Abstract
We present the concept, design and first in vivo tests of a novel non-contact scanning imaging system for time-domain near-infrared spectroscopy of tissues. Employing a supercontinuum laser in combination with an acousto-optic tunable filter as light source, the tissue was scanned by a galvanometer scanner from a distance of more than 10 cm. The distance between the illumination spot (source) and the detection spot from which the diffusely remitted photons were collected was small (few mm) and kept fixed during the scan. A fast-gated single-photon avalanche diode was employed to eliminate the intense early part of the diffusely remitted signal and to detect late photons only. Polarization-selective detection was additionally applied to suppress specular reflections from the object. An array of gated time-of-flight distributions of photons was recorded by imaging TCSPC synchronized with the movement of the galvanometer scanner. A tissue area of several cm2 was scanned with 32 × 32 pixels within a frame rate of 1 s−1. The wavelength was switched line by line between two bands centred at 760 and 860 nm. Concentration changes of oxy- and deoxy-haemoglobin were derived from changes in photon counts in a selected time window of the gated distributions at the two wavelengths. First in vivo tests included the recording of haemodynamics during arm occlusion as well as brain activation tasks. These tests demonstrated the successful non-contact imaging of haemoglobin concentration changes in deeper tissues. Additional applications seem feasible by increasing the spectral information content of the non-contact scanning approach. To this end we implemented and tested the non-contact scanning in combination with eight-wavelength multiplexing.
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