Open AccessTime domain diffuse correlation spectroscopy: modeling the effects of laser coherence length and instrument response function
Author(s) -
Xiaojun Cheng,
Davide Tamborini,
Stefan A. Carp,
Oleg Shatrovoy,
Brandon Zimmerman,
Danil Tyulmankov,
Andrew M. Siegel,
Megan Blackwell,
Maria Angela Franceschini,
David A. Boas
Publication year - 2018
Publication title -
optics letters/optics index
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.524
H-Index - 272
eISSN - 1071-2763
pISSN - 0146-9592
DOI - 10.1364/ol.43.002756
Subject(s) - autocorrelation , speckle pattern , optics , path length , coherence length , coherence (philosophical gambling strategy) , physics , laser , optical path length , optical path , mathematics , statistics , superconductivity , quantum mechanics
Diffuse correlation spectroscopy (DCS) is an optical technique that non-invasively quantifies an index of blood flow (BF i ) by measuring the temporal autocorrelation function of the intensity fluctuations of light diffusely remitted from the tissue. Traditional DCS measurements use continuous wave (CW) lasers with coherence lengths longer than the photon path lengths in the sample to ensure that the diffusely remitted light is coherent and generates a speckle pattern. Recently, we proposed time domain DCS (TD-DCS) to allow measurements of the speckle fluctuations for specific path lengths of light through the tissue, which has the distinct advantage of permitting an analysis of selected long path lengths of light to improve the depth sensitivity of the measurement. However, compared to CW-DCS, factors including the instrument response function (IRF), the detection gate width, and the finite coherence length need to be considered in the model analysis of the experimental data. Here we present a TD-DCS model describing how the intensity autocorrelation functions measured for different path lengths of light depend on the coherence length, pulse width of the laser, detection gate width, IRF, BF i , and optical properties of the scattering sample. Predictions of the model are compared with experimental results using a homogeneous liquid phantom sample that mimics human tissue optical properties. The BF i s obtained from the TD-DCS model for different path lengths of light agree with the BF i obtained from CW-DCS measurements, while the standard simplified model underestimates the BF i by a factor of ∼2. This Letter establishes the theoretical foundation of the TD-DCS technique and provides guidance for future BF i measurements in tissue.