Interferometric near-infrared spectroscopy (iNIRS) of human tissues in the presence of motion (Conference Presentation)

Interferometric near-infrared spectroscopy (iNIRS) is a time-of-flight- (TOF-) resolved sensing method for direct and simultaneous quantification of tissue optical properties (absorption and reduced scattering) and dynamics (blood flow index) in vivo with a single modality. The technique has previously been validated in Intralipid phantoms, and applied to continuously and non-invasively monitor optical properties and blood flow index in the brains of head-fixed, anesthetized mice. A demonstration of robust iNIRS measurements in human tissues with motion would support the viability of iNIRS for clinical applications. Here, we perform non-contact iNIRS in human tissues. We show that phase drift caused by involuntary motion during acquisition significantly distorts the optical field autocorrelation, particularly at early TOFs. To solve this issue, we present a novel numerical phase drift correction method to isolate field dynamics due to just red blood cell motion within the sample. Upon correction, TOF-resolved autocorrelations exhibit exponential decay behavior, whether acquired from Intralipid, the human forearm, or the human forehead. We confirm the link between bulk motion artifacts and phase drift by simultaneous, co-registered iNIRS and Optical Coherence Tomography measurements. By applying conventional, time-resolved diffusion theory and diffusing wave spectroscopy theory, we quantify optical properties and time-of-flight-resolved dynamics in Intralipid, the human forearm, and the human brain. Finally, we explore strategies for increased photon collection through parallelization of iNIRS, to probe greater depths in the human brain. This work conclusively shows that diffuse optical measurements of field dynamics are possible, even in the presence of motion artifacts.