10-14.

A photoplethysmographic imaging system with supplementary capabilities

Corral F, Paez G, Strojnik M

Optica Applicata

2014

Vol. 44, nr 2

191--204

We perform a temporal and spectral analysis of simulated and experimental photoplethysmographic signals. We obtain technical requirements for an advanced photoplethysmographic imaging system able to add photoplethysmographic waveform and oximetry maps to the conventional measurements. The imaging system is centered on measuring the pulsatile signals produced by diffuse reflectance on the inner layers of the skin. We consider controlled illumination conditions for the system, with visible and near infrared components. This work comprises backscattering evaluation, waveform analysis and spectral dependence of photoplethysmographic signal. We determine the resolution requirement for the system by evaluating the amplitude of the backscattered signal using Monte Carlo simulations. We determine the bandwidth limit for the signal acquisition by Fourier analysis from a set of plethysmographic waveforms. Finally, the spectral dependence of the system is obtained from experimental results. We establish the requirements for the photoplethysmographic imaging system, including the source, subject and detector conditions.