Broadband continuous-wave technique to measure baseline values and changes in the tissue chromophore concentrations

Abstract

We present a broad-band, continuous-wave spectral approach to quantify the baseline optical properties of tissue and changes in the concentration of a chromophore, which can assist to quantify the regional blood flow from dynamic contrast-enhanced near-infrared spectroscopy data. Experiments were conducted on phantoms and piglets. The baseline optical properties of tissue were determined by a multi-parameter wavelength-dependent data fit of a photon diffusion equation solution for a homogeneous medium. These baseline optical properties were used to find the changes in Indocyanine green concentration time course in the tissue. The changes were obtained by fitting the dynamic data at the peak wavelength of the chromophore absorption, which were used later to estimate the cerebral blood flow using a bolus tracking method.

Keywords: (290.1990) Diffusion; (290.5820) Scattering measurements; (300.6340) Spectroscopy, infrared.

Fig. 1

Second derivative data fit.

Fig. 2

First derivative fits for (a) infinite medium,10% milk: ${\mu }_s{}^{\prime }$ = 3.6 mm⁻¹, (%FC_H2O) = 86%; (b) semi-infinite medium,10% milk: ${\mu }_s{}^{\prime }$ = 3.6 mm⁻¹, (%FC_H2O) = 86%; (c) semi-infinite medium, 2% milk: ${\mu }_s{}^{\prime }$ = 0.9 mm⁻¹, (%FC_H2O) = 97%

Fig. 3

First derivative of absorbance for a set of data from pig’s open brain fit of the model (blue) to the base line data (red)

Fig. 4

Fit of the model (blue) to the baseline data (red), R² > 0.90 (a) baseline, (b) occlusion

Fig. 5

Time traces of the brain ICG concentrations during baseline and occlusion