Optical Probe and Frequency-Domain Instrumentation to Study Spatial and Temporal Correlations of Fluctuations in Tissues

Abstract

We have used Photon Density Wave Fluctuation Correlation Spectroscopy (PDW-FCS) to study spatial and temporal correlations of large-scale (~1 mm) optical fluctuations in turbid media such as tissues. Our method uses high frequency (110 MHz) intensity modulated near-infrared light traveling in multiply scattering media. We measure the power spectra of the average value (DC), modulation amplitude (AC) and phase (Φ) of the photon density wave launched in the turbid medium. We have designed an optical probe, consisting of two source-detector pairs, which in conjunction with a correlation algorithm restricts the region probed by the photon density wave.

Fast cerebral functional signal in the 100‐ms range detected in the visual cortex by frequency‐domain near‐infrared spectrophotometry

“…Changes in the optical properties of this common volume are the origin of the common components of the signals. A single bundle is very sensitive to fluctuations directly below the source or detector, whereas the π‐signal is more sensitive to deeper layers of tissue and less influenced by superficial tissue than each light bundle separately (Filiaci, 2001; Filiaci et al, 1998). Consequently, we had expected to find more significant fast signals in the π‐signals than in the signals of the separate bundles.…”

“…The product of the variations in modulation amplitude (AC), mean light intensity (DC), and phase (φ) were considered. By using this design we decreased the influence of optical fluctuations near the surface and increased the sensitivity to deeper and more localized volumes of the tissue (Filiaci, 2001; Filiaci et al, 1998).…”

Different Time Evolution of Oxyhemoglobin and Deoxyhemoglobin Concentration Changes in the Visual and Motor Cortices during Functional Stimulation: A Near-Infrared Spectroscopy Study

“…3) of subject 2. a geometry with two crossed source detector pairs where we combined the light of two laser diodes for each wavelength (670 and 830 nm) to achieve a better signal to noise ratio. This geometry had been developed and described by our group earlier (Filiaci et al, 1998). The source-detector distance was 3.5 cm and the probe covered an area of 2.4 ϫ 2.4 cm.…”

“…The fact that the patterns are more localized in the visual cortex than in the motor cortex can also be attributed in part to the crossed source detector pair arrangement, which is expected to give a better spatial resolution (Filiaci et al, 1998).…”

Detecting cerebral functional slow and fast signals by frequency-domain near-infrared spectroscopy using two different sensors

“…Using this arrangement the two paths of light correspond to the two diagonals of the quadrangle and the effective sourcedetector separation was 2.8cm. This sensor is called rc sensor because when the product of the two signals at the TuF 10-1/427 428/TuF 10-2 detector is taken, one reduces the sensitivity to fluctuations near the surface and is more sensitive to signals referring to deeper regions of tissue [3]. For this arrangement we used liquid light guides of 5mm diameter to improve the signal.…”