Highly parallel, 1060 nm interferometric diffusing wave spectroscopy with a time-of-flight filter

Interferometric diffuse optics (iDO) has recently emerged as a promising class of near-infrared (NIR) light technologies for monitoring human brain signals associated with coherent light fluctuations. In this work, we demonstrate a line scan interferometric diffusing wave spectroscopy (iDWS) system at 1060 nm, a wavelength that has a multitude of benefits for high-speed cerebral blood flow index (BFI) monitoring. Pulsatile BFI measurements on the forehead of a moderately dark-skinned (Fitzpatrick Type V) subject with medium-length black hair up to a source-collector (S-C) separation of 5.5 cm on the forehead and 4.0 cm over the parietal cortex are demonstrated in continuous wave (CW) mode. On this high-throughput platform, we further implement a simple time-of-flight filter (TOF) via source wavelength tuning. The TOF filter can be turned on and off, and its width can be changed electronically, enabling probing different sample depths without requiring multiple S-C separations. At 4 cm S-C separation, an electronic TOF filter afforded a 2.92-fold reduction in scalp sensitivity over CW mode. With further optimization, the combination of TOF filtering with highly parallel detection in the 1060 nm range promises to improve depth sensitivity and signal-to-noise ratio of iDO in neuromonitoring applications.