Abstract
We introduce a new, non-invasive, diffuse optical technique, speckle contrast optical spectroscopy (SCOS), for probing deep tissue blood flow using the statistical properties of laser speckle contrast and the photon diffusion model for a point source. The feasibility of the method is tested using liquid phantoms which demonstrate that SCOS is capable of measuring the dynamic properties of turbid media non-invasively. We further present an in vivo measurement in a human forearm muscle using SCOS in two modalities: one with the dependence of the speckle contrast on the source-detector separation and another on the exposure time. In doing so, we also introduce crucial corrections to the speckle contrast that account for the variance of the shot and sensor dark noises.
Highlights
Non-invasive, optical imaging of blood flow has many applications in bio-medicine [1, 2]
Several optical approaches for non-invasive, in vivo blood flow measurements rely on the statistics of the laser speckles; laser Doppler flowmetry (LDF) uses the frequency broadening [3], diffuse correlation spectroscopy (DCS) [4,5,6] uses the light intensity auto-correlation and laser speckle flowmetry (LSF) [7] uses the spatio-temporal blurring of the speckles
The squares represent the speckle contrast calculated without any noise correction but it is seen that after about 1.7 cm there is a systematic deviation from the expected decay
Summary
Non-invasive, optical imaging of blood flow has many applications in bio-medicine [1, 2]. Several optical approaches for non-invasive, in vivo blood flow measurements rely on the statistics of the laser speckles; laser Doppler flowmetry (LDF) uses the frequency broadening [3], diffuse correlation spectroscopy (DCS) [4,5,6] uses the light intensity auto-correlation and laser speckle flowmetry (LSF) [7] uses the spatio-temporal blurring of the speckles. We present speckle contrast optical spectroscopy (SCOS) which, in a similar fashion to LSF, uses the speckle contrast but with point sources placed at a distance as in DCS, i.e. detecting photons that have undergone multiple scattering. This provides detection of many speckles in parallel but with extended path lengths for deep tissue sampling
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