Estimation of light detection efficiency for different light guides used in time-resolved near-infrared spectroscopy

Time-resolved near-infrared spectroscopy is a technique enabling the assessment of changes in oxygenation and perfusion of tissue with depth discrimination. A challenge in time-resolved measurements remains to provide sufficiently high efficiency of photons detection together with high temporal resolution of the setup. The aim of this study was to compare the performance of different fiber bundles and liquid light guides which can be used in time-resolved near-infrared spectroscopy measurements. The comparison was carried out by measurements of the instrument response function and of the responsivity of the optical detection system equipped with different types of light guides. The responsivity was estimated employing a test phantom with known diffuse transmittance factor. The results suggest that application of liquid light guides provides higher efficiency of photon collection in comparison to fiber bundles which are typically used in tissue optics instrumentation.